bullbullbull IITC bullbullbull Innovation and Technology 1l1Inrer Centre Univeraity of Miskolc

XXIII microCAD International Scientific Conference

19middot20 March 2009

E szekci6 Aramlas- es hotechnika

Section E Fluid and Heat Engineering

--( NKTH NemzeU Kutatsl es Technologial ~Iivatal

A projekt a Nemzeti Kutatasi es Technologiai Hivatal tamogatasaval val6sult meg

Kiadja a Miskolci Egyetem Innovaci6s es Technol6gia TranszJer Centnlll1a KiadasertJelelifs Dr Dobr6ka Mihaly rektorhelyettes Szcrkcsztok Dr Lehoczky Laszl6 osztalyvezeto Nyomda ME Sokszorosito Uzeme Uzemvezetif Kovacs Tiborne Nyomdaszam ME Tu-1132009 ISBN 978-963-661-866-7 6 ISBN 978-963-661-870-4

NUMERICAL MODELING OF THE FLOW PAST AN AIRFOIL CHARACTERIZED BY A LAMINAR SEPARATION BUBBLE

Patricia Arallyl Tamas Regert2

I Undergraduate 2 PhD Assistant Professor

Department of Fluid Mechanics Mechanical Faclllty Budapest University of Technology and Economics Hungary

ABSTRACT

This paper discusses the RANS and URANS modeling possibility of a complex three-dimensional flow field forming around an airfoil which is characterized by the presence of a short laminar separation bubble on its suction side and a turbulent separation in the vicinity of the trailing edge The wing section is placed in a confined computational domain that models the closed test section of a wind tunnel or also can be interpreted as a duct The flow is modeled by using the k-CI) SST turbulence model with the y-Ree laminarturbulent transition model that is supposed to be applicable for predicting laminar separation-induced transition which is of major importance in the present case

1 INTRODUCTION

The investigation of the flow past airfoils is one of the basic topics of the research in fluid dynamics The main operational area of airfoils is the aircraft industry where wings and other lifting surfaces are usually designed based on twoshydimensional flow approaches [1] [2] Also two-dimensional flow concept is applied for the development of blades used for turbomachinery applications although most recently the flow is modeled in 3D space The flow field however is becoming three-dimensional in all real circumstances The origin of three-dimensionality is due to the finite extension of the blades wing sections or the space in which they are operating This influences both the operational characteristics and the determination of their theoretical two-dimensional aerodynamic characteristics In case of low angle-of-attack situations the two-dimensional approach acts as a very good approximation but for higher performances when high lift is needed the angle-of-attack is increasing and the two-dimensional has to be handled with skepticism The airfoil of the present investigation is an RAF 6 type low Reynolds number airfoil which was designed mainly for airscrews of old military aircraft and later it was used frequently as the airfoil of fan blades The airfoil has a flat pressure side and a specially designed suction side that operates with the presence of a short laminar separation bubble which is generated via quick transition in curvature just downstream the leading edge This laminar separation bubble increases lift and induces boundary layer transition from laminar to turbulence for maintaining attached flow until the trailing edge The flow field was visualized experimentally and discussed in [6]

--( NKTH NemzeU Kutatsl es Technologial ~Iivatal

A projekt a Nemzeti Kutatasi es Technologiai Hivatal tamogatasaval val6sult meg

Kiadja a Miskolci Egyetem Innovaci6s es Technol6gia TranszJer Centnlll1a KiadasertJelelifs Dr Dobr6ka Mihaly rektorhelyettes Szcrkcsztok Dr Lehoczky Laszl6 osztalyvezeto Nyomda ME Sokszorosito Uzeme Uzemvezetif Kovacs Tiborne Nyomdaszam ME Tu-1132009 ISBN 978-963-661-866-7 6 ISBN 978-963-661-870-4

NUMERICAL MODELING OF THE FLOW PAST AN AIRFOIL CHARACTERIZED BY A LAMINAR SEPARATION BUBBLE

Patricia Arallyl Tamas Regert2

I Undergraduate 2 PhD Assistant Professor

Department of Fluid Mechanics Mechanical Faclllty Budapest University of Technology and Economics Hungary

ABSTRACT

This paper discusses the RANS and URANS modeling possibility of a complex three-dimensional flow field forming around an airfoil which is characterized by the presence of a short laminar separation bubble on its suction side and a turbulent separation in the vicinity of the trailing edge The wing section is placed in a confined computational domain that models the closed test section of a wind tunnel or also can be interpreted as a duct The flow is modeled by using the k-CI) SST turbulence model with the y-Ree laminarturbulent transition model that is supposed to be applicable for predicting laminar separation-induced transition which is of major importance in the present case

