Numerical Analysis of Inner Flow Loss Evolutions in a Low-Aspect Ratio Transonic Compressor Rotor at Windmilling Conditions

This paper conducts a detailed numerical investigation to study the evolutions of flow topology and aerodynamic losses in a low-aspect ratio compressor rotor operating from freewindmill condition (near stall point) to highly loaded windmill condition (near choke point). Firstly, a simplified numerical calculation method based on energy transfer between rotor blade and working fluid is employed to capture the windmill points at low rotational speeds. Then, the influences of windmill on tip leakage loss are analyzed. At windmilling conditions, the tip leakage flow travels across the clearance from suction to pressure side and causes blockages near the pressure surface in the casing end-wall region, which is quite different from the flow phenomenon at freewindmill conditions. Finally, the influences of windmill on flow separations are investigated. In tip region, with the rotor operating from freewindmill to highly loaded windmill condition, the flow separation switches from suction surface separation to pressure surface separation, and both the intensity and size are increased. Unlike near the tip, the hub separations always appear on the suction surface and a radial growth is observed near the trailing edge at the highly loaded windmilling condition, which is not presented at both the near stall and windmill points.