Journal of Non-Newtonian Fluid Mechanics最新文献

{"title":"Viscoelastic instability in viscosity-stratified channel flow with viscous heating effects","authors":"Ankush","doi":"10.1016/j.jnnfm.2025.105443","DOIUrl":"10.1016/j.jnnfm.2025.105443","url":null,"abstract":"<div><div>The linear instability analysis of the isothermal pressure-driven flow of an Oldroyd-B fluid through a plane channel with viscous heating effects is carried out. The temperature dependence of the viscosity of solute, solvent, and polymeric solution is described using the Nahme law. There is no external temperature imposed in the system, the temperature gradient arises purely from frictional dissipation. The Reynolds number <span><math><mrow><mo>(</mo><mi>R</mi><mi>e</mi><mo>)</mo></mrow></math></span>, Nahme number <span><math><mrow><mo>(</mo><mi>N</mi><mi>a</mi><mo>)</mo></mrow></math></span>, Peclet number <span><math><mrow><mo>(</mo><mi>P</mi><mi>e</mi><mo>)</mo></mrow></math></span>, Deborah number <span><math><mrow><mo>(</mo><mi>D</mi><mi>e</mi><mo>)</mo></mrow></math></span>, the ratio of solvent to solution viscosity <span><math><mrow><mo>(</mo><mi>β</mi><mo>)</mo></mrow></math></span>, and the dimensionless heating coefficient for polymeric solution <span><math><mrow><mo>(</mo><mi>α</mi><mo>)</mo></mrow></math></span> are the dimensionless parameters that modify the instability characteristics of the flow. The Chebyshev spectral collocation method is employed to numerically solve the generalised eigenvalue problem. The viscous heating in the flow is characterised by Nahme number. It is observed that the unstable area under the neutral stability curves increases as we increase the viscous heating effects. Moreover, it is found that there exist a minimum and maximum threshold value of Deborah number for which linear instability persists. An increase in the <span><math><mi>β</mi></math></span> value expands the parameter range for instability. The Peclet number <span><math><mrow><mo>(</mo><mi>P</mi><mi>e</mi><mo>)</mo></mrow></math></span> and dimensionless heating coefficient <span><math><mrow><mo>(</mo><mi>α</mi><mo>)</mo></mrow></math></span> do not alter the linear stability characteristics.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"344 ","pages":"Article 105443"},"PeriodicalIF":2.7,"publicationDate":"2025-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144633530","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}

{"title":"A cluster of N-bubbles driven along a channel at high imposed driving pressure: Bubble areas, film lengths and vertex locations","authors":"P. Grassia ,&nbsp;H. Rajabi ,&nbsp;C. Torres-Ulloa ,&nbsp;J. Hernández-Montelongo ,&nbsp;J. Potter ,&nbsp;J. Moston","doi":"10.1016/j.jnnfm.2025.105455","DOIUrl":"10.1016/j.jnnfm.2025.105455","url":null,"abstract":"<div><div>A two-dimensional foam staircase structure is considered with <span><math><mi>N</mi></math></span> 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 <span><math><mi>N</mi></math></span>. Behaviours in the limit of large <span><math><mi>N</mi></math></span> are identified, albeit tentatively, as the methodology for computing the staircase structure is found to be highly stiff. Indeed, as <span><math><mi>N</mi></math></span> increases, tiny changes in the staircase configuration at the downstream end lead to large geometric changes at the upstream end, limiting the domain of <span><math><mi>N</mi></math></span> values for which structures can be readily computed.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"344 ","pages":"Article 105455"},"PeriodicalIF":2.7,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144580069","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}

