Parallel DNS for Flow Separation and Transition around Airfoil

Abstract

Direct numerical simulation (DNS) for the flow separation and transition around a NACA 0012 airfoil with an attack angle of 4o and Reynolds number of 100,000 is conducted and analyzed in this chapter. The details of the flow separation, formation of the detached shear layer, Kelvin- Helmoholtz instability (inviscid shear layer instability) and vortex shedding, interaction of non-linear waves, breakdown, and re-attachment are obtained and analyzed. Though no external disturbances are introduced, the self-excited mechanism is observed which may reveal the origin of the disturbance for airfoil with attack angles. The power spectral density of pressure shows the low frequency of vortex shedding caused by the Kelvin-Helmoholt instability dominates the process from the leading edge to trailing edge. The simulation shows that the nonlinear wave interaction and breakdown is driven by the generation and growth of the stream-wise vortex which leads to deformation, stretching, and the eventual breakdown of the shed prime vortex.