空化紊流流动的数值计算模型及其验证

本文介绍了一种空化紊流流动的数值计算模型,并计算了射流放水阀内部的空化流动现象。该模型基于均相平衡模型和液相与汽相传输方程,基本方程采用N-S方程,空化模型采用Kunz等提出的汽液质量转换模型。紊流封闭采用标准的κ-ε素流模型;稳定流动计算采用扩展的SIMPLE压力修正方法,非稳定计算采用PISO算法。为评价该数值模型,计算了绕射流放水阀的空化流动,并与实验结果进行了对比,计算结果与实验结果取得较好的一致,说明该流动模型和计算方法是可靠的。     

水平管内二氟乙烷两相流动摩擦压降实验研究

对制冷剂二氟乙烷(HFC-152a)在内径为8mm的水平管内进行了两相流动沸腾摩擦压降的实验测量.实验测量的压力范围为0.19—0.41MPa,热流密度范围为14—62kW/m2,流量范围为128—200kg/m2s.实验测量表明:HFC-152a的两相摩擦压降随质量流量、质量含气率的增大而增大;热流密度则对摩擦压降的直接影响很小,但通过影响两相流流型间接影响了摩擦压降;当流型由分层流动转变为半环状流或环状流时,总压降中加速压降所占比例有所减小,而摩擦压降所占比例则有所增大;摩擦压降随饱和压力的增大而减小.使用两个应用广泛的压降计算式进行了计算.实验测试结果与计算结果对比后发现,Friedel模型与实验结果偏差较大,而Müller-Steinhagen-Heck模型则与实验结果符合较好.     

底排装置非定常环状伴随射流的特性分析

为了研究环形喷口底排弹出膛口时的尾部二次燃烧特性和环状伴随射流流动特性,针对底排燃烧室在瞬态泄压条件下的强非稳态扰动过程,建立了环状喷口射流与超声速来流相互作用的二维轴对称化学非平衡流模型,数值研究环形喷口底排装置的非定常伴随射流燃烧流动演化特性。计算结果表明:环形喷口射流在泄压初期挤压形成高度欠膨胀的中心射流,随着喷口压力降低,逐渐转变为亚音速环状射流。泄压中期,燃烧反应强度由射流边缘向中心轴线方向逐渐加剧,在气体回流作用下,尾部流场温度快速升高。在泄压过程中,不同初始压力下的底部压力和轴线温度变化趋于一致。随着燃烧室内初始压力增大,底压系数峰值增加,降压时间延长。1.5 ms后,初始压力对尾部流场无明显影响。     

分层流与环状流中聚合物减阻效应研究

对天然气管道在多相流状态下的管道效率与减阻率的关系进行了理论分析,以水-空气混合流体模拟天然气管道中的分层流与环状流,在65 mm的水平管中对聚合物的多相流减阻进行了试验研究。理论计算与试验结果都表明,聚合物对多相流的减阻率随表观气速的增大而略有降低;对液体有62％减阻率的聚合物,对环状流的减阻率可达到40％左右,对分层流的减阻率可达到26％左右,使多相流的管道效率明显提高。     

椭圆管连续螺旋折流板换热器布管方式对壳侧传热和阻力性能的影响

以椭圆管连续螺旋折流板换热器作为研究对象,提出了三角形横置和竖置与同心圆环状和发散状四种布管方式,用ANSYS CFX进行数值模拟,并采用三场协同原理分析其壳侧综合性能。结果表明:同心圆环状布管流场最易形成旋转流动,壳侧压降最小;以三场协同原理作为评价标准得出,同心圆环状布管综合性能最优,其它依次是三角形竖置布管、三角形横置布管、同心发散状布管。     

球床内气液两相流流型及压降实验研究

在本实验参数范围内可将孔隙流道内空气/水两相流动划分为泡状流、泡状-弹状混合流、弹状流、弹状-环状混合流和环状流五种流型。本文修正后的Tung/Dhir流型转变模型与实验符合较好。依据单相流动压降数据,对Ergun公式参数进行了拟合,提出了适用于本实验特点的单相压降公式。并在此基础上利用渗透率系数提出了两相流动压降计算经验公式,与前人的公式相比,适用范围更广,计算误差也较小。     

