Role of shear-thinning on the dynamics of rinsing flow by an impinging jet

Using a jet of one fluid to ablate a second liquid that coats a planar substrate produces a variety of interesting flow structures. These rinsing flows can create alternating layers of jet and coating fluids, creating difficulties in imaging the resulting radial hydraulic jumps for qualitative and quantitative data extraction. This study is an extension of the work done by Hsu et al. [“Role of fluid elasticity on the dynamics of rinsing flow by an impinging jet,” Phys. Fluids. 23, 033101 (2011)10.1063/1.3567215] and presents a method to reveal the positions of the free surfaces in rinsing flows as well as exploring the role of shear thinning in this flow process. Following the previous work, we used an impinging jet of water to rinse coating fluids of varying rheologies to understand the flow structures during the transient growth of the resulting hydraulic jumps, observing rheological dependencies on the jump magnitude and velocity and overall topography. While many instabilities have been shown to arise during rinsing flows, the flow profile strongly depends on the local viscosity ratio of the jet fluid to the coating fluid. Four classes of test liquids, each having approximately equal low-shear viscosities, have been chosen for this study: a Newtonian solution, a shear-thinning and elastic polymer solution, a Boger fluid (an elastic fluid with constant shear viscosity), and a shear-thinning but inelastic colloid suspension. The shear-thinning of the coating liquid is shown to affect the overall velocity of the radial growth and the geometry of the hydraulic jumps associated with both liquids. To confirm that the local shear viscosity controls many of the observed phenomena, experiments on Newtonian fluids having various shear viscosities are also presented.