Research on cavitation phenomena in pilot stage of jet pipe servo-valve with a rectangular nozzle based on large-eddy simulations

Abstract

The flow field in the pilot stage of a jet pipe servo-valve significantly affects the performance of the valve. Cavitation with pressure oscillations occur in the pilot stage and lead to the appearance of high-frequency noise and vibration. To obtain dynamic characteristics of cavitation and study the relationship between the cavitation and inlet pressure, we use large-eddy simulations (LESs) to calculate the unsteady flow field in the pilot stage with a rectangular nozzle. The simulation results show that fixed cavitation and vortex cavitation exist, and travelling cavitation begins to occur when inlet pressure reaches 7MPa. The increment of inlet pressure enhances cavitation and cavitation shedding. The cavitation-shedding process under different inlet pressures is monitored via LES. Different points are studied, which differ in terms of cavitation type and the development of cavitation regions. By applying a fast Fourier transform, we obtain the main frequencies of the pressure oscillations of each cavitation under different inlet pressures. The influences of outlet pressure and wedge length are also studied. When outlet pressure and wedge length increase, cavitation phenomena are weakened effectively. When the wedge length increases, the main frequency of vortex cavitation increases whereas that of travelling cavitation decreases. Upon increasing the wedge length, the volume fraction of vapor phase and the energy ratio at the surface at y= −0.3mm to the exit of the nozzle decrease, and both decrease sharply from 0.03 to 0.04mm. Considering the above characteristics and the ease of the process, the optimal length of the wedge is 0.03mm.