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Dr. HDr. Hui Huui Hu
Department of Aerospace EngineeringDepartment of Aerospace EngineeringIowa State University Iowa State University
Ames, Iowa 50011, U.S.AAmes, Iowa 50011, U.S.A
Short CourseShort Course: : Advanced Flow Diagnostic Advanced Flow Diagnostic Techniques for Thermal Fluid StudiesTechniques for Thermal Fluid Studies
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Course Course OverviewOverview•• This short course aims to give a comprehensive introduction of tThis short course aims to give a comprehensive introduction of the advanced measurement he advanced measurement
techniques widely used for fluid mechanics, aerodynamics, heat ttechniques widely used for fluid mechanics, aerodynamics, heat transfer and combustion studies. ransfer and combustion studies. •• Demonstration lab experiments will also be incorporated in this Demonstration lab experiments will also be incorporated in this coursecourse..•• Lecture Notes are available at:Lecture Notes are available at: http://www.public.iastate.edu/~huhui/teaching/2010http://www.public.iastate.edu/~huhui/teaching/2010--GECDGECD--shortshort--
course/GECDcourse/GECD--shortshort--course.htmlcourse.html
•• Topics to be covered in this short course:Topics to be covered in this short course:–– Pressure Gauge and Transducers Pressure Gauge and Transducers –– Pressure Sensitive Painting (PSP); Temperature Sensitive PaintinPressure Sensitive Painting (PSP); Temperature Sensitive Painting (TSP)g (TSP)–– Shadowgraph and Shadowgraph and SchlierenSchlieren photographyphotography–– Hot Wire Anemometry (HWA)Hot Wire Anemometry (HWA)–– Laser Doppler Laser Doppler VelocimetryVelocimetry (LDV) and Planar Doppler (LDV) and Planar Doppler VelocimetryVelocimetry (PDV) (PDV) –– Particle Image Particle Image VelocimetryVelocimetry ( classic PIV, Stereo PIV, 3( classic PIV, Stereo PIV, 3--D PIV; Holograph PIV, microD PIV; Holograph PIV, micro--PIV)PIV)–– Laser Induced Fluorescence (LIF) and Planar LIFLaser Induced Fluorescence (LIF) and Planar LIF–– Molecular Tagging Molecular Tagging VelocimetryVelocimetry and Thermometry (MTV&T).and Thermometry (MTV&T).
•• Schedule of the short course:Schedule of the short course:–– 0066--JulyJuly, Tuesday,, Tuesday, 11--4pm at GECD4pm at GECD:: Introductions and fundamentals, PSP/TSPIntroductions and fundamentals, PSP/TSP–– 1313--JulyJuly, Tuesday,, Tuesday, 11--4pm at GECD4pm at GECD:: SchlierenSchlieren and Shadowgraph, HWA, LDV/PDV and Shadowgraph, HWA, LDV/PDV –– 2020--JulyJuly, Tuesday,, Tuesday, 11--4pm at GECD4pm at GECD:: PIV; Stereo PIV and 3PIV; Stereo PIV and 3--D PIVD PIV–– 1010--AugAug, Tuesday,, Tuesday, 11--4pm at GECD4pm at GECD:: LIF, MTV and MTT, QD imagingLIF, MTV and MTT, QD imaging–– 1717--AugAug, Tuesday,, Tuesday, 11--4pm at ISU Lab4pm at ISU Lab: : 5~7 demonstration experiments5~7 demonstration experiments
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AFD, CFD and EFDAFD, CFD and EFD
Flow PhysicsFlow Physics
ComputationaComputationallFluid DynamicsFluid Dynamics
(CFD)(CFD)
Analytical FluidAnalytical FluidDynamicsDynamics
((AFD)AFD)
Experimental Fluid Experimental Fluid DynamicDynamics s
(EFD)(EFD)
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Basics and Fundamentals about Experiments and InstrumentationsBasics and Fundamentals about Experiments and Instrumentations
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Review of Fundamentals about Experiments and InstrumentationsReview of Fundamentals about Experiments and Instrumentations
•• Basic concepts and fundamental principlesBasic concepts and fundamental principles•• Similitude and dimension analysis Similitude and dimension analysis •• Measurement uncertainty analysisMeasurement uncertainty analysis•• Fluid Mechanical apparatus: wind tunnels and Fluid Mechanical apparatus: wind tunnels and
water tunnelswater tunnels
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Measurable PropertiesMeasurable Properties
•• Material Properties: Material Properties: (Most of them can be found in handbooks)(Most of them can be found in handbooks)
•• Kinematic Properties: Kinematic Properties: Describes the fluid motion w/o considering the force. Describes the fluid motion w/o considering the force. (Position, V, displacement, acceleration, (Position, V, displacement, acceleration, momentum, volume flow rate, mass flow rate, etc)momentum, volume flow rate, mass flow rate, etc)
•• Dynamic properties: Dynamic properties: Related to applied forces. Related to applied forces. (Pressure, shear stress , Torque)(Pressure, shear stress , Torque)
•• Thermodynamic properties: Thermodynamic properties: Heat and Work. Heat and Work. (T, e, h, S)(T, e, h, S)
D,,volume,specific γμρ ,, m
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Descriptions of Flow Motion
tLV
t ΔΔ
=→Δ 0
lim
( ) ( )txVtxU ii ,, 0=
⎪⎪⎪
⎩
⎪⎪⎪
⎨
⎧
⇒∂∂
+∂∂
+∂∂
+∂∂
=
∇•+∂∂
=
⇒=
domainEulerianxUU
xUU
xUU
tU
UUtUa
domainLangragianDtVDa
33
22
11
)(rrrr
rrr
r
rr
⎟⎟⎠
⎞⎜⎜⎝
⎛
∂∂
+∂∂
=j
i
j
iij x
UxU
e21
⎟⎟⎠
⎞⎜⎜⎝
⎛
∂∂
+∂∂
=j
i
j
iij x
UxU
μτ
•• LagrangianLagrangian Method Method Focused on fluid particlesFocused on fluid particles
•• EulerianEulerian Method: Method: Focused on space location.Focused on space location.
Acceleration: Acceleration:
Rate of Strain:Rate of Strain:
Shear stress:Shear stress:
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Primary Properties and Secondary propertiesPrimary Properties and Secondary properties
•• Primary Properties:Primary Properties: Properties which are independent to each other Properties which are independent to each other
•• Secondary Properties:Secondary Properties: Related to other properties through their definition or Related to other properties through their definition or basic principles basic principles
SrSrStoradianStoradianSolid AngleSolid Angle
radradRadiusRadiusPlane AnglePlane Angle
CdCdCandelaCandelaLuminous intensityLuminous intensity
molmolmolemoleAmount of substanceAmount of substance
AAIIElectric currentElectric current
KKTTTemperatureTemperature
ssttTimeTime
kgkgmmMassMass
MMLLLengthLength
UnitUnitAbbreviationsAbbreviationsNameName
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Similitude and Dimensional AnalysisSimilitude and Dimensional Analysis
• Similitude: • The study of predicting prototype conditions
from model observations.
F-22 Raptor Air Superiority Fighter
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Similitude and Dimensional AnalysisSimilitude and Dimensional Analysis
),,,( VDfpl μρ=Δ
)(2 μρ
ρVD
Vp
Φ=Δ
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Buckingham Buckingham ππ -- TheoremTheorem
•• Step 1: Step 1: List all the variables that are involved in the problem.List all the variables that are involved in the problem.•• Step 2: Step 2: Express each of the variables in terms of basic dimensions.Express each of the variables in terms of basic dimensions.
–– Basic dimension: M, L,T, F Basic dimension: M, L,T, F –– Force Force -- F=MLTF=MLT--22, density , density -- ρρ =ML=ML--33; or ; or ρρ =FL=FL--33TT2.2.
•• Step 3: Step 3: Determine the required number of piDetermine the required number of pi--terms.terms.–– Number of piNumber of pi--terms is equal to terms is equal to kk--rr, where k is the number of , where k is the number of vearibelvearibel in in
the problem, r is the number if reference dimensions required tothe problem, r is the number if reference dimensions required to described described the variables.the variables.
•• Step 4: Step 4: Select a number of repeating variables, where the number requireSelect a number of repeating variables, where the number required is equal to d is equal to the number of reference dimensions.the number of reference dimensions.
•• Step 5;Step 5; Form a piForm a pi--term by multiplying one of the nonterm by multiplying one of the non--repeating variables by the repeating variables by the product of repeating variables, each raised to an exponent that product of repeating variables, each raised to an exponent that will make the will make the combination dimensionless.combination dimensionless.
•• Step 6:Step 6: Repeat Step 5 for each of the remaining nonRepeat Step 5 for each of the remaining non--repeating variables.repeating variables.•• Step 7:Step 7: Check all the resulting pi terms to make sure they are dimensionCheck all the resulting pi terms to make sure they are dimensionlessless•• Step 8:Step 8: Express the final form as a relationship among the piExpress the final form as a relationship among the pi--terms, and think about terms, and think about
what it means.what it means.
