POTENTIAL-FIELD INTERACTIONS IN A LOW-SPEED CENTRIFUGAL-COMPRESSOR

A series of experiments is performed to investigate the unsteady aerod ynamic response of a centrifugal compressor impeller resulting from it s interaction with the potential field of the downstream radial-vaned diffuser. Fundamental unsteady impeller-diffuser aerodynamic interacti on data are acquired at two impeller-diffuser radial spacings over a w ide range of now rates. The detailed diffuser vane-generated unsteady aerodynamic forcing function and the resulting impeller-blade unsteady aerodynamic response are measured and analyzed. Very near the diffuse r-vane leading-edge plane, multiple harmonics are required to describe the spatially nonuniform static pressure field generated by the diffu ser vanes. However, the higher harmonic components associated with thi s potential flow-generated forcing-function decay very rapidly across the vaneless space, and the impeller blades respond primarily to the f irst harmonic. The maximum impeller-blade unsteady aerodynamic loading also occurs near the midchord region, and not near the exit where the diffuser vane generated forcing function is largest, Increasing the r adial spacing between the impeller and diffuser significantly reduces both the amplitude of the forcing function and resulting impeller-blad e unsteady aerodynamic loading.