Numerical model of predicting surge boundaries in high-speed centrifugal compressors

A numerical model of the whole compression system is established in this paper. The introduction of the Laval nozzle and opening boundary methods adaptively simulate the physical fluctuating boundary conditions during the surge without any artificial hypothesis. Based on the model, the steady simulation method has the capacity to well predict the low-order systematical oscillations during the surge by monitoring flow parameters on several representative surfaces. The surge boundaries of a high-speed centrifugal compressor, including the mild surge and the deep surge, are predicted based on the current numerical model in different flow regimes. The discrepancies of the mild surge boundary between experimental data and numerical predictions are within 5% in the transonic regime, but within 0.5% in the subsonic and supersonic regimes. The sensitivities of the mild surge to the throttle opening degree differ much in different flow regimes: the highest is in the transonic regime and the lowest is in the supersonic regime. In the supersonic regime, there exist various mild surges in a wide range of throttle opening degrees and an unstable equilibrium point (UEP) which is the most typical characteristic of the two-regime surge. To the best knowledge of the authors, it is the first time that all the oscillation characteristics of various mild surges and the existence of UEP in the supersonic regime are well predicted by one numerical method.