柔性管内油水环状流流动结构数值模拟

海洋中柔性管道受到外界猛烈撞击，撞击物的不同会导致管道内流道结构发生不同的改变.为探寻流道结构变化对环状流动结构的影响规律，采用N-S方程和湍流模型描述流体运动，用VoF模型与CSF模型追踪油水界面，建立数值方程与分析模型，分析流道不同形式的结构变形、不同程度变形和不同流速下油水环状流在管内的湍动能和漩涡结构演变，及环状流流型的演变和压力场的演变.分析结果表明:凹陷变形程度越大，漩涡的强度及面积越大，V形变形影响远大于○形变形影响，环状流的流型发生改变时仍然保持着水相包裹油相的稳定状态，最大压缩区域的油水界面压强也随之增大，且增速变大.所得结论对研究油水环状流在柔性管道运输中的稳定性具有一定指导意义.      

有液滴卷吸时的环状流换热系数的预测模型

本文对垂直上升光管中环状流流动沸腾的理论模型进行了分析,以液膜紊流的动量方程和能量方程为基础,推导了环状流的数学模型,通过求解动量方程和能量方程,获得了流动沸腾换热系数的预测模型,并对该预测模型进行了数值求解,将预测的换热系数同实验值作了比较。     

微通道中水蒸气凝结过程流型变化的分子动力学研究

本文建立了外力作用下流体流动和凝结过程的分子动力学模型.在蒸汽压力为3.7177 MPa时,模拟得到了不同外力条件下水蒸气凝结过程的流型,分别为环状流、射状流、塞状流、泡状流、带有小汽泡的液体流,模拟结果与相关文献中实验流型吻合较好.模拟发现水蒸气在0.3833 MPa压力下凝结时,出现一种新的波动流流型.最后对凝结过程中流型间转换机理进行了讨论.     

环状光纤单模条件和远场能量分布特性

基于弱波导近似,通过数值计算得出了环状光纤保持单模状态时对芯-包层折射率差值和导光层厚度的要求,同时讨论了这些设计参数对远场能量分布的影响。计算结果表明:当环状光纤工作在单模状态时,从光纤出射的环形光束衍射至远场时形成一个中央亮斑,具有很高的能量集中度。此外,减小芯-包层折射率差值与导光层厚度有利于进一步减小远场衍射的光斑宽度。     

水平管气液段塞流流量瞬变特性模拟研究

以Taitel 和Barnea(1998,1999)提出的段塞流跟踪模型为基础,进一步考虑加速压降的影响,建立了新的瞬态段塞流跟踪模型,并采用面向对象技术编制了数值模拟软件,实现了数值跟踪。计算结果与King等的段塞流气体流量瞬变实验数据对比表明,瞬态跟踪模型较好地预测了气体流量上升造成的段塞流压力“过升”现象,以及长液塞的出现;当气体流量下降时出现的压力“过降”现象和短暂分层流现象也由模型准确预测,分析认为,由于段塞流压降远高于分层流型,因此大部分液塞消失而出现的短暂分层流导致了压力过降。     

Free energy and entropy production in planar Couette flow far from equilibrium

The macroscopic thermodynamic stability of a system of 108 diatomic molecules undergoing planar Couette flow far from equilibrium is reported. The system is perturbed from the steady state using a nondissipative variable colour field which induces a polarization in the system. It is found that the steady state for the system corresponds to an extremum in the generalized free energy and entropy production. However, while the free energy is always a minimum, the entropy production may be either a minimum or a maximum depending upon the direction of the colour field. These results, for a molecular system, are fundamentally different from those for an equivalent atomic system.     

