This work is focused on the numerical investigation of the unsteady effects in a stage of a centrifugal compressor with vaneless diffuser. Different turbulence models implemented in NUMECA FINE/TURBO 8.9.1 software package as well as different configurations of computational domain were investigated. Conclusions about applicability of the certain models were made on the basis of the comparison of the results against the experimental data. Satisfactory agreement with experimental data was obtained in the region of high gas flow rates.