),( ,321 rk−ΠΠΠΦ=Π K
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Buckingham Buckingham ππ -- TheoremTheorem
•• Example Example
neededistermsrK −⇒== π23;5TFL
LTVTFL
LDFLpl
2
1
24
3
−
−
−
−
=
=
=
==Δ
μ
ρ),,,( VDfpl μρ=Δ
cbal VDp ρΔ=Π1
cbaVD ρμ=Π2
210002413
12
1
02043
01)()())((
VDp
cba
cbcba
cLTFTFLLTLFL lcba
ρΔ
=Π⇒⎪⎩
⎪⎨
⎧
−=−==
⇒⎪⎩
⎪⎨
⎧
=+−=−++−
=+⇒=−−−
VDcba
cbcba
cLTFTFLLTLTFL cba
ρμ
=Π⇒⎪⎩
⎪⎨
⎧
−=−=−=
⇒⎪⎩
⎪⎨
⎧
=+−=−++−
=+⇒=−−−
20002412
111
021042
01)()())((
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Commonly used dimensionless parametersCommonly used dimensionless parameters
L
force tensionsurface force inertialWe Number, Weber
force inertialforce lcentrifugaStr Number, Strohal
forcegravity force inertial FrNumber,Froude
massmomentum:Number Schmidt
diffusion heatdiffusion momentum:Number Prandtl
force inertialLift:tCoefficien Lift
force inertialDrag:tCoefficienDrag
force inertialforcepressure Eu number, Euler
force viscousforce inertialRe number, Reynolds
forcelity compressibforce inertialM Number, Mach
∝=
∝=
∝=
==
==
==
==
∝Δ
=
∝=
∝=
σρ
ϖ
γ
γ
ρ
ρ
ρ
μρ
lVVl
V
USc
V
V
LC
V
DC
V
p
VLcV
c
L
D
2
2
2
2
lg
Pr
21
21
21
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SimilitudeSimilitude
• Geometric similarity: the model have the same shape as the prototype:
F-16 F-22
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Similitude
•• Kinematic similarity: condition where the Kinematic similarity: condition where the velcoityvelcoity ratio is a constant between ratio is a constant between all corresponding points in the flow field. all corresponding points in the flow field. –– The streamline pattern around the model is the same as that arouThe streamline pattern around the model is the same as that around the nd the
prototypeprototype
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SimilitudeSimilitude
• Dynamic similarity: Forces which act on corresponding masses in the model flow and prototype flow are in the same ratio through out the entire flow.
pmpg
pI
mg
mI
pg
mg
pI
mI
pmp
pI
m
mI
p
m
pI
mI
pmpp
pI
mp
mI
pp
mp
pI
mI
pg
mg
p
m
pp
mp
pI
mI
FrFrFF
FF
FF
FF
FF
FF
FF
FF
EuEuFF
FF
FF
FF
FF
FF
FF
FF
=⇒=⇒=⇒
=⇒=⇒=⇒
=⇒=⇒=⇒
====
)()(
)()(
)()(
)()(
ReRe)()(
)()(
)()(
)()(
)()(
)()(
)()(
)()(
constant)()(
)()(
)()(
)()(
μμμ
μ
μ
μ
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Wind Tunnels and Water TunnelsWind Tunnels and Water Tunnels
• Producing the desired flow field with controlled conditions
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Types of Wind TunnelsTypes of Wind Tunnels
Based on Flow Speed:Based on Flow Speed:•• Subsonic or low speed wind tunnels (M<<1.0)Subsonic or low speed wind tunnels (M<<1.0)•• Transonic wind tunnels (MTransonic wind tunnels (M≈≈1.0)1.0)•• Supersonic wing tunnels (1.0 <M<5.0)Supersonic wing tunnels (1.0 <M<5.0)•• Hypersonic wind tunnels (M>5.0) Hypersonic wind tunnels (M>5.0)
Based on Shape:• Open circuit wind tunnel: • Closed circuit wind tunnel:
Other special wind tunnels:• Icing wind tunnel• Tornado simulators • …
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Open Circuit Wind Tunnel
•• Suction wind tunnel:Suction wind tunnel: With the inlet open to atmosphere, axial fan or With the inlet open to atmosphere, axial fan or centrifugal blower is installed after test section. centrifugal blower is installed after test section.
•• Blow down wind tunnel:Blow down wind tunnel: A blower is installed at the inlet of wind tunnel A blower is installed at the inlet of wind tunnel which throws the air into wind tunnel. which throws the air into wind tunnel.
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Closed circuit wind tunnelClosed circuit wind tunnel
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Components of a Wind TunnelComponents of a Wind Tunnel•• Test section Test section •• Contraction sectionContraction section•• Diffuser sectionDiffuser section•• Setting chamberSetting chamber•• Screens and similar structuresScreens and similar structures•• Cooling system / radiatorsCooling system / radiators•• Motors /fans Motors /fans
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Function of Contraction
A1
V1
ΔV1ΔV2
V2
A2
10%
2
11 A
Ac = 001.0100
1.01
1
12
2
2 ==Δ
=Δ
VV
cVV
1.01
1 =ΔVVif
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Water TunnelsWater Tunnels
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Towing TankTowing Tank
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Measurement UncertaintiesMeasurement Uncertainties
•• ““AccuracyAccuracy”” is generally used to indicate the relative closeness of agreemeis generally used to indicate the relative closeness of agreement between nt between an experimentallyan experimentally--determined value of a quantity and its true value. determined value of a quantity and its true value.
•• ““ErrorError”” is the difference between the experimentallyis the difference between the experimentally--determined value and its true determined value and its true value; therefore, as error decreases, accuracy is said to increavalue; therefore, as error decreases, accuracy is said to increase. se.
•• Since the true value is not known, it is necessary to estimate eSince the true value is not known, it is necessary to estimate error, and that estimate rror, and that estimate is called an uncertainty, U. is called an uncertainty, U.
•• Uncertainty estimates are made at some confidence levelUncertainty estimates are made at some confidence level——a 95% confidence a 95% confidence estimate, for example, means that the true value of the quantityestimate, for example, means that the true value of the quantity is expected to be is expected to be within the within the ±±U interval about the experimentallyU interval about the experimentally--determined value 95 times out of 100.determined value 95 times out of 100.
truemtruemeasurederror AAEAAA −=⇒−=
smVsmVsmVsmV
t
t
/5error t Measuremen,/100/1error t Measuremen,/10
t?measuremen accurate more is CaseWhich
=Δ==Δ= true
errorrelative A
AE =
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Measurement UncertaintiesMeasurement Uncertainties
•• Total error, Total error, UU, can be considered to be composed of two components:, can be considered to be composed of two components:
–– a random (precision) component, a random (precision) component,
–– a systematic (bias) component,a systematic (bias) component,
–– We usually donWe usually don’’t know these exactly, so we estimate them with t know these exactly, so we estimate them with PP and and BB, respectively., respectively.
•• Precision Error: Random errorPrecision Error: Random error–– Normal Distribution or Gaussian DistributionNormal Distribution or Gaussian Distribution
•• Bias Error: Fixed Error, System ErrorBias Error: Fixed Error, System Error–– Constant Throughout the experimentConstant Throughout the experiment–– Can be positive or NegativeCan be positive or Negative
222 PBU +=X
True valueX=100
Bias errorBias error
precision errorprecision error
measured valueX=101
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Measurement UncertaintiesMeasurement Uncertainties
•• Precise but biasedPrecise but biased•• Unbiased but ImpreciseUnbiased but Imprecise•• Biased and ImpreciseBiased and Imprecise•• Precise and Unbiased Precise and Unbiased
222 PBE +=Qualification of measurement error:Qualification of measurement error:
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Repeatability Repeatability and and ReproducibilityReproducibility
Both Bias and Precision ErrorsBoth Bias and Precision ErrorsReproducibilityReproducibility
Precision ErrorPrecision ErrorRepeatabilityRepeatability
• Repeatability is the variability of the measurements obtained by one person while measuring the same item repeatedly. This is also known as the inherent precision of the measurement equipment.
• Consider the probability density functions shown in Figure 1. The density functions were constructed from measurements of the thickness of a piece of metal with Gage A and Gage B. The density functions demonstrate that Gage B is more repeatable than Gage A.
• Reproducibility is the variability of the measurement system caused by differences in operator behavior. Mathematically, it is the variability of the average values obtained by several operators while measuring the same item.
• Figure 2 displays the probability density functions of the measurements for three operators. The variability of the individual operators are the same, but because each operator has a different bias, the total variability of the measurement system is higher when three operators are used than when one operator is used.
ReproducibilityReproducibility
Repeatability
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Measurement UncertaintiesMeasurement Uncertainties
•• We almost always are dealing with a data reduction equation to gWe almost always are dealing with a data reduction equation to get to our et to our final results. final results.
–– In this case, we must not only deal with uncertainty in the measIn this case, we must not only deal with uncertainty in the measured values but ured values but uncertainty in the final results.uncertainty in the final results.
•• A general form looks like this:A general form looks like this:
–– R is the result determined from J independent variables.R is the result determined from J independent variables.
( )JXXXXRR ,,,, 321 K=
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Example
ρρ
ρ
pppV
BernoulliVpp
statictotal
statictotal
Δ=
−=
+=
2)(2
)(,21 2
222RRR PBU +=
Uncertainty in velocity V:Uncertainty in velocity V:
∑∑==
⎥⎦
⎤⎢⎣
⎡∂∂
=⎥⎦
⎤⎢⎣
⎡∂∂
=J
ii
iR
J
ii
iR P
XRPB
XRB
1
22
1
22 ;
∑=
=M
jii j
BB1
2
For a large number of samples (N>10) ii SP 2=
( )[ ] ( ) ⎥⎦
⎤⎢⎣
⎡=⎥
⎦
⎤⎢⎣
⎡−
−= ∑∑
==
N
kkii
N
kikii X
NXXX
NS
1
21
1
2 1;1
1
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TTechnical Basis for Optical Instrumentationechnical Basis for Optical Instrumentation
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The nature of lightThe nature of light
•• According to classical electromagnetic theory, light is considerAccording to classical electromagnetic theory, light is considered to be ed to be radiation that propagates through vacuum in free spaced in the fradiation that propagates through vacuum in free spaced in the form of orm of electromagnetic waves, both oscillating transversely to the direelectromagnetic waves, both oscillating transversely to the direction of wave ction of wave propagation and normal to each other.propagation and normal to each other.
