Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session C14: Convection and Buoyancy-driven Flows: Rotating Rayleigh-Benard |
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Chair: Herman Clercx, Eindhoven University of Technology Room: 307/308 |
Sunday, November 24, 2019 8:00AM - 8:13AM |
C14.00001: A comparative experimental and numerical study of rotating Rayleigh-B\'{e}nard convection in a cylindrical cell Gerardo Paolillo, Carlo Salvatore Greco, Richard Stevens, Tommaso Astarita, Roberto Verzicco, Gennaro Cardone Rotating Rayleigh-B\'{e}nard convection (RBC) is the buoyancy-driven flow resulting from temperature gradients parallel to the gravity in the presence of rotation. In this work we comparatively present the results from an experimental and numerical investigation of RBC in a cylindrical cell with aspect ratio of 1/2 in non-rotating conditions and at different Rossby numbers. On the experimental side, time-resolved tomo-PTV is used to perform whole-field velocity measurements in a cell immersed in a water tank with constant controlled bulk temperature. This setup is accurately modeled in the direct numerical simulations by including the presence of the sidewall in the computational domain and solving the temperature field in both the fluid and solid regions. Excellent agreement between experiments and DNS is found for the non-rotating convection, whereas some discrepancies are observed when rotation is added. The latter might be related to the specific motions in the water tank at the outside of the experimental cell. [Preview Abstract] |
Sunday, November 24, 2019 8:13AM - 8:26AM |
C14.00002: Large Scale Vortices in the Rotating Rayleigh-Benard setup with no-slip boundaries Andres Aguirre-Guzman, Matteo Madonia, Jonathan Cheng, Rodolfo Ostilla-Monico, Herman Clercx, Rudie Kunnen In rotating Rayleigh-B\'enard (RRB) convection, the buoyancy-driven flow between two horizontal plates subject to rotation, different regimes are accessible depending on the strength of buoyancy and rotation. Under intense forcing (high Rayleigh number $Ra$), turbulent convection is obtained and, if rotation is strong enough (low Ekman number $Ek$), vertical motions are greatly suppressed. This allows for a quasi-two-dimensional turbulent state. In such conditions an inverse energy cascade is possible, leading to large-scale vortices (LSVs) in the flow. LSVs have been observed for stress-free top/bottom boundaries, but not yet for the no-slip case until now. In the latter, Ekman pumping from the viscous layer induces vertical velocities that affect the 2D flow. This vertical component however is attenuated when rotation is increased. We directly simulate RRB flow at $Ek\sim10^{-7}$ and $Ra\sim10^{10}-10^{12}$ in a horizontally periodic box with no-slip boundaries for two fluids with Prandtl number $Pr=0.1$ (towards liquid metals) and 5.2 (water). We show that LSVs are possible when viscous effects are strongly confined to the boundaries and no longer influence the bulk flow. At both $Pr$s, the flow is quasi-2D and a domain-filling vortex dipole is observed. [Preview Abstract] |
Sunday, November 24, 2019 8:26AM - 8:39AM |
C14.00003: Probing Regimes and Transitions in Rapidly Rotating Rayleigh-Bénard Convection Matteo Madonia, Jonathan Cheng, Andrés Aguirre-Guzmán, Herman Clercx, Rudie Kunnen Rayleigh-Bénard convection and rapidly rotating flows are two topics that have been frequently explored by fluid dynamicists; the former is driven by buoyancy and the latter is dominated by the Coriolis force. The interiors of many celestial bodies (e. g. Earth’s outer core, Jupiter’s atmosphere) consist of fluids that experience these two effects simultaneously at extreme values of the governing parameters, known as the geostrophic regime. Our setup TROCONVEX is able to investigate a far broader range of parameter space than previous studies by using a variety of tank heights up to 4 m tall, allowing us to explore the geostrophic regime in unprecedented detail and check predictions from asymptotic theories. Here we present heat transfer results, derived from temperature measurements from different states of the geostrophic regime. Various power-law scaling ranges between the governing parameters can be inferred, indicating that different flow morphologies are anticipated. With temperature measurements in the sidewall we plot temperature profiles of the different cases and more clearly distinguish these transitions based on the vertical temperature gradient at mid-height. Rescaled parameters show universality of such transitions. [Preview Abstract] |
