Bifurcations and chaos transition of the flow over an airfoil at low Reynolds number varying the angle of attack

The study of an airfoil at low Reynolds number regime was found to be a typical problem where the inception of bifurcations leads the flow evolution from a stationary or periodic behaviour to a purely chaotic one. The present work extends the present literature where numerical investigations of the flow field past two-dimensional symmetric airfoils were performed by fixing the incidence and changing the Reynolds number (Re). Conversely, here the Reynolds number was fixed at Re = 10 0 0 and the angle of attack (AoA) varied from 0 o to 90 o . Different flow Modes and bifurcation phenomena are detected and, in ad- dition, new non-linear phenomena are also identified. The latter consists of tripling period regimes and its bifurcations up to chaotic conditions. Moreover, for increasing AoA, an in- verse transition from chaotic to periodic regimes is also observed. An in-depth study of these different flows is provided and new links with the time evolution of the forces act- ing on the airfoil, as well as with the wake structures observed, are offered. Phase portrait diagrams are evaluated through the time records of the lift force in order to highlight the eventual presence of limit cycles in the solutions. Accurate numerical simulations are per- formed with a Vortex Particle Method in a two-dimensional framework, using high spatial resolutions to solve in detail both the near-field and the far-field regions.