Journal of Non-Newtonian Fluid Mechanics最新文献

A lattice Boltzmann flux solver with log-conformation representation for the simulations of viscoelastic flows at high Weissenberg numbers

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-11-26 DOI: 10.1016/j.jnnfm.2024.105351

Hua Zhang , Chang Shu , Lian-Ping Wang , Yaguang Liu

In this work, a viscoelastic lattice Boltzmann flux solver (VLBFS) with log-conformation representation is proposed for simulating the incompressible flows of a viscoelastic fluid at high Weissenberg number conditions. Compared with the original lattice Boltzmann flux solver (LBFS), the present method has two main new features. First, the method solves the polymer constitutive equations with log-conformation representation. Second, an upwind-biased scheme is incorporated in the interpolation when performing flux reconstructions at the cell interface. With the aid of these two treatments, the numerical stability of VLBFS is significantly improved, making it capable of solving high Weissenberg number problems (HWNP). Compared with using the lattice Boltzmann method (LBM) to solve the viscoelastic fluid flow, VLBFS inherits the advantages of LBFS, such as flexible mesh generation, decoupling of the grid spacing and time interval, and low memory requirement. VLBFS can also precisely recover the macroscopic constitutive equation. The present method has been critically validated using three benchmark cases, namely, the plane Poiseuille flow, lid-driven cavity flow, and 4:1 abrupt planar contraction flow. The numerical results fully demonstrate the solver’s powerful ability in simulating HWNP.

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引用次数: 0

Analysis of the shear thickening behavior of a fumed silica suspension using QL-LAOS approach

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-11-26 DOI: 10.1016/j.jnnfm.2024.105355

E. Fernández-Díaz , F.J. Rubio-Hernández , J.F. Velázquez-Navarro

The feasibility of applying quasi-linear large amplitude oscillatory shear (QL-LAOS) approach to a shear thickening (ST) fumed silica suspension was tested. While the characteristic time has been used as the parameter for the original QL-LAOS analysis of shear thinning fluids, we obtained that a description based upon increasing stiffness is more appropriate for ST fumed silica suspensions. Very low

(\leq 1.5)

third to first harmonics ratio were obtained indicating the need of alternative criteria to identify QL-LAOS behavior in ST suspensions. Consequently, a method based upon the best fit of an ellipse to the experimental Lissajous-Bowditch curves was proposed. Compliances were obtained from areas of viscous and elastic fitted ellipses. The dependence of the material functions obtained by using a Jeffrey´s mechanical viscoelastic framework with angular frequency supports the idea of ST microstructure evolves by increasing with shear the number of small hydroclusters.

{"title":"Analysis of the shear thickening behavior of a fumed silica suspension using QL-LAOS approach","authors":"E. Fernández-Díaz , F.J. Rubio-Hernández , J.F. Velázquez-Navarro","doi":"10.1016/j.jnnfm.2024.105355","DOIUrl":"10.1016/j.jnnfm.2024.105355","url":null,"abstract":"<div><div>The feasibility of applying quasi-linear large amplitude oscillatory shear (QL-LAOS) approach to a shear thickening (ST) fumed silica suspension was tested. While the characteristic time has been used as the parameter for the original QL-LAOS analysis of shear thinning fluids, we obtained that a description based upon increasing stiffness is more appropriate for ST fumed silica suspensions. Very low <span><math><mrow><mo>(</mo><mrow><mo>≤</mo><mn>1.5</mn></mrow><mo>)</mo></mrow></math></span> third to first harmonics ratio were obtained indicating the need of alternative criteria to identify QL-LAOS behavior in ST suspensions. Consequently, a method based upon the best fit of an ellipse to the experimental Lissajous-Bowditch curves was proposed. Compliances were obtained from areas of viscous and elastic fitted ellipses. The dependence of the material functions obtained by using a Jeffrey´s mechanical viscoelastic framework with angular frequency supports the idea of ST microstructure evolves by increasing with shear the number of small hydroclusters.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"335 ","pages":"Article 105355"},"PeriodicalIF":2.7,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142744986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

The influence of thixotropy on bubble growth in thixotropic yield stress fluids: Insights from numerical simulations

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-11-19 DOI: 10.1016/j.jnnfm.2024.105353

