Journal of Non-Newtonian Fluid Mechanics最新文献

{"title":"Research on the flow around a circular cylinder near a wall for shear-thinning power-law fluids","authors":"Xiang Qiu ,&nbsp;Xu Ding ,&nbsp;Yizhou Tao ,&nbsp;Junwang Qu ,&nbsp;Jiahua Li ,&nbsp;Yulu Liu","doi":"10.1016/j.jnnfm.2024.105323","DOIUrl":"10.1016/j.jnnfm.2024.105323","url":null,"abstract":"<div><div>In this study, direct numerical simulations (DNS) was used to investigate the flow behavior of power-law fluids flow around a circular cylinder near a wall at the Reynolds number of 200. The power-law index <span><math><mi>n</mi></math></span> represents the typical situation of shear-thinning fluids (<span><math><mrow><mi>n</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>2</mn></mrow></math></span> to 1.0), whereas the gap ratio <span><math><mrow><mi>G</mi><mo>/</mo><mi>D</mi></mrow></math></span> ranges from 0.2 to 1.0 (where <span><math><mi>G</mi></math></span> represents the gap between the cylinder and the plane wall and <span><math><mi>D</mi></math></span> represents the diameter of the cylinder). This study aimed to analyze the influence of the power-law index and gap ratio on the time-averaged flow, vortex dynamics, and the force exerted on the cylinder. The results indicate that for <span><math><mrow><mi>G</mi><mo>/</mo><mi>D</mi><mo>≥</mo><mn>0</mn><mo>.</mo><mn>5</mn></mrow></math></span> and <span><math><mrow><mi>n</mi><mo>≤</mo><mn>0</mn><mo>.</mo><mn>5</mn></mrow></math></span>, two secondary vortex structures form behind the cylinder because of the induction of the primary vortices, and they are in reverse rotation. An analysis of the signed enstrophy revealed a positive correlation between the strengths of the primary and secondary vortices, both of which diminished as the gap ratio decreased and increased as the power-law index decreased. Notably, vortex shedding was observed at <span><math><mrow><mi>G</mi><mo>/</mo><mi>D</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>3</mn></mrow></math></span> when <span><math><mrow><mi>n</mi><mo>≤</mo><mn>0</mn><mo>.</mo><mn>3</mn></mrow></math></span>, which is absent in Newtonian fluids. Through the analysis of vorticity transport equation, the development of vorticity is attributed to changes in the convection term, viscosity diffusion term and viscosity gradient term. By examining the key points, the formation of secondary vortex structure and the reason of vortex shedding at <span><math><mrow><mi>G</mi><mo>/</mo><mi>D</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>3</mn></mrow></math></span> in power-law fluids are explained. Furthermore, the time-averaged drag coefficient <span><math><msub><mrow><mover><mrow><mi>C</mi></mrow><mo>¯</mo></mover></mrow><mrow><mi>D</mi></mrow></msub></math></span> initially decreases and then increases with decreasing <span><math><mi>n</mi></math></span>, and decreases with decreasing <span><math><mrow><mi>G</mi><mo>/</mo><mi>D</mi></mrow></math></span>. The time-averaged lift coefficient <span><math><msub><mrow><mover><mrow><mi>C</mi></mrow><mo>¯</mo></mover></mrow><mrow><mi>L</mi></mrow></msub></math></span> exhibits a typical L-type curve with increasing gap ratios, where <span><math><msub><mrow><mover><mrow><mi>C</mi></mrow><mo>¯</mo></mover></mrow><mrow><mi>L</mi></mrow></msub></math></span> initially decreases and then increases.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"333 ","pages":"Article 105323"},"PeriodicalIF":2.7,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142311023","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 importance of initial extension rate on elasto-capillary thinning of dilute polymer solutions","authors":"Ann Aisling,&nbsp;Renee Saraka,&nbsp;Nicolas J. Alvarez","doi":"10.1016/j.jnnfm.2024.105321","DOIUrl":"10.1016/j.jnnfm.2024.105321","url":null,"abstract":"<div><div>This work focuses on inferring the molecular state of the polymer chain required to induce stress relaxation and the accurate measure of the polymer’s longest relaxation time in uniaxial stretching of dilute polymer solutions. This work is facilitated by the discovery that constant velocity applied at early times leads to initial constant extension rate before