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Fluid Dynamics Seminar

Monday, March 29, 2010, 4:00 PM
Cullimore Hall 611
New Jersey Institute of Technology

Nonlinear dynamics of coiling and folding in viscoelastic jets

Trushant Majmudar

Courant Inst. Math. Sciences, New York University

Abstract

In this presentation I will talk about two research projects I have been involved with recently. The first project deals with free surface jets of viscoelastic fluids. Free surface jets of non-Newtonian fluids, although relevant in many industrial processes like bottle-filling, remain poorly understood in terms of fundamental fluid dynamics. Instability in viscous Newtonian jets results in coiling of the jet. We have examined the effects of viscoelasticity on the dynamics of a jet as the fluid properties and kinematic parameters are varied. We use model worm-like micellar solutions (surfactants in shampoos) to experimentally investigate transitions in jetting dynamics as the flow rate and the height of drop are varied, for fluids with different viscosities and elastic relaxation times. We observe coiling, folding, and irregular meandering as the height of the fall is increased. We observe complex nonlinear spatio-temporal dynamics of the jet and uncover a transition from periodic to quasi-periodic to multi-frequency, broad-spectrum dynamics. Beyond this regime, the dynamics smoothly crosses over to exhibit the "leaping shampoo", or the Kaye effect. Our study enables us to view seemingly disparate jet dynamics as one coherent sequence of successive instabilities and transitions between them. I will also talk about some recent work on the locomotion C elegans in complex environments. C elegans have two basic gaits; crawling on soft solids, and swimming in liquids. Free dwelling nematodes are found in soils, whereas in the laboratory, the studies of their sensing and locomotion mechanisms are carried out on simple gel substrates. We investigate the locomotion strategies of the worm placed in an array of micro-pillars, which is meant to mimic a more complex soil-like environment. I will report observations on the changes in the locomotion of the worm as it traverses through this maze.