Study On Influence Of Spillway Outlet Flow Of Small Reservoir

There are a large number of small reservoirs in China,which play an irreplaceable role in the national economy.However,some small reservoirs are limited by the total investment of the project,so there is not too much money to build the power elimination facilities,and the downstream river scour is serious.The energy dissipation effect of scour pit is similar to falling-sill bottom-flow dissipation,and it can be changed into a more regular energy dissipation structure through manual intervention,which can be applied to the energy dissipation of small reservoirs.Taking the spillway of a small reservoir as an example,the empirical formula of the scour pit was used to predict the depth of the scour pit.According to the prediction,the numerical model of the spillway was established,based on the standard k-εturbulence model and SIMPLE algorithm,VOF two-phase flow model is used to track the free surface of the discharge flow,and the hydraulic characteristics of the end of the spillway at six scour pit depths are compared and analyzed.The main conclusions are as follows:(1)By comparing and analyzing the simulated values of discharge,water surface line along the path and velocity distribution with the calculated values of the empirical formula,the results generally agree well.However,the error of water surface profile and velocity in the front section of spillway is large,ranging from 3.5% to 4%,because the water depth of control section is larger than the actual value when using empirical formula to calculate water surface profile.The results of numerical simulation are reliable and can be used for further research.(2)With the increase of the depth of scour pit,the velocity near the bottom decreases gradually.When approaching the bed,the allowable anti-scour velocity is close to the value estimated by the empirical formula of scour pit,which indicates that it is feasible to use numerical simulation to predict the depth of scour pit.(3)When the depth of the scour pit is small,there is no obvious water cushion in it,and the main stream flows downstream close to the bottom;With the increase of depth,the water cushion is thickened,and the main stream is inclined to the downstream to form a roll,and its range will gradually expand.The dynamic pressure at the bottom of the scour pit decreases with the increase of scour depth,but the total pressure increases first,then decreases,and finally increases again.When the depth of scour pit grows from 3m to 4m,the decrease rate of dynamic pressure is close to the increase rate of static pressure,and the total pressure remains unchanged.(4)When the depth of the scour pit is greater than 4m,the downstream velocity is lower than the allowable anti-scour velocity of the riverbed,which meets the requirements of energy dissipation.Moreover,with the increase of the scour pit depth,the energy dissipation rate does not change much,indicating that the energy dissipation of the scour pit has an upper limit.This method can be applied to the energy dissipation of small reservoirs.