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Experimental Investigation of Inlet Distortion in a 4.5-Stage Axial Compressor


 Inlet distortion is a subject of increasing interest in compressors over the last years. Circumferential inhomogeneities can significantly influence the behavior and the aeroelastic response of transonic compressors in gas turbines in the field of airplane propulsion as well as power generation. The circumferential inhomogeneities can result from boundary layer ingestion as planned in many future airplane concepts or from restrictions of the space available leading to short aerodynamically unfavorable intakes. As modern front rows of axial compressors react more and more sensitive to inhomogeneities because of the thinner profiles in the transonic flow regime, understanding the behavior is vital. Therefore, an experimental investigation of the inlet distortion effects on a 4.5 stage axial transonic compressor, Rig250, which is representative of the front stages of a modern high pressure compressor, has been investigated at DLR Cologne.
 The inhomogeneity is a total pressure distortion which is applied to the inflow upstream of the strut and the swan neck. The distortion is achieved by a perforated metal plate which can be rotated by 360° at its position. Thereby traverse measurements are possible, which allow a better understanding of the effects of the flow as the sensor positions on the casing and on the blades and vanes are fixed. As these traverses take longer time for measuring only some points are measured with traverses. The compressor has been tested with and without this inlet distortion to get a direct comparison. On the compressor map the 100 % speed line up to surge has been investigated. The inlet distortion shows only a small influence on the surge margin.