Experimental investigations in an air-filled differentially-heated cavity at large Rayleigh Numbers

Abstract

Abstract. A large-scale experimental differentially heated cavity was built and instrumented. Rayleigh numbers up to 1.2×10 11 can be obtained with a temperature difference, ∆T=20°C, between the hot and cold walls leaning in the range of validity of the Boussinesq approximation. Previous data obtained locally for mean velocity by 2D LDV in the range give rise to questions regarding the general air flow circulation in the cavity. Particularly, a downstream flow along the vertical boundary layer was observed. This reverse flow caused by the temperature stratification outside this layer is not present in the upstream parts and was not previously observed in smaller cavities. The question of the global circulation in this cavity is thus posed. Evolution laws providing Nusselt numbers are also given and when possible compared to the literature for a large range of Rayleigh numbers.

Coupled velocity and temperature measurements in an air-filled differentially heated cavity at Ra=1.2E11

“…Near the cold side at these elevations, the flow is only descending along the wall, 〈 * 〉 is always negative (Figure 4, right). No recirculation area is observed in this cold wall region, but a diminution of the thickness of the dynamic boundary layer can be observed between Z*=0.85, where the flow still exhibits unsteady laminar behaviour, and Z*=0.75, where the transition to the turbulence starts (as suggested by the evolution of the wall heat flux [20]). The horizontal component of the mean velocity ( Figure 5) is slightly positive away from both walls.…”

Turbulent natural convection of a confined flow in a cubic enclosure: Effect of transient boundary conditions

“…The vertical ascending and descending boundary layers become turbulent from a certain elevation along the walls. Saury et al [11] or Belleoud et al [12,13] later studied a higher Rayleigh number flow (Ra = 1.2×10 11 ) in a vertical differentially heated cavity. Results have been compared to numerical simulations by Trias et al [14] with good agreement.…”