High-fidelity Multipoint Hydrostructural Optimization of a 3-D Hydrofoil
N. Garg, G. K. W. Kenway, J. R. R. A. Martins, and Y. L. Young
Journal of Fluids and Structures, 7115–39, 2017
The design optimization of flexible hydrofoils and propellers requires coupled hydrodynamic and structural analysis to achieve truly optimal, physically realizable, and structurally sound designs. To address this need, we develop an efficient high-fidelity hydrostructural design optimization approach that can handle large numbers of design variables, multiple design points, as well as design constraints on cavitation, maximum von Mises stress, and manufacturing tolerances. The hydrostructural solver couples a 3-D nearly incompressible Reynolds-averaged Navier–Stokes solver with a 3-D structural finite-element solver. We validate the solver by comparing the hydrodynamic load coefficients and tip bending deformations of a cantilevered aluminum alloy hydrofoil with a NACA 0009 cross section and a trapezoidal planform. We use a coupled adjoint approach for efficient computation of the performance and constraint function derivatives with respect to 210 shape design variables. A single-point hydrostructural optimization of the NACA 0009 baseline hydrofoil yields a 12.4% increase in lift-to-drag ratio, a 2.5% reduction in mass, and a 45% increase in the cavitation inception speed. However, the performance of the single-point optimized hydrofoil is found to be worse than the baseline at off-design conditions. On the other hand, a multipoint optimization yields improved performance over the entire range of expected operating conditions with a weighted average increase in lift-to-drag ratio of 8.5%, and an increased cavitation inception speed of 38%. We compare the hydrostructural optimal result to an equivalent hydrodynamic-only optimization, and we show that only the hydrostructural optimized design satisfies the stress constraint up to the highest expected loading condition, highlighting the need for coupled hydrostructural optimization. The proposed approach enables multipoint optimization of hydrodynamic performance for hydrofoils and marine propulsors with respect to detailed shape while enforcing design constraints. This constitutes a powerful new tool for improving existing designs, and exploring new concepts.