Cavitation Characteristics of Long Orifices in Unsteady Flows.

As regards fluid power systems, cavitation under unsteady flow conditions plays an important role regarding their dynamic characteristics.To clarify the unsteady cavitation mechanisms, as the first step, cavitation of long orifices in unsteady flows was studied.Sinusoidal and stepwise flows were obtained from a variable displacement piston pump.Long orifices made of steel were 2.0mm and 2.5mm in diameter, and the length/diameter ratios were 5.0 and 4.0 respectively.The fluid tested was ISO VG 32.Gavitation was detected mainly in the pressure ripples obtained by the pressure sensor positioned on the outlet side of the orifice.Also, a strobo-light and TV camera was used to observe the cavitation clouds.The test results, related to inception and desinence of cavitation choking, were mainly shown as the relationship between cavitation number and the amplitude and frequency (0.0-1.0Hz)in case of the sinusoidal flow, and the step height of the stepwise flow.In conclusion, it could be shown that the cavitation in an unsteady flow occurs much easier than that in a steady flow and discontinuous cavitation choking with stepwise flow input could be explained by the numerical results for the unsteady pipe flows.