Turbocharging has become a fundamental technology to realize engine downsizing, which is an attractive strategy for low carbon vehicles in the near term. The stable operation of turbocharger compressors at low and high flow rates is crucial to provide peak torque demand and rated power for turbocharged automotive engines.

The scroll or volute is a key component in centrifugal compressors as its design not only impacts the compressor efficiency but also affects the operating range. This component causes a distorted pressure field upstream which can contribute to stall on the impeller, inducing surge. As the flow inside the volute is fully three dimensional and turbulent, a better understanding of flow mechanisms is key to enable a volute design methodology.

In this study, a centrifugal compressor stage has been modelled numerically and validated by experimental results, to identify the geometric parameters of the volute which contribute to the main flow losses. By solving Reynolds average Navier-Stokes (RANS) equations using a commercial code, the threedimensional flow field of the compressor was modelled. Based on detailed analysis of this flow field, and the impact of various geometric parameters, an optimized volute was developed. The results showed that the total-to-total isentropic efficiency and surge margin could be improved by 1.5% and 4.5%, respectively at design speed.

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