Yixuan Hou , Zhao Jin , Xinzhe Que , Yongchao Zhou , Yiping Zhang

Bubble behaviors in structured fluids are of great interests in industrial applications, while there is currently a lack of understanding regarding the effect of thixotropic microstructure on the bubble formation process. To this end, this study explores the influence of thixotropy on bubble growth in thixotropic yield stress fluids by numerical simulations using the Arbitrary Lagrangian-Eulerian (ALE) method. The numerical results reveal that, with the increase in the thixotropy number, the bubbles at detachment transform from inverted conical to spherical shapes at lower gas flow rates, and from spindle to conical shapes at higher gas flow rates, along with the decreased detachment volume and time. It is also found that the effect of gas flow rate varies with different thixotropy numbers. The flow field of the structured fluid reveals that the increases in gas flow rate primarily promote the structural destruction near the bubble tip, while the increase in thixotropy number facilitate the fluid flow around the bubble, with the significant reduction of the low-shear zones and expansion of the yielded zones near the equatorial plane. As a result, modulating the fluid flow with thixotropy number mainly influences the hydrodynamic pressure on the bubble. Based on a force balance model, the forces acting on the bubble are then calculated by integrating the stress on the interface, and it is found that thixotropy number controls the bubble detachment state with the drag effect. Accordingly, the mechanisms governing the influence of thixotropy on drag effect are discussed considering the flow field characteristics and the correlations of drag coefficients. This work helps to deepen the understanding of the bubble behaviors in structured fluids.

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引用次数: 0

Suppression and augmentation in vortex shedding frequency due to fluid elasticity

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-11-19 DOI: 10.1016/j.jnnfm.2024.105348

A. Chauhan, Sana Raffi, C. Sasmal

Several previous experimental and numerical studies have demonstrated the suppression of vortex shedding frequency from bluff bodies, such as circular cylinders, due to fluid elasticity induced by adding solid polymer additives to a solvent like water, even in parts per million (ppm) quantities. However, this study reveals a more complex relationship between the two using extensive two-dimensional (2D) direct numerical simulations (DNS) of flows past a circular cylinder at a fixed Reynolds number of 100. Our findings show that the vortex shedding frequency initially decreases with increasing Weissenberg number (a measure of fluid elasticity), reaches a minimum at a critical Weissenberg number, and then increases with further increments in the Weissenberg number. The same non-monotonic trend is also observed in the temporal variation of the spanwise velocity component fluctuation within the flow domain. This study aims to elucidate the reasons behind these non-monotonic trends in vortex shedding frequency and velocity component fluctuations as functions of the Weissenberg number. Our detailed analysis attributes these trends to significant alterations in the vortex-shedding mechanism as fluid elasticity increases due to the appearance of inertio-elastic instability at higher Weissenberg numbers. Our findings also align with limited experimental observations of similar unexpected behaviors in viscoelastic fluids, providing new insights into the underlying mechanisms. Moreover, the study highlights that shear-thinning behavior in viscoelastic fluids counteracts these non-monotonic trends, instead promoting a monotonic increase in vortex shedding frequency with the Weissenberg number. Finally, the 2D simulation results show both qualitative and quantitative agreement with limited three-dimensional (3D) simulations conducted at higher Weissenberg numbers where the flow may transit from 2D to 3D due to the appearance of inertio-elastic instability.

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引用次数: 0

Viscoelastic model hierarchy for fiber melt spinning of semi-crystalline polymers

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-11-16 DOI: 10.1016/j.jnnfm.2024.105349

Manuel Ettmüller , Walter Arne , Nicole Marheineke , Raimund Wegener

In the fiber melt spinning of semi-crystalline polymers, the degree of crystallization can be non-homogeneous over the cross-section of the fiber, affecting the properties of the end product. For simulation-based process design, the question arises as to which fiber quantities and hence model equations must be resolved in radial direction to capture all practically relevant effects and at the same time imply a model that can be computed with reasonable effort. In this paper, we present a hierarchy of viscoelastic two-phase fiber models ranging from a complex, fully resolved and highly expensive three-dimensional description to a cross-sectionally averaged, cheap-to-evaluate one-dimensional model. In particular, we propose a novel stress-averaged one-two-dimensional fiber model, which circumvents additional assumptions on the inlet profiles needed in the established stress-resolved fiber model by Doufas et al. (2001). Simulation results demonstrate the performance and application regime of the dimensionally reduced models. The novel stress-averaged variant provides fast and reliable results, especially in the regime of low flow-enhanced crystallization.

