Linear modal instabilities around post-stall swept finite wings at low Reynolds numbers

Linear modal instabilities of flow over finite-span untapered wings have been investigated numerically at Reynolds number 400, a range angles attack and sweep on two having aspect ratios 4 8. Base flows generated by direct numerical simulation, marching the unsteady incompressible three-dimensional Navier-Stokes equations to steady state, or using selective frequency damping obtain stationary linearly unstable flows. Unstable linear global modes swept identified for first time spectral-element time-stepping solvers. The effect wing geometry parameters these has examined in detail. An increase angle was found destabilize flow, while an had opposite effect. On unswept wings, TriGlobal analysis revealed that most mode peaks midspan region wake; peak structure moves towards tip as is increased. Data-driven then employed study effects conditions nonlinear wake. dominant low Kelvin-Helmholtz-like instability, qualitatively analogous with infinite-span under same conditions. At higher moderate angles, denominated interaction mode. high this evolves into elongated streamwise vortices ratio shorter it becomes indistinguishable from tip-vortex instability.