SOME AERODYNAMIC ASPECTS OF CENTRIFUGAL IMPELLER FLOW.

Experiments were conducted on an 875 mm diameter low speed centrifugal impeller with three types of interchangeable vane shapes. The impellers were tested over a range of flow coefficients. The flow was measured both upstream and downstream of the impeller. Static pressures on the vane surfaces and the rear shroud of a specimen vane channel were recorded with the aid of a ten-cell pressure transfer device specially designed for the purpose. Calculations were made for the boundary layer development on the vane surfaces, based on the relative local surface velocities, after the methods of E. Truckenbrodt, D. A. Spence, and A. Walz. Flow visualization studies with the carbon-black technique indicated a low velocity region midway between the shrouds on the vane suction surface and also a heavy separation region under the front shroud. It was evident from the experimental results, that a sort of flow 'instability' at inlet appears at low flow rates through the impeller, which however was not clearly identified, as either a state of stalling or return flows in the region. Flow-induced prewhirl was found to exist to a certain degree.