Wall-modeled large-eddy simulations of transonic buffet of a supercritical airfoil subjected to wind-tunnel confinement effects

Airflow over airfoils in the transonic regime is frequently accompanied by the phenomenon of transonic buffet, a highly unsteady shock-wave/boundary-layer interaction affecting a large portion of the flow field. In this study, wall-modeled large-eddy simulations (WMLES) are conducted to analyze oscillatory lambda shock motions and complex patterns of boundary layer separation over a supercritical OAT15A airfoil at a freestream Mach number of 0.72 and an angle of attack of 5°. The study replicates experiments by Schauerte & Schreyer (2023) in the Trisonic Wind Tunnel facility at the Institute of Aerodynamics, RWTH Aachen University, and aims to characterize the confinement effects of the wind tunnel test section on the buffet characteristics, as various experimental and computational studies have previously reported varying buffet conditions for identical airfoils. We investigate the ability of WMLES to replicate the buffet cycle through time signals of oscillatory shock motion and their power spectral density (PSD) spectra, further comparing with particle-image velocimetry (PIV) and focusing Schlieren measurements. The numerical methodology employs an unstructured-mesh, finite-volume, second-order shock-capturing LES flow solver, with an equilibrium wall-stress wall-model and an eddy-viscosity subgrid-scale model, with the computational domain including the boundary layers developed over the wind tunnel walls. Simulations with varying test section domains are pursued to investigate the impact of confinement effects on buffet characteristics.