Inlet Duct Treatment for Stability Improvement on a High Pressure Ratio Centrifugal Compressor

The operating range of a centrifugal compressor, determined by surge and choke flow rate, is a key issue for turbocharging since a vehicle internal combustion engine (ICE) is usually operated across a wide range. In this paper a new flow control method is developed and validated numerically, in which an array of circumferentially distributed holes is designed in the inner wall of the inlet duct of a high pressure ratio centrifugal compressor of a turbocharger. Firstly the numerical method is validated by experimental results of the original turbocharging centrifugal compressor with a pressure ratio of 4. Next the validated method is used to investigate the new flow control method and its effect on the compressor’s performance. Results show that the method can enhance the compressor stability and widen the operating range effectively at all investigated speeds. At meantime, the choke flow reduces slightly. The flow details in the compressor are further analysed according to the CFD results. It is found that the flow near the blade tip at inlet is pre-swirled by the method as the conventional IGV does while the flow in the middle span or near the hub remains in an axial direction. As a result, the stability of the compressor is enhanced by the pre-swirl effect at the tip while minimally sacrificing the choke flow rate, thus the map is extended effectively by the flow control method.