Performance improvement of a centrifugal compressor stage using a wedge diffuser with leading-edge sweep and pre-compression

The geometry of the vane's leading-edge (LE) of a wedge diffuser determines the aerodynamic matching between the impeller and diffuser of a centrifugal compressor stage and is crucial for the performance and stable operation range (SOR) of the stage. This study presents an improved design of the vane's LE of the centrifugal compressor-III stage using the combined sweep and pre-compression configurations and performs a detailed numerical investigation to identify the effects of the geometrical modifications on the characteristics of flow in the vaneless and semi-vaneless regions and the interior of the vane passage. The influences of the surface roughness and the turbulence model on the simulation quality were first explored. The simulation results reveal that the local high-velocity flow at the vane's LE extends from the semi-vaneless region to the throat under near-choke conditions and reduces the effective through-flow area, which deteriorates the diffuser's performance. The LE modification could partially suppress the shock loss and regulate the flow at the inlet and interior of the vane passage. The adiabatic efficiency and total pressure ratio improve by 0.69% and 1.03% under the design flow rate, respectively, and the choke margin and overall SOR increase by 6.35% and 12.35%, respectively, at the design rotational speed for the M-II model. The analysis of the flow characteristics in the vane passage reveals that the swept vane reduces the separation on the vane surfaces and the energy loss, which mainly contributes to the improved stage performance. The pre-compression section generates a more uniform flow in the spanwise direction at the diffuser's inlet and improves the choke margin. The findings of this study are of reference significance for the design of high-performance diffusers.