Influences of tip leakage flows on flow field at design condition in transonic centrifugal compressor with splitter blade

Abstract

A tip leakage flow is well known to have predominant influence on a loss generation in a compressor. An impeller for a transonic centrifugal compressor is generally composed of the main and the splitter blades to gain the choke flow rate. In this study, in order to clarify the individual influence of the tip leakage flows from the main and the splitter blades on the flow behavior in the transonic centrifugal compressor at design condition, the flows in the compressor at four conditions prescribed by the presence or the absence of the tip clearances of the main and the splitter blades were analyzed numerically. The computed results clarified a series of interactive influences of the tip leakage vortices on the flow field as follows. The tip leakage vortex from the leading edge of the main blade increased the incidence angle for the splitter blade by its blockage effect. The increased incidence angle generated the tip leakage vortex from the leading edge of the splitter blade and intensified the acceleration of the flow over the suction surface of the splitter blade. The accelerated flow produced the negative blade loading of the adjacent main blade by reducing the static pressure on the pressure surface of the main blade, which generated the tip leakage vortex appearing from the pressure side of the main blade. The tip leakage vortex from the leading edge of the splitter blade reduced the flow acceleration on the suction surface of the splitter blade by its blockage effect. As a consequence it strongly contributed to the reduction of the loss generation by suppressing the formation of the shock wave on the suction surface of the splitter blade and by decreasing the negative blade loading of the main blade.