Numerical investigation of the influence of vaneless diffusers on the flow and performance of a centrifugal compressor

Aimming at studying numerically the influence of the vaneless diffuser on the three-dimensional viscous flowfield and performance of the centrifugal compressors three-dimensional viscous CFD code developed by the authors was applied with several acceleration methods: Local time-step, multigrid and residual smoothing. Additionally, the imposed mass-flow was developed instead of the traditional static pressure as the exit boundary condition to improve the computational efficiency, and the exit static pressure will be updated automatically until it was matched with the imposed mass-flow at convergence. The flowfield and performance of a centrifugal compressor was predicted and analysed, which was composed of a Krain's impeller and two types of vaneless diffuser specially: One was constant area vaneless diffuser and the other was the straight-wall. The results show that the efficiency of the straight-wall vaneless diffuser is obviously lower than that of the constant area, and a separate flow occurs nearby the exit of the centrifugal impeller with the straight-wall diffuser. However, the type of vaneless diffuser has little influence on the aerodynamics performance of the centrifugal impeller. Finally, it is suggested that the constant-area vaneless diffuser should be selected as the downstream extended area of the centrifugal impeller during the prediction for the centrifugal impeller.