Adjoint based aero-structural design optimisation of a transonic fan blade

A novel optimisation process has been proposed in this paper to maximize the aerodynamic efficiency of a modern fan blade while satisfying the structural constraint imposed by the material limits. The method developed is based on the discrete adjoint for the aerodynamic efficiency sensitivity evaluation with the structural constraint provided by a response surface method for the structural stress. To facilitate a large number of sampling points required in the response surface generation, a fast, meshless method was used for the stress calculations. The method was applied to the optimisation of a practical fan blade, representative of modern, high-bypass-ratio turbofan jet engines. It is demonstrated that the fan blade efficiency can be improved by 0.6% while maintaining the stress below a prescribed value of 500 MPa assuming a titanium alloy material. It is shown that without the stress constraint, the efficiency benefit is larger, namely 0.9% but the maximum stress value increases considerably beyond the material’s acceptable criterion, to almost 1000 MPa. The method is built in a modular way and can be adapted to accommodate a range of different turbomachinery blade designs. Flutter analysis for the optimised fan blade has also been carried out due to its practical importance.