Journal of Non-Newtonian Fluid Mechanics最新文献_第6页

The role of viscoelastic stress in an abruptly converging/diverging channel under the thin film approximation 薄膜近似下粘弹性应力在突然收敛/发散通道中的作用

IF 2.8 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-11-01 Epub Date: 2025-08-07 DOI: 10.1016/j.jnnfm.2025.105469

M.H. Sari , H. Ahmed , C. Putignano , G. Carbone , L. Biancofiore

We analyze a viscoelastic fluid, modeled by the Oldroyd-B constitutive equation, flowing in a sliding abruptly converging/diverging channel. We have chosen this geometry since it has connections to the typical elastohydrodynamic lubricated (EHL), for which recently (Sarı et al., 2024) have illustrated how a viscoelastic lubricant has a positive effect on the tribological performance by raising load and decreasing friction coefficient. We assume that the channel is thin and the magnitude of the “jump” is small enough allowing to take advantage of the thin film approximation. We observe that the step location is a critical factor for generating viscoelastic pressure due to the positive and constant increase in the volumetric flow rate. Presence of viscoelasticity quantified by the ratio between fluid relaxation time and residence time, called Deborah number. A high Deborah number leads to a significant increment in pressure if the step is close to the inlet, while, if it is close to an outlet, the pressure decreases compared to Newtonian flows. While in most of the work, the pressure at the boundaries (inlet and outlet) is set to zero, we also tested more realistic boundary conditions in which the pressure is equal to the average elastic stress, showing that the two kinds of boundary conditions have a similar qualitative behavior. Lastly, a texture geometry, composed by one converging followed by one diverging steps, is inspected to mimic an EHL profile. We find what is the optimal distance between the steps to maximize the load. The role of the elastic stress in this texture profile is finally discussed.

本文用Oldroyd-B本构方程模拟了一种粘弹性流体，该流体在一个滑动的突然收敛/发散通道中流动。我们之所以选择这种几何结构，是因为它与典型的弹性流体动力润滑（EHL）有联系，最近（sarir et al., 2024）已经说明了粘弹性润滑剂如何通过提高载荷和降低摩擦系数对摩擦学性能产生积极影响。我们假设通道很薄，“跳跃”的幅度足够小，可以利用薄膜近似。我们观察到，台阶位置是产生粘弹性压力的关键因素，因为体积流量不断增加。粘弹性的存在由流体松弛时间与停留时间之比量化，称为黛博拉数。如果阶跃靠近入口，高底波拉数会导致压力显著增加，而如果阶跃靠近出口，则与牛顿流相比压力降低。虽然在大多数工作中，边界（入口和出口）的压力被设置为零，但我们也测试了更现实的边界条件，其中压力等于平均弹性应力，表明两种边界条件具有相似的定性行为。最后，由一个收敛步骤和一个发散步骤组成的纹理几何形状被检查以模拟EHL轮廓。我们找到了使负荷最大化的最优步骤之间的距离。最后讨论了弹性应力在该织构中的作用。

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引用次数: 0

Pairwise interactions of active particles in a yield stress fluid 屈服应力流体中活性粒子的成对相互作用

IF 2.8 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-11-01 Epub Date: 2025-09-03 DOI: 10.1016/j.jnnfm.2025.105486

Yan Xia , Zhaosheng Yu , Xiao Hu , Chenlin Zhu , Zhaowu Lin

In this work, we numerically investigate the hydrodynamic interactions between two active particles (modeled as squirmers) in a Bingham yield stress fluid, and quantify the influence of the Bingham number and squirmer type on reorientation and scattering in face-to-face and crossing configurations. In the face-to-face configuration, increased Bingham number leads to greater reorientation of neutral and puller-type squirmers. In crossing interactions, yield stress suppresses the strong deflection observed in Newtonian fluids at small incidence angles. In contrast, for larger initial angles, the final separation angle between the squirmers is significantly increased in a yield stress fluid compared to that in a Newtonian fluid. To elucidate the underlying mechanism, we compute hydrodynamic torques on particles by constraining their orientations while allowing translation. In the face-to-face configuration, we find that yield stress amplifies the near-field torques on each particle, driving them to rotate away from one another and thereby increasing scattering. In the side-by-side configuration, yield stress qualitatively alters the sign and magnitude of the hydrodynamic torque on neutral and puller-type squirmers, reducing their tendency to rotate away and thereby favoring sustained parallel swimming. These results provide insight into the rheological behavior and transport properties of active suspensions in complex fluids.