)(2sin),(
)(2sin),(
0
0
TtxBtxBTtxEtxE
zZ
yy
−=
−=
λπ
λπ
λλ : : is wavelengthis wavelengthT :T : is the period of the oscillationis the period of the oscillation
νν: : The reciprocal of the period, is called frequency, The reciprocal of the period, is called frequency, νν =1/T=1/T
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The nature of lightThe nature of light--11
•• Light propagation velocity, V= f Light propagation velocity, V= f λλ•• Light propagation velocity in Vacuum, C Light propagation velocity in Vacuum, C = 2.998= 2.998××10108 8 m/sm/s•• Wave front: the locus of all points along the different paths thWave front: the locus of all points along the different paths that have the same at have the same
phase.phase.•• If all the wave fronts are plane, then, the light is considered If all the wave fronts are plane, then, the light is considered to be a plane wave.to be a plane wave.•• If all the wave fronts are spherical or cylindrical, then, the lIf all the wave fronts are spherical or cylindrical, then, the light is considered to be a ight is considered to be a
spherical or cylindrical wave.spherical or cylindrical wave.•• Light propagation is associated with electric and magnetic fieldLight propagation is associated with electric and magnetic fields. They are in phase s. They are in phase
and their amplitudes are related as:and their amplitudes are related as:
•• It is usually sufficiently to analyze electromagnetic waves by cIt is usually sufficiently to analyze electromagnetic waves by considering only onsidering only electric field.electric field.
•• The polarization is associate with the orientation of the plane The polarization is associate with the orientation of the plane of the plane of of the plane of oscillation of the electric field.oscillation of the electric field.
•• Concepts of linearly polarized light, elliptically polarized ligConcepts of linearly polarized light, elliptically polarized light and circularly ht and circularly polarized light, polarized light, unpolarizedunpolarized or randomly polarized light.or randomly polarized light.
00 zy cBE =
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The nature of light The nature of light --22
10101414 nm < nm < λλ < 10< 101717 nmnmElectrical power wavesElectrical power waves101088 nm < nm < λλ < 10< 101313 nmnmRadio and TelevisionRadio and Television101077 nm < nm < λλ < 10< 1099 nmnmRadarRadar101066 nm < nm < λλ < 10< 1099 nmnmMicrowavesMicrowaves750 nm < 750 nm < λλ < 10< 1077 nmnmSpace heatingSpace heating380 nm < 380 nm < λλ < 750 nm< 750 nmVisible lightVisible light10 nm < 10 nm < λλ < 380 nm< 380 nmDisinfecting radiationDisinfecting radiation1010--22 nm < nm < λλ < 10< 1022 nmnmXX--raysrays1010--44 nm < nm < λλ < 10< 10--11 nmnmGamma raysGamma raysλλ < 10< 10--44 nmnmCosmic raysCosmic rays
WAVELENGTH WAVELENGTH RANGERANGE
RADIATION TYPERADIATION TYPE
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The nature of light The nature of light --22
•• The colors: visible light consists of radiation with wavelength The colors: visible light consists of radiation with wavelength in the range of in the range of 380~750nm (1nm=10380~750nm (1nm=10--99m) which corresponds to the frequency range between 4.0 m) which corresponds to the frequency range between 4.0 ××10 10 15 15 to 7.9 to 7.9 ××10 10 1515 Hz.Hz.
750 nm < 750 nm < λλ < 1000 nm< 1000 nminfraredinfrared647 nm < 647 nm < λλ < 750 nm< 750 nmRed Red 585 nm < 585 nm < λλ < 647 nm< 647 nmOrangeOrange575 nm < 575 nm < λλ < 585 nm< 585 nmYellow Yellow 491 nm < 491 nm < λλ < 575 nm< 575 nmGreenGreen424 nm < 424 nm < λλ < 491 nm< 491 nmBlueBlue380 nm < 380 nm < λλ < 424 nm< 424 nmViolet Violet 0.85 nm < 0.85 nm < λλ < 380 nm< 380 nmUltraviolet (UV)Ultraviolet (UV)
WAVELENGTH WAVELENGTH RANGERANGE
COLORCOLOR
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The nature of light The nature of light –– as photonsas photons–– Photon scattering.Photon scattering.
•• one finds experimentally that the frequency of the scattered wavone finds experimentally that the frequency of the scattered wave is changed, e is changed, which does not come out of a wave picture of light. However, whewhich does not come out of a wave picture of light. However, when the light is n the light is viewed as a photon with energy proportional to the associated liviewed as a photon with energy proportional to the associated light wave, ght wave, excellent agreement with experiment is found. excellent agreement with experiment is found.
–– The photoelectric effect: The photoelectric effect: •• When light is shone at a metal plate, it is found that electronsWhen light is shone at a metal plate, it is found that electrons are ejected. are ejected.
These electrons then get accelerated to a nearby plate by an extThese electrons then get accelerated to a nearby plate by an external potential ernal potential difference, and a photoelectric current is established, as belowdifference, and a photoelectric current is established, as below
•• The photons hit an electron in the metal, giving up its energy, The photons hit an electron in the metal, giving up its energy, This is enough This is enough to free the electron from the attractive forces holding it in thto free the electron from the attractive forces holding it in the metal, and it is e metal, and it is accelerated towards the other side, causing a flow of charges anaccelerated towards the other side, causing a flow of charges and hence a d hence a current.current.
•• It is found experimentally that the photoelectric current dependIt is found experimentally that the photoelectric current depends critically on s critically on the frequency of the light being used. This is a feature of the the frequency of the light being used. This is a feature of the energy that the energy that the electrons gain when struck by the light, but in the wave pictureelectrons gain when struck by the light, but in the wave picture the energy of the energy of the light depends on the amplitude, and not on the frequency. the light depends on the amplitude, and not on the frequency.
•• However, in the photon picture of light the energy of the photonHowever, in the photon picture of light the energy of the photon is is proportional to the frequency of the associated wave, which therproportional to the frequency of the associated wave, which therefore provides efore provides a natural explanation of the frequency dependence of the photoela natural explanation of the frequency dependence of the photoelectric ectric current.current.
•• The explanation, which was first given by Einstein and which wonThe explanation, which was first given by Einstein and which won him the him the Nobel Prize.Nobel Prize.
JsconstPlanckh
3410624.6 −×== νε
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Light propagate through mediaLight propagate through media
•• Refractive index:Refractive index:
•• Index of refraction of a material generally increasing slightly Index of refraction of a material generally increasing slightly with decreasing with decreasing wavelength of the light. Such phenomena is called wavelength of the light. Such phenomena is called dispersion.dispersion.
1/ 0 >==λλvcn
ρρ
L
L
KKn
−+
=1
21
2.422.42DiamondDiamond
1.921.92zirconzircon
1.771.77sapphiresapphire589nm589nm
1.591.59PolystyrenePolystyrene
1.581.58LexanLexan
1.511.51PlexiglasPlexiglas
1.57~1.891.57~1.89Flint glassFlint glass1.5011.501BenzeneBenzene1.000131.00013HH22
1.521.52Crown glassCrown glass1.4721.472TurpentineTurpentine1.000451.00045COCO22
1.471.47Pyrex glassPyrex glass1.3611.361Ethyl alcoholEthyl alcohol1.000361.00036HeHe
1.461.46Fused quartzFused quartz1.3331.333WaterWater1.000291.00029AirAir
nnSolidSolidnnLiquidLiquidnnGasGas
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Light propagate through mediaLight propagate through media
•• Refraction: Refraction: –– When light propagates through a homogenous medium, its path woulWhen light propagates through a homogenous medium, its path would be d be
straight, whereas, if the medium is nonstraight, whereas, if the medium is non--homogeneous or if the light across from homogeneous or if the light across from one medium to another, the path may change direction gradually oone medium to another, the path may change direction gradually or abruptly. r abruptly. The change of light propagation direction is called refraction.The change of light propagation direction is called refraction.
–– Optically denser medium (n1<n2)Optically denser medium (n1<n2)
1
2
2
1
sinsin
nn
=ϕϕ
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Light propagate through mediaLight propagate through media
•• Total refraction Total refraction
•• reflection reflection
)/(sin2/
sinsin
121
1max2
1221
1
2
2
1
nnnn
nn
cri−=⇒>
>⇒>
=
ϕπϕϕϕ
ϕϕ
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Light propagate through mediaLight propagate through media
•• Optical lens Optical lens Convex lensConvex lens
Concave lensConcave lens
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Light propagate through mediaLight propagate through media
1/ 0 >==λλvcn
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AbsorptionAbsorption
•• Light is transmitted through a material, it will be Light is transmitted through a material, it will be absorbed by the molecules of the materialabsorbed by the molecules of the material
•• BeerBeer’’s law:s law:
–– αα iis the absorption or attenuation coefficients the absorption or attenuation coefficient
–– LcLc=1/=1/αα is called penetration depth.is called penetration depth.
–– When L=When L=LLcc, I/I, I/I00=1/e=37%, i.e., 63% energy =1/e=37%, i.e., 63% energy was absorbedwas absorbed
–– Metals have very small Metals have very small LcLc=1/=1/αα..
–– Copper, Copper, LcLc=0.6nm for 100 nm UV light=0.6nm for 100 nm UV light
–– Copper, Copper, LcLc=6.0nm for 1000 nm infrared light.=6.0nm for 1000 nm infrared light.
–– 2nm copper plate as the high pass filter.2nm copper plate as the high pass filter.
)exp(0 LII α−=
LL
I0
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illuminationillumination
•• Light sourceLight source–– Thermal source: Thermal source:
•• Lamps: Continuous wave (CW)Lamps: Continuous wave (CW)
–– Laser sourcesLaser sources•• Continuous wave (CW)Continuous wave (CW)•• Pulsed laserPulsed laser•• Singe wavelengthSinge wavelength
–– Point source:Point source:
–– Plane source:Plane source:
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Light sourceLight source
–– Thermal light source: Thermal light source: •• Emit electromagnetic radiation as a result of being Emit electromagnetic radiation as a result of being
heated to highheated to high--temperaturetemperature
•• Line sources:Line sources:
•• Continuum sources:Continuum sources:–– Incandescent lamps: heated tungsten filament in a Incandescent lamps: heated tungsten filament in a
evacuated glass container.evacuated glass container.–– Electric discharge lamps: fluorescent lamps. Filled with Electric discharge lamps: fluorescent lamps. Filled with
mercury vapor at low pressure and utilize an electric mercury vapor at low pressure and utilize an electric discharge through it to produce light in ultraviolet (UV) discharge through it to produce light in ultraviolet (UV) range. Through fluorescent, it is convert to visible light.range. Through fluorescent, it is convert to visible light.
