An Experimental Study Of Turbulent Structures And Fish Movement In Rectangular Orifice Fishway

Ecological environment is the most popular word in the current society.In order to communicate the migration routes of fish and maintain the diversity of living organisms,fish passages are usually set up in water conservancy hubs such as tidal gates,drainage gates,flood gates and dams to achieve harmonious development of water conservancy projects and ecological environment.The fishway is a low-headed hydraulic structure that allows fish to overcome obstacles to achieve spawning,swimming,and wintering.The effect of the fish pass is not only related to the hydraulic characteristics of the fish pond,but also depends on the fish's traceability.According to research data,there are still less than half of the fish passes that can be traced through the fish passes that have been built around the world! Therefore,it is of great practical significance to further study the hydraulic characteristics of fish passes based on fish migration habits,especially the mechanism of fish turbulence structure affecting fish migration.Turbulent structures and fish movement in rectangular central and bottom orifices fishway were experimentally studied.The experimentations were carried out in a large scale fishway model in the Laboratory of Port,Waterway and Coastal Engineering at Zhejiang University of Technology.Two typical flow rate corresponding to preference velocity of fish was selected.Different orifice locations(central and bottom orifices)were considered.Different planes of flow depth(h=24,19,14,12,10,8,6,4,2,0,-2,-4,-6,-8,-10,-12,-14,-19,-24,-29 cm)were chosen.The 11 transverse lines(x=5,10,15,20,25,30,40,50,60,70,80cm)were arranged along different planes of depth.The 17 measuring points(y=-25,-20,-15,-10,-8,-6,-4,-2,0,2,4,6,8,10,15,20,25 cm)were taken along each transverse line.Three-dimensional instaneous velocity and flow direction at each measuring point were measured by Acoustic Doppler Velocimeter(ADV).Three-dimensional time-averaged velocity distributions,decay of the maximum velocity along flow direction,velocity vectors,turbulence intensity distributions and Reynolds stress distributions at different planes of flow depth and different longitudinal profiled in the pool of rectangular orifice fishway were analyzed.Research indicates:(1)The longitudinal flow velocity of the mesopores forms a three-dimensional turbulent jet in different sections.The longitudinal flow velocity in the longitudinal direction is gradually decreased from the maximum value at the center of the orifice to the both sides in the lateral direction and the vertical direction.The distribution is Gaussian and tends to be flat along the path,which is consistent with the velocity distribution of three-dimensional turbulent jets,but different from planar turbulent jets;the longitudinal velocity of the bottom hole is also approximately Gaussian in different cross sections.The flow velocity is gradually reduced from the orifice to both sides,and a three-dimensional wall jet is formed along the bottom,but different from the plane wall jet.The lateral flow velocity of different orifice types decreases along the longitudinal section in the range of the orifice,and the flow velocity outside the orifice changes less along the path.The vertical flow velocity distribution is characterized by the presence of vortices in the vertical direction of the mesopores and bottom holes.In the horizontal and longitudinal sections,the longitudinal maximum flow velocity is attenuated along the path;(2)The mesoporous plate and the bottom plate have the same trend in the horizontal section.The turbulence intensity at the orifice is much larger than at the non-hole;the turbulent intensity changes in different water depth planes at non-orifices tend to be gentle.In the vertical section,the turbulence intensity reaches the maximum at the interface between the orifice and the non-hole,and its distribution is roughly symmetric with the center of the orifice;(3)The Reynolds stress at the orifice on the same line is much larger than at the non-hole;the Reynolds stress at the orifice is gradually stable and the amplitude is small;in the case of the bottom hole,the variable amplitude region of the Reynolds stress is larger than in the case of the middle hole.In addition,swimming behaviors of target fish in the fishway were observed by high speed photography based on the fish tests with implanted T-shaped tag.Relation between target fish and turbulent structures in rectangular orifice fishway were analyzed.From the high-speed photography,the paragliding of the fish object was observed and combined with the turbulent flow structure.The selection of the immediate and immediate environment of the fish object was related to the turbulence intensity and the Reynolds stress.Especially in the peak region of the turbulent intensity distribution and the large variation zone of the Reynolds stress,it seems that this turbulent feature creates a musical "rhythm" for the fish object.The middle hole and the bottom hole are more suitable for fish objects that prefer to swim in the middle and lower layers.