Pure miscible jets in a viscoplastic ambient fluid

We experimentally consider miscible jet flow dynamics wherein a Newtonian fluid is horizontally issued from a circular nozzle into a domain filled with the same-density viscoplastic ambient fluid. Motivated by the jet cleaning process in the plug and abandonment of oil and gas wells, the domain is separated into two main zones using a perforated wall. We attempt to gain insights into the effects of the main flow parameters, e.g., the injection velocity and the rheological characteristics, on the jet behaviour. To do so, we employ a combination of experimental methods, including the high-speed imaging, the planar laser-induced fluorescence (PLIF), and the tomographic particle image velocimetry (Tomo-PIV). To quantify the miscible jet behaviour, we define various jet characteristics, including the laminar length, the mixing index, and the turbulent kinetic energy. Based on our findings, increasing the injection velocity results in decreasing the laminar length. In addition, the non-Newtonian ambient fluid prevents jet evolution, damps the mixing between the jet and ambient fluids, and significantly affects the turbulent kinetic energy. Finally, we succeed in classifying different jet flow regimes versus the governing dimensionless numbers.