{"title":"Quantitative characterization of the ribbons and elastic vortices in viscoelastic Taylor-Couette flow with Boger fluids","authors":"Noureddine Latrache ,&nbsp;Fayçal Kelai ,&nbsp;Yang Bai ,&nbsp;Olivier Crumeyrolle ,&nbsp;Innocent Mutabazi","doi":"10.1016/j.jnnfm.2025.105457","DOIUrl":"10.1016/j.jnnfm.2025.105457","url":null,"abstract":"<div><div>Instabilities modes in viscoelastic Taylor-Couette flow are investigated using space-time diagrams and particle image velocimetry (PIV) of flow patterns in the meridional cross-section. The working solution is an aqueous mixture of the polymer solution of Polyethylene oxide (PEO) and Polyethylene glycol (PEG). The concentrations of the PEG and the POE are chosen in such a way to obtain solutions with constant shear viscosities (characteristic of Boger fluids) and a wide spectrum of values of the molecular elastic number in a single Taylor-Couette system. The interplay between the elasticity of the polymer solution and the inertia forces induced by the rotation of the cylinders leads to different critical modes: stationary Taylor vortices for very small values of the elasticity, ribbons i.e. superposition of spirals of opposite helicity for intermediate values of the elasticity and elastic vortices for large values of the elasticity and weak inertia forces. The elasto-rotational Rayleigh discriminant and linear stability analysis show the role of elasticity in the destabilization of the base flow and on the threshold of critical modes. The elastic vortices are characterized by regions of strong inflows separated by outflows; they form flame patterns in the spatiotemporal diagrams. The amplitude of the radial velocity at the centre of vortices is used as the order parameter of the ribbons dynamics. The Ginzburg-Landau theory offers a framework to describe the destabilization of regular ribbons with the introduction of a dissymmetry parameter. Spatiotemporal properties of elastic vortices (such as the drift velocity, the fraction, the size and the lifetime of inflows) are measured for different values of the criticality. The scaling exponents of energy spectra for inertio-elastic turbulence are determined for viscoelastic Taylor-Couette flow with the inner or outer sole rotating cylinder; the obtained values are compared with those from other experiments and from numerical simulations. PIV measurements have allowed to determine the power of the radial force at the inflow which shows that the driving mechanism of the elastic instability is active from the outer cylinder toward the inner cylinder.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"343 ","pages":"Article 105457"},"PeriodicalIF":2.7,"publicationDate":"2025-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144522552","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}

{"title":"Pair interactions of viscous drops suspended in a shear-thinning viscous and viscoelastic shear flow","authors":"Haoqian Wang,&nbsp;Anik Tarafder,&nbsp;Kausik Sarkar","doi":"10.1016/j.jnnfm.2025.105454","DOIUrl":"10.1016/j.jnnfm.2025.105454","url":null,"abstract":"<div><div>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 <em>n</em> &lt;1) introduces reversed trajectories, where after interaction the drops reverse directions, and viscoelasticity (nonzero Weissenberg number <em>Wi</em>) 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 <em>n-Ca</em> phase plot. Passing trajectories transition into reversed ones for small <em>n</em> (more shear-thinning) and low capillary numbers <em>Ca</em> with the critical <em>n</em> for transition increasing with decreasing capillary number. In a viscoelastic medium, one finds all three trajectories in an <em>n-Wi</em> phase plot: reversed trajectories for low <em>Wi</em> and low <em>n</em>, tumbling for high <em>Wi</em> and high <em>n</em>, 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 <em>Ca</em> values (less deformable drops). Physical reasoning for the reversed streamlines in the presence of shear-thinning is offered, relating it to the pressure field.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"344 ","pages":"Article 105454"},"PeriodicalIF":2.7,"publicationDate":"2025-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144534353","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}