1 INTRODUCTION

The investigation of the flow past airfoils is one of the basic topics of the research in fluid dynamics The main operational area of airfoils is the aircraft industry where wings and other lifting surfaces are usually designed based on twoshydimensional flow approaches [1] [2] Also two-dimensional flow concept is applied for the development of blades used for turbomachinery applications although most recently the flow is modeled in 3D space The flow field however is becoming three-dimensional in all real circumstances The origin of three-dimensionality is due to the finite extension of the blades wing sections or the space in which they are operating This influences both the operational characteristics and the determination of their theoretical two-dimensional aerodynamic characteristics In case of low angle-of-attack situations the two-dimensional approach acts as a very good approximation but for higher performances when high lift is needed the angle-of-attack is increasing and the two-dimensional has to be handled with skepticism The airfoil of the present investigation is an RAF 6 type low Reynolds number airfoil which was designed mainly for airscrews of old military aircraft and later it was used frequently as the airfoil of fan blades The airfoil has a flat pressure side and a specially designed suction side that operates with the presence of a short laminar separation bubble which is generated via quick transition in curvature just downstream the leading edge This laminar separation bubble increases lift and induces boundary layer transition from laminar to turbulence for maintaining attached flow until the trailing edge The flow field was visualized experimentally and discussed in [6]

rr -shy

JIII

WIND TUNNEL DESIGN FOR FLOW AND THERMODYNAMICS MEASUREMENTS

Peter Bellcs Szilard SzabO University ojMiskolc HungGlY

1 INTRODUCTION

Flows around heated prism shaped bodies have also been investigated by many reshysearchers [1] Velocity fields have also been determined by different kind of measshyurement techniques Temperature fields have also been measured by complicated techniques [2] Wind tunnel is made for complex measurements [3] Flows around different kind of bodies (mainly prism shaped) will be investigated by LOV (Laser Doppler Velocimetry) PIV (Particle Image Velocimetry) and CTA (Constant Temshyperature Anemometry) measurement techniques Temperature fields will be measshyured by CTA (temperature module and probe) and Schlieren system in this wind tunnel Design and numerical analysis are presented in next chapters

2 REQUIREMENTS

Following properties and technical parameters of wind tunnel were determined bull Cross-section of test area (500 mm) x (500 mm) bull Length of test area 800 mm bull Wide velocity range in test area U = 02+15 m s bull Steady flow in cross section of test area bull Low turbulence intensity bull Dust-free medium in test area (for CTA system) bull Open wind tunnel (funnel for oil fog) bull Test area is placed at the end of the wind tunnel (thermo-camera measurements) bull Flows around heated bodies (electric heating or by means of hot water) will be

investigated in wind tunnel Bodies are placed in test area of the wind tunnel (normal to the flow direction)

bull Following measurement techniques will be adapted for wind tunnel o Schlieren System (temperature field) o Constant Temperature Anemometry (CT A) (velocity and temperature field) o Laser Doppler Anemometry (LOA) (velocity field) o Particle Image Velocimetry (PIV) (velocity field)

bull Wind tunnel is stable (with bracing) for precious measurements Wind tunnel design is adapted for project (velocity measurement technique develshyopment) [4-6]

3 STRUCTURE OF WIND TUNNEL

Wind tunnel design is showed in Figure I Air is ensured with fan for the wind tunshynel Fan is changeable according to the different ranges of velocity Wind tunnel is disposed with axial and radial fan (with frequency changer)

21

~

~

strengthening no

1250 1500

Figure 1 Schematic of wind tunnel

Air filter is connected to the suction-pipe of fan (it is not the case in Figure I) Difshyfuser is adapted for velocity reducing after the fan Woven-wire cloths are placed in diffuser (for steady flow) Flow director section is placed after the diffuser Wovenshywire cloths are placed in flow director and cross section of flow director is(1200 mm)x (1200 mm) Nozzle is placed after flow director (steady velocity proshyfile) Test section is placed after the nozzle Dimension of the test section is b x h x 1= (500 mm)x (500 mm)x (1500 mm) Test section is made from fibreglass for

optical measurement techniques The best place for measurements is middle of the test section (conditions are suitable)

4 DESIGN OF NOZZLE

Structure of nozzle is showed in Figure 2 Design of nozzle is made by Witoszynski [7] principle

(1)TXl A ++~lH7rrH7rHT

Where bull A =HxH =12 x 12 m1 (cross section of flow director)

bull L = c~ (length)

bull A2 = h xh = 05 x 05 m2 (test section) Transversal dimension of side wall

f(x) = ~ JfW (2)2

22

Where bull X (nozzle axes) Witoszynski suggested [7] c = 3 (length of nozzle) Parameter (c ) is addicted on HI h ratio therefore we choose c = 423 (H If ratio is relative large)

-----1

I I I I (

--------1

Figure 2 Schematic of the nozzle

Projection of nozzle is showed Figure 3 (in symmetry plane)

06 lt

05

04

03

02

0 1 fIx)

- fIx)

-ltgt1

-01

-03

-04

-05

-06 ---=

o 01 02 03 0 05 06 07 08 09 11 12 J)

Figure 3 Projection of nozzle

Pattern of side walls are needed for production

23

s(x) = j l+(d~X)r middotdx (3)

Where

bull Cs) curve length (depend on x coordinate) bull C~) see in Figure 2 Evolved length of side walls are drawn in (sy) coordinate system (from s(x)f(x) and - f(x) data) See in Figure 4

06

1 laquotil05

04

03

I 02 x

01 N

015 0 -01-5 -g ~ -02

0

-03

-04

-05

1 6o - QI Q2 03 Q4 Q5 Q6 Q7 Q8 Q9 I 11 12 13

curve length laquox) 1m]

