Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session D10: Convection and Buoyancy Driven Flows: General |
Hide Abstracts |
Sponsoring Units: DFD GPC Chair: Herman Clercx, Technische Universiteit Eindhoven Room: B118-119 |
Sunday, November 20, 2016 2:57PM - 3:10PM |
D10.00001: Rotating thermal convection at very large Rayleigh numbers Stephan Weiss, Dennis van Gils, Guenter Ahlers, Eberhard Bodenschatz The large scale thermal convection systems in geo- and astrophysics are usually influenced by Coriolis forces caused by the rotation of their celestial bodies. To better understand the influence of rotation on the convective flow field and the heat transport at these conditions, we study Rayleigh-B\'enard convection, using pressurized sulfur hexaflouride (SF$_6$) at up to 19\,bars in a cylinder of diameter D=1.12\,m and a height of L=2.24\,m. The gas is heated from below and cooled from above and the convection cell sits on a rotating table inside a large pressure vessel (the ``Uboot of G\"ottingen''). With this setup Rayleigh numbers of up to $Ra=10^{15}$ can be reached, while Ekman numbers as low as $Ek=10^{-8}$ are possible. The Prandtl number in these experiment is kept constant at $Pr\simeq 0.8$. We report on heat flux measurements (expressed by the Nusselt number Nu) as well as measurements from more than 150 temperature probes inside the flow. [Preview Abstract] |
Sunday, November 20, 2016 3:10PM - 3:23PM |
D10.00002: An experimental study on columnar vortex structures in rotating Rayleigh-Benard convection Yuji Tasaka, Kodai Fujita, Yuichi Murai, Takatoshi Yanagisawa A scanning PIV system was developed to investigate columnar vortex structures in rotating Rayleigh-Benard convection in a range of Taylor number, $6.0 \times 10^6 \le Ta \le 1.0 \times 10^8$, at constant Rayleigh number, $Ra = 1.0 \times 10^7$. Horizontal vortex advection that is much slower than the vertical scanning motion by a motor driven stage of a laser light sheet allows capturing quasi-instantaneous 3D vortex structures. Vortex distributions at each scanning plane were represented by contour of stream function calculated from a planner velocity vector field measured by PIV with assuming quasi-two dimensional flow field at the planes. 3D structure at each $Ta$ number was visualized by iso-surface of the stream function and the vertical velocity component was estimated from the planner velocity fields via equation of continuity for incompressible fluids. These results suggested that the flow transportation is emphasized by straightening of the columnar vortices with increasing $Ta$. This may correspond to improvement of Nusselt number with background rotation at the present range of $Ta$. [Preview Abstract] |
Sunday, November 20, 2016 3:23PM - 3:36PM |
D10.00003: Thermal boundary layer measurements in turbulent rotating Rayleigh-B\'enard convection Jin-Qiang Zhong, Hui-Min Li, Wen-Dan Yan We report measurements of the temperature boundary layer (BL) profile T($z$) in rotating Rayleigh-B\'enard convection along the centerline of a cylindrical sample. The measurements are taken for two Prandtl numbers Pr=6 and 40, with Rayleigh numbers in the range $5.8{\times}10^8{\le}$Ra${\le}6.3{\times}10^9$ and inversed Rossby numbers $0{\le}$1/Ro${\le}8$. In this parameter range pronounced enhancement of the heat transport (up to $22{\%}$ in Nu) is observed. Measurements of T($z$) reveal two regimes in which the effects of the applied rotations on the BL profiles differ markedly. In a low-Ra and high-Pr regime, the thermal BL thickness $\lambda$ decreases with increasing 1/Ro in accord with the global Nu-enhancement. In the other regime with relatively high Ra$>2.2{\times}10^9$ and low Pr, however, $\lambda$ is found to be independent of 1/Ro. The root-mean-square temperature prfiles $\sigma(z)$ exhibit power-low dependence $\sigma(z){\propto}z^{\beta(Ro)}$ when $z>\lambda$. The exponent $\beta$(Ro) is $-0.6{\pm}0.05$ when 1/Ro=0, but increases with increasing 1/Ro and is asymptotic to $\beta(\infty)$=$-0.2{\pm}0.02$ at large 1/Ro, indicating temperature fluctuation remains dominant in a broader domain outside the thermal BL that is ascribed to the Ekman pumping effect. [Preview Abstract] |
Sunday, November 20, 2016 3:36PM - 3:49PM |
