Experimental Hydraulic Investigation of Angled Fish Protection Systems—Comparison of Circular Bars and Cables
Abstract
:1. Introduction
1.1. General
1.2. Basic Equations
1.3. Literature Values
2. Materials and Methods
2.1. Experimental Setup
2.2. Measurement
2.3. Investigated Parameters
3. Results
3.1. Overview
3.2. Measurement Accuracy and Data Verification
3.3. Head Loss Through Supporting Structures and Surface Friction
3.4. Head Loss Coefficients of the Rack Configurations
3.5. Empirical Relations to Predict Head Loss of Angled Racks
4. Discussion
4.1. Accuracy and Scale Effects
4.2. Effect of Blockage and Angle
4.3. Prediction of Head Loss Coefficients of Angled Racks with Empirical Equations
4.4. Transferability of the Results to Technical Applications and Outlook
5. Conclusions
- Head loss coefficient ξ is independent from the Bar–Reynolds number in the studied range of of 750–3500 and scale effects can be neglected.
- The coefficient ξ is significantly affected by the blockage ratio and the rack angle (Section 3.4, Table 3). The strong increase of head loss with decreasing bar spacings, which are necessary for fish protection, can be countered by designing lower rack angles (α≤ 45°).
- With increasing blockage ratios, the head loss coefficient at the FFF is up to 53% higher compared to the CBTR. This phenomenon is likely resulting from the effect of flow-induced cable vibrations and hence a further increase of blockage. Since amplitudes and frequencies of the vibrations are depending on parameters such as preload forces, cable length or flow velocity, the transferability to full-scale applications is limited.
- Head loss at the CBTR and FFF can be roughly estimated with a modified version of Equation (10) originally published by Meusburger [18], where the horizontal angle is used instead of the vertical rack inclination. However, the comparison of measured and estimated head loss revealed a systematic bias, which is more pronounced for rack options with low angles and high blockage.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Notation
A | = area (m2) | α | = rack angle in relation to the vertical wall (°) |
b | = spacing between the bars (m) | β | = rack angle in relation to the ground plane (°) |
B | = width of the flume (m) | λ | = scale factor (-) |
F | = Froude number (-) | ρ | = mass density of water ≈ 997 (kg m−3) |
g | = gravity acceleration (m s−2) | = kinematic viscosity (m2 s−1) | |
h | = water depth (m) | = head loss coefficient (-) | |
hv | = head loss (m) | ξ* | = total head loss coefficient (-) |
= bar shape coefficient (-) | = predicted head loss coefficient | ||
k | = constant | = measured head loss coefficient | |
l | = bar length (in cross section) (m) | = ξ due to supports and surface friction (-) | |
= pressure (Pa) | = differential pressure (Pa) | ||
p | = blockage ratio (-) | CBTR | circular bar trash rack |
Q | = discharge (m3 s−1) | DPT | differential pressure transducer |
= Reynolds Number (-) | FFF | Flexible Fish Fence | |
= Bar–Reynolds Number (-) | PG | point gauge | |
s | = diameter of the bar/cable (m) | US | ultrasonic sensor |
v1,2 | = velocity (m s−1) | ||
z | = elevation (m) |
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Parameter | Rods | Cables |
---|---|---|
Bar diameter s (mm) | 5 | 5 |
* Spacing b (mm) | 5, 10, 15 | 5, 10, 15 |
* Angle α (°) | 90, 45, 30 | 40, 30, 20 |
* Discharge Q (l s−1) | 50–200 | 80–230 |
Bar shape coefficient (-) | 1.79 | 1.79 |
(-) | 0.33, 0.5, 1,0 | 0.33, 0.5, 1.0 |
Blockage ratio p (-) | 0.25, 0.33, 0.5 | 0.25, 0.33, 0.5 |
Bar length l (m) | 0.80, 1.24, 1.60 | 1.25, 1.60, 2.34 |
Approach velocity v (m s−1) | 0.16–0.63 | 0.25–0.72 |
Bar–Reynolds-No. (-) | 750–3000 | 1250–3500 |
Reynolds-No. (-) | 31,000–125,000 | 50,000–144,000 |
Froude F (-) | 0.08–0.3 | 0.13–0.36 |
US1 | US2 | US3 | US4 | US5 | US6 | US7 | PG | US8 | |
---|---|---|---|---|---|---|---|---|---|
x (m) | 5.3 | 6.5 | 7.5 | 8.3 | 11.3 | 13.7 | 16.1 | 17 | 17.3 |
CBTR | FFF | Difference | |||||
---|---|---|---|---|---|---|---|
p (-) | α (°) | (-) | p (-) | α (°) | (-) | (-) | (%) |
0.25 | 45 | 0.198 | 0.25 | 20 | 0.075 | - | - |
0.33 | 45 | 0.37 | 0.33 | 20 | 0.162 | - | - |
0.50 | 45 | 0.957 | 0.50 | 20 | 0.385 | - | - |
0.25 | 30 | 0.146 | 0.25 | 30 | 0.148 | 0.002 | 1.4% |
0.33 | 30 | 0.242 | 0.33 | 30 | 0.322 | 0.08 | 33.1% |
0.50 | 30 | 0.533 | 0.50 | 30 | 0.818 | 0.285 | 53.5% |
0.25 | 90 | 0.449 | 0.25 | 40 | 0.305 | - | - |
0.33 | 90 | 0.775 | 0.33 | 40 | 0.488 | - | - |
0.50 | 90 | 1.884 | 0.50 | 40 | 1.295 | - | - |
CBTR | 1.80 | 1.3 | 1.7 | 0.9904 | 0.0414 |
FFF | 3.19 | 1.44 | 1.96 | 0.9861 | 0.0006 |
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Böttcher, H.; Gabl, R.; Aufleger, M. Experimental Hydraulic Investigation of Angled Fish Protection Systems—Comparison of Circular Bars and Cables. Water 2019, 11, 1056. https://doi.org/10.3390/w11051056
Böttcher H, Gabl R, Aufleger M. Experimental Hydraulic Investigation of Angled Fish Protection Systems—Comparison of Circular Bars and Cables. Water. 2019; 11(5):1056. https://doi.org/10.3390/w11051056
Chicago/Turabian StyleBöttcher, Heidi, Roman Gabl, and Markus Aufleger. 2019. "Experimental Hydraulic Investigation of Angled Fish Protection Systems—Comparison of Circular Bars and Cables" Water 11, no. 5: 1056. https://doi.org/10.3390/w11051056