Discussion of “Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor—Part 1: Measurement” (Song, J., Kim, S., Park, T. C., Cha, B.-J., Lim, D. H., Hong, J. S., Lee, T. W., and Song, S. J., ASME J. Eng. Gas Turbines

Abstract

My commendations to the authors for this long-awaited (and greatly needed) contribution regarding measured direct and cross-coupled stiffness (Kxy) coefficients of a centrifugal–compressor impeller. As noted by the authors, several previous researchers have measured rotordynamic coefficients for pump impellers. Ohashi and Shoji [1] also provided measured test results for pump–impeller rotordynamic coefficients.Given the available test results for pump impellers and the present single dataset for a centrifugal compressor, can the authors tell us their estimates for the Mach numbers produced in the leakage annulus for their tests? Are they small enough to make any reasonable comparisons between prior pump measurements and the current centrifugal–compressor–impeller results?