（Department of Fluid Control and Automation，Harbin Institute of Technology，Harbin 150001，China）

Abstract：Aiming at the problems of that cavitation of hydraulic valve will cause the noise，performance degradation and even lead tohydraulic valve failure，cavitation phenomenon appearing in the flow field between the flapper and nozzle of an electrohydraulic servovalve was studied，and the 3D flow field model was established by Pro/E software. Its grid was divided and boundary conditions were setby Gambit software prior to implementing the simulation. The mathematical models of the flow field were established，which combinedstandard turbulence model and gas-liquid mixture. The flow field distribution and cavitation characteristics in the different nozzle inlet

velocity were analyzed by FLUENT software with finite element simulation method. Images of cavitation phenomenon in the flow fieldwere observed and recorded through high-speed video cameras. The results indicate that at flow conditions with lower Reynolds numbers，cavitation begins to form at the nozzle outer wall and the flapper leading edge. Further increasing of Reynolds numbers，attached cavity onthe flapper curved surface grows up gradually and with the jet flow velocity increasing，cloud-like cavitation is observed. Some numericalcalculated results at different flow conditions are verified by the experimental data，which show the cavitation model in the flow fieldbetween the flapper and nozzle of an electrohydraulic servo valve and the numerical calculation method are reasonable.

Key words：servo valve；cavitation；flow field；nozzle；flapper