Numerical Simulation and Reduced-Order Aerodynamic Modeling of a Lambda Wing Configuration

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This work is a contribution to the North Atlantic Treaty Organization Science and Technology Organization Task Group AVT-201 on stability and control estimation methods. Specifically, this study uses the Cobalt and Kestrel computational fluid dynamics flow solvers to predict and create reduced-order models for the aerodynamic force and moment coefficients of a generic uninhabited combat air vehicle under static and dynamic conditions and compare them with wind tunnel data. The particular reduced-order method investigated in this work is based on response functions. The geometry under investigation is known as DLR-F19, which is a lambda-wing configuration with a 53 deg angle of sweep at the leading edge. Each wing has two control surfaces on the trailing edge, hinged along the 75% chord line. Two different gridding strategies are employed: one uses an overset grid method for simulation of control-surface deflections without the need for regridding, and the other is to create a new grid for each control-surface deflection. The simulation results of these grids are compared in order to identify the effect of gaps present in the overset method. A grid is also created to study the presence of the sting geometry as tested in the experiments. Validation results are shown for different turbulence models at selected flight conditions. Overall, a good agreement between computational results and the wind tunnel experimental data for total force coefficients is achieved. However, delayed detached eddy simulations are required for angles of attack greater than 20 deg. The reduced-order modeling results show that predictions from a nonlinear model match quite well with full-order data of small amplitude motions. Small discrepancies can be seen in the plots of large-amplitude motions as well. The model predictions get worse when the belly sting geometry is included in simulations because of the nonlinear hysteresis behavior of a wake formed behind the sting.