PTV measurements of oscillating grid turbulence in water and polymer solutions

Abstract

Particle Tracking Velocimetry (PTV) is applied to measure the flow in an oscillating grid stirred tank filled with either water or shear thinning dilute polymer solutions (DPS) of Xanthan Gum (XG). There are many interests of studying turbulence in such complex non-Newtonian fluids (e.g. in the pharmaceutical, cosmetic, or food industry), and grid stirred tanks are commonly used for fundamental studies of turbulence in Newtonian fluids. Yet the case of oscillating grid flows in shear thinning solutions has been addressed recently by Lacassagne et al. (Exp Fluids 61(1):15, Phys Fluids 31(8):083102, 2019a, b), with only a single two dimensional (2D) Particle Image Velocimetry (PIV) characterization of mean flow and turbulence properties in the central vertical plane of the tank. Here, PTV data processed by the Shake The Box algorithm allows for the time resolved, three dimensional (3D) 3 components (3C) measurement of Lagrangian velocities for a large number of tracked particles in a central volume of interest of the tank. The possibility of projecting this Lagrangian information on an Eulerian grid is explored, and projected Eulerian results are compared with 2D PIV data from the previous work. Even if the mean flow is difficult to reproduce at the lowest polymer concentrations, a good agreement is found between measured turbulent decay laws, thus endorsing the use of this 3D-PTV metrology for the study of oscillating grid turbulence in DPS. The many possibilities of further analysis offered by the 3D3C nature of the data, either in the original Lagrangian form or in the projected Eulerian one, are finally discussed. Graphic Abstract

Turbulent mass transfer near gas-liquid interfaces in water and shear-thinning dilute polymer solution

“…Extensive effort has been and is still being made to relate mass transfer velocity k L to local turbulence properties [20,48] and our experimental contribution can be used to power this modelling effort, that is now facing the challenge of complex fluid rheology encountered in many industrial applications [49]. Three-component information brought by SPIV, or other more elaborate three-dimensional methods such as PTV [38] applied near-surface, could be useful in the context of surface divergence modelling [50,48]. As for experiments, a natural next step further would be to investigate more shear-thinning fluids (higher polymer concentration) [25,19] for which the hydrodynamic behaviour in the viscous sub-layer significantly differs from the Newtonian one.…”

“…Turbulence is generated in the liquid phase by an oscillating grid device previously described and used in [25,37,19,38,39], and sketched in figure 2.…”

Comparison of particle image velocimetry and the underlying agents dynamics in collectively moving self propelled particles

“…Hence, should decrease if the particle size gets much closer to the grid size, . For the statistical purpose, the grid size is chosen large enough so that it includes a significant number of particles 36 , 37 . Hence, the grid size was set to be pixels, unless stated otherwise.…”