Investigations Of Three-dimensional Flow Characteristics In Vertical Slot Fishway

Barrage projects such as gate and dam buildings play a great role in flood control,navigation,and power generation,but they also destroy fish migratory channels and block fish gene exchange.The vertical slot fishway is a common artificially constructed fish migration channel type.At present,studies on the slope of vertical slot fishway mainly focus on large span comparisons（5%,10%,15%,20%）,and the adopted pool size,baffle type,and other parameters are not uniform,so that the understanding of the changes in hydraulic characteristics caused by slope lacks some continuity;in addition,studies have shown that the arrangement of obstacles will directly affect the fishway flow field,so its location needs to be considered.In this thesis,by combining model tests and numerical simulations,we analyze the flow structure of two common baffle types of fishway,and conduct a systematic study on the effects of slope changes and cylindrical obstacles on the hydraulic characteristics of fishway,with the following main results.（1）Compared with the round-ended hook-shaped partition,the mainstream curvature inside the fishway pool of the folded hook-shaped partition is smaller,and the range of the left-sided reflux zone is larger,and the phenomenon that the two ends are wide and the middle is narrow is reduced.However,when the size of the pool is reduced only for the round-end hooked partition,the effect of the partition on the flow pattern becomes greater and the mainstream will again have an"Ω"shape.The maximum velocities measured in the pool are all at the same measurement points.This indicates that the high-velocity flow is similarly affected by the vertical joints in a certain range.In addition,the velocities in the reflux zone are lower in each pattern,which provides a suitable resting area for fish.（2）With the increase of slope,the flow field in the pool gradually shifts from two-dimensional to three-dimensional,and the area closer to the water surface is influenced by the downward flow of the previous pool,and the mainstream range expands,resulting in a shrinking area for fish to rest.However,near the near bottom（H_b）,the flow pattern is relatively stable even if the slope increases.The increase in slope accelerated the flow of water within the fishway pool,and the maximum and average velocities in the vertical slot area increased significantly.（3）Under a larger slope,the magnitude and distribution of turbulent kinetic energy（TKE）and unit volume dissipation rate（E）need to be focused on,especially the E in the local area may far exceed the calculation result of the theoretical equation and affect fish migration.Compared with other hydraulic characteristics,the range of vorticity exceeding the threshold value at a fishway slope of 6.0%is also relatively limited in the pool,but its range is mainly concentrated near the vertical slot of the fishway,which may interfere with the upstream movement of fish.（4）The arrangement of the cylinder at a location close to the vertical slot does not necessarily improve the flow conditions,and in addition to the undesirable reduction in velocity,it may also lead to a significant reduction in the extent of the low-velocity reflux zone.At the same time,the flow pattern inside the cell is affected by the cylinder in an"Ω"shape,and a larger reflux zone is formed on the right side of the mainstream.When the position of the cylinder continues to move down,the effect of the cylinder on the improvement of the flow field inside the cell is weakened.（5）When the cylinder is too close to the vertical slot,the improvement of turbulence within the pool is not obvious due to the direct impact of the mainstream,and E_max may exceed that of the conventional pool.When the cylinder is properly positioned,both TKE and E inside the pool are at a lower level.The position of the cylinder closer to the vertical slot will compress the water flow through the vertical slot and force deflection,and a larger area of high vorticity will appear on the right side of the cylinder,which will instead interfere with fish passage and reduce the efficiency of fishway.