Investigation on flow mechanism of an advanced transonic centrifugal compressor with free-form impeller at design and off-design speeds

A transonic centrifugal compressor with a ruled-impeller (that is, impeller blades are generated by a set of points swept by a moving straight line) was used as the baseline, and the impeller blades were redesigned using non-ruled surfaces (referred to as the 'free-form impeller') in this study to reveal the potential of this design approach to improve the performance of high-pressure-ratio centrifugal compressors. By using the method of Computational Fluid Dynamics (CFD) simulation, the performance characteristic and the flow field inside the impeller and diffuser of the baseline compressor and the free-form one were comparatively analyzed in detail. The results show that the free-form impeller design can improve the performance of the compressor in many aspects no matter at design or off-design speeds. The barreled-sweep inducer can reduce the losses from the shock wave at design speed and extend the compressor stable operating range at off-design speeds. The positive compound-lean impeller blades can suppress the reverse flow at impeller outlet. The flow downstream of the free-form impeller was also improved due to a more uniform outlet flow field provided by it at. This study aims to provide a valuable reference for applying free-form design methods to future advanced centrifugal compressors.