Research On Safety Valve Used In EMU Brake System

Safety valve is an important part of the EMU air supply system,it's used to prevent the pressure from exceeding allowable value,to ensure the safety of the supply and apply air equipments.The experimental study of safety valve has the inherent shortcomings,such as high cost and low efficiency,and the numerical simulation method can reduce the number of tests and research on the internal flow field of the valve in depth.In this paper,ANSYS-CFX software is used to simulate the variation of the internal flow field parameters of the safety valve at different opening heights.The main study contents is summarized as follows:The structure,working principle and force of the traditional spring safety valve is analyzed.According to the characteristics of the EMU to improve the safety valve structure,the structure of the safety valve is more simple,smaller size,more convenient pressure adjustment,more convenient maintenance and repair,so that it can be better applied to the EMU.Simple structures mesh in structured grids,complex structures mesh in unstructured grids,and then using the GGI rules to interface the improved safety valve.Using the AMESim software to establish the simulation model of the safety valve and to get the inlet pressure at different opening height.Setting the parameters and boundary conditions and simulating the new model.By analyzing the relevant flow field parameters,it is found that the spool opening height has a great influence on the air pressure and velocity of the valve.With the increase of the opening height,the influence is gradually reduced;The maximum total pressure and the maximum static pressure in the flow field decrease with the increase of the opening height of the spool,but its position is constant.The maximum Mach in the flow field is greater than 1 and increases with the increasing of the height of the spool,the position of the maximum is variable,but it is not at the throat neck;There are mutations of the flow field parameters,and parameter mutations are related to the abrupt changes in geometry stucture.The size of the reseating pressure adjustment hole has little effect on the lower flow field law,and only changes the maximum,minimum pressure and velocity of the flow field;The size of the hole has a significant effect on the upper flow field.As the opening degree increases,the area where the velocity of the adjustment hole is large will gradually move up and the value of the maximum velocity will gradually decrease.With the increase of the opening degree of the adjustment hole,the vertical force of the spool is increased,which shows that it is feasible to adjust reseating pressure separately.In the stable discharge stage,the air at the throat of the safety valve is subsonic flow and is not the supersonic flow predicted by the nozzle theory.