A study of cavitation and noise in rectangular orifices with one chamfered edge

Rotary valves are constructed using a sleeve that contains axially aligned rectangular sharp-edged slots. The sleeve rotates on a shaft that also contains axially aligned rectangular chamfer-edged slots. Flow through the valve is controlled by the alignment of the sleeve slots and the shaft slots. The rectangular orifices through which the fluid flows are only tens of micrometers wide at small valve openings and as a result of the sharp edge-chamfered edge arrangement, the flow is presented with very different flow passages, depending upon the direction of flow through the orifices. In one direction the flow is led into the orifice through two converging surfaces and this flow is referred to as "upflow". The flow in the opposite direction is referred to as "downflow". Cavitation can be a serious problem in these valves. A novel test rig was constructed to allow the cavitating hydraulic fluid flowing through a single orifice in either direction to be viewed. It was found that the "upflow" configuration was significantly less prone to cavitation and associated noise than the "downflow" configuration.