Unsteady Aerodynamic Shape Optimization of a Vertical Axis Wind Turbine Under the Framework of DAFoam

Floating vertical axis wind turbine has become a hot topic in recent years for the potential enormous in offshore wind power generation. Aerodynamic shape optimization of blades is a relatively effective solution for increasing the efficiency of wind energy utilization of vertical axis wind turbines. In the present paper, a triple-blade H-type VAWT with a NACA0021 airfoil section is selected as the initial research object. An adjoint-based tool called DAFoam is applied for aerodynamic shape optimization of VAWT. This approach is coupled with unsteady RANS equation and discrete adjoint method. The overset mesh technology solves the unsteady rotational motion of the wind turbine blades. 2D airfoil parameterization can be achieved through the FFD method, whilst an update mesh is created by the mesh deformation approach. At the rated tip speed ratio (λ = 2.5) of VAWT, the time average wind energy utilization coefficient of the blades within a rotating cycle is set as a criterion for evaluating the aerodynamic performance of VAWT. The optimization results show that the wind energy utilization coefficient of the optimized VAWT blade increases more than 7.6% (from original 0.223 to final 0.24). In comparison to its original configuration, the airfoil's leading-edge region is evidently thicker after several optimization iterations. This article innovatively integrates the adjoint optimization method in aircraft aerodynamic design into VAWT blade efficiency improvement. On the one hand, it avoids repeated flow field calculation caused by multiple design variables. On the other hand, high-precision unsteady numerical calculations ensure optimization effectiveness.