二相流基本方程的封闭问题及水气二相流数学模型

讨论了平均二相流基本方程的封闭问题。在此基础上 ,从建立数学模型的角度 ,提出将水利工程中的水气二相流划分为稀疏气泡流区、气相连续流区和掺气形成区 (稠密气泡流 )三个区 ;根据已有的方程封闭的研究成果 ,提出了可用于稀疏气泡流计算的双流体模型。     

矩形微通道内气液两相流压力降特性

以氮气为气相介质,以不同表面张力的液体(纯水、0.01%SDS溶液、乙醇)为液相介质,对3种矩形微通道(200μm×200μm,400μm×400μm和800μm×800μm)内两相流压力降进行可视化试验,同时对微通道内两相流压力降梯度进行了测量,并将测量值与均相流模型、分相流模型和以流型为基础模型的预测值进行了对比.结果表明:两相流压力降受表面张力、通道尺寸和两相流速度影响;以流型为基础模型的理论预测方法预测效果最好.     

并列矩形微通道可视化研究和压降计算

对当量直径为177.8μm、长为3mm的矩形截面并列微通道进行了试验研究,通过高速摄影仪对并列微通道内空气-水的两相流动进行了可视化研究,试验中观察到几种典型的流型;利用分相流模型、均相流模型对并列微通道的整体压降进行预测,并与测得的试验值进行了对比,通过计算各个模型的平均绝对误差来比较其预测效果.结果表明:均相流模型对整体压降的预测效果好于分相流模型;均相流模型中,用Dukler黏度计算式得到的预测值平均绝对误差最小,预测效果最好.     

喷嘴处气穴现象的数值模拟分析

Fluent软件是用于模拟和分析在复杂几何区域内的流体流动与热交换问题的专用CFD软件。将k-e模型与多相流技术Mixture模型相结合,借助Fluent软件进行多相流分析,对喷嘴处的气穴流场进行了数值模拟,并计算了模型内二维轴对称气穴流场的液态水的体积分数分布及压力分布。     

多维喷雾两相流模型的计算和验证

本文提出了一个反映瞬态喷雾两相作用主要因素的二维轴对称喷雾两相流模型。文章讨论了模型的主要假设,给出了计算公式和离散化方法。文章中所提供的计算示例以及试验对照证明了模型的可行性和实用性。     

柴油机热态喷雾二维两相流模型研究

摘要本文提出了一个柴油机热态喷雾二维两相流理论模型.模型强调了液滴的湍流扩散、高压蒸发特征以及与气相场的强烈耦合作用.给出了根据该理论模型所编制的TDSP软件的部分计算结果,并就这些结果进行了分析讨论.     

跨努森数区域的微通道内流动计算模拟研究

采用一阶和修正二阶的滑移连续介质模型,对跨努森数区域的低速微通道流进行二维和三维数值模拟。用实验结果和DSMC方法验证滑移连续介质模型在跨努森数区域中的适用性,并详细讨论了微通道流的可压缩效应、稀薄效应、低雷诺数效应和三维特性。研究表明,努森数是表征稀薄效应和模型适用性的特征参数,滑移连续介质模型适用于努森数小于0.150的氮气流动;马赫数不再是微通道流可压缩效应的唯一标识参数;雷诺数是表征低雷诺数效应和三维特性的关键参数,高宽比大于20的微通道流具备良好的二维特性。     

船用核汽轮机装置仿真研究

建立了适合船用核汽轮机装置实时仿真分析计算的两相流仿真模型。利用该仿真模型对快速变负荷工况下船用核汽轮机装置的动态特性进行了计算分析。结果表明,该模型能准确模拟核汽轮机装置的变负荷运行特性,满足核动力二回路系统实时仿真分析要求。模型已经成功应用于两型船用核动力训练模拟器的开发,对操纵人员的培训及操作规程的验证具有重要意义。     

基于GIS的克里金法对二维水质模型的改进

为研究天然河道水体污染在二维空间上的分布特征并提高二维水质模型的使用效率,以绵远河某排污口为例,选取BOD作为预测因子并采用二维水质模型进行研究。针对传统二维水质模型中出现的问题,基于GIS技术及数据库方法,将克里金法与传统二维水质模型相耦合,充分考虑了空间因素对预测值的影响,提出了二维修正模型,建立了水体污染预测系统。结果表明,与传统二维水质模型相比,二维修正模型更符合连续水体特征,适用性更强,对水环境污染预测具有重要的参考价值。     

柴油机尾气颗粒捕集气固两相流模拟研究

本文运用离散相模型和多孔介质模型建立了柴油机颗粒捕集器的二维物理模型和气固两相流模型.研究表明模拟的多孔介质流场压力与实验测量结果相对误差小于±5%,模拟的颗粒捕集率达到75%～92%,且与流速和颗粒直径有关,研究结果对颗粒捕集器的优化设计提供了依据.     

