In this paper, an optimization design approach to recirculation flow type casing treatment for centrifugal compressors of turbochargers has been performed. The optimization code is a global exploring system based on a metamodel assisted evolutionary algorithm. In this study, the objective functions of the optimization are adiabatic efficiency at design flow rate and near surge flow rate condition. Several optimized shapes on a “Pareto front” are selected in order to discuss the effect of casing treatment at the point of view of suppression of flow separation and a reduction of leading edge flow separation. The influence of optimized recirculation flow rate on the optimization output is also discussed. Increase in adiabatic efficiency of optimized casing treatment at near surge flow rate is discussed by the streamwise relative velocity distribution, reversed flow zone, static entropy distribution and flow incidence at impeller inlet. Detailed sensitivity of design variables on the adiabatic efficiency at design and off-design conditions was carried out.

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