–– Flash lamps: tubes containing a noble gas such xenon, Flash lamps: tubes containing a noble gas such xenon, krypton or argon. For their operation, high voltage stored krypton or argon. For their operation, high voltage stored in a capacitor is discharged through the gas, producing a in a capacitor is discharged through the gas, producing a highly luminous corona discharge. Light pulse is about highly luminous corona discharge. Light pulse is about 11μμs or 1 ms.s or 1 ms.
–– Sparks: produced by the electric breakdown of a gas Sparks: produced by the electric breakdown of a gas (helium, neo, argon or air) during an electric discharge (helium, neo, argon or air) during an electric discharge between electrodes. The choice of different electrodes between electrodes. The choice of different electrodes produces sparks of different shapes.produces sparks of different shapes.
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LaserLaser
–– Laser: Light Amplification by Stimulated Emission of Laser: Light Amplification by Stimulated Emission of Radiation (LASER)Radiation (LASER)
–– Advantages of laser light over thermal light source: Advantages of laser light over thermal light source:
•• Coherent light (with all light wave front in phase)Coherent light (with all light wave front in phase)
•• Collimated and concentrated (parallel light with Collimated and concentrated (parallel light with small cross area)small cross area)
•• Monochromic (energy concentrated in a very Monochromic (energy concentrated in a very narrow wavelength band)narrow wavelength band)
–– How a laser works:How a laser works:
•• Radiation energy is produced by an activated Radiation energy is produced by an activated medium( can be gas, crystal or semiconductor or medium( can be gas, crystal or semiconductor or liquid solution). liquid solution).
•• The medium consists of particles (atom, ions or The medium consists of particles (atom, ions or molecules).molecules).
•• When a photo, having energy When a photo, having energy hvhv, approaching the , approaching the particles, the photo may be absorbed cause an particles, the photo may be absorbed cause an electron or atoms to be raised temporarily to electron or atoms to be raised temporarily to highhigh--energy level.energy level.
•• When the excited electron or molecule to return When the excited electron or molecule to return ground level, ground level, spontaneous emissionspontaneous emission or or stimulated stimulated emissionemission would take place. would take place.
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LaserLaser
–– Spontaneous emissionSpontaneous emission: emit a photo with the : emit a photo with the same energy as that absorbed one, but in same energy as that absorbed one, but in random direction.random direction.
–– Stimulated emission:Stimulated emission: An electron or atom is An electron or atom is already at a higher energy level could become already at a higher energy level could become excited by an incident photo, without absorb excited by an incident photo, without absorb the photo, it will emission another photo with the photo, it will emission another photo with identical energy (frequency), phase, and identical energy (frequency), phase, and direction as the incident photon.direction as the incident photon.
–– External power source is required to maintain External power source is required to maintain the population of the atoms in higher energy the population of the atoms in higher energy level in order to make to stimulated emission level in order to make to stimulated emission taking place continuously.taking place continuously.
–– Optical cavity.Optical cavity.
–– QQ--switchswitch
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Commonly used LasersCommonly used Lasers
–– HeliumHelium--neon (Heneon (He--Ne) laserNe) laser
•• Active medium is helium neon atomsActive medium is helium neon atoms
•• Continuous wave laserContinuous wave laser
•• Power 0.3 ~15 Power 0.3 ~15 mWmW
•• λλ =633nm (red)=633nm (red)
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Commonly used LasersCommonly used Lasers
–– ArgonArgon--ion (ion (ArAr--ion) laserion) laser
•• Active medium is argon atoms Active medium is argon atoms maintained at the ion state.maintained at the ion state.
•• Continuous wave laserContinuous wave laser
•• Power level: 100 Power level: 100 mWmW ~10 W~10 W
•• Have seven wavelengthsHave seven wavelengths
•• λλ =488nm (blue)=488nm (blue)
•• λλ =514.5nm (green)=514.5nm (green)•• LDV applicationLDV application
•• LIF in liquid flowsLIF in liquid flows
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Commonly used LasersCommonly used Lasers
–– NdNd--YAG laserYAG laser
•• SolidSolid--state laserstate laser
•• Active medium: neodymium (NdActive medium: neodymium (Nd+3+3) as active ) as active medium incorporated as an impurity into a medium incorporated as an impurity into a crystal of crystal of YattiumYattium--AluminiumAluminium--GarnetGarnet (YAG) (YAG) as a hostas a host
•• Flash lamp is used as external sourceFlash lamp is used as external source
•• pulsed laser: 10 pulsed laser: 10 --400mJ/pulse or more400mJ/pulse or more
•• Pulse duration: 100ps ~ 10ns Pulse duration: 100ps ~ 10ns
•• WavelenghtWavelenght of tube of tube λλ =1064nm (infrared)=1064nm (infrared)
•• SHG: SHG: λλ =532nm (green), THG: =532nm (green), THG: λλ =355nm =355nm (UV), FHG: (UV), FHG: λλ =266nm (=266nm (deepUVdeepUV))
•• PIV, MTV, PLIFPIV, MTV, PLIF
•• Repetition rate can be as high as 30 Hz.Repetition rate can be as high as 30 Hz.
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Commonly used LasersCommonly used Lasers
–– Copper Vapor laserCopper Vapor laser
•• Active medium: copper vaporActive medium: copper vapor
•• Pulsed laser: 10mJ/pulse or morePulsed laser: 10mJ/pulse or more
•• Pulse duration: 15 ~ 60ns Pulse duration: 15 ~ 60ns
•• λλ =510.6nm (green), =510.6nm (green), λλ =578.2nm (yellow) =578.2nm (yellow) •• Repetition rate can be as high as Repetition rate can be as high as
f=5,000~15,000 Hz.f=5,000~15,000 Hz.
•• HighHigh--speed PIV, LIF and othersspeed PIV, LIF and others
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Commonly used LasersCommonly used Lasers
–– Dye laserDye laser
•• Active medium: complex multiActive medium: complex multi--atomic atomic organic moleculesorganic molecules
•• λλ =200nm ~ 1500nm=200nm ~ 1500nm
–– ExcimerExcimer laserlaser
•• Gas laser Gas laser KrFKrF and and XeclXecl
•• HighHigh--energyenergy
•• UV wavelengthUV wavelength
•• Pulsed laserPulsed laser
•• high repetition frequencyhigh repetition frequency
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Light ScatteringLight Scattering
•• Scattering Scattering –– Scattering is a general physical process whereby Scattering is a general physical process whereby
some forms of radiation, such as light, are forced some forms of radiation, such as light, are forced to deviate from a straight trajectory by one or to deviate from a straight trajectory by one or more localized nonmore localized non--uniformities in the medium uniformities in the medium through which it passes. through which it passes.
•• Elastic Scattering Elastic Scattering –– Excited electron or atoms emits a photo have Excited electron or atoms emits a photo have
exact the same frequency as the incident one.exact the same frequency as the incident one.
•• Inelastic scattering Inelastic scattering –– Excited electron or atoms emits a photo have a Excited electron or atoms emits a photo have a
frequency different from the incident one.frequency different from the incident one.
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Elastic scatteringElastic scattering•• Rayleigh Scattering Rayleigh Scattering
–– Light scattering from particles that are smaller than 1/15 of thLight scattering from particles that are smaller than 1/15 of the incident light wavelength (d< e incident light wavelength (d< λλ/15/15).).
–– Efficiency of the scattering from a particle is expressed in terEfficiency of the scattering from a particle is expressed in terms of scattering cross section.ms of scattering cross section.
•• Mie Scattering Mie Scattering –– Light scattering from a particles with its size close on bigger Light scattering from a particles with its size close on bigger than the incident light wavelength than the incident light wavelength
(d > (d > λλ).).–– Conservation of polarization directionConservation of polarization direction–– Angle dependentAngle dependent
•• Forward scattering Forward scattering •• Back scatteringBack scattering
.1065.6
)(
0
229
20
atomtheofwavelengthticcharateristheismT
TR
λσ
λλσσ
−×=
=
. d=1μm b. d=10μm c. d=30μm
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Inelastic ScatteringInelastic Scattering•• Raman Scattering Raman Scattering
–– Inelastic scattering from molecules.Inelastic scattering from molecules.–– Chance to occur is about 10Chance to occur is about 10--5 5 s 10s 10--2 2 of times lower than the Rayleigh scatteringof times lower than the Rayleigh scattering–– scattering cross section is several orders smaller than the Raylscattering cross section is several orders smaller than the Rayleigh scatteringeigh scattering–– Stoke transition : the energy of the emitted photo is higher thaStoke transition : the energy of the emitted photo is higher than the absorbed photo. n the absorbed photo. –– AntiAnti--stoke transition: the energy of the emitted photo is lower than stoke transition: the energy of the emitted photo is lower than the absorbed photo.the absorbed photo.–– Time between the absorption and emission: 10Time between the absorption and emission: 10--14 14 s.s.–– antianti--stokes line will be stronger when the temperature is low.stokes line will be stronger when the temperature is low.––
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Fluorescence and phosphorescenceFluorescence and phosphorescence
–– Rayleigh and Raman scattering occurs essentially instantaneouslyRayleigh and Raman scattering occurs essentially instantaneously. Not allowing . Not allowing other energy conversion phenomena to occur.other energy conversion phenomena to occur.
–– Fluorescence and phosphorescence: Photoluminescence with time deFluorescence and phosphorescence: Photoluminescence with time delaylay–– FluorescenceFluorescence
•• Emission when the excited from singlet state to ground,Emission when the excited from singlet state to ground,•• lifetime is about 10lifetime is about 10--10 10 ~ 10~ 10--5 5 s. s.