流化床密相区流动特性的数值模拟

流化床内气固两相流动一直是实验研究和数值模拟的热点。基于Eulerian双流体模型,本文建立了流化床内的气固两相流动模型,采用FLUENT软件对流化床密相区两相流动特性、床内气泡的产生运动和爆裂等特性进行了数值模拟。模型中,将颗粒相看作是连续介质,建立与气相相同形式的数学模型;采用了离散介质动力理论,引入颗粒温度来描述固相粘性应力,并用气固曳力进行气固两相耦合。模拟得到了气泡产生、运动和爆裂的变化过程,与实验结果相一致。采用不同的曳力模型对流化床稠密两相流动进行了模拟,与Kuipers实验对比,结果表明采用Gidaspow曳力模型描述流化床稠密两相流动特性更准确。     

考虑壁面粗糙度的双流体颗粒-壁面碰撞模型

提出了考虑壁面粗糙度的双流体颗粒－壁面碰撞模型，将轨道模型中颗粒碰壁模型考虑壁面粗糙度和双流体模型中用概率密度函数积分法处理颗粒与光滑壁面碰撞模型的优点结合起来，引入壁面粗糙度对碰壁颗粒湍流影响的机理。数值模拟结果表明，由于考虑了各方面雷诺应力之间的相互转化，雷诺应力从平均运动中得到能量，以及壁面对运动的衰减作用等因素，包括摩擦系数、恢复系统、壁面粗糙度等物理参数的颗粒－壁面碰撞模型作为边界条件时，得到的结果与实验符合得更好。     

低流速净蒸汽产生点模型预测过冷沸腾空泡率

空泡率是汽液两相流动的基本参数之一,而已有过冷沸腾空泡率计算方法研究以高质量流速为主,且大量文献报道现有空泡率模型难以适用于低流速过冷沸腾工况。本文基于低流速过冷沸腾净蒸汽产生点(NVG)理论模型,进一步建立了计算过冷沸腾空泡率的分布拟合模型。在较宽广的压力、质量流速、热流密度和流道尺寸范围内将模型计算结果与现有空泡率实验数据进行了比较,低流速工况下该模型与实验数据符合良好,表明该模型可适用于低流速过冷沸腾工况。     

电容式气固两相流相浓度传感器的研究

采用两台极板交错放置的电容器和具有误差补偿功能的高频振荡电路研制一种新型的电容式两相流相浓度传感器，实验结果表明，该传感器具有较高的灵敏度和稳定性，较平垣的灵敏度场和较好的测量线性度，可以满足实际两相流相浓度的测量要求。     

Applications of Electrical Capacitance Tomography in Two Phase Flow Visualization

The successful application of Electrical Capacitance Tomography (ECT) depends heavily on the image reconstruction speed and quality. The two requirements usually cannot be satisfied simultaneously. Also, for a large number of acquired 2D ECT images, a 3D presentation of them is much desired to track the variations of the material distribution in a third dimension. To facilitate ECT for practical flow analyses in process engineering, the authors have recently developed algorithms for 3D image presentation and for online iterative image reconstruction that only takes the same time as a linear back projection method but yields good image qualities as the Landweber iterative method does. The new methods have been successfully applied to visualize several classes of two phase flows, namely fluidization, cyclone separation, circulating rate determination in circulating fluidized beds, pneumatic conveying, rotating drum mixing. Special characteristics in each case have been discussed and valuable results are obtained, which are reported in this paper.     

