海上摇晃条件下油轮货油温降规律数值模拟研究

油轮在海上运输过程中会发生旋转运动和平移运动,货油温降过程为伴随着自由液面运动的非稳态混合对流过程,水热力规律较静止情况更为复杂。基于FLUENT动网格的VOF模型对摇摆(旋转运动)条件下的原油自由液面运动规律及舱内货油温降规律进行系统研究。结果表明,摇摆一方面不断改变浮升力相对于船舱的方向,使得自然对流不断被扰动;另一方面导致自由液面与船舱内壁及舱内顶部空气间的相对运动,使静止条件下的自然对流变成强制对流。以上两方面的影响均对舱内原油与舱外海水间的传热产生了显著的强化作用,使得温降速率与旋转角速度呈正相关。     

液态金属镓自然对流换热数值模拟

为更好地得到液态金属的流动和传热特性,模拟了液态金属流体镓(Ga)自然对流流动和传热过程.采用单流体模型研究液态金属流体Ga的流动特性和传热机理,考虑边界条件对自然对流的影响,选用合适的边界条件进行了模拟.结果表明,该工况下的传热以导热为主,速度矢量是顺时针旋转分布,并与实验数据较好吻合.Gr数对液态金属Ga自然对流影...     

风雨联合作用下的桥梁主梁静力特性

针对风雨联合作用下的大跨度桥梁风雨致静力作用问题,以开槽双箱梁桥梁主梁节段模型为研究对象,利用在大气边界层风洞中搭建的风雨联合作用试验系统,完成节段模型在风雨耦合作用环境下的静力特性试验。通过分析桥梁主梁风雨致静力相对纯风作用下风致静力增量,进而获取降雨对桥梁主梁风致静力作用影响的相关规律。试验结果显示:流场的改变以及水膜作用对桥梁主梁风致阻力影响较大,雨的冲击力有一定贡献。雨的质量、冲击力以及流场改变和水膜作用对桥梁主梁风致升力均有一定贡献;流场改变和水膜作用相对于雨的质量、冲击力对桥梁主梁风致扭矩贡献较大。试验结果表明:流场的改变以及水膜作用对桥梁结构的静力特性影响突出。     

Liquid spreading on a pre-wetted biomimetic surface inspired by a dog’s tongue

Liquid film flow widely exists in industries due to its high thermal efficiency and low flow flux. The spreading of the liquid film is strongly influenced by the properties of the working surface. A biomimetic surface with multi-scale structures inspired by the skin of a dog’s tongue is proposed in this paper for the enhancement of heat and mass transfer. The spreading and flow behaviors of a gravity-driven liquid falling down the pre-wetted biomimetic surface are compared with that on the smooth surfaces, via the combination of numerical simulations using the volume of fluid (VOF) method, and experimental measurements using high-speed imaging. On the pre-wetted smooth substrate, liquid merges with two droplets before the free surface of the liquid slowly develops into a parabolic shape. In contrast, on the biomimetic surface, liquid rapidly and uniformly spreads into a thin film which could effectively enhance mass transfer in both spanwise and streamwise directions. The characteristics and distribution of the microstructures on the proposed biomimetic surface are potentially to be used to guide the design of the surface in high efficiency heat exchangers and reactors.     

Characters of surface deformation and surface wave in thermal capillary convection

In the field of fluid mechanics, free surface phenomena is one of the most important physical processes. In the present research work, the surface deformation and surface wave caused by temperature difference of sidewalls in a rectangular cavity have been investigated. The horizontal cross-section of the container is 52 mm×42 mm, and there is a silicon oil layer of height 3.5 mm in the experimental cavity. Temperature differ- ence between the two side walls of the cavity is increased gradually, and the flow on the liquid layer will develop from stable convection to un-stable convection. An optical diag- nostic system consisting of a modified Michelson interferometer and image processor has been developed for study of the surface deformation and surface wave of thermal capillary convection. The Fourier transformation method is used to interferometer fringe analysis. The quantitative results of surface deformation and surface wave have been calculated from a serial of the interference fringe patterns. The characters of surface deformation and surface wave have been obtained. They are related with temperature gradient and surface tension. Surface deformation is fluctuant with time, which shows the character of surface wave. The cycle period of the wave is 4.8 s, and the amplitudes are from 0 to 0.55 μm. The phase of the wave near the cool side of the cavity is opposite and correlative to that near the hot side. The present experiment proves that the surface wave of thermal capillary convection exists on liquid free surface, and it is wrapped in surface deformation.     