Rhoda mine BRhoda mine B
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Fluorescence and phosphorescenceFluorescence and phosphorescence
–– phosphorescencephosphorescence
•• Emission when the excited atom or Emission when the excited atom or molecule from triplet state to ground,molecule from triplet state to ground,
•• lifetime is about 10lifetime is about 10-- 4 4 ~ 10~ 10--5 5 s. s.
0
1000
2000
3000
4000
5000
200 300 400 500 600 700 800
T = 32.0oCT= 25.4 oCT= 19.7 oCT= 14.5 oCT = 10.2oCT= 3 .40 oC
W avelength (nm )
Rel
ativ
e in
tens
ity
Spectraphotom eter O utput vs W ave length
fluorescencefluorescence
PhosphorescencePhosphorescence
MTV chemical: MTV chemical: 11--BrNpBrNp••MMββ--CDCD••ROH complex ROH complex
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Light sensing and recordingLight sensing and recording
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LensesLenses
•• Focus length: Focus length: •• Depth of focus:Depth of focus:•• ff--numbers or focal ratio : is defined as the ratio of focal numbers or focal ratio : is defined as the ratio of focal
distance of the lens and its clear aperture diameter.distance of the lens and its clear aperture diameter.
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Photo detectorPhoto detector
•• Photo detector is a device to convert light to an electric Photo detector is a device to convert light to an electric current through photo electric effect.current through photo electric effect.
•• Quantum efficiency: Quantum efficiency:
•• Noise: Noise: –– Shot noise: due to random fluctuation of the rate Shot noise: due to random fluctuation of the rate
of photon collection and back ground illuminationof photon collection and back ground illumination
–– Thermal noise: caused by amplification of current Thermal noise: caused by amplification of current inside the photo detector and by external inside the photo detector and by external amplifier.amplifier.
•• Dark current: the current produced by the photo Dark current: the current produced by the photo detector even in the absence of a desirable light detector even in the absence of a desirable light source.source.
•• Two kinds of photo detectors: Two kinds of photo detectors: –– Photomultiplier tubes (PMT) Photomultiplier tubes (PMT) –– photodiodes (PD) or photo electric cellsphotodiodes (PD) or photo electric cells
electrons emitted ofNumber :photons absorbed ofNumber :
p
e
p
eq
NN
NN
=η
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Photo detectorPhoto detector
•• Photomultiplier tubes (PMT) Photomultiplier tubes (PMT) –– Photocathode: absorbs photons Photocathode: absorbs photons
and emits electrons.and emits electrons.–– Dynodes: increase number of Dynodes: increase number of
photonsphotons–– Anodes: outputAnodes: output
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Photo detectorPhoto detector
•• photodiodes (PD) or photo electric cellsphotodiodes (PD) or photo electric cells–– PP--n junctions of semiconductors, n junctions of semiconductors,
commonly siliconcommonly silicon--silicon type.silicon type.–– High quantum efficiency High quantum efficiency –– But not internal amplification But not internal amplification
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Linearity and Dynamic Range of a Digital CameraLinearity and Dynamic Range of a Digital Camera
•• Linearity:Linearity:–– Intensified CCD cameras usually need to Intensified CCD cameras usually need to
check its linearitycheck its linearity
•• Dynamic Range:Dynamic Range:–– The ratio between the fullThe ratio between the full--well capacity well capacity
and the dark current noise.and the dark current noise.–– For example, for a 8For example, for a 8--bit CCD camera, bit CCD camera,
maximum intensity is 2maximum intensity is 288=256, dark =256, dark current noise is about 25, then Dynamic current noise is about 25, then Dynamic range is about 10.range is about 10.
–– Available bits number:Available bits number:•• 8 bit, 16 bit, 24 bit8 bit, 16 bit, 24 bit
0
500
1000
1500
2000
2500
3000
3500
4000
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
y = a+bx+cx2+dx3
a=1.26, b=1.05, c=-5.36E-5, d=-1.67E-9Gain level 100%Gain level 90%Gain level 80%Gain level 70%y=x
single frame modeexposure time 300usf=2.8
input intensity
outp
ut in
tens
ity
Input Photon Input Photon
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Interlaced CamerasInterlaced Cameras
• The fastest response time of human being for images is about ~ 15Hz• Video format:
– PAL (Phase Alternating Line ) format with frame rate of f=25Hz (sometimes in 50Hz). Used by U.K., Germany, Spain, Portugal, Italy, China, India, most of Africa, and the Middle East
– NTSC format: established by National Television Standards Committee (NTSC) with frame rate of f=30Hz. Used by U.S., Canada, Mexico, some parts of Central and South America, Japan, Taiwan, and Korea.
Even fieldEven field(2,4,6(2,4,6……640)640)
Old fieldOld field(1,3,5(1,3,5……639)639)
Even field
Odd field
16.6ms16.6ms
1 frameF=30Hz
480 pixels by 640 pixels480 pixels by 640 pixels
Interlaced cameraInterlaced camera
timetime
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Progressive scan cameraProgressive scan camera
•• All image systems produce a clear image of the background All image systems produce a clear image of the background •• Jagged edges from motion with interlaced scan Jagged edges from motion with interlaced scan •• Motion blur caused by the lack of resolution in the 2CIF sample Motion blur caused by the lack of resolution in the 2CIF sample •• Only progressive scan makes it possible to identify the driverOnly progressive scan makes it possible to identify the driver
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Mystery of flying rodsMystery of flying rods
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Digital cameraDigital camera
•• CCD camera and Intensified CCD (ICCD) camera:CCD camera and Intensified CCD (ICCD) camera:
–– Spatial resolution: 1K by 1k, 4K by 4KSpatial resolution: 1K by 1k, 4K by 4K
–– Frame rate : 30 Hz, High speed camera 1khz ~10K Frame rate : 30 Hz, High speed camera 1khz ~10K hzhz–– In a CCD sensor, every pixel's charge is transferred through a vIn a CCD sensor, every pixel's charge is transferred through a very limited number ery limited number
of output nodes (often just one) to be converted to voltage, bufof output nodes (often just one) to be converted to voltage, buffered, and sent offfered, and sent off--chip as an analog signal. All of the pixel can be devoted to ligchip as an analog signal. All of the pixel can be devoted to light capture, and the ht capture, and the output's uniformity (a key factor in image quality) is high. output's uniformity (a key factor in image quality) is high.
•• CMOS (Complementary metalCMOS (Complementary metal--oxide semiconductor) camerasoxide semiconductor) cameras
–– In a CMOS sensor, each pixel has its own chargeIn a CMOS sensor, each pixel has its own charge--toto--voltage conversion, and the voltage conversion, and the sensor often also includes amplifiers, noisesensor often also includes amplifiers, noise--correction, and digitization circuits, so correction, and digitization circuits, so that the chip outputs digital bitsthat the chip outputs digital bits
–– These other functions increase the design complexity and reduce These other functions increase the design complexity and reduce the area the area available for light capture. With each pixel doing its own conveavailable for light capture. With each pixel doing its own conversion, uniformity is rsion, uniformity is lower. But the chip can be built to require less offlower. But the chip can be built to require less off--chip circuitry for basic operationchip circuitry for basic operation
•• In summary for CMOS camerasIn summary for CMOS cameras
–– Low costLow cost–– Operation versatilityOperation versatility
–– High speedHigh speed
–– Quality is not as high as CCD camerasQuality is not as high as CCD cameras
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Pressure Gauge and TransducersPressure Gauge and Transducers
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Measurement Techniques for ThermalMeasurement Techniques for Thermal--Fluids StudiesFluids Studies
ThermalThermal--Fluids Fluids measurementmeasurementtechniquestechniques
Intrusive Intrusive techniquestechniques
NonNon--intrusiveintrusivetechniquestechniques
•• PitotPitot probeprobe•• hotwire, hot filmhotwire, hot film•• thermocouplesthermocouples•• etc ...etc ...
•• Laser Doppler Laser Doppler VelocimetryVelocimetry (LDV)(LDV)•• Planar Doppler Planar Doppler VelocimetryVelocimetry (PDV)(PDV)•• Particle Image Particle Image VelocimetryVelocimetry (PIV)(PIV)•• etcetc……
particleparticle--based based techniquestechniques
•• Laser Induced Fluorescence (LIF)Laser Induced Fluorescence (LIF)•• Molecular Tagging Molecular Tagging VelocimetryVelocimetry (MTV)(MTV)•• Molecular Tagging Molecular Tagging TherometryTherometry (MTT)(MTT)•• Pressure Sensitive Paint (PSP)Pressure Sensitive Paint (PSP)•• Temperature Sensitive Paint (TSP)Temperature Sensitive Paint (TSP)•• Quantum Dot ImagingQuantum Dot Imaging•• etc etc ……
moleculemolecule--based based techniquestechniques
Pressure, velocity, temperature, density (concentration), etc..
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IntroductionIntroduction
•• Pressure measurements are the primary measurements made in most Pressure measurements are the primary measurements made in most practical aerodynamic testing or basic fluid mechanics experimenpractical aerodynamic testing or basic fluid mechanics experiments.ts.
•• Surface pressure measurements are used for:Surface pressure measurements are used for:•• Identifying specific flow phenomena (boundary layer separation, Identifying specific flow phenomena (boundary layer separation,
shock wave impingement, etc) that are not easily measured by shock wave impingement, etc) that are not easily measured by ““standard pressure tapstandard pressure tap”” measurements.measurements.
