Facility and equipment

Overview

The fundamental study of convective flows is a very important issue in these days quite relevant to very ongoing questions related to the earth climate, the weather or the properties of the geomagnetic field as well as to a large number of technical applications. Despite of the giant progress in the computational technique it is still quite hard or sometimes even impossible to predict these very complex flows and therefore simplified model experiments are an exclusive way to study their properties. One of the best-known and in the last hundred years intensively explored models is the Rayleigh-Bènard (RB) experiment: an adiabatic box that is heated from below and cooled from above (see figure). The BOI presents such an apparatus in which a turbulent air flow can be investigated up to Rayleigh numbers of Ra=1012 (Ra=b*g*DT*H3/(n*k)). The experimental facility consists of a virtually adiabatic cylinder filled with air and shielded at the sidewall by an active heating system. An electricallly heated plate at the bottom as well as a free hanging cooling plate at the top triggers the convective motion of the air in between. Both plates, with diameters of 7 meters, are carefully designed to maintain a very constant and homogeneous temperature with a deviation below 1 K. A further unique feature of the apparatus is that the distance between the two plates can be varied continuously between 0.05 meters and 6.30 meters by lifting the cooling plate. While experiments using the maximum height are interesting to depict flows with highest complexity and the broadest variation of turbulent structures, the geometry at moderate heights is closer to the geometry of typical geophysical flows. Compared with a similar low-temperature helium facility at ICTP able of achieving higher Rayleigh numbers (up to Ra=1017) with rotation, in our facility the access for the measurement of velocity or temperature is very easy and these quantities can be measured with an unrivalled spatial and temporal resolution. The BOI also complements other turbulence facilities like the Göttingen Turbulence Tunnel or the CICLoPE, being basically large wind tunnels, since it enables the user to study thermally driven, highly turbulent flows at very small velocities.

BOI (Barrel of Ilmenau)

In order to investigate the flow field inside the cell a broad variety of modern flow measurement technique is available:a 3d Laser-Doppler velocimeter for local measurements, a 3D-Tomo-Particle image velocimeter, a 3d Hotwire velocimeter for ultrafast measurements, 3d Particle Tracking velocimeter for global field measurements (under development), a real-time Infrared camera Variocam HR mit 640 x 480 pixels and a 4 channel measurement system with 125 µm temperatur probes. All the experimental data shall be published in a standardized form in the joint database of the EuHIT infrastructure.

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Technical data and physical parameters

 

diameter: m

             7,15

             Rayleigh number:

        105 ... 1012

plate distance: m

        0,20 ... 6,30

             aspect ratio:

       1,13 ... 40

temperatur of the heating plate: °C

           10 ... 80

             Prandtl number:

             0,7

temperatur of the cooling plate:  °C

           10 ... 80

             Nusselt number:

        ... 650

sidewall:

          no heat flux

             Reynolds number:                

        ... 3x105

working fluid:

                air

 

 

 

 

Potential user applications

Turbulent Rayleigh-Bénard convection:

  • Measurement of velocity and temperature in turbulent convective air flows
  • Generation of reference data for numerical simulations
  • Reference object for RB experiments with alternative fluids like He@5K, SF6
  • Heat reservoir with thermal stratification

Indoor flows:

  • Investigation of free and mixed convection
  • Convective air flow around local heat sources / sinks in virtually infinite spaces
  • Stability of stratified air volumina

Shielded model room with well-defined boundary conditions

  • Investigation of pilot air flows (free jets, thermal plumes etc.) in a virtually infinite space
  • Test of novel large-scale measurement technique for all fluidmechanical quantities

Moist air flows 

  • Heat transport at high level of humidity, humidity boundary layer
  • Condensation
  • Cloud formation
  • Heat transfer from liquid surfaces to a surrounding gas