e. mignot , n. rivière, d. doppler, i. vinkovic, p.-h. bazin
DESCRIPTION
E. Mignot , N. Rivière, D. Doppler, I. Vinkovic, P.-H. Bazin Laboratoire de Mécanique des Fluides et d’Acoustique Université de Lyon ( France). Hydrodynamique environnementale expérimentale au LMFA. Elargissement Thèse Han Lei. Ecoulement torrentiel autour d’un obstacle. Cavité. - PowerPoint PPT PresentationTRANSCRIPT
E. Mignot, N. Rivière, D. Doppler, I. Vinkovic, P.-H. BazinLaboratoire de Mécanique des Fluides et d’Acoustique
Université de Lyon (France)
2
y
x
Qxi
Qxo Qyi
Qyo L=2m
b=0.3my
Channel intersection : 0.3x0.3m,Slopes 0-5%, 0<Fr<5
ElargissementThèse Han Lei
Hydrodynamique environnementale expérimentale au LMFA
Thèse Cai WeiCavité
IntersectionsThèse PH Bazin
d
h,U
L
g
B
gTv
Tc
Ecoulement torrentielautour d’un obstacle
QMaj QminQMaj Qmin
Lit composé
Jet torrentiel
* Torrentiel - Fluvial* 3-4 branches* Distribution Q - PIV* Simple - obstacles
E. Mignot, N. Rivière, P.-H. BazinLaboratoire de Mécanique des Fluides et d’Acoustique
Université de Lyon (France)
Open-channel bifurcations:Open-channel bifurcations: Impact of singularitiesImpact of singularities
on the discharge distributionon the discharge distribution
Introduction
• Delta
• Cut-off
• IslandNatural bifurcationsNatural bifurcations
Introduction
• Severe floods in dense urbanized areas
Flow takes place in streets and crossroads
(Bonneaud, 2002)
Artificial bifurcationsArtificial bifurcations
Some crossroads are3-branch bifurcations
Subcritical, 3 branch, open-channel, bifurcation
6
Introduction
(Neary et al., 1999)
General flow pattern:• Dividing interface• Recirculation zone• Secondary flows
Main concern : Prediction of discharge distribution
Qu Qd
Qb
7
Introduction
Ramamurthy et al. (1990)
• Momentum /x : Ramamurthy et al. (1990)• Energy : head loss coefficient unknown
Empirical relationship (Rivière et al., 2007)
Available Equations to describe the flowDischarge distribution
Valid if no obstacle
Qu
Qd
Qb
);(d
b
dd
u
u
bq C
C
gCbC
Qf
Q
QR
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 0,2 0,4 0,6 0,8 1
Rq ex p.
Rq
co
rr.
+5%
-5%
Rq-sub (eq.4)
Rq (exp.)
Rq (correl.)
Rivière et al. (2007)
8
Topic
Quantify impact of obstacles near the bifurcation?
Present experiment
Modification of discharge distribution depends on
• Flow characteristics (h, U, b …)• Obstacle shape and size
• Obstacle location
(Bonneaud, 2002)
Qu
Qd
Qb
9
Experimental set-up
White light sheet
PIV technics
(LMFA – INSA Lyon – Université de Lyon)
- 3 or 4 open-channels- Central intersection- Glass walls (optical access)
Add particles = PSP 50 mHigh-frequency camera (30Hz)
Velocity measurement
Discharge measurement
Water depth measurement
UpstreamTank
DownstreamTank
LateralTank
PumpQu
Qb
Cd
Cb
Boundary conditions:
Qu: upstream flow-rate
Cd: downstream weir crest
Cb: branch weir crest
10
Qu
Qb
Qd
Lu=2m Ld=2.6m
Lb=2.6m
PIV area
Experimental approach(LMFA – INSA Lyon – Université de Lyon)
Experimental scheme
Channel section
20 c
m
b=30 cm
Measurements:
Qb: branch flow-rate
hu, hb, hd depths
1 2 3 4 5
6 7 8 9 11
4cm
4cm
5cm
5cm
Methodology• Fixed boundary conditions (Qu, Cb, Cd)• Measure discharge distribution• Introduce 9 obstacle one after the other• Measure the modification of outlet discharges
Obstacle configurations
12
Results : Discharge distribution
Qu=2L/s
Qb=0.75L/s Qb=0.74L/s
Qb=0.77L/s
Qb=0.70L/s
Qb=0.73L/s
No obstacle O-1 O-2
O-4 O-7O-3
Qb=0.75L/s
Streamwise acceleration
Lateral branch blockage
Downstream blockageO-5
Qb=0.76L/s
Side deflection
Ux
13
Influence of the Froude number
-15
-10
-5
0
5
10
0.2 0.3 0.4 0.5 0.6 0.7 0.8
∆R
q
1 2 3 4 5 6 7 8 9
Previously described
Fru0 (without obstacle)
If Fru0 , impact of obstacles Stagnation point depth and so horizontal pressure gradients
3
2
7
Rq0 0.39 ; hu0 /b 0.14
u
bb
Q
QQ 0
obstacle Qb
obstacle Qb
Influence of the other flow parameters
incoming Froude nb.
discharge distribution
inlet water depth
Dimensional analysis
14
b
hR u
h0
0 0
00
u
bq Q
QR 2/3
02/1
00
u
uu
hbg
QFr
As Fr , impact of obstacle More complex
Influence of the other flow parameters
Rq : moves the separating streamline compared with the obstacle
Rq : modifies recirculation width
15
Influence of the initial discharge distribution
-8
-6
-4
-2
0
2
4
6
0.2 0.3 0.4 0.5 0.6 0.7 0.8Rq0
∆R
q
1 2 3 4 5 6 7 8 9u
bb
Q
QQ 0
u
bq Q
QR 0
0
hu0 /b 0.15 ; Fru0 0.445
3
2
7
O0-C O2-C O3-C O7-C 1
2
3
O0-C O2-C O3-C O7-C 1
2
3
2 3
Rq0
Rq0
16
Conclusions
•Magnitude of discharge modification depends on• Location of obstacle• Froude number of inflow / reference distribution• shape / size not studied here
• Obstacles modify the discharge distribution by about [-15 ; +10 %]• Non negligible modifications when compared to other errors:
Sidewalks – Roughness – Shape of crossroads – Exchange with buildings - sewer networks … ?
Current works
• Separating streamline• Rapid main flow• Slow recirculation zone
Applications* Turbulent modeling* Pollutant dispersion
Reynolds shear stress
Streamlines Fieldlines Separating streamline
17