•• Validation of computational codesValidation of computational codes•• Loads calculations by integration of the surfaces pressuresLoads calculations by integration of the surfaces pressures
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Pressure measurements
• Pressure is defined as the amount of force that presses on a certain area. – The pressure on the surface will increase if you make the force on an area bigger. – Making the area smaller and keeping the force the same also increase the pressure.– Pressure is a scalar
dAdF
AFP nn ==
dA
ndF
τ̂
n̂
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Pressure measurements
ambabsolutegauge PPP −=
Manometer
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Mechanical Pressure Gauges Mechanical Pressure Gauges --11
Fluid chamberFluid chamber
weightweight
pumppump
cylindercylinderplungerplunger
Calibration Calibration pressurepressure
PP
Deadweight gauges:• High accuracy
• Usually used for the calibration of other instruments
• Application range : 102~108 pa
•Uncertainty is within 0.01% ~0.05% of the reading
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Mechanical Pressure Gauges Mechanical Pressure Gauges --22
ElasticElastic--element gauges:element gauges:
•• Contain an elastic elements that deforms under pressure and Contain an elastic elements that deforms under pressure and creates a linear or angular displacementcreates a linear or angular displacement
•• The displacement is either displayed on a dial by means of The displacement is either displayed on a dial by means of purely mechanical linkages or transformed to an electric signal purely mechanical linkages or transformed to an electric signal that can be displayed or recorder at will.that can be displayed or recorder at will.
•• They usually used for monitoring supply pressureThey usually used for monitoring supply pressurep
p
p
Cross sectional shape Curved Bourdon tube
Twisted Bourdon tube
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Electrical Pressure transducersElectrical Pressure transducers
•• These devices provides an electric output signal that is These devices provides an electric output signal that is linearly or nonlinearly dependent on the absolute pressure or linearly or nonlinearly dependent on the absolute pressure or a pressure difference.a pressure difference.
•• They can be categorized as:They can be categorized as:–– Molecular transducers: Molecular transducers:
•• Applied pressure or force produces a change (on the Applied pressure or force produces a change (on the molecular level) of a electrical property of material.molecular level) of a electrical property of material.
•• PiezoPiezo--electric material such as quartz crystal: change electric material such as quartz crystal: change in internal dipole moments of the molecules of the in internal dipole moments of the molecules of the crystal when the pressure or force is applied.crystal when the pressure or force is applied.
–– Parametrical transducers:Parametrical transducers:•• The gross electrical parameter (resistance, The gross electrical parameter (resistance,
inductance, capacitance) of an associate electrical inductance, capacitance) of an associate electrical parameter is altered by applied force.parameter is altered by applied force.
•• VariableVariable--capacitance transducercapacitance transducer p
E
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Wall Pressure measurements Wall Pressure measurements --11
•• Making small orifice (pressure tap) facing the flow.Making small orifice (pressure tap) facing the flow.
•• Machining small hole could be difficultMachining small hole could be difficult•• d = 0.5~3.0mm in practiced = 0.5~3.0mm in practice•• l/dl/d = 5 ~ 15 is common used= 5 ~ 15 is common used
•• Potential effect on the wall roughnessPotential effect on the wall roughness•• Effects of unsteady shock wave, and shockEffects of unsteady shock wave, and shock--
boundaryboundary--layer interactions for transonic and layer interactions for transonic and supersonic flows:supersonic flows:
•• PSP method to be introduced laterPSP method to be introduced later
V, P
PPmm
ll
dd
0>−=Δ PPp m
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Wall Pressure measurements Wall Pressure measurements -- 22
•• For a unsteady flow, the dynamic response of a For a unsteady flow, the dynamic response of a pressure acquisition system is a key issue!pressure acquisition system is a key issue!
–– Dynamic response of the pressure transducersDynamic response of the pressure transducers–– Dynamic response of the connection tubingDynamic response of the connection tubing
•• Remote connectionRemote connection–– Dynamic response is lowDynamic response is low–– Spatial resolution is highSpatial resolution is high
•• Cavity mountingCavity mounting–– Dynamic response is goodDynamic response is good–– Spatial resolution is highSpatial resolution is high
•• Flush mountingFlush mounting–– Dynamic response is highDynamic response is high–– Spatial resolution is lowSpatial resolution is low
Pressure Pressure transducerstransducers
VV
Connection Connection tubingtubing
pressure pressure transducertransducer
VV
VV
pressure pressure transducertransducer
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Pressure Measurements inside Flow FieldPressure Measurements inside Flow Field
•• NonNon--intrusive technique is unavailable for direct intrusive technique is unavailable for direct pressure measurementspressure measurements
–– Based on NBased on N--S equation to calculate pressure field using S equation to calculate pressure field using the measured (PIV) velocity field. the measured (PIV) velocity field.
•• Static probe: for static pressure measurementsStatic probe: for static pressure measurements•• PitotPitot probe: for total pressure measurementsprobe: for total pressure measurements•• PitotPitot--static probe: for static and total pressures static probe: for static and total pressures
measurements (velocity measurements)measurements (velocity measurements)•• MultiMulti--hole probe:hole probe:
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Pressure Sensitive Paint (PSP) / Pressure Sensitive Paint (PSP) / Temperature Sensitive Paint (TSP)Temperature Sensitive Paint (TSP)
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IntroductionIntroduction
Conventional pressure measurements: Transducers or tapsConventional pressure measurements: Transducers or taps•• Discrete preDiscrete pre--determined locationsdetermined locations•• Very high accuracy (< 0.05% FS)Very high accuracy (< 0.05% FS)•• Well understood with long testing backgroundWell understood with long testing background•• High data rate with scanned systems (1000+)High data rate with scanned systems (1000+)•• Limitations to were they can be installedLimitations to were they can be installed•• Potential effect on the flow field Potential effect on the flow field –– intrusive measurementsintrusive measurements•• Expensive installation costsExpensive installation costs
-0.10-0.05
00.050.100.15
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
X/C
Y/C
airfoilairfoil
test sectiontest section
incomingincomingflowflow
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Pressure Sensitive Paint (PSP)Pressure Sensitive Paint (PSP)
•• Sprayed over entire exterior surfaceSprayed over entire exterior surface•• nonnon--intrusive pressure measurementsintrusive pressure measurements•• high spatial resolution with resolution limited only by detectiohigh spatial resolution with resolution limited only by detection systemn system•• Limited to optical access applicationsLimited to optical access applications•• Inexpensive application costsInexpensive application costs•• Relatively expensive initial costs to setup the systemRelatively expensive initial costs to setup the system•• HighHigh--speed applicationsspeed applications•• Newer method that is still being fully explored for lowNewer method that is still being fully explored for low--speed applications.speed applications.
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Basic Principles of Pressure Sensitive Paint (PSP)Pressure Sensitive Paint (PSP)
•• Composition of Air: 78.08% NComposition of Air: 78.08% N22, 20.95% O, 20.95% O22, 0.93% , 0.93% ArAr, 0.03% CO, 0.03% CO22, 0.002% Ne, plus , 0.002% Ne, plus lesser amounts of Methane, Helium, Krypton, Hydrogen, Xenon.lesser amounts of Methane, Helium, Krypton, Hydrogen, Xenon.
•• The pressure of air can be determined if the particle pressure oThe pressure of air can be determined if the particle pressure of oxygen (i.e. oxygen f oxygen (i.e. oxygen concentration) can be measured. concentration) can be measured.
•• A typical pressure sensitive paint is comprised of two main partA typical pressure sensitive paint is comprised of two main parts: an oxygen sensitive s: an oxygen sensitive fluorescent molecule and an oxygen permeable binderfluorescent molecule and an oxygen permeable binder
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Basic Principles of Pressure Sensitive Paint (PSP)Pressure Sensitive Paint (PSP)
•• The pressure sensitive paint method is based on the sensitivity The pressure sensitive paint method is based on the sensitivity of certain luminescent of certain luminescent molecules to the presence of oxygen. molecules to the presence of oxygen.
–– When a luminescent molecule absorbs a photon, it is excited to aWhen a luminescent molecule absorbs a photon, it is excited to an upper singlet energy n upper singlet energy state. The molecule then typically recovers to the ground state state. The molecule then typically recovers to the ground state by the emission of a photon by the emission of a photon of a longer wavelength (i.e. fluorescence or phosphorescence ). of a longer wavelength (i.e. fluorescence or phosphorescence ).
–– In some materials, oxygen can interact with the molecule so thatIn some materials, oxygen can interact with the molecule so that the transition to the the transition to the ground state is ground state is radiationlessradiationless, this process is known as oxygen quenching. , this process is known as oxygen quenching.
–– The rate at which these two processes compete is dependent on thThe rate at which these two processes compete is dependent on the partial pressure of e partial pressure of oxygen present, with a higher oxygen pressure quenching the moleoxygen present, with a higher oxygen pressure quenching the molecule more, thus giving cule more, thus giving off a lower intensity of light.off a lower intensity of light.
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Basic Principles of Pressure Sensitive Paint (PSP)Pressure Sensitive Paint (PSP)
•• For oxygen quenching, the intensity decrease can be described byFor oxygen quenching, the intensity decrease can be described by the wellthe well--known known SternStern--VolmerVolmer equation:equation:
•• ττ is the lifetime, I is the intensityis the lifetime, I is the intensity•• KKSVSV is the Sternis the Stern--VolmerVolmer constantconstant•• Q is the quencher or partial pressure of oxygenQ is the quencher or partial pressure of oxygen
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Advantages of Pressure Sensitive Paint (PSP)Advantages of Pressure Sensitive Paint (PSP)
•• Pressure sensitive paint has numerous advantages over conventionPressure sensitive paint has numerous advantages over conventional pressure taps and al pressure taps and transducers. transducers.
–– The most obvious is that PSP is a field measurement, allowing foThe most obvious is that PSP is a field measurement, allowing for a surface pressure r a surface pressure determination over the entire model, not just at discrete pointsdetermination over the entire model, not just at discrete points. Hence, PSP provides a much . Hence, PSP provides a much greater spatial resolution than pressure taps, and disturbances greater spatial resolution than pressure taps, and disturbances in the flow are immediately in the flow are immediately observable. observable.
