Numerical investigation of advanced design concepts for high-pressure ratio centrifugal compressors in turbocharging applications

This work focuses on the design, performance and operability improvement of centrifugal compressors for single stage turbochargers with pressure ratios beyond today´s traditional levels. The following areas have been addressed: -1D matching/sizing a compressor and a turbine for a turbocharger application -Compressor design with high flow coefficient and high pressure ratio -Main and splitter blade leading edge sweep -Transonic inducer design and double splitter design -Tandem inducer design -Operating range Leading edge sweep for high flow coefficient compressors showed, that the impeller stall was driven by an interaction between the leading edge tip vortex and the splitter leading edge. Applying forward sweep to the main blade of the compressor, or applying aft sweep to the splitter leading edge helped to delay this interaction and increased the operating range of the compressor. The usage of forward sweep on the main blade led to a performance increase of the compressor due to a reduction of shock losses. A transonic inducer design was carried out to improve the compressor performance and operability. This work revealed that lessons learnt from axial compressors design are applicable to centrifugal compressors and that by applying negative camber and little or no turning along a portion of the inducer it is possible to reduce the relative Mach number at the tip of the main blade and reduce the shock losses through the passage. Considering advanced double splitter designs showed that an increase of flow capacity and compressor efficiency can be achieved by reducing the number of main blades, and by adding a short and a long splitter staggered in a way that the splitters are aligned with the shock at the tip of the impeller (Longer splitter along the suction side of main blade, and short splitter along the pressure side). The analyses conducted on tandem inducer designs have shown the significance of clocking axial position and overlap, and demonstrated that the best configuration is the one where the inducer blade is aligned with the main blade since it will generate the least amount of losses. The investigations also showed that the leakage flow towards the shroud between the main blade and the inducer blade can improve the performance of the compressor by reducing the losses on the diffuser. Finally, the present work also described the impact of swirl on ported shroud configurations.