Analysis and modelling of the turbulent diffusion of turbulent heat fluxes in natural convection

Chandra, Laltu; Grötzbach, G.

doi:10.1016/j.ijheatfluidflow.2008.01.009

Cited by 9 publications

(5 citation statements)

References 26 publications

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“…The investigation of roll structures in thermal RBC is well-documented (Getling 1998;Worner & Grotzbach 1998;Chandra & Grotzbach 2008). Here, threedimensional roll structures are produced by the input of thermal energy as opposed to electrical energy and several studies have drawn analogies between the two areas of physics (Tobazeon 1984;Castellanos 1991;Atten 1996Atten , 1998Vazquez, Perez & Castellanos 1996).…”

Section: Introductionmentioning

confidence: 99%

“…Hence, the electrical potential energy gradient is now no longer a constant in either space or time. Thermal RBC is well-understood and extensive research exists which is aimed towards the better understanding of both ordered convective motion as well as more turbulent convective motion (Xi & Gunton 1993;Worner & Grotzbach 1998;Chavanne et al 2001;Shishkina & Wagner 2006;Chandra & Grotzbach 2008;Verzicco & Sreenivasan 2008). The analogous dielectric EHD however has not been as well-examined, and in this paper analysis of turbulent dielectric EHD in three dimensions is presented for the first time.…”

Section: Introductionmentioning

confidence: 99%

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Turbulent three-dimensional dielectric electrohydrodynamic convection between two plates

Kourmatzis

Shrimpton

2012

J. Fluid Mech.

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The fundamental mechanisms responsible for the creation of electrohydrodynamically driven roll structures in free electroconvection between two plates are analysed with reference to traditional Rayleigh-Bénard convection (RBC). Previously available knowledge limited to two dimensions is extended to three-dimensions, and a wide range of electric Reynolds numbers is analysed, extending into a fully inherently three-dimensional turbulent regime. Results reveal that structures appearing in threedimensional electrohydrodynamics (EHD) are similar to those observed for RBC, and while two-dimensional EHD results bear some similarities with the three-dimensional results there are distinct differences. Analysis of two-point correlations and integral length scales show that full three-dimensional electroconvection is more chaotic than in two dimensions and this is also noted by qualitatively observing the roll structures that arise for both low (Re E = 1) and high electric Reynolds numbers (up to Re E = 120). Furthermore, calculations of mean profiles and second-order moments along with energy budgets and spectra have examined the validity of neglecting the fluctuating electric field E i in the Reynolds-averaged EHD equations and provide insight into the generation and transport mechanisms of turbulent EHD. Spectral and spatial data clearly indicate how fluctuating energy is transferred from electrical to hydrodynamic forms, on moving through the domain away from the charging electrode. It is shown that E i is not negligible close to the walls and terms acting as sources and sinks in the turbulent kinetic energy, turbulent scalar flux and turbulent scalar variance equations are examined. Profiles of hydrodynamic terms in the budgets resemble those in the literature for RBC; however there are terms specific to EHD that are significant, indicating that the transfer of energy in EHD is also attributed to further electrodynamic terms and a strong coupling exists between the charge flux and variance, due to the ionic drift term.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Turbulent three-dimensional dielectric electrohydrodynamic convection between two plates

Kourmatzis

Shrimpton

2012

J. Fluid Mech.

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“…(2008)) the error close to the wall can be significant, however what may be seen is that in the bulk where the isotropy assumption is valid, the agreement between the closures and the DNS values is excellent. In RBC scalar flux models, particularly in pressure scrambling models, it is common for the error between DNS and model closure to reach its minimum after approximately y/L=0.2 (Dol et al (1997); Chandra and Grotzbach (2008)) and this is observed here for EHD as well using most of the timescale definitions.…”

Section: Turbulent Scalar Flux Model Closuresmentioning

confidence: 56%

“…Dol et al (1997) observed significant errors of the order 100% when using the Daly Harlow approximation with thermal convection, and this is reflected here in the case of electro-convection, with the closure result providing only a qualitative agreement with the DNS and being within the error bounds for RBC (Dol et al (1997); Chandra and Grotzbach (2008)). In Chandra and Grotzbach (2008), errors in higher order gradient terms of Φ u 2 u 2 could exceed 100% near to the walls and with significant errors also apparent in the domain bulk. For the EHD closure, the agreement up to y/L=0.1 is to within 5% for most timescale variants however increasing to errors which can locally exceed 100% between y/L=0.…”

Section: Turbulent Scalar Flux Model Closuresmentioning

confidence: 76%

Turbulence closure models for free electroconvection

Kourmatzis

Shrimpton

2018

International Journal of Heat and Fluid Flow

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Electroconvection has been simulated in a number of recent studies, given its application in heat transfer enhancement, electrostatic atomizers and flow control. In practical applications, such as in charge injection atomizers, the electric Reynolds number can be sufficiently high such that the well-described ordered large scale electrohydrodynamic (EHD) instabilities that normally appear in electroconvection can dissipate and form into a wider distribution of length-scales. This purely electrohydrodynamically driven chaotic flow has features that resemble turbulent natural convection, and can dominate the operational regime of practical devices. Despite its practical relevance, Reynolds averaged turbulence model closures for EHD are unavailable, which currently makes direct numerical simulation the main viable option for EHD flows. Closure of EHD turbulence in free electro-convection is examined here through implementation of Reynolds stress model (RSM) closures using EHD specific timescales for the unclosed terms appearing in the turbulent scalar flux and space-charge scalar variance equations. A new closure for the highly non-linear triple correlation (q E u ), a term which is specific to EHD, is also presented. The work demonstrates that Reynolds stress closures are a feasible modeling route for EHD flows, with errors approaching similar values as in thermal Rayleigh-Benard convection at analogous levels of turbulence.

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“…It is known that turbulent kinetic energy k tends to be augmented in unstable stratification; the effect on ε is less clear. In the present simulations, the buoyancy effects on ε are neglected simply by setting G b to 0 in the transport equation for ε.…”

Section: Numerical Models and Methodsmentioning

confidence: 99%

Simulations of Axial Mixing of Liquids in a Long Horizontal Pipe for Industrial Applications

Zhao¹,

Derksen²,

Gupta

2010

Energy Fuels

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Various industrial applications require the use of common pipelines or tubing to simultaneously or sequentially deliver multiple types of liquids. Dependent upon the application, long pipelines or tubing can range from several meters to several kilometers in length, composed of significant horizontal and vertical sections. Axial mixing is an important aspect of such flows of liquids in succession from a safety and reliability point of view. It is anticipated that mixing is due to turbulence and buoyancy, with the latter as a result of density differences of the mixing fluids. This paper sets out a numerical simulation model based on computational fluid dynamics (CFD) to fundamentally understand the mixing behavior of two miscible fluids under actual industrial-project-specific conditions. To benchmark its accuracy, the simulation model is first verified with respect to its numerical parameters using a short, 10 m pipe. Subsequently, a 100 m horizontal pipe is modeled, and we show that these results can be used to extrapolate longer length pipes. Finally, the sensitivity of mixing with respect to the Reynolds and Richardson numbers (characterizing buoyancy) has been investigated.

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Analysis and modelling of the turbulent diffusion of turbulent heat fluxes in natural convection

Cited by 9 publications

References 26 publications

Turbulent three-dimensional dielectric electrohydrodynamic convection between two plates

Turbulent three-dimensional dielectric electrohydrodynamic convection between two plates

Turbulence closure models for free electroconvection

Simulations of Axial Mixing of Liquids in a Long Horizontal Pipe for Industrial Applications

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