When a drop is subjected to an external flow, the balance between the interfacial tension and the flow forcing determines the drop shape while the imbalance between them leads to drop breakup. We numerically investigate deformation of a three-dimensional viscous drop forced by a potential vortex and other time-dependent extensional flows. Such flows represent oscillating forces present in multiphase flows such as due to turbulent eddies. The Simulation is performed at non-zero Reynolds numbers to explore the effects of inertia using a front-tracking finite difference method. We investigate the effects of interfacial tension, viscosity, density ratio, periodicity, and inertia on the drop deformation. Introduction of inertia and time dependence to the imposed flow lead to some unusual dynamics in the drop deformation such as increased deformation with increased surface tension–resonance. Such phenomena are analyzed and explained with the help of a simple ordinary differential equation model. A new mechanism for frequency-specific drop breakup in turbulence flow is suggested.
The viscoelastic flow computation has historically been riddled with severe numerical problems at high Weissenberg numbers, with single phase two-dimensional benchmark flows being actively pursued as late as in the 90s and 2000s. Our group is one of the first few to simulate multiphase viscoelastic flow computation. We have developed a front-tracking finite difference tool with a robust scheme for viscoelastic constitutive relations (Oldroyd B, FENE etc) that mitigates many of the numerical problems. There have been contraditory observations regarding effects of viscoelasticity on drop deformation–whether it increases or decreases. We have numerically simulated and with perturbative analysis explained the nonmonotonic nature of the deformation and breakup resolving this controversy. Currently, the focus is the effects of viscoelasticity on drop migration. The physics is simultaneously being used to applications such as biological problems (blood, cells, vescicles etc) involving viscoelasticity.
Even though ultrasound remains the safest and the most popular (one in every three imaging in the world) means of imaging, its utility is limited due to poor contrast. 20% of the 17 million echocardiography performed in the United States in 2000 were suboptimal, i.e. did not provide definitive diagnosis for coronary heart disease. Microbubbles intravenously injected into patients’ body can enhance the contrast of ultrasound images. A good contrast agent will enable reliable imaging of a
The objective of the modern medicine is an early cost-effective accurate diagnosis of a disease, and its quick remediation with minimum side effects. Our collaborative research with Profssor Mallik of NDSU Pharmacy investigates a novel methodology using liposomes coupled with a noninvasive ultrasound mediated control and property detremination. The lipsome can contain various biomaterials such as fluorescent dyes, enzyme inhibitors, anti-cancer drugs, magnetic resonance contrast agents etc. d
In response to an inflammation in the body, leukocytes (white blood cell) interact with the endothelium (interior wall of blood vessel) through a series of steps– capture, rolling, adhesion and transmigration– critical for proper functioning of the immune system. We are numerically simulating this process using a Front-tracking finite-difference method. The viscoelastcity of the cell membrane, cytoplasm and nucleus are incorporated and allowed to change with time in response to th
Mixtures of immiscible liquids display a wide spectrum of behaviors, and thereby offer a means of achieving tunable material properties. Often they consist of small fraction of a specialized additive in a less expensive bulk liquid. The liquids phase separate into an emulsion containing discrete droplets of various sizes dispersed in a continuous phase. In industrial processing, the flow continually deforms the suspended drops leading to their coalescence and breakup. The evolving microstruct