Download - Jucnciton loss methodology.pdf
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KC
Which Junction Loss Methodology Do We Use?
By:Roger T. Kilgore, PE
Kilgore Consulting and Management&
Joe Krolak, PEFederal Highway Administration
August 8, 2001
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KC
Proposed Access Hole Energy Loss Method
By:Roger T. Kilgore, PE
Kilgore Consulting and Management
August 26, 2003
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Why do we care?
Although minor, junction losses can add up.Simple methods require selection of
arbitrary energy loss coefficients.Complex methods require many variables
and may be computationally challenging.Unreasonable results have been reported
with existing methods.
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Junction Loss Defined
oi EEE =
EiEo
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Available Methods
Absolute MethodStandard Method
HEC-22 approach based on 1989 Lab Report by Chang and Kilgore (HYDRAIN V5.0)
HYDRA approach based on 1994 Research Report by Chang, Kilgore, Woo, and Mistichelli (HYDRAIN V6.x)
Generic Method Power Loss Approach, Chang, et al., 1994
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Standard Method
=
g2V
KE2
o
Where does K come from? HEC-22 has values ranging from 0.15 to 1.5 Many situations not represented
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FHWA Approaches for K
Based on laboratory resultsConsidered variations in parameters
=
g2V
KE2
o
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HEC-22 Approach
bpQdDo CCCCCKK =Where,
Ko = relative junction sizeCD = relative pipe diameterCd = flow depthsCQ = lateral inflowsCp = plunging flowCb = benching
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Independent Variables for K
Dimensionless ratiosCompute a single
number, KMultiply K by outflow
pipe velocity head
b/DoDo/Diya/DoQi/Qoh/Do(h-ya)/DoBenching type
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HYDRA Approach
b4321 C)CCCC(K +=Where,
C1 = relative junction sizeC2 = water depth in manholeC3 = lateral inflow, plunging flowC4 = relative pipe diameterCb = benching
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Independent Variables for K
Dimensionless ratiosCompute a single
number, KMultiply K by outflow
pipe velocity head
b/DoDo/Diya/DoQi/Qoh/Do(h-ya)/DoBenching type
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Generic Method
+
=
g2V
Kg2
VKE
2i
i
2o
o
Loss coefficients on the inflow and outflow velocity heads.Conceptual model of entrance and exit losses.
Where do we get the Ko and Ki values?
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Power Loss Approach
+
+
= lossesplunging
g2V
g2V
E2i
i
2o
o
Power in Power out = Power LostGeneric method is a simplification of the Power
Loss method.o and i are functions of similar parameters
discussed earlier.Iterative; closed form.
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Issues
Standard Method: Focus on a K factor which is multiplied by an outflow velocity headPower Loss Method: Iterative solution requiredGeneric Method: Provides no source for K valuesDependence on Velocity Head
Inlet control Supercritical Flow Relationship between lab/computed velocities
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Revisit Definition
oi EEE =
Ei
Entrance Loss
Exit LossEo
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Proposed Method
1. Entrance Losses: access hole depth, ya12. Additional Losses: benching, angle
inflows, and plunging inflows, revised access hole depth, ya
3. Exit Losses: each inflow pipe
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Known: HGL0 and EGLo
Downstream conditions.Datum: invert of outflow pipe.
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1. Entrance Losses
Estimate initial ya1Adapt concepts of inlet control and full
flow for culverts.
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Full Flow
Full Flow: HGLo > Do
oc
2o
oooc,a Eg2V
Pyy +++=
=
g2V
KE2
oooc
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Ko
2.0Ko =
Captures the contraction losses entering the outflow pipe, as in a culvertEntrance loss coefficients from HDS-5 range
from 0.2 to 0.9b/Do, relative access hole size, not a factor
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Inlet Control
Entrance to outlet pipe controls flow into outlet pipe.Weir or orifice flow: calculate both and
take largest headwaterDischarge Intensity:
5.0oo
o
DAQ
5.2o
o
Dg2Q
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Submerged (Orifice)
oo
icsa DDgQy
2
52293
=
.,.
3.9 coefficient is best fit
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Unsubmerged (weir)
oo
icua DDgQy
670
52232
.
