Experimental and numerical investigations of dynamic stall on a pitching airfoil

The dynamic stall process on a pitching NACA 0012 airfoil was investigated by two experimental techniques-particle image velocimetry (PIV) and laser-sheet visualizations-and a numerical code based on the Navier-Stokes equations. The freestream velocity was 28 m/s, leading to a Reynolds number (based on airfoil chord) of 3.73 X 10 5 . The airfoil motion was a sinusoidal function between 5 and 25 deg of incidence, with a frequency of 6.67 Hz corresponding to a reduced frequency (based on airfoil half-chord) of 0.15. The out-of-plane component of the vorticity could be derived from the PIV velocity fields. The comparison between experimental and numerical results was conducted for the four main phases of the dynamic stall process, i.e., attached flow, development of the dynamic stall vortex, poststall vortex shedding, and reattachment. In general, the computational results agreed very well with the experimental results. However, some discrepancies were observed and discussed. The cycle-to-cycle nonreproducibility of the flowfield during the phase of massive separation is also mentioned.