Evaluation of Buoyancy-induced Flows by a White-light Digital Technique

Optical techniques have a long tradition in studying flow phenomena. In particular, speckle photography, introduced in 1968, has been extensively used. White-light speckle photography has certain advantages with respect to traditional speckle photography, which makes it a more robust method. The aim of this work is to evaluate quantitatively advantages and disadvantages of the technique using both simulation and experimental results. The simulation study is proposed to analyse the sensitivity of the technique to different data processing algorithms used to extract the speckle displacement, with particular attention devoted to a reliable estimation of the correlation peak. In fact, as well known, the peak location in the correlation surface gives the relative displacement between the two speckle images and, hence, the temperature gradient.