Figure 4 Evolved length of side walls

5 NUMERICAL SIMULATION OF WIND TUNNEL

Velocity profile and turbulence intensity were determined in test section Fan was selected by air drag of wind tunnel These data were determined by numerical simushylation Simulation was made by FLUENT for wind tunnel Properties of wind tunnel were determined by CFD (Computational Fluid Dynamics) technique Geometrical model of wind tunnel was made by GAMBIT software (Figure 5) Six woven wire cloths are showed in wind tunnel

24

Figure 5 Geometrical model of wind tunnel

Mesh of wind tunnel (for simulation) was generated by GAMBIT Mesh is hexa type number of cells are 183229 parameter of mesh quality 0586 Mesh model is showed in Figure 6

Figure 6 Mesh model

bull

bull

bull

Woven wire cloths were defined in Fluent (such as perforated plates) Perforated plates were determined with porous jump boundary condition Porous jump model is established by Van Winkle and another correlation technique (see [8]) Velocity inlet boundary condition (diffuser inlet) was used for calculation Simulations were made with two different velocity profile (equal and sloping veshylocity profile) Sloping velocity profile was determined from radial fan propershyties

Pressure outlet boundary condition (end of test section) was used for simulashytions

25

Calculations results are showed in Table I

Table 1 Results of calculations

Middle of test section Wind Required

Volume tunnel fan total Mean tur-

Turbulence Velocity flow rate pressure pressure Mean

bulence intensity

Mark inl et pro- loss increase velocity intensity

(In the file middle)

Q iJpch LJPror U 7 1central

m3s Pa Pa mls

A Sloping 373 488 624 149 142 00779

B Equal 373 489 624 149 IAI 00782

C Equal 200 141 180 80 0842 00563

D Equal 008 020 026 03 0184 00779 - shy --- shy

Data were calculated (Table I) bull Volume flow rate of air Q bull Pressure difference behveen the inlet and the outlet of wind tunnel

tPch = Pin - Pout (4)

bull Fan total pressure increase

LJ - LJ P 2 - 40 P U 2 (5)Pror - -Pc +2 Cor c +2

bull Mean velocity of middle test section U bull Turbulence intensity in middle of test section

J[Ff 1 I~ J(j2 + V 2 + u ) (6)I= ----u- =Vmiddot ~ 3~r y

Conclusion [rom results o Turbulence intensity does not depend on the velocity profile o Turbulence intensity is addicted on velocity increase (linear relationship) o Relationship between volume flow rate and wind tunnel air drag is quadratic

(see in Figure 7) This figure is made [rom data of Table I (include filter drag) Figure 7 contains the radial fan construction curves (different fan revolutions per minute) Based on figure required fan rpms are determined by velocity in test section (required velocity) Low velocity is made by axial fan

26

4000

3500

---ltgt--- 1440 3000 shy

--1300 __ 1200

2500 ____ 1000

-+- 900 2000 iii

-800c 700 ~

1500 -0---- 600

--0--500

- cha nnel 1000 shy

500

0 -shy0 4 6 7 Q Ims]

Figure 7 Wind tunnel and fan (different revolutions per minute) character curve

Results of numerical simulations are showed in the next figures Velocity distribushytion is showed (Velocity inlet 6m s) in wind tunnel centre axes (Figure 8) Effect of diffuser and nozzle is showed in Figure 8 (velocity is not changed in test secshytion) Pressure distribution is displayed in wind tunnel centre axes (Figure 9) Efshyfect of woven wire cloths (pressure decrease) is showed in wind tunnel centre axes Velocity distribution is displayed in wind tunnel centre plane (Figure 10) Velocity distribution is examined in two cases (Case B equal velocity profile and Case A sloping velocity profile) Velocity profile and turbulent intensity in middle of test section are shown in Figure II

gOOe+OO U [ms]

BOOe+OO

t 700e+00

BOOe+OO

SOOe+OO

400 emiddot00 shy

300+00

2 0 Oe+O 0

~]100 e -00

-3e-03 -2e+ 03 -le-03 l e + 03 2 e - 03 3e +03

Figure 8 Velocity distribution in wind tunnel centre axes

27

J 60 e + 0 2 - P-- h I (Pal L- I II I I J40e+02-ltll 111 1 120e+02 shy 1111Ul II IiM- 1 I J00e+02

80 Oe+O I

600e+Ol shy

400e+Ol

2 00e+Ol shy j ~x~l ---

-3e+03 -2e+03 -le+03 I e+03 2e+03 3e+03 OOOe+OO

Figure 9 Pressure distribution in wind turrnel centre axes

- bull -1 ~ bull - I

Figure 10 Velocity distribution in wind turrnel centre plane [ms]

(Case B and A)

I

1 bullbull 1middot I if Ili~middotimiddot

L I - --===-~=-=----- I II bull - 11 I

z[mm] zrmm

Figure 11 Velocity distribution and turbulence intensity in test section

(Case A and B)

28

6 CONCLUSIONS

Wind tunnel properties (velocity distribution static pressure turbulent intensity) were determined by numerical analysis Results have shown that wind tunnel fulfils the requirements described in the first chapter About the examination wind tunnel will be good for precise measurement techniques Wind tunnel will be controlled by CTA system

