Flow measurements in high Rayleigh number confined thermal convection

One basic concept in the description of turbulent flows is the transport of kinetic energy from large to small scales by a cascading process of turbulent eddies. However, there are various examples of turbulent flows in nature where a large scale organised motion is embedded in a background of turbulent fluctuations and an inverse transport of energy can be inferred. Under laboratory conditions, such negative eddy viscosity phenomena are observed e.g. in turbulent Rayleigh-Bénard convection where a large-scale recirculating motion, sometimes called 'the wind' is driven by the small-scale buoyant plumes that are released from the upper and the lower thermal boundary layers. In order to confirm the latter conjecture and to get a deeper understanding of the dynamical processes in turbulent buoyant flows an experimental facility was built that allows for the measurement of velocities by particle image velocimetry (PIV). The measurements showed that on the average over the box the eddy viscosity always stays positive and that 'the wind' is not the effect of an inverse cascade..

Contacts

B. Lüthi, Michele Guala, Alexander Liberzon

Agency/Funding

Own resources of the professorship

Partners

Department of Fluid Mechanics, Tel-Aviv University

Publication

Burr, U., W. Kinzelbach, A. Tsinober (2003) Is the turbulent „wind“ in convective flows driven by fluctuations? Physics of Fluids, 8(15), 2313-2320.

Status

Ongoing after finishing the first phase experiment