scholarly journals The influence of the cell inclination on the heat transport and large-scale circulation in liquid metal convection

2019 ◽  
Vol 884 ◽  
Author(s):  
Lukas Zwirner ◽  
Ruslan Khalilov ◽  
Ilya Kolesnichenko ◽  
Andrey Mamykin ◽  
Sergei Mandrykin ◽  
...  
Keyword(s):  
Liquid Metal ◽  
Heat Transport ◽  
Large Scale ◽  
Large Scale Circulation ◽  
Image Position

scholarly journals Combined measurement of velocity and temperature in liquid metal convection

2019 ◽  
Vol 876 ◽  
pp. 1108-1128 ◽  
Author(s):  
Till Zürner ◽  
Felix Schindler ◽  
Tobias Vogt ◽  
Sven Eckert ◽  
Jörg Schumacher
Keyword(s):  
Reynolds Number ◽  
Liquid Metal ◽  
Large Scale ◽  
Scale Up ◽  
Convection Cell ◽  
Small Scale ◽  
Convection Flow ◽  
Large Scale Circulation ◽  
Large Scale Flow ◽  
The Impact

Combined measurements of velocity components and temperature in a turbulent Rayleigh–Bénard convection flow at a low Prandtl number of $Pr=0.029$ and Rayleigh numbers of $10^{6}\leqslant Ra\leqslant 6\times 10^{7}$ are conducted in a series of experiments with durations of more than a thousand free-fall time units. Multiple crossing ultrasound beam lines and an array of thermocouples at mid-height allow for a detailed analysis and characterization of the complex three-dimensional dynamics of the single large-scale circulation roll in a cylindrical convection cell of unit aspect ratio which is filled with the liquid metal alloy GaInSn. We measure the internal temporal correlations of the complex large-scale flow and distinguish between short-term oscillations associated with a sloshing motion in the mid-plane as well as varying orientation angles of the velocity close to the top/bottom plates and the slow azimuthal drift of the mean orientation of the roll as a whole that proceeds on a time scale up to a hundred times slower. The coherent large-scale circulation drives a vigorous turbulence in the whole cell that is quantified by direct Reynolds number measurements at different locations in the cell. The velocity increment statistics in the bulk of the cell displays characteristic properties of intermittent small-scale fluid turbulence. We also show that the impact of the symmetry-breaking large-scale flow persists to small-scale velocity fluctuations thus preventing the establishment of fully isotropic turbulence in the cell centre. Reynolds number amplitudes depend sensitively on beam-line position in the cell such that different definitions have to be compared. The global momentum and heat transfer scalings with Rayleigh number are found to agree with those of direct numerical simulations and other laboratory experiments.

Turbulent thermal convection in a cell with ordered rough boundaries

2000 ◽  
Vol 407 ◽  
pp. 57-84 ◽  
Author(s):  
Y.-B. DU ◽  
P. TONG
Keyword(s):  
Secondary Flow ◽  
Heat Transport ◽  
Large Scale ◽  
Horizontal Shear ◽  
Large Scale Circulation ◽  
Thermal Plumes ◽  
A Cell ◽  
Efficient Heat Transfer ◽  
Rough Boundaries ◽  
Rough Cell

A novel convection experiment is conducted in a cell with rough upper and lower surfaces. The measured heat transport in the rough cell is found to be increased by more than 76%. Flow visualization and near-wall temperature measurements reveal new dynamics for the emission of thermal plumes. The experiment shows that the interaction between the horizontal shear flow due to the large-scale circulation and the ordered rough surface creates a secondary flow (eddies) in the groove region. The secondary flow together with the large-scale circulation enhance the detachment of the thermal boundary layer from the tip of the rough elements. These extra thermal plumes are responsible for the enhanced heat transport in the rough cell. The discovery of the enhanced heat transport has important applications in engineering for more efficient heat transfer.

scholarly journals Effect of tilting on turbulent convection: cylindrical samples with aspect ratio

