| The double vertical slot fishway, one of the basic types of vertical slot fishways, provides for double sided migration and is appropriate for large numbers of migrating fish. However, research on double vertical slot fishways has rarely been reported in China. In this study, a three dimensional numerical simulation model was used to investigate the flow structure and hydraulic parameters of the double vertical slot fishway with various pool-aspect ratios (the ratio of fishway length to width). The results provide a technical reference for the design of double vertical slot fishways. Based on previous research on single vertical slot fishways, several basic parameters for the double vertical slot fishway model were selected: upstream lateral baffle slope, 45°; lateral baffle length, 0.25B and slot width, 0.15B; where B is pool width. In the numerical model, the inflow and outflow boundaries were both set at a hydrostatic pressure of 2 meters, the top boundary was set at atmospheric pressure (1.01×105Pa) and all other boundaries were set as walls. The flow structure and hydraulic parameters of the general pools were then calculated using different length-to-width ratios (4:8, 5:8, 5.5:8, 5.75:8, 6:8, 6.5:8, 7:8, 8:8, 9:8). Results show that there are three typical flow structures in the pool, with different mainstream curves, velocity attenuation curves and recirculation area sizes. The three typical flow structures correspond to three ranges of length-to-width ratio (4:8-5.5:8, 5.75:8-6.5:8, 7:8-9:8). With increasing length-to-width ratio, the length and attenuation rate of the mainstream increased, while the distance between the two mainstreams decreased. The recirculation zones between mainstreams decreased correspondingly and the size of the recirculation region outside the mainstreams increased. The flow structure most appropriate in the pools occurs at a length-to-width ratio in the range 5.75-6.5:8. When the width of the mainstreams is relatively wide, the pools can be more fully utilized because mainstream velocity drops off rapidly and recirculation zones form that help fish pass successfully. |
