Polymers are ubiquitous in nature (e.g. DNA, cellulose) or as plastics. When dissolved, flexible polymer molecules can behave as nanosprings. They can absorb energy from the surrounding fluid as they stretch in a flow, and in turn, slow down the solvent. They make the fluid viscoelastic. Even a small amount of polymeric additives can dramatically change the flow behaviour of Newtonian liquids. For instance, it is estimated that about 95% of all pesticides are wasted because of the formation of fine mist during spraying, or because drops just bounce off the hydrophobic surfaces of leaves on impact. Polymeric additives suppress micro-droplet formation (see adjoining figure). These additives can also reduce turbulent friction by as much as 40%. The connections between polymer size, chemistry and concentration, and the flow properties of their solutions are however not yet well understood. We, in the Complex Fluid Systems group, are developing mathematical models that can connect the nanoscale fluid mechanics of polymer molecules with the macroscale flow behaviour of their solutions.
The long-term goal is bespoke design of polymer solutions for use in flow applications such as spraying, surface-coatings, ink-jet printing, turbulence control, etc. PhD projects in this research area will explore the exciting world of viscoelastic fluids, their modeling and computation for both fundamental understanding and for enabling design of novel applications. There are several projects available:
• CFD of filaments of polymer solutions
• Obtaining predictions of viscoelastic behaviour in controlled flows
• Constructing new models for viscoelastic stresses in polymer solutions
Interesting things happen when groups of highly-mobile individuals get together! Complex collective patterns of motion emerge in systems as diverse as bird flocks,
wildebeest herds, human crowds, marching ants, fish shoals, etc. This is also true of
suspensions of particles propelled by chemical reactions, e.g. suspensions of swimming cells or of synthetic nanomotors. Such suspensions are now regarded as a new kind of matter –“active fluids” — whose mechanical properties are very different from those of normal, passive matter. For example, some of these fluids can self-mix! Or exhibit negative viscosities!
It is necessary to understand these properties better to exploit them in engineering
applications. We, in the Complex Fluid Systems group, are developing mathematical
models that connect the properties of the mobile particles with the mechanical
properties of the suspensions and their behaviour in flows.
PhD projects in this research area are aimed at exploring the emerging area of collective motion and active fluids, their modeling and computation. There are several projects available:
• Mixing and instabilities in active fluids
• Poiseuille & Couette flows of active fluids
• Simulations of hydrodynamics of active polymers
• Simulations of active particles interacting with a passive external matrix
Freely swimming cells are marvellous microfluidic machines. Many such cells, such as sperm cells, swim by “beating” flexible tails called flagella. These flexible propellers are
driven by an incredibly complex nanomachine, called the axoneme. Protein nanomotors, called dyneins, act in concert within this engine to drive complex beating patterns in the flagellum. Understanding how the engine works and controls these beating patterns to propel and steer the swimming cell is a mystery is the key to solving many biological and medical problems, and also to designing autonomously swimming micro-robots. We, in the Complex Fluids Group, are studying the interplay between the action of the motors, the elastic resistance of the flexible body, and the viscous forces inside and outside the cell. We are developing mathematical models that connect the physical parameters that govern this system to the various beating patterns that arise under different physical conditions. We aim to not only understand how these cells swim but also design artificial active filaments that are propelled by chemical reactions. PhD projects in this research area are aimed at modeling and simulations of fluid-structure interactions at low Reynolds numbers. There are several projects available:
• Image-analysis of experimentally obtained videos of flagellar beating in cells
• Modeling & simulations of fluid-structure interactions in internally-driven microfilaments
• Predicting beating patterns and swimming trajectories under different conditions e.g. in the presence of walls
• Modeling the axoneme engine