Turbulent Rayleigh-Bénard convection under strong non-Oberbeck-Boussinesq conditions

Yik, Hiu-Fai; Valori, Valentina; Weiss, Stephan

doi:10.1103/physrevfluids.5.103502

Cited by 20 publications

(5 citation statements)

References 31 publications

(90 reference statements)

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“…With this technique, one can study buoyancy without heating the fluid. When a large density difference (e.g., above 5-10%) is obtained by heating a fluid, the results of the measurements are affected by non-Oberbeck-Boussinesq effects [22,23,24], because the approximation of constant fluid properties and density that depends linearly on temperature only in the buoyancy term is not applicable. The mixing of fluids with non-uniform refractive index causes deviations of the laser light and of the light scattered by the seeding particles [25,26,27].…”

Section: Methodsmentioning

confidence: 99%

High-Fidelity Experiments of Turbulent Buoyant Jets from Simultaneous Particle Image Velocimetry and Laser Induced Fluorescence

Valori,

Qin,

Petrov

et al. 2023

20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-20)

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Accurate models of turbulent buoyant flows are essential for the design of nuclear reactors thermal hydraulics and passive safety systems. However, available models fail to fully capture the physics of turbulent mixing when buoyancy becomes predominant with respect to momentum. Therefore, highfidelity experiments of well-controlled fundamental flows are needed to develop and validate more accurate models. We performed experiments of positive and negative turbulent buoyant jets, both in uniform and stratified environments, with the aim of understanding the thermal hydraulics of turbulent mixing with variable density and providing high-fidelity data for the development and validation of turbulence models. Non-intrusive, simultaneous Particle Image Velocimetry and Laser Induced Fluorescence measurements were carried out to acquire instantaneous velocity and concentration fields on a vertical section parallel to the axis of a jet in the self-similar region. The Refractive Index Matching method was applied to measure high-resolution buoyant jets with up to 8.6% density difference. These data are free of the typical errors that characterize optical measurements of buoyancy driven flows (e.g., natural and mixed convection) where the refractive index of the fluid is inhomogeneous throughout the measurement domain. Turbulent statistics and entrainment of buoyant jets in uniform and stratified environments are presented. These data are compared with non-buoyant jets in uniform environment, as a reference to investigate the effects of buoyancy and stratification on turbulent mixing. The results will be used for the assessment of current turbulence models and as basis for the development of a new one that captures turbulent mixing.

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Section: Methodsmentioning

confidence: 99%

High-Fidelity Experiments of Turbulent Buoyant Jets from Simultaneous Particle Image Velocimetry and Laser Induced Fluorescence

Valori,

Qin,

Petrov

et al. 2023

20th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-20)

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“…2010; Shishkina, Weiss & Bodenschatz 2016; Weiss et al. 2018; Roche 2020; Yik, Valori & Weiss 2020), as well as in water and glycerol (Manga & Weeraratne 1999; Ahlers et al. 2006; Sugiyama et al.…”

Section: Oberbeck–boussinesq Approximationmentioning

confidence: 99%

“…For instance, Ahlers et al (2008) conducted such an investigation for ethane. Various studies have explored NOB effects in RB convection in cryogenic helium and pressurized SF 6 (Roche et al 2010;Shishkina, Weiss & Bodenschatz 2016;Weiss et al 2018;Roche 2020;Yik, Valori & Weiss 2020), as well as in water and glycerol (Manga & Weeraratne 1999;Ahlers et al 2006;Sugiyama et al 2009;Horn, Shishkina & Wagner 2013;Horn & Shishkina 2014).…”

Section: Oberbeck-boussinesq Approximationmentioning

confidence: 99%

What Rayleigh numbers are achievable under Oberbeck–Boussinesq conditions?

