Numerical investigation on the combined effects of pinching and rotation on the performance of a high-speed centrifugal compressor with a vaneless diffuser

Computational investigations are carried out on a high-speed centrifugal compressor with the vaneless diffuser to study the combined pinch and rotation effect. The axial inlet width of the rotating vaneless diffuser is reduced at diffuser inlet, either at the hub wall or at the shroud wall, or both the walls. The reduction is varied from 0% (base case) to 20% at an interval of 5%. Numerical simulations are conducted for different speed range by varying the rotating diffuser diameter ratio from 1.25–1.75. Among all these cases, the best performance of 25% increase in pressure recovery with uniform diffusion and 2.3% increase in isentropic efficiency is obtained with 15% shroud pinch at a diameter ratio of 1.375 at the design mass flow rate.