Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session CH: Convection and Buoyancy Driven Flows II |
Hide Abstracts |
Chair: Colm-cille Caulfield, University of Cambridge Room: Long Beach Convention Center 103C |
Sunday, November 21, 2010 1:00PM - 1:13PM |
CH.00001: Spatially Localized Binary Fluid Convection Edgar Knobloch, David Lo Jacono, Alain Bergeon Three-dimensional convection in a binary mixture in a porous medium heated from below is studied. For negative separation ratios steady convection patterns, spatially localized in one\footnote{D. Lo Jacono, A. Bergeon and E. Knobloch, Phys. Fluids {\bf 22}, 073601 (2010).} or two dimensions, are computed and numerical continuation is used to examine the growth, stability and proliferation of each pattern as parameters are varied. The results are complemented by direct numerical simulations with periodic boundary conditions in the horizontal. [Preview Abstract] |
Sunday, November 21, 2010 1:13PM - 1:26PM |
CH.00002: Evolution of Double-Diffusive Convection in Low-Aspect Ratio Containers Suhas Pol, Harindra Fernando, Stephen Webb Laboratory experiments and phenomenological modeling were undertaken to investigate the influence of container sidewalls on the evolution of diffusive layering in confined double-diffusive systems. Such flow configurations are common in engineering situations, including underground storage caverns of national strategic petroleum reserves. The laboratory flow configuration consisted of a linearly salt stratified fluid subjected to either heating from below or uniform heating from both the bottom and sidewalls. The growth of the mixed layers separated by diffusive interfaces was monitored using PIV and traversing temperature/conductivity probe techniques. The importance of aspect ratio effects was inferred from the bottom-layer growth measurements, which undergoes a transition upon onset of side-wall effects (aspect ratio $\sim$ 1). A second transition was noticed at an aspect ratio $\sim$ 2 when elongated eddies break down in to smaller sizes. The combined side and bottom wall heating case was strikingly different from the bottom heating case, wherein layers of approximately equal heights are generated rather rapidly in the former as a result of convective plumes rising along the sidewalls and their arrest by the background stable density gradient. Theoretical arguments were advanced to explain and parameterize experimental observations. [Preview Abstract] |
Sunday, November 21, 2010 1:26PM - 1:39PM |
CH.00003: Turbulent Rayleigh-Benard convection in containers with rectangular wall roughness elements Olga Shishkina, Claus Wagner The work is devoted to numerical investigation of the heat transport in turbulent Rayleigh-Benard convection enhanced by roughness of the heated/cooled plates. The roughness is determined by rectangular obstacles, which are located at the plates and are heated/cooled in the same way as the corresponding plates. Based on the obtained numerical results a theoretical model to predict the heat transport (Nusselt number) in natural convection in enclosed domains with heated/cooled obstacles is developed. [Preview Abstract] |
Sunday, November 21, 2010 1:39PM - 1:52PM |
CH.00004: Convective Heat Transfer in Bulk- and Boundary-Dominated Regimes in Turbulent Thermal Convection Ping Wei, Rui Ni, Xiao-Zheng Zhao, Ke-Qing Xia We report Nusselt number measurements in Rayleigh-B\'enard convection systems with modified boundary conditions and over the range of the Rayleigh number ($Ra$) spanning from $3\times10^8$ to $8\times10^9$ and with the Prandtl number $Pr \sim 4.3$. These measurements were made in three convection cells: (1) both the top and bottom plates of the cell have plat smooth surface; (2) the top plate has a flat smooth surface while the bottom plate has a rough surface in the form of regularly-arrayed pyramids; and (3) the top plate is rough as in (2) but the bottom plate is smooth. All these cells have cylindrical shape with aspect ratio one. The experimental results suggest that the $Nu \sim Ra$ relationship can be represented by the combination of two power laws, corresponding to the bulk-dominant regime (exponent = 1/2) and boundary layer dominant one (exponent =1/4) of the Grossmann-Lohse model. The behaviors of the coefficients of the two power laws suggest that the roughness of the plate can enhance the contribution of bulk and push the system to change from the boundary dominant state to bulk dominant state. [Preview Abstract] |
Sunday, November 21, 2010 1:52PM - 2:05PM |
CH.00005: Convective - diffusive mixing promoted by natural convection Luis M. de la Cruz, Eduardo Ramos Mixing processes in fluids include two that can be clearly identified, advective and diffusive. We report a theoretical study of combined advective - diffusive mixing of a contaminant inside a cubic cavity with time-dependent boundary conditions. Advective mixing can be achieved by natural convection inside box-shaped cavities by imposing periodic hot and cold temperatures on opposite walls. Using these boundary conditions, no moving walls are required to mix the fluid inside the container. Regardless of the dynamic state of the fluid, a contaminant with an initial non-uniform concentration distribution inside the box will diffuse to smooth out the gradients and attaining asymptotically uniform concentration. Our model is based on the numerical solution of the conservation equations under the boundary conditions described above to generate natural convection. Advective mixing is evaluated with Lagrangian tracking and diffusive mixing is calculated with the Diffusive Strip Method of Meunier and Villermaux. We describe mixing efficiencies for cases dominated by each effect for an initially blob of contaminant. [Preview Abstract] |
Sunday, November 21, 2010 2:05PM - 2:18PM |
