Abstract:
To design helicopter rotor efficiently, an adjoint-based and RBF surrogate model coupled method is applied for aerodynamic design of hovering rotor with high aerodynamic performance in a non-inertial reference frame. The OC-O type body-fitted grids are generated around the rotor blade, and the DDM method and "Inverse map" method are utilized for the rapid identification of hole cells and hole boundary donor cells respectively. Based on the embedded grid system, the RANS equations coupled with S-A turbulence model in rotating frame are used as the governing equations, the upwind scheme of Roe with three-order MUSCL interpolation scheme is adopted for spatial discretisation, the LU-SGS implicit method and OpenMP parallel strategy are employed to accelerate the flowfield calculation. On the basis of the highly-efficient and highly-accurate CFD method, the adjoint-based design method is firstly derived to design the rotor airfoil with superior comprehensive performance according to multi-objective and multi-constrained design characteristics for hovering rotor airfoil. The RBF surrogate mode method is then employed to design the twist distributions and planform of the rotor with the aim of highest Figure of Merit for hovering rotor with optimized airfoil. After validating the accuracy of CFD tools by OA209 rotor airfoil and UH-60A hovering rotor, a baseline rectangular rotor with SC1095 airfoil is selected to comprehensively optimize the airfoil, the twist distribution and the planform of the rotor. Through comprehensive optimization, the aerodynamic characteristics of the final optimized rotor is superior and its highest FM value has nearly 14.7% increase when compared with the baseline rotor, which demonstrates the effectiveness and high-efficiency of the adjoint-based and RBF coupled method for the design of a hovering rotor with high performance.