7 ACKNOWLEDGEMENTS

The authors are grateful to NKTH-OTKA (68207) and to the Hungarian-German Intergovernmental SampT co-operation program DAAD-MOB 2412007-08 for the financial support of this research

REFERENCES [I] Baranyi L Szab6 Sz Bo1l6 B Bordas R Analysis of Flow Around a

Heated Circular Cylinder The 7hJSME-KSME Thermal and Fluids Engishyneering Conference No08-201 2008 Sapporo CD ROM A 115 1-4p

[2] S Garg G S Settles Measurements of a supersonic turbulent boundary layer by focusing Schlieren deflectometry Experiments ill Fluids 25 254shy264 1998

[3] Pope A Wind-tunnel Testing John Wiley amp Sons New York 1954 [4] Szabo Sz Juhasz A Messung der Geschwindigkeitsverteilung in groBen

Stromungsquerschnitten VGB PowerTech 72003 51-56 [5] Baranyi L Computation of unsteady momentum and heat transfer from

a fixed circular cylinder in laminar flow Journal of Computational and Applied Mechanics 4( I) (2003) 13-25

[6] Bo1l6 B Investigation of flow around an electrically heated cylinder (in Hungarian) Miskolc Gep 20075-6 5-9

[7] Sc Popow Stromungstechnisches Messwesen VEB Verlag Technik Bershylin 1960

[8] Perry John H Chemical engineers handbook (in Hungarian) Muszaki Kishyado Budapest 1968

29

~

~

strengthening no

1250 1500

Figure 1 Schematic of wind tunnel

Air filter is connected to the suction-pipe of fan (it is not the case in Figure I) Difshyfuser is adapted for velocity reducing after the fan Woven-wire cloths are placed in diffuser (for steady flow) Flow director section is placed after the diffuser Wovenshywire cloths are placed in flow director and cross section of flow director is(1200 mm)x (1200 mm) Nozzle is placed after flow director (steady velocity proshyfile) Test section is placed after the nozzle Dimension of the test section is b x h x 1= (500 mm)x (500 mm)x (1500 mm) Test section is made from fibreglass for

optical measurement techniques The best place for measurements is middle of the test section (conditions are suitable)

4 DESIGN OF NOZZLE

Structure of nozzle is showed in Figure 2 Design of nozzle is made by Witoszynski [7] principle

(1)TXl A ++~lH7rrH7rHT

Where bull A =HxH =12 x 12 m1 (cross section of flow director)

bull L = c~ (length)

bull A2 = h xh = 05 x 05 m2 (test section) Transversal dimension of side wall

f(x) = ~ JfW (2)2

22

Where bull X (nozzle axes) Witoszynski suggested [7] c = 3 (length of nozzle) Parameter (c ) is addicted on HI h ratio therefore we choose c = 423 (H If ratio is relative large)

-----1

I I I I (

--------1

Figure 2 Schematic of the nozzle

Projection of nozzle is showed Figure 3 (in symmetry plane)

06 lt

05

04

03

02

0 1 fIx)

- fIx)

-ltgt1

-01

-03

-04

-05

-06 ---=

o 01 02 03 0 05 06 07 08 09 11 12 J)

Figure 3 Projection of nozzle

Pattern of side walls are needed for production

23

s(x) = j l+(d~X)r middotdx (3)

Where

bull Cs) curve length (depend on x coordinate) bull C~) see in Figure 2 Evolved length of side walls are drawn in (sy) coordinate system (from s(x)f(x) and - f(x) data) See in Figure 4

06

1 laquotil05

04

03

I 02 x

01 N

015 0 -01-5 -g ~ -02

0

-03

-04

-05

1 6o - QI Q2 03 Q4 Q5 Q6 Q7 Q8 Q9 I 11 12 13

curve length laquox) 1m]

Figure 4 Evolved length of side walls

5 NUMERICAL SIMULATION OF WIND TUNNEL

Velocity profile and turbulence intensity were determined in test section Fan was selected by air drag of wind tunnel These data were determined by numerical simushylation Simulation was made by FLUENT for wind tunnel Properties of wind tunnel were determined by CFD (Computational Fluid Dynamics) technique Geometrical model of wind tunnel was made by GAMBIT software (Figure 5) Six woven wire cloths are showed in wind tunnel

24

Figure 5 Geometrical model of wind tunnel

Mesh of wind tunnel (for simulation) was generated by GAMBIT Mesh is hexa type number of cells are 183229 parameter of mesh quality 0586 Mesh model is showed in Figure 6

Figure 6 Mesh model

bull

bull

bull

Woven wire cloths were defined in Fluent (such as perforated plates) Perforated plates were determined with porous jump boundary condition Porous jump model is established by Van Winkle and another correlation technique (see [8]) Velocity inlet boundary condition (diffuser inlet) was used for calculation Simulations were made with two different velocity profile (equal and sloping veshylocity profile) Sloping velocity profile was determined from radial fan propershyties

Pressure outlet boundary condition (end of test section) was used for simulashytions

