浮力-热毛细对流表面位型研究

将栅线结构光源系统与图像处理技术相结合,形成一种实时诊断浮力-热毛细对流表面形貌的光学测量系统.研究两端带有温差的矩形池内薄层流体的表面变形.应用图像互相关方法对实验结果进行计算和分析,得到了流体表面变形定量的实验结果.实验结果表明了在浮力-热毛细对流的发展过程中,出现流体表面变形,温度梯度、表面张力、浮力、液固亲润问题、以及壁面温度决定了该表面变形大小和变形方向.     

搭载实践十号卫星的蒸发液滴空间实验研究

实践十号蒸发对流实验以微重力环境中的蒸发相变流体界面过程为主要研究内容,利用空间微重力条件下浮力对流消失和热毛细对流起主导作用的特殊环境,实验研究置于加热底板的蒸发液滴相变过程中表面蒸发与表面张力驱动对流的耦合机理.利用研制的空间蒸发对流装置完成了在轨工况的科学匹配实验,得到了不同工况(温度、液滴大小、加热底板材料)下蒸发液滴形貌和热流量、蒸发速率等变化规律.为后续空间实验结果的比对分析提供了前期结果.     

大尺寸液桥热毛细对流失稳性地面实验研究

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.      

半浮区液桥振荡对流的微重力实验

利用日本微重力中心８００ｍ落井装置，完成了半浮区液桥振荡对流的微重力实验，对振荡对流的典型物理量诸如内部温度、流场、自由面边缘变化及表面波进行了综合测量。实验结果给出了振荡对流由地球重力环境向微重力环境的过渡，以及不同几何参数半浮区液桥的振荡特征，并首次获得了微重力环境下热毛细对流的表面波位形及边缘振荡特征．     

有关多层流体对流的研究

简述多层不相混流体系统的研究发展，尤其是在空间材料生长过程中的应用；介绍多层流体系统内流体对流及传热现象，以及利用理论分析、实验研究和数值模拟方法研究二层及三层流体内的自然对流及热毛细对流的成果，并分析探讨覆盖液体层对被覆盖液体的动力控制特性及其系统的稳定性     

薄膜沿加热平板下落的稳定性分布

本文分析了薄膜沿加热平板下落的稳定性。在时间模式下，发现流动的不稳定性是由表面波不稳定和加毛细不稳定构成的，同时当流体的热扩散越大以及界面热量损失越小时，热毛细不稳定越剧烈，在时空模式下，流动随着Marangoni数的增大。流动有可能从对流不稳定过渡到绝对不稳定，这一结论尚待实验验证。     

浮力对混合对流流动及换热特性的影响

用热线和冷线相结合的技术测量垂直圆管内逆混合对流流体的平均速度、 温度以及它们的脉动. 较详细地研究了浮力对逆混合对流的流动特性和传热特性的影响. 评 估了实验中采用的冷线测量温度补偿速度探头温度敏感的影响. 逆混合对流的传热结果用无 量纲参数Ω (Ω= Grd / Red2 )来表示，其中，基于管道直 径的雷诺数Red变化范围为900~18000, 浮力参数Ω变化范围为 0.004899~0.5047. 研究结果表明，浮力对逆混合对流的换热有强化作用. 随着葛拉晓夫数Grd的增加，温度脉动，流向雷诺正应力和流向温度通量增 大，并且在靠近壁面的流体区域尤其明显. 热线与冷线相结合的技术适合于研究非绝热的流 动测量，可以用于研究浮力对流动和换热特性的影响.     

半浮区热毛细对流的不稳定性与转捩

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．      

半浮区热毛细对流的不稳定性与转捩

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．     

矩形液池热毛细对流转捩途径研究

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.      

旋涡与行进表面水波相互作用的实验研究

采用振动板式造波器在二维水槽中生成近似单色的行进表面水波，采用夹板式涡发生器生成稳定上浮的涡对，在Ｆｒｏｕｄｅ数约为０．５的条件下，得到了水下涡对与不同波长和振幅的行进表面水波相互作用时的干扰图象，以实验方法验证了理论分析和数值计算的结果，并为进一步研究旋涡与行进表面水波的相互作用提供了一种实验研究方法     

实践十号卫星项目——热毛细对流振荡特征的地面研究

上部开口环形液池在水平径向温度梯度作用下会出现内部温度和自由面的振荡,本文研究了二者发生的临界条件.环形液池内柱加热外壁制冷,以0.5℃/min的速率线性升温得到水平径向温差,T型热电偶测量液层内部单点温度,高精度激光位移传感器测量液层自由面某点形变.随两端温差增加,当超过某一临界温度△T_(cr)时,开始出现振荡.实验结果表明,对同一种硅油,两种振荡的临界条件随液层厚度具有相同的变化趋势.对不同普朗特(Prandtl)数(Pr)的硅油,振荡临界条件临界马兰哥尼数(Ma_(cr))随着邦德数(Bo)的增加而变大.本文工作是中国科学院科学先导专项SJ-10返回式科学实验卫星项目-热毛细对流表面波空间实验研究的地面研究结果,该工作为空间实验提供前期的基础科学研究数据和实验保障.     

The unstable modes of natural convection boundary layer

The instability of natural convection boundary layer around a vertical heated flat plate is analyzed theoretically in this paper. The results illustrate that the “loop” in the neutral curve is not a real loop but a twist of the curve in the frequency-wave number-Grashof number space, and there is only one unstable mode at small Prandtl numbers. Specially, when the Prandtl number is large enough two unstable modes will be found in the “loop” region. Along the amplyfying surface intersection the two unstable modes have the same Grashof number, wave number and frequency but different amplifying rates. Their instability characteristics are analyzed and the criterion for determining the existence of the multi-unstable modes is also discussed.     

