Experimental and Numerical Investigations of Dynamic Stall at IRPHE/ASI Laboratory

This work concerns the experimental and numerical simulation of Dynamic Stall occuring on an airfoil in 2D/3D unsteady flow configuration. The flow unsteadiness is simulated by means of oscillating motions of the airfoil in translation, pitch and combined translation/pitch, which produce variations of velocity V and/or incidence a around the airfoil. The unsteadiness, characterized by overall and local analysis from experiments conducted on a 2D OA209 airfoil and a half-wing of the same airfoil, exhibits the influence of the finite span of the wing. The present results show that the main influence of the finite span is to delay the stalling vortex occurence and to modify the vortex chordwise propagation velocity along the upper surface. This involves a characteristic delay of the dynamic stall incidence and strongly affects the instantaneous behavior of lift, drag and moment. The dynamic stall calculation in the 3D flow configuration has been based on a semiempirical approach (GBCN code), which consists to apply the 2D version of the GBCN code at the successive spanwise airfoil sections z/h along the half-wing. Comparisons between calculation and experiment concerning the normal coefficient hysteresis loops Cn=Cn(α) are also presented to evaluate the prediction efficiency of this pseudo-3D numerical approach. The present paper also concerns an experimental investigation of the unsteady boundary-layer on a NACA0012 airfoil oscillating in a 2D flow configuration, that aims to bring up some basic data for future Navier-Stokes approach of Dynamic Stall. The study emphasizes on an Embedded Laser Doppler Velocimetry (ELDV) measurement method, suited for unsteady boundary-layer investigation on oscillating airfoils. Using this ELDV method, unsteady features on transition and separation/reattachment of the boundary-layer are investigated in both steady and unsteady flow configurations.