在这项工作中，我们数值研究了宾厄姆屈服应力流体中两个活跃粒子（模拟为蠕动子）之间的流体动力学相互作用，并量化了宾厄姆数和蠕动子类型对面对面和交叉构型中重定向和散射的影响。在面对面配置中，宾厄姆数的增加导致中性和拉杆型蠕动器的重新定向更大。在交叉相互作用中，屈服应力抑制牛顿流体在小入射角下观察到的强偏转。相反，对于较大的初始角，与牛顿流体相比，屈服应力流体中蠕动器之间的最终分离角显着增加。为了阐明潜在的机制，我们通过在允许平移的同时限制粒子的方向来计算粒子的流体动力扭矩。在面对面的结构中，我们发现屈服应力放大了每个粒子上的近场扭矩，驱动它们相互旋转，从而增加了散射。在并排配置中，屈服应力定性地改变了中性和拉杆式蠕动器的流体动力扭矩的符号和大小，减少了它们旋转远离的倾向，从而有利于持续的平行游动。这些结果有助于深入了解活性悬浮液在复杂流体中的流变行为和输运特性。

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引用次数: 0

Tracking polymer orientation and flow leading to unsteady cross-slot flow: High-speed imaging and modeling 跟踪导致非定常交叉槽流动的聚合物取向和流动：高速成像和建模

IF 2.8 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-11-01 Epub Date: 2025-08-05 DOI: 10.1016/j.jnnfm.2025.105471

Paul F. Salipante , Michael Cromer , Gerardo E. Pradillo , Steven D. Hudson

Viscoelastic flow instabilities limit polymer processing rates. High-speed optical measurements of stress and flow are used to provide insight into the relationships between polymer orientation and flow field that lead to viscoelastic fluctuations and instability. The flow of high-molar-mass polyethylene oxide solutions through a cross-slot geometry transitions from a symmetric flow into an asymmetric flow that continually switches its asymmetric configuration at sufficiently high flow rates. Data was acquired by synchronized particle velocimetry and polarization imaging at sub-ms resolution. Three-dimensional numerical simulations using the Giesekus constitutive model demonstrate similar flow switching behavior. Both experiments and simulations show a growth of flow–polymer misalignment near stagnation points prior to switching of the flow asymmetry direction. The role of polymer misalignment demonstrates the important role of stagnation points in flow fields, and this understanding may suggest ways to improve control of instabilities for more efficient processing.

粘弹性流动的不稳定性限制了聚合物的加工速度。高速光学应力和流动测量用于深入了解聚合物取向和流场之间的关系，从而导致粘弹性波动和不稳定性。高摩尔质量的聚乙烯氧化物溶液通过交叉槽几何结构从对称流动转变为不对称流动，并在足够高的流速下不断转换其不对称结构。数据通过同步粒子测速和亚毫秒分辨率的偏振成像获得。采用Giesekus本构模型的三维数值模拟显示了类似的流动切换行为。实验和模拟结果都表明，在流动不对称方向转换之前，流动-聚合物不对准在驻点附近增长。聚合物错位的作用表明了流场中驻点的重要作用，这一认识可能为提高不稳定性的控制提供了更有效的处理方法。

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引用次数: 0

A cluster of N-bubbles driven along a channel at high imposed driving pressure: Bubble areas, film lengths and vertex locations 在高驱动压力下沿通道驱动的n个气泡簇：气泡面积、薄膜长度和顶点位置

