Research Of Flow Forces On The Flapper In The Field Of A Flapper-Nozzle Pilot Valve

Since the flow field in the pilot stage of flapper-nozzle hydraulic servo valves has many characteristics that are small scale, high velocity, easily forming vortex and cavitation, the flapper in the flow field is affected by unstable flow forces leading to oscillation and noise that reduce the stability and working performance of the servo valve and even damage the whole hydraulic control system. So it’s necessary and critical to build the mathematical model of the flow forces that means to analysis the changing laws of the flow forces, the flapper position and supply pressure in order to improve the performance of the servo valve.In this paper, the mathematical models of the flow forces on the flapper which is related to basic theory of fluid mechanics and working principle of servo valve are established to analyze the changing law of the flow forces on the flapper. Combining with the continuity equation of gas-liquid mixture, LASMM turbulence model, the momentum equation of gas-liquid mixture and Singhal cavitation model, the mathematical models of the flow field in the pilot stage are established. The 3D flow field model is built by Solidworks software. Its boundary conditions are set up by DesignModeler of Workbench software. Its grid is divided by Meshing of Workbench software. The 3D model software with different position of the flapper, different supply pressure and if cavitation model included is simulated by Fluent software. The values of flow force under different conditions is predicted. Curve graphs which show the changing laws of flow force, flapper position and supply pressure are plotted by Origin software. The displacement of armature is measured by laser displacement sensor. Then the flow forces on the flapper and actual displacement of flapper under different conditions are calculated by the values of armature displacement. Under the experiment condition the changing laws of the three conditions which are the flow forces, the position of flapper and supply pressure are shown in the curve graphs. And the experiment results verify the simulation results reliably.In conclusion, the mathematical models of flow force on the flapper which are based on the theory of fluid mechanics and the working principle of servo valve are built to get the changing laws of the flow forces on the flapper. Further with the methods of the finite element analysis and measure experiment, the changing laws of the flow forces on the flapper are summarized. The research of this paper are of theoretic significance for the further research of oscillation and self-excited noise generation mechanism.