Rudie Kunnen

The role of Stewartson and Ekman layers in turbulent rotating Rayleigh-Bénard convection

When the classical Rayleigh–Benard (RB) system is rotated about its vertical axis roughly three regimes can be identified. In regime I (weak rotation) the large-scale circulation (LSC) is the dominant feature of the flow. In regime II (moderate rotation) the LSC is replaced by vertically aligned vortices. Regime III (strong rotation) is characterized by suppression of the vertical velocity fluctuations. Using results from experiments and direct numerical simulations of RB convection for a cell with a diameter-to-height aspect ratio equal to one at Ra~10 8-10 9 (Pr=4-6) and 0<~1/Ro<~25 we identified the characteristics of the azimuthal temperature profiles at the sidewall in the different regimes. In regime I the azimuthal wall temperature profile shows a cosine shape and a vertical temperature gradient due to plumes that travel with the LSC close to the sidewall. In regimes II and III this cosine profile disappears, but the vertical wall temperature gradient is still observed. It turns out that the vertical wall temperature gradient in regimes II and III has a different origin than that observed in regime I. It is caused by boundary layer dynamics characteristic for rotating flows, which drives a secondary flow that transports hot fluid up the sidewall in the lower part of the container and cold fluid downwards along the sidewall in the top part.

Transition to geostrophic convection : the role of the boundary conditions

We conduct computations of rotating Rayleigh–Benard convection in the so-called geostrophic regime, characterized by strong thermal forcing (high Rayleigh numbers) and strong rotation (small Ekman numbers). We employ the full Navier–Stokes equations in our computations and compare no-slip and stress-free boundaries for the plates. The Ekman boundary layers, that exist in the no-slip case but not for stress-free, enhance convective heat transfer and prevent the formation of large-scale flow structures.

Vortex plume distribution in confined turbulent rotating convection

Vortical columns are key features of rapidly rotating turbulent Rayleigh-Benard convection. In this work we probe the structure of the sidewall boundary layers experimentally and show how they affect the spatial vortex distribution in a cylindrical cell. The cell has a diameter-to-height aspect ratio and is operated at Rayleigh number and Prandtl number 6.4. The vortices are detected using particle image velocimetry. We find that for inverse Rossby numbers (expressing the rotation rate in a dimensionless form) the sidewall boundary layer exhibits a rotation-dependent thickness and a characteristic radial profile in the root-mean-square azimuthal velocity with two peaks rather than a single peak typical for the non-rotating case. These properties point to Stewartson-type boundary layers, which can actually cover most of the domain for rotation rates just above the transition point. A zonal ordering of vortices into two azimuthal bands at moderate rotation rates can be attributed to the sidewall boundary layer. Additionally, we present experimental confirmation of the tendency of like-signed vortices to cluster on opposite sides of the cylinder for . At higher rotation rates and away from the sidewall the vortices are nearly uniformly distributed.

Direct Numerical Simulation of Turbulent Rotating Rayleigh–Bénard Convection

The influence of rotation on turbulent convection is investigated with direct numerical simulation. The classical Rayleigh-Benard con guration is augmented with steady rotation about the vertical axis. Correspondingly, characterisation of the dynamics requires both the dimensionless Rayleigh number

On the Collision Detection for Ellipsoidal Particles in Turbulence

Ra

Lanthanide-based laser-induced phosphorescence for spray diagnostics

and the Taylor number

Numerical Investigation of the Combined Effects of Gravity and Turbulence on the Motion of Small and Heavy Particles

Ta

Influence of turbulence on the drop growth in warm clouds, Part I: comparison of numerically and experimentally determined collision kernels

. With increasing

Extreme small-scale clustering of droplets in turbulence driven by hydrodynamic interactions

Ta

Velocity and acceleration statistics in rapidly rotating Rayleigh–Bénard convection

the root-mean-square (rms) velocity variations are found to decrease, while the rms temperature variations increase. Under rotation a mean vertical temperature gradient develops in the bulk. Compared to the non-rotating case, at constant