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-10-01 Epub Date: 2025-07-05 DOI: 10.1016/j.jnnfm.2025.105455

P. Grassia , H. Rajabi , C. Torres-Ulloa , J. Hernández-Montelongo , J. Potter , J. Moston

A two-dimensional foam staircase structure is considered with

N

bubbles stacked in a zigzag fashion along a channel. A model is analysed for determining the configuration of a staircase set into motion under the action of a high imposed driving pressure. Minimum and also maximum permitted bubble sizes for which the staircase structure survives are identified. Both minimum and maximum sizes are found to be decreasing functions of

N

. Behaviours in the limit of large

N

are identified, albeit tentatively, as the methodology for computing the staircase structure is found to be highly stiff. Indeed, as

N

increases, tiny changes in the staircase configuration at the downstream end lead to large geometric changes at the upstream end, limiting the domain of

N

values for which structures can be readily computed.

考虑了一个二维泡沫楼梯结构，其中N个气泡沿通道以之字形堆叠。分析了一个模型，用于确定在高施加的驱动压力作用下运动的楼梯的结构。确定了楼梯结构存活的最小和最大允许气泡尺寸。最小和最大尺寸都被发现是N的递减函数。在大N极限下的行为被确定，尽管是暂时的，因为计算楼梯结构的方法被发现是高度僵硬的。实际上，随着N的增加，下游端阶梯结构的微小变化会导致上游端发生较大的几何变化，从而限制了易于计算结构的N值范围。

引用次数: 0

Saffman – Taylor instability in poorly miscible viscoelastic flows 低混相粘弹性流中的Saffman - Taylor不稳定性

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-10-01 Epub Date: 2025-07-10 DOI: 10.1016/j.jnnfm.2025.105468

Oleg A. Logvinov , Isabel M. Irurzun

A renowned problem of a viscous fluid displacement by a less viscous one from a Hele-Shaw cell was considered. Both fluids exhibited viscoelastic Maxwell rheology with upper convective derivative. A unified approach, which is independent of particular rheology, was applied to derive averaged two-dimensional equations of motion (so-called Hele-Shaw models). The equations were based on Reynolds class averaging procedure. Linear stability analysis was performed under these new governing equations with a special set of boundary conditions for the case of viscoelastic fluids. Dispersion curves showed that, in contrast to the purely Newtonian case, two regimes of disturbance growth were possible: viscous and elastic. We studied the influence of the main dimensionless parameters, in particular, two Deborah numbers for a displacing and a displaced fluid, and the viscosity ratio, on the growth of small disturbances on the interface. In accordance with previous theoretical studies, in the elastic regime there is a disturbance with an infinite growth rate.

本文考虑了一个著名的赫尔-肖单元中粘性较低的流体取代粘性流体的问题。两种流体均表现出粘弹性麦克斯韦流变性，具有上对流导数。一种独立于特定流变学的统一方法被应用于推导平均二维运动方程（所谓的Hele-Shaw模型）。方程基于Reynolds类平均程序。对于粘弹性流体，在新的控制方程和一组特殊的边界条件下进行了线性稳定性分析。色散曲线表明，与纯牛顿的情况相反，扰动增长的两种形式是可能的：粘性和弹性。我们研究了主要的无量纲参数，特别是置换流体和被置换流体的两个Deborah数和粘度比对界面上小扰动生长的影响。根据以往的理论研究，在弹性状态下存在一个无限增长速率的扰动。

引用次数: 0

A generalized lumped-parameter model for analyzing external gear machines with shear-thinning operating fluids 具有剪切变薄工作流体的外齿轮机的广义集总参数模型

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-10-01 Epub Date: 2025-07-20 DOI: 10.1016/j.jnnfm.2025.105470

