A New Approach to Prediction of Aircraft Spin

Abstract

Abstract : Unsteady Reynolds-averaged Navier-Stokes and Detached-Eddy Simulation are used to predict the flow around a forebody cross-section modeled by a rounded-corner square. The inlet velocity is inclined at 10 degrees to the main flow, the configuration modeling the massively separated flow around the forebody of a jet fighter rotating at high angle of attack. Simulations are performed at sub- and super-critical Reynolds numbers, corresponding to either laminar or turbulent boundary layer separation from the forebody. DES predictions show that following flow detachment, a chaotic and three-dimensional wake rapidly develops. The temporal evolution of the streamwise and lateral (side) forces acting on the body exhibit strong modulation due to the spanwise variation of the flow. Grid refinement deepens the structure of the resolved range of turbulent scales, predictions using unstructured meshes are also demonstrated to be equally accurate as those on structured grids. For the super-critical flow, the pressure distribution is close to the measured values, both the streamwise and side forces are in adequate agreement with measurements, and the effect of numerical parameters are well-understood. For the sub-critical flow, DES side-force predictions do not follow the experimental measurements far enough to achieve reversal. Possible causes for the discrepancy are discussed.