Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000nyasa.898....1p&link_type=abstract
Annals of the New York Academy of Sciences: Astrophysical Turbulence and Convection, vol. 898, p. 1
Astronomy and Astrophysics
Astrophysics
7
Convection, Convection Cells, Slabs, Spheroids, Boundary Conditions, Equations Of Motion, Kolmogorov Theory, Mixing Length Flow Theory, Thermal Conductivity, Three Dimensional Models, Simulation, Compressible Flow, Turbulent Flow
Scientific paper
Three-dimensional numerical simulations of compressible turbulent thermally driven convection, in both slab and spheroidal geometries, are reviewed and analyzed in terms of velocity spectra and mixing-length theory. The same ideal gas model is used in both geometries, and resulting flows are compared. The piecewise-parabolic method (PPM), with either thermal conductivity or photospheric boundary conditions, is used to solve the fluid equations of motion. Fluid motions in both geometries exhibit a Kolmogorov-like k(sup -5/3) range in their velocity spectra. The longest wavelength modes are energetically dominant in both geometries, typically leading to one convection cell dominating the flow. In spheroidal geometry, a dipolar flow dominates the largest scale convective motions. Downflows are intensely turbulent and up drafts are relatively laminar in both geometries. In slab geometry, correlations between temperature and velocity fluctuations, which lead to the enthalpy flux, are fairly independent of depth. In spheroidal geometry this same correlation increases linearly with radius over the inner 70 percent by radius, in which the local pressure scale heights are a sizable fraction of the radius. The effects from the impenetrable boundary conditions in the slab geometry models are confused with the effects from non-local convection. In spheroidal geometry nonlocal effects, due to coherent plumes, are seen as far as several pressure scale heights from the lower boundary and are clearly distinguishable from boundary effects.
Jacobs Michael L.
Porter David H.
Woodward Paul R.
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