Study On Adaptive Analysis And Optimization Scheme Of Water Flow Field In 180° Turn Fishway To Target Fish

In order to make full use of the few water resources,people built sluice gates and dams on natural rivers to meet the water demand,which alleviated the problem of water shortage well,but at the same time cut off the connectivity between the upstream and downstream of the rivers,so that fish could not lay eggs and forage upstream on a regular basis,thus destroying biodiversity.In order to make up for this problem,it is necessary to find an effective ecological compensation measure,and the fishway emerges as the times require.In order to make full use of the site conditions and save the space,many fish lanes need to design 180 ° turn sections.However,the research on this kind of fishway started late in our country,and it is not clear about the distribution of flow field and whether it can satisfy the up-tracking of the target fish under the design scheme.In this paper,the three-dimensional numerical simulation method is used to simulate the whole fishway engineering of Sanwan Hydropower Project,and the up-tracking adaptability of the fish to Songjiang bass is analyzed.The computational domain grid adopts tetrahedral grid,and the RNG K-model in Fluent is selected to calculate the transient state of the computational domain.Compared with the results of physical experiments,it is found that the error of the numerical simulation results is within the allowable range.The conclusions of the study on the fishway engineering are as follows:(1)According to the research on the flow pattern of the straight section of the fish channel and the main flow area and the recirculation area of the fish chamber and the rest room,it is found that the main flow line in the fish chamber and the rest room is inverted "S" distribution,and the swing amplitude of the main flow line in the rest room is about 3 times of that in the fish chamber.The main flow velocity in the fish chamber and the rest room increases first,then decreases and then increases along the flow direction.The distribution relationship of the backflow area on both sides of the fish chamber and the rest room is obtained.The flow velocity in the recirculation area in the fish chamber and the rest room is small in the middle and increases gradually around.The research shows that the flow pattern of the straight section and the velocity and location of the main flow area and the recirculation area in the fish chamber and the rest room are reasonable,which meets the upstream requirements of the target fish.(2)Study the distribution law of vertical velocity at vertical slit,and find that the distribution of vertical velocity at vertical slit swings in a small range.The transverse velocity near the left wall of the vertical slit is lower,and the velocity at the bottom layer is higher than that at the middle layer and surface layer.Under each operating condition,the flow velocity of Songjiang perch can account for more than 30% of the width of the vertical slit through the vertical slit section,which is not conducive to the up-tracking of Songjiang perch due to the narrow passage range.The results show that the cobblestone at the bottom of the fishway can effectively improve the flow velocity at the vertical slit.(3)By studying the turbulent kinetic energy of a single conventional fish room and a rest room,the distribution rules of the turbulent kinetic energy of the fish room and the rest room are obtained,and the distribution of the turbulent kinetic energy of the fish room and the rest room at the operating water level H = 2.0m is slightly larger than that at the operating water level H = 1.5m;the study shows that the distribution of the turbulent kinetic energy of the fish room and the rest room is smoothly connected and belongs to the low turbulence kinetic energy zone,which meets the up-tracking requirements for target fish.(4)Based on the study of the flow pattern of the 180 ° turning section,it is found that there is a serious wall adherence phenomenon in the turning section,the circumfluence area is concentrated and the scope is too large,and the local flow velocity is too low in the mainstream area,which is not conducive to the up-tracking of the target fish.Therefore,an optimized design scheme is put forward.The result shows that the flow pattern at the turning section can be effectively optimized by adding a guide plate.(5)In the study of the flow pattern of the exit section of the fishway and the flow pattern of the turn section at different angles,it is found that the flow pattern of the exit section can correctly guide the fish to ascend,and the exit does not interfere with the flow;the flow field of the pool chamber in the turn sections with an angle θ=24 °,61 ° and 75 °,and a turning radius R=20m is similar to that of the straight section,and no adherence phenomenon occurs.Studies have shown that all the above paragraphs meet the retrospective requirements of the target fish.