Convective flow field measurement by speckle velocimetry

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Abstract
A 2-D velocity map in a cylindrical Rayleigh-Bénard flow is determined by means of a speckle photography technique. Automatic velocity measurements are performed by two different methods : (i) Isovelocity contours are drawn by spatial filtering; (ii) Local illumination by a laser beam produces Young's fringes which are analysed by an image processing system. New methods are proposed for digital analysis of the speckle fringes