Weiss,

Emran,

Shishkina

2024

J. Fluid Mech.

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The validity of the Oberbeck–Boussinesq (OB) approximation in Rayleigh–Bénard (RB) convection is studied using the Gray & Giorgini (Intl J. Heat Mass Transfer, vol. 19, 1976, pp. 545–551) criterion that requires that the residuals, i.e. the terms that distinguish the full governing equations from their OB approximations, are kept below a certain small threshold $\hat {\sigma }$ . This gives constraints on the temperature and pressure variations of the fluid properties (density, absolute viscosity, specific heat at constant pressure $c_p$ , thermal expansion coefficient and thermal conductivity) and on the magnitudes of the pressure work and viscous dissipation terms in the heat equation, which all can be formulated as bounds regarding the maximum temperature difference in the system, $\varDelta$ , and the container height, $L$ . Thus for any given fluid and $\hat {\sigma }$ , one can calculate the OB-validity region (in terms of $\varDelta$ and $L$ ) and also the maximum achievable Rayleigh number ${{Ra}}_{max,\hat {\sigma }}$ , and we did so for fluids water, air, helium and pressurized SF $_6$ at room temperature, and cryogenic helium, for $\hat {\sigma }=5\,\%$ , $10\,\%$ and $20\,\%$ . For the most popular fluids in high- ${{Ra}}$ RB measurements, which are cryogenic helium and pressurized SF $_6$ , we have identified the most critical residual, which is associated with the temperature dependence of $c_p$ . Our direct numerical simulations (DNS) showed, however, that even when the values of $c_p$ can differ almost twice within the convection cell, this feature alone cannot explain a sudden and strong enhancement in the heat transport in the system, compared with its OB analogue.

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“…However, when the temperature difference Δ between the hot and cold walls is large enough, the drastic changing of fluid properties should be taken into consideration. In this situation, the top-bottom symmetry of the system is broken and the bulk temperature θ c deviates from the arithmetic mean temperature of hot and cold walls θ m , which are known as non-OB (known as NOB) effects (Wu & Libchaber 1991;Yik, Valori & Weiss 2020).…”

Section: Asymmetric Mean Temperature Fieldsmentioning

confidence: 99%

Effects of radius ratio on annular centrifugal Rayleigh–Bénard convection

et al. 2021

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We report on a three-dimensional direct numerical simulation study of flow structure and heat transport in the annular centrifugal Rayleigh–Bénard convection (ACRBC) system, with cold inner and hot outer cylinders corotating axially, for the Rayleigh number range $Ra \in [{10^6},{10^8}]$ and radius ratio range $\eta = {R_i}/{R_o} \in [0.3,0.9]$ ( $R_i$ and $R_o$ are the radius of the inner and outer cylinders, respectively). This study focuses on the dependence of flow dynamics, heat transport and asymmetric mean temperature fields on the radius ratio $\eta$ . For the inverse Rossby number $Ro^{-1} = 1$ , as the Coriolis force balances inertial force, the flow is in the inertial regime. The mechanisms of zonal flow revolving in the prograde direction in this regime are attributed to the asymmetric movements of plumes and the different curvatures of the cylinders. The number of roll pairs is smaller than the circular roll hypothesis as the convection rolls are probably elongated by zonal flow. The physical mechanism of zonal flow is verified by the dependence of the drift frequency of the large-scale circulation (LSC) rolls and the space- and time-averaged azimuthal velocity on $\eta$ . The larger $\eta$ is, the weaker the zonal flow becomes. We show that the heat transport efficiency increases with $\eta$ . It is also found that the bulk temperature deviates from the arithmetic mean temperature and the deviation increases as $\eta$ decreases. This effect can be explained by a simple model that accounts for the curvature effects and the radially dependent centrifugal force in ACRBC.

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Turbulent Rayleigh-Bénard convection under strong non-Oberbeck-Boussinesq conditions

Cited by 20 publications

References 31 publications

High-Fidelity Experiments of Turbulent Buoyant Jets from Simultaneous Particle Image Velocimetry and Laser Induced Fluorescence

High-Fidelity Experiments of Turbulent Buoyant Jets from Simultaneous Particle Image Velocimetry and Laser Induced Fluorescence

What Rayleigh numbers are achievable under Oberbeck–Boussinesq conditions?

Effects of radius ratio on annular centrifugal Rayleigh–Bénard convection

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