Journal of Non-Newtonian Fluid Mechanics最新文献

英文中文

Flow enhancement produced by a pulsatile flow of shear-thinning fluids in circular and concentric annular tubes 剪切稀化流体在圆形和同心环形管中的脉动流动所产生的流动增强效应

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-10-28 DOI: 10.1016/j.jnnfm.2024.105346

J. Báez-Amador , R. Baños , J. Arcos , F. Méndez , O. Bautista

Although the analysis of the flow enhancement of non-Newtonian fluids produced by pulsatile flows through tubes is common in the literature, the case of Carreau fluid has not been analyzed, which is the aim of this work. This study determines the flow enhancement caused by the pulsatile fluid flow through (a) a circular tube and (b) a concentric annular tube. We show that the flow rate enhancement of the shear-thinning fluid is controlled by the Carreau number

C u

, the Womersley number

W o

, the fluid power-law index

n

, the ratio between the outer and inner radii

κ

, a parameter

β

that represents the ratio between the infinite and zero-shear viscosities, and the amplitude of the oscillatory signal

ɛ

. In both cases (a) and (b), a numerical solution of the start-up of the hydrodynamic is evaluated. With the aid of the velocity solution, the volumetric flow rate is determined under periodic conditions after the initial transient has vanished. Then, the fractional increase in the mean flow rate

I

due to the pulsatile pressure gradient is calculated. Furthermore, an asymptotic solution for small, intermediate, and very large values of the Carreau number is performed to provide physical insight into flow enhancement.

虽然分析非牛顿流体脉动流过管子时产生的流动增强在文献中很常见，但尚未对卡略流体的情况进行分析，而这正是本研究的目的所在。本研究确定了脉动流体流经 (a) 圆管和 (b) 同心环形管时产生的流量增强。我们发现，剪切稀化流体的流速增强受卡略数 Cu、沃默斯利数 Wo、流体幂律指数 n、内外半径之比 κ、表示无限剪切粘度和零剪切粘度之比的参数 β 以及振荡信号振幅 ɛ 的控制。在(a)和(b)两种情况下，都对流体动力的启动进行了数值求解。借助速度解法，可以确定初始瞬态消失后周期条件下的容积流量。然后，计算出脉动压力梯度导致的平均流速 I 的部分增长。此外，还对卡略数的小值、中间值和极大值进行了渐近求解，以提供对流动增强的物理洞察。

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引用次数: 0

A fully-coupled implementation of the contravariant deformation tensor formulation for viscoelastic flows 粘弹性流动的反常变形张量公式的全耦合实现

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-10-28 DOI: 10.1016/j.jnnfm.2024.105345

Nick O. Jaensson, Martien A. Hulsen

We present a fully-coupled numerical scheme for computing steady and time-dependent viscoelastic flows. The scheme relies on the contravariant deformation tensor formulation and uses a Newton–Raphson iteration to solve the non-linear system of equations. The contravariant reformulation allows for the computation and implementation of the analytical Jacobian relatively easily, especially compared to other reformulations such as the log-conformation. The contravariant deformation tensor rotates in steady state shearing flows, which is solved here by “resetting” it as a pre-processing step in the numerical scheme, rather than a post-processing step. We use the finite element method with standard stabilization techniques (SUPG and DEVSS-G) for the spatial discretization. The numerical scheme is tested in three viscoelastic flow problems which are studied in terms of stability and accuracy: planar Couette flow, 2D flow around a cylinder and 3D flow around a sphere. For all problems, quadratic convergence is observed in both the difference between iterations and the residuals during the Newton–Raphson procedure. Moreover, we observe that the residuals are several orders smaller than the difference between iterations. A distinct advantage of the numerical scheme presented here, is that it significantly relaxes the requirement on the time-step size in time-dependent problems, as compared to explicit or semi-implicit methods. Moreover, steady states can be efficiently computed if the initial guess in the Newton–Raphson iteration is close enough to the solution.

