Erosion characteristics and the corresponding self-resonating oscillations of cavitating jet on oblique surfaces

Abstract

The erosion and the corresponding self-resonating oscillations of the cavitating jet were experimentally investigated on the oblique surfaces. To evaluate the intensities of erosion and self-resonating oscillations of the jet, mass loss, surface morphology of the eroded specimens, upstream fluctuating pressure and unsteady cavitation noise were obtained at a series of stand-off distance ratios ld/dt in the cases where the oblique angles are α = 0ffi, 5ffi, 15ffi and 30ffi. In the low ld/dt range, with the increase of a, the erosion gradually transforms from two isolated circular erosion rings at a = 0ffi into irregular oval shaped rings at a = 5ffi and separated horseshoe shaped rings at a = 15ffi. The self-resonating oscillations and cavitation were weak in this range because the dominating frequency f0 is away from the design frequency of the organ-pipe nozzle, resulting in the depressed aggressive ability in the low ld/dt range. With increasing ld/dt, the cavitation is enhanced before the self-resonating oscillations achieving more energy. The spectral decomposition reveals the existence of an intermediate state at the optimum standoff distance, where the energy of self-resonating oscillations and the cavitation reach a balance to realize the severest erosion damage.