Sunday, November 24, 2019 8:39AM - 8:52AM |
C14.00004: Effects of Lateral Confinement on Rapidly Rotating Rayleigh-Benard Convection Rudie Kunnen, Xander DeWit, Andres Aguirre Guzman, Matteo Madonia, Jonathan Cheng, Herman Clercx The study of the so-called geostrophic regime of rotating convection has received much recent attention. Named after the dominant geostrophic balance of pressure gradient and Coriolis acceleration in rotating flows, it is the appropriate regime to describe large-scale geophysical and astrophysical flows. Current state-of-the-art experiments have grown tall but remained comparatively narrow to accommodate the requirement of extreme parameter values (high Rayleigh numbers indicating strong thermal forcing but at the same time low Ekman numbers implying strong rotational constraint) while minimizing centrifugal buoyancy. Here we compare simulations of rotating convection in a slender cylinder and in a laterally periodic domain to address the effects of lateral confinement. In the cylinder a strong wall mode recirculation develops, that precesses anticyclonically and provides a significant contribution to the overall heat transfer (Nusselt number). However, the central convection outside of the wall-mode region displays heat-transfer properties identical to those of the periodic domain. Hence the slender cylinder is a valid geometry to study laterally unbounded convection on the provision that the wall region is excluded from the analysis. [Preview Abstract] |
Sunday, November 24, 2019 8:52AM - 9:05AM |
C14.00005: Heat transport by rotating Rayleigh-Bénard convection in cylindrical cells with various aspect ratios Jin-Qiang Zhong, Hao-Yuan Lu, Jun-Qiang Shi Rotating convection has been of interest for decades, yet there exists no generally accepted scaling law for heat transfer behavior in the geostrophic turbulence regime. We present high-precision measurements of the Nusselt number Nu as functions of the Rayleigh number Ra and the Ekman number Ek using cylindrical cells with various aspect ratio $\Gamma$. For a given $\Gamma$ data for Nu(Ra, Ek) in the geostrophic regime can be represented through one single power function $Nu{=}(Ra/Ra_c)^{\gamma}$, where $Ra_c{=}8.7Ek^{-4/3}$ is the critical Ra for the onset of convection. However, our experimental and numerical results reveal that the exponent $\gamma$ increases steeply with increasing $\Gamma$, leading to various parameter scaling for the transition towards the geostrophic regime. The present study may provide hints to reconcile previous results of the heat-transport scaling relationship in geostrophic turbulence. [Preview Abstract] |
Sunday, November 24, 2019 9:05AM - 9:18AM |
C14.00006: Rigorous and numerical upper bounds on heat transport in rapidly rotating Rayleigh B\'enard convection Jared Whitehead, Benjamin Pachev We present recent rigorous and numerical upper bounds on the heat transport for rapidly rotating Rayleigh-B\'enard convection using the asymptotically derived non-hydrostatic quasi-geostrophic equations. We also discuss the challenges inherent to developing upper bounds in the presence of rapid rotation, and propose some novel approaches to the same. [Preview Abstract] |
Sunday, November 24, 2019 9:18AM - 9:31AM |
