Turbulence is the erratic flow of a gas or a liquid.  Its is all around us, and understanding it is of great practical importance for industrial processes, for transportation, and for understanding our environment and climate.

Turbulence is an unsolved problem of classical physics: no closed equation exists that can predict the statistical properties of the erratic flow.  Although the equation of motion of the flow is well established, we do not know how to use it for the prediction of turbulence.

Our research covers many aspects of turbulence; it is a combination of  experiments,  numerical simulations, and theory.  Although the research is aimed at fundamental issues, it has a variety of applications for geophysical and industial flow situations.

Large-scale fully developed three-dimensional turbulence is studied in the laboratory's windtunnel.  Key questions are how to stir turbulence using an active grid, and the organisation of the smallest vortices in turbulence.  We use multichannel hot-wire anemometry, particle-image velocimetry, and we work on an exciting new technology to write in air. We also observe what happens to turbulence is a stream when we approach its free surface.  Turbulence extremely efficiently mixes tracers that are added to the flow.  Mixing in stratified flows, and turbulence in a rotating frame are important in a geophysical setting.

2D turbulence. During the last few years the research interests were gradually extended to include 2D turbulence. Within the framework of a large FOM programme, laboratory experiments are performed on 2D turbulence in stratified fluids - either decaying or continuously forced.  As in other projects, high-resolution numerical simulations play a crucial role here. Aspects that are studied: self-organization, effects of domain boundaries, and dispersion (chaotic advection) properties.

Vortex dynamics  Turbulence can be viewed as a manifestation of extremely complicated interactions of vortices, ranging from very large to extremely small and from intensive to much weaker, often in complicated configurations. In order to gain a better understanding of this aspect of turbulence, some of the research projects are aimed at a study of the dynamics of vortices, often in well-conditioned, idealised situations.
One of the projects concerns the dynamics of coherent vortex structures in rotating and stratified fluids. For this purpose, experiments are carried out in rotating tanks and in containers with salt-stratified fluids. The presence of background rotation and stratification implies that flows tend to become (quasi-)two-dimensional (2D). In a combined theoretical/numerical/experimental approach fundamental studies are performed on the formation of vortices (monopoles, dipoles, tripoles, ...), their stability, interaction and transport properties. Besides, attention is given to bottom-topography effects on vortices in a rotating fluid.

Physics of the atmosphere  After many years of doing research on turbulence and vortices in the controlled environment of a laboratory it seems fruitful to exploit our expertise to study the dynamics of and transport in the earth's atmosphere. It is of course needless to say that understanding these issues is of great practical importance and is directly related to the ongoing research on climate change and the ozone problem. One topic that quite recently we got interested in is the dynamics of the so-called Antarctic Polar vortex and its associated transport properties. A second topic of our interest concerns changes in the chemical composition, temperature and circulation of the stratosphere.

In addition, work is in progress on the spin-up of a contained fluid, on 3D mixing of viscous fluids, and on the dynamics of granular media.


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