{"title":"Formation of standing waves in granular chute flows induced by mild basal topography","authors":"Giorgos Kanellopoulos","doi":"10.1016/j.jnnfm.2025.105453","DOIUrl":"10.1016/j.jnnfm.2025.105453","url":null,"abstract":"<div><div>This study demonstrates that standing waves can arise in dry granular flows within a chute with mild sloped basal topography, even when the applied Froude number remains subcritical (<span><math><mrow><mi>F</mi><mi>r</mi><mo>&lt;</mo><mn>1</mn></mrow></math></span>) and below the critical threshold for surface wave instability (<span><math><mrow><mi>F</mi><mi>r</mi><mo>&lt;</mo><mi>F</mi><msub><mrow><mi>r</mi></mrow><mrow><mi>c</mi><mi>r</mi></mrow></msub></mrow></math></span>). In the absence of basal topography, a stable uniform flow would be possible in this regime. By employing the Saint-Venant equations augmented with the <span><math><mrow><mi>μ</mi><mrow><mo>(</mo><mi>I</mi><mo>)</mo></mrow></mrow></math></span> rheology, we numerically observe the formation of these standing waves and confirm the negligible influence of the viscous diffusive term. A key finding is that these standing waves can be described by a single non-linear inviscid ordinary differential equation. While this equation lacks an analytical solution, we introduce a modified Euler’s method, a semi-analytical approach based on the equation’s direction field, to accurately capture the wave profile. For the special case of very gentle slopes, an implicit analytical approximation can be derived directly from the curve that corresponds to the zero inclination direction field (nullcline). Finally, we conduct numerical simulations using the full Saint-Venant equations to demonstrate that in the opposite Froude regime, when <span><math><mrow><mi>F</mi><mi>r</mi><mo>&gt;</mo><mi>F</mi><msub><mrow><mi>r</mi></mrow><mrow><mi>c</mi><mi>r</mi></mrow></msub></mrow></math></span>, even a very mild basal topography can induce the formation of roll waves and, furthermore, accelerate the coarsening process. It is shown that the generated roll waves can reach a steady state, even when the basal topography is present along the entire length of the chute. These results highlight the significant influence of topography on flow dynamics across different Froude number regimes.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"343 ","pages":"Article 105453"},"PeriodicalIF":2.7,"publicationDate":"2025-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144522553","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}

{"title":"Stagnation point flow of a viscoplastic fluid","authors":"Jesse J. Taylor-West,&nbsp;Andrew J. Hogg","doi":"10.1016/j.jnnfm.2025.105445","DOIUrl":"10.1016/j.jnnfm.2025.105445","url":null,"abstract":"<div><div>Stagnation points occur in many configurations, such as flow around blunt objects, flow through a T-junction, and squeeze flow between plates. For viscoplastic fluids, vanishing strain rate at a stagnation point results in regions of stagnant unyielded fluid, or “plugs”. We explore the planar flow of a Bingham fluid in the neighbourhood of a stagnation point in a general flow configuration. When the Bingham number is small, this local problem reduces to the prototypical problem of stagnating flow against an infinite planar boundary, varying only with the stagnation angle with which the flow approaches the boundary. We compute numerical solutions of this idealised problem, using the augmented-Lagrangian algorithm, and determine the geometry of the stagnation-point plug as a function of this stagnation angle. As the angle decreases, the plug becomes larger, is elongated in the flow direction, and becomes increasingly asymmetric. However, for all angles, the plug features a right-angle at its vertex, a result that we demonstrate numerically and prove direct from the model equations. We also show how local stagnation plugs are embedded in global flows, illustrating the results from the specific case studies of recirculating flow in a sharp corner and uniform flow around an elliptic cylinder.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"343 ","pages":"Article 105445"},"PeriodicalIF":2.7,"publicationDate":"2025-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144366714","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}

