Measuring velocity fields in wind tunnels with holographic interferometry

This paper investigates the feasibility of using holographic interferometry in wind tunnel flows for measuring velocity fields rather than density or temperature fields. First results were obtained in a vortex street behind a cylinder at Re = 190(U-infinity = 0.7 m/s). The light scattered from an il luminated fluid plane was holographically recorded twice with the same refe rence beam. Using a time interval of 10 mus, local fluid displacements smal ler than a few microns were recorded. The holographic plate was placed in f ront and as close as possible to the fluid plane. The interferograms obtain ed from the hologram reconstruction give information about one velocity com ponent, at 45 degrees with the illuminated plane. The alignment of the cyli nder axis with this 45 degrees direction provided definite confirmation abo ut the vortex street having a non-negligible axial velocity. The constant v elocity fluid region has proven to be very useful for quantifying the veloc ity information contained in the interferogram.