Experimental study of near-wall transport and structures in turbulent Rayleigh-Bénard convection
Final Report Abstract
The heat transfer between a solid body and a surrounding fluid is a major process in many natural and technical flows. It has been studied experimentally in the so-called "Barrel of Ilmenau" – a large-scale Rayleigh-Bénard experiment with a height of eight Meters and a diameter of seven Meters. In our work, we focused on the flow field close to the horizontal plates as well as on the interface between these so-called boundary layers and the well-mixed core region. The flow field close to the plates, but also in the bulk region is very complex and three-dimensional and a comprehensive characterization requires volumetric flow measurement technique. In a first work package, we measured it in the vicinity of the cooling plate using tomographic Particle Image Velocimetry technique. The measurements have been undertaken at Rayleigh numbers between 𝑅𝑅𝑅𝑅=10 8 und 𝑅𝑅𝑅𝑅 = 10 12 at fixed aspect ratio Gamma = 1 and fixed Prandtl number 𝑃𝑃𝑃𝑃=0,7. We found that the boundary layers in turbulent Rayleigh-Bénard convection start to become turbulent already at a Ra number as low as 𝑅𝑅𝑅𝑅 ≈ 10 9. At𝑅𝑅𝑅𝑅≈10 12,turbulence dominates the near-wallflowfield.Inorderto studythe evolution of plumes and their interaction with the bulk, we also measured the flowfield in horizontal cross sections through the entire Rayleigh-Bénard cell. Despite a multitude of technical challenges and problems, which are essentially linked to the large size of the measurement field (40 m2),two complete sets of data at aspect ratios Gamma Gamma = 1.4 and Gamma Gamma = 3.0 could be acquired.
Publications
- (2018) A local sensor for joint temperature and velocity measurements in turbulent flows. The Review of scientific instruments 89 (1) 015005
Salort, Julien; Rusaouën, Éléonore; Robert, Laurent; Du Puits, Ronald; Loesch, Alice; Pirotte, Olivier; Roche, Philippe-E; Castaing, Bernard; Chillà, Francesca
(See online at https://doi.org/10.1063/1.4989430) - The near-wall flow field in turbulent convection in air: A fully three-dimensional insight from tomographic PIV. 16th European Turbulence Conference, 21.-24. August 2017, Stockholm, Sweden
R. Kaiser, R. du Puits
