Direct numerical simulation of the flow around an airfoil with unsteady wake

Direct numerical simulations of a NACA-0012 airfoil at zero degrees incidence are presented for a range of Mach and Reynolds numbers. At Reynolds number 10,000, the flow around the airfoil is found to be dominated by vortex shedding from an unstable wake. Frequencies are found to collapse using a Strouhal number based on trailing edge displacement thickness, while amplitude increases with Mach number. At Reynolds number 50,000, vortex shedding from an unstable wake is again present. At certain Mach numbers an additional low-frequency large-amplitude mode of oscillation is observed. Behaviour of the upper and lower boundary layers, as well as the local fluid properties, is described over the course of the low frequency cycle. The onset of the low frequency oscillation is mapped in terms of Reynolds and Mach numbers