Measuring fluid velocities with speckle patterns

Abstract

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.

Analysis of image series through global digital image correlation

“…The same type of approach was developed independently in the context of fluid mechanics (i.e., particle image velocimetry or PIV [5]) starting in the late 1970's [7,8,9]. Very early on, regularization techniques [10,11] were proposed [12,13] since the gray level conservation, i.e., the underlying conservation principle to determine the optical flow, is very difficult to achieve 2 when using particles in a 3D flow observed with a single camera.…”

Refractive index profiling across a candle flame using speckle techniques

“…Speckle pattern photography and speckle interferometry techniques have been widely used in measuring fluid velocities or mechanical displacements (Barker and Fourney 1977;Iwata et al 1978;Simpkins and Dudderar 1978;Barakat et al 1987), strains (Erf 1978;Barker and Fourney 1976), and vibrations (Bolognini et al 1980). Speckle photography has the advantage of requiring neither high mechanical stability nor high-quality optical instruments, all of which are needed when using speckle interferometry.…”

A new technique for the determination of the third velocity component with PIV

“…With the use of PIV technique it is possible to obtain information about the two components of the particle velocity vector projected on a plane (Dudderar and Simpkins 1977;Grousson and Mallick 1977;Barker and Fourney 1977;Adrian 1984;Merzkirch 1987;Cenedese and Paglialunga 1987). The plane is selected by illuminating the flow with a laser light sheet obtained by expanding a laser beam in one direction by means of a suitable optical arrangement.…”