Application of unstructured adaptive moving body methodology to the simulation of fuel tank separation from an F-16 fighter

Abstract

This paper describes recent algorithm development, modifications, validation, and application of the FEFL097 Arbitrary Lagrangian-Eulerian (ALE) methodology on unstructured grids, to the simulation of fuel tank release from an F-16 C/D fighter. This improvement/validation effort is part of an ongoing research effort to develop a cost-efficient and accurate numerical methodology capable of simulating the motion of complex-geometry, three-dimensional bodies embedded in external, temporally and spatially evolving flow fields. The emphasis of the effort presented in this paper is to evaluate the accuracy, efficiency, and fidelity of the current Eulerian methodology to predict the transient separation of a fuel-tank from a fighter aircraft, evaluated against data obtained in both wind-tunnel and flight tests. To that end, the Eulerian methodology was first used to model the flow about a fully-loaded F-16 C/D fighter at a transonic speed, M=0.85, at several angles of attack. These simulations identified and quantified several shocks on the wing, fuel-tank, and the Mk-82 stores, in agreement with the available experimental data. The ability of the Eulerian methodology to accurately predict time-dependent, compressible, complexgeometry moving body processes was evaluated via a transient simulation of the 370 gallon fuel tank (including the pylon) separation from the F-16 C/D * Senior Research Scientist, Associate Fellow AIAA. *Research Scientist, Member AIAA. **Research Professor, Member AIAA. Copyright ©1997 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. fighter at M=0.851, straight and level flight, and an angle-of-attack of two degrees. Analysis of the results evaluated the role of the inertial forces in determining the tank trajectory. The transient simulation incorporated all the kinematic forces and boundary conditions acting on and between the separating fuel tank and the plane. Comparison of the numerical results with both wind tunnel and flight data indicates that the predicted results for inertia-dominated processes were in better agreement with the flight data than the captive-state wind tunnel results. The simulation was able to accurately predict the pitch forces and pitch angle temporal evolution. Less accurate predictions were obtained for the yaw forces. This resulted due to the crude geometric definition of the pylon/holder assembly for the three Mk-82 stores at the adjacent station. The flow through this assembly generated a shock whose impact on the fuel tank contributed significantly to the yaw forces and moments. Finally, viscous dominated processes such as roll were poorly predicted by the Eulerian methodology.