Austin Zapata , Andrea Vacca , Rich Diemar , Mark Hamersky , David Oertel

External gear machines are frequently used to transport non-Newtonian fluids in high pressure applications. However, a coexistence of low viscosity and significant shear thinning can present pumping challenges for off-the-shelf EGM designs. These difficulties arise in part due to the effects of viscoelasticity on the displacing action of the pump and the internal flow leakages. Previous studies have focused on three-dimensional CFD, but limited work has been done on a simulation tool for these effects which considers the radial micromotions of the gears. In this work, a fast lumped-parameter model for the simulation of external gear machines with non-Newtonian operating fluids is developed by dividing the pump into several control volumes and flow paths between them. A method of estimating flow for non-Newtonian fluid models is proposed as well as a novel Reynolds-type equation, and both are implemented within the model. The article then proceeds to compare the mean flow and pressure ripple predicted by this model with experiments to validate the methodology. The mean relative error of the model for the steady-state flowrate prediction is found to be 1.5 % and that of the amplitude prediction for the transient pressure ripple response is found to be 7.4 %. Finally, the results of the model are discussed and conclusions are drawn.

外啮合齿轮机经常用于输送非牛顿流体在高压应用。然而，低粘度和显著剪切变薄的共存给现成的EGM设计带来了挑战。出现这些困难的部分原因是粘弹性对泵的驱替作用和内部流动泄漏的影响。以前的研究主要集中在三维CFD上，但是在考虑齿轮径向微运动的这些影响的模拟工具上做了有限的工作。本文通过将泵划分为若干控制容积和控制容积之间的流道，建立了一种用于非牛顿工作流体外啮合齿轮机仿真的快速集总参数模型。提出了一种非牛顿流体模型的流量估计方法和一种新的雷诺方程，并在模型内实现。然后，将该模型预测的平均流量和压力脉动与实验进行比较，以验证该方法。该模型对稳态流量预测的平均相对误差为1.5%，对瞬态压力脉动响应的幅值预测的平均相对误差为7.4%。最后，对模型的结果进行了讨论，并得出了结论。

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引用次数: 0

Smooth thin-layer asymptotic expansions for free-surface yield-stress flows 自由表面屈服应力流动的光滑薄层渐近展开式

IF 2.8 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-10-01 Epub Date: 2025-07-25 DOI: 10.1016/j.jnnfm.2025.105456

Danila Denisenko, Gaël Loïc Richard, Guillaume Chambon

We derive two asymptotic expansions with a smooth velocity field for free-surface viscoplastic flows down an inclined plane in the shallow-flow approximation. The first expansion is based on the classical Herschel–Bulkley constitutive law by using asymptotic matching at the interface between the pseudo-plug and the sheared layer. In contrast to previous works, where authors considered only one term in the transition layer, we compute two extra terms to guarantee a smooth transition of the inertial contribution from the sheared layer to the pseudo-plug. However, the terms associated to the transition layer are solutions of nonintegrable equations, thus preventing the potential use of this expansion for deriving a shallow-flow model. The second asymptotic expansion is based on an alternative tensorial extension of the Herschel–Bulkley law, for which the alignment between the yield-stress tensor and the strain-rate tensor is relaxed, while the von Mises criterion is kept. In this case, smooth asymptotic expansions of the velocity field are given by fully analytical expressions. Comparison of these two expansions with experiments shows that both give essentially equivalent and relatively good agreement.

在浅流近似下，导出沿斜面自由表面粘塑性流动的两个光滑速度场渐近展开式。第一个扩展是基于经典的Herschel-Bulkley本构定律，通过在伪塞和剪切层之间的界面处使用渐近匹配。与以前的工作相反，作者只考虑过渡层中的一个项，我们计算了两个额外的项，以保证从剪切层到伪插头的惯性贡献的平滑过渡。然而，与过渡层相关的项是不可积方程的解，因此阻止了该展开用于推导浅流模型的潜在使用。第二次渐近展开是基于Herschel-Bulkley定律的备选张量扩展，其中屈服应力张量和应变速率张量之间的对齐被放宽，而von Mises准则保持不变。在这种情况下，速度场的光滑渐近展开式由完全解析表达式给出。两种展开式与实验结果的比较表明，两种展开式具有基本等价和较好的一致性。

