Turbulence Model and Grid Resolution Effects on F-16 Nonlinear Aeroelastic Computations

Abstract

To obtain a better understanding and prediction of the limit-cycle oscillation (LCO) response characteristics of the F-16 aircraft, time-accurate, high-fidelity, unsteady Reynolds-averaged Navier–Stokes (URANS) numerical simulations coupled with a NASTRAN-generated finite-element method structural modal model were performed. Kestrel’s modal solver was used with the structural modal model to produce second-order, time-accurate, fluid–structure interaction (FSI) results. The ability of Kestrel to locate the flutter boundary and investigate the effect of the computational turbulence model and mesh on the nonlinearities that may lead to LCO is discussed herein. Independent of any nonlinear structural damping mechanism, the numerical simulations predicted a strong aerodynamic nonlinear trend between the altitude and the structural damping ratio that is trending toward LCO. This suggests that the nonlinear aerodynamic forces manifested in the fluid viscous effects are bounding or limiting the oscillation response and that the use of a high-fidelity URANS flow solver has underscored the significance and importance of accurately simulating the fluid viscous effects. Nevertheless, due to the limited improvement in the observed results obtained during the current turbulence model and aerodynamic grid resolution study, subsequent investigations of the flight-test-focused Mach number region, the modal frequency calibration, and the potential impact of the fuel state are recommended.