Two- and three-dimensional wake transitions of a NACA0012 airfoil

Flow transitions are an important fluid-dynamic phenomena for many reasons, including the direct effect on aerodynamic forces acting body. In present study, two-dimensional (2-D) and three-dimensional (3-D) wake of a NACA0012 airfoil studied angles attack in range $0^\circ \leq \alpha 20^\circ$ Reynolds numbers $500 {\textit {Re}} 5000$ . The study uses water-channel experiments 2-D 3-D numerical simulations based nodal spectral-element method, level-set function-based immersed-interface method Floquet stability analysis. different states categorised time-instantaneous structure, non-dimensional frequency force coefficients. transition boundaries summarised regime map. critical angle number supercritical Hopf bifurcation (i.e. steady to periodic transition) varies as $\alpha _1 {\sim} {Re}}^{-0.65}$ , while onset three dimensionality _{3D} {Re}}^{-0.5}$ Over entire range, flow occurs through mode C (subharmonic) transition. Beyond this initial transition, further instabilities base arise investigated. For instance, at $ {Re}}=2000$ _{3D,2}=11.0^\circ$ coexists together with modes related A QP seen stationary circular cylinder wake. contrast, {Re}}=5000$ _{3D,2}=8.0^\circ$ dominant QP. Three-dimensional well beyond indicate that vortex-street approximately maintained fully saturated wakes spanwise-averaged sense.