C14.00007: Centrifugal Buoyancy and Non-Boussinesq Heat Transfer in Rotating Rayleigh-B\'{e}nard Convection Jonathan Cheng, Sietze Oostveen, Matteo Madonia, Rudie Kunnen In laboratory experiments of rotating Rayleigh-B\'{e}nard convection, conditions differ from the idealized problem in several significant ways. Important among these differences are the presence of centrifugal buoyancy -- which causes colder fluid to be driven radially outward and is characterized by the Froude number (Fr) -- and non-Boussinesq effects -- where variations in the fluid properties break the vertical symmetry of the temperature field. Here, we present a suite of rotating convection simulations under fixed heat flux and Coriolis influence, but with varying centrifugal forcing. The heat transfer is suppressed as Fr increases, with the transition occurring in agreement with the force balance arguments of Horn {\&} Aurnou, Phys. Rev. Lett. 120:204502, 2018. We compare the influence of centrifugation with that of non-Boussinesq effects by examining sidewall temperature gradients in the TROCONVEX rotating convection lab setup. At the sidewall, we expect these two effects to compete against one another. When the Rayleigh number is increased we observe the expected positive shift in the midplane temperature (Ahlers et al., J. Fluid Mech. 596:409-445, 2006), and when Fr is increased, the positive shift is present but reduced. [Preview Abstract] |
Sunday, November 24, 2019 9:31AM - 9:44AM |
C14.00008: Boundary Zonal Flow (BZF) in rotating turbulent convection Eberhard Bodenschatz, Xuan Zhang, Dennis Van Gils, Susanne Horn, Marcel Wedi, Lukas Zwirner, Guenter Ahlers, Robert Ecke, Stephan Weiss, Olga Shishkina We report the discovery and overall properties of a wall-localized mode of turbulent, rotating thermal convection, denoted as a boundary zonal flow (BZF). We use both direct numerical simulation and experimental measurements to investigate the BZF mode that emerges strongly in cylindrical cells with diameter to height ratios $\Gamma < 1$ and that appears to play a similar role for rotating convection as does the large scale circulation (LSC) of non-rotating convection. The coherent precessing structure of the BZF is manifest in bimodal temperature distributions and in very significant concentration of vertical heat transport near the boundary. The consequences of the BZF for the study of turbulent rotating thermal convection are discussed. [Preview Abstract] |
Sunday, November 24, 2019 9:44AM - 9:57AM |
C14.00009: Properties of the Boundary Zonal Flow (BZF) in rapidly rotating turbulent convection Xuan Zhang, Lukas Zwirner, Susanne Horn, Dennis van Gils, Marcel Wedi, Guenter Ahlers, Stephan Weiss, Eberhard Bodenschatz, Robert Ecke, Olga Shishkina Properties of the boundary zonal flow (BZF) in rapidly rotating Rayleigh-Benard convection are investigated numerically. Based on direct numerical simulations (DNS) using the finite-volume code GOLDFISH, we analyze in detail the BZF and, in particular, the traveling-mode structures and their dependencies on Ekman number. We also investigate the role of the BZF in the global heat transport in the system as well as the influence of the Prandtl number and the aspect ratio of the cylindrical convection cell on the BZF properties. [Preview Abstract] |
Sunday, November 24, 2019 9:57AM - 10:10AM |
C14.00010: Experimental investigation of the Boundary Zonal Flow (BZF) in rotating turbulent convection Stephan Weiss, Dennis Van Gils, Marcel Wedi, Xuan Zhang, Susanne Horn, Lukas Zwirner, Robert Ecke, Olga Shishkina, Guenter Ahlers, Eberhard Bodenschatz We report on measurements in rotating turbulent Rayleigh-B\'enard convection, in a 2.20\, m high cylindrical cell of aspect ratio between its diameter and height of $\Gamma =1/2$. The working fluids are nitrogen and pressurized (up to 19\,bar) sulfur hexafluoride (SF$_6$). We cover a large Rayleigh number range of $5\times 10^9 \leq Ra\leq 5\times 10^{14}$ at Prandtl numbers in the range $0.74\leq Pr\leq 0.96$. Using thermal probes close to the cylindrical sidewalls we measure characteristic properties of the recently found boundary zonal flow (BZF) as a function of Ra and the rotation rate, i.e., the inverse Rossby number (1/Ro). We also discuss in our talk the influence of the BZF on the heat transport. [Preview Abstract] |
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