D10.00004: Flow anisotropy in rotating buoyancy-driven turbulence Hadi Rajaei, Kim Alards, Rudie Kunnen, Federico Toschi, Herman Clercx We report a combined experimental--numerical study of the effects of background rotation on large- and small-scale isotropy in rotating Rayleigh--Benard convection (RBC) from both Eulerian and Lagrangian points of view. 3D particle tracking velocimetry (3D-PTV) and direct numerical simulations (DNS) are employed at three different heights within the cylindrical cell. The Lagrangian velocity fluctuation is utilized to evaluate the large-scale isotropy for different rotation rates. Furthermore, we examine the experimental measurements of the Lagrangian acceleration of neutrally buoyant particles and the second-order Eulerian structure function to evaluate the small-scale isotropy as a function of rotation rate. It is found that background rotation enhances large-scale anisotropy at the cell center and close to the top plate, while decreases it at intermediate height. The large-scale anisotropy, induced by rotation, has negligible effect on the small scales at the cell center, whereas the small scales remain anisotropic close to the top plate. [Preview Abstract] |
Sunday, November 20, 2016 3:49PM - 4:02PM |
D10.00005: Geometry of tracer trajectories in turbulent rotating convection Kim Alards, Hadi Rajaei, Rudie Kunnen, Federico Toschi, Herman Clercx In Rayleigh-B\'{e}nard convection rotation is known to cause transitions in flow structures and to change the level of anisotropy close to the horizontal plates. To analyze this effect of rotation, we collect curvature and torsion statistics of passive tracer trajectories in rotating Rayleigh-B\'{e}nard convection, using both experiments and direct numerical simulations. In previous studies, focusing on homogeneous isotropic turbulence (HIT), curvature and torsion PDFs are found to reveal pronounced power laws. In the center of the convection cell, where the flow is closest to HIT, we recover these power laws, regardless of the rotation rate. However, near the top plate, where we expect the flow to be anisotropic, the scaling of the PDFs deviates from the HIT prediction for lower rotation rates. This indicates that anisotropy clearly affects the geometry of tracer trajectories. Another effect of rotation is observed as a shift of curvature and torsion PDFs towards higher values. We expect this shift to be related to the length scale of typical flow structures. Using curvature and torsion statistics, we can characterize how these typical length scales evolve under rotation and moreover analyze the effect of rotation on more complicated flow characteristics, such as anisotropy. [Preview Abstract] |
Sunday, November 20, 2016 4:02PM - 4:15PM |
D10.00006: Study on analysis of ionic wind for heat transfer enhancement$.$ Han Seo Ko, Dong Ho Shin Local heat transfer technology was investigated using ionic wind generation in this study. Characteristics of ionic wind using wire and plate electrodes were studied by experimental and numerical methods. A particle image velocitimetry (PIV) test was conducted for a study of a boundary layer controlled by the ionic wind on the heated surface in the wind tunnel. It was found that the coulombic force consistently acted on the surface to reduce the effect of the viscous boundary layer. The boundary layer was formed on the heated surface and controlled by the ionic wind regardless of the Reynolds number of the bulk flow. The heat transfer coefficient increased and decreased, 11{\%} and 19{\%} in average on the heated surface by the ionic wind, for the condition of lower (100\textasciitilde 200) and higher (2500\textasciitilde 3500) Reynolds numbers of the bulk flow, respectively. It was concluded that the ionic wind can be used for enhancing the convection heat transfer rate or insulating the local surface according to its operating condition. The results of the local heat transfer controlled by the ionic wind were applied for the heat exchanger and the performance was confirmed by the experimental and numerical methods. [Preview Abstract] |
Sunday, November 20, 2016 4:15PM - 4:28PM |
D10.00007: Interfacial condensation induced by sub-cooled liquid jet Enrique Rame, R. Balasubramaniam When a sub-cooled liquid jet impinges on the free surface between a liquid and its vapor, vapor will condense at a rate dependent on the sub-cooling, the jet strength and fluid properties. In 1966 and during the examination of a different type of condensation flow, Shekriladeze found an approximate result, valid at large condensation rates, that decouples the flow in the liquid phase from that of the vapor, without putting it in the context of a formal asymptotic approximation. In this talk we will develop an asymptotic approximation that contains Shekriladze's result, and extend the calculations to the case when a non-condensable gas is present in the vapor phase. [Preview Abstract] |