reaching the Rayleigh–Plateau instability. Such constant rate experiments are used to correlate initial stretching kinematics with the thinning dynamics in the final thinning regime. We show that there is a minimum initial strain-rate required to induce rate independent elastic effects, and measure the longest relaxation time of the material. Below the minimum extension rate, insufficient stretching of the chain is observed before capillary instability, such that the polymer stress is comparable to the capillary stress at long times and stress relaxation is not achieved. Above the minimum strain-rate, the chain reaches a critical stretch before instability, such that during the unstable filament thinning the polymer stress is significantly larger than the capillary stress and rate-independent stress relaxation is observed. Using a single relaxation mode FENE model, we show that the minimum strain rate leads to a required initial stretch of the chain before reaching the Rayleigh–Plateau limit. These results indicate that the chain conformation before entering the Rayleigh Instability Regime, and the stretching induced during the instability, determines the elastic behavior of the filament. Lastly, this work introduces a characteristic dimensionless group, called the stretchability factor, that can be used to quantitatively compare different materials based on the overall material deformation/kinematic behavior, not just the relaxation time. Overall, these results demonstrate a useful methodology to study the stretching of dilute solutions using a constant velocity stretching scheme.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"333 ","pages":"Article 105321"},"PeriodicalIF":2.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S037702572400137X/pdfft?md5=d1f32f9cee619f02d115117fa2418228&pid=1-s2.0-S037702572400137X-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142315745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A numerical investigation of laminar planar hydraulic jump in Herschel-Bulkley fluid","authors":"Banashree Samanta ,&nbsp;Manish Kaushal ,&nbsp;Gargi Das ,&nbsp;Subhabrata Ray","doi":"10.1016/j.jnnfm.2024.105325","DOIUrl":"10.1016/j.jnnfm.2024.105325","url":null,"abstract":"<div><div>Laminar planar hydraulic jump during viscoplastic liquid flow in a horizontal channel is investigated through experiments and numerical simulation using Herschel-Bulkley (HB) model. The simulations are performed using the phase-field method with Papanastasiou regularization parameter and validated against experimental results. Both experiments and simulations show the free surface height to gradually increase upstream of jump and recede after the jump with a remarkable increase in free surface height and surface waviness at the jump. The model further reveals that an increase in any of the rheological parameters [yield stress (<span><math><msub><mi>τ</mi><mi>o</mi></msub></math></span>) flow behaviour index (<em>n</em>) and flow consistency index (<em>k</em>)] keeping the other properties constant increases film thickness. This increases jump strength and shifts jump towards the entry. However, each parameter influences free surface profile and jump characteristics in a different way. While a higher τ<em>_o</em> suppresses the development of the shear zone and results in a thicker plug zone, a higher <em>n</em> increases shear zone thickness and decreases the plug zone thickness. On the other hand, a higher <em>k</em> increases both shear and plug zone thickness. The steady state fully developed self-similar velocity profile is independent of <em>k</em> and depends on <span><math><msub><mi>τ</mi><mi>o</mi></msub></math></span> and <em>n</em>. Different jump types, obtained from simulations, are presented as phase diagrams in non-dimensional coordinates for a generalised approach.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"333 ","pages":"Article 105325"},"PeriodicalIF":2.