Numerical experiments on transonic buffet

With the aim of investigate the effects of acoustic waves on the transonic buffet phenomenon, unsteady Reynolds-averaged Navier-Stokes simulations (URANS) have been carried out for the flow over a supercritical airfoil by means of an energy-consistent finite-volume solver, at chord Reynolds number Re = 3000000, free-stream Mach number M = 0.7, and angle of incidence of 7 deg. In our previous work [3AF International Conference on Applied Aerodynamics, (2016)] we have shown that URANS contains the essential physical ingredients to make up for transonic buffet. The propagation velocities of coherent disturbances are estimated by cross-correlating the pressure signal at different points, to quantify the actual occurrence of alleged influence of acoustic waves on turbulence and vice-versa. To ascertain whether (as subtended by standard models) buffet involves an acoustic feedback loop, we perform numerical experiments by artificially imposing numerical barriers to upstream propagating acoustic waves, either on the suction or on the pressure side of the airfoil. The results of the numerical experiments are compared with URANS results in the absence of acoustic barriers, in terms of mean and root-mean-square wall-pressure.