我们提出了一种全耦合数值方案，用于计算稳定且随时间变化的粘弹性流动。该方案依赖于反变变形张量公式，并使用牛顿-拉斐森迭代来求解非线性方程组。与对数构型等其他重构公式相比，避变重构公式可以相对轻松地计算和实现分析雅各布因子。在稳态剪切流中，协变变形张量会发生旋转，这里的解决方法是将其 "重置 "作为数值方案中的预处理步骤，而不是后处理步骤。我们使用有限元法和标准稳定技术（SUPG 和 DEVSS-G）进行空间离散化。我们在三个粘弹性流动问题中对该数值方案进行了测试，研究了其稳定性和准确性：平面 Couette 流动、环绕圆柱体的二维流动和环绕球体的三维流动。对于所有问题，在牛顿-拉斐森过程中，迭代差和残差都呈二次收敛。此外，我们还观察到残差比迭代差小几个数量级。与显式或半隐式方法相比，本文提出的数值方案的一个显著优势是，它大大放宽了对时间相关问题中时间步长的要求。此外，如果牛顿-拉斐森迭代中的初始猜测足够接近解，则可以高效地计算稳定状态。

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引用次数: 0

Slot coating of time-dependent structured materials: Effects of thixotropy on the flow dynamics and operating limits 随时间变化的结构材料槽涂层：触变性对流动动力学和工作极限的影响

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-10-22 DOI: 10.1016/j.jnnfm.2024.105344

C. Sanchez-Perez, D. Maza, I.R. Siqueira, P.R. de Souza Mendes, M.S. Carvalho

Some of the most common liquid-like formulations rooted in the coating industry consist of rheologically complex structured materials such as inks, paints, and slurries. Yet, the impact of time-dependent structuring effects due to thixotropy on thin film coating applications remains elusive and still unclear. Here, we present a computational study of the effects of thixotropy on slot coating of time-dependent structured materials. By coupling a recent fluidity-based constitutive model for thixotropic materials with a well-established finite element/elliptic mesh generation method for free surface flows, we assess the role of thixotropy by comparing the predictions from the thixotropic model with those from a simple Generalized Newtonian Fluid model that uses the same flow curve for the material steady-state equilibrium viscosity. We find that thixotropy can indeed have a major impact on slot coating applications, potentially bringing strong implications not only to the flow dynamics but also to the operating limits of the process. In conclusion, the results and discussions we present in this study underscore the importance of accounting for thixotropy to genuinely model and fundamentally understand the behavior of time-dependent structured materials with complex rheology in processing flows like those ubiquitous across the broad fields of coating science and engineering.

涂料工业中最常见的一些液态配方由流变学结构复杂的材料组成，如油墨、油漆和泥浆。然而，由触变性引起的随时间变化的结构效应对薄膜涂层应用的影响仍然难以捉摸，尚不清楚。在此，我们介绍了触变性对随时间变化的结构材料的槽涂层影响的计算研究。通过将最新的基于流体力学的触变性材料构成模型与成熟的自由表面流有限元/椭圆网格生成方法相结合，我们比较了触变性模型与简单的广义牛顿流体模型的预测结果，评估了触变性的作用，后者使用相同的流动曲线来计算材料的稳态平衡粘度。我们发现，触变性确实会对槽涂层应用产生重大影响，不仅会对流动动力学产生重大影响，还会对工艺的操作极限产生重大影响。总之，我们在本研究中介绍的结果和讨论强调了考虑触变性对真正建模和从根本上理解具有复杂流变性的随时间变化的结构材料在加工流中的行为的重要性，这些材料在涂层科学和工程的广泛领域中无处不在。

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引用次数: 0

Analytic solution for the linear rheology of living polymers 活聚合物线性流变学的解析解

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-10-19 DOI: 10.1016/j.jnnfm.2024.105343

Vickie Chen , Charles T. Drucker , Claire Love , Jonathon Peterson , Joseph D. Peterson

It is often said that well-entangled and fast-breaking living polymers (such as wormlike micelles) exhibit a single relaxation time in their reptation dynamics, but the full story is somewhat more complicated. Understanding departures from single-Maxwell behavior is crucial for fitting and interpreting experimental data, but in some limiting cases numerical methods for solving living polymer models can struggle to produce reliable predictions/interpretations. In this work, we develop an analytic solution for the shuffling model of living polymers. The analytic solution is a converging infinite series, and it converges fastest in the fast-breaking limit where other methods can struggle.

