Convergence characteristics of a vortex-lattice method for nonlinear configuration aerodynamics

The convergence characteristics of a vortex-lattice method for the high-angle-of-attack, nonlinear aerodynamics of aircraft and missile configurations are studied parametrically. The solution for the vortex intensities is determined by the tangency boundary condition on all of the configuration surfaces, including the three-dimensional, rolled-up wakes that characterize such flowfields. The a priori unknown position of the wake that renders this problem nonlinear is determined by an iterative process. Since there is no proof for the existence and uniqueness of this process, this paper investigates the effects of several geometrical and numerical parameters on the converged solution. It was found that the convergence of the iterative solution procedure is usually rapid and is not affected by initial conditions of the first iteration and by the integration method of the wake streamlines. Grid refinement leads to a converged solution, but its final values vary with wing surface paneling and wake discretization schemes within some range in the vicinity of the experimental data.