共查询到20条相似文献,搜索用时 560 毫秒
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在双流体模型中引入界面浓度输运方程,利用界面浓度和气泡平均Sauter直径模化各相间作用力。引入一附加 湍动能输运方程模化气泡诱导引起的液相湍流。利用该模型对方截面鼓泡床内气液两相流进行三维瞬态数值模拟。计算结 果表明该模型能较好得模拟方截面鼓泡床内气液两相流时均和瞬态流动特征。 相似文献
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A numerical scheme is developed to simulate electro-osmotic flow and mass transport in a microchannel which includes a 180° turn. The model has been used to predict the behaviour of electro-osmotically driven flows. The detailed structure of the flow field in a microchannel in combination with species mass diffusion can explain the concentration dispersion introduced by a 180° turn. The results of our simulations agree both qualitatively and quantitatively with experimental observation. It is demonstrated that an improved electro-osmotic force model could simulate the electrokinetically driven flow well without making detailed calculations of the electric charge density distribution within the electrical double layer. Additionally, because this model applies forces to the liquid as opposed to imposing local velocities, it should also be appropriate for use where pressure gradients exist in the flow field. 相似文献
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Ghost Fluid方法与双介质可压缩流动计算 总被引:1,自引:1,他引:0
应用带有Isobaric修正的GhostFluid方法配合LevelSet方法计算可压缩双介质无粘流动.该方法可以消除计算流体界面时所产生的数值跳动和耗散,且编程上比界面跟踪法简单.应用WENO格式数值求解欧拉方程和LevelSet方程,对由刚性气体状态方程所支配的一二维双介质流动进行数值计算,得到了分辨率较高的计算结果. 相似文献
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A two-fluid continuum model is developed to describe mass transport in electro- and magnetorheological suspensions. The particle flux is related to the field-induced stresses. Solutions of the resulting mass balance show column formation in the absence of flow, and stripe formation when a suspension is subjected simultaneously to an applied electric field and shear flow. 相似文献
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The purpose of this study is to set up a dynamically linked 1D and 2D hydrodynamic and sediment transport models for dam break flow.The 1D-2D coupling model solves the generalized shallow water equations,the non-equilibrium sediment transport and bed change equations in a coupled fashion using an explicit finite volume method.It considers interactions among transient flow,strong sediment transport and rapid bed change by including bed change and variable flow density in the flow continuity and momentum equations.An unstructured Quadtree rectangular grid with local refinement is used in the 2D model.The intercell flux is computed by the HLL approximate Riemann solver with shock captured capability for computing the dry-to-wet interface for all models.The effects of pressure and gravity are included in source term in this coupling model which can simplify the computation and eliminate numerical imbalance between source and flux terms.The developed model has been tested against experimental and real-life case of dam-break flow over fix bed and movable bed.The results are compared with analytical solution and measured data with good agreement.The simulation results demonstrate that the coupling model is capable of calculating the flow,erosion and deposition for dam break flows in complicated natural domains. 相似文献
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P. K. Ezhil Kumar 《Combustion Theory and Modelling》2017,21(4):658-676
In the present work, reacting flow characteristics of a 2D trapped vortex combustor (TVC) have been investigated numerically. Turbulent flow prevailing in the combustor is modelled using the two equation shear stress transport (SST) k-ω model and the turbulence–chemistry interactions are modelled using the eddy dissipation concept (EDC) model. Validation study reveals that the data generated by numerical model for reacting flow cases matches reasonably well with the experimental data. Simulation results indicate that for a particular operating condition, the flow structure within the cavity for reacting flow cases is significantly different from non-reacting flow cases. Besides this, under reacting flow condition, the vortex core location shifts with variation in operating condition. This study also reveals significant differences in the velocity gradient at the shear layer between reacting and non-reacting flow conditions. Furthermore, the turbulent kinetic energy at the cavity zone increases for the reacting flow condition, which is attributed to the volume expansion associated with the combustion processes. Also, temperature contours at locations downstream of the trailing edge indicate that both cavity flames are merged together for higher primary air velocity cases, and this is essential for efficient performance of TVC. 相似文献