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142311021","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":"Laminar planar jets of elastoviscoplastic fluids","authors":"Giovanni Soligo,&nbsp;Marco Edoardo Rosti","doi":"10.1016/j.jnnfm.2024.105322","DOIUrl":"10.1016/j.jnnfm.2024.105322","url":null,"abstract":"<div><div>We perform numerical simulations of planar jets of elastoviscoplastic (EVP) fluid (Saramito (2007) model) at low Reynolds number. Three different configurations are considered: <span><math><mrow><mo>(</mo><mi>i</mi><mo>)</mo></mrow></math></span> EVP jet in EVP ambient fluid, <span><math><mrow><mo>(</mo><mi>i</mi><mi>i</mi><mo>)</mo></mrow></math></span> EVP jet in Newtonian ambient fluid (miscible), and <span><math><mrow><mo>(</mo><mi>i</mi><mi>i</mi><mi>i</mi><mo>)</mo></mrow></math></span> EVP jet in Newtonian ambient fluid (immiscible). We investigate the effect of the Bingham number, <em>i.e.</em> of the dimensionless yield stress of the EVP fluid, on the jet dynamics, and find a good agreement with the scaling for laminar, Newtonian jets for the centerline velocity <span><math><mrow><msub><mrow><mi>u</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>/</mo><msub><mrow><mi>u</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>∝</mo><msup><mrow><mrow><mo>(</mo><mi>x</mi><mo>/</mo><mi>h</mi><mo>)</mo></mrow></mrow><mrow><mo>−</mo><mn>1</mn><mo>/</mo><mn>3</mn></mrow></msup></mrow></math></span> and for the jet thickness <span><math><mrow><msub><mrow><mi>δ</mi></mrow><mrow><mi>m</mi><mi>o</mi><mi>m</mi></mrow></msub><mo>/</mo><mi>h</mi><mo>∝</mo><msup><mrow><mrow><mo>(</mo><mi>x</mi><mo>/</mo><mi>h</mi><mo>)</mo></mrow></mrow><mrow><mn>2</mn><mo>/</mo><mn>3</mn></mrow></msup></mrow></math></span> at small Bingham number. This is lost once substantial regions of the fluid become unyielded, where we find that the spreading rate of the jet and the decay rate of the centerline velocity increase with the Bingham number, due to the regions of unyielded fluid inducing a blockage effect on the jet. The most striking difference among the three configurations we considered is the extent and position of the regions of unyielded fluid: large portions of ambient and jet fluids (in particular, away from the inlet) are unyielded for the EVP jet in EVP ambient fluid, whereas for the other two configurations, the regions of unyielded fluid are limited to the jet, as expected. We derive a power law scaling for the centerline yield variable and confirm it with the results from our numerical simulations. The yield variable determines the transition from the viscoelastic Oldroyd-B fluid (yielded) to the viscoelastic Kelvin–Voigt material (unyielded).</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"333 ","pages":"Article 105322"},"PeriodicalIF":2.7,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142322464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Inelastic fluid models with an objective stretch rate parameter","authors":"Donggang Yao ,&nbsp;Martin Zatloukal","doi":"10.1016/j.jnnfm.2024.105320","DOIUrl":"10.1016/j.jnnfm.2024.105320","url":null,"abstract":"<div><div>This paper presents an extension to the Generalized Newtonian Fluid (GNF) model, where the effects of different flow modes can be discerned. While existing GNF models have proven valuable in simulating processes like molding and extrusion, they often struggle to differentiate between distinct flow modes such as planar extension and simple shear. To address this challenge, we propose a modified GNF model that integrates an objective flow-type parameter, aiming to refine flow characterization. Emphasis is placed on defining the flow-type parameter to be able to transcend viscometric flows, remain frame-indifferent, quantify deformation magnitude, and differentiate between diverse flow modes. Inspired by the new advances in vortex identification in turbulent flow, we introduce a new stretch rate tensor and a new stretch rate parameter that are derived from the real Schur form of the objective velocity gradient tensor. These elements are embedded into the constitutive modeling of non-Newtonian fluid flow. The resulting model is employed to fit polymer melt data from the literature, demonstrating excellent fitting to combined shear and extension data. The basic model uses 5 to 6 parameters for data fitting, and further enhancement may be achieved by incorporating other extracted information of the stretch rate tensor.