In the operation of a centrifugal compressor of turbocharger, instability phenomena such as rotating stall and surge are induced at a lower flow rate close to the maximum pressure ratio. In this study, the compressed air at the exit of centrifugal compressor was re-circulated and injected to the impeller inlet by using two injection nozzles in order to suppress the surge phenomenon. The most effective circumferential position was examined to reduce the flow rate at the surge inception. Moreover, the influences of the injection on the fluctuating property of the flow field before and after the surge inception were investigated by examining the frequency of static pressure fluctuation on the wall surface and visualizing the compressor wall surface by oil-film visualization technique.

The integration of wave energy conversion devices into an existing or new coastal caisson breakwater can reduce the power generation cost. Moreover, this integrated breakwater can improve the wave resisting stability and performance as a breakwater by absorbing the wave energy. Therefore, the caisson breakwater wave power system can be treated as one of the most effective techniques to improve the power scenario in the ocean energy rich countries. In this system, an oscillating water column (OWC) due to the wave motion drives the air column in the air chamber, and results in an alternating air-flow. An air turbine for this alternating airflow is used to convert the pneumatic energy into the mechanical energy. The McCormick counter-rotating turbine for wave energy conversion has been proposed and tested so far. Although the average efficiency of this turbine is approximately 0.3, the present study aims to investigate the possible reasons of performance deterioration by using computational fluid dynamic (CFD) analyses.