Two-dimensional compressible convection extending over multiple scale heights
Two-dimensional simulations are used to study fully compressible thermal convection spanning multiple-density scale heights typical of a stellar envelope. The fluid is assumed to be a perfect gas with constant thermal conductivity and dynamic viscosity. The unstably stratified layer is thus represented by a polytropic index typically taken to be n = 1 (with n = 3/2 equivalent to an adiabatic stratification). The mean density ratio (bottom to top of the layer) ranges from about 1 to 21, with Rayleigh numbers up to about 1000 times critical. These highly nonlinear flows are studied with a two-dimensional numerical scheme based on a modified two-step Lax-Wendroff method. The convective motions in these simulations span the full height of the unstable layer, with no tendency to form a succession of rolls in the vertical as has been assumed in mixing length treatments of convection. Further, the flows remain subsonic because the center of the cell shifts toward the bottom of the layer as the density stratification is strengthened. The flows then display prominent downward-directed plumes surrounded by broader regions of upflow. The flow asymmetry leads to a kinetic energy flux which is directed downward, whereas the enthalpy or convective flux is upward. such asymmetry comes about because pressure fluctuations accentuate buoyancy driving in the downward plumes and can lead to buoyancy braking in the surrounding ascending flows. Compressional work is significant in the overall energetics.
- Research Organization:
- Colorado Univ., Boulder (USA)
- OSTI ID:
- 6060761
- Report Number(s):
- AD-A-162861/9/XAB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
STELLAR ATMOSPHERES
COMPRESSIBLE FLOW
CONVECTION
ASYMMETRY
DENSITY
DYNAMICS
ENTHALPY
GAS FLOW
HEIGHT
KINETIC ENERGY
MOTION
NUMERICAL ANALYSIS
PLUMES
SCALE HEIGHT
STARS
STRATIFICATION
SUBSONIC FLOW
THERMAL CONDUCTIVITY
VISCOSITY
ATMOSPHERES
DIMENSIONS
ENERGY
ENERGY TRANSFER
FLUID FLOW
HEAT TRANSFER
MASS TRANSFER
MATHEMATICS
MECHANICS
PHYSICAL PROPERTIES
THERMODYNAMIC PROPERTIES
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
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