DETAILED FLOW MEASUREMENTS WITHIN THE IMPELLER AND THE VANELESS DIFFUSER OF A CENTRIFUGAL TURBOMACHINE

The flow within the impeller and the Vaneless diffuser of a centrifuga l turbomachine model operating at the nominal point has been experimen tally investigated. The radial and circumferential velocities and the associated turbulent fluctuations have been:measured on seven cross-se ctional circumferential surfaces, four within the impeller and three i n the vaneless diffuser by means of a four-beam two-color fibre optic laser-Doppler velocimeter. To complete the flow investigation, LDV mea surements have been performed on the blade-to-blade plane at mid-span. Data acquired have been processed by means of a phase locked ensemble -average technique in order to separate periodic from turbulent fluctu ations. The results show the impeller flow structure, the development and decay of the blade and through-flow wakes and the main features of the diffusing flow. The present experimental work provides a well doc umented data base suitable for the assessment of turbomachinery flow p rediction codes. (C) 1998 Elsevier Science Inc. All rights reserved.