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A new formulation of Kapila’s five-equation model for inviscid, non-heat-conducting, compressible two-fluid flow is derived, together with an appropriate numerical method. The new formulation uses flow equations based on conservation laws and exchange laws only. The two fluids exchange momentum and energy, for which exchange terms are derived from physical laws. All equations are written as a single system of equations in integral form. No equation is used to describe the topology of the two-fluid flow. Relations for the Riemann invariants of the governing equations are derived, and used in the construction of an Osher-type approximate Riemann solver. A consistent finite-volume discretization of the exchange terms is proposed. The exchange terms have distinct contributions in the cell interior and at the cell faces. For the exchange-term evaluation at the cell faces, the same Riemann solver as used for the flux evaluation is exploited. Numerical results are presented for two-fluid shock-tube and shock-bubble-interaction problems, the former also for a two-fluid mixture case. All results show good resemblance with reference results. 相似文献
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针对窜流型油藏的特点,抽象出物理原型,同时考虑纵向和横向扩散,建立层内突进传质扩散数学模型.应用拉普拉斯变换,求得层内突进传质扩散数学模型的解析解,并得到小段塞情况下的解析解.应用通用有限元分析软件,建立层内突进传质扩散的几何模型,并求得层内突进传质扩散数学模型的数值解.绘制层内突进传质扩散数学模型的浓度分布二维剖面及不同时间步的浓度变化剖面;通过无因次距离和无因次浓度关系及孔隙体积与无因次浓度关系可以看出,贝克莱特(Pe)数越大,峰值浓度越高,见剂时间越晚.通过解析解及数值解结合的方法,可加深对传质扩散本质的理解. 相似文献
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Pieter Rauwoens Jan Vierendeels Erik Dick Bart Merci 《Journal of computational physics》2009,228(13):4714-4744
In this paper, we develop the discrete compatibility-constraint pressure-correction algorithm for transient simulations of variable density flows at low-Mach numbers. The constraint for the velocity field is constructed from a combination of the discrete equations of continuity and scalar (e.g. energy) transport, imposing that the newly predicted state must be compatible, in agreement with the equation of state. This way, mass and scalar conservation are guaranteed and the equation of state is exactly fulfilled at every time step. For comparison reasons, two other types of well-known pressure-correction algorithms are also used. The first class, denoted as continuity-constraint pressure-correction, is based on a constraint for the velocity field that is derived solely from the continuity equation. The second class, denoted as analytical compatibility-constraint pressure-correction, constructs the constraint from an analytical combination of the material derivative of the equation of state and the continuity and scalar equations. The algorithms are tested for three example fluid configurations: a single-fluid ideal gas, a two-fluid inert mixture and a two-fluid reacting mixture. The latter is special in the sense that the equation of state is non-linear and not everywhere differentiable. The continuity-constraint pressure-correction algorithm yields unstable solutions if density ratios are high. The analytical compatibility-constraint pressure-correction algorithm yields stable results, but the predicted states do not correspond to the equation of state. The discrete compatibility-constraint pressure-correction algorithm performs well on all test cases: the simulation results are stable and exactly match the equation of state. 相似文献
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G. V. Ostrovskaya 《Technical Physics》2008,53(11):1391-1400
The problem of the motion of plasma carrying a pulsed current in a steady-state magnetic field is solved in terms of two-fluid
magnetohydrodynamics. The initial directions of the force and current vectors are determined, and the relations that determine
their time evolution are obtained. The time dependences of the slope of the two-fluid plasma flow trajectory with respect
to the one-fluid plasma motion direction are calculated. The smaller the ion mass in the plasma, the faster the decrease in
