Convection under variable rotation (BSc/MSc)

Image from numerical simulation displaying cold (blue) and hot (red) plumes gathering in a central column.

It is quite well-known that rotation affects the heat transfer between two plates at different temperatures, because the background rotation changes the nature of the turbulent flow. When the rotation speed Ω of the container is modulated, the flow and the heat transfer show a number of intriguing phenomena (like a growth and oscillating behavior of the Nusselt number, followed by a complete collapse) that are still not understood. Further numerical simulations and/or experiments are needed to unravel these phenomena.

Rudie Kunnen, Bernard Geurts, GertJan van Heijst

Contact: Rudie Kunnen

Rayleigh-Benard convection in rarefied gas (BSc)

Velocity vectors normalized with respect to the hot plate thermal velocity for the case of convective rolls formation (left) and suppression (right).

The formation of a convective flow in a layer of fluid confined between two horizontal parallel plates, heated from below and under the effect of an acceleration, is a classical problem in fluid mechanics known as Rayleigh-Benard problem. In the continuum limit, it is well known that onset of convective instability occurs if the temperature difference between the plates is sufficiently large. In the case of a rarefied gas, however, a number of intriguing phenomena not present in the continuum case occurs such as the complete suppression of convection even for very mild rarefaction conditions.

Using and, if needed, modifying a Direct Simulation Monte Carlo (DSMC) code developed at WDY, pecularities of Rayleigh-Benard problem for a rarefied gas, such as relations between Nusselt, Knudsen and Rayleigh numbers, will be investigated.

Federico Toschi, Herman Clercx, Gianluca Di Staso

Contact: Federico Toschi


Inertial particles in rotating Rayleigh-Bénard convection (BSc/MSc)

Trajectories of tracer particles in cylindrical Rayleigh-Bénard convection.

Particle dispersion in turbulence plays an important role in the atmosphere, think of air pollution by high concentration of aerosols or rain droplets in clouds. Another important phenomenon in the atmosphere is convection, which is highly influenced by the rotation of the earth. In this study we are interested in a combination of the two: particle dispersion in turbulent rotating convection.

The classical convection model chosen for this research is Rayleigh-Bénard convection, where a buoyancy driven flow is generated by heating a fluid from below and cooling it from above. Direct Numerical Simulations (DNS) are used to model Rayleigh-Bénard turbulence and the system is rotated around its axis. The motion of inertial particles is described by a modified version of the Maxey-Riley equations, in which different forces on the particles are included, such as Stokes drag, added mass, buoyancy and the Basset memory force.

As a starting point the simple case of tracer particles, that perfectly follow the flow, has been studied. In figure 1 examples of trajectories for both non-rotating and rotating RB convection are shown and the effect of rotation on the particle dispersion is clearly visible. The goal of this project is to see how inertial particles behave different from these simple tracers and whether inertial particle dispersion in turbulent convection is comparable to that of previous studies on inertial particle dispersion in turbulent flows.

To explore the importance of the different forces present in the Maxey-Riley equations a force balance is computed. All the computations will be done for different rotation rates in order to investigate the effect of rotation on the particle dispersion.

Federico Toschi, Kim Alards

Contact: Federico Toschi