25

Calculations results are showed in Table I

Table 1 Results of calculations

Middle of test section Wind Required

Volume tunnel fan total Mean tur-

Turbulence Velocity flow rate pressure pressure Mean

bulence intensity

Mark inl et pro- loss increase velocity intensity

(In the file middle)

Q iJpch LJPror U 7 1central

m3s Pa Pa mls

A Sloping 373 488 624 149 142 00779

B Equal 373 489 624 149 IAI 00782

C Equal 200 141 180 80 0842 00563

D Equal 008 020 026 03 0184 00779 - shy --- shy

Data were calculated (Table I) bull Volume flow rate of air Q bull Pressure difference behveen the inlet and the outlet of wind tunnel

tPch = Pin - Pout (4)

bull Fan total pressure increase

LJ - LJ P 2 - 40 P U 2 (5)Pror - -Pc +2 Cor c +2

bull Mean velocity of middle test section U bull Turbulence intensity in middle of test section

J[Ff 1 I~ J(j2 + V 2 + u ) (6)I= ----u- =Vmiddot ~ 3~r y

Conclusion [rom results o Turbulence intensity does not depend on the velocity profile o Turbulence intensity is addicted on velocity increase (linear relationship) o Relationship between volume flow rate and wind tunnel air drag is quadratic

(see in Figure 7) This figure is made [rom data of Table I (include filter drag) Figure 7 contains the radial fan construction curves (different fan revolutions per minute) Based on figure required fan rpms are determined by velocity in test section (required velocity) Low velocity is made by axial fan

26

4000

3500

---ltgt--- 1440 3000 shy

--1300 __ 1200

2500 ____ 1000

-+- 900 2000 iii

-800c 700 ~

1500 -0---- 600

--0--500

- cha nnel 1000 shy

500

0 -shy0 4 6 7 Q Ims]

Figure 7 Wind tunnel and fan (different revolutions per minute) character curve

Results of numerical simulations are showed in the next figures Velocity distribushytion is showed (Velocity inlet 6m s) in wind tunnel centre axes (Figure 8) Effect of diffuser and nozzle is showed in Figure 8 (velocity is not changed in test secshytion) Pressure distribution is displayed in wind tunnel centre axes (Figure 9) Efshyfect of woven wire cloths (pressure decrease) is showed in wind tunnel centre axes Velocity distribution is displayed in wind tunnel centre plane (Figure 10) Velocity distribution is examined in two cases (Case B equal velocity profile and Case A sloping velocity profile) Velocity profile and turbulent intensity in middle of test section are shown in Figure II

gOOe+OO U [ms]

BOOe+OO

t 700e+00

BOOe+OO

SOOe+OO

400 emiddot00 shy

300+00

2 0 Oe+O 0

~]100 e -00

-3e-03 -2e+ 03 -le-03 l e + 03 2 e - 03 3e +03

Figure 8 Velocity distribution in wind tunnel centre axes

27

J 60 e + 0 2 - P-- h I (Pal L- I II I I J40e+02-ltll 111 1 120e+02 shy 1111Ul II IiM- 1 I J00e+02

80 Oe+O I

600e+Ol shy

400e+Ol

2 00e+Ol shy j ~x~l ---

-3e+03 -2e+03 -le+03 I e+03 2e+03 3e+03 OOOe+OO

Figure 9 Pressure distribution in wind turrnel centre axes

- bull -1 ~ bull - I

Figure 10 Velocity distribution in wind turrnel centre plane [ms]

(Case B and A)

I

1 bullbull 1middot I if Ili~middotimiddot

L I - --===-~=-=----- I II bull - 11 I

z[mm] zrmm

Figure 11 Velocity distribution and turbulence intensity in test section

(Case A and B)

28

6 CONCLUSIONS

Wind tunnel properties (velocity distribution static pressure turbulent intensity) were determined by numerical analysis Results have shown that wind tunnel fulfils the requirements described in the first chapter About the examination wind tunnel will be good for precise measurement techniques Wind tunnel will be controlled by CTA system

7 ACKNOWLEDGEMENTS

The authors are grateful to NKTH-OTKA (68207) and to the Hungarian-German Intergovernmental SampT co-operation program DAAD-MOB 2412007-08 for the financial support of this research

REFERENCES [I] Baranyi L Szab6 Sz Bo1l6 B Bordas R Analysis of Flow Around a

Heated Circular Cylinder The 7hJSME-KSME Thermal and Fluids Engishyneering Conference No08-201 2008 Sapporo CD ROM A 115 1-4p

[2] S Garg G S Settles Measurements of a supersonic turbulent boundary layer by focusing Schlieren deflectometry Experiments ill Fluids 25 254shy264 1998

[3] Pope A Wind-tunnel Testing John Wiley amp Sons New York 1954 [4] Szabo Sz Juhasz A Messung der Geschwindigkeitsverteilung in groBen

Stromungsquerschnitten VGB PowerTech 72003 51-56 [5] Baranyi L Computation of unsteady momentum and heat transfer from

a fixed circular cylinder in laminar flow Journal of Computational and Applied Mechanics 4( I) (2003) 13-25

[6] Bo1l6 B Investigation of flow around an electrically heated cylinder (in Hungarian) Miskolc Gep 20075-6 5-9

