Optimization Study On Hydraulic Characteristics Of Lateral Inlet/outlet And Reservoir Cofferdam Circulation

The lateral inlet/outlet is the crucial structure which connecting the water tunnel and the reservoir area of pumped storage power station,which needs proper pattern to ensure that hydraulic indexes is adequate under inlet and oulet flow conditions.The reservoir flow pattern will also affect the operation of the inlet and outlet.Therefore,it’s necessary to take some effective measures to eliminate the unfavorable circulation of the reservoir area.We has optimized pattern of a lateral inlet/outlet and cofferdam,using the computational fluid dynamics and physical modeling method in a case study of Weifang.The main work are as follows:(1)Physical modeling of lateral inlet/outlet of Weifang.Under inlet and outlet conditions of dead water level,we measured head loss and velocity distribution of trash fence section and open channel,we also calculated the flow rate of each orifice.The researches indicate that all hydraulic indexes meet the requirements of hydraulics.However,its body pattern has the space existence for further study.Therefore,we used the computational fluid dynamics(CFD)method for further body pattern optimization.(2)Establishing and verifying the lateral inlet/outlet numerical model of Weifang Lower Reservoir.The three-dimensional CFD calculation models of inlet/outlet monomer and overall reservoir area were built receptively.Using the physical modeling results to verify the numerical results,which indicate that the numerical results are accurate and reliable.(3)Analyzing and optimizing the hydraulic indexes namely head loss,internal flow,and each orifice flow distribution.The researches indicate that the local head loss near the diversion pier accounts for a large proportion of the total head loss.Taking the middle orifice for example,there is the reflux area above the adjustment section under bidirectional flow condition.The adjustment section had the function of homogenizing the velocity of the trash fence section only under outlet flow condition.When its length is 0.2 times the length of the diffusion section,the velocity non-uniformity coefficient of the trash rack section can meet the requirements of less than 2.When the spacing ratio of the middle lateral holes at the pier head is 0.9 and the length of the transition section is 3 times the tunnel diameter,the unequal distribution of each orifice can be less than 10% under bidirectional flow.(4)Optimizing the slope bottom line of the cofferdam to eliminate the circulation near the cofferdam.The result indicated that the water surface flow is stable under the inlet condition and adverse circulation was favorable to form near the cofferdam under the outlet condition when there is residual cofferdam in front of the lateral inlet/outlet.When the cofferdam’s slope bottom edge is along thedirection of the diffusion flow in the open channel section,the flow spreads smoothly and evenly into thereservoir area,greatly improving the flow conditions.