Appropriate Lift Slope Model for Nonlinear Vortex Lattice Method

This work examines the formulation of the lift slope term used to compute the distribution of the effective angle-of-attack coupling variable within the nonlinear vortex lattice method (NL-VLM). This variable plays a significant role in the accuracy of the solution for transonic flow over swept wings. A new formulation is proposed, aiming to improve accuracy for such cases without any additional computational cost. First, a literature survey highlights significant differences among reported terms used. Second, the new proposed formulation is derived from an analysis of the VLM model on a swept geometry considering compressibility corrections. Finally, tests on an infinite swept wing and a finite swept wing relevant to commercial aircraft application demonstrate an increased accuracy. The results confirmed the superiority of the proposed method over previous models used in the literature.