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

KC

Proposed Access Hole Energy Loss Method

By:Roger T. Kilgore, PE

Kilgore Consulting and Management

August 26, 2003

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.

Junction Loss Defined

oi EEE =

EiEo

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

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

FHWA Approaches for K

Based on laboratory resultsConsidered variations in parameters

=

g2V

KE2

o

HEC-22 Approach

bpQdDo CCCCCKK =Where,

Ko = relative junction sizeCD = relative pipe diameterCd = flow depthsCQ = lateral inflowsCp = plunging flowCb = benching

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

HYDRA Approach

b4321 C)CCCC(K +=Where,

C1 = relative junction sizeC2 = water depth in manholeC3 = lateral inflow, plunging flowC4 = relative pipe diameterCb = benching

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

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?

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.

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

Revisit Definition

oi EEE =

Ei

Entrance Loss

Exit LossEo

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

Known: HGL0 and EGLo

Downstream conditions.Datum: invert of outflow pipe.

1. Entrance Losses

Estimate initial ya1Adapt concepts of inlet control and full

flow for culverts.

Full Flow

Full Flow: HGLo > Do

oc

2o

oooc,a Eg2V

Pyy +++=

=

g2V

KE2

oooc

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

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

Submerged (Orifice)

oo

icsa DDgQy

2

52293

=

.,.

3.9 coefficient is best fit

Unsubmerged (weir)

oo

icua DDgQy

670

52232

.

.,.

=

2.3 coefficient is best fit

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

2. Additional Losses

BenchingAngled inflowPlunging inflow

HBaa EEEyy +++= 1

Reference Dimension

+++= 2

20

2

2

1 22 ooo

a

oa gA

QPy

gAQ

yCE )(

= 21

o

a

Dby

f

( )[ ]ooa PyyCE += 1

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.

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

Plunging Inflows, CH

( )

+

= 30

750

1350 ..

. io

iH HQ

QC0

1aii D

yzH

=

Include each inflow pipe where zi > ya1Includes inlet flow, if present.

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

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

Calculate HGLi and EGLi

Calculated for each pipe.Process continues upstream.

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

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

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

)

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

)

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

)

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

)

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

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