{"title":"The critical plastocapillary number for a Newtonian liquid filament embedded into a viscoplastic fluid","authors":"Mohammad Tanver Hossain ,&nbsp;Wonsik Eom ,&nbsp;Arjun Shah ,&nbsp;Andrew Lowe ,&nbsp;Douglas Fudge ,&nbsp;Sameh H. Tawfick ,&nbsp;Randy H. Ewoldt","doi":"10.1016/j.jnnfm.2025.105440","DOIUrl":"10.1016/j.jnnfm.2025.105440","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The yield stress of a viscoplastic material can stabilize an embedded fluid tunnel against capillarity-induced breakup, enabling remarkable technologies such as embedded 3D printing of intricate, freeform, and small components. However, there is persistent disagreement in the published literature between the observed minimum stable diameter, &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;min&lt;/mo&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, and the theoretical plastocapillary length &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;p&lt;/mi&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;σ&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;y&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, with interfacial tension &lt;span&gt;&lt;math&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; and bath yield stress &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;σ&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;y&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, leading to a prior hypothesis that the apparent surface tension &lt;span&gt;&lt;math&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; is much smaller to enforce &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;min&lt;/mo&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;p&lt;/mi&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. Here we introduce and experimentally test a new hypothesis that the critical diameter is set by the dimensionless plastocapaillary number, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;Y&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;σ&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;y&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, having a non-trivial critical value different than one, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;Y&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;≠&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, and therefore the prior hypothesis of adjusting &lt;span&gt;&lt;math&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; to enforce &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;p&lt;/mi&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;min&lt;/mo&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; is incorrect. We study several Newtonian inks (uncured polydimethylsiloxane (PDMS), highly refined mineral oil, silicone oil) extruded into a wide range of non-Newtonian viscoplastic bath materials (polyacrylic acid microgels, polysaccharide microgels, nanoclay gel, and micro-organogels). Across this wide parameter space, we observe a critical value of &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;Y&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;21&lt;/mn&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;03&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. We explain this being less than one by analogy to other critical dimensionless groups with yield stress fluids, such as the gravitational stability of a suspended sphere or bubble, where the yield stress acts upon an effective area larger than the naïve estimate set only by embedded object diameter &lt;span&gt;&lt;math&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;. These results provide a new way to understand and predict the minimum stable diameter of embedded liquid filaments, as in embedded","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"343 ","pages":"Article 105440"},"PeriodicalIF":2.7,"publicationDate":"2025-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144322765","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}

{"title":"Spontaneous imbibition of power-law fluids in filled capillaries of axially varying geometries","authors":"Shabina Ashraf ,&nbsp;Karan Gupta","doi":"10.1016/j.jnnfm.2025.105442","DOIUrl":"10.1016/j.jnnfm.2025.105442","url":null,"abstract":"<div><div>Imbibition of wetting fluids in confined pore spaces is a ubiquitous phenomenon in nature. Several attempts have been made to understand the invasion of Newtonian fluids in capillaries. The imbibition of non-Newtonian fluids, however, is relatively less explored owing to the dynamic shear rate during the imbibition process. In this work, we develop equations governing the displacement of one power-law fluid with another power-law fluid in axially diverging and converging capillaries. Using lubrication approximation, the governing equations in one-dimension are developed to model the advancing interface with time for various combinations of shear-thinning, shear-thickening, and Newtonian fluids. For this imbibition phenomenon, we explore the effect of imbibing and residing fluid power-law indices, their time scales, interfacial properties, and the impact of the geometric parameters. The developed equations serve as a comprehensive mathematical model, and the self-imbibition relations available in literature can be retrieved from the developed model by considering special cases. We also identify early and late regimes of flow where the viscous resistance of either the imbibing or the residing fluid dominates the imbibition. This study will help design geometrical parameters for pore space with desired flow properties, and has wide applications in microfluidics.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"343 ","pages":"Article 105442"},"PeriodicalIF":2.7,"publicationDate":"2025-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144253741","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}

