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本文计算系列二维湍流热对流, Prandtl(Pr)数和Rayleigh(Ra)数范围分别为0.25—100和1×107—1×1012, 研究Reynolds(Re)数的变化规律. 以最大速度计算的Re数与Ra数存在标度律关系, 但中间出现间断. 研究表明, 大尺度环流形态由椭圆形到圆形的突变引起流动失稳, 导致最大速度值间断下降, 影响Re数变化趋势的连续性. 所有Pr数对应的流态突变特征Re数为常值, Rec约为1.4 × 104, 即当Re数达到特征Rec时, 大尺度环流形态会发生从椭圆形到圆形的突变. 间断点对应的Rac与Pr数之间存在标度关系Rac-Pr1.5. 对Ra数进行补偿平移, 所有Pr数的Re与RaPr–1.5的变化曲线重合, 不同Pr数有相同的间断临界点位置, RacPr–1.5 = 109.Rayleigh number (Ra) dependence in Rayleigh-Bénard (RB) convection has been studied by many investigators, but the reported power-law scaling expressions are different in these researches. Previous studies have found that when Ra reaches a critical value, the flow patterns change and a transition appears in the scaling of Nu(Ra) (where Nu represents Nusselt number) and Re(Ra) (where Re denotes Reynold number). The Grossmann-Lohse(GL) model divides the Ra-Pr(where Pr refers to Prandtl number) phase into several regions to predict the scaling expressions of Nu(Ra,Pr) and Re(Ra,Pr), indicating that the thermal dissipation behavior and kinetic dissipation behaviors are diverse in the different regions. Moreover, some physical quantities also show a transition and some structures in the flow fields, such as large scale circulation and boundary layer, change when Ra increases. In this work, we conduct a series of numerical simulations in two-dimensional RB convection with Ra ranging from 107 to 1012 and Pr ranging from 0.25 to 100, which is unprecedentedly wide. The relationship between the maximum velocity and Ra is investigated, and an unexpected drop happens when Ra reaches a critical value Rac, and Rac increases with Pr increasing. The Re number, which is defined as a maximum velocity, also shows a plateau at Rac. Before and after Rac, the Ra scaling exponent of Re remains 0.55, which gets smaller at very high Ra. Specially, under different Pr values, the plateau appears at Rec ≈ 1.4 × 104. In addition, a scaling Rac~Pr1.5 is found and the Ra is compensated for by Pr–1.5 to disscuss the relationship between Re and RaPr–1.5. It is interesting that the Re(RaPr–1.5) expressons at different Pr values well coincide, indicating a self-similarity of Re(RaPr–1.5). The plateau appears at RaPr–1.5 = 1 × 109, meaning that Rec would reach 1.4 × 104 at any Pr value when RaPr–1.5 = 1 × 109. To further investigate the plateau of Re, the flow patterns are compared with time-averaged velocity fields and we find that the large scale circulation (LSC) changes from ellipse to circle at Rac. In other words, the flow pattern will change into circular LSC at Rec at different Pr values, and Rec is a constant as mentioned above. This finding can help us to distinguish the two flow patterns with given Ra and Pr, and to predict the Re scaling in an appropriate range of Ra with different Pr values.
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Keywords:
- thermal convection /
- Reynolds number /
- flow pattern /
- Prandtl number
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[27] Bao Y, Luo J H, Ye M X 2017 J. Mech. 34 159Google Scholar
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[29] Shishkina O, Stevens R J A M, Grossmann S, Lohse D 2010 New J. Phys. 12 075022Google Scholar
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[31] Gao Z Y, Bao Y, Huang S D 2019 72nd Annual Meeting of the APS Division of Fluid Dynamics Seattle, Washington, November 23–26, G14.00003
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[1] Malkus W V R 1954 Proc. R. Soc. Lond. A 225 196Google Scholar
[2] Globe S, Dropkin D 1959 J. Heat Transfer 81 24Google Scholar
[3] Shraiman B I, Siggia E D 1990 Phys. Rev. A 42 3650Google Scholar
[4] Grossmann S, Lohse D 2000 J. Fluid Mech. 407 27Google Scholar
[5] Grossmann S, Lohse D 2001 Phys. Rev. Lett. 86 3316Google Scholar
[6] Grossmann S, Lohse D 2002 Phys. Rev. E 66 016305Google Scholar
[7] Grossmann S, Lohse D 2004 Phys. Fluids 16 4462Google Scholar
[8] Stevens R J A M, Van Der Poel E P, Grossmann S, Lohse D 2013 J. Fluid Mech. 730 295Google Scholar
[9] Xia K Q, Lam S, Zhou S Q 2002 Phys. Rev. Lett. 88 064501Google Scholar
[10] van der Poel E P, Stevens R J A M, Lohse D 2013 J. Fluid Mech. 736 177Google Scholar
[11] Khurana A 1988 Phys. Today 41 17Google Scholar
[12] Willis G E, Deardorff J W 1970 J. Fluid Mech. 44 661Google Scholar
[13] Krishnamurti R 1970 J. Fluid Mech. 42 309Google Scholar
[14] Ahlers G 1974 Phys. Rev. Lett. 33 1185Google Scholar
[15] McLaughlin J B, Martin P C 1974 Phys. Rev. Lett. 33 1189Google Scholar
[16] Heslot F, Castaing B, Libchaber A 1987 Phys. Rev. A 36 5870Google Scholar
[17] Castaing B, Gunaratne G, Heslot F, Kadanoff L, Libchaber A, Thomae S, Wu X Z, Zaleski S, Zanetti G 1989 J. Fluid Mech. 204 1Google Scholar
[18] Sano M, Wu X Z, Libchaber A 1989 Phys. Rev. A 40 6421Google Scholar
[19] 包芸, 何建超, 高振源 2019 68 164701Google Scholar
Bao Y, He J C, Gao Z Y 2019 Acta Phys. Sin. 68 164701Google Scholar
[20] Gao Z Y, Luo J H, Bao Y 2018 Chin. Phys. B 27 104702Google Scholar
[21] Verzicco R, Camuss I R 1999 J. Fluid Mech. 383 55Google Scholar
[22] Kerr R M 1996 J. Fluid Mech. 310 139Google Scholar
[23] Li X M, He J D, Tian Y, Hao P, Huang S D 2021 J. Fluid Mech. 915 A60Google Scholar
[24] Chen X, Huang S D, Xia K Q, Xi H D 2019 J. Fluid Mech. 877 R1Google Scholar
[25] Xu A, Chen X, Xi H D 2021 Phys. Fluids 910 A33Google Scholar
[26] Werne J, Deluca EE, Rosner R, Cattaneo F 1991 Phys. Rev. Lett. 67 3919Google Scholar
[27] Bao Y, Luo J H, Ye M X 2017 J. Mech. 34 159Google Scholar
[28] Sun X H 1995 Parallel Comput. 21 1241Google Scholar
[29] Shishkina O, Stevens R J A M, Grossmann S, Lohse D 2010 New J. Phys. 12 075022Google Scholar
[30] He J C, Fang M W, Gao Z Y, Huang S D, Bao Y 2021 Chin. Phys. B 30 094701Google Scholar
[31] Gao Z Y, Bao Y, Huang S D 2019 72nd Annual Meeting of the APS Division of Fluid Dynamics Seattle, Washington, November 23–26, G14.00003
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