共查询到19条相似文献,搜索用时 171 毫秒
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多孔介质中高Péclet数和大黏性比下混溶流体的流动和扩散广泛存在于二氧化碳驱油、化工生产等工业过程中.用数值方法对该问题进行研究时,关键在于如何正确描述高Péclet数和大黏性比下多孔介质内流体的行为.为此,提出了一种基于多松弛模型和格子动理模型的耦合格子Boltzmann模型.通过Chapman-Enskog分析,证明该模型能有效求解不可压Navier-Stokes方程和对流扩散方程.数值结果表明,该模型不仅具有二阶精度和良好的稳健性,而且对于高Péclet数和大黏性比的问题具有良好的数值稳定性,为模拟此类问题提供了有效工具. 相似文献
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引入一个新的能量分布函数,利用该能量分布函数与粒子速度分布函数耦合来求解一个热流场. 因而,这一能量分布函数与粒子速度分布函数和Boltzmann方程构成了一个新的格子Boltzmann模型. 这一模型满足质量、动量和能量守恒的准则. 用该模型对垂直平板间的狭缝热对流进行了数值模拟,数值结果表明,在Prandtl数为1,Grashof数在1.3×102—1×106之间时,流场将出现多个旋涡结构的流型. 得出了与Lee相一致的结论.
关键词:
能量分布函数
Boltzmann方程
热对流 相似文献
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采用格子Boltzmann方法(LBM)建立了气液固三相耦合的动力学模型,研究了相同尺度下上浮气泡与复杂壁面的相互耦合作用.首先,基于黏性流体理论,通过构建一组格子Boltzmann(LB)方程来描述气液两相的运动,并以LB离散体积力的形式计入了黏性力、表面张力和重力.同时,采用LBM中的Half-way反弹模型与有限差分格式相结合的方式进行固壁边界的处理.然后,利用本文建立的模型,对不同特征尺寸比条件下,气泡与考虑边缘效应的平面固壁和曲面固壁的耦合特性进行了研究.研究发现固壁边界条件以及特征尺寸比对气泡的运动和拓扑结构的变化都具有明显的非线性影响.最后,研究了流体属性对气泡与复杂壁面耦合规律的影响. 相似文献
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《中国科学:物理学 力学 天文学(英文版)》2010,(8)
The principle of the unsteady aerothermodynamics was theoretically investigated for the attached flow. Firstly, two simplified models with analytic solutions to the N-S equations were selected for the research, namely the compressible unsteady flows on the infinite flat plate with both time-varying wall velocity and time-varying wall temperature boundary conditions. The unsteady temperature field and the unsteady wall heat flux (heat flow) were analytically solved for the second model. Then, the interaction characteristic of the unsteady temperature field and the unsteady velocity field in the simplified models and the effects of the interaction on the transient wall heat transfer were studied by these two analytic solutions. The unsteady heat flux, which is governed by the energy equation, is directly related to the unsteady compression work and viscous dissipation which originates from the velocity field governed by the momentum equation. The main parameters and their roles in how the unsteady velocity field affects the unsteady heat flux were discussed for the simplified models. Lastly, the similarity criteria of the unsteady aerothermodynamics were derived based on the compressible boundary layer equations. Along with the Strouhal number Stu, the unsteadiness criterion of the velocity field, StT number, the unsteadiness criterion of the temperature field was proposed for the first time. Different from the traditional method used in unsteady aerodynamics which measures the flow unsteadiness only by the Stu number, present results show that the flow unsteadiness in unsteady aerothermodynamics should be comprehensively estimated by comparing the relative magnitudes of the temperature field unsteadiness criterion StT number with the coefficients of other terms in the dimensionless energy equation. 相似文献
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Lin Zheng Zhaoli GuoBaochang Shi Chuguang Zheng 《Journal of computational physics》2010,229(16):5843-5856
A lattice Boltzmann equation (LBE) for axisymmetric thermal flows is proposed. The model is derived from the kinetic theory which exhibits several features that distinguish it from other previous LBE models. First, the present thermal LBE model is derived from the continuous Boltzmann equation, which has a solid foundation and clear physical significance; Second, the model can recover the energy equation with the viscous dissipation term and work of pressure which are usually ignored by traditional methods and the existing thermal LBE models; Finally, unlike the existing thermal LBE models, no velocity and temperature gradients appear in the force terms which are easy to realize in the present model. The model is validated by thermal flow in a pipe, thermal buoyancy-driven flow, and swirling flow in vertical cylinder by rotating the top and bottom walls. It is found that the numerical results agreed excellently with analytical solution or other numerical results. 相似文献
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完全变光滑长度SPH法及其实现 总被引:8,自引:4,他引:4
提出完全变光滑长度SPH法及其算法实现.方程组基于对称形式核函数近似,SPH密度演化方程与变光滑长度方程隐式关联;在Springel提出的全守恒SPH方程组基础上,通过将分散核近似形式改进为对称核近似形式得到SPH动量方程和能量方程.采用迭代求解密度演化方程和变光滑长度方程,显式求解SPH动量方程和能量方程,增加的计算量相对很少.给出三个1D激波管算例和2D Sedov算例验证方法的有效性.数值结果表明,算法保持动量和能量的守恒律,解决了传统SPH法中由于变光滑长度影响带来的计算误差,且在模拟2DSedov问题时能得到比Springel方法更准确的压强峰值位置和中心压强值.特别适合于模拟爆炸与冲击、大变形大扭曲等密度梯度和光滑长度梯度剧烈变化的问题. 相似文献
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N. Sebald 《Applied Physics A: Materials Science & Processing》1980,21(3):221-236
A straight, steady-state cross-flow arc is burning in an N2 wind tunnel. The arc is held in position by the balance of the Lorentz forces produced by an external magnetic field perpendicular
to the arc axis and by the viscous forces of the gas flow acting on the arc column. The temperature field in the discharge
is determined spectroscopically using the radiation of N I lines. Because of the lack of rotational symmetry an inversion
method developed by Maldonado was used to determine the local emission coefficient from the measured integrated spectral intensity
distributions across the arc in various directions. For known local temperature the mass flow field inside the arc may be
evaluated from the convective term of the energy equation and the continuity equation. This is done by expanding the terms
of these two equations around the point of the temperature maximum into Fourier-Taylor series and determining coefficients
of the same order and power. The solution of the resulting set of algebraic equations yields the unknown coefficients of the
mass flow. The flow field obtained by these calculations shows a relatively strong counterflow through the arc core. In the
region for which the series expansion holds a partial structure pertaining to a closed double vortex can be recognized.
