Roudet, Matthieu and Billet, AnneMarie and Risso, Frédéric and Roig, Véronique PIV with volume lighting in a narrow cell: An efficient method to measure large velocity fields of rapidly varying flows. (2011) Experimental Thermal and Fluid Science, vol. 35 (n° 6). pp. 10301037. ISSN 08941777

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Official URL: http://dx.doi.org/10.1016/J.EXPTHERMFLUSCI.2011.02.004
Abstract
In this work we test a methodology for PIV measurements when alargefield of view is required in planar confined geometries. Using a depth of fieldlarger than the channel width, we intend to measure the inplane variations of the velocity of the fluid averaged through the width of the channel, and we examine in which operating conditions this becomes possible. Measurements of the flow through anarrow channel by PIV are challenging because of the strong velocity gradients that develop between the walls. In particular, all techniques that use small particles as tracers have to deal with the possible migration of the tracers in the direction perpendicular to the walls. Among the complex mechanisms for migration, we focus on the so called Segré–Silberberg effect which can lead to transverse migration of neutrally buoyant tracers of finite size. We report experimental PIV measurements in a HeleShaw cell of 1 mm gap, which have been carried out by using neutrally buoyant tracers of size around 10 μm. By considering steady flows, we have observed, in particular flow regimes, the effect of an accumulation of the tracers at a certain distance to the wall due to the so called Segré–Silberberg effect. The particle migration is expected to occur at any Reynolds numbers but the migration velocity depends on the Reynolds number. A significant migration therefore takes place each time the observation duration is large enough compared to the migration time. For a given observation duration, the tracers remain uniformly distributed at low Reynolds numbers whereas they all accumulate at the equilibrium position at large ones. When using volumelighting, the PIV algorithm provides the average velocity of the flow through the gap at low Reynolds number, while it leads to the velocity of the flow at the equilibrium position of the tracers at large Reynolds numbers. By considering unsteady flows, we have observed that the migration does not occur if the timescale of flow variation is short compared to the time required for the parabolic flow to develop across the gap. In this case, there is no transverse velocity gradient and the PIV algorithm provides the fluid velocity. Altogether, these results allow us to propose guidelines for the interpretation of PIV measurements in confined flow, which are based on the theoretical predictions of the tracer migration derived by Asmolov [1].
Item Type:  Article 

Additional Information:  Thanks to Elsevier editor. The definitive version is available at http://www.sciencedirect.com The original PDF of the article can be found at : http://www.sciencedirect.com/science/article/pii/S089417771100046X 
Audience (journal):  International peerreviewed journal 
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Institution:  French research institutions > Centre National de la Recherche Scientifique  CNRS Université de Toulouse > Institut National Polytechnique de Toulouse  INPT Université de Toulouse > Université Paul SabatierToulouse III  UPS 
Laboratory name:  Laboratoire de Génie Chimique  LGC (Toulouse, France)  Réaction, mélange & séparation (RMS) Institut de Mécanique des Fluides de Toulouse  IMFT (Toulouse, France) 
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Deposited By:  Audrey LEFEVRE 
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