Fast heat transfer by smart flow control

Biomimetics (MSc)

De natuur heeft veel organismen uitgerust met intelligente tactieken om voedsel of soortgenoten te vinden. Chemische stoffen, afgescheiden door een bron, worden meegenomen door de stroming. Door de turbulente stroming wordt de wolk van deze stof snel verspreid, zodat slechts af en toe een flard van deze stof voorbij komt. Dit is echter voldoende voor de organismen om op efficiënte wijze de bron te vinden. Zoekstrategieën als deze kunnen ook voor mensen nuttig zijn: denk aan het snel kunnen opsporen van onderzeese lekkages met onderwaterrobots. In dit project willen we zo’n zoekstrategie, ‘infotaxis’ genaamd, toepassen op een eenvoudige 2D stroming. In een numerieke simulatie laat een bron regelmatig een tracer los die wordt meegevoerd door de stroming. Met de zoekstrategie wordt de bron zo snel mogelijk gelokaliseerd.

Rudie Kunnen, Herman Clercx

Contact: Rudie Kunnen

Visualisatie van de stroming rondom een zwemmer door middel van luchtbelletjes (BSc)

Centrale vraag: Hoe kunnen wervels worden gedetecteerd in een snelheidsveld van bellentracers? Het gebruik van luchtbellen als tracer is niet geheel ideaal. Bellen hebben een eigen dynamica. Naast dat bellen sterk reageren op het snelheidsveld van hun omgeving, hebben de bellen onderling interacties met elkaar en spiraliseren of zigzaggen de bellen
terwijl ze naar het oppervlak stijgen. Uit de beweging van de bellen moeten de wervels gegeneerd door zwemmer worden gedestilleerd. Uiteraard wordt dit bemoeilijkt door de eigen dynamica van de bellen. Door op een slimme manier de data te verwerken (bijvoorbeeld filteren of middelen) moet er onderscheid kunnen worden gemaakt tussen de wervels en de rest van het snelheidsveld.

Doel: In dit project zal men vooral numeriek aan de slag gaan. Met behulp van een model kunnen kunstmatige beelden worden gemaakt van bellen die door een bekend snelheidsveld heen bewegen. Hier kan een verstoring op worden gelegd. Het doel is om zo goed mogelijk het snelheidsveld van de stroming uit het snelheidsveld van de bellen te destilleren.

Josje van Houwelingen, Willem van de Water, Rudie Kunnen

Contact: Rudie Kunnen

Benchmarking earthquake models (BSc)

Numerical studies on slip-stick faulting have until now depended on ad-hoc constitutive laws which for most cases are not known a-priori. A novel formulation based on the multicomponent Lattice Boltzmann method* has been developed to find a quantitative connection between the physics of complex soft-glassy materials below yield stress and the dynamics of stick-slip faulting events leading to earthquakes.

Synthetic earthquake catalogs are being generated from plastic events (stick-slip causing topological changes) occurring in a sheared emulsion of poly-disperse droplets, using an in-house code developed of the method mentioned above. The student will use tools of statistical physics to benchmark these catalogs against classical earthquake models like the 2D Burridge-Knopoff (BR) and cellular-automaton based Self Organized Criticality (SOC) –like models.

Pinaki Kumar, Federico Toschi

Contact: Federico Toschi

Levitate glowing droplets with ultrasound (BSc)

Project aim: To create and test a setup to levitate phosphorescent droplets using an acoustic levitator.

Studying liquid droplets is useful for a variety of applications, from evaporation to selfcontained reaction vessels, or even the breakup of droplets. It is difficult, however, to create a contactless environment for droplets. Levitation of droplets would allow a great boundary condition for any experiment. By using an ultrasound speaker in combination with a parallel reflector, it is possible to trap the droplet in the air with pressure waves through acoustic streaming. This relatively simple setup traps the droplet at zero-amplitude pressure nodes of the standing wave between the speaker and the reflector. What effect does this have on the droplet? Can the droplet be accurately positioned? How does an evaporating droplet phosphoresce? You can find out! By using high-speed cameras, high power lasers, and your own setup you will be able to investigate all the dynamics and intracacies of levitating droplets.

Contact: Willem van de Water

New developments for the light attenuation technique (BSc/MSc)

Experimental project; collaboration with Dr. Stuart Dalziel (DAMTP, University of Cambridge). The light attenuation technique is used to measure the thickness of a bed of translucent particles. A light bank is placed under the bed and a camera on top. The light that goes through the bed and reaches the camera depends on the thickness of the bed. Currently, this technique is being used in several projects in our laboratory. However, we have noticed some shortcomings that result in unwanted errors when there are large gradients in the bed thickness. The student involved in this project will develop novel modifications to the technique to reduce the errors, and design procedures to test the technique and quantify its accuracy. The student is also expected to interact closely with other students using this technique.

Matias Duran Matute, Samuel Gonzalez Vera, GertJan van Heijst

Contact: Matias Duran Matute

Statistical Crowd Dynamics (MSc)

In this area, a number of projects involve an exciting mixture of fundamental physics research and technological development. They are addressed to physics students interested in statistical physics at crossroads between fluid dynamics and social sciences and that are IT & computing enthusiasts willing to face state-of-the-art challenges. Crowd dynamics is a recent research topic aiming at understanding and modeling the coordinated behavior of walking pedestrians. Our investigations employ extensive, reallife, automatic pedestrian tracking through grids of overhead Microsoft Kinect sensors (cf. the figure). We pursue both real-time and offline analyses via ad hoc algorithms. It is our
ultimate aim to develop particle-like models whose dynamics reproduce in statistical sense our observations. The interest toward these models goes far beyond physics with relevance, e.g., in transport and safety engineering.

Alessandro Corbetta, Federico Toschi

Contact: Federico Toschi

Thermoelectrically magnetohydrodynamic (TEMHD) driven flows of electrically conducting fluids (BSc/MSc)

Temperature gradients in an electrically conducting fluid may give rise to an electric current (the Seebeck effect), which in combination with an externally imposed magnetic field gives rise to a Lorentz force that can drive a flow in the fluid. This pumping or stirring is of particular importance in industrial metallurgy and for liquid-metal flows in thermonuclear fusion reactors. Using a multiphysics approach this project aims to study the flow of a conducting fluid through TEMHD pumping incorporating also convection using numerical simulation. For that we adopt a two-dimensional model of a channel flow of a liquid metal that is exposed to an incoming heat flux. We are especially interested in the flows ability to carry off the incoming heat as well as the time scales that are associated with transient behaviour in the velocity field.

Contact: Leon Kamp

Ventilation flow (BSc/MSc)

Ventilation flows are important for keeping a healthy indoor environment by removing for example pollutants in an efficient way. One way to enhance the ventilation efficiency of such flows is by making them time-dependent. Recent computational fluid dynamics (CFD) simulations suggest that the air exchange efficiency for an enclosure that is ventilated by a time-varying in- and outflow can be much higher than for a steady ventilation flow. The present project (Bachelor or Master) aims to better understand enhanced ventilation efficiency for time-dependent flows using concepts from dynamical system theory combined with two-dimensional direct numerical simulation (DNS) of incompressible flows in a rectangular  enclosure with an in- and an outflow opening.

Leon Kamp, GertJan van Heijst, Twan van Hooff (fac B)

Contact: Leon Kamp