The terms of the momentum equation are calculated on the basis of these results. In order to obtain a better understanding
of the importance attributed to the individual local forces acting on the plasma, a simple model was devised which separates
the momentum equation into gradient and curl terms. The discussion shows that the gradient part of the Lorentz force causes
mainly the pressure gradient, while the much smaller rotational part of thej×B forces is responsible for propelling the mass flow. The momentum transport inside the arc as well as in its neighbourhood
is due to the viscous forces and to the pressure gradient. By contrast, at larger distances from the arc it is essentially
the inertial force that determines the momentum transport. It is shown that viscosity as a damping mechanism is necessary
for the existence of stationary flow fields as investigated in this work. 相似文献
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Impact Parameter and Bombarding Energy Dependence of Collective Flow in the Dynamics Process of Intermediate High Energy Heavy Ion Collision 下载免费PDF全文
The time processes of collective flow were calculated by use of BUU equation with momentum dependence mean field and nucleonhucleon collisions in medium.It is shown that the momentum dependence mean field effect and the medium effect on the collective flow are obvious and sensitive to impact parameter and bombarding energy. 相似文献
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Carmen Molina-París Paul R. Anderson Stephen A. Ramsey 《International Journal of Theoretical Physics》2001,40(12):2231-2258
The renormalization of a scalar field theory with a quartic self-coupling via adiabatic regularization in a Robertson-Walker spacetime is discussed. The adiabatic counterterms are presented in a way that is most conducive to numerical computations. A variation of the adiabatic regularization method is presented which leads to analytic approximations for the energy–momentum tensor of the quantum field and the quantum contribution to the effective mass of the mean field. Conservation of the energy–momentum tensor for the field is discussed and it is shown that the part of the energy–momentum tensor which depends only on the mean field is not conserved but the full renormalized energy–momentum tensor is conserved, as expected and required by the semiclassical Einstein's equation. It is also shown that if the analytic approximations are used the resulting approximate energy–momentum tensor is conserved. This allows a self-consistent backreaction calculation to be performed using the analytic approximations. The usefulness of the approximations is discussed. 相似文献
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A numerical scheme is presented for accurate simulation of fluid flow using the lattice Boltzmann equation (LBE) on unstructured mesh. A finite volume approach is adopted to discretize the LBE on a cell-centered, arbitrary shaped, triangular tessellation. The formulation includes a formal, second order discretization using a Total Variation Diminishing (TVD) scheme for the terms representing advection of the distribution function in physical space, due to microscopic particle motion. The advantage of the LBE approach is exploited by implementing the scheme in a new computer code to run on a parallel computing system. Performance of the new formulation is systematically investigated by simulating four benchmark flows of increasing complexity, namely (1) flow in a plane channel, (2) unsteady Couette flow, (3) flow caused by a moving lid over a 2D square cavity and (4) flow over a circular cylinder. For each of these flows, the present scheme is validated with the results from Navier–Stokes computations as well as lattice Boltzmann simulations on regular mesh. It is shown that the scheme is robust and accurate for the different test problems studied. 相似文献
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The effect of interfacial energy anisotropy on planar interface instability in a succinonitrile alloy under a small temperature gradient 下载免费PDF全文
The morphological stability of a planar interface with different crystallographic orientations is studied under a small positive temperature gradient using a transparent model alloy of succinonitrile.Novel experimental apparatus is constructed to provide a temperature gradient of about 0.37 K/mm.Under this small temperature gradient,the planar interface instability depends largely on the crystallographic orientation.It is shown experimentally that the effect of interfacial energy anisotropy on planar interface stability cannot be neglected even in a small temperature gradient system.Higher interfacial energy anisotropy leads the planar interface to become more unstable,which is different from the stabilizing effect of the interfacial energy on the planar interface.The experimental results are in agreement with previous theoretical calculations and phase field simulations. 相似文献