[7] Sc Popow Stromungstechnisches Messwesen VEB Verlag Technik Bershylin 1960

[8] Perry John H Chemical engineers handbook (in Hungarian) Muszaki Kishyado Budapest 1968

29

s(x) = j l+(d~X)r middotdx (3)

Where

bull Cs) curve length (depend on x coordinate) bull C~) see in Figure 2 Evolved length of side walls are drawn in (sy) coordinate system (from s(x)f(x) and - f(x) data) See in Figure 4

06

1 laquotil05

04

03

I 02 x

01 N

015 0 -01-5 -g ~ -02

0

-03

-04

-05

1 6o - QI Q2 03 Q4 Q5 Q6 Q7 Q8 Q9 I 11 12 13

curve length laquox) 1m]

Figure 4 Evolved length of side walls

5 NUMERICAL SIMULATION OF WIND TUNNEL

Velocity profile and turbulence intensity were determined in test section Fan was selected by air drag of wind tunnel These data were determined by numerical simushylation Simulation was made by FLUENT for wind tunnel Properties of wind tunnel were determined by CFD (Computational Fluid Dynamics) technique Geometrical model of wind tunnel was made by GAMBIT software (Figure 5) Six woven wire cloths are showed in wind tunnel

24

Figure 5 Geometrical model of wind tunnel

Mesh of wind tunnel (for simulation) was generated by GAMBIT Mesh is hexa type number of cells are 183229 parameter of mesh quality 0586 Mesh model is showed in Figure 6

Figure 6 Mesh model

bull

bull

bull

Woven wire cloths were defined in Fluent (such as perforated plates) Perforated plates were determined with porous jump boundary condition Porous jump model is established by Van Winkle and another correlation technique (see [8]) Velocity inlet boundary condition (diffuser inlet) was used for calculation Simulations were made with two different velocity profile (equal and sloping veshylocity profile) Sloping velocity profile was determined from radial fan propershyties

Pressure outlet boundary condition (end of test section) was used for simulashytions

25

Calculations results are showed in Table I

Table 1 Results of calculations

Middle of test section Wind Required

Volume tunnel fan total Mean tur-

Turbulence Velocity flow rate pressure pressure Mean

bulence intensity

Mark inl et pro- loss increase velocity intensity

(In the file middle)

Q iJpch LJPror U 7 1central

m3s Pa Pa mls

A Sloping 373 488 624 149 142 00779

B Equal 373 489 624 149 IAI 00782

C Equal 200 141 180 80 0842 00563

D Equal 008 020 026 03 0184 00779 - shy --- shy

Data were calculated (Table I) bull Volume flow rate of air Q bull Pressure difference behveen the inlet and the outlet of wind tunnel

tPch = Pin - Pout (4)

bull Fan total pressure increase

LJ - LJ P 2 - 40 P U 2 (5)Pror - -Pc +2 Cor c +2

bull Mean velocity of middle test section U bull Turbulence intensity in middle of test section

J[Ff 1 I~ J(j2 + V 2 + u ) (6)I= ----u- =Vmiddot ~ 3~r y

Conclusion [rom results o Turbulence intensity does not depend on the velocity profile o Turbulence intensity is addicted on velocity increase (linear relationship) o Relationship between volume flow rate and wind tunnel air drag is quadratic

(see in Figure 7) This figure is made [rom data of Table I (include filter drag) Figure 7 contains the radial fan construction curves (different fan revolutions per minute) Based on figure required fan rpms are determined by velocity in test section (required velocity) Low velocity is made by axial fan

26

4000

3500

---ltgt--- 1440 3000 shy

--1300 __ 1200

2500 ____ 1000

-+- 900 2000 iii

-800c 700 ~

1500 -0---- 600

--0--500

- cha nnel 1000 shy

500

0 -shy0 4 6 7 Q Ims]

Figure 7 Wind tunnel and fan (different revolutions per minute) character curve

Results of numerical simulations are showed in the next figures Velocity distribushytion is showed (Velocity inlet 6m s) in wind tunnel centre axes (Figure 8) Effect of diffuser and nozzle is showed in Figure 8 (velocity is not changed in test secshytion) Pressure distribution is displayed in wind tunnel centre axes (Figure 9) Efshyfect of woven wire cloths (pressure decrease) is showed in wind tunnel centre axes Velocity distribution is displayed in wind tunnel centre plane (Figure 10) Velocity distribution is examined in two cases (Case B equal velocity profile and Case A sloping velocity profile) Velocity profile and turbulent intensity in middle of test section are shown in Figure II

gOOe+OO U [ms]

BOOe+OO

t 700e+00

BOOe+OO

SOOe+OO

400 emiddot00 shy

300+00

2 0 Oe+O 0

~]100 e -00

-3e-03 -2e+ 03 -le-03 l e + 03 2 e - 03 3e +03

Figure 8 Velocity distribution in wind tunnel centre axes

27

J 60 e + 0 2 - P-- h I (Pal L- I II I I J40e+02-ltll 111 1 120e+02 shy 1111Ul II IiM- 1 I J00e+02

