AN EXPERIMENTAL INVESTIGATION OF STATOR INDUCED UNSTEADINESS ON CENTRIFUGAL IMPELLER OUTFLOW

Detailed flow measurements were taken in a centrifugal turbomachine mo del to investigate the aerodynamic influence of the vaned diffuser on the impeller flow. The model consists of an unshrouded centrifugal imp eller with backswept blades and a rotatable vaned diffuser, Which enab les a continuous variation of the vaned diffuser location with respect to the measuring points. Phase-locked ensemble-averaged velocity comp onents have been measured with hot-wire probes at the impeller outlet for 30 different relative positions of the probe with respect to the d iffuser vanes. The data also include the distribution of the ensemble- averaged static pressure at the impeller front end, taken by means of miniature fast response pressure transducers flush-mounted at the impe ller stationary casing. By circumferentially averaging the results obt ained for the different circumferential probe locations, the periodica lly perturbed impeller flow has been split into a relative steady flow and a stator-generated unsteadiness. The results for the different pr obe positions have also been correlated in time to obtain instantaneou s flow field images in the relative frame, which provide information o n the various aspects of the diffuser vane upstream influence on the r elative flow leaving the impeller.