CH.00006: Direct Numerical Simulation of turbulent mixed convection in thermally-stratified channel flow Francesco Zonta, Alfredo Soldati Direct numerical simulation of turbulence was used to study the evolution of thermally-stratified channel flow. We studied both stable and unstable stratification and we investigated the influence on the flow evolution of both viscosity and thermal expansion coefficient, which depend on temperature. We compared the obtained results against a companion base simulation of neutrally-buoyant (unstratified) flows. Statistical results and instantaneous flow field visualizations gathered for different values of the flow Reynolds number will be shown to highlight the role played by buoyancy and mean shear in mixed convection problems. Large-scale thermal convection associated to enhanced wall-normal momentum transport is observed for unstable stratification; whereas internal gravity waves accompanied by reduced momentum transport efficiency is observed for stable stratification. [Preview Abstract] |
Sunday, November 21, 2010 2:18PM - 2:31PM |
CH.00007: Symmetry-breaking bifurcations of central forced and heated convection in a spherical fluid shell L.S. Tuckerman, F. Feudel, K. Bergemann, C. Egbers, B. Futterer, M. Gellert, R. Hollerbach We study convection in a spherical shell under a gravitational force designed to mimic the GeoFlow microgravity experiment, using a combination of time-dependent simulation and path-following methods. With an outer radius which is twice that of the inner radius, the critical modes are spherical harmonics with $\ell=4$, leading generically to transcritical bifurcations involving axisymmetric and octahedral branches, in agreement with predictions by Michel, Ihrig \& Golubitsky, Chossat, Matthews, and Busse \& Riahi. A secondary bifurcation involving the $\ell=5$ mode leads to an additional seven-cell branch. All three steady patterns are simultaneously stable for $7 150 < Ra < 17 450$. For $Ra > 18 710$, simulations lead to time-dependent states, some periodic and some chaotic. The period varies greatly: some of the orbits belong to different branches and a global bifurcation is suspected of delimiting the lower limit of periodic states. [Preview Abstract] |
Sunday, November 21, 2010 2:31PM - 2:44PM |
CH.00008: Natural convection of a rotating-fluid sphere with axial gravity and uniform heat source Gerardo Anguiano, Ruben Avila, Satya Atluri The flow patterns and the heat transfer rate of a
rotating-Boussinesq fluid sphere are presented. The convective
flow is induced by (i) a gravity field acting axially downwards
(ii) a homogeneous internal heat source in the fluid, and (iii)
a uniform low temperature at the wall of the sphere. We show the
influence of the Taylor number on the heat transfer rate for
different Rayleigh numbers. The natural convection analysis is
carried out from the subcritical steady state (pure conduction)
regime to the supercritical non-steady state regime. The mesh
based Spectral Element method (SEM) has been used to solve the
fluid equations in a Cartesian coordinate system in a rotating
reference frame. The fluid sphere is discretized by using
non-regular hexahedra with straight sides macro elements. Using
this approach the singularity that appears at the poles of the
sphere, when the governing equations are formulated in the
spherical coordinate system, is avoided. The flow patterns and
the heat transfer rates for the considered Rayleigh numbers
($0 |
Sunday, November 21, 2010 2:44PM - 2:57PM |
CH.00009: Finite-size effects lead to supercritical bifurcations in turbulent rotating Rayleigh-B\'enard convection Stephan Weiss, Richard Stevens, Jin-Qiang Zhong, Herman Clercx, Detlef Lohse, Guenter Ahlers \newcommand\Ro{\mbox{\textrm Ro}} Discontinuous transitions between different turbulent states are rare, since turbulence is expected to sample all of phase space over wide parameter ranges. However, it was found\footnote {R.J.A.M. Stevens, J.-Q. Zhong, H.J.H. Clercx, G. Ahlers, and D. Lohse, Phys. Rev. Lett. 103, 024503 (2009).} in turbulent rotating thermal convection of a fluid between two parallel horizontal plates that the Nusselt number Nu is strongly enhanced when the inverse Rossby number $1/\Ro$, which is proportional to the rotation rate $\Omega$, exceeds a critical value $1/\Ro_c$. The enhancement is due to the formation of Ekman vorticies that extract additional fluid out of the thermal boundary layers at the sample top and bottom. As found in experiments and numerical simulations in cylindrical systems, $1/\Ro_c$ is proportional to $1/\Gamma$ where $\Gamma\equiv D/L$ (with D being the cell diameter and L the cell height). We present a Ginzburg-Landau like model that explains the existence of a bifurcation at finite $1/\Ro_c$ as a finite-size effect, and yields the proportionality between $1/\Ro_c$ and $1/ \Gamma$. [Preview Abstract] |
Sunday, November 21, 2010 2:57PM - 3:10PM |
CH.00010: Rotating Rayleigh-Benard convection in a cylindrical cell with aspect ratio two Jim V. Overkamp, Richard J.A.M. Stevens, Detlef Lohse, Herman J.H. Clercx Turbulent thermal convection occurs for example in the Earth's atmosphere and in the Earth's liquid outer core, which can be represented by the rotating Rayleigh-B{\'{e}}nard problem. We investigate the effect of rotation on heat transport and the presence of the large-scale circulation (LSC) in a cylindrical cell with aspect ratio $\Gamma=2$. The Rayleigh number $Ra$ in these experiments is varied between $2\times 10^8$ and $1.5 \times 10^9$, with Prandtl number $Pr\approx 4.4$. Non-rotating measurements of heat transport agree with literature data (both for cells with $\Gamma=1$ and $2$). Heat transport in rotating Rayleigh-B{\'{e}}nard convection (rotation vector parallel with the cylinder axis) is increased by up to 20\% ($Ra=3\times 10^8 $), which is larger than reported heat transfer enhancements for $\Gamma=1$ cells (and similar $Ra$). The onset of this enhancement by rotation is located at a higher Rossby value than for the cell with $\Gamma=1$. This is likely caused by the weaker, elliptical LSC, allowing Ekman pumping to take over heat transport more easily. The disappearance of the LSC around $Ro=7$ is also indirectly confirmed by temperature measurements along the sidewall of the convection cell. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700