Blade Loading and Shock Wave in a Transonic Circular Cascade Diffuser

Abstract

A low-solidity circular cascade, conformally transformed from a high-stagger linear cascade of double-circular-arc vanes with solidity 0.69, was tested as a part of diffuser systems of a transonic centrifugal compressor and the static pressures were measured around a vane of the cascade and on the side wall between cascade vanes in detail. The blade loading of cascade vane was discussed by integrating the pressure distribution around the vane. The experimental data for lift-coefficient of vane were almost on a single straight line with positive gradient against angle-of-attack over a wide range of inflow Mach number and inflow angle. The maximum lift coefficient reached about 1.5 and the vane worked well to the surge condition of the compressor. The structure of shock wave was also discussed by drawing a contour map of the flow Mach number between cascade vanes. The normal shock wave was observed on the suction surface of vane and it moved upstream along the suction surface with the decrease in inflow angle. The vane did not fall in stall even though the Mach number upstream of the shock wave was over 1.4.