The interplay between Newtonian and viscoplastic fluids holds considerable significance across diverse applications, including drug delivery systems, 3D printing, mixing processes, and the oil and gas industry. In our study, we specifically focus on the dynamics of a horizontally injected Newtonian fluid into a domain filled with a viscoplastic ambient fluid, a scenario inspired by the jet cleaning process in the oil and gas industries. Employing a combination of advanced experimental techniques, including time-resolved tomographic particle image velocimetry, high-speed imaging, and planar laser-induced fluorescence, we unveil a fascinating phenomenon: the appearance of captivating interfacial fingers at the Newtonian jet’s boundary when it interacts with the viscoplastic ambient fluid. Interestingly, there is a critical advancement length for the onset of finger growth, controlled by the ratio of yield stress to jet inertia. Our study also reveals that this interaction leads to a decrease in mean velocity and an increase in fluctuation velocity, offering valuable insights into the complex dynamics at play.
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Hassanzadeh, H., I. A. Frigaard, and S. M. Taghavi. "Neutrally buoyant miscible jets into viscoplastic ambient fluids." Journal of Non-Newtonian Fluid Mechanics 320 (2023): 105107