Performance Characterization of the Effect of Axial Positioning of Bend Skewed Casing Treatment Retrofitted to a Transonic Axial Flow Compressor

Abstract

The performance of an aero-engines to a large extend depends on the performance behavior of axial flow compressors and is restricted by the compressor instabilities like rotating stall and surge. In the present study, attempts have been made to design and develop the bend skewed casing treatment geometries with lower porosities to improve the stable operating range of single stage axial flow compressor. Experimental investigations were undertaken to study the impact of axial position of one of the casing treatment geometry on the single stage transonic axial flow compressor. The transonic compressor used for the current experimental studies has a stage total to total pressure ratio of 1.35, corrected mass flow rate of 22 kg/s at an operating speed of 12930 rpm. The compressor stage steady and unsteady state response for 20%, 40%, 60% and 100% axial chord coverage relative to the rotor tip chord of the bend skewed casing treatment with a porosity of 33% was studied experimentally. The objective was to identify the optimum axial location; which will give maximum improvement in the stall margin with minimal loss of compressor stage efficiency. Through an experimental study it was observed that the axial location of bend skewed casing treatment plays a very crucial role in governing the performance of the transonic compressor. For all the investigated axial coverages, compressor stall margin increases but the optimum performance in terms of stall margin improvement and efficiency gains were observed at 20% and 40% of the rotor chord. This trend shows good agreement with existing published literature. An improvement of 31.7% in the stall margin with an increase in the stage efficiency was obtained at one of the axial coverage. Maximum improvement of 37% in the stall margin above the solid casing was noticed at 60% axial coverage. The stalling characteristics of the compressor stage also changes with the axial positions. In the presence of solid casing the nature of stall was abrupt and stalls cells travels at half the rotor speed. The blade element performance also studied at the rotor exit using pre-calibrated aerodynamic probe.