Robustness of heat transfer in confined inclined convection at high Prandtl number

Abstract

We investigate the dependency of the magnitude of heat transfer in a convection cell as a function of its inclination by means of experiments and simulations. The study is performed with a working fluid of large Prandtl number, Pr ≃ 480, and at Rayleigh numbers Ra ≃ 10 8 and Ra ≃ 5 × 10 8 in a quasi-two-dimensional rectangular cell with unit aspect ratio. By changing the inclination angle (β) of the convection cell, the character of the flow can be changed from moderately turbulent, for β = 0 o , to laminar and steady at β = 90 o . The global heat transfer is found to be insensitive to the drastic reduction of turbulent intensity, with maximal relative variations of the order of 20% at Ra ≃ 10 8 and 10% at Ra ≃ 5 × 10 8 , while the Reynolds number, based on the global root-meansquare velocity, is strongly affected with a decay of more than 85% occurring in the laminar regime. We show that the intensity of the heat flux in the turbulent regime can be only weakly enhanced by establishing a large scale circulation flow by means of small inclinations. On the other hand, in the laminar regime the heat is transported solely by a slow large scale circulation flow which exhibits large correlations between the velocity and temperature fields. For inclination angles close to the transition regime in-between the turbulent-like and laminar state, a quasi-periodic heat-flow bursting phenomenon is observed.

On the effective horizontal buoyancy in turbulent thermal convection generated by cell tilting

“…2014; Shishkina & Horn 2016; Teimurazov & Frick 2017; Jiang et al. 2019). The main reason is that we have adopted a different normalization scheme and our experiment follows a straight line in the parameter space shown in figure 1.…”

“…(2014) reported a monotonic decrease in Nusselt number for increasing in a rectangular cell (aspect ratios and ). Jiang, Sun & Calzavarini (2019) conducted both experimental and numerical studies in a similar convection cell but with much higher Prandtl number () and they reported a peculiar bimodal curve. For low Prandtl number, on the other hand, Frick et al.…”

Rotation of anisotropic particles in Rayleigh–Bénard turbulence

“…The above-described models are simulated numerically by means of a tested code (Calzavarini 2019) which makes use of a Lattice Boltzmann Method (known as LBM) algorithm for the treatment of the fluid and thermal part and of a second-order-in-time tracking algorithm with trilinear interpolation of fields at the particle positions. The code has been used for the simulation of convection in a closed cavity (Jiang, Calzavarini & Sun 2019), convection with particles (Calzavarini etal. 2020) and HIT flows with inertial particles (Mathai et al 2016 a ; Calzavarini et al 2018).…”

Effects of Prandtl number in quasi-two-dimensional Rayleigh–Bénard convection

“…2015; Shishkina & Horn 2016; Wang et al. 2018; Jiang, Sun & Calzavarini 2019; Zwirner et al. 2020), using mixed or time-modulated thermal boundary conditions (Ripesi et al.…”