Experimental and numerical investigation of cavitation phenomenon in flapper-nozzle pilot stage of an electrohydraulic servo-valve

Cavitation in the flapper-nozzle pilot stage is an important source for the noise, performance deterioration and even failure of electrohydraulic servo-valves. In this paper, experimental and numerical investigations of cavitation phenomenon appearing in the flow field between the flapper and nozzle of an electrohydraulic servo-valve are carried out. Experimental observations are conducted with variation of Reynolds number ranging from 630 to 2500 based on the nozzle inlet velocity and diameter. Images of cavitation phenomenon in the flow field are recorded and compared with CFD simulation results to confirm the occurrence and locations of cavitation sources. The computed numerical results show a good agreement with experimental observations. From both types of results, the nozzle inner wall tip, nozzle outer wall tip and flapper leading edge are shown as the locations of cavitation sources. At flow conditions with lower Reynolds numbers, onset cavitation and inception are found at the nozzle outer wall and the flapper leading edge. Further increasing of Reynolds numbers creates a separated flow and then jet flow. Attached cavity is found on the flapper curved surface together with the separated flow and cloud-like cavitation comes with the jet flow. Since numerical results can confirm all of the recorded observations, a reliable computational scheme is also provided by this paper.