{"title":"GPU acceleration of a hi-fidelity algorithm for direct numerical simulation of polymer-induced/modified turbulence","authors":"Fenghui Lin ,&nbsp;Zi-Mo Liao ,&nbsp;Zhiye Zhao ,&nbsp;Nansheng Liu ,&nbsp;Xi-Yun Lu ,&nbsp;Bamin Khomami","doi":"10.1016/j.jnnfm.2025.105437","DOIUrl":"10.1016/j.jnnfm.2025.105437","url":null,"abstract":"<div><div>This paper presents an efficient GPU implementation for the direct numerical simulation (DNS) of polymer-induced/modified turbulence, utilizing the open-source finite-difference incompressible Navier–Stokes solver, <span><math><mrow><mi>C</mi><mi>a</mi><mi>N</mi><mi>S</mi></mrow></math></span>. The implementation incorporates a versatile viscoelastic solver for two commonly used constitutive equations in DNS of elastic or elastically modified turbulence, namely, the FENE-P and the Giesekus models. Consistent with <span><math><mrow><mi>C</mi><mi>a</mi><mi>N</mi><mi>S</mi></mrow></math></span>, the viscoelastic solver uses CUDA Fortran and makes extensive use of kernel loop directives (CUF kernels). To improve the fidelity and robustness of this implementation, a tensor-based interpolation method combined with a shock-capturing WENO scheme is employed for spatial discretization of the polymer constitutive equations. We demonstrate the accuracy and robustness of our code by comparison with existing theoretical and simulation results. In addition, the algorithm exhibits superior scalability with up to eight Nvidia GPU devices in benchmark channel flows. In turn, we use this expeditious code for high-fidelity and efficient large-scale DNS of viscoelastic turbulent flows. To that end, we demonstrate the broad applicability of our implementation in a host of polymer-induced/modified turbulence in channel flows. This includes the maximum drag reduction asymptote, as well as elasto-inertial turbulence, and purely elastic turbulent flows. Overall, this GPU-accelerated simulation technique has all the required ingredients to become the method of choice for large-scale viscoelastic computations aimed at faithfully capturing polymer-induced flow phenomena.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"342 ","pages":"Article 105437"},"PeriodicalIF":2.7,"publicationDate":"2025-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144213217","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}

{"title":"Experimental study on the relationship between extensional and shear rheology of low-viscosity power-law fluids","authors":"Yuzuki Matsumoto ,&nbsp;Misa Kawaguchi ,&nbsp;Yoshiyuki Tagawa","doi":"10.1016/j.jnnfm.2025.105436","DOIUrl":"10.1016/j.jnnfm.2025.105436","url":null,"abstract":"<div><div>This paper investigates the relationship between extensional and shear viscosity of low-viscosity power-law fluids. We show the first experimental evidence of the conditions satisfying the same power exponents for extensional and shear viscosity, as indicated by the Carreau model. The extensional and shear viscosity are respectively measured by capillary breakup extensional rheometry dripping-onto-substrate (CaBER-DoS) and by a shear rheometer for various Ohnesorge number <span><math><mrow><mi>O</mi><mi>h</mi></mrow></math></span>. The viscosity ranges measured are about <span><math><mrow><mi>O</mi><mrow><mo>(</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>0</mn></mrow></msup><mo>)</mo></mrow></mrow></math></span> to <span><math><mrow><mi>O</mi><mrow><mo>(</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>4</mn></mrow></msup><mo>)</mo></mrow></mrow></math></span> mPa s for shear viscosity and <span><math><mrow><mi>O</mi><mrow><mo>(</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>1</mn></mrow></msup><mo>)</mo></mrow></mrow></math></span> to <span><math><mrow><mi>O</mi><mrow><mo>(</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>3</mn></mrow></msup><mo>)</mo></mrow></mrow></math></span> mPa s for apparent extensional viscosity. Our experimental results show that, at least for the range of <span><math><mrow><mi>O</mi><mi>h</mi><mo>&gt;</mo><mn>1</mn></mrow></math></span>, the power-law expression for the liquid filament radius, apparent extensional viscosity, and shear viscosity holds, even for low-viscosity fluids under our experimental conditions.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"343 ","pages":"Article 105436"},"PeriodicalIF":2.7,"publicationDate":"2025-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144223191","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}