Study On Discharge Capacity And Hydrodynamic Characteristics Of Flat Grate Street Inlet

In recent years,flood season "city to see the sea" nearly normal.As an important structure of connecting surface and underground pipe,it is very important to determine the discharge capacity of rainwater inlet accurately.The discharge capacity and hydrodynamic characteristics of flat grate with different grate types were studied by model test and numerical simulation.The structure of a complete grate was carefully considered,the froude number is used as a similar criterion to build a test platform.133 groups of constant flow tests were carried out for two kinds of rainwater grate(horizontal lattice bar and along lattice bar)in the grate.At the same time,the mathematical model is used to simulate the effect of the position of connecting pipe on the discharge rate of rainwater outlet.It is of great significance to improve the calculation accuracy of urban flood model and the layout of rainwater outlet for flood control and drainage.(1)The discharge process of rainwater outlet includes three discharge modes,namely weir flow,orifice outflow and nozzle outflow.An empirical formula for the discharge capacity of the flat grate varies with the water depth in front of the grate is put forward,the empirical formula for discharge of flat grate along lattice and horizontal bar is(?)(2)In the weir flow mode and orifice outflow,It is concluded that the discharge efficiency is related to the type of grate.In the nozzle outlet mode,the discharge efficiency is only related to the diameter of the connecting pipe,and has nothing to do with the type of rain strainer.(3)The correlation coefficient of the discharge capacity formula is calibrated by using the test data,and the specific formula in the form of the formula is obtained.Compared with the existing formulas,it is found that the smaller the thickness of the rain grate,the greater the discharge capacity.Discharge formula of dimensional analysis method of flat grate horizontal and lattice bar is Q=0.46*A uFr-0.901 and Q=0.46*AuFr-0.874(4)The empirical discharge formula,dimensional analysis discharge formula and the current gates discharge capacity characteristic curve were compared and analyzed.Under the condition of low water depth(weir outflow mode),the calculated value of the discharge formula is basically consistent with the recommended value.With the increasing of the water depth before grate,the deviation between the calculated value and the recommended value becomes larger and larger,and the calculated value is smaller.(5)By comparing the simulation results at different positions of the side branch pipe,it is found that the discharge capacity from large to small at different positions of the pipe is:The rainwater goes down to the downstream side(parallel to the flow direction)>The rainwater goes down to the side face(vertical to the flow direction)>The rainwater goes down to the upstream side(parallel to the flow direction).And there is a large difference in discharge between each other.It is concluded that when the rainwater grate and connecting pipe are set in the direction of water flow,the discharge efficiency of rainwater outlet is the maximum.