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Turbulent fluxes of entropy and internal energy in temperature stratified flows
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Ben-Gurion University of the Negev, Israel.
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Ben-Gurion University of the Negev, Israel.
2015 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 81, no 5, 395810504Article in journal (Refereed) PublishedText
Abstract [en]

We derive equations for the mean entropy and the mean internal energy in low-Mach-number temperature stratified turbulence (i.e. for turbulent convection or stably stratified turbulence), and show that turbulent flux of entropy is given by Fs=σus, where σ is the mean fluid density, s is fluctuation of entropy and overbars denote averaging over an ensemble of turbulent velocity fields, u. We demonstrate that the turbulent flux of entropy is different from the turbulent convective flux, Fc=T σ us , of the fluid internal energy, where T is the mean fluid temperature. This turbulent convective flux is well-known in the astrophysical and geophysical literature, and it cannot be used as a turbulent flux in the equation for the mean entropy. This result is exact for low-Mach-number temperature stratified turbulence and is independent of the model used. We also derive equations for the velocity-entropy correlation, us, in the limits of small and large Péclet numbers, using the quasi-linear approach and the spectral τ approximation, respectively. This study is important in view of different applications to astrophysical and geophysical temperature stratified turbulence.

Place, publisher, year, edition, pages
Cambridge University Press, 2015. Vol. 81, no 5, 395810504
Keyword [en]
Aerodynamics, Astrophysics, Entropy, Fluid dynamics, Geophysics, Turbulence, Velocity, Fluid densities, Internal energies, Low Mach numbers, Mean fluid temperatures, Stratified flows, Stratified turbulence, Turbulent convection, Turbulent velocity fields, Mach number
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-181240DOI: 10.1017/S0022377815000963ISI: 000367573800044ScopusID: 2-s2.0-84945218456OAI: oai:DiVA.org:kth-181240DiVA: diva2:902929
Note

QC 20160212

Available from: 2016-02-12 Created: 2016-01-29 Last updated: 2016-02-12Bibliographically approved

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