Gyroflow
A rotating platform for geophysical fluid dynamics

F. Moisy, C. Lamriben, P.P. Cortet, M. Rabaud What is Gyroflow? Gyroflow is a rotating platform designed for research in geophysical fluid dynamics. This platform, 2 m in diameter, can rotate up to 1 ton of experiment and instruments, at a maximum angular velocity of 30 rpm. It is installed in the laboratory FAST (Fluides, Automatique et Systèmes Thermiques), in Orsay (France), since september 2009.

What is a geophysical flow?

Geophysical flows are flows dominated by the effets of rotation (through the Coriolis force) and stratification (through the buoyancy force due to a density gradient).

Large scale ocean currents and atmospheric circulations provide illustrations of the remarkable features of geophysical flows: quasi-two-dimensionality and the presence of large scale coherent vortices.

Geophysical flows are also present in gaseous planets - e.g., Jupiter's red spot -, in stars, or in the liquid cores of planets.

The platform is rotating.

What is the effect of the Coriolis force on a flow

The Coriolis force deflects the trajectory of fluid particles, in a way similar to the effect of a magnetic field on charged particles. In an incompressible fluid, the resulting circular trajectory gives rise to an anisotropic propagative wave, called an inertial wave.

In the limit of large rotation rates, this inertial wave reduces to a column of fluid parallel to the rotation axis (Taylor-Proudman column), in which the flow is purely two-dimensional.

When the flow is turbulent, the effect of the Coriolis force is subtle: large scales may be dominated by the rotation, whereas small scales are not, because of their fast dynamics compared to the rotation rate. As a consequence, the large scales can be described as a system of superimposed inertial waves, leading to a partial two-dimensionalization of turbulence.

The first experiment on the Gyroflow platform

The first experiment on the Gyroflow platform began in october 2009. Its goal is to characterize the influence of a background rotation on the dynamics of a decaying rotating turbulence.

In this experiment, a grid is translated in a 200 L water tank (see the movie), and measurements are made using a co-rotating Particle Image Velocimetry (PIV) system. The goals of this experiment are: To characterize the anisotropic energy flux towards the 2D mode. To characterize the geometrical properties of the vertical motions which, although not directly affected by the Coriolis force, may play an important role in the turbulence decay at large time. To understand the Coriolis-induced symmetry breaking between cyclones (rotating in the direction of the platform) and anticyclones.

Velocity field measured by PIV, showing a population of cyclones (Morize, 2006).

More information?

Download the poster (in french) Former small-scale rotating platform Experiments performed on the "Coriolis" rotating platform

Acknowledgments

The project Gyroflow has been funded by RTRA "Triangle de la Physique" (project 2008-080T) and Agence Nationale de la Recherche (project 06-BLAN-0363-01).

Support from laboratoire FAST (Université Paris-Sud 11, Université Pierre et Marie Curie, CNRS), and Groupe Instabilités et Turbulence from CEA / SPEC, is also acknowledged.

Publications

• Anisotropy and cyclone-anticyclone asymmetry in decaying rotating turbulence
  F. Moisy, C. Morize, M. Rabaud and J. Sommeria, J. Fluid Mech. (submitted 2009).
• Structure functions and energy transfers in a decaying rotating turbulence experiment
  F. Moisy, L. Agostini, G. Tan, 12th Euromech European Turbulence Conference, Marburg, Sept. 7 - 10, 2009.
• On the decrease of intermittency in decaying rotating turbulence
  J. Seiwert, C. Morize, F. Moisy, Phys. Fluids 20, 071702 (2008).
• Experimental observation using particle image velocimetry of inertial waves in a rotating fluid
  L. Messio, C. Morize, M. Rabaud, F. Moisy, Exp. in Fluids 44, 519–528 (2008).
• On the cyclone-anticyclone asymmetry in decaying rotating turbulence
  C. Morize, F. Moisy, M. Rabaud and J. Sommeria, CD-ROM Conference on Turbulence and Interactions TI2006, May 29 - June 2, 2006, Porquerolles, France (2006).
• Energy decay of rotating turbulence in confined geometry
  C. Morize and F. Moisy, Phys. Fluids 18, 065107 (2006).
• Decaying grid-generated turbulence in a rotating tank
  C. Morize, F. Moisy and M. Rabaud, Phys. Fluids 17 (9), 095105 (2005).