Stephan the importance of confluences in hydraulic network models of rivers
1. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 1
Source: The Internet
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
2. DEPT. OF CIVIL ENGINEERING
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pag. 2
Confluence research @ Ugent
Laurent Schindfessel
Extreme discharge ratios
Large-eddy simulation
Stéphan Creëlle
Mixing & headloss prediction
Experiments
Promotor: Tom De Mulder
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
4. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 4
h3
Q1
Q2
h1
h2
Q1+Q2
?
?
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
5. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 5
h1=h2
h1/h2 [-]
q [-]
Generally
accepted
Equation 1?
Equation 2?
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
6. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 6
Multiple solutions reported in
literature
Equality model Energy approach Momentum approach
-simple
-easy to implement
h1=h2=h3
-simple
-errors up to
50% h3
E1+E2+ ΔE=E3
-empirical loss coeff.
-combines easily
with other energy
loss formulations
-limited information
M1,x+M2,x+ SF=M3,x
-allows for best calculation
of different terms
-additional computational
effort
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
7. DEPT. OF CIVIL ENGINEERING
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M1+M2 cos θ − M3=P3 − P1 − P2cos θ − PWALLS sin θ
3
1
M1,x+M2,x-M3,x =-SF
𝑀3, 𝑃3
𝑀2, 𝑃2
𝑀2, 𝑃2
𝑃 𝑊𝐴𝐿𝐿𝑆
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
8. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 8
Can be expressed with the variables of the problem:
𝑃 =
𝜌ℎ2
𝑊
2
?
𝑀 =
𝜌𝑄2
ℎ𝑊
M1+M2 cos θ − M3=P3 − P1 − P2cos θ − PWALLS sin θ
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
9. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 9
Taylor(1944)
ℎ 𝑇𝐼𝑊 = ℎ 𝑇𝑂𝑊 = ℎ2
Can be expressed with the variables of the problem:
𝑀 =
𝜌𝑄2
ℎ𝑊
𝑃 =
𝜌ℎ2
𝑊
2
?
M1+M2 cos θ − M3=P3 − P1 − P2cos θ − PWALLS sin θ
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
10. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 10
Taylor(1944)
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
11. DEPT. OF CIVIL ENGINEERING
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pag. 11
Taylor(1944)
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
12. DEPT. OF CIVIL ENGINEERING
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pag. 12
Webber & Greated(1966)
Pressure difference over the
channel walls due to
contraction to the
downstream corner
Change in physical inflow
angle α in the TCS
Cause of deviations?
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
16. DEPT. OF CIVIL ENGINEERING
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Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
pag. 16
Conclusions:
-Head losses near confluences become more significant when:
-Froude numbers increase
-The confluence angle increases
-For low angles and Froude numbers, the equality model can
suffice. For the other cases, an energy or momentum
approach should be incorporated.
-The momentum conservation approach delivers the most applicable
results, but for high angles the tributary momentum contribution should be
formulated accurately.
17. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
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Work in progress:
-Description of the tributary momentum contribution, based on
theoretical description of the velocity profiles in the tributary
branch, in order to obtain more reliable results, and to
eliminate the need for empirical expressions for the tributary
momentum contribution or inflow angle
-Experimental measurements of the flow behaviour of the flow
in the tributary branch in the approach of the confluence area.
-Description of the mixing, momentum exchange and
uniformization process in and downstream of the confluence,
based on experimental measurements of the surface
velocities.
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
18. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 18
Thanks for your attention!
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
19. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 19
References:
Taylor, E. H. (1944). Flow characteristics at rectangular open-channel
junctions. Trans. ASCE(107), 893–912.
Webber, N. B., & Greated, C. (1966). An investigation of flow behaviour at
the junction of rectangular channels. Paper presented at the ICE
Proceedings.
Hsu, C.-C., Wu, F.-S., & Lee, W.-J. (1998). Flow at 90 equal-width open-
channel junction. Journal of Hydraulic Engineering, 124(2), 186-191.
Hager, W. (1989). Transitional Flow in Channel Junctions. Journal of
Hydraulic Engineering, 115(2), 243-259. doi: doi:10.1061/(ASCE)0733-
9429(1989)115:2(243)
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
20. DEPT. OF CIVIL ENGINEERING
Hydraulics laboratory
pag. 20
Assumptions:
1) All channels have a rectangular shaped cross-section with width W,
2) The beds of the main channel and the tributary are concordant, fixed and
horizontal,
3) In the cross-sections 1, 2 and 3, the flow is uniform and the water surface is
horizontal,
4) Friction losses due to the banks and the beds can be neglected,
5) Pressure distributions are hydrostatic in the sections considered and along the
walls
Stéphan Creëlle- Stephan.Creelle@ugent.be –Tom De Mulder
Belgian Hydraulics Day - 5/10/2015 – FHR Antwerp
