Combined high-speed and high-lift wing aerodynamic optimization using a coupled VLM-2.5D RANS approach

The paper presents a numerical framework for the aerodynamic analysis of aircraft wings in transonic cruise and take-off/landing compatible with preliminary and conceptual design phase requirements based on the Non-Linear Vortex Lattice Method (NL-VLM). The purpose of this work is to demonstrate the applicability of the VLM-2.5D RANS approach for aircraft design optimization. The algorithm captures wing sweep effects, important in the transonic regime and near CLmax conditions, by a stripwise viscous-inviscid coupling strategy with an infinite-swept wing (2.5D) Reynolds-Averaged Navier-Stokes (RANS) solver. Aerodynamic forces are evaluated through spanwise integration of the 2.5D RANS solutions and a trefftz-plane analysis of the VLM solver. The framework allows calculations of single and multi-element configurations without modifying the VLM mesh. A novel CLmax criteria is proposed based on recently observed stall-cells patterns that captures CLmax, αmax and the spanwise location of the stall, which represent important design parameters. The applicability of the framework to aircraft design is demonstrated by embedding the analysis tools into a gradient-free Covariance Matrix Adaptation Evolution Strategy. After a verification phase, validation is performed on high-speed, high-lift and combined high-speed/high-lift optimizations cases. In particular, the capability of the numerical algorithms towards multi-topology optimization is demonstrated.