the slope of the trajectory with time. The calculation results agree well with the data of our experiments [1–7] on studying
the current sheets in 3D magnetic fields with an X line and support the necessity of taking into account the two-fluid properties of plasma when current sheets form in heavy
inert gases. 相似文献
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The flow of liquid helium through a single nanohole with radius smaller than 25 nm was studied. Mass flow was induced by applying a pressure difference of up to 1.4 bar across a 50 nm thick Si(3)N(4) membrane and was measured directly by means of mass spectrometry. In liquid He I, we experimentally show that the fluid is not clamped by the short pipe with diameter-to-length ratio D/L?1, despite the small diameter of the nanohole. This viscous flow is quantitatively understood by making use of a model of flow in short pipes. In liquid He II, a two-fluid model for mass flow is used to extract the superfluid velocity in the nanohole for different pressure heads at temperatures close to the superfluid transition. These velocities compare well to existing data for the critical superflow of liquid helium in other confined systems. 相似文献
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针对气液混输管线与立管系统严重段塞流问题, 采用严重段塞流形成条件一致的等效原则, 发展了一种将三维管道系统等效为二维管道系统的计算流体力学(CFD)数值模拟方法. 以文献中某下倾管与立管组合系统为对象, 结合其实验工况, 对严重段塞流气液流动过程进行了数值模拟, 获得了其周期、压力波动幅值及喷发时间等关键参数的变化规律, 数值模拟与文献所述实验结果符合. 在此基础上, 建立了立管入口气液折算速度、立管含气率以及立管出口平均速度的理论模型, 获得了这些关键参数随时间的变化规律, 并给出了确定立管内气液流型变化的理论方法, 理论结果与CFD数值模拟结果一致. 建立的CFD方法大幅缩减了严重段塞流数值模拟所需的时间和资源, 推导的理论模型揭示了严重段塞流特性参数之间的关联, 可以对严重段塞流所引发的危害进行快速评估及预测,具有一定的工程应用价值. 相似文献
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叶片式混输泵内气液两相流的数值计算 总被引:1,自引:0,他引:1
气液两相流的数值模拟是多相混输技术研究中的一个难点.本文假定混输泵叶轮内为泡状流动,基于雷诺时均N-S方程和气液两相双流体模型,采用SIMPLEC算法,对叶片式混输泵叶轮内部两相三维紊流流场进行了数值计算,分析了水气混合工况下的流场分布特点.对含气率GVF=15%工况下的扬程特性进行了预测并与试验结果进行对比.数值计算结果表明,混输泵叶轮流道采用较小的径向尺寸差能较好地避免离心力所引起的气液分离,防止气堵现象的发生;叶轮进口部分存在的低压旋涡区容易使气体积聚,因此有必要进一步改进叶轮进口区的水力设计. 相似文献
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In a wind-blown sand layer, it has been found that wind transport of
particles is always associated with separation of electric charge. This
electrification in turn produces some electrostatic forces in addition to
the gravitational and fluid friction forces that affect the movement of
saltating sand particles, further, the wind-blown sand saltation. To
evaluate this effect quantitatively, this paper presents a simulation of
evolution of wind-blown sand grains after the electrostatic forces exerted
on the grains are taken into account in the wind feedback mechanism of
wind-blown saltation. That is, the coupling interaction between the wind
flow and the saltating sand particles is employed in the simulation to the
non-stationary wind and sand flows when considering fluid drag, gravitation,
and a kind of electrostatic force generated from a distribution of electric
field changing with time in the evolution process of the sand saltation. On
the basis of the proposed simulation model, a numerical program is given to
perform the simulation of this dynamic process and some characteristic
quantities, e.g., duration of the system to reach the steady state, and
curves of the saltating grain number, grain transport rate, mass-flux
profile, and wind profile varying with time during the non-stationary
evolution are displayed. The obtained numerical results exhibit that the
electrostatic force is closely related to the average charge-to-mass ratio
of sand particles and has obvious influence on these characteristic
quantities. The obtained results also show that the duration of the system
to reach the steady state, the sand transport rate and the mass flux profile
coincide well with experimental results by Shao and Raupach (1992) when the
average charge-to-mass ratio of sand particles is 60 μC/kg for the sand
particles with average diameter of 0.25 mm. When the average charge-to-mass
ratios of sand particles are taken as some other certain values, the
calculation results still show that the mass flux profiles are well in
agreement with the experimental data by Rasmussen and Mikkelsen (1998) for
another category of sand particles, which tell us that the electrostatic
force is one of main factors that have to be considered in the research of
mechanism of wind-blown sand saltation. 相似文献