•• PSP also has the advantage of being a nonPSP also has the advantage of being a non--intrusive technique. intrusive technique. –– Use of PSP, for the most part, does not affect the flow around tUse of PSP, for the most part, does not affect the flow around the model, allowing its use he model, allowing its use
over the entire model surface.over the entire model surface.–– The use of PSP eliminates the need for a large number of pressurThe use of PSP eliminates the need for a large number of pressure taps, which leads to more e taps, which leads to more
than one benefit. Since pressure taps do not need to be installethan one benefit. Since pressure taps do not need to be installed, models can be constructed d, models can be constructed in less time, and with less money than before. in less time, and with less money than before.
–– Also, since holes do not need to be drilled in the model for theAlso, since holes do not need to be drilled in the model for the installation of taps, the model installation of taps, the model strength is increased, and higher Reynolds numbers can be obtainstrength is increased, and higher Reynolds numbers can be obtained. ed.
–– Not only does the PSP method reduce the cost of the model constrNot only does the PSP method reduce the cost of the model construction, but it also reduces uction, but it also reduces the cost of the instrumentation needed for data collection. In athe cost of the instrumentation needed for data collection. In addition, the equipment needed ddition, the equipment needed for PSP costs less than pressure taps, but it can also be easilyfor PSP costs less than pressure taps, but it can also be easily reused for numerous models. reused for numerous models.
•• In aircraft design, PSP has the potential to save both time and In aircraft design, PSP has the potential to save both time and money. money. –– The continuous data distribution on the model provided by PSP caThe continuous data distribution on the model provided by PSP can easily be integrated over n easily be integrated over
specific components, which can provide detailed surface loads. specific components, which can provide detailed surface loads. –– Since a model for use with the PSP technique is faster to constrSince a model for use with the PSP technique is faster to construct, this allows for load data uct, this allows for load data
to be known much earlier in the design processto be known much earlier in the design process
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Disadvantages of Pressure Sensitive Paint (PSP)Pressure Sensitive Paint (PSP)
•• One of these characteristics is that the response of the luminesOne of these characteristics is that the response of the luminescent molecules in the PSP cent molecules in the PSP coating degrades with time of exposure to the excitation illumincoating degrades with time of exposure to the excitation illumination. ation.
–– This degradation occurs because of a photochemical reaction thatThis degradation occurs because of a photochemical reaction that occurs when the occurs when the molecules are excited. molecules are excited.
–– Eventually, this degradation of the molecules determines the useEventually, this degradation of the molecules determines the useful life of the PSP ful life of the PSP coating. coating.
–– This characteristic becomes more important for larger models, asThis characteristic becomes more important for larger models, as the cost and time of the cost and time of PSP reapplication becomes a significant factor. PSP reapplication becomes a significant factor.
•• A second undesirable characteristic of PSP is that the emission A second undesirable characteristic of PSP is that the emission intensity is affected by the intensity is affected by the local temperature. local temperature.
–– This behavior is due to the effect temperature has on the energyThis behavior is due to the effect temperature has on the energy state of the state of the luminescent molecules, and the oxygen permeability of the binderluminescent molecules, and the oxygen permeability of the binder. .
–– This temperature dependence becomes even more significant in comThis temperature dependence becomes even more significant in compressible flow pressible flow tests, where the recovery temperature over the model surface is tests, where the recovery temperature over the model surface is not uniform.not uniform.
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ImplementationImplementation of of Pressure Sensitive Paint (PSP)Pressure Sensitive Paint (PSP)
•• Intensity based Methods (most common)Intensity based Methods (most common)–– FullFull--field using camerafield using camera–– Point systems using scanning laserPoint systems using scanning laser
•• lifetime based Methods (lifetime decay)lifetime based Methods (lifetime decay)–– FullFull--field using camerafield using camera–– Point systems using scanning laserPoint systems using scanning laser
••
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Intensity based PSPIntensity based PSP
•• The SternThe Stern--VolmerVolmer equation is rewritten in the equation is rewritten in the popular intensity ratio form:popular intensity ratio form:
•• A and B are highly dependent on the A and B are highly dependent on the luminophoreluminophore and binder material as well as and binder material as well as the temperature sensitivity of the materials the temperature sensitivity of the materials used to make the paint. A 2nd order curve used to make the paint. A 2nd order curve generated from calibration data is most often generated from calibration data is most often used.used.
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Intensity based PSPIntensity based PSP
•• Requires two readings, a reference at Requires two readings, a reference at constant pressure (wind off) and an constant pressure (wind off) and an unknown data point (windunknown data point (wind--on)on)
•• Ratio of intensities IRatio of intensities IREFREF/I is inversely /I is inversely proportional to the air pressureproportional to the air pressure
•• The excitation and detection systems must be The excitation and detection systems must be spectrally separated, (>10spectrally separated, (>10--6 attenuation in 6 attenuation in stop band).stop band).
•• Simplest technique, most sensitive Simplest technique, most sensitive •• Very sensitive to motion between windVery sensitive to motion between wind--off off
and windand wind--onon•• A long period of time can elapse between A long period of time can elapse between
reference and data.reference and data.•• images resulting in significant changes in images resulting in significant changes in
contamination of paint, light stability, etc contamination of paint, light stability, etc that cannot be normalized by the reference that cannot be normalized by the reference condition.condition.
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Intensity based PSPIntensity based PSP
•• Advantages:Advantages:•• Eliminate wind off images and image Eliminate wind off images and image
registration problems. It works in theory registration problems. It works in theory •• In practice, due to homogeneity problems In practice, due to homogeneity problems
of dispersing of two kinds of molecules, it of dispersing of two kinds of molecules, it actually requires a double set of ratios, actually requires a double set of ratios, often called ratio of ratios method.often called ratio of ratios method.
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Intensity based PSPIntensity based PSP--temperature compensationtemperature compensation
•• Advantages:Advantages:•• Measure temperature to compensate Measure temperature to compensate
for temperature sensitivity of PSP.for temperature sensitivity of PSP.•• This technique requires all four This technique requires all four
images to be aligned.images to be aligned.
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LifetimeLifetime--based PSPbased PSP
•• Easiest to do with a point measurement, but Easiest to do with a point measurement, but can use time resolved cameras to measure can use time resolved cameras to measure lifetime decays of the probe molecules.lifetime decays of the probe molecules.
•• Point measurements require a pulsed light Point measurements require a pulsed light source and detector (PMT, PD)source and detector (PMT, PD)
•• Time resolved imaging requires a double Time resolved imaging requires a double pulse type experiment to measure the decay pulse type experiment to measure the decay times (gated camera, interline transfer times (gated camera, interline transfer camera capable of multiple flash integration).camera capable of multiple flash integration).
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LifetimeLifetime--based PSPbased PSP
•• Benefits:Benefits:–– Eliminates the need for aligning two or three Eliminates the need for aligning two or three
images since the pair of (or three ) images are images since the pair of (or three ) images are taken at the same condition relatively close in taken at the same condition relatively close in time (microtime (micro--seconds).seconds).
–– Pressure and temperature distributions can be Pressure and temperature distributions can be determined simultaneously. determined simultaneously.
•• Disadvantages:Disadvantages:–– Requires three gates to generate two equations Requires three gates to generate two equations
of gate ratios to solve for pressure and of gate ratios to solve for pressure and temperature at each point (pixel).temperature at each point (pixel).
–– Camera noise is much higher, especially gated Camera noise is much higher, especially gated intensified cameras.intensified cameras.
–– Paints have tended to be more spatially noisy Paints have tended to be more spatially noisy from lifetime differences between molecules from lifetime differences between molecules (homogeneity problem).(homogeneity problem).
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PSP/TSP coatingsPSP/TSP coatings
•• PSP coatings used at NASA GRCPSP coatings used at NASA GRC–– Boeing PF2B Boeing PF2B –– ruthenium ruthenium bathophenanthrolinebathophenanthroline in silicone rubber binder in silicone rubber binder
(soft(soft–– paint, chlorinated solvent)paint, chlorinated solvent)–– UW (ISSI) FIB UW (ISSI) FIB –– PtTFPPPtTFPP in FIB copolymer binder (hard, good steady state in FIB copolymer binder (hard, good steady state
paint)paint)–– NASA Langley NASA Langley –– PtTFPPPtTFPP in FEM (very hard, very smooth finish)in FEM (very hard, very smooth finish)–– ISSI solISSI sol--gel gel –– Ru(ph2Ru(ph2--phen) and phen) and PtTFPPPtTFPP on solon sol--gels (higher frequency gels (higher frequency
response)response)–– Anodized aluminum Anodized aluminum –– dip coated Ru(ph2dip coated Ru(ph2--phen) on anodized surface (very phen) on anodized surface (very
high freq. response)high freq. response)–– UW UW PtOEPPtOEP in MAX acrylic copolymer (ice paint)in MAX acrylic copolymer (ice paint)
•• TSP coatings TSP coatings –– Boeing TSP (range: 0 to 100Boeing TSP (range: 0 to 100°°C, sensitivity ~ C, sensitivity ~ --3%/3%/°°C)C)–– EuTTAEuTTA in commercial clear or shellac (in commercial clear or shellac (--20 to 8020 to 80°°C, ~ C, ~ --4%/4%/°°C)C)–– ThermographicThermographic phosphors in high temp binders (phosphors in high temp binders (--20 to >100020 to >1000°°C)C)
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Intensity based PSPIntensity based PSP•• Excitation:Excitation:
–– Continuous Sources: Continuous Sources: LEDsLEDs, Filtered lamps , Filtered lamps (Halogen, Xenon), Lasers(Halogen, Xenon), Lasers
–– Pulsed Sources for instantaneous or periodic Pulsed Sources for instantaneous or periodic measurements: measurements: LEDsLEDs, Xenon, strobes/flash, Xenon, strobes/flash
•• DetectorsDetectors–– Cooled Scientific grade CCD cameras (slow Cooled Scientific grade CCD cameras (slow
scan, low noise), PMT, PDscan, low noise), PMT, PD
Typical PSP absorption and emission spectra Typical PSP absorption and emission spectra [from McLachlan and Bell, 1995][from McLachlan and Bell, 1995]
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Calibration for PSPCalibration for PSP•• AA--priori Calibrationspriori Calibrations•• Paints are typically calibrated in a cell that varies pressure aPaints are typically calibrated in a cell that varies pressure and temperature and has a nd temperature and has a
reference measurement reference measurement –– this calibration is used when no onthis calibration is used when no on--model instrumentation model instrumentation exists. exists.
