Effect of Inlet Distortion Reduced Frequency on Centrifugal Compressor Performance and Stability

Characterizing the circumferential angle of inlet total pressure distortion by which a compressor responds in both performance and stability changes is paramount for inlet–gas turbine integration. Past computational simulations for centrifugal compressors have shown that the acoustic propagation time of information through the rotor passage over the dwell time of the rotor in the distorted state dictates this response to distortion. This is known as the acoustic reduced frequency, and a critical value has been shown computationally for centrifugal compressors to be unity. This effort utilizes the Single Stage Centrifugal Compressor at Purdue University to validate this critical value and behavior experimentally utilizing once-per-rev total pressure distortion screens. The compressor was mapped at 80, 90, and 100% corrected speed, which corresponded to subsonic, transonic, and supersonic relative-frame inlet flow Mach numbers. The efficiency of the compressor was minimally affected at transonic and supersonic operation by distortions with reduced frequencies greater than one and then exponentially decayed as distortion extents were increased, causing the reduced frequency to drop below unity. The compressor surged at the same numerical value of work coefficient for all inlet distortion configurations. The surge margin was minimally affected by distortion extents with reduced frequencies above one.