Steady state natural convection is numerically investigated in an enclosure using variable thermal conductivity, viscosity and thermal expansion coefficient of Al2O3–water nanofluid. This study has been conducted for a wide range of Rayleigh numbers (103≤ Ra ≤ 106), concentrations of nanoparticles (0% ≤ Φ ≤ 7%), enclosure aspect ratios (0.5 ≤ AR ≤ 2) and temperature differences between the cold...

We use a four-dimensional variational data assimilation (4D-VAR) algorithm to observe the growth of 2-D plumes from a point heat source. In order to test the predictability of the 4D-VAR technique for 2-D plumes, we perturb the initial conditions and compare the resulting predictions to the predictions given by a direct numerical simulation (DNS) without any 4D-VAR correction. We have studied p...

Convective motions in a fluid layer are affected by its orientation with respect to the gravitational field. We investigate the long-term stability of a thermally stressed layer of a binary liquid mixture and show that pattern formation is strongly affected by marginal inclinations as small as a few milliradians. At small Rayleigh numbers, the mass transfer is dominated by the induced large sca...

We present experimental results for Rayleigh-Bénard convection with rotation about a vertical axis at dimensionless rotation rates 0 # V # 250 and e ; DTyDTc 2 1 & 0.2. Critical Rayleigh numbers and wave numbers agree with predictions of linear-stability analysis. For V * 70 and small e the patterns are cellular with local fourfold coordination and differ from the theoretically expected Küppers...

The initial bifurcations in rotating Rayleigh-Bénard convection are studied in the range of dimensionless rotation rate 0 < Ω < 2150 for an aspect-ratio-2.5 cylindrical cell. We used simultaneous optical shadowgraph, heat transport and local temperature measurements to determine the stability and characteristics of the azimuthally-periodic wall convection state. We also show that the second tra...

In this work, the steady and laminar mixed convection of nanofluid in horizontal concentric annulus withrotating inner cylinder is investigated numerically. The inner and outer cylinders are kept at constanttemperature Ti and To respectively, where Ti>To. The annular space is filled with Alumina-water nanofluid.The governing equations with the corresponded boundary conditions in the polar coord...

The Mixed Scale Diffusivity Model, originally developed in the case of the differentially heated cavity, is applied to compute turbulent Rayleigh-Bénard flow in an infinite fluid layer at Pr = 0.71 for a large range of Rayleigh numbers (6.3 × 10 – 2 × 10). The effect of this SGS modelling, which adjusts locally the SGS diffusivity to the thermal scales of the flow and results in variable PrSGS ...

[1] The planform of sublithospheric convection is studied by a 3-D linear stability analysis of longitudinal rolls in the presence of vertical shear. Rayleigh numbers up to 10 are considered. The transition Rayleigh number over which longitudinal rolls are unstable is derived as a function of surface velocity. Effects of nonlinear vertical shear are shown to be insignificant unless nonlinearity...

The Rayleigh-Bénard theory by Grossmann and Lohse [J. Fluid Mech. 407, 27 (2000)] is extended towards very large Prandtl numbers Pr. The Nusselt number Nu is found here to be independent of Pr. However, for fixed Rayleigh numbers Ra a maximum in the Nu(Pr) dependence is predicted. We moreover offer the full functional dependences of Nu(Ra,Pr) and Re(Ra,Pr) within this extended theory, rather th...

We report results from Direct Numerical Simulation (DNS) of rotating Rayleigh-Bénard convection, regarding the scaling of heat transfer with the Rayleigh number for rotating systems at a fixed rate of rotation. The Prandtl number, Pr = 6.4, is kept constant. We perform simulations, using a spectral element method, for Rayleigh numbers Ra from 10 to 10, and Rossby numbers Ro from 0.09 to∞. We fi...