Shape Optimization of a Curved Duct with Free Form Deformations

Abstract

The Free Form Deformation method was applied to an S-duct geometry to reduce total pressure losses and flow distortion. The deformation method was coupled with a multiobjective genetic algorithm to optimize the shape of a diffusing S-duct, which was numerically and experimentally investigated in previous works. During the optimization process, 200 deformed shapes were tested with steady-state CFD simulations and the performances were evaluated both in terms of total pressure losses and swirl angle at the outlet. It was obtained a Pareto front with a maximum total pressure losses reduction of 20% and a maximum swirl reduction of 10%. The two extreme points of the Pareto front were further investigated by unsteady Detached Eddy Simulations to assess also the impact of the optimization on the flow instability. Surprisingly, one of the solutions showed stable and stationary vortical structures. This is in strong contrast with the previous investigations of the flow field time history of the baseline configuration, which outlined strong oscillations of the flow field combined with a high increase of the distortion parameters in comparison with the time-averaged flow field.

Computational Design Optimization for S-Ducts

“…In recent works [6,7] free-form deformation method coupled with multi-objective genetic algorithm was employed to improve aerodynamic characteristics in a diffusing S-Duct. The aim of this work was the reduction of flow distortion and pressure losses through optimization of the intake shape by means of CFD.…”

“…The lattice nodes are named control points since their movement in space lead to deformations in the duct shape. Both in [6,7] employed the same parameterization with a total of 80 control points and 240 degrees of freedom.…”

“…There are several different types of optimization algorithm. In [6] the Non-dominated Sorted Genetic Algorithm [12] was employed. The Pareto front obtained after 360 evaluations shows a maximum total pressure losses reduction of 20% and a maximum swirl reduction of 10% (Table 1).…”

“…In previous works [6] the parameterization of the same baseline geometry was performed with a 3D parallelepipedic lattice. This solution allows recreation of a precise baseline geometry.…”

“…This means that every cross-section have 12 do f . In previous work [6], 36 do f were imposed. Therefore, to maintain the same number, three cross-sections between the two fixed section at the inlet and outlet were imposed in our parameterization (l = 7).…”