人们常说，缠结良好且快速断裂的活聚合物（如蠕虫状胶束）在其爬行动力学中表现出单一的弛豫时间，但事实并非如此。理解单麦克斯韦行为的偏离对于拟合和解释实验数据至关重要，但在某些限制性情况下，求解活聚合物模型的数值方法很难产生可靠的预测/解释。在这项工作中，我们开发了活体聚合物洗牌模型的解析解。解析解是一个收敛无穷级数，在其他方法难以解决的快速突破极限中收敛最快。

引用次数: 0

The motion of a self-propelling two-sphere swimmer in a weakly viscoelastic fluid 弱粘弹性流体中自航双球游泳者的运动

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-10-15 DOI: 10.1016/j.jnnfm.2024.105330

Mary Agnes Joens , Patrick S. Doyle , Gareth H. McKinley

We study analytically the propulsion of a force- and torque-free swimmer composed of two counterrotating spheres of differing radii through a viscoelastic fluid described by the Giesekus constitutive model. Our analysis includes both swimmers composed of directly touching spheres and those composed of spheres separated by some finite distance. The propulsion speed of the swimmer is calculated by first expanding the equations of motion and the Giesekus constitutive model as a power series in the Weissenberg number, and then using the Lorentz reciprocal theorem to determine the first-order propulsion speed using the known flow fields for rotating and translating two-sphere geometries at zeroth order. We calculate the relative rotation speeds of the two spheres necessary to maintain the torque-free condition, including an approximate correction for fluid elasticity. The impact of the separation distance between the two spheres, the ratio of their radii, and the value of the Giesekus mobility parameter

α

on the propulsion speed are all examined; we find that the propulsion speed of the swimmer is maximized for two touching spheres with a radius ratio of approximately 0.7, with a Giesekus mobility parameter of

α = 0

, corresponding to an Oldroyd-B fluid. We also quantify how increased shear-thinning in the fluid, represented by increasing values of

α

, results in a significant decrease in the swimmer speed. Finally, through calculations of the fluid stresses around the two-sphere swimmer, we demonstrate the development of enhanced hoop stresses around the smaller sphere, which drive the expulsion of stretched fluid behind the smaller sphere and induce motion of the swimmer in the direction of the larger sphere.

我们通过分析研究了由两个不同半径的对转球体组成的无力和无力矩游泳者在粘弹性流体中的推进问题，粘弹性流体由吉塞克斯构成模型描述。我们的分析既包括由直接接触的球体组成的泳者，也包括由相隔一定距离的球体组成的泳者。计算游泳者的推进速度时，首先将运动方程和吉塞克斯构成模型展开为韦森伯格数的幂级数，然后利用洛伦兹倒易定理，利用已知的旋转和平移双球几何体的零阶流场确定一阶推进速度。我们计算了保持无扭矩条件所需的两个球体的相对旋转速度，包括对流体弹性的近似修正。我们研究了两个球体之间的分离距离、半径比以及吉塞克斯流动参数 α 值对推进速度的影响；我们发现，当两个接触球体的半径比约为 0.7，吉塞克斯流动参数 α=0 时，游泳者的推进速度最大，这与奥尔德罗伊德-B 流体相对应。我们还量化了流体中剪切稀化的增加（α 值增加）如何导致游泳者速度的显著下降。最后，通过计算双球游泳者周围的流体应力，我们证明了较小球体周围增强的箍应力的发展，这种箍应力驱动较小球体后面的拉伸流体排出，并诱导游泳者向较大球体的方向运动。

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引用次数: 0

A revisit of the development of viscoplastic flow in pipes and channels 管道和渠道中粘塑性流动的发展回顾

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-10-10 DOI: 10.1016/j.jnnfm.2024.105341

Alexandros Syrakos , Evgenios Gryparis , Georgios C. Georgiou

This study revisits the development of viscoplastic flow in pipes and channels, focusing on the flow of a Bingham plastic. Using finite element simulations and the Papanastasiou regularisation, results are obtained across a range of Reynolds and Bingham numbers. The novel contributions of this work include: (a) investigating a definition of the development length based on wall shear stress, a critical parameter in numerous applications; (b) considering alternative definitions of the Reynolds number in an effort to collapse the development length curves onto a single master curve, independent of the Bingham number; (c) examining the patterns of yielded and unyielded regions within the flow domain; and (d) assessing the impact of the regularisation parameter on the accuracy of the results. The findings enhance the existing literature, providing a more comprehensive understanding of this classic flow problem.