2013 ◽  
Vol 715 ◽  
pp. 314-334 ◽  
Author(s):  
Stephan Weiss ◽  
Guenter Ahlers
Keyword(s):  
Aspect Ratio ◽  
Heat Transport ◽  
Large Scale ◽  
Rotational Symmetry ◽  
Torsional Oscillation ◽  
Large Scale Circulation ◽  
Cylindrical Cell ◽  
Quantitative Measurements ◽  
Gravity Measurements ◽  
Cylindrical Samples

AbstractWe report measurements of the properties of turbulent thermal convection of a fluid with a Prandtl number $\mathit{Pr}= 4. 38$ in a cylindrical cell with an aspect ratio $\Gamma = 0. 50$. The rotational symmetry was broken by a small tilt of the sample axis relative to gravity. Measurements of the heat transport (as expressed by the Nusselt number Nu), as well as properties of the large-scale circulation (LSC) obtained from temperature measurements along the sidewall, are presented. In contradistinction to similar experiments using containers of aspect ratio $\Gamma = 1. 00$ (Ahlers et al., J. Fluid Mech., vol. 557, 2006b, pp. 347–367) and $\Gamma = 0. 50$ (Chillà et al., Eur. Phys. J. B, vol. 40, 2004, pp. 223–227; Sun, Xi & Xia, Phys. Rev. Lett., vol. 95, 2005, p. 074502; Roche et al., New J. Phys., vol. 12, 2010, p. 085014), we see a very small increase of the heat transport for tilt angles up to about 0.1 rad. Based on measurements of properties of the LSC we explain this increase by a stabilization of the single-roll state (SRS) of the LSC and a destabilization of the double-roll state (DRS) (it is known from previous work that the SRS has a slightly larger heat transport than the DRS). Quantitative measurements of the strength and the orientation of the LSC show that its azimuthal diffusion is suppressed with increasing tilt whereas the torsional oscillation becomes more pronounced and its frequency increases.

scholarly journals Characteristics of Large-Scale Circulation Affecting the Inter-Annual Precipitation Variability in Northern Sumatra Island during Boreal Summer

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 136
Author(s):  
Yahya Darmawan ◽  
Huang-Hsiung Hsu ◽  
Jia-Yuh Yu
Keyword(s):  
Large Scale ◽  
Precipitation Variability ◽  
Specific Humidity ◽  
Boreal Summer ◽  
Moisture Budget ◽  
Large Scale Circulation ◽  
Budget Analysis ◽  
Sumatra Island ◽  
Precipitation Anomalies ◽  
The Impact

This study aims to explore the contrasting characteristics of large-scale circulation that led to the precipitation anomalies over the northern parts of Sumatra Island. Further, the impact of varying the Asian–Australian Monsoon (AAM) was investigated for triggering the precipitation variability over the study area. The moisture budget analysis was applied to quantify the most dominant component that induces precipitation variability during the JJA (June, July, and August) period. Then, the composite analysis and statistical approach were applied to confirm the result of the moisture budget. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Anaysis Interim (ERA-Interim) from 1981 to 2016, we identified 9 (nine) dry and 6 (six) wet years based on precipitation anomalies, respectively. The dry years (wet years) anomalies over the study area were mostly supported by downward (upward) vertical velocity anomaly instead of other variables such as specific humidity, horizontal velocity, and evaporation. In the dry years (wet years), there is a strengthening (weakening) of the descent motion, which triggers a reduction (increase) of convection over the study area. The overall downward (upward) motion of westerly (easterly) winds appears to suppress (support) the convection and lead to negative (positive) precipitation anomaly in the whole region but with the largest anomaly over northern parts of Sumatra. The AAM variability proven has a significant role in the precipitation variability over the study area. A teleconnection between the AAM and other global circulations implies the precipitation variability over the northern part of Sumatra Island as a regional phenomenon. The large-scale tropical circulation is possibly related to the PWC modulation (Pacific Walker Circulation).

scholarly journals 2016 Monsoon Convection and its place in the Large-Scale Circulation using Doppler Radars

2021 ◽  
Author(s):  
Alexander John Doyle ◽  
Thorwald Hendrik Matthias Stein ◽  
Andrew Turner
Keyword(s):  
Large Scale ◽  
Large Scale Circulation
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