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引用次数: 0

Dynamics of bubbles rising in viscoelastic liquids and birefringence measurement in the presence of a surfactant 粘弹性液体中气泡上升的动力学及表面活性剂存在下的双折射测量

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-10-01 Epub Date: 2025-07-17 DOI: 10.1016/j.jnnfm.2025.105458

Pınar Eribol , Arda Inanc , Ebru Sarioglu , Erkan Senses , A. Kerem Uguz

A comprehensive study was conducted on the dynamics of bubbles in a 0.10–0.40 wt% polyacrylamide (PAAM) solution in the presence and absence of a surfactant, considering various shape parameters and dimensionless numbers, for a broad range of bubble volumes, from 5 to 2000 mm³. A detailed rheological analysis is performed for the chemical solutions. A safe injection period is determined such that a bubble is unaffected by another one. Unsteady results are presented. Steadiness of the bubble is checked for various shape parameters, and safe column length is determined. Uncertainty analysis is also performed. Cusp formation at the bubble tail and its correlation with the surrounding stress were assessed using flow birefringence. No discontinuity in bubble velocity is reported. As the water-soluble surfactant, sodium dodecyl sulfate (SDS), is added at 10 and 100 ppm concentration, the bubbles stretch out more in the vertical direction, and cusp formation commences at a lower volume and is more pronounced.

在0.10-0.40 wt%的PAAM溶液中，考虑到各种形状参数和无因次数，在5 - 2000 mm3的气泡体积范围内，对存在和不存在表面活性剂的气泡动力学进行了全面研究。对化学溶液进行了详细的流变分析。安全注入周期的确定使得一个气泡不受另一个气泡的影响。给出了非定常结果。对各种形状参数进行了气泡稳定性校核，并确定了安全柱长。并进行了不确定度分析。用流动双折射法评价了气泡尾部尖点的形成及其与周围应力的相关性。气泡速度无间断现象。当水溶性表面活性剂十二烷基硫酸钠（SDS）在10 ppm和100 ppm浓度下添加时，气泡在垂直方向上伸展得更大，尖头形成的体积更小，而且更明显。

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引用次数: 0

Pair interactions of viscous drops suspended in a shear-thinning viscous and viscoelastic shear flow 剪切减薄黏性和粘弹性剪切流中悬浮黏性液滴的对相互作用

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-10-01 Epub Date: 2025-06-22 DOI: 10.1016/j.jnnfm.2025.105454

Haoqian Wang, Anik Tarafder, Kausik Sarkar

Pair interactions of viscous (constant viscosity) drops suspended in a shear-thinning viscous and viscoelastic shear flow are numerically investigated using a front-tracking method. Apart from the usual passing trajectories, where drops interact and slide past each other in the streamwise direction, we note two new trajectories. Shear-thinning (power law index n <1) introduces reversed trajectories, where after interaction the drops reverse directions, and viscoelasticity (nonzero Weissenberg number Wi) gives rise to tumbling trajectories, where the drops revolve around each other. In a viscous medium, only passing and reversed trajectories are seen in an n-Ca phase plot. Passing trajectories transition into reversed ones for small n (more shear-thinning) and low capillary numbers Ca with the critical n for transition increasing with decreasing capillary number. In a viscoelastic medium, one finds all three trajectories in an n-Wi phase plot: reversed trajectories for low Wi and low n, tumbling for high Wi and high n, and passing trajectories in between. The trajectories are explained in terms of the streamline topology around a single drop in shear: a region of reversed streamlines due to shear-thinning, and a region of spiraling streamlines due to viscoelasticity, both effects being more prominent for low Ca values (less deformable drops). Physical reasoning for the reversed streamlines in the presence of shear-thinning is offered, relating it to the pressure field.