Sunday, November 20, 2016 4:28PM - 4:41PM |
D10.00008: On the thermal convection in a viscoelastic Jeffreys fluid layer heated from below confined between walls of finite thickness and thermal conductivity. Ildebrando Pérez-Reyes, René O. Vargas-Aguilar The thickness and thermal conductivity of the bounding walls are of interest in the hydrodynamic stability of a viscoelastic fluid layer. In this work the linear hydrodynamic stability is studied by means of the Galerkin method. The two ideal cases of thermal insulating and perfect thermal conducting walls are bridged by taking into account these two properties. Curves of criticality for the Rayleigh number, the wavenumber and the frequency of oscillation against the thermal conductivity for fixed wall thickness, Prandtl number and relaxation and retardation times are presented. Here, the dimensionless retardation time $E$ was set to 0.05 and 0.1 while the dimensionless relaxation time $F$ was set to 0.1 and 100. The role of the thermal conductivity and of the thickness of the walls are discussed. One important result of this investigation is that for non ideal thermal conducting conditions the system is more stable when the thickness of the fluid layer is larger in comparison to that of the boundaries. A discussion on the effect of $E$ and $F$ on the stability is given as well. [Preview Abstract] |
Sunday, November 20, 2016 4:41PM - 4:54PM |
D10.00009: Thermal Convection on an Irradiated Target Igbal Mehmedagic, Siva Thangam The present work involves the computational modeling of metallic targets subject to steady and high intensity heat flux. The ablation and associated fluid dynamics when metallic surfaces are exposed to high intensity laser fluence at normal atmospheric conditions is modelled. The incident energy from the laser is partly absorbed and partly reflected by the surface during ablation and subsequent vaporization of the melt. Computational findings based on effective representation and prediction of the heat transfer, melting and vaporization of the targeting material as well as plume formation and expansion are presented and discussed in the context of various ablation mechanisms, variable thermo-physical and optical properties, plume expansion and surface geometry. The energy distribution during the process between the bulk and vapor phase strongly depends on optical and thermodynamic properties of the irradiated material, radiation wavelength, and laser intensity. The relevance of the findings to various manufacturing processes as well as for the development of protective shields is discussed. [Preview Abstract] |
Sunday, November 20, 2016 4:54PM - 5:07PM |
D10.00010: CFD Validation Benchmark Dataset for Natural Convection in Nuclear Fuel Rod Bundles Barton Smith, Kyle Jones The present study provide CFD validation benchmark data for coupled fluid flow/convection heat transfer on the exterior of heated rods arranged in a $2 \times 2$ array. The rod model incorporates grids with swirling veins to resemble a nuclear fuel bundle. The four heated aluminum rods are suspended in an open-circuit wind tunnel. Boundary conditions (BCs) are measured and uncertainties calculated to provide all quantities necessary to successfully conduct a CFD validation exercise. System response quantities (SRQs) are measured for comparing the simulation output to the experiment. Stereoscopic Particle Image Velocimetry (SPIV) is used to non-intrusively measure 3-component velocity fields. A through-plane measurement is used for the inflow while laser sheet planes aligned with the flow direction at several downstream locations are used for system response quantities. Two constant heat flux rod surface conditions are presented (400 W/m$^2$ and 700 W/m$^2$) achieving a peak Rayleigh number of ${\sim}10^{10}$. Uncertainty for all measured variables is reported. The boundary conditions, system response, and all material properties are now available online for download. [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