Abstract: A multi-objective inverse design approach of natural laminar flow (NLF) airfoils based on the N-factor method for target pressure distribution is developed. XFOIL code is used to calculate pressure distribution and transition locations to reduce computational cost. It requires special care to design target pressure distribution, and the N-factor design method is used to perform the work with a substantial amount of NLF while maintaining aerodynamic constraints. The pressures in the recovery region are designed according to the Stratford separation criteria. Optimization method based on response surface methodology is used to calculate the target airfoil. Quadratic polynomials are employed to construct the response surface model and the set of candidate design points in design space is selected to satisfy D-optimality. The reduced response surface model without the second-order cross items can greatly reduce computation cost. The design results show that the amount of the NLF satisfies the target requirements, and that the design approach used in the study is applicable to a wide rang of airfoils.

Key words: natural laminar flow, airfoil, multi-objective, response surface methodology, inverse design