Rotor wake behavior in a transonic compressor stage and its effect on the loading and performance of the stator

Abstract

The structure and behavior of wakes from a transonic compressor rotor and their effects on the loading and performance of the downstream stator have been studied experimentally. The rotor is 2 feet in diameter with a tip Mach number of 1.23 and a measured pressure ratio of 1.66. Time and space resolved measurements have been completed of the rotor and stator outlet flows, as well as of the pressure distribution on the surface of the stator blades. The data is analyzed and the rotor-stator viscous interaction is studied both qualitatively and quantitatively. It is found that the wakes from this rotor have large flow angle and flow Mach number variations from the mean flow, significant pressure fluctuations and a large degree of variation from blade to blade and from hub to tip. There is a significant total pressure defect and practically no static pressure variation associated with the stator wakes. Wakes from the rotor exist nearly undiminished in the exit flow of the stator and decay in the annular duct behind the stator. The pressure at all the points along the chord over each of the stator blades' surfaces, fluctuates nearly in phase in response to the rotor wakes, that is the unsteady chordwise pressure distribution is determined by the changes in angle of incidence to the blade and not by the local velocity fluctuations within the passage. There are large unsteady forces on the stator blade, induced by the rotor wakes, as high as 25% of the steady forces. The stator force due to the rotor wakes lags the incidence of the wake on the leading edge by approximately 1800 for most radii.