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近二十年来,微重力流体开展了半浮区液桥热毛细对流的不稳定性与转捩的研究.文中给出了热毛细振荡对流发生的临界参数,分析了液桥几何位形(尺度比,体积比)、物理参数及传热参数对临界Maxangoni的影响.报导了有关的地面模拟实验,微重力实验以及本问题的线性稳定性分析、能量分析和数值模拟结果,并介绍了定常轴对称热毛细对流通过非定常振荡热毛细对流到湍流的转捩过程和三种热毛细振荡对流的产生机理. 相似文献
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开展大尺寸液桥浮力-热毛细对流地面实验, 探究流场转捩的临界条件及临界状态附近的流动情况. 通过粒子图像测速方法(PIV) 获得流体速度场, 研究液桥内部定常和转捩后的流场结构以及流体运动规律;并用红外热像仪测量液桥自由面温度分布, 研究流体流动的时空演化和温度振荡. 实验发现大尺寸半浮区液桥浮力-热毛细对流临界值与几何参数有关, 在大普朗特(Prandtl) 数情况下, 流场存在由稳定态向不稳定态再到混沌的转捩过程, 在临界马兰哥尼(Marangoni) 数附近, 流场内会出现行波现象, 流动模式也会随高径比的变化而发生变化;当继续增大马兰哥尼数, 流动会进入混沌状态. 相似文献
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主要研究矩形液池热毛细对流的分岔转捩. 通过测量流体内部温度振荡情况, 详细研究了热毛细对流的转捩过程和转捩途径. 实验发现, 矩形液池热毛细对流的转捩过程依次经历了定常、规则振荡、不规则振荡的阶段. 对于不同普朗特数的硅油在不同长高比情况下, 通向混沌的途径不同. 在转捩过程中, 随着温差的增加, 普朗特数在16 (1cSt) 以下和普朗特数为25 (1.5cSt)、长高比为26 的硅油热毛细对流主要以准周期分岔的转捩方式为主;而普朗特数为25 以上的则以倍周期分岔的转捩方式为主;两种分岔有时还会伴随有切分岔形式的出现.实验中还观察到了表面波动和对流涡胞振荡等现象. 相似文献
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大普朗特数大液桥浮力-热毛细对流地面实验 总被引:1,自引:1,他引:0
通过地面实验研究大尺寸液桥的浮力-热毛细对流. 实验采用2cst硅油(Pr=28.571),研究了不同高径比(A=l/d)和体积比的液桥起振,分析了温度振荡频率及相位变化,探讨了热流体波的问题. 实验液桥的桥柱直径为20mm,由于受重力的限制,建立了3~4.25mm范围内的矮桥. 通过伸入液桥内部不同位置的热电偶的温度信号,发现流场是同时起振的,不同的桥高和体积比有不同的振荡模式,并且随着温差的增加,频率近似以线性增加,各点的振荡相位是一个连续性变化的过程. 不同高径比的液桥转捩到混沌的途径是不一样的. 相似文献
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浮区热毛细对流 总被引:1,自引:0,他引:1
概述了浮区中平行于自由面的表面张力梯度驱动热毛细对流领域的研究.
研究兴趣集中于振荡热毛细对流的起振,
或者说从定常流动到振荡流动的转捩. 起振依赖于一系列的临界参数,
临界关系可以表示为这些临界参数的复杂函数. 实验结果表明,
振荡流中速度的变化和平均流动的速度有相同的量级, 而其它量的变化,
比如温度和自由面半径的波动, 相比于它们的平均量而言则要小得多.
因此, 起振应是流体中动力学过程的结果, 该问题是强非线性的.
在过去几十年中, 一些理论模型被引入来研究这个问题,
使用的方法包括理论分析方法、 线性不稳定性分析方法、
能量稳定性分析方法以及非定常的三维直接数值模拟.
其中直接数值模拟被认为是对强非线性过程进行深入分析的最适合方法,
通常能得到和实验较符合的结果.
从振荡热毛细对流向湍流的转捩提供了一个研究混沌行为的新系统,
开创了一个非线性科学的新前沿, 是一个集中了大量近期工作的研究热点.
