OPTIMIZATION OF AN ASYMMETRICAL VANED DIFFUSER TO IMPROVE PERFORMANCE AND DURABILITY OF A RADIAL COMPRESSOR

Abstract The diffuser design of a radial compressor greatly impacts its performance and durability. In the case of a vaned diffuser, one possibility of improving compressor efficiency lies in the reduction of the vaneless space between impeller and diffuser. However, such reduction comes at the cost of increased High Cycle Fatigue (HCF) risk, as synchronous excitation of the impeller, mainly caused by the potential field of the diffuser vanes, increases. This study investigates the potential of increasing efficiency by reducing the gap between impeller and diffuser, while simultaneously reducing vane order excitation with circumferentially non-uniform vane spacing. Initially, a symmetrical design is created using a multi-objective, surrogate model based optimization, targeting efficiency and pressure recovery, which serves as a reference. The same optimization procedure is repeated for a design where the gap between impeller and diffuser is halved. To mitigate the increased HCF risk, another optimization is carried out, altering vane placement asymmetrically by applying a simplified model to reduce the HCF risk, while also targeting high efficiency. Compared to the reference design, the efficiency of the compressor increases from from 85.7 % to 86.8 %. A forced response analysis is carried out, revealing the HCF risk of the most critical Resonance Crossing (RC) to increase by a factor of 2.65 through the reduction of the vaneless space and being reduced by a factor of 1.55 with the introduction of the asymmetrical design.