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 illuminated fluid plane was holographically recorded twice with the same reference beam. Using a time interval of 10 mus, local fluid displacements smaller than a few microns were recorded. The holographic plate was placed in front and as close as possible to the fluid plane. The interferograms obtained from the hologram reconstruction give information about one velocity component, at 45 degrees with the illuminated plane. The alignment of the cylinder axis with this 45 degrees direction provided definite confirmation about the vortex street having a non-negligible axial velocity. The constant velocity fluid region has proven to be very useful for quantifying the velocity information contained in the interferogram.