液膜表面波在切应力作用下的线性稳定性

基于液膜表面的力平衡方程和边界条件,建立了在切应力作用下表征沿倾斜壁面下降液膜流动特性的O-S方程。利用摄动方法,求得了液膜表面波扰动的无量纲流函数扰动和波速表达式,分析了切应力、雷诺数和波数对稳定性的影响。研究表明:切应力是影响液膜稳定性的重要因素之一,同向切应力起不稳定性作用,反向切应力起稳定性用;液膜表面波的稳定性随雷诺数增大逐渐减弱;反向切应力使临界雷诺数增大、扰动增长率减小,同向切应力则起相反作用;表面波扰动的传播速度与波数有关,长波的传播速度低于短波,同向切应力使其传播速度增大,反向切应力使其减小。     

毛细作用气液分离过程的理论分析

针对分液冷凝换热器的毛细作用气液分离流动过程,建立了稳定流动情况下的一维数学模型.模型综合考虑了静压、重力、毛细压力、切应力的影响 ;考察了在稳定状态下孔径、孔数以及其组合方式对液膜高度的影响,同时还考察了入口干度和流量对液膜高度的影响;发现孔径和孔数对液膜高度影响基本相同,都是随着数值的增大而液膜高度减小.孔径为1.3 mm、孔数为8时液膜高度都分别为零,气液分离失效,但是干度和流量的对液膜高度影响趋势却相反.在干度为0.5、流量为0.058 kg/s时液膜高度也都分别为零,气液分离失效.     

室内空气自然对流的二维数值模拟

用具有SIMPLE算法。QUICK差分格式对封闭空腔内的流体自然对流进行了数值模拟计算,考察了Ra数对对流换热的影响．结果表明,在相同的条件下,随着Ra数的增加,对流换热加强．     

低温重力热管传热性能的理论与实验研究

为给重力热管在低温区的应用提供理论依据,以液氮作为工质对其稳态传热特性进行了实验研究.分别对冷凝段、蒸发段液膜和液池进行分析,建立了综合的数学模型.根据质量和能量守恒方程迭代计算得到了液池高度和液膜沿管长的分布.在液池模型中,通过假设空泡系数的分布,基于其他实验研究的结论提出了自然对流与核态沸腾换热面积公式.当工质液体体积与重力热管总体积的比值为13.5%和15.2%时,计算值与实验值吻合较好.理论和实验研究结果均表明,在蒸发段内液膜和液池的位置对蒸发段壁温的分布有较大的影响.     

Heat transfer for Marangoni convection over a vapor-liquid interface due to an imposed temperature gradient

A similarity analysis for Marangoni convection induced flow over a vapor-liquid interface due to an imposed temperature gradient was carried out. The analysis assumes that the surface tension varies linearly with temperature but the temperature variation is a power law function of the location. The similarity solutions are presented numerically and the associated transfer characteristics are discussed.     

微重力下绕汽柱Marangoni对流的流场及温度场分析

针对在沸腾现象中出现的汽柱现象，抽象出单个汽柱，建立了绕汽柱Marangoni对流的物理模型和数学模型。采用涡量—流函数，利用有限差分法数值模拟了微重力条件下绕汽柱Marangoni对流，得到了汽柱附近液体区域的温度场和流场分布，并进一步分析了无量纲参数Ma、Pr对Marangoni对流的作用规律。结果表明：汽柱汽-液界面上温度梯度的存在，诱发了Marangoni对流；Marangoni对流随着Ma数的增大而在整个液体区域内扩展增强，导致温度分布的非均匀程度愈强烈；Pr数愈大，整个液体区域内的Marangoni对流有减弱趋势，温度分布的非线性程度减弱。这一结论为太空临界热控制提供了一定的理论基础。     

二维剪切液膜流表面波的线性稳定性特征

当气液界面存在气流剪切作用时,将在不同程度上影响液膜流动的水动力学特征和流动稳定性。基于层流剪切液膜流动的稳态解,分析了切应力对液膜流动状态的影响。采用积分法,建立了沿倾斜壁面下降的二维剪切液膜流表面波扰动演化方程,模型中包含界面切应力、雷诺数、波数和倾角等参数的影响。研究表明:行波和惯性波的波速受均雷诺数和切应力的影响;同向切应力为不稳定性因素,逆向切应力的稳定性影响与雷诺数有关;同向切应力使临界雷诺数减小,逆向切应力使其增大,切应力对临界雷诺数的影响在不同倾角下也有所不同。     

一种抑制热对流不稳定方法

本研究中建立了以晶体生长系统为基础的数学物理模型,该模型为一个长高比为2∶1的方腔内的热对流,该热对流由两种驱动力引起,即浮力(由Grashof数来描述)与表面张力(由Marangoni数来描述)。大量的数值模拟显示,不同的Grashof数与Marangoni数组合产生不同的流动情况,且一个合适的表面张力能够抑制由浮力引起的热对流不稳定性。     

Liquid film falling behaviour on horizontal circular cylinder

The flow pattern behaviour of falling liquid film over three horizontal cylinders was evaluated. These flows can take three forms: discrete droplets, individual jets, and continuous sheet, and special attention is paid to the effects of the physical properties and geometrical parameters of the first two forms (droplets and jets) because these forms are more important in heat-transfer behaviour and less research has been published for these forms. The flow modes and experimental results were successfully compared with previous experimental literatures, and also the effects of liquid flow rate, tube diameter, and tube spacing on departure site spacing, in both drop and jet modes, were evaluated in the low Galileo number and high viscosity fluid (cooking oil), to help developing criteria for determining falling film modes and their transitions, and to understand the heat transfer characteristics associated with each mode.     

