Measuring fluid velocities with speckle patterns

A new full-field technique for mapping lines of constant velocity in a fluid flow is demonstrated. The technique utilizes light scattered from scattering sites within a selected plane of interest of the flow field. The laser-speckle pattern thus formed is used with the established methods of speckle photography and interferometry to determine the velocity field. A double pulsed ruby laser is used to measure the velocity profile in a circular pipe. Turbulent flow fields will place a limitation on the technique; this limit is primarily a function of available equipment.