New Optimisation Methods for Scale-Resolving Turbulent Flow Simulation

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In fluid mechanics, shape design problems have been traditionally tackled with steady Reynolds-Averaged-Navier-Stokes (RANS) equations for flow analysis and using adjoint sensitivity methods to obtain the gradient of flow quantities, such as the drag of an lifting body, with respect to design parameters. Current adjoint methods, however, are ineffective when coupled to unsteady, scale-resolving turbulent flow simulations. This is fundamentally due to the chaotic nature of turbulence and its high sensitivity to perturbations. In practice, the adjoint equation produces exponentially growing solutions, leading to unphysical gradients that do not reflect the true influence of design changes. With current trends in engineering design, where unsteady turbulent flow simulation will gradually replace RANS for flow analysis and design, better adjoint methods for design and optimisation are needed.