We report temperature cross correlation and velocity profile measurements in the aspect-ratio-one convection cell filled with water. A sharp transition from a random chaotic state to a correlated turbulent state of finite coherence time is found when the Rayleigh number becomes larger than a critical value Ra(c) approximately equal to 5 x 10(7). The experiment reveals a unique mechanism for the...

We analyse simultaneous velocity and temperature measurements in turbulent thermal convection. Our results show the existence of a cross-scaling between the normalized velocity and temperature structure functions, as implied by the Bolgiano–Obukhov scaling, at the centre of the convection cell. We find that the cross-scaling exponents are, however, different from the values implied by the Bolgi...

Turbulent heating may play an important role in galaxy-cluster plasmas, but if turbulent heating is to balance radiative cooling in a quasi-steady state, some mechanism must regulate the turbulent velocity so that it is neither too large nor too small. This paper explores one possible regulating mechanism associated with an active galactic nucleus at cluster center. A steady-state model for the...

We investigate the early stages of mass convection in a colloidal suspension at high solutal Rayleigh number Ras. From the time evolution of shadowgraph images and by assuming a diffusive growth of the boundary layers we obtain an indirect measurement of the concentration boundary layer thickness delta* at the onset of convection. We show that the dimensionless boundary layer thickness delta=de...

Turbulent mixed convection in channel flows with heterogeneous surfaces is studied using direct numerical simulations. The relative importance between buoyancy and shear effects, characterized by the bulk Richardson number $Ri_b$, varied order to cover flow regimes of forced, natural convection, which are associated different large-scale organization. surface consists streamwise-aligned ridges,...

Using a nonlocal time-dependent theory of convection, we have calculated the linear non-adiabatic oscillations of the Horizontal Branch (HB) stars, with both the dynamic and thermodynamic coupling between convection and oscillations carefully treated. Turbulent pressure and turbulent viscosity have been included consistently in our equations of non-adiabatic pulsation. When the coupling between...

A theoretical approach proposed by Elperin et al. Phys. Rev. E 66, 066305 2002 is developed further to investigate formation of large-scale coherent structures in a nonrotating turbulent convection via excitation of a large-scale instability. In particular, the convective-wind instability that causes formation of large-scale coherent motions in the form of cells, can be excited in a shear-free ...

The hydrodynamic and thermal lattice Boltzmann methods are applied to investigate the turbulent convective heat transfer in the wavy channel flows. In this study, the turbulent phenomena are modeling by large-eddy simulations with the Smagorinsky model. As a benchmark, the laminar and turbulent backward-facing step flows are simulated first. The results give good agreement with other numerical ...

Convection in a fluid heated from below, known as Rayleigh-Bénard convection, is an important turbulent process that occurs in the sun, planetary atmospheres, industrial manufacturing, and many other places. Physicists and engineers have made much progress in understanding this phenomenon in simple laboratory geometries, but still have a way to go before they are able to extrapolate to the extr...

mixed convection fluid flow and heat transfer of water-al2o3 nanofluid inside a lid-driven square cavity has been examined numerically in order to find the optimal distribution of discrete heat sources on the wall of a cavity. the effects of different heat source length, richardson number and grashof number on optimal heat source location has been investigated. moreover, the average nusselt num...