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"334 ","pages":"Article 105320"},"PeriodicalIF":2.7,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142417118","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":"Extensional rheology of elastoviscous aqueous PEO/PEG or DMS Boger fluids and weakly elastic alternatives for investigating viscoelastic flows and instabilities","authors":"Alexander Kubinski ,&nbsp;Fahed Albreiki ,&nbsp;Jelena Dinic,&nbsp;Prerana Rathore,&nbsp;Vivek Sharma","doi":"10.1016/j.jnnfm.2024.105319","DOIUrl":"10.1016/j.jnnfm.2024.105319","url":null,"abstract":"<div><div>Boger fluids that exhibit a rate-independent shear viscosity (typically ∼ 1 Pa∙s = 1000x water viscosity) and elasticity measurable using torsional rheometers (modulus, relaxation time, or first normal stress difference) are considered as the realization of viscoelastic fluids described by the Oldroyd-B model. However, Boger fluids, conventionally formulated as dilute solutions of high molecular weight (M_w) polymers in relatively high viscosity solvents (or solutions of oligomers or lower M_w polymer), are unsuitable for emulating polymeric fluids used in coating formulations that are lower in viscosity, appear inelastic in torsional shear rheometry, and yet appear prone to viscoelastic instabilities. Therefore, Dontula, Macosko, and Scriven (DMS) (AIChE J, 1998) chose to create an alternative model of elastic fluids by dissolving ultrahigh molecular weight (UHM_w) poly(ethylene oxide) (PEO) in an aqueous solution of its lower M_w analog, often referred to as poly(ethylene glycol) or PEG. Even though numerous studies of printing and coating flow instabilities use this aqueous PEO/PEG or DMS Boger fluids as model viscoelastic fluids, only a few explicitly measured elastic properties, especially using relaxation time, and hardly any characterized extensional rheology. In this contribution, we recreate the DMS Boger fluids to examine their elasticity and extensional rheology response using dripping-onto-substrate (DoS) rheometry that relies on an analysis of capillarity-driven pinching dynamics. Though the aqueous PEG solution is often treated as a viscous and Newtonian solvent, we discover that in DoS rheometry, both the PEG solution and the DMS Boger fluid display power law response followed by elastocapillary, in contradiction with the assumptions and the response expected of the Oldroyd-B model. Furthermore, the solution of entangled PEG chains influences specific viscosity, pinching dynamics, and measured extensional rheology response in striking contrast with Newtonian solvents of the same viscosity. Lastly, we describe the possibility of using dilute, aqueous solutions of UHM_w PEO as model viscoelastic fluids for coating flows, for both elasticity and extensional viscosity can be determined using DoS rheometry. Due to their water-like viscosity, the aqueous PEO solutions appeal as model fluids that have elasticity, emulate Newtonian fluids in the early stages of pinching, and have a relaxation time tunable by changing polymer M_w or concentration.</div></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"333 ","pages":"Article 105319"},"PeriodicalIF":2.7,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142322462","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magnus force reduction in a shear-thinning fluid","authors":"Sai Peng ,&nbsp;Xiang Li ,&nbsp;Li Yu ,&nbsp;Xiaoyang Xu ,&nbsp;Peng Yu","doi":"10.1016/j.jnnfm.2024.105309","DOIUrl":"10.1016/j.jnnfm.2024.105309","url":null,"abstract":"<div><p>This study aims to investigate the impact of fluid shear-thinning on the Magnus forces acting on a rotating cylinder or a sphere immersed in an unbounded flow using direct numerical simulation. The Carreau model is employed to represent the shear-thinning fluid, with the considered Reynolds number (<em>Re</em>) ranging from 0.01 to 100, Carreau number (<em>Cu</em>) from 0 to 100, power-law index (<em>n</em>) from 0.1 to 1, and viscosity ratio (<em>β</em>) from 0.001 to 0.5. The rotation rate (<em>α</em>) is fixed at 6. A characteristic Reynolds number, <em>Re</em>_c, based on a viscosity evaluated at the characteristic shear