A numerical investigation of the effect of vaned diffuser water cooling on the internal flow field of a centrifugal compressor

Due to their high pressure rises, the gas temperature of high-speed centrifugal compressors can be very high to the detriment of compressor aerodynamic performance. A water-cooled vaned diffuser technique is proposed to alleviate this problem. Compressor housing integrated water-cooling passages are employed to introduce cooling water to the vanes through holes near the vane centre. The technique was applied to a 180 mm turbocharger compressor running at the tip speed of 452 m/s, and numerical studies with conjugate heat transfer and fluid-structure thermal interaction were carried out to find the effects of the cooling to compressor performance and the mechanical stress of diffuser vanes. The results show that compressor efficiency is improved by the cooling, and the improvement increases as compressor mass flow reduces. At modest pressure ratios around 3.3, the maximum improvement of 1.09 percentage points is achieved using 30°C inlet water temperature. The cooling is found to significantly reduce the air temperature near diffuser passage solid walls, thus lead to more uniform air temperatures at compressor exit. The reduction of 1.33°C and 2.21°C in the diffuser outlet temperature have been found at 1.68 kg/s air mass flow with 70°C and 30°C water inlet temperature respectively. Moreover, the thermal stress in diffuser vanes is shown to be lower with the cooling.