Laser holographic interferometry for an unsteady airfoil undergoing dynamic stall

Laser holographic interferometry was used to study a two-dimensiona l NACA 0012 airfoil undergoing dynamic stall. The airfoil, fabricated from graphite fiber and epoxy, was tested at Mach numbers of 0.3-0.6, Reynolds numbers of 0.5 x 106 to 2.0 x 106, reduced frequencies of 0.015-0.15, and mean angles of attack of 010 deg with amplitudes of 10 deg. Density and pressure fields were obtained from dual-plate interferograms. Double-pulse interferograms, which seemed to show the wake boundaries better, were also taken. Comparisons of pressures with orifice pressures were good for the attached flow cases. For the separated flow cases, which had a vortex embedded in the flow, the comparisons were poor. Vortices, wake structures, and the dynamic stall process can be seen by holographic interferometry.