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引用次数: 0

Enhancing polymer fiber orientation with 3D-printed shell–core structures

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-11-15 DOI: 10.1016/j.jnnfm.2024.105352

Mengfan Lou, Zhenyu Ouyang

This study numerically investigates the flow dynamics and fiber orientation in enhanced polymer shell–core structures during 3D printing using the smoothed particle hydrodynamics method. A microstructure-based fiber suspension model, coupled with a shear-thinning viscosity model, is employed to assess the effects of varying material viscosities, fiber aspect ratios and volume fractions, and substrate speeds on fiber orientation distribution. Our results demonstrate that fiber orientation in deposited layers is particularly sensitive to variations in the viscosity of the shell material, while changes in the core material viscosity have a smaller and more localized impact on fiber orientation. Furthermore, fiber orientation is strongly influenced by the product of the fiber aspect ratio α_r and volume fraction ϕ; as α_rϕ increases, fibers tend to align with the flow direction of materials. However, adjusting the fiber aspect ratio and volume fraction while maintaining the same α_rϕ results in slight changes to fiber alignment. Additionally, lower substrate speeds cause upstream material accumulation, increasing deposition layer height and creating differences in fiber orientation between the core and shell regions. An appropriate increase in substrate speed can mitigate these effects.

{"title":"Enhancing polymer fiber orientation with 3D-printed shell–core structures","authors":"Mengfan Lou, Zhenyu Ouyang","doi":"10.1016/j.jnnfm.2024.105352","DOIUrl":"10.1016/j.jnnfm.2024.105352","url":null,"abstract":"<div><div>This study numerically investigates the flow dynamics and fiber orientation in enhanced polymer shell–core structures during 3D printing using the smoothed particle hydrodynamics method. A microstructure-based fiber suspension model, coupled with a shear-thinning viscosity model, is employed to assess the effects of varying material viscosities, fiber aspect ratios and volume fractions, and substrate speeds on fiber orientation distribution. Our results demonstrate that fiber orientation in deposited layers is particularly sensitive to variations in the viscosity of the shell material, while changes in the core material viscosity have a smaller and more localized impact on fiber orientation. Furthermore, fiber orientation is strongly influenced by the product of the fiber aspect ratio <em>α<sub>r</sub></em> and volume fraction <em>ϕ</em>; as <em>α<sub>r</sub>ϕ</em> increases, fibers tend to align with the flow direction of materials. However, adjusting the fiber aspect ratio and volume fraction while maintaining the same <em>α<sub>r</sub>ϕ</em> results in slight changes to fiber alignment. Additionally, lower substrate speeds cause upstream material accumulation, increasing deposition layer height and creating differences in fiber orientation between the core and shell regions. An appropriate increase in substrate speed can mitigate these effects.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"335 ","pages":"Article 105352"},"PeriodicalIF":2.7,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142745105","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Pressure drop reduction due to coupling between shear-thinning fluid flow and a weakly deformable channel wall: A reciprocal theorem approach

IF 2.7 2区工程技术 Q2 MECHANICS

Journal of Non-Newtonian Fluid Mechanics

Pub Date : 2024-11-14 DOI: 10.1016/j.jnnfm.2024.105347

Shrihari D. Pande, Ivan C. Christov

We employ the Lorentz reciprocal theorem to derive a closed-form expression for the pressure drop reduction due to the coupling between shear-thinning fluid flow and a weakly deformable channel wall in terms of the shear rate and the viscosity function (and its derivative) of the underlying rigid-channel flow. The methodology is applied in parallel to fluids for which the generalized Newtonian viscosity depends on either the shear rate or the shear stress magnitude. When the viscosity model allows for a closed-form solution for the axial velocity profile in a straight and rigid channel, the pressure drop reduction can be evaluated in closed form, which we demonstrate for the power-law and Ellis viscosity models as featured examples and to enable comparisons to previous works. Importantly, the pressure drop reduction under the Ellis model is valid for both small and large Carreau (or Ellis) numbers, and we show that it reduces to the analytical expression under the power-law model for large Carreau (small Ellis) numbers.

引用次数: 0

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