Abstract: Unsteady numerical simulations of the centrifugal compressor with and without volute were carried out to investigate the effect of vaneless diffuser and volute on compressor instability. Combined with dynamic mode decomposition (DMD) method, the three-dimensional flow field of the volute is decomposed and reconstructed under design and stall condition. It is shown that the dominating perturbation of volute under design condition is the one induced by main blade passing, while the perturbation with higher frequency due to main and splitter blades is suppressed by the volute. The occurrence of stall in the compressor is delayed by the volute compared with the compressor without volute. A standing wave comes into being in the volute during stall, and the flow filed of volute fluctuates along the tangential direction. The occurrence of volute stall indicates that the volute loses the ability to suppress the instability perturbation, and the compressor is occupied by stall. The application of DMD method on volute provides the detailed flow information under specific perturbation frequency before and after stall.

Key words: centrifugal compressor, volute, unsteady flow filed, dynamic mode decomposition (DMD), stability