Design optimization of a three-dimensional diffusing S-duct using a modified SST turbulent model

This paper examines design optimization of a three-dimensional diffusing S-duct using a modified k-ω shear stress transport (SST) turbulent model as a turbulence prediction method. According to based-Reynolds-stress and based-separation ideas, a robust solution procedure for the model is described and a grid convergence study is presented. An automated system employs this model to design an S-duct. The aerodynamic performances of the optimal duct are investigated in on-design and off-design conditions. It is shown that the sensitivity of the modified model with respect to shape variations allows its use in the design system. Using a multi-objective optimization strategy, this design system significantly improves aerodynamic performance of the S-duct and has low computation cost and excellent design efficiency. The centerline's curvature and the cross-sectional area ratio become reasonable to avoid overexpansion of the optimal duct. Compared with the original design, the flow distortion coefficient of the optimal duct is reduced by 16.3% and the total pressure recovery factor is increased by 1.1% in on-design condition.