Numerical simulations and global stability analyses of transonic buffet and subsonic stall

This paper studies the three-dimensional cellular patterns appearing on wings in subsonic stall and tran-sonic buffet conditions. URANS simulations are carried out for three-dimensional infinite swept configurations closed by periodic boundary conditions in the span-wise direction. In both flow conditions the occurrence of stall/buffet cells is observed, as well as their convection at a speed proportional to the sweep angle. In transonic buffet conditions, this phenomenon is superimposed to the well-documented two-dimensional buffet instability. These results indicate that the discrepancies between two-dimensional and three-dimensional buffet are caused by the occurrence of buffet cells and that this phenomenon is similar to the one observed at low speed. These numerical simulations are complemented by global linear stability analyses, showing unstable modes reminiscent of stall/buffet cells.