We consider the Nusselt–Rayleigh number problem of Rayleigh–Bénard convection and make hypothesis that velocity thermal boundary layer widths, $\delta _u$ _T$ , in absence a strong mean flow are controlled by dissipation scales turbulence outside layers and, therefore, order Kolmogorov Batchelor scales, respectively. Under this assumption, we derive $Nu \sim Ra^{1/3}$ high $Ra$ limit, independe...

To understand turbulent convection at very high Rayleigh numbers typical of natural phenomena, computational studies in slender cells are an option if the needed resources have to be optimized within available limits. However, accompanying horizontal confinement affects some properties flow. Here, we explore characteristics fluctuations velocity and temperature fields a cylindrical cell aspect ...

In this investigation, the 2D flow between two horizontally positioned concentric cylinders (gravity perpendicular to axis of cylinders), where inner cylinder is kept at constant temperature Ti higher than outer border To, analyzed. Buoyancy forces initiate movement fluid and generated studied in a fixed geometry for values Prandtl numbers (Pr) 0.01 1, Rayleigh (Ra) 102 5·106. To solve problem,...

It is shown, by the means of distributed chaos approach and using the experimental data, that at very large Rayleigh number Ra > 10 and Prandtl number Pr ∼ 1 the Rayleigh-Bénard turbulence can undergo a transition related to spontaneous breaking of the fundamental Lagrangian relabeling symmetry. Due to the Noether’s theorem helicity plays central role in this process. After the transition the t...

The three-dlmensional, incompressible Navler-Stokes and energy equations with the Bousslnesq assumption have been directly simulated at a Rayleigh number of 3.8 x 105 and a Prandtl number of 0.76. In the vertical direction, wall boundaries were used and in the horizontal, periodic boundary conditions were applied. A spectral/finite difference numerical method was used to simulate the flow. At t...

Numerical simulation is a comprehensive tool in modern process development which is extensively used for promotion of crystal growth processes. Multi-crystalline silicon is an important material with advantages of low-production cost and high conversion efficiency of PV solar cells. The control of grains as well as the grain boundaries is particularly important to the crystal quality and thus t...

A computational study has been made for a three dimensional double diffusive convection with molten Pb-Sn by using finite volume method. In this work, two vertical walls have different temperature and different concentration while remaining walls are adiabatic. Buoyancy ratio, which changes between N = -0.1 and -10, is the main governing parameter during work. Other parameters are taken as fixe...

Given the contrasting short-term temperature dependences of gross primary production (GPP) and autotrophic respiration, the fraction of GPP respired by trees is predicted to increase with warming, providing a positive feedback to climate change. However, physiological acclimation may dampen or eliminate this response. We measured the fluxes of aboveground respiration (Ra ), GPP and their ratio ...

We report measurements of the thermal dissipation rate in turbulent Rayleigh-Bénard convection using a four-thermistor temperature gradient probe. The have been undertaken cell filled with air (Prandtl number Pr=0.7). focus this work is on large aspect ratios Γ (ratio between horizontal and vertical extension cell), for which reason four datasets range Rayleigh Ra=3.9×106 to Ra=1.8×109 were tak...

We prove a new upper bound on the vertical heat transport in Rayleigh-Bénard convection of the form c Ra 1 3 (lnRa) 2 3 under the assumption that the ratio of Prandtl number over Rayleigh number satisfies Pr Ra ≥ c0 where the non-dimensional constant c0 depends on the aspect ratio of the domain only. This new rigorous bound agrees with the (optimal) Ra 1 3 bound (modulo logarithmic correction) ...