Graduate Seminar in Fluid Mechanics
4:10 pm Presentation
“Formation of Compound Droplets by Turbulent Buoyant Oil Jet and Plume”
Presented by XINZHI XUE (Adviser: Prof. Katz)
Buoyant jet and plume are important in many engineering and environmental applications. In the regime of high Reynolds and Ohnesorge number, knowledge breakup of a liquid jet in another immiscible liquid is limited, however, it is relevant to e.g., to oil well blowout on the sea floor. In this study, refractive index matched silicone oil and sugar water are used as surrogate to crude oil and seawater. Their density, viscosity ratio, and interfacial tension are closely matched with the original liquids. Simultaneous planar laser-induced fluorescence and particle image velocimetry are applied to dissect the jet center plane for flow visualization, as well as quantitative concentration and velocity measurements. Initially, the oil jet entrains water layers as the shear layer rolls up along the jet periphery. While a few droplets form in this process, the primary fragmentation of oil to ligaments occurs 6-12 and 7-13 nozzle diameters downstream of the nozzle at Re=1358 and 2122, respectively. In both cases, compound droplets, containing multiple water droplets, some with smaller oil droplets, form regularly. The origin of some of the encapsulated water droplets can be traced back to the entrained water ligaments. They persist for at least up to 30 nozzle diameters – the current measurement range. Random forest-based segmentation is applied to measure the compound droplet statistics, showing that this phenomenon increases the overall interfacial area by 23% and 15% for Re=1358 and 2122, respectively, increasing with droplet size. The interior water droplets are also less deformed than the exterior oil droplets and ligaments, indicating that the interior interfaces are subjected to less shear. Such longer-lived quiescent interfaces might facilitate increased biochemical interaction between the oil and the water.
4:35 pm Presentation
“Vortex Shedding from a Circular Cylinder in Shear-Thinning Carreau Fluids”
Presented by SHANTANU BAILOOR (Advisers: Profs. Mittal & Zaki)
Results from numerical simulations of two-dimensional, shear-thinning Carreau fluid flow over an unconfined circular cylinder are presented in this paper. Parametric sweeps are performed over the various Carreau model parameters, and trends of the time-averaged force coefficients and vortex characteristics are reported. In general, increased shear-thinning results in lower viscous forces on the body but greater pressure forces, resulting in a complex non-monotonic drag response. Lift forces generally increased with shear-thinning due to the dominant pressure contribution. The decrease in fluid viscosity also led to shorter vortex formation lengths and the consequent rise in the Strouhal frequency of vortex shedding. It is expected that these results will be useful for verification of computational models of unsteady non-Newtonian flows.