.,.
=
2.3 coefficient is best fit
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Initial Depth
0.0000.1000.2000.3000.4000.5000.600
0.0000 0.0100 0.0200 0.0300 0.0400
Q (m3/s)
y
a
1
(
m
)
Full Flow IC sub IC unsub
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2. Additional Losses
BenchingAngled inflowPlunging inflow
HBaa EEEyy +++= 1
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Reference Dimension
+++= 2
20
2
2
1 22 ooo
a
oa gA
QPy
gAQ
yCE )(
= 21
o
a
Dby
f
( )[ ]ooa PyyCE += 1
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Benching, CB
Floor Configuration
Bench Submerged*
Bench Unsubmerged*
Flat (level) -0.05 -0.05 Depressed 0.0 0.0 Half Benched -0.05 -0.65 Full Benched** -0.25 -0.93 Improved** -0.60 -0.98
*Submerged: ya>2.5 Do**Not tested in FHWA data.
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Angle Inflows, C
=
i
iiw
Q
250 wC cos.=
Include each inflow pipe where zi < ya1 is angle with respect to outflow pipe,
e.g. for straight through = 180o
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Plunging Inflows, CH
( )
+
= 30
750
1350 ..
. io
iH HQ
QC0
1aii D
yzH
=
Include each inflow pipe where zi > ya1Includes inlet flow, if present.
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3. Exit Losses
If ya < zi then there are no exit losses and the EGL is computed using inflow pipe hydraulic parameters If not, compute exit losses:
=
4i
2i
ii gDQ
KE
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Ki55.0
ii D
b46.0K
=
Captures the expansion losses entering the access holeb/Di = relative access hole size1 < b/Di < 4Effect of access hole size modest
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Calculate HGLi and EGLi
Calculated for each pipe.Process continues upstream.
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FHWA Data Set
All Runs 740 configurations/discharges 1618 inflow pipes 2.2 inflow pipes/run
Base Runs 1 inflow pipe and equal inverts 68 runs
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Performance
Access Hole Depth, ya HEC-22: RMS = 0.094 m HYDRAIN: RMS = 0.048 m* Proposed: RMS = 0.047 m
Inflow Energy Gradeline, Ei HEC-22: RMS = 0.072 m HYDRAIN: not reported. Proposed: RMS = 0.037 m
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Proposed: ya
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.00 0.10 0.20 0.30 0.40 0.50 0.60ya (obs) (m)
y
a
(
c
a
l
c
)
(
m
)
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HEC-22: ya
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.00 0.10 0.20 0.30 0.40 0.50 0.60ya (obs) (m)
y
a
(
c
a
l
c
)
(
m
)
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Proposed: Ei
0.000.100.200.300.400.500.600.700.800.90
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90Ei (obs) (m)
E
i
(
c
a
l
c
)
(
m
)
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HEC-22: Ei
0.000.100.200.300.400.500.600.700.800.90
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90Ei (obs) (m)
E
i
(
c
a
l
c
)
(
m
)
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Reasons for Adoption
1. Hydraulically sound fundamentals2. Move away from velocity head for
supercritical and inlet control flows3. Direct, non-iterative procedure4. Simpler format 5. Equivalent or better RMS
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Next Steps
Perform selected additional laboratory experimentsRefine method
Which Junction Loss Methodology Do We Use?Proposed Access Hole Energy Loss MethodWhy do we care?Junction Loss DefinedAvailable MethodsStandard MethodFHWA Approaches for KHEC-22 ApproachIndependent Variables for KHYDRA ApproachIndependent Variables for KGeneric MethodPower Loss ApproachIssuesRevisit DefinitionProposed MethodKnown: HGL0 and EGLo1. Entrance LossesFull FlowKoInlet ControlSubmerged (Orifice)Unsubmerged (weir)Initial Depth2. Additional LossesReference DimensionBenching, CBAngle Inflows, CqPlunging Inflows, CH3. Exit LossesKiCalculate HGLi and EGLiFHWA Data SetPerformanceProposed: yaHEC-22: yaProposed: EiHEC-22: EiReasons for AdoptionNext Steps