本研究重新审视了管道和通道中粘塑性流动的发展，重点关注宾汉塑料的流动。利用有限元模拟和帕帕纳斯提欧正则化，得出了一系列雷诺数和宾汉数的结果。这项工作的新贡献包括(a) 研究了基于壁面剪应力的发展长度定义，这是众多应用中的一个关键参数；(b) 考虑了雷诺数的替代定义，努力将发展长度曲线折叠到一条主曲线上，与宾厄姆数无关；(c) 研究了流域内屈服和未屈服区域的模式；以及 (d) 评估了正则化参数对结果准确性的影响。这些研究结果丰富了现有文献，使人们对这一经典流动问题有了更全面的了解。

引用次数: 0

Master curves for unidirectional flows of FENE-P fluids in rectilinear and curvilinear geometries FENE-P 流体在直线和曲线几何形状中单向流动的主曲线

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-10-05 DOI: 10.1016/j.jnnfm.2024.105332

P.S.D. Surya Phani Tej , Pratyush Kumar Mohanty , V. Shankar

We demonstrate that velocity profiles for steady, unidirectional shear flows of the FENE-P (Finitely-Extensible Nonlinear Elastic, with Peterlin closure) fluid, undergoing canonical rectilinear (pressure-driven flow in a rectangular channel or a circular pipe) or curvilinear (in Taylor–Couette or Dean configurations) flows, obey universal master curves that are a function only of the ratio

W i / L

, for a fixed solvent to solution viscosity parameter

β

. Here,

W i

is the Weissenberg number defined as the product of the dumbbell relaxation time and an appropriate shear rate, while

L

is the ratio of the maximum extension of the polymer to its equilibrium root-mean-square end-to-end distance. The data collapse and the resulting master curves for the velocity profile is a generalization of the recent demonstration of master curves for polymer viscosity and first normal stress coefficient for a FENE-P fluid under steady simple shear flow (Yamani and McKinley, 2023). For pressure-driven channel and pipe flows, we derive simple analytical expressions for the velocity profiles, in the high shear-rate regime of

W i / L ≫ 1

, that readily elucidate the role of finite extensibility of the polymer on the velocity profiles. In the

W i / L ≫ 1

regime, for all the flows considered, the limit of zero solvent (

β = 0

) is shown to be singular, owing to the absence of a high-shear plateau in the total solution viscosity, resulting in very different velocity profiles for

β = 0

and

β \to 0

我们证明，FENE-P（有限延伸非线性弹性，具有彼得林封闭性）流体的稳定单向剪切流的速度剖面，在经历典型的直线流（矩形通道或圆形管道中的压力驱动流）或曲线流（泰勒-库埃特或迪恩构型）时，服从通用主曲线，该曲线仅是 Wi/L 比值的函数，适用于固定的溶剂与溶液粘度参数 β。这里，Wi 是韦森伯格数，定义为哑铃弛豫时间与适当剪切速率的乘积，而 L 是聚合物的最大延伸与其平衡均方根端对端距离的比值。数据折叠和由此产生的速度剖面主曲线是对最近展示的稳定简单剪切流条件下 FENE-P 流体的聚合物粘度和第一法向应力系数主曲线的概括（Yamani 和 McKinley，2023 年）。对于压力驱动的通道流和管道流，我们推导出了 Wi/L≫1 高剪切速率条件下速度剖面的简单分析表达式，从而轻松阐明了聚合物的有限延伸性对速度剖面的影响。在 Wi/L ≫1 条件下，对于所考虑的所有流动，由于溶液总粘度不存在高剪切高原，溶剂为零的极限（β=0）被证明是奇异的，从而导致 β=0 和 β→0 时的速度曲线截然不同。

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引用次数: 0

Stokes layers in complex fluids 复杂流体中的斯托克斯层

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-10-03 DOI: 10.1016/j.jnnfm.2024.105328

D.R. Hewitt , N.J. Balmforth

Stokes’s second problem is reconsidered for three models of complex fluids: an elasto-viscoplastic fluid, a thixotropic viscoplastic fluid and a discontinuously shear-thickening fluid. In each case, the Stokes-layer dynamics is interrogated with a view to examining the signatures of the detailed rheology. Significant deformations are possible below the yield stress for elasto-viscoplastic fluids as a result of the excitation of elastic waves, particularly near resonances. Thixotropic fluids with viscosity bifurcations layer internally, but surface-speed signatures mostly appear similar to those for simple yield-stress fluids. Stokes-layer oscillations of discontinuous shear thickening fluids can prompt abrupt increases in viscosity, introducing sudden jumps in surface speed. Pre-existing experimental results for layers of kaolin slurries in a motorized, oscillating tray are reconsidered and compared with the results for elasto-viscoplastic and thixotropic fluids.

