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Abstract: We analyze stellar convection with the aid of 3D hydrodynamic simulations,introducing the turbulent cascade into our theoretical analysis. We deviseclosures of the Reynolds-decomposed mean field equations by simple physicalmodeling of the simulations we relate temperature and density fluctuations viacoefficients; the procedure CABS, Convection Algorithms Based on Simulationsis terrestrially testable and is amenable to systematic improvement. We developa turbulent kinetic energy equation which contains both nonlocal and timedependent terms, and is appropriate if the convective transit time is shorterthan the evolutionary time scale. The interpretation of mixing-length theoryMLT as generally used in astrophysics is incorrect; MLT forces the mixinglength to be an imposed constant. Direct tests show that the damping associatedwith the flow is that suggested by Kolmogorov. The eddy size is approximatelythe depth of the convection zone, and this dissipation length corresponds tothe -mixing length-. New terms involving local heating by turbulent dissipationshould appear in the stellar evolution equations. The enthalpy flux-convective luminosity- is directly connected to the buoyant acceleration,and hence the velocity scale. MLT tends to systematically underestimate thisvelocity scale. Quantitative comparison with a variety of 3D simulationsreveals a previously recognized consistency. Examples of application to stellarevolution will be presented in subsequent papers in this series.



Author: David Arnett, Casey Meakin, P. A. Young

Source: https://arxiv.org/



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