Experimental observation elucidates vortex ring life cycle in non-Newtonian fluids
Experimental observation elucidates vortex ring life cycle in non-Newtonian fluids lead image
A vortex ring is a vortex of spinning fluid that propagates itself forward perpendicular to its toroidal axis. It is a common phenomenon occurring in a wide range of fluidic situations, from the blood flow created by a pumping human heart, to the air flow created by a moving helicopter blade. While the underlying theory and behavior of vortex rings have been studied for more than 100 years, past works have mainly focused on vortex rings in typical, Newtonian fluids, and the physics of vortex rings in shear-thinning non-Newtonian fluids remains relatively underexplored.
Bentata et al. reported their experimental findings on the generation, evolution and dissipation of vortex rings in non-Newtonian fluids. Their study extends previous works by looking at the entire life cycle of a vortex ring, over a range of Reynolds numbers not previously considered. The rings were generated using a cylinder-piston device submerged in the fluid and the resulting vortex ring was characterized using particle image velocimetry.
Their results show that the generation phase of the vortex ring depends largely on the shear-thinning property of the fluid, whereas the subsequent evolution of the ring is independent of the power-law index controlling the shear-thinning viscosity. The authors also found that the dissipation of the ring is characterized by a final flow dynamics at constant viscosity. The study reveals the prominent role of the dimensionless Carreau number and the Reynolds number as important control parameters for ring dissipation.
This work can help to better understand the behavior of vortex rings in non-Newtonian fluids, which is important for understanding mixing and injection operations in biological and industrial processes.
Source: “Experimental study of low inertia vortex rings in shear-thinning fluids,” by O. Bentata, D. Anne-Archard, and P. Brancher, Physics of Fluids (2018). The article can be accessed at https://doi.org/10.1063/1.5048841 .