环形HYLTE喷管耦合段及光腔区流场的数值模拟

参考传热学相关理论,估算燃烧室的传热损耗分数及相应的平衡温度,确定了主喷管的入口参数设置。在此基础上,对环形HYLTE喷管的耦合段及光腔区流场进行3维的数值模拟,给出了F原子质量分数、静温、静压的空间分布,得到了光腔区各支谱线的小信号增益系数变化曲线。将计算结果与实验结果进行比对,光谱测量结果及移动光轴实验证实了计算模型的合理性。     

Numerical analysis of plasma arc physical characteristics under additional constraint of keyhole

The physical characteristics of a plasma arc affect the stability of the keyhole and weld pool directly during keyhole plasma arc welding(KPAW). There will be significant change for these characteristics because of the interaction between the keyhole weld pool and plasma arc after penetration. Therefore, in order to obtain the temperature field, flow field, and arc pressure of a plasma arc under the reaction of the keyhole, the physical model of a plasma arc with a pre-set keyhole was established. In addition, the tungsten and base metal were established into the calculated domain, which can reflect the effect of plasma arc to weld pool further. Based on magneto hydrodynamics and Maxwell equations, a two-dimensional steady state mathematical model was established. Considering the heat production of anode and cathode, the distribution of temperature field, flow field, welding current density, and plasma arc pressure were solved out by the finite difference method. From the calculated results, it is found that the plasma arc was compressed a second time by the keyhole. This additional constraint results in an obvious rise of the plasma arc pressure and flow velocity at the minimum diameter place of the keyhole, while the temperature field is impacted slightly. Finally, the observational and metallographic experiments are conducted, and the shapes of plasma arc and fusion line agree with the simulated results generally.     

Entropy Production Rate Changes in Lysogeny/Lysis Switch Regulation of Bacteriophage Lambda

According to the chemical kinetic model of lysogeny/lysis switch in Escherichia coli (E. coli) infected by bacteriophage λ, the entropy production rates of steady states are calculated. The results show that the lysogenic state has lower entropy production rate than lytic state, which provides an explanation on why the lysogenic state of λ phage is so stable. We also notice that the entropy production rates of both lysogenic state and lytic state are lower than that of saddle-point and bifurcation state, which is consistent with the principle of minimum entropy production for living organism in nonequilibrium stationary state. Subsequently, the relations between CI and Cro degradation rates at two bifurcations and the changes of entropy production rate with CI and Cro degradation are deduced. The theory and method can be used to calculate entropy change in other molecular network.     

Electron self-organization in electronic devices

The open systems, which contain a huge number of electrons supplied from outside along with the energy, are described by a functional that takes into account the Lagrangians of all particles and is called the integral Lagrangian. A nonextremal principle is formulated that postulates that the value of this functional decreases as the system approaches the steady state. The principle is extended to the systems occurring near thermodynamic equilibrium (where it is virtually equivalent to the principle of minimum energy dissipation), as well as to the nonlinear systems, including those in which the motion of particles is described by equations of classical mechanics. The applicability of the principle is demonstrated by the examples of a vacuum diode, magnetron diode, and Gunn diode.     

热质的运动与传递-热子气状态方程

基于相对论原理,提出能量的运动可以产生压强．在热质概念的基础上,针对理想气体,根据分子动理论建立了热子气状态方程,从而得到理想气体分子的热运动动能压强的表达式．基于硬球势能模型通过分子动力学模拟验证了热子气状态方程的正确性．     

决定论性逐步加速交通流模型的渐近稳态行为

研究Nagel-Schreckenberg(NS)交通流元胞自动机模型在不考虑车辆随机延迟情况下的决定论性模型的基本图,即渐近稳态的车流平均速度作为车辆密度的函数关系．证明决定论性NS模型,在车流的自组织作用下,其渐近稳态的基本图,与决定论性Fukui-Ishibashi(FI)交通流模型的基本图完全相同．这个结果表明,若把FI交通流模型中的车辆突然加速方式（即车辆速度可以在仅仅一个时步内加速到其最高速限M或前方空距所允许的最大速度）,改变为车辆逐步加速方式（车辆速度在每一时步中最多仅能增加一个速度单位）,则车辆的自组织相互作用,并不会改变其车流的长时间渐近稳态行为． 关键词：