Occlusion in Bottom Intakes with Circular Bars by Flow with Gravel-Sized Sediment. An Experimental Study
Abstract
:1. Introduction
2. Experimental Setting
2.1. Physical Device
2.2. Sediment Experimental Tests with Racks Made of Circular Bars (m = 0.28)
2.3. Previous Studies of T-Shaped Bottom Rack Occlusion by Flow with Gravel-Sized Sediment
- Reduced void ratio according to rack occlusion, termed the effective void ratio, m’.
- Visualization of preferential occlusion area related to the streamline curvature.
- The most efficient longitudinal rack slope, which in T-shaped bars was 30%.
- Finally, a methodology was proposed to obtain the wetted rack length, taking into account the sediment transport and occlusion as well as its comparison with the lengths proposed by Krochin [6].
2.4. Methodology to Define the Effective Void Ratio
3. Results and Discussion
3.1. Sediment Tests with Circular Bars
3.1.1. Deposition of Gravels over Racks
3.1.2. Effective Void Ratio
3.2. Relation between Hydraulic Parameters at the Beginning of the Rack with Ratio m’/m
3.3. Comparison of Occlusion in Racks with Circular and T-Shaped Flat Bars
3.4. Methodology to Calculate the Effective Wetted Rack Length, Lm’, for the Design of Bottom Intakes Considering the Gravel-Sized Sediments
- Calculate L1m, the wetted rack length in the slit of two bars, considering the initial void ratio, m, by using Equation (2) coupled with Equation (3) in the case of circular bars or with Equation (8) in the case of T-shaped bars [17]:
- Calculate the effective void ratio from the proposed Equations (6) and (7) depending on the rack slope and velocity at the beginning of the rack, U0;
- Calculate L1m′, the wetted rack length in the slit of two bars, considering the effective void ratio that takes into account the clogging effects obtained, m, by using Equation (2) coupled with Equation (3) in the case of circular bars, or with Equation (8) in the case of T-shaped bars;
- Calculate Lm, i.e., the wetted rack length over a bar using the methodology of Garcia et al. [23].
4. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Notations
a, b | constant of adjustment depending on the shape of bars and the space between them in Equation (10) |
b1 | space between bars |
bw | bar width |
CD | drag coefficient of gravels |
mean discharge coefficient for energy head | |
CqH | discharge coefficient for flow depth |
Cq0 | static discharge coefficient |
d50, d90, d10, dmin, dmax, d50c | characteristic diameters of gravels |
f | percentage of rack occluded |
g | gravitational acceleration |
H0 | energy head at the beginning of the rack in reference to the rack plane |
Hmin | minimum energy head obtained when the Froude number equals the unity, and there is critical depth |
hc | critical depth |
h0 | flow depth at the beginning of the rack |
k | obstruction parameter defined as k = (1 − f) m |
Lm | wetted rack length |
Lm′ | effective wetted rack length considering rack occlusion |
L1m | wetted rack length in the slit of two bars, considering the initial void ratio |
L1m′ | wetted rack length in the slit of two bars, considering the effective void ratio |
m | void ratio |
m’ | effective void ratio considering rack occlusion |
q1, q2 | specific approaching and rejected flow, respectively |
U | mean velocity of the flow over the rack |
U0 | mean velocity of the flow at the beginning of the rack |
W | mean weight of the gravels deposited over the racks |
x | longitudinal coordinate along the rack |
υ | kinematic viscosity of water |
ρ | density of water |
θ | angle of the rack plane with the horizontal |
drag force | |
Re0 | Reynolds number calculated at the beginning of the rack |
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Author | Bar Space, b1 (m) | Longitudinal Rack Slope (%) | Increment of Rack Length (%) | Obstruction Factor (%) | Bar Profile |
