Numerical and experimental investigation of a centrifugal compressor with an inducer casing bleed system

State-of-the-art centrifugal compressors for turbocharger applications are required to provide broad compressor maps, high pressure ratios and high efficiency levels. Usually these requirements are perceived as contradictory and represent challenging design targets. Various techniques for map width enhancements have been reported since the early 1980s. ABB Turbo Systems Limited has adopted a simple bleed system for internal flow recirculation to a high flowrate, high efficiency, pressure ratio 4.2 centrifugal compressor stage. After initial test runs had proved the effectiveness of the bleed system, computational fluid dynamics (CFD) calculations were performed in order to gain insight into the flow pattern in both the compressor stage and the bleed system. The simulations explain the effectiveness by comparing them with simulations without the bleed channel. Selected streamline and iso-surface plots show the effect of the bleed channel flow on the main flow through the impeller. Four more variants of bleed channels have been modelled and investigated by CFD in order to optimize the bleed slot location and dimension. The most promising configuration, which showed a significant improvement in map width without a loss in efficiency, was subsequently built and tested. This test confirmed the validity of the CFD simulation results.