Topology Optimization and Experimental Validation of an Additively Manufactured U-Bend Channel

Serpentine channels are a common feature seen in heat ex-changer geometries. For example, they are present in midchord regions of gas turbine blades to prevent material failure at high turbine inlet temperatures. Due to their serpentine nature, these channels contain 180 deg turns or U-bends. These U-bends are responsible for nearly 20% of the pressure drop in such channels (Verstraete et al., 2013, “Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels-Part I: Numerical Method,” ASME J. Turbomach., 135(5), p. 051015). A topology optimization (TO) method has been used in this study to optimize the shape of a baseline U-bend for minimum pressure drop, at a Reynolds number of 17,000. TO uses a variable permeability approach to design an optimum flow-path by manipulation of solid blockage distribution in the flow-path. The pressure drop across the channel was lowered by 50% when compared to a standard U-bend channel profile from literature. Postprocessing was performed to extract the flow-path and run a forward simulation in star-ccm+ after remeshing with wall refinement. A 3D printed model of the TO shape and benchmark U-bend was created using acrylonitrile butadiene styrene as the printing material, to confirm the results of the turbulent fluid TO, which is a relatively untouched topic in current TO literature. Experimental results showed deviation from computational fluid dynamics (CFD) by about 5%. Comparison of the TO optimum was carried out with an in-house parametric shape optimization using surrogate model-based Bayesian optimization (BO) and a similar shape optimization study from literature. A higher reduction in pressure drop was seen in the case of the TO geometry when compared to the benchmark and the BO cases.