---|---|---|---|---|---|
Ract-Madoux et al. [11] | 0.100 | 20 | – | – | Thick trapezoidal, rail-type, round head (next to circular) |
White et al. [12] | 0.030–0.076 | 20 | – | – | Prismatic heptagon |
Krochin [6] | 0.020–0.060 | 20 | – | 0.15–0.30 | Prismatic |
Simmler [13], Drobir [5] | 0.150 (d95 = 0.060) | 20–30 | 0.50–1.00 | – | Several rounded profiles (next to circular) |
Lauterjung and Schmidt [1] | – | 9–70 | 0.20 | – | Same as Reference [13] |
Bouvard [14] | 0.100–0.120/0.002–0.03 SHP | 30–60 | 0.50–1.00 | – | Same as Reference [11] |
Raudkivi [15] | >0.005 | 20 | – | – | Trapezoidal, inverted railway tracks |
Andaroodi and Schleiss [2] | 0.020–0.040 SHP | 84–100 | 0.20 | – | Bulb-ended, round head |
Castillo et al. [7], Carrillo et al. [16], Castillo et al. [17], García [18] | 0.006–0.045 | 30 | – | 0.30 | T-shaped |
Description | Rack Length (m) | Rack Width (m) | Bar Type (mm) | Width of the Bars, bw (mm) | Direction of the Bars | Spacing between Bars, b1 (mm) | Void Ratio | Longitudinal Slope (%) |
---|---|---|---|---|---|---|---|---|
Present work | 0.90 | 0.50 | O30/30 | 30 | Longitudinal | 11.7 | 0.28 | 0, 10, 20, 30, 33, and 35 |
Previous works [7] | 0.90 | 0.50 | T30/25/2 | 30 | Longitudinal | 8.5 | 0.22 | 0, 10, 20, 30, and 33 |
T30/25/2 | 11.7 | 0.28 |
d50 (mm) | Blade | Disc | Rod | Sphere |
---|---|---|---|---|
22.0 | 8% | 30% | 19% | 43% |
Incoming Flow (l/s/m) | Percentage of Derived Flow (%) | |||||
---|---|---|---|---|---|---|
Longitudinal Slope (%) | ||||||
0 | 10 | 20 | 30 | 33 | 35 | |
114.6 | 76 | 77 | 78 | 81 | 80 | 84 |
138.3 | 69 | 71 | 74 | 76 | 76 | 75 |
155.5 | 64 | 68 | 71 | 73 | 72 | 74 |
198.0 | 56 | 62 | 66 | 67 | 67 | 67 |
Incoming Flow (l/s/m) | Effective Void Ratio | |||||
---|---|---|---|---|---|---|
Longitudinal Slope (%) | ||||||
0 | 10 | 20 | 30 | 33 | 35 | |
114.6 | 0.070 | 0.069 | 0.069 | 0.073 | 0.073 | 0.077 |
138.3 | 0.071 | 0.073 | 0.077 | 0.079 | 0.080 | 0.078 |
155.5 | 0.071 | 0.075 | 0.079 | 0.083 | 0.083 | 0.085 |
198.0 | 0.072 | 0.080 | 0.088 | 0.091 | 0.092 | 0.092 |
Case | q1 (m3/s/m) | L1m (m) | L1m′ (m) | Lm (m) | Lm − L1m (m) | Lm − L1m + L1m′ (m) | Lm′/hc (m) |
---|---|---|---|---|---|---|---|
T-shaped bars, 10% slope | 0.100 | 0.62 | 1.18 | 0.82 | 0.20 | 1.38 | 13.75 |
0.200 | 1.02 | 1.32 | 1.26 | 0.24 | 1.56 | 9.78 | |
0.300 | 1.32 | 1.72 | 1.62 | 0.30 | 2.02 | 9.66 | |
0.400 | 1.64 | 2.06 | 1.94 | 0.30 | 2.36 | 9.29 | |
0.500 | 1.90 | 2.36 | 2.22 | 0.32 | 2.68 | 9.11 | |
T-shaped bars, 30% slope | 0.100 | 0.66 | 0.94 | 0.97 | 0.31 | 1.25 | 12.45 |
0.200 | 1.08 | 1.08 | 1.49 | 0.41 | 1.49 | 9.34 | |
0.300 | 1.44 | 1.44 | 1.92 | 0.48 | 1.92 | 9.15 | |
0.400 | 1.76 | 1.76 | 2.29 | 0.53 | 2.29 | 9.02 | |
0.500 | 2.04 | 2.04 | 2.63 | 0.59 | 2.63 | 8.92 | |
Circular bars | 0.100 | 0.35 | 1.03 | 0.65 | 0.30 | 1.32 | 13.14 |
0.200 | 0.56 | 1.40 | 0.99 | 0.43 | 1.83 | 11.44 | |
0.300 | 0.74 | 1.66 | 1.28 | 0.54 | 2.20 | 10.49 | |
0.400 | 0.895 | 1.88 | 1.52 | 0.63 | 2.51 | 9.89 | |
0.500 | 1.04 | 2.07 | 1.75 | 0.71 | 2.78 | 9.44 |
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Garcia, J.T.; Castillo, L.G.; Haro, P.L.; Carrillo, J.M. Occlusion in Bottom Intakes with Circular Bars by Flow with Gravel-Sized Sediment. An Experimental Study. Water 2018, 10, 1699. https://doi.org/10.3390/w10111699
Garcia JT, Castillo LG, Haro PL, Carrillo JM. Occlusion in Bottom Intakes with Circular Bars by Flow with Gravel-Sized Sediment. An Experimental Study. Water. 2018; 10(11):1699. https://doi.org/10.3390/w10111699
Chicago/Turabian StyleGarcia, Juan T., Luis G. Castillo, Patricia L. Haro, and Jose M. Carrillo. 2018. "Occlusion in Bottom Intakes with Circular Bars by Flow with Gravel-Sized Sediment. An Experimental Study" Water 10, no. 11: 1699. https://doi.org/10.3390/w10111699