Design optimization of natural-laminar-flow airfoil for complicated flight conditions

The transition location of Natural-Laminar-Flow (NLF) airfoil is sensitive to flight conditions. Therefore, researchers should consider early transition to turbulence influenced by complicated flight conditions carefully when designing NLF airfoil. The (Formula presneted) transition model is combined with the shear stress transport (SST)_{k - ω} turbulence model to predict the transition region for a laminar-turbulent boundary layer. Multi-objective Particle Swarm Optimization (PSO) algorithm and aerodynamic optimization method based on surrogate model are used to build an optimization platform. Using robust design optimization method based on probabilistic approach, the aforementioned platform has been exploited to achieve the optimal airfoil with a tradeoff of aerodynamic performances under fully-turbulent and free transition conditions. An airfoil’s aerodynamic performances under free transition and fully-turbulent conditions are balanced to make sure its good performance under both flow conditions. The result indicates the aerodynamic performance of the NLF airfoil optimized under free transition condition shows a significant deterioration under fully-turbulent condition. Meanwhile, the airfoil with a tradeoff of aerodynamic performances under fully-turbulent and free transition conditions holds robust aerodynamic performance when early transition to turbulence occurs.