Steady and unsteady simulations were conducted to investigate the complicated flow in a transonic centrifugal compressor with splitter blade.Results from the steady and unsteady simulations were compared and the interactions between impeller and diffuser were studied in detail.The results indicate that the impeller/diffuser interaction can affect a range of 30% impeller chord for impeller trailing edge on impeller performance and whole chord length on diffuser performance.The potential effects of the diffuser caused an unsteady pressure disturbance for the impeller exit

leading to the unsteadiness of impeller load

tip leakage flow and losses.While the unsteadiness of impeller exit flow caused periodical variation of inlet flow conditions for the diffuser

and the inlet flow angle was found to be the most significant parameter in setting diffuser performance

resulting in significant unsteadiness of blade load and total pressure recovery coefficient.