Two Dimensional Compressible Convection Extending Over Multiple Scale Heights
Two Dimensional Compressible Convection Extending Over Multiple Scale Heights
复制标题
跨越多个尺度高度的二维可压缩对流
DOI：
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发表时间：
1984
期刊：
影响因子：
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通讯作者：
J. Massaguer
中科院分区：
文献类型：
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作者：
N. Hurlburt;J. Toomre;J. Massaguer
二维模拟被用来研究完全可压缩的热对流跨越多密度尺度高度典型的恒星信封。流体被假定为具有恒定的热导率和动态粘度的理想气体。因此，不稳定分层层由通常取为n = 1的多变指数表示（其中n = 3/2相当于绝热分层）。平均密度比（层的底部到顶部）的范围从约1到21，其中瑞利数高达约1000倍临界值。这些高度非线性流动的研究与二维数值方案的基础上修改的两步Lax-Wendroff方法。在这些模拟中的对流运动跨越整个高度的不稳定层，没有倾向于形成一个连续的辊在垂直方向上已被假定在对流的混合长度处理。此外，流动保持亚音速，因为随着密度分层的加强，单元的中心向层的底部移动。然后，流动显示出明显的向下的羽流，周围是更广泛的上流区域。流动的不对称性导致动能通量向下，而焓通量或对流通量向上。这种不对称性的产生是因为压力波动增强了向下羽流中的浮力驱动，并可能导致周围上升气流中的浮力制动。压缩功在总能量学中是重要的。«少
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. suchmore » 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.« less