The Numerical Simulation Study On The Shape Optimization Of Pre-aerator Stepped Spillways

Set up aerator in front of the stepped spillway,high-velocity flow causes a water tongue through the aerator,force the gas into the bottom of the flow,increase the air concentration of the water in order to protect the stepped surface,reduce the stepped surface pressure,the pre aeration stepped spillway can effectively solve the contradiction problem of the high dam sluices in the building in high water head and large discharge under the run time,between increase efficiency of energy dissipation and improve the resistance to cavitation damage.Nowadays,numerical simulation has become a commonly used research method in high-velocity hydraulics.Based on the basic equation of two-phase flow,numerical simulation is used to research the water-gas two-phase flow problem and the aeration for preventing cavitation erosion in Hydraulic engineering,which provides a convenient and efficient way for engineering design and program optimization.Combined with the medium spillway of a large hydropower station,the finite volume method is used to discretize the governing equation,Selected the Air entrainment model,the Multiphase flow model and the Turbulent model to simulated.To carry out numerical simulation calculation for the two-phase flow of high-velocity of pre-aerator stepped spillways under different simulated conditions,Explore how the shoulder height,bottom slope of the spillway affect the flow regime,the depth distribution of the water,aeration cavity length,the air concentration of the water,the pressure distribution,velocity distribution,efficiency of energy dissipation and other hydraulic characteristics of the spillway.The paper also studies the adaptability of the design of the pre-aerator stepped spillways with aerator height and the shoulder height,bottom slope of the spillway,so as to provide reference for the actual construction of the project.The result of research shows that the height of step is beneficial to energy dissipation of the pre-aerator stepped spillways,but it increases negative pressure of the steps surface of the horizontal and vertical and the risk of cavitation damage in the overflow surface.To increase the height of the aerator can effectively increase the aeration protect cavity length and increase the gas concentration distribution along the near wall and steps,and reduce the risk of the cavitation erosion damage caused by the negative pressure;Spillway bottom slope is 1:4.25 when the first few steps away from the wall of mixed gas concentration and pressure distribution is better than the other two kinds of working condition of spillway of the bottom slope,and the bottom of the spillway slope when slow energy dissipation effect is increased but the effect is not obvious,by aeration of the height to 0.8 meters can get good energy dissipation effect,study the optimal condition of bench height is 2.5 meters,the bottom of the spillway slope is 1:4.25,and the height of 0.8 meters of aeration condition b-3.