Un Co Rr Ec Te D Pr Oo F Fludyn 599
نویسندگان
چکیده
An inÿnite uid with a vertical cubic temperature proÿle in the absence of uid motion is considered as a model for penetrative convection in which a central unstably stratiÿed uid layer is bounded above and below by stably stratiÿed layers. Turbulence statistics from direct and large eddy numerical simulations for the mean temperature gradient, the velocity and temperature variances and the heat ux are presented for Rayleigh numbers R up to four orders of magnitude above critical. By means of a simpliÿed second-moment closure, analytical scaling laws for the statistics are determined. For high Rayleigh numbers, the mean temperature gradient approaches zero in a central well-mixed layer, a reduced positive (stable) value in upper and lower partially mixed layers, and an unmixed value far above and below. The temperature variance is a factor of R 1=3 larger in the partially mixed layers compared to the well-mixed layer; the velocity variance and heat ux scales the same in both layers. Approximation of the three layers by a two layer model yields an estimate for the height of the mixed layer: the height decreases slowly with increasing Rayleigh number and at the highest Rayleigh number simulated is approximately 30% longer than the unstable layer in the absence of uid motion.
منابع مشابه
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8 Article history: 9 Received 7 September 2009 10 Received in revised form 10 February 2010 11 Accepted 11 February 2010 12 Available online xxxx 1345 16
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This paper presents majorization results for PH-generators. Based on the majorization results, bounds on the moments and Laplace-Stieltjes transforms of phase-type distributions are found. Exponential distributions and Coxian distributions are identified to be extremal PH-distributions with respect to all the moments and Laplace-Stieltjes transforms for certain subsets of PH-distributions. UN C...
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