Non-Darcy natural convection from a vertical wavy surface in a porous medium

We examine the combined effect of spatially stationary surface waves and the presence of fluid inertia on the free convection induced by a vertical heated surface embedded in a fluid-saturated porous medium. We consider the boundary-layer regime where the Darcy-Rayleigh number, Ra, is very large, and assume that the surface waves have O(1) amplitude and wavelength. The resulting boundary-layer equations are found to be nonsimilar only when the surface is nonuniform and inertia effects are present; self-similarity results when either or both effects are absent. Detailed results for the local and global rates of heat transfer are presented for a range of values of the inertia parameter and the surface wave amplitude.     

Improvement of moving particle semi‐implicit method for simulation of progressive water waves

Precise simulation of the propagation of surface water waves, especially when involving breaking wave, takes a significant place in computational fluid dynamics. Because of the strong nonlinear properties, the treatment of large surface deformation of free surface flow has always been a challenging work in the development of numerical models. In this paper, the moving particle semi‐implicit (MPS) method, an entirely Lagrangian method, is modified to simulate wave motion in a 2‐D numerical wave flume preferably. In terms of consecutive pressure distribution, a new and simple free surface detection criterion is proposed to enhance the free surface recognition in the MPS method. In addition, a revised gradient model is deduced to diminish the effect of nonuniform particle distribution and then to reduce the numerical wave attenuation occurring in the original MPS model. The applicability and stability of the improved MPS method are firstly demonstrated by the calculation of hydrostatic problem. It is revealed that these modifications are effective to suppress the pressure oscillation, weaken the local particle clustering, and boost the stability of numerical algorithm. It is then applied to investigate the propagation of progressive waves on a flat bed and the wave breaking on a mild slope. Comparisons with the analytical solutions and experimental results indicate that the improved MPS model can give better results about the profiles and heights of surface waves in contrast with the previous MPS models. Copyright © 2017 John Wiley & Sons, Ltd.     

Water waves generated due to initial axisymmetric disturbances in water with an ice-cover

This paper is concerned with the generation of water waves due to prescribed initial axisymmetric disturbances in a deep ocean with an ice-cover modelled as a thin elastic plate. The initial disturbances are either in the form of an impulsive pressure distributed over a certain region of the ice-cover or an initial displacement of the ice-cover. Assuming linear theory, the problem is formulated as an initial-value problem in the velocity potential describing the ensuing motion in the fluid. In the mathematical analysis, the Laplace and Hankel transform techniques have been utilised to obtain the deformation of the ice-covered surface as an infinite integral in each case. The method of stationary phase is used to evaluate the integral for large values of time and distance. Figures are drawn to show the effect of the presence of ice-cover on the wave motion.     

Behavior of the surface of a bubbly liquid after detonation wave impact

In safety engineering, one position of interest inside heterogeneous systems of the type liquid–gas is the contact surface between these two phases. Under certain conditions, e.g. shock wave impact, phenomena can take place at this position that can have a significant influence on the explosion behavior of the system. In this work an investigation is presented about the existence of such phenomena on the surface of liquid cyclohexane with or without the existence of oxygen containing bubbles. The observations have been performed during the time before, as well as after, a detonation wave reflection on that surface. High-speed pressure and optical measurements have been applied. Apart from the experimental observations, also a theoretical analysis and discussion is presented in this contribution, which contains the comparison between calculated and experimental values.     

Radiation effect on mixed convection from a horizontal surface in a porous medium

The effect of thermal radiation on the non-Darcy mixed convection flow over a non-isothermal horizontal surface immersed in a saturated porous medium has been studied. The wall temperature is assumed to have a power-law variation with the distance measured from the leading edge of the plate. The non-linear coupled parabolic partial differential equations governing the flow have been solved numerically using a finite-difference scheme. For some particular cases, the self-similar solution has also been obtained. The heat transfer is found to be strongly influenced by the radiative flux number, buoyancy parameter, variation of wall temperature, non-Darcy parameter and the nature of the free stream velocity.     

Free convection heat transfer from an isothermal wavy surface in a porous enclosure

The coupled streamfuction–temperature equations governing the Darcian flow and convection process in a fluid-saturated porous enclosure with an isothermal sinusoidal bottom sun face, has been numerically analyzed using a finite element method (FEM). No restrictions have been imposed on the geometrical non-linearity arising from the parameters like wave amplitude (a), number of waves per unit length (N), wave phase (Φ), aspect ratio (A) and also on the flow driving parameter Rayleigh number (Ra). The numerical simulations for varying values of Ra bring about interesting flow features, like the transformation of a unicellular flow to a multicellular flow. Both with increasing amplitude and increasing number of waves per unit length, owing to the shift in the separation and reattachment points, a row–column pattern of multicellular flow transforms to a simple row of multicellular flow. A cycle of n celluar and n+1 cellular flows, with the flow in adjacent cells in the opposite direction, periodically manifest with phase varying between 0 and 360°. The global heat transfer into the system has been found to decrease with increasing amplitude and increasing number of waves per unit length. Only marginal changes in the global heat flux are observed, either with increasing Ra or varying Φ. Effectively, sinusoidal bottom surface undulations of the isothermal wall of a porous enclosure reduces the heat transfer into the system. © 1998 John Wiley & Sons, Ltd.