Treffer: A two-level turbulent density-based topology optimization method: A low-resistance U-bend channel flow.

• The M&T-Forchheimer model results in a lower pressure drop than the other two models. • A modified energy dissipation function adds inertial loss for porous media flows. • The resistance reduction improves from 14.6–20.6% to 17.9–36.8% after two-level optimization. The resistance of duct components in building distribution systems significantly affects the energy consumption of fans. In this study, a novel flow governing equation based on the M&T-Forchheimer model is proposed for a component's low-resistance topology optimization (TopOpt) by introducing a Forchheimer penalty term into the k − ε model. Moreover, a new and modified energy dissipation function is proposed to characterize the additional friction power loss caused by material permeability and refine the energy dissipation index. On this basis, a two-level TopOpt method is proposed to design a low-resistance structure using a U-bend as a case. The optimization results show that, compared with the M-Brinkman and M-Forchheimer models, the M&T-Forchheimer model reduces the pressure drop by 2.8% and 16.6% in the first-level TopOpt, and by 6.6% and 20.3% in the second-level TopOpt, respectively. In order to verify the validity of the optimization results, the flow resistance performance of the optimized structure is evaluated in this study by combining three dimensional high-fidelity numerical simulations with experimental tests. Within the aspect ratio of 0.25–2, the first-level optimized U-bend achieves a resistance reduction of 14.6–20.6% compared with the initial U-bend, and the second-level optimization improves it to 17.9–36.8%. The range and intensity of the high-energy dissipation region of the optimized U-bend are significantly reduced. In addition, the numerical simulation results are in good agreement with the full-scale experimental data, verifying the validity and engineering applicability of the proposed method. [ABSTRACT FROM AUTHOR]

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