Unsteady Flow Simulation of High-Lift stall Hysteresis using a Lattice Boltzmann Approach

A Lattice-Boltzmann flow solver is used for the prediction of the unsteady flow field around the Trap Wing high–lift configuration used in the first High–Lift Prediction Workshop. The numerical approach and the meshing technique are briefly described. The simulation model includes the effects of wind tunnel walls, the geometries of the slat/flap brackets and the laminar to turbulent transitional regions. Simulation results are compared to the uncorrected force and moment wind tunnel measurements as well as the pressure distributions at various spanwise sections. The numerical approach is further developed to include a time varying angle of attack resembling the continuous measurements of increasing/decreasing incidence in the wind tunnel. This approach aims at investigating the hysteresis effects which were documented during measurements. The simulation predictions are compared to available measurements and the flow phenomena during the hysteresis effects are analyzed based on the simulated unsteady flow structures, particularly the stall behavior. Numerical predictions correctly capture the hysteresis effects around the stall region and are shown to be related to the interaction between the slat and main wing separations near the wing tip. The simulations furthermore indicate that a longer time period and dynamic modifications of the laminar regions during simulation may be needed to further improve quantitative predictions.