汽轮机湿蒸汽两相凝结流动数值研究的现状与进展

着重针对汽轮机中存在自发凝结的湿蒸汽两相流动 ,论述了湿蒸汽两相流动数值研究进展现状及其待解决的问题 ,以期对此方面的研究及其工程应用起到促进作用。文中结合作者目前进行的有关湿蒸汽两相凝结流动数值研究 ,对湿蒸汽透平级中两相流动的数值模型、求解方法等关键问题进行了阐述和探讨 ,给出了作者对一维喷管、二维喷管以及叶栅进行数值模拟的部分算例结果 ,以说明所发展的数值模拟方法的可行性和准确程度。     

A FOUR-EQUATION MODEL FOR PREDICTION OF GAS-SOLID TURBULENT FLOWS

A four-equation model is proposed for prediction of dilute turbulent gas-solid flows where the ratio of the particle and the gas densities is large. The model is based on explicit algebraic relations for Reynolds stresses and turbulent fluxes of the void fraction, which were derived in an earlier work within the context of Reynolds-averaged Navier-Stokes (RANS) methodology. These relations are manipulated here to derive nonlinear eddy-viscosity-type models for thin-shear flows. Further, new models are proposed for third-order correlations which are also simplified for thin-shear flows. These models are used to propose four transport equations for the turbulence kinetic energy of the carrier phase and its rate of dissipation, the turbulence kinetic energy of the dispersed phase, and the velocity covariance of the two phases. The final four-equation model is implemented for prediction of a particle-laden turbulent jet, and encouraging agreements with available laboratory data are observed.     

确定油田注汽锅炉单相流和双相流界面的方法探讨

根据油田注汽锅炉特殊的结构特性、热力特性,探索和运用分段假设试算的方法,确定油田注汽锅炉的单相流和双相流界面,从而对整个水汽系统进行合理分段,为油田注汽锅炉汽水系统的阻力准确计算提供依据,并经实践验证.     

A new scalar fluctuation model to predict mixing in evaporating two-phase flows

A scalar fluctuation model for two phase flows is proposed for RANS (Reynolds Average Navier Stokes) simulations. It is a two equation model based on the variance v of the gaseous fuel mass fraction and on the scalar dissipation χ. For each quantity a transport equation is solved. The models developed by Mantel and Borghi [11] and Newman et al. [9] are used to close the transport equation of χ for gaseous flows. These models (and an algebraic closure for χ) are compared to (Direct Numerical Simulation) DNS results obtained by Eswaran and Pope [12] in the case of mixing in a gaseous homogeneous stationary turbulence. To get a correct agreement between the RANS models and the DNS results, we had to adjust some constants in these models. It is shown that with the algebraic model it is not possible to correctly reproduce the trends observed in the DNS. Then, the closure proposed by Demoulin and Borghi [13] for the spray source term in the variance equation is adopted. The modelling of the spray source term in the scalar dissipation equation represents the main theoretical work of this paper. Comparisons between experiments and computations are performed in order to validate the complete model. These comparisons are performed on a Gasoline Direct Injection optical access engine. To make comparisons between computations and experiments possible, it is necessary to filter the computed variance. This procedure allows to account for the filtering performed by the pixels of the CCD camera used in the experiments. The two- equation models of Newman et al. and Mantel and Borghi used with the variance and scalar dissipation source terms proposed in this paper predict a high turbulence to mixing time ratio r=τ_tτ_m=χυ?k during the evaporation of droplets. This high mixing rate allows the model of Newman et al. to correctly reproduce fluctuation levels in the spark zone as well as the intense fluctuation in the spray region, while the model of Mantel and Borghi tends to over-estimate fluctuation levels. On the contrary, the algebraic closure imposes a fixed ratio r of the order of 2, which leads to a very high over-prediction of fluctuation levels. These results show that a two-equation model with appropriate spray source terms is needed for correctly modeling the mixing in two-phase flows.     

固液两相流泵的研究现状及展望

重点阐述了固液两相流泵的研究现状及其进展.在内部流动特性方面介绍了固体颗粒在叶轮内部的流动规律,研究了泵内部过流部件的磨损规律及抗磨措施;外部特性主要介绍了泵的几何参数对泵性能的影响.介绍了四种固液两相流泵的水力设计方法,并进行了分析,指出了四种设计方法对固液两相流理论发展的影响.从理论、试验研究和实际应用等方面分析了固液两相流泵性能优化的方向,并对固液相流泵的设计和应用作出了展望.