Three-dimensional Numerical Simulation Research On Hydrodynamic Characteristics Of Rainwater Inlet

Under the combined effects of urbanization and global warming,extreme precipitation events occur frequently,causing urban flooding problems to become increasingly serious.The rainwater inlet is the connection point between the surface runoff and the underground rainwater pipe network,which can transport surface runoff to the drainage pipe network,play a role in reducing ground surface water and reducing surface runoff,and is a key factor in the drainage system.It's discharge effect directly affects the removal efficiency of water on land,which is of great significance to alleviating urban waterlogging.Reasonable and scientific setting of rainwater inlet is the key to the design of pavement drainage system.This paper takes rainwater inlet as the research object,using the commercial software AnsysFluent6.3 to perform numerical simulations on three different types of rainwater inlet models which include unilateral layout rainwater inlet,central layout rainwater inlet and through-type rainwater inlet.The VOF method was applied to track the flow surface.The gas-liquid two-phase time-averaged equations were closed with RNG k-? turbulence model.The coupling velocity and pressure equations were solved with the PISO method.Research and analysis of streamline distribution,flow velocity distribution and flow pattern characteristics under different incoming flow conditions.And based on the numerical simulation data and the dimensional analysis method,the empirical formula between the discharge coefficient of the rainwater inlet and the Froude number of the flow in front of the rainwater inlet is constructed.The following conclusions are reached:(1)According to the results of numerical simulation calculations,we observed the flow pattern of the water flow above the rain grate,and found that:when the water depth of the unilateral layout rainwater inlet is shallow,the water flows smoothly into the rain well;when the water depth is large,the water flow completely covers the grate,The water flows from the entire rain grate into the rain well,and a vortex is formed on the water surface directly above the rain grate.The comparison of the structure of the vortex is consistent with the actual situation.The centrally arranged rainwater inlet,when the incoming water depth is shallow,the water flows smoothly into the rainwater well;when the incoming water depth is large,the water flow above the grate tends to develop into a whirlpool,which is consistent with the actual situation.Water fins will be formed above the water flow of the rainwater inlet across the road,which is consistent with the actual situation.(2)Based on the results obtained by numerical simulation of the the unilateral layout rainwater inlet,data processing is carried out,and the empirical formula is obtained as Cw=-0.7905Fr2+0.8918Fr+0.208,R2=0.8763 which has a high correlation coefficient.(3)Based on the results obtained by numerical simulation of the central layout rainwater,data processing is carried out,and the empirical formula is obtained as Cw=-0.2755Fr4+1.0755Fr3-1.4745Fr2+0.7609Fr-0.0215,R2=0.8755 which has a high correlation coefficient.(4)Based on the results obtained by numerical simulation of the through-type rainwater intlet,data processing is carried out,and the empirical formula is obtained as Cw=-0.1192Fr2+0.2398Fr+0.0507,R2=0.7809 which has a high correlation coefficient.(5)This paper proposes the calculation formulas for the discharge coefficients of three layout schemes,which can be used to calculate the discharge flow of the three layout rainwater inlets.