Numerical and Experimental Investigations of Cavitation Phenomena inside the Pilot Stage of the Deflector Jet Servo-Valve

Two-stage electrohydraulic servo-valves play an important role in the most modern hydraulic servo control systems for fight wing controls, manufacturing robots, and many engineering applications. The existence of cavitation inside the pilot stage is one of the root causes of self-excited noise, cavitation erosion, system jam, and frequent failures of electrohydraulic servo-valves. Thus, experimental and numerical investigations of the flow field and cavitation phenomena inside the pilot stage of deflector jet servo-valve under different supply pressures conditions are conducted in this paper. An assembly for experimental verification of the flow visualization process that represents the deflector jet pilot stage is produced and discussed. To test and verify the numerical simulations for cavitation phenomena, the flow field characteristics in the deflector jet pilot stage are investigated by using experimental flow visualization. The cavitation inception inside the pilot stage of the deflector jet servo-valve is experimentally confirmed through flow visualization. More importantly, the attached cloud-like cavitation or bubble shedding is observed along with the jet flow and the significant locations of cavitation inception are also identified for varying supply pressures. The profile of turbulent intensity confirms to conclude that turbulent pressure fluctuations contribute to cavitation. The result also shows that the increment of supply pressure intensifies cavitation and output pressure plays a significant role in reducing the intensity of cavitation inside the pilot stage of deflector jet servo-valve. Finally, the numerical results show good agreement with experimental results.