Table-top geophysical turbulence

The author gives a brief overview of the experimental and numerical studies on (transport in) geophysical turbulence which have been and are currently being carried out in the Fluid Dynamics Laboratory at TU/e. The main topics include rotating turbulence, (rotating) thermal convection and dispersion of inertial particles in stratified turbulence. The second part of my talk will address several issues related with (rotating) thermal convection. Rayleigh-Bénard convection is a classical problem in which a fluid layer enclosed between two parallel horizontal walls is heated from below and cooled at the top. In a rotating frame of reference the dynamics can change considerably through the fundamental involvement of a combination of buoyancy and Coriolis forces. The rotating Rayleigh-Bénard (RRB) setting is important for many applications, e.g., in engineering and climate modelling. Direct numerical simulation (DNS) is used to calculate the heat transfer, flow structuring and small-scale turbulent properties at systematically varied rotation rates. The DNS code solves the incompressible Navier-Stokes equations in a cylinder in a rotating frame of reference, coupled to the heat equation within the Boussinesq approximation. The results from the DNS will be compared to data from SPIV measurements in a water-filled cylindrical convection cell. Turbulent convection is actively driven by buoyancy effects, i.e., temperature is an active scalar. Hence a considerable influence of buoyancy on the velocity and temperature structure function is expected. Bolgiano and Obukhov (BO) derived scaling laws for this regime that are different from the classical Kolmogorov (K41) result. The BO scaling is valid at length scales larger than the so-called Bolgiano length, while for smaller scales K41 is recovered. Whether a BO scaling regime can be found in Rayleigh-Bénard convection is an ongoing debate. We present numerical and experimental evidence for BO scaling. In measurements using SPIV the BO scaling was also found, in agreement with the numerical data.