针对三种复杂流体模型重新考虑了斯托克斯的第二个问题：弹塑性粘塑性流体、触变性粘塑性流体和非连续剪切增稠流体。在每种情况下，都对斯托克斯层动力学进行了分析，以研究详细的流变学特征。由于弹性波的激发，尤其是在共振附近，弹塑性流体在屈服应力以下可能发生显著变形。具有粘度分叉的触变性流体会在内部形成一层，但表面速度特征大多与简单屈服应力流体相似。不连续剪切增稠流体的斯托克斯层振荡会促使粘度突然增加，从而带来表面速度的突然跳跃。对机动振荡托盘中高岭土浆料层的已有实验结果进行了重新考虑，并与弹塑性和触变性流体的实验结果进行了比较。

引用次数: 0

RANS predictions of turbulent non-isothermal viscoplastic fluid in pipe with sudden expansion 管道中突然膨胀的湍流非等温粘塑性流体的 RANS 预测

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-10-01 DOI: 10.1016/j.jnnfm.2024.105329

Maksim A. Pakhomov , Uzak K. Zhapbasbayev

A transition of Newtonian turbulent fluid to viscoplastic non-Newtonian fluid by cooling in a pipe with a sudden expansion is numerically studied. A recirculation region with negative velocities appears for fluid velocity profiles corresponding to the zone of flow recirculation. A small corner eddy disappears for a non-Newtonian fluid. Significant anisotropy between axial and radial components of Reynolds stresses is numerically shown. The heat transfer distributions along the pipe surface for turbulent non- and Newtonian fluids are qualitatively similar. The peak of heat transfer is shifted upstream in the Schwedoff-Bingham fluid in comparison with the Newtonian one. Authors’ numerical predictions are compared with numerical simulations by other authors for turbulent Schwedoff-Bingham fluids.

数值研究了牛顿湍流流体在突然膨胀的管道中通过冷却向粘塑性非牛顿流体的过渡。在与流动再循环区域相对应的流体速度剖面上，出现了一个具有负速度的再循环区域。对于非牛顿流体，一个小的角涡旋消失了。数值显示雷诺应力的轴向和径向分量之间存在明显的各向异性。湍流非牛顿流体和牛顿流体沿管道表面的传热分布在本质上是相似的。与牛顿流体相比，Schwedoff-Bingham 流体的传热峰值向上游移动。作者的数值预测与其他作者对湍流 Schwedoff-Bingham 流体的数值模拟进行了比较。

引用次数: 0

Theoretical study on nonlinear seepage mechanism in fractal dendritic fracture network of low permeability coal with water injection 注水低渗透煤分形树枝状断裂网非线性渗流机制理论研究

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-09-23 DOI: 10.1016/j.jnnfm.2024.105327

Zhen Liu , Shuai Dong , He Yang , Wenzhi Yang , Muyao Zhu

Coal seam water injection technology is adopted by many mines as an effective means of dust reduction in coal mines. There is a threshold pressure gradient phenomenon in the process of water injection in low permeability coal seam, which makes the flow of pressure water in the fracture structure of coal body present nonlinear seepage characteristics. To reveal the theoretical relationship between the structural parameters of coal and the nonlinear seepage characteristics, firstly, the Bingham fluid constitutive equation is used to describe the non-Newtonian behavior in low-permeability coal. Combined with the fractal tree-like bifurcation fracture network model, a mathematical analytical model of threshold pressure gradient is established. Secondly, the model was verified by high-pressure water invasion and radial seepage experiments, and the sensitivity of the model was analyzed. The results show that the error between the theoretical calculation value and the experimental measurement value is between 8.65 % and 42.4 %, which verifies the validity of the model. The above research results can provide a theoretical basis for improving the water injection effect of low permeability coal seam.

煤层注水技术作为煤矿降尘的有效手段，被许多煤矿采用。低透气性煤层注水过程中存在临界压力梯度现象，使得压力水在煤体断裂构造中的流动呈现非线性渗流特征。为揭示煤体结构参数与非线性渗流特性之间的理论关系，首先利用宾汉流体构成方程描述了低渗透煤中的非牛顿流体行为。结合分形树状分叉断裂网络模型，建立了阈值压力梯度的数学分析模型。其次，通过高压水入侵和径向渗流实验对模型进行了验证，并分析了模型的敏感性。结果表明，理论计算值与实验测量值的误差在 8.65 % 到 42.4 % 之间，验证了模型的有效性。上述研究成果可为改善低渗透煤层的注水效果提供理论依据。

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