Study On The Hydraulic Characteristics And Structure Optimization Of T-Shape And H-Shape Fishways

The construction of water conservancy projects truncates the natural river,hinders the feeding and reproduction of migratory aquatic organisms,and results in the reduction and even the extinction of migratory aquatic organisms.In order to restore the connectivity and biological diversity of the river and mitigate the negative impact,the construction of water conservation projects is often accompanied by the building of some fish passage facilities,and fishway is one of the widely used fish passage facilities.Fishway design should not only consider the swimming ability of target fishes,but also consider the hydraulic conditions of water flow,such as the flow pattern,water depth,velocity distribution and turbulent kinetic energy.At present,most fishways are designed for economic species with strong swimming ability,such as salmon,while domestic fish species are mainly four major Chinese carps,which are relatively smaller in size and weaker in swimming ability,and therefore are not very suitable for traditional fishways.On account of this,in this paper,by solving the three-dimensional Reynolds-averaged Navier-Stokes equations and the well-known K-Omega-SST turbulence model,the effect of vertical slot size on the internal flow field of T-shape fishway is analyzed,and further the internal structure layout is optimized.Finally,a brand-new type of fishway with H-shape pier and short baffle is proposed.The main research results of this paper including the following aspects:（1）In terms of the size and the distribution of the recirculation zones within the pool,the vertical-slot size of the T-shape fishway only has a significant impact on the recirculation zone for the Z=0.1h plane（h is the average water depth in the pool of the corresponding scheme;Z is the vertical coordinate of fishway）,which is close to the bottom wall.Besides,the HSF-2scheme,which has a vertical-slot width of 0.50m,one H-shape pier and two symmetrical short baffles,is obviously superior to other schemes studied in this paper.The four pairs of recirculation areas within the HSF-2 scheme are of moderate sizes and uniformly scattered,which not only helps avoid disorientation but also provides a more widely distributed resting area.（2）In all T-shape fishway schemes,the minimum value of the maximum time-average velocity magnitude Max{U_magnitude}within the pool appears in TSF-2 scheme with a vertical slot width of 0.50m.In addition,aiming at the T-shape fishway,when compared with other vertical slot sizes,the vertical slot width of 0.50m leads to the smallest time averaged velocity magnitude and and relatively smaller turbulent kinetic energy distribution within the pool.Therefore,as far as the T-shape fishway is concerned,when the width of the vertical slot is equal to 0.50m,the flow field is deemed to be more friendly to fishes and more suitable for fish upstream.（3）By adding two symmetric short baffles and transforming the T-shape pier into the H-shape pier,for which the trajectory line of the maximum velocity in the fishway is presented as the"V"shape rather than the"U"shape and the circumstance of the main flow closing to the wall can be improved.In addition,the maximum time-averaged velocity magnitude Max{U_magnitude}in HSF-2 scheme is minimum when compared with other schemes.These results indicate that the combined energy-dissipation effect of H-shape pier and short baffles can greatly consume the energy carried by the flow in the fishway,and thus reduce the resistance of water flow during the upward movement of fishes.（4）When compared with other schemes,the average turbulent kinetic energy of HSF-2scheme is much smaller,and the volume proportion of k≤0.10 m²/s² and k≤0.05 m²/s² is relatively larger,which means that HSF-2 is beneficial to the avoidance of being disoriented or getting hurt for fishes.In conclusion,HSF-2 scheme can alse provide a more suitable turbulent environment for fish migration.