以水为工质的铜基微通道热沉的流态可视化与传热特性

设计了微通道流态观测系统,在低雷诺数(34～191)条件下,对以水为工质的一种铜基微通道热沉的流态、温差、压降与其传热特性的关系进行研究。通过可视化观察发现,此微通道的主要流态形式为环状流并随着热流密度的进一步增大呈现周期性震荡。在微通道出现干涸现象时,流体流量迅速下降至零。低入口雷诺数下,首次发现了微通道热沉底部轴向温度呈现中间低两边高的现象。这可能由于流态为充分沸腾的环状流时,与壁面的换热效率最高导致的。微通道热沉的压降损失随着雷诺数和热流密度的增加而增大。分析结果表明,流体流态是影响铜-水微通道热沉换热特性的决定性因素。     

Temperature distribution in front of the liquid-solid interface in the undercooled pure melt influenced by a transverse far field flow

The directional solidification in the undercooled pure melt influenced by a transverse far field flow was studied by using the multiple scale method. The result shows that in the boundary layer near the liquid-solid interface, when affected by a transverse far field flow, the temperature distribution in the direction of crystal growth presents an oscillatory and decay front in the side of liq- uid phase. The crucial distinguishing feature of a temperature pattern due to the transverse convection is the additional periodic modulation of the pattern in the growth direction. The wave number and eigenvalue that satisfy the Mullins-Sekerka dispersion rela- tion are suppressed by the transverse far field flow.     

下降液膜二维剪切表面波的演化方程

基于边界层理论,采用积分方法,建立了沿倾斜壁面下降、表面有气流作用的液膜二维表面波扰动演化方程。模型中包含了界面切应力、雷诺数、表面张力、倾角、流体物性的影响,为进一步分析上述因素对液膜流动稳定性的影响,提供了一种合理的数学模型。     

MOCVD生长GaN薄膜的实时干涉曲线分析

金属有机化学气相沉积（MOCVD）生长系统中通常用激光干涉曲线对材料生长进行实时监控.根据薄膜干涉原理,通过建立反射模型,对GaN薄膜的生长干涉曲线振幅的变化与其生长模式及表面粗糙度的关系进行了详细的阐述和分析.结果表明：干涉曲线中的振幅会随薄膜表面粗糙度的增大而衰减,其衰减程度与粗糙的变化快慢有关,根据材料的实时干涉曲线可揭示其在不同生长过程中的生长模式和定量分析样品表面粗糙度.     

Coupling Frequency of the Liquid Sloshing in a Cylindrical Tank with a Flexible Baffle

Liquid sloshing problems are very common inreal life and in industrial processes[1-20].The diffi-cultiesinherent tothese problems are very challengingfor mathematical and computational analysis.In as-tronautic engineering,theliquidloadinspacecraft hasbeen increased significantly,and it is i mportant toguarantee the stability of spacecraft by suppressingliquid sloshing.Ring and vertical cruciform baffles,floatinglids and mats,andflexible baffles are very ef-fective inliquid wave control.It is c…     

Investigation on Liquid Breakup Regimes and Atomization Performance of Slinger

甩油盘液体破碎形态及雾化性能研究

覃文隆

（中国飞行试验研究院,西安 710089）

摘要：

在Dahm的研究基础上,对甩油盘的液体形态、雾化性能等进行研究。在圆形出孔中,当液体与壁面之间夹角小于时,表面张力会阻止液体在科氏力作用下聚集到出孔一侧。Dahm提出的判定液柱、液膜形态的公式并不能准确衡量液体的形态,提出排水池假说、相对滑移假说来解释此现象。sub与super与韦伯数相关,当we小是为sub,we大时为sup,而当we在中间状态时无法判定。液体的一次雾化与相应特征长度下的we有关,但二次雾化会产生大量微小液滴,液雾SMD与相应特征长度下We相关系数不大。整体上液雾SMD与We成指数关系,特征长度为出孔内液膜厚度,相关系数接近0.9。

关键词：旋转雾化,甩油盘,液体破碎形态,液雾SMD