Automated design of a three-dimensional subsonic diffuser

A novel methodology is developed to integrate state-of-the-art computationa l fluid dynamics analysis, NURBS, and optimization theory to reduce total p ressure distortion and sustain total pressure recovery within a curved thre e-dimensional subsonic S-duct diffuser by automated redesign of the diffuse r shape. Two independent design variables are used. The change of the surfa ce shape is assumed to be Gaussian. GASP with the modified Baldwin-Lomax tu rbulence model (Baldwin, B. S., and Lomax, ii., "Thin Layer Approximation a nd Algebraic Model for Separated Turbulent Flows," AIAA Paper 78-257, 1978) is employed for the flowfield prediction and proved to give good agreement with the experimental surface pressure for the baseline S-duct diffuser ge ometry. The automated design optimization is performed with a gradient-base d method to minimize the total pressure distortion based on the two design variables. The best configuration obtained reduced distortion by typically 70% while keeping the total recovery essentially the same. The results indi cate that the mechanism responsible for improved diffuser performance is th e suppression of detrimental secondary Rows by changing the surface shape t o redirect the flow.