EXPERIMENTAL AND THEORETICAL STUDY ON CAVITATION CHARACTERISTICS OF LONG ORIFICES IN STEADY AND UNSTEADY FLOWS

In fluid power systems, cavitation under unsteady flow conditions plays an important role regarding their dynamic characteristics. To clarify the feature of unsteady cavitation, cavitation of long orifices in unsteady flows was studied. Sinusoidal and stepwise flows were obtained from a variable displacement piston pump. Cavitation was detected mainly in the pressure ripples obtained by a pressure sensor located at the outlet of the orifice. Also, a video-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 1.0 Hz) in case of the sinusoidal flow-, and the step height of the stepwise flow.Also, by the finite volume method, the two- and three-dimensional distributions of pressure and velocity in the long orifice were obtained. The low pressure region which occurred just behind the inlet corner of the orifice was verified. The theoretical results can explain the experimental ones.