Modeling of Surge in Free-Spool Centrifugal Compressors: Experimental Validation

The derivation of a compressor characteristic, and the experimental validation of a dynamic model for a variable speed centrifugal compressor using this characteristic, are presented. The dynamic compressor model of Fink et al. is used, and a variable speed compressor characteristic is derived by the use of energy transfer and loss analysis. It is demonstrated that taking into account the losses due to friction, incidence, mixing, and blade loading results in compressor characteristics that closely match the measured characteristics. The simulated response of the dynamic model was found to be in excellent agreement with the experimental results, both for set point changes using fuel flow and blow off and for surge oscillations. Analysis of the power spectrum of the in-surge rotational speed and pressure oscillations reveal that the simulated nonlinear oscillations match experimental values up to the third harmonic, both with respect to frequency and amplitude.