Numerical Investigation to Assess the Performance of Free Rotating Vaneless Diffuser for a Centrifugal Compressor Stage

Numerical investigation is carried out on a low-pressure ratio centrifugal compressor stage to study the effects of the rotational speed of a rotating vaneless diffuser on flow diffusion using various flow parameters and performance characteristics parameters. The results obtained are compared with a stage having conventional stationary vaneless diffuser. Rotational speed of the rotating vaneless diffuser plays a major role in determining the extent of net gain in energy level of the fluid and drop in stagnation pressure losses. The net gain in energy level result as rise in kinetic energy level of the fluid. By an effective diffusion process, this results into an improved static pressure and stagnation pressure distribution at stage exit and FreeRVDSR0.75 undergoes a comparatively better diffusion process. Based on this study, it can be concluded that the diffusion process efficacy of a compressor stage with rotating vaneless diffuser is better in the free type at diffuser’s rotational speed above 0.50 times the impeller’s rotational speed.