•• InIn--situ Calibrationsitu Calibration–– Uses standard onUses standard on--model instrumentation to calibrate the paint/images in placemodel instrumentation to calibrate the paint/images in place–– Compensates for temperature differences from reference data, spaCompensates for temperature differences from reference data, spatial temperature tial temperature
differences are averaged among all the points used to generate adifferences are averaged among all the points used to generate a calibrationcalibration•• In practice both calibrations are typically usedIn practice both calibrations are typically used
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Calibration setupCalibration setup
Heat sinkHeat sink--external flowexternal flow
Silica quartz windowSilica quartz window
Pressure Pressure GuageGuage
DSA ModuleDSA Module
UV LampUV Lamp
Test sample insideTest sample inside
CCDCCDCameraCamera FilterFilter
Pressure controlPressure control
• Pressure air pipe to control the pressure in the chamber• Water recirculation to control the temperature on the
sample plate
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PSP calibration image processPSP calibration image process
X (mm)
Y(m
m)
-10 -5 0 5 10-10
-5
0
5
1.41.351.31.251.21.151.11.0510.950.90.850.80.750.70.650.60.550.5
IntensityRatio
X (mm)
Y(m
m)
-10 -5 0 5 10-10
-5
0
5
120011001000900800700600500400300200100
Intensity
X (mm)
Y(m
m)
-10 -5 0 5 10-10
-5
0
5
120011001000900800700600500400300200100
Intensity
X (mm)Y
(mm
)
-10 -5 0 5 10-10
-5
0
5
1.41.351.31.251.21.151.11.0510.950.90.850.80.750.70.650.60.550.5
IntensityRatio
X (mm)
Y(m
m)
-10 -5 0 5 10-10
-5
0
5
120011001000900800700600500400300200100
Intensity
X (mm)
Y(m
m)
-10 -5 0 5 10-10
-5
0
5
120011001000900800700600500400300200100
Intensity
Reference Intensity: Iref
Reference Intensity: Iref
P/Pref=7.2: Intensity Intensity ratio: Iref/I
P/Pref=0.23 Intensity Intensity ratio: Iref/I
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Calibration curve Calibration curve –– Positive pressurePositive pressure
• Fit function: y=0.00149x^3-0.0510x^2+0.672x+0.436• Error level is below 1%
Calibration curve for the paint positive pressure and error analysis
-0.010
-0.005
0
0.005
0.010
1.0 1.5 2.0 2.5 3.0 3.5
Intensity ratio under different pressureEr
ror %
((I r-I av
e)/Iav
e100%
)
1.0
1.5
2.0
2.5
3.0
3.5
1 2 3 4 5 6 7
y = +0.00149x3 -0.0510x2 +0.672x1 +0.436, max dev:0.0241, r2=1.00
P/Pref
Inte
nsity
Rat
io, I
ref/I
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0.6
0.7
0.8
0.9
1.0
0.2 0.4 0.6 0.8 1.0
y = +0.217x3 -0.617x2 +0.946x1 +0.456, max dev:0.00550, r2=1.00
Pressure Ratio P/Prref
Inte
nsity
Rat
io I re
f /I
Calibration curve Calibration curve –– Vacuum pressureVacuum pressure
Calibration curve for the PSP paint under vacuum pressure and error analysis
Fit function: y=0.217x^3-0.617x^2+0.946x+0.456Error level is below 1%
-0.010
-0.005
0
0.005
0.010
0.2 0.4 0.6 0.8 1.0
Pressure ratioEr
orr%
(( Ir- I
r ef)/
I r ef1
00%
)
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Uncertainty for PSPUncertainty for PSP•• Characterization of the paint and calibration errors (aCharacterization of the paint and calibration errors (a--priori, inpriori, in--situ calibration, situ calibration,
photo degradation, paint contamination, paint intrusiveness, timphoto degradation, paint contamination, paint intrusiveness, time response)e response)•• Measurement system errors (detector noise, illumination spectralMeasurement system errors (detector noise, illumination spectral and temporal and temporal
stability, spectral leakage)stability, spectral leakage)•• Signal analysis errors (registration from model motion and deforSignal analysis errors (registration from model motion and deformation, mation,
incomplete temperature compensation, self illumination, incomplete temperature compensation, self illumination, resectioningresectioning on a nonon a non--deformed grid)deformed grid)
•• The major contributor is temperature uncertainty which can accouThe major contributor is temperature uncertainty which can account for up to nt for up to 90% of the total uncertainty90% of the total uncertainty
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Applications of PSP TechniqueApplications of PSP Technique
PSP combined with PIVPSP combined with PIV
PSP measurement resultPSP measurement result
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Application ExamplesApplication Examples
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Application ExamplesApplication Examples
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Application ExamplesApplication Examples
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Application ExamplesApplication Examples
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Application ExamplesApplication Examples
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Application ExamplesApplication Examples
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Application ExamplesApplication Examples
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Application ExamplesApplication Examples
Copyright Copyright ©© by Dr. Hui Hu @ Iowa State University. All Rights Reserved!by Dr. Hui Hu @ Iowa State University. All Rights Reserved!
PSP Technique for Low Speed ApplicationsPSP Technique for Low Speed Applications
PSP measurements of PSP measurements of a 2002 Ford Thunderbirda 2002 Ford Thunderbird
VV∞∞=50m/s=50m/s
Copyright Copyright ©© by Dr. Hui Hu @ Iowa State University. All Rights Reserved!by Dr. Hui Hu @ Iowa State University. All Rights Reserved!
Applications of PSP TechniqueApplications of PSP Technique
TimeTime--resolved PSP measurements on the front and lateral side surfacesresolved PSP measurements on the front and lateral side surfaces of a 3of a 3--D D square cylinder (square cylinder (YoritaYorita et al. 2010) et al. 2010)
VV∞∞=50m/s=50m/s
Copyright Copyright ©© by Dr. Hui Hu @ Iowa State University. All Rights Reserved!by Dr. Hui Hu @ Iowa State University. All Rights Reserved!
Wall Slot Jets Pertinent toWall Slot Jets Pertinent to Trailing Edge Cooling of Turbine BladesTrailing Edge Cooling of Turbine Blades
•• Thermodynamic analysis reveals that Thermodynamic analysis reveals that thermal efficiency and power output thermal efficiency and power output of a gas turbine can be increased of a gas turbine can be increased with higher turbine inlet with higher turbine inlet temperatures temperatures
•• Advanced gas turbines are operated Advanced gas turbines are operated at peak turbine inlet temperature at peak turbine inlet temperature about about 17001700 °°C, C, which is well beyond which is well beyond the maximum endurable temperature the maximum endurable temperature for the blade material. for the blade material.
Copyright Copyright ©© by Dr. Hui Hu @ Iowa State University. All Rights Reserved!by Dr. Hui Hu @ Iowa State University. All Rights Reserved!
Damaged turbine blades
•• Protect the blade against the risk of damageProtect the blade against the risk of damage–– New material to endure higher temperatureNew material to endure higher temperature–– StateState--ofof--art cooling techniques for film cooing and trailing edge coolingart cooling techniques for film cooing and trailing edge cooling
Majority of Majority of damages starting damages starting at tips and at tips and trailing edgestrailing edges
Copyright Copyright ©© by Dr. Hui Hu @ Iowa State University. All Rights Reserved!by Dr. Hui Hu @ Iowa State University. All Rights Reserved!
Experimental SetupExperimental Setup
Not on scale
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Raw Images for cooling effectiveness
Black image Reference Image
Air image Nitrogen image
116
Copyright Copyright ©© by Dr. Hui Hu @ Iowa State University. All Rights Reserved!by Dr. Hui Hu @ Iowa State University. All Rights Reserved!
X/H
Z/H
0 2 4 6 8
-2
0
210.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050
C.E.M=0.43
X/H
Z/H
0 2 4 6 8
-2
0
210.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050
C.E.M=1.6
Cooling EffectivenessCooling Effectiveness measurements by using PSP techniquemeasurements by using PSP technique
Copyright Copyright ©© by Dr. Hui Hu @ Iowa State University. All Rights Reserved!by Dr. Hui Hu @ Iowa State University. All Rights Reserved!
Cooling EffectivenessCooling Effectiveness Measurements by using PSP techniqueMeasurements by using PSP technique
-3
-2
-1
0
1
2
3
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
M=1.6M=1.1M=0.76M=0.64M=0.52M=0.43M=0.25
X/H=4
Cooling Effectiveness η
Z/H
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 1 2 3 4 5 6 7 8 9
M=1.6M=1.1M=0.76M=0.64M=0.52M=0.43M=0.25
X/H
Coo
ling
Effe
ctiv
enes
s η
X/H
Z/H
0 2 4 6 8
-2
0
210.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050
C.E.M=0.43
X/H
Z/H
0 2 4 6 8
-2
0
210.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050
C.E.M=0.52
X/H
Z/H
0 2 4 6 8
-2
0
210.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.05
C.E.M=0.64
X/H
Z/H
0 2 4 6 8
-2
0
210.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050
C.E.M=0.76
X/H
Z/H
0 2 4 6 8
-2
0
2
10.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.05
C.E.M=1.1
X/H
Z/H
0 2 4 6 8
-2
0
210.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050
C.E.M=1.6
118
Copyright Copyright ©© by Dr. Hui Hu @ Iowa State University. All Rights Reserved!by Dr. Hui Hu @ Iowa State University. All Rights Reserved!
Thank you for your time!Thank you for your time!Questions?Questions?