Experimental Determination Of The Reverse Flow Onset In A Centrifugal Impeller

Abstract

The importance of problems related to machines operating at partial flow rate led to Societe Hydrotechnique de France (S.H.F.) to form a working group on the subject. In order to better understand partial flow phenomena and to validate flow calculations and correlations, this group has defined an experimental program, the main results of which are presented in this paper. A low specific speed, 7 bladed impeller was designed. Two different size similar pump models were then manufactured for experiments with water (outlet diameter 354 mm) and air (outlet diameter 17mm). The paper gives test results issued from flow visualization and measurements of various quantities varying with flow rate. Flow visualization were made in the inlet and outlet regions of the impeller using threads, smoke and cavitation. A determination of the critical flow rate at the inlet and outlet was also made using the measurements of; pump power input, mean and fluctuating wall pressures, mean and fluctuating velocities (with directional probes, laser velocimeter, and hot wires). The influence of the variations pof some parameters has been examined; *comparison of vaneless and 6 vanes diffuser, * effect of diffuser width modification, * influence of variable leakage flow rate, * comparison of results obtained with water and air. These results were finally compared with correlations available in the technical literature and were used to validate the computer programs developed.