An Experimental Study Of Turbulent Structures And Fish Movement In Combined Fishway Of Overflow Weir And Vertical Slot

With the rapid development of enconomy and society,demand of human beings for water resources is increasing day by day,and thus many hydraulic structures such as sluices and dams were built on the river.These projects have brought some negative impacts on the ecological environment while benefiting and eliminating harm,including negative effects on natural fish populations.In order to reduce the damage to aquatic ecosystems by hydraulic structures such as sluices and dams,repair fish habitats,protect fish resources,coordinate the contradiction between water resources development and fish resource protection,and restore river biodiversity,fishways play a important role.A very important function of the fishway is to help fish migration.As far as the fishway has been completed so far,the fish passage effect is not very satisfactory.Therefore,further research on the hydraulic characteristics of the fishway has important guiding significance for fishway design,especially the characteristics of the turbulent structure of the fishway.Turbelent structures such as flow characteristics,main stream trajectory,three-dimensional flow velocity,turbulence intensity,reynolds stress,frenquency-spectrum characteristics,correlation function,turbulence scales(micro-scale,integral scale)were experimentally studied by Acoustic Doppler Velocimetry(ADV)in a combined fishway with a overflow weir and a vertical slot as well as fish movement in fishway were experimentally investigated.Two vertical slot arrangements were considered in the test,namely the staggered and identical arrangements.The six different depths were taken for each arrrangement(z=10、20、30、40、44、48cm).The fifteen transverse lines were take along each water depth plane(x=5、10、15、20、30、50、70、90、110、130、150、160、165、170、175cm).The sixteen measuring points were laid along each transverse line.For each arrangement,the turbulent structures on different horizontal profiles,longitudinal profiles,and cross-sections were respectively studied,and a comparison between the two arrangements was made.The experimental results show:(1)the main flow region of combined fishway with an overflow weir and a vertical slot was affected by both the notch weir falling jet and the vertical slot wall jet,and the surface layer was mainly affected by weir flow;The main flow trajectory in the case of staggered arrangement exhibited an L-shaped curve,and the main flow trajectory in the case of identical arrangement was linear;the main flow velocity decays along the flow direction,and the decays more rapidly in the case of steggered arrangement;(2)Among the three-dimensional turbulence intensity,the longitudinal turbulence intensity Tx is the highest,due to the influence of the weir flow,the turbulence intensity of the weir flow region in the front of the pool is higher,and the influence range of the turbulence intensity in the case of staggered arrangement is larger than that in the case of identical arrangement;(3)the Reynolds stress has a larger amplitude in the weir flow region and the vertical slot wall jet region,and in which the Reynolds stress in the longitudinal section has the maximum amplitude in the weir flow region,which is much larger than that on the other two planes;(4)the auto-correlation coefficient of the weir flow region is larger than that of the vertical slot wall jet region,and the period is longer;(5)The vertical slot wall jet region and weir flow region both have a dominant frequency in the low frequency domain,and the white noise of the vertical slot wall jet region in the case of staggered arrangement is much larger than that in the case of identical arrangement;(6)The integral scale of the weir flow region is obviously larger than that of the vertical slot wall jet area;the vortex structure of the weir flow region in the case of staggered arrangement changes periodically,while the vortex structure of the weir flow region in the case of identical arrangement is relatively simple.(7)The micro-scale of the vertical slot wall jet region is larger than that of the weir flow region;the micro-scale of in the case of staggered arrangement is larger than that in the case of identical arrangement;the arrangement in the case of staggered arrangement is more likely to produce some large-scale micro vortices than the arrangement in the case of identical arrangement;In addition,swimming behaviors of target fish in the fishway were observed by high speed photography based on the fish tests.Reaction and detection of target fish to instant and would-be swimming environment as well as relation with turbulent structures in a combined fishway with a overflow weir and a vertical slot were analyzed.