Abstract: Steady and unsteady numerical simulations of a small centrifugal compressor are presented in this paper. First, the steady and unsteady time-averaged results are compared. Then, the unsteady interaction between the impeller and diffuser is investigated by analyzing the spectrum characteristics of pressure fluctuations at the outlet of the impeller and the inlet of the radial diffuser. Finally, the unsteady influences of the impeller with and without splitters on the radial diffuser inlet are studied. Results show that the unsteady time-averaged total pressure ratio and isentropic efficiency are respectively 3.7% and 0.1% higher than those of the steady at the same mass flow; in the centrifugal compressor with splitters, pressure fluctuations at the blade passing frequency are the main fluctuations at the outlet of the impeller and the inlet of the radial diffuser. Besides, it is obvious that there are fluctuations two times the radial diffuser blade passing frequency at the outlet of the splitter and half times the impeller blade passing frequency at the inlet of the radial diffuser blades caused by the splitter. These unsteady pressure fluctuations will likely affect the fatigue strength of the centrifugal compressor.

Key words: centrifugal compressors, splitter blade, impeller-diffuser interaction, unsteady flow, numerical simulation