80 Oe+O I

600e+Ol shy

400e+Ol

2 00e+Ol shy j ~x~l ---

-3e+03 -2e+03 -le+03 I e+03 2e+03 3e+03 OOOe+OO

Figure 9 Pressure distribution in wind turrnel centre axes

- bull -1 ~ bull - I

Figure 10 Velocity distribution in wind turrnel centre plane [ms]

(Case B and A)

I

1 bullbull 1middot I if Ili~middotimiddot

L I - --===-~=-=----- I II bull - 11 I

z[mm] zrmm

Figure 11 Velocity distribution and turbulence intensity in test section

(Case A and B)

28

6 CONCLUSIONS

Wind tunnel properties (velocity distribution static pressure turbulent intensity) were determined by numerical analysis Results have shown that wind tunnel fulfils the requirements described in the first chapter About the examination wind tunnel will be good for precise measurement techniques Wind tunnel will be controlled by CTA system

7 ACKNOWLEDGEMENTS

The authors are grateful to NKTH-OTKA (68207) and to the Hungarian-German Intergovernmental SampT co-operation program DAAD-MOB 2412007-08 for the financial support of this research

REFERENCES [I] Baranyi L Szab6 Sz Bo1l6 B Bordas R Analysis of Flow Around a

Heated Circular Cylinder The 7hJSME-KSME Thermal and Fluids Engishyneering Conference No08-201 2008 Sapporo CD ROM A 115 1-4p

[2] S Garg G S Settles Measurements of a supersonic turbulent boundary layer by focusing Schlieren deflectometry Experiments ill Fluids 25 254shy264 1998

[3] Pope A Wind-tunnel Testing John Wiley amp Sons New York 1954 [4] Szabo Sz Juhasz A Messung der Geschwindigkeitsverteilung in groBen

Stromungsquerschnitten VGB PowerTech 72003 51-56 [5] Baranyi L Computation of unsteady momentum and heat transfer from

a fixed circular cylinder in laminar flow Journal of Computational and Applied Mechanics 4( I) (2003) 13-25

[6] Bo1l6 B Investigation of flow around an electrically heated cylinder (in Hungarian) Miskolc Gep 20075-6 5-9

[7] Sc Popow Stromungstechnisches Messwesen VEB Verlag Technik Bershylin 1960

[8] Perry John H Chemical engineers handbook (in Hungarian) Muszaki Kishyado Budapest 1968

29

Calculations results are showed in Table I

Table 1 Results of calculations

Middle of test section Wind Required

Volume tunnel fan total Mean tur-

Turbulence Velocity flow rate pressure pressure Mean

bulence intensity

Mark inl et pro- loss increase velocity intensity

(In the file middle)

Q iJpch LJPror U 7 1central

m3s Pa Pa mls

A Sloping 373 488 624 149 142 00779

B Equal 373 489 624 149 IAI 00782

C Equal 200 141 180 80 0842 00563

D Equal 008 020 026 03 0184 00779 - shy --- shy

Data were calculated (Table I) bull Volume flow rate of air Q bull Pressure difference behveen the inlet and the outlet of wind tunnel

tPch = Pin - Pout (4)

bull Fan total pressure increase

LJ - LJ P 2 - 40 P U 2 (5)Pror - -Pc +2 Cor c +2

bull Mean velocity of middle test section U bull Turbulence intensity in middle of test section

J[Ff 1 I~ J(j2 + V 2 + u ) (6)I= ----u- =Vmiddot ~ 3~r y

Conclusion [rom results o Turbulence intensity does not depend on the velocity profile o Turbulence intensity is addicted on velocity increase (linear relationship) o Relationship between volume flow rate and wind tunnel air drag is quadratic

(see in Figure 7) This figure is made [rom data of Table I (include filter drag) Figure 7 contains the radial fan construction curves (different fan revolutions per minute) Based on figure required fan rpms are determined by velocity in test section (required velocity) Low velocity is made by axial fan

26

4000

3500

---ltgt--- 1440 3000 shy

--1300 __ 1200

2500 ____ 1000

-+- 900 2000 iii

-800c 700 ~

1500 -0---- 600

--0--500

- cha nnel 1000 shy

500

0 -shy0 4 6 7 Q Ims]

Figure 7 Wind tunnel and fan (different revolutions per minute) character curve

Results of numerical simulations are showed in the next figures Velocity distribushytion is showed (Velocity inlet 6m s) in wind tunnel centre axes (Figure 8) Effect of diffuser and nozzle is showed in Figure 8 (velocity is not changed in test secshytion) Pressure distribution is displayed in wind tunnel centre axes (Figure 9) Efshyfect of woven wire cloths (pressure decrease) is showed in wind tunnel centre axes Velocity distribution is displayed in wind tunnel centre plane (Figure 10) Velocity distribution is examined in two cases (Case B equal velocity profile and Case A sloping velocity profile) Velocity profile and turbulent intensity in middle of test section are shown in Figure II

gOOe+OO U [ms]

BOOe+OO

t 700e+00

BOOe+OO

SOOe+OO

400 emiddot00 shy

300+00

2 0 Oe+O 0

~]100 e -00

-3e-03 -2e+ 03 -le-03 l e + 03 2 e - 03 3e +03

Figure 8 Velocity distribution in wind tunnel centre axes

27

J 60 e + 0 2 - P-- h I (Pal L- I II I I J40e+02-ltll 111 1 120e+02 shy 1111Ul II IiM- 1 I J00e+02