该文对浮区热毛细对流作了一个回顾, 包括理论模型和分析,
以及实验研究. 相似文献
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束继祖 《Acta Mechanica Sinica》2003,19(2):127-133
In the present paper, the experimental studies on thermocapillary convection are reviewed. The author‘s interest is mainly focused on the onset of oscillatory thermocapillary convection,the features of oscillatory flow pattern, and the critical Marangoni number related with temperature and free surface oscillation. The coordinated measurement in a microgravity environment of a drops haft is also addressed. 相似文献
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Effect of vertical heat transfer on thermocapillary convection in an open shallow rectangular cavity
In order to understand the effect of the vertical heat transfer on thermocapillary convection characteristics in a differentially
heated open shallow rectangular cavity, a series of two- and three-dimensional numerical simulations were carried out by means
of the finite volume method. The cavity was filled with the 1cSt silicone oil (Prandtl number Pr = 13.9) and the aspect ratio ranged from 12 to 30. Results show that thermocapillary convection is stable at a small Marangoni
number. With the increase of the heat flux on the bottom surface, thermocapillary convection transits to the asymmetrical
bi-cellular pattern with the opposite rotation direction. The roll near the hot wall shrinks as the Marangoni number increases.
At a large Marangoni number, numerical simulations predict two types of the oscillatory thermocapillary flow. One is the hydrothermal
wave, which is dominant only in a thin cavity. The other appears in a deeper cavity and is characterized by oscillating multi-cellular
flow. The critical Marangoni number for the onset of the oscillatory flow increases first and then decreases with the increase
of the vertical heat flux. The three-dimensional numerical simulation can predict the propagating direction of the hydrothermal
wave. The velocity and temperature fields obtained by three-dimensional simulation in the meridian plane are very close to
those obtained by two-dimensional simulation. 相似文献
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Finite-amplitude convective motions that arise in a two-layer system under the influence of the thermocapillary mechanism are studied. Numerical calculations have been made by the grid method for different relationships between the parameters of the fluids. A new type of instability of equilibrium is found — thermocapillary oscillations. The evolution of the oscillatory motions as the Marangoni number changes is studied. The following forms of transitions between convection regimes are established: transition from oscillatory to steady motion through an unbounded increase in the period; bifurcation of the period, accompanied by rearrangement of the three-dimensional structure of the flow. It is shown that the thermogravitational instability mechanism leads to suppression of the oscillations. 相似文献
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In a two-layer system loss of stability may be monotonic or oscillatory in character. Increasing oscillatory perturbations have been detected in the case of both Rayleigh [1, 2] and thermocapillary convection [3–5]; however, for many systems the minimum of the neutral curve corresponds to monotonic perturbations. In [5] an example was given of a system for which oscillatory instability is most dangerous when the thermogravitational and thermocapillary instability mechanisms are simultaneously operative. In this paper the occurrence of convection in a two-layer system due to the combined action of the Rayleigh (volume) and thermocapillary (surface) instability mechanisms is systematically investigated. It is shown that when the Rayleigh mechanism operates primarily in the upper layer of fluid, in the presence of a thermocapillary effect oscillatory instability may be the more dangerous. If thermogravitational convection is excited in the lower layer of fluid, the instability will be monotonic.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 166–170, January–February, 1987. 相似文献
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Liping Yao Zhong Zeng Yi Zhang Zhouhua Qiu Huan Mei Liangqi Zhang Yongxiang Zhang 《Heat and Mass Transfer》2012,48(12):2103-2111
The effects of rotating magnetic field (RMF) on the three-dimensional thermocapillary flow of semiconductor melt (Pr?=?0.01) in a floating half-zone model under microgravity are investigated numerically by the finite volume method. The results indicate that the thermocapillary flow without magnetic field is a steady three-dimensional convection for Ma?=?40 in a floating half-zone model with As?=?1, and the convection evolves to an oscillatory three-dimensional flow by applying 1–6?mT RMF with 50?Hz rotating frequency. Based on the fast Fourier transform spectrum, the convection is confirmed to be a periodically oscillating flow, the oscillatory main frequency, 1.59?×?10?3?Hz for 1?mT RMF and 5.84?×?10?2?Hz for 6?mT RMF, increases with the magnetic strength. However, with increasing the magnetic field strength up to 7?mT, the three-dimensional thermocapillary flow is effectively controlled and the convection turns into a steady axisymmetrical one. 相似文献