An experimental and numerical investigation of stator-rotor interactions in a transonic compressor
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Although it is known that the flow field in a turbomachine is unsteady, current design tools do not explicitly account for it. In this dissertation blade-row interactions between an upstream stator row and downstream transonic rotor row are investigated. Experimental data acquired from a transonic compressor rig is presented that documents how changes in axial blade-row spacing and stator solidity affect compressor performance. Unsteady CFD simulations of the compressor are used to show what part of the compressor is responsible for performance changes and how unsteady fluid mechanics cause these changes.;Mass flow rate, pressure ratio, and efficiency all decreased as the spacing between the wake generator and rotor was reduced. The number of blades in the wake generator blade-row also affected the stage performance. The higher the wake generator blade-row solidity the lower the pressure ratio, efficiency, and mass flow rate. The experimental data suggest the drop in performance is a result of increased loss production due to blade-row interactions.;A numerical simulation using the code MSU-TURBO was able to account for the change in efficiency observed experimentally between far and close spacing at an operating point near peak efficiency. At close spacing the rotor bow shock is actually chopped by the stator trailing edge forming a pressure wave on the upper surface of the stator that propagates upstream until it weakens. In the reference frame relative to this pressure wave, the flow is supersonic and a moving shock wave exists that produces an entropy rise. The lower efficiency, pressure ratio, and mass flow rate measured at close spacing is a result of this extra loss. The magnitude of loss production is affected by the strength of the bow shock at the location it interacts with the trailing edge of the stator. Furthermore, the more blades present in the stator the more loss producing interactions take place. At far spacing the rotor bow shock has degenerated into a bow wave where it interacts with the stator trailing edge and is not chopped, therefore no pressure wave forms on the wake generator upper surface.