Studies of Transonic Aircraft Flows and Prediction of Initial Buffet Using Large-Eddy Simulation

This paper utilizes the large-eddy simulation (LES) paradigm with a physics-based turbulence modeling approach, including a dynamic subgrid-scale model and an equilibrium wall model, to examine the flow over the NASA transonic Common Research Model (CRM), a flow configuration that has been the focus of several AIAA Drag Prediction Workshops (DPWs). The current work explores sensitivities to laminar-to-turbulent transition, wind tunnel mounting system, grid resolution, and grid topology and makes suggestions for current best practices in the context of LESs of transonic aircraft flows. It is found that promoting the flow transition to turbulence via an array of cylindrical trip dots, including the sting mounting system, and leveraging stranded boundary-layer grids all tend to improve the quality of the LES solutions. Non-monotonic grid convergence in the LES calculations is observed to be strongly sensitive to grid topology, with stranded meshes rectifying this issue relative to their hexagonal close-packed counterparts. The details of the boundary-layer profiles, both at the leading edge of the wing and within the shock-induced separation bubble, are studied, with thicknesses and integral measures reported, providing details about the boundary-layer characteristics to turbulence modelers not typically available from complex aircraft flows. Finally, an assessment of the initial buffet prediction capabilities of LES is made in the context of a simpler NACA 0012 flow, with computational predictions showing reasonable agreement with available experimental data for the angle of attack at initial buffet onset and shock oscillation frequency associated with sustained buffet.