Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E2: Convection and Buoyancy-Driven Flows III: Rayleigh-BĂ©nard Convection |
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Chair: Yuri Feldman, California Institute of Technology Room: 23A |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E2.00001: Turbulent thermal convection with polymer additives and with smooth and rough top and bottom plates Ke-Qing Xia, Ping Wei, Rui Ni, Xiao-Ming Li We present an experimental study of heat transport in turbulent Rayleigh-B\'{e}nard (RB) convection with polymer additives made in two convection cells, one with a smooth top and bottom plates and the other with a rough top and bottom plates. For the cell with smooth plates, a reduction of the measured Nusselt number (Nu) was observed. For the cell with rough plates, however, an enhancement ($\sim 4\%$) of Nu of was observed when the polymer concentration is greater than 120 ppm. This increase in Nu is corroborated by an increased large-scale circulation (LSC) velocity in the same cell when polymers are added. In contrast, the LSC velocity in the smooth cell is found to be essentially the same with and without polymers. Results from local velocity field and energy dissipation rate measurements will also be presented. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E2.00002: On Laminar and Turbulent Free Convection in Thin Spherical Shells Yuri Feldman, Tim Colonius Laminar and turbulent free convection flow inside thin spherical shells with isothermal cold and hot boundaries and internal/external radius ratios in the range of 0.85$\le r_{i}/r_{o}\le $0.95 is numerically investigated. The accuracy of the results has been verified by grid independence analysis and DNS-LES comparisons of the flow characteristics for the typical cases. The functional \textit{Nu-Ra} dependency is extensively investigated for the range of 10$^{3}\le $Ra$\le $ 10$^{10}$ including laminar, transitional and fully turbulent flow regimes. For thin shells, we observe considerable deviations from the existing engineering correlations. The deviations tend to increase for transitional and fully turbulent flows. A new correlation for \textit{Nu-Ra} dependency is proposed and favorably verified by independently obtained experimental end numerical results. The influence of non-uniform temperature distribution along the shell boundaries on the overall heat flux rate is also discussed. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E2.00003: Natural convection in a partially heated cylindrical container Jose Nu\~nez, Eduardo Ramos In this contribution, we study the stability of the natural convection flow in a vertical cylinder heated from below and cooled from above and with partial heating on the lateral wall with a numerical model. A mixed Fourier Galerkin- Finite volume method was used for the numerical integration. The results indicate that for small Rayleigh numbers the flow is axisymmetric with the motion confined to the upper part where the temperature gradients are concentrated. At Ra=1.5e+4 the axisymmetric flow loses stability to a non-axisymmetric motion with an azimuthal mode k=1, through a pitchfork bifurcation. Further increase in the Rayleigh number results in a time dependent flow with alternate flows with modes k=2, 3. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E2.00004: Constant- flux discrete heating in a unit aspect-ratio annulus Juan M. Lopez, Sankar Mani, Younghae Do, Francisco Marques Natural convection in an annulus with a discrete heat source on the inner cylinder is studied numerically. The outer cylinder is isothermally cooled at a fixed low temperature, and the top wall, the bottom wall and unheated portions of the inner cylinder are thermally insulated. For low applied heat flux through the heater, as measured non-dimensionally by a Grashof number, $Gr$, the flow in the annular gap consists of a weak single-cell overturning meridional flow and heat is transported primarily via conduction. As the nonlinear convection terms become more important, the meridional circulation sweeps the isotherms from being almost vertical near the outer cylinder to almost horizontal near the bottom wall. By the end of the transition from the conductiondominated regime ($Gr<10^4$) to the convection-dominated regime ($Gr\sim10^6$), the flow becomes segregated into three distinct regions and there is a strong wall plume originating at the heater that reaches the top and forms a large scale wavy structure along the top. For $Gr\sim 10^{10}$, this wavy structure becomes unstable to 3D instability with high azimuthal wavenumbers $m\sim 30$. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E2.00005: Heat transfer through suspensions of particles in turbulent convection Andrea Scagliarini, Armann Gylfason, Federico Toschi We study, by means of numerical simulations the turbulent dynamics of a layer of liquid confined between two plates, heated form below and cooled from above (as in the standard Rayleigh-B\'enard setup), with suspended solid particles. We consider both the cases where particles exert or not a back-reaction on the fluid flow. In particular we will address the dependence of the heat transfer (quantified by the Nusselt number) on particles volume fraction, heat diffusivity and of particle properties. [Preview Abstract] |
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