A multi-objective design optimization is performed on a U-bend in serpentine internal cooling channels. The aim is to achieve both minimized total pressure loss and maximized heat transfer ability. The optimization technique used is a two-level routine developed at the Von Karman Institute for Fluid Dynamics (VKI), featuring a Differential Evolution algorithm assisted by a metamodel, which is continuously updated during the course of the optimization process to increase its accuracy The geometries are carefully parameterized by means of Bezier curves. In total, 26 geometrical parameters are used as design variables, allowing an extensive variation of the U-bend geometries. The fluid dynamic and heat transfer performances of the selected geometries are predicted by a Reynolds-averaged Navier-Stokes solver in OpenFOAM. The result shows that dozens of optimized geometries of enhanced performances in both design objectives can be obtained after a few numbers of iterations. The enhancement ranges from roughly 12∼30% decrease in total pressure loss and a 8∼17% increase in heat flow rate. A clear trade-off between pressure loss and heat transfer is observed, allowing designers to select a compromising geometry between both criteria after the optimization process, depending on the application type of the internal cooling channel. Generally, a stronger secondary flow motion in the channel will be responsible for higher heat transfer at the cost of increased losses. A discussion is held on the geometrical features that have an impact on the secondary flow motion strength and lead to general applicable conclusions.

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