80 Oe+O I

600e+Ol shy

400e+Ol

2 00e+Ol shy j ~x~l ---

-3e+03 -2e+03 -le+03 I e+03 2e+03 3e+03 OOOe+OO

Figure 9 Pressure distribution in wind turrnel centre axes

- bull -1 ~ bull - I

Figure 10 Velocity distribution in wind turrnel centre plane [ms]

(Case B and A)

I

1 bullbull 1middot I if Ili~middotimiddot

L I - --===-~=-=----- I II bull - 11 I

z[mm] zrmm

Figure 11 Velocity distribution and turbulence intensity in test section

(Case A and B)

28

6 CONCLUSIONS

Wind tunnel properties (velocity distribution static pressure turbulent intensity) were determined by numerical analysis Results have shown that wind tunnel fulfils the requirements described in the first chapter About the examination wind tunnel will be good for precise measurement techniques Wind tunnel will be controlled by CTA system

7 ACKNOWLEDGEMENTS

The authors are grateful to NKTH-OTKA (68207) and to the Hungarian-German Intergovernmental SampT co-operation program DAAD-MOB 2412007-08 for the financial support of this research

REFERENCES [I] Baranyi L Szab6 Sz Bo1l6 B Bordas R Analysis of Flow Around a

Heated Circular Cylinder The 7hJSME-KSME Thermal and Fluids Engishyneering Conference No08-201 2008 Sapporo CD ROM A 115 1-4p

[2] S Garg G S Settles Measurements of a supersonic turbulent boundary layer by focusing Schlieren deflectometry Experiments ill Fluids 25 254shy264 1998

[3] Pope A Wind-tunnel Testing John Wiley amp Sons New York 1954 [4] Szabo Sz Juhasz A Messung der Geschwindigkeitsverteilung in groBen

Stromungsquerschnitten VGB PowerTech 72003 51-56 [5] Baranyi L Computation of unsteady momentum and heat transfer from

a fixed circular cylinder in laminar flow Journal of Computational and Applied Mechanics 4( I) (2003) 13-25

[6] Bo1l6 B Investigation of flow around an electrically heated cylinder (in Hungarian) Miskolc Gep 20075-6 5-9

[7] Sc Popow Stromungstechnisches Messwesen VEB Verlag Technik Bershylin 1960

[8] Perry John H Chemical engineers handbook (in Hungarian) Muszaki Kishyado Budapest 1968

29

J 60 e + 0 2 - P-- h I (Pal L- I II I I J40e+02-ltll 111 1 120e+02 shy 1111Ul II IiM- 1 I J00e+02

80 Oe+O I

600e+Ol shy

400e+Ol

2 00e+Ol shy j ~x~l ---

-3e+03 -2e+03 -le+03 I e+03 2e+03 3e+03 OOOe+OO

Figure 9 Pressure distribution in wind turrnel centre axes

- bull -1 ~ bull - I

Figure 10 Velocity distribution in wind turrnel centre plane [ms]

(Case B and A)

I

1 bullbull 1middot I if Ili~middotimiddot

L I - --===-~=-=----- I II bull - 11 I

z[mm] zrmm

Figure 11 Velocity distribution and turbulence intensity in test section

(Case A and B)

28

6 CONCLUSIONS

Wind tunnel properties (velocity distribution static pressure turbulent intensity) were determined by numerical analysis Results have shown that wind tunnel fulfils the requirements described in the first chapter About the examination wind tunnel will be good for precise measurement techniques Wind tunnel will be controlled by CTA system

7 ACKNOWLEDGEMENTS

The authors are grateful to NKTH-OTKA (68207) and to the Hungarian-German Intergovernmental SampT co-operation program DAAD-MOB 2412007-08 for the financial support of this research

REFERENCES [I] Baranyi L Szab6 Sz Bo1l6 B Bordas R Analysis of Flow Around a

Heated Circular Cylinder The 7hJSME-KSME Thermal and Fluids Engishyneering Conference No08-201 2008 Sapporo CD ROM A 115 1-4p

[2] S Garg G S Settles Measurements of a supersonic turbulent boundary layer by focusing Schlieren deflectometry Experiments ill Fluids 25 254shy264 1998

[3] Pope A Wind-tunnel Testing John Wiley amp Sons New York 1954 [4] Szabo Sz Juhasz A Messung der Geschwindigkeitsverteilung in groBen

Stromungsquerschnitten VGB PowerTech 72003 51-56 [5] Baranyi L Computation of unsteady momentum and heat transfer from

a fixed circular cylinder in laminar flow Journal of Computational and Applied Mechanics 4( I) (2003) 13-25

[6] Bo1l6 B Investigation of flow around an electrically heated cylinder (in Hungarian) Miskolc Gep 20075-6 5-9

[7] Sc Popow Stromungstechnisches Messwesen VEB Verlag Technik Bershylin 1960

[8] Perry John H Chemical engineers handbook (in Hungarian) Muszaki Kishyado Budapest 1968

29