Teaching fluids

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Last day of class with some undergraduate students: “Fluid Mechanics of the Cardiovascular System” course at QMUL

I am really passionate about teaching fluid mechanics. It is a beautiful subject that sharpen useful engineering skills: the ability to make approximations, to solve PDEs analytically and numerically, and the ability to decompose a complex problem into treatable ones.

Teaching and learning fluid mechanics is hard. Many students just hate the subject. But sometimes a few students make you forget the daily frustrations of being a teacher.

interfacialslippaper

Fluid interfaces are often covered with particulate material. This can be done on purpose to change the mechanical properties of the fluid interface, leading for instance to interface stabilisation for applications to emulsions and foams. In many cases, fluid interfaces are “naturally dirty” , due to the adsorption of fine soil particles or bacteria. In all these cases, it would be desirable to know the response of the particle-covered interface to the flow of adjacent liquid phases.

We have modelled the particle-laden interface as a Navier slip surface and employed numerical simulations to study the dependence of particle microstructure and concentration on the slip length, from which the interfacial drag can be easily calculated.

A draft of the paper is available here.

Recreating the cardiovascular system?

We are studying the mechanisms leading to the formation of peptide-surfactant “interfacial gels”, a new category of soft materials that hold promise in the field of regenerative medicine. In a recent paper published on Nature Chemistry we showed that these gels can be used to create tubular branched structures from an initially spherical membrane. The hope is that one day these membranes could be used to recreate portions of the cardiovascular systems.

We are now analysing the process of formation of the membrane more in detail and measuring solute diffusion across the membrane. This will give us insights into the structure of the membrane and time-dependent changes in its physico-chemical characteristics.

Shear-induced encapsulation of polymers: annular flow in a circular channel

Shear-induced  encapsulation of polymers:  annular flow in a circular channel

When two polymers are mixed, and the mixture pumped through a small circular tube, the less viscous fluid has a tendency to segregate to the wall, forming a cylindrical liquid sheet that encapsulates the more viscous liquid.  In this Master project, we have studied how the length required for the encapsulation phenomenon to occur depends on the viscosity ratio and the temperature. This project is done in collaboration with James Busfield and Lewis Tunnicliffe, QMUL, and Martyn Bennet, Artis/Avon Rubber Ltd. The Master student visited us from Universita’ Federico II, Naples.

For more info: Technical Report.pdf

Wetting and spreading in textiles

Wetting and spreading in textiles

We are interested in the mechanisms of static wetting and spreading of drops on textiles, by focusing specifically on “oily” liquids. Designing textiles that repel oils is particularly challenging, because of their low surface tension and large viscosity. Through a combination of experimental observations – via electron and optical microscopy – and mathematical analysis  we are trying to understand why, and when, oil-repellent textiles fail in their function, and the laws governing oil spreading in realistic textiles having a multi-scale microstructure. We are also interested in how particulate material is transported by spreading liquids in textiles. This project is funded by QMUL’s Materials Research Institute, with the financial support of the Defence Science and Technology Laboratory.

Simulation of particle-stabilised drops and fluid interfaces

Simulation of particle-stabilised drops and fluid interfaces

Colloids can be used to alter the surface tension of fluid interfaces or prevent coalescence between drops or bubbles (e.g. to stabilise ice cream or other emulsions). We have developed a numerical method based on a point-particle approximation that enables to simulate the dynamics of several thousand particles interacting with fluid interfaces on a common desktop PC. The method includes hydrodynamic coupling, and can be used to get insights into collective particle effects. We are currently using the code to study how the inter-particle force due to an isotropic repulsive potential affect the surface tension and the shape of a pendant drop. This PhD project is funded by the European Community through the Marie Curie Career Integration Grant “FlowMat”

 

 

Breakup of particle-covered drop

Phase separation arrested by amphiphilic particles

Exfoliating graphene in liquids: fluid structure interaction problems at the nanoscale

Exfoliating graphene in liquids: fluid structure interaction problems at the nanoscale

We are broadly interested in understanding the fluid mechanical principles governing the dispersion and fracture of mono and multi-layer graphene flakes in linear flow fields (shear and extension). We are particularly interested in understanding the mechanics of flow-induced exfoliation.  This PhD project, focus of the PhD of Giulia Salussolia, is funded by the European Community through the Marie Curie Career Integration Grant “FlowMat”.