采用前沿跟踪方法，对剪切-稀化粘弹性剪切流中悬浮液对相互作用进行了数值研究。除了通常的通过轨迹，水滴相互作用并在流向上相互滑动，我们注意到两个新的轨迹。剪切减薄（幂律指数n <；1）引入了反向轨迹，其中相互作用后液滴反转方向，粘弹性（非零Weissenberg数Wi）产生了翻滚轨迹，其中液滴相互旋转。在粘性介质中，在n-Ca相图中只能看到通过和反转的轨迹。小n（剪切变薄）和低毛细数Ca时，过渡的临界n随着毛细数的减少而增加。在粘弹性介质中，可以在n-Wi相位图中找到所有三种轨迹：低Wi和低n的反向轨迹，高Wi和高n的翻滚轨迹，以及介于两者之间的通过轨迹。轨迹可以用围绕单个剪切滴的流线拓扑来解释：由于剪切变薄而形成的反向流线区域，以及由于粘弹性而形成的螺旋流线区域，这两种影响在低Ca值（变形滴较少）时更为突出。给出了在剪切变薄的情况下出现反流线的物理原因，并将其与压力场联系起来。

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引用次数: 0

Enhanced double distribution function lattice Boltzmann method for simulation of viscoelastic and shear-thinning fluids flow 粘弹性和剪切稀化流体流动模拟的增强双分布函数晶格玻尔兹曼方法

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2025-10-01 Epub Date: 2025-07-16 DOI: 10.1016/j.jnnfm.2025.105467

Hamed Vaseghnia , Espen Jettestuen , Knut Erik Teigen Giljarhus , Olav Aursjø , Jan Ludvig Vinningland , Aksel Hiorth

In this study, we use a two-dimensional multiple relaxation time (MRT) approach for simulating polymeric fluids. A correction term is introduced into the source term to remove non-physical terms and improve numerical accuracy of the simulations. The correction term preserves the locality of the collision process and ensures numerical stability across a range of Weissenberg numbers when coupled with non-linear constitutive equations.

This approach is applied to the Phan-Thien-Tanner (PTT) model and the Oldroyd-B model, where the first exhibits viscoelastic and shear-thinning behavior while the second is purely viscoelastic. To evaluate the numerical accuracy and stability of the proposed MRT-LBM approach, we apply it to planar Poiseuille flow as well as simplified four-roll mill benchmarks. In the case of the four-roll mill, we specifically examine the effects of shear-thinning and viscoelasticity in steady elongational flows and their transitions to oscillatory and chaotic or turbulent behaviors, known as elastic instability. Our results indicate that the non-linearity in the stress-strain rate relationship and the microstructural dynamics of polymer chains, as described by non-linear constitutive models, make the standard BGK-LBM approach incapable to accurately capture the complex behavior of polymers without introducing numerical artifacts. On the other hand the MRT-LBM method maintains numerical stability and accuracy across a broad range of Weissenberg (up to

W i = 20

) and should therefore be the method of choice when simulating these types of flows.

在这项研究中，我们使用二维多重弛豫时间（MRT）方法来模拟聚合物流体。在源项中引入校正项，消除了非物理项，提高了模拟的数值精度。校正项保留了碰撞过程的局部性，并确保了当与非线性本构方程耦合时，在Weissenberg数范围内的数值稳定性。该方法适用于Phan-Thien-Tanner （PTT）模型和Oldroyd-B模型，前者表现为粘弹性和剪切减薄行为，而后者则是纯粘弹性的。为了评估所提出的MRT-LBM方法的数值精度和稳定性，我们将其应用于平面泊泽维尔流和简化的四辊轧机基准。在四辊轧机的情况下，我们特别研究了剪切变薄和粘弹性在稳定拉长流动中的影响，以及它们向振荡和混沌或湍流行为的转变，即弹性不稳定性。我们的研究结果表明，非线性本构模型所描述的应力-应变速率关系和聚合物链微观结构动力学的非线性，使得标准的BGK-LBM方法在不引入数值伪影的情况下无法准确捕捉聚合物的复杂行为。另一方面，MRT-LBM方法在广泛的Weissenberg范围内（高达Wi=20）保持数值稳定性和准确性，因此应该是模拟这些类型流动时的首选方法。

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引用次数: 0