Experimental and numerical data for the heat transfer as a function of Rayleigh, Prandtl, Rossby numbers in turbulent rotating Rayleigh-B\'enard convection are presented. For relatively small $\mathrm{Ra}\ensuremath{\approx}{10}^{8}$ large Pr modest rotation can enhance by up to 30%. At larger Ra there is less heat-transfer enhancement, at $\mathrm{Pr}\ensuremath{\lesssim}0.7$ no enhancement all. We suggest that small-Pr behavior due breakdown heat-transfer-enhancing Ekman pumping because...

Weakly rotating turbulent Rayleigh-B\'enard convection was studied experimentally and numerically. With increasing rotation large enough Rayleigh number a supercritical bifurcation from state with nearly rotation-independent heat transport to another enhanced transfer is observed at critical inverse Rossby $1/{\mathrm{Ro}}_{c}\ensuremath{\simeq}0.4$. The strength of the large-scale roll either or essentially unmodified depending on parameters for $1/\mathrm{Ro}<1/{\mathrm{Ro}}_{c}$, but...

Many natural and engineering systems are simultaneously subjected to a driving force stabilizing force. The interplay between the two forces, especially for highly nonlinear such as fluid flow, often results in surprising features. Here we reveal features three different types of Rayleigh-B\'enard (RB) convection, i.e., buoyancy-driven flow with density being affected by scalar field. In cases forces considered, namely (i) horizontal confinement, (ii) rotation around vertical axis, (iii)...

Measurements of the Nusselt number Nu and properties large-scale circulation (LSC) for turbulent Rayleigh–Bénard convection are presented in presence rotation about a vertical axis at angular speeds 0 ≤ Ω ≲ 2 rad s −1 . The sample chamber was cylindrical with height equal to diameter, fluid contained it water. LSC studied by measuring sidewall temperatures as function azimuthal position. measurements covered Rayleigh-number range 3 × 10 8 Ra , Prandtl-number 3.0 Pr 6.4 Rossby-number (1/ Ro ∝...

In turbulent thermal convection in cylindrical samples with an aspect ratio $\ensuremath{\Gamma}\ensuremath{\equiv}D/L$ ($D$ is the diameter and $L$ height), Nusselt number Nu enhanced when sample rotated about its vertical axis because of formation Ekman vortices that extract additional fluid out boundary layers at top bottom. We show from experiments direct numerical simulations enhancement occurs only above a bifurcation point critical inverse Rossby $1/{\mathrm{Ro}}_{c}$,...

We report measurements of turbulent heat transport in samples ethane (C2H6) heated from below while the applied temperature difference DeltaT straddled liquid-vapor coexistence curve T(phi)(P). When sample top T(t) decreased T(phi), droplet condensation occurred and latent vaporization H provided an additional heat-transport mechanism. The effective conductivity lambda(eff) increased linearly with decreasing T(t), reached a maximum value lambda(eff)(*) that was order magnitude larger than...

Vortices in rotating turbulent flows move as Brownian particles with direct transition from ballistic to diffusive regimes.

We present high-precision experimental and numerical studies of the Nusselt number $Nu$ as functions Rayleigh $Ra$ in geostrophic rotating convection with domain aspect ratio ${\Gamma}$ varying from 0.4 to 3.8 Ekman Ek $2.0{\times}10^{-7}$ $2.7{\times}10^{-5}$. The heat-transport data $Nu(Ra)$ reveal a gradual transition buoyancy-dominated at large $Ek$, whereas becomes sharp decreasing $Ek$. determine power-law scaling $Nu{\sim}Ra^{\gamma}$, show that boundary flows give rise pronounced...

In thermal convection, coherent flow structures emerge at high Rayleigh numbers as a result of intrinsic hydrodynamic instability and self-organization. They range from small-scale plumes that are produced near both the top bottom boundaries to large-scale circulations across entire convective volume. These exert viscous forces upon any boundary. Such will affect boundary which is free deform or change position. our experiment, we study dynamics floats on upper surface fluid. This seemingly...

We present spatially resolved measurements of the columnar vortex structures in rotating Rayleigh-Benard convection. The scaled radial profiles azimuthal velocity uϕ(r) and vertical vorticity ω(r) vortices are analyzed compared with predictions asymptotic theory. results reveal that theory predicts accurately geostrophic convection regime. In weak rotation regime, it is found experimental data deviate from theoretical predictions. Our mean velocity, vortices, strength shield structure all...

Abstract

The motion of a free-moving plate atop turbulent thermal convection exhibits diverse dynamics that displays characteristics both deterministic and chaotic motions. Early experiments performed by Zhong & Zhang ( Phys. Rev. E, vol. 75 (5), 2007, 055301) found an oscillatory trapped state existing for floating on convective fluid in rectangular tank. They proposed piecewise smooth physical model (ZZ model) successfully captures this transition states. However, their was therefore could not...

