Effect of housing size on the performance of a centrifugal compressor for turbocharger application: An experimental and numerical study

Currently, engine downsizing through turbocharging is widespread in the automotive industry to improve fuel economy and emissions. The engine downsizing demands compact and high performance centrifugal compressors for turbochargers. A compressor contains mainly an impeller and housing, which often uses a vaneless diffuser and an overhanging volute. High-speed flow from the impeller is decelerated in the diffuser and volute, to recover static pressure for boosting the engine. The volute flow characteristics and pressure recovery depend on the housing size, which determines the overall compressor performance and size. This study evaluates the effect of four different housing sizes viz., baseline, 12% scaled up, and 12% and 20% scaled-down geometrically, through experimental and numerical analysis. The experiments are conducted using different housing sizes with a given impeller to measure the compressor pressure ratio and efficiency. Also, steady-state numerical simulations are performed to examine the flow mechanisms causing pressure losses due to changes in housing size. Then, the simulation is also done for different volute surface roughness levels in each housing to establish its effect on compressor performance. From the results, it is found that there is no marked change in compressor efficiency between the baseline and 12% scaled-up housing. Whereas, the scaled-down housings (12% and 20%) showed efficiency drop of about 2-5 percentage points at near-choke flow rate. The CFD analyses of these scaled down housings with reduced cross-sectional area indicated substantial increase of meridional velocity, which results in higher swirl velocity in the volute causing more pressure losses. Besides, the increased volute surface roughness is realized to cause extra pressure loss due to higher wall shear stress. It amounts to additional efficiency reduction of 0.5-1 percentage points at the same near-choke flow.