Numerical Simulation Study On Overflow Process Of Combined Drainage Facilities

At present,the drainage system of most cities is still based on the confluence system.The rainstorm not only causes serious waterlogging problems in cities,but also has a significant impact on the surrounding water environment.The hydraulic characteristics of overflow facilities directly affect the drainage capacity and overflow condition of the combined system pipe network.The simulation of overflow facilities can provide ideas for the overflow control of the combined system in the future.At present,the relevant research on overflow facilities is still insufficient,so it is very necessary to conduct three-dimensional numerical simulation research on the hydraulic characteristics of two common facilities.This article takes rainwater overflow wells and pipeline overflow weirs as research objects,establishes a numerical calculation model,and uses Fluent software for simulation.Select RNG kεA simulation scheme was established by combining the turbulence model and the VOF twophase flow model.The finite volume method was used to discretize the control equation,and the SIMPLE-C algorithm was used to solve the coupling equation of velocity and pressure.The flow velocity,flow rate changes,and interception effect of the two overflow facility models were studied and analyzed under different flow velocity conditions.The rapid simulation technology uses long-and short-term neural network models to fit and predict multiple operating conditions.The conclusion is as follows:(1)Establish a stormwater overflow well model,through the simulation found that the overflow well has a good buffering effect on the water flow.The flow line in the well alone is smooth under gravity or pressure conditions.The water flow on the weir has lateral flow characteristics under high flow velocity,and the drainage flow rate of the left and right-side interceptor pipes under low flow velocity will produce fluctuation phenomenon.As the inlet flow velocity increases,the retention efficiency gradually decreases.With low flow velocities and high retention efficiency,there is still no guarantee that the downstream drainage pipes will not discharge rainwater.(2)In the study of pipeline overflow weir model,numerical simulation and experimental results are close.In the case of gravity flow and pressure flow pipeline weir flow line is uniformly distributed.The flow velocity of the cross-section in the pipeline decreases gradually with the flow,and the influence of the internal weir on the flow velocity.Only under the gravity drive,the flow rate and head on the weir is proportional type function relationship,when the pipeline flow rate reaches 0.5-1.5m/s interval.The flow on the weir is converted from gravity-driven to heavy pressure-driven,more than a certain flow rate will be completely converted to pressure-driven,when the head no longer changes and the flow rate increases with the increase in flow rate.The pipe is in the gravity flow state,after the weir will produce the tube water jump,in the higher flow rate can produce the tube inundation water jump.When the flow rate reaches a certain level,at this time and the pressurized pipe barrier flow is similar.(3)With the LSTM prediction model,it is found that the data prediction of stormwater overflow wells is better and the predicted data can fit the actual data in most cases.The overall fitting and prediction error of pipe overflow weir is less than 0.2,which is good.The data under some working conditions have strong oscillation,and the prediction effect is not satisfactory.The activation function test was conducted for the flow rate on the weir in the 0.1 m/s working condition and it was found that the activation function may not be obvious,and specific analysis is needed for each case.