Computational investigation of impeller-diffuser interaction in a centrifugal compressor with different types of diffusers

A computational study has been conducted to analyse the performance of a centrifugal compressor with different types of diffusers under various levels of impeller-diffuser interactions. Vaneless (VLD), vaned (VD), low solidity vaned (LSVD), and partial vaned diffusers (PVD) are used for this purpose. The study is carried out using commercial software ANSYS CFX. The interaction level is varied by varying the radial gap between the impeller and diffuser by keeping the diffuser vane at three different radial locations. Numerical simulations have been conducted for four different flow coefficients. At design flow coefficient maximum efficiency occurs when the leading edge is at R(3) (ratio of radius of the diffuser leading edge to the impeller tip radius) = 1.10 for all vane-type diffuser configurations. At below design flow coefficient higher stage efficiency occurs when the diffuser vanes are kept far away (R(3) = 1.15) and at above design flow coefficient R(3) = 1.05 gives better efficiency. The highest diffuser pressure recovery coefficient (C(p)) is observed :For VD at design flow coefficient. For VLD, the C(p) value increases with flow coefficient. In the case of VD and LSVD configurations the exit flow from the impeller is disturbed when the diffuser vanes are closer, and these disturbances are more evident in the last 10 per cent of the impeller flow. In the case of the impeller with PVD the interaction effects are minimum.