Abstract We report theoretical and experimental investigations of the flow instability responsible for mushy-layer convection with chimneys, drainage channels devoid solid, during steady-state solidification aqueous ammonium chloride. Under certain growth conditions a state steady no is unstable to onset convection, resulting in formation chimneys. present regime diagrams quantify as function initial liquid concentration, porous-medium Rayleigh number, sample width. For given increasing both...

Laboratory experiments and a theoretical model shed light on the dynamical phenomena observed in turbulent Rayleigh-B\'enard convection with modulated rotations, including phase lags roll movement nonlinear amplitude responses of circulation strength.

Continents exert a thermal blanket effect to the mantle underneath by locally accumulating heat and modifying flow structures, which in turn affects continent motion. This dynamic feedback is studied numerically with simplified model of an insulating plate over thermally convecting fluid infinite Prandtl number at Rayleigh numbers order $10^{6}$ . Several plate–fluid coupling modes are revealed as size varies. In particular, small plates show long durations stagnancy cold downwellings....

We experimentally study the dynamical states of a freely moving, floating heat blanket that is coupled with thermally convecting fluid. This boundary modifies large-scale flow pattern in bulk and destabilizes system, leading to spontaneous oscillations. As moving exceeds critical size, system makes transition from an oscillatory state weakly confined state, which executes only small excursions response random bypassing thermal plumes. To explain observed transition, we provide...

We present measurements of the azimuthal rotation velocity $\dot{{\it\theta}}(t)$ and thermal amplitude ${\it\delta}(t)$ large-scale circulation in turbulent Rayleigh–Bénard convection with modulated rotation. Both exhibit clear oscillations at modulation frequency ${\it\omega}$ . Fluid acceleration driven by oscillating Coriolis force causes an increasing phase lag when increases. The applied produces oscillatory boundary layers resulting time-varying viscous drag modifies periodically....

Abstract When a fluid system is subject to strong rotation, centrifugal motion expected, i.e., denser (lighter) moves outward (inward) from (toward) the axis of rotation. Here we demonstrate, both experimentally and numerically, existence an unexpected warm lighter vortices in rotating thermal convection. This anomalous vortex occurs under rapid rotations when buoyancy sufficiently induce symmetry-breaking vorticity field, cold anticyclones overrides that cyclones. We show through...

We investigate the spatial distribution and dynamics of vortices in rotating Rayleigh–Bénard convection a reduced Rayleigh number range $1.3\le Ra/Ra_{c}\le 83.1$ . Under slow rotations ( $Ra\approx 80\,Ra_{c}$ ), are distributed randomly, which is manifested by size Voronoi cells vortex centres being standard $\varGamma$ distribution. The exhibit Brownian-type horizontal motion parameter $Ra\gtrsim 10\,Ra_{c}$ probability density functions displacements are, however, non-Gaussian at short...

Based on our previous experimental study, we present a one-dimensional phenomenological model of thermal blanket floating the upper surface thermally convecting fluid. The captures most important interactions between solid and fluid underneath. By blanketing effect, presence plate modifies flow structure below; in turn, exerts viscous drag that causes boundary to move. An oscillatory state trapped are found this model, which is excellent agreement with observations. also offers details...

When subjected to a radial temperature gradient, Taylor-Couette flows undergo evolution of flow states with increasing rotations: first transition from asymmetric vertical convection spiral vortices, and second turbulence characterized by Taylor vortices. In the latter turbulent state, transport heat angular momentum exhibits similar power-law scaling. Our data analysis spatial distributions flux densities reveals mutual structures through which both are transported efficiently.

We present measurements of the azimuthal orientation {\theta}(t) and thermal amplitude {\delta}(t) large-scale circulation (LSC) turbulent rotating convection within an unprecedented large Rossby number range 1<Ro<314. Results reveal persistent rotation LSC flow in retrograde direction over entire Ro range. The speed ratio remains a constant 0.13(${\pm}$0.01) for 10<Ro<70, but starts to increase with increasing when Ro>70. identify mechanism through which mean can be enhanced by stochastic...

We present measurements of temperature fluctuations in turbulent rotating Rayleigh-Bénard convection. The variance exhibits power-law dependence on the fluid height outside thermal boundary layers irrespective rates. Rotations increase magnitudes variance, but reduce skewness and kurtosis, leading to Gaussian-like distributions. derive a general theoretical expression for all statistical moments terms dynamical properties plumes, based findings that both amplitude time width plumes are...