Biospeckle PIV (Particle Image Velocimetry) for analyzing fluid flow

Abstract

In this paper, we present an alternative protocol for use with the Particle Image Velocimetry (PIV) technique in fluid and particle flow monitoring, without the use of external particles seeded as targets in the cross-correlation of the flow images. Dynamic laser speckle patterns, or biospeckle laser (BSL) patterns, with grains varying over time, were the basis of our method. A pre-processing step using a frequency approach is involved. In order to avoid the usual “boiling” effect of BSL, the primary characteristic of dynamic laser speckle, the time series of images were first manipulated in the frequency domain thereby isolating the translational expression within the signal. Our hypothesis that grains in the speckle patterns can be used to implement PIV, and isolate the translational information, was tested using a simulated speckle pattern in a pure translational flow, an actual flow of water in a translucent tube illuminated by a laser beam, and a micro-flow in a torn leaf reacting to the broken internal pressure. Results confirmed this hypothesis regarding the use of BSL associated to a PIV technique and illustrated a protocol to deal with the boiling effect that undermines the translational information in the speckle patterns.