rate, <span><math><mrow><msub><mover><mi>γ</mi><mo>˙</mo></mover><mi>α</mi></msub><mspace></mspace><mo>=</mo><mspace></mspace><mi>α</mi><msub><mi>U</mi><mi>∞</mi></msub><mo>/</mo><mn>2</mn><mi>a</mi></mrow></math></span>, is introduced. It is found that, at a constant <em>Re</em>_c, compared to that in a Newtonian fluid, the Magnus force exerted on the rotating cylinder or sphere in the shear-thinning fluid is reduced. This reduction results from the difference in viscosity distribution between the upper and lower sides of the cylinder or sphere. Furthermore, our analysis demonstrates that the logarithmic reduction in the Magnus force coefficient can be expressed as a linear combination of the logarithm of the strain rate difference and the logarithm of the shear strain rate sensitive function at two limit states, <em>Cu</em>→0 or <em>Cu</em>→∞. This work may be helpful to deepen the understanding of complex rheological behavior encountered in swirling flow hydrodynamics.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"333 ","pages":"Article 105309"},"PeriodicalIF":2.7,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142149200","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":"Migration of particles suspended in yield stress fluids: Insights from numerical simulation of pipe flow of 3D printable concrete","authors":"Vishwanath Ravindran ,&nbsp;Thiyagarajan Ranganathan ,&nbsp;A.V. Rahul","doi":"10.1016/j.jnnfm.2024.105305","DOIUrl":"10.1016/j.jnnfm.2024.105305","url":null,"abstract":"<div><p>In this work, we present a numerical model to analyse particle migration and its impact on local rheological properties when a high-yield stress suspension like 3D printable concrete is transported through a narrow circular pipe. The particle migration is studied through the lens of suspension rheology, where the effect of local particle concentration on rheological properties is accounted for using Krieger–Dougherty-type models. 3D printable mixtures with different aggregate-to-binder (a/b) ratios and flows at various discharge rates are evaluated. It is observed that, depending on the discharge rate and a/b ratio, the flow behaviour could deviate from that expected in a Poiseuille flow of Bingham fluid owing to shear-induced particle migration. Interestingly, as a consequence of particle migration, the formation of a local unsheared region close to the pipe wall is observed, apart from the plug zone at the pipe centre in the partially unsheared pipe flow of Bingham fluids. Often, for concrete pipe flow simulation, the particle size is not small enough to warrant local treatment since the finite size of the particle is not fully reflected in the flow domain. In this work, the developed numerical model is also extended to account for the finite particle size to study the transition between the sheared and unsheared regions and assess the effect of considering finite size in our simulation. Finally, the model’s capability to predict global pressure loss in pipe flow is assessed through comparisons with experimental results.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"332 ","pages":"Article 105305"},"PeriodicalIF":2.7,"publicationDate":"2024-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142095342","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":"σOWCh: Optimally Windowed Chirp rheometry using combined motor transducer/single head rheometers","authors":"Rebecca E. Hudson-Kershaw ,&nbsp;Mohua Das ,&nbsp;Gareth H. McKinley ,&nbsp;Daniel J. Curtis","doi":"10.1016/j.jnnfm.2024.105307","DOIUrl":"10.1016/j.jnnfm.2024.105307","url":null,"abstract":"<div><p>Recent advances in rheometry exploiting frequency-modulated (chirp) waveforms have dramatically reduced the time required to perform linear viscoelastic characterisation of complex materials. However, the technique was optimised for ‘separate motor transducer’ instruments, in which the drive motor imposing the strain deformation is decoupled from the torque transducer. Whilst the use of optimised windowed chirps (OWCh) using other rheometers has been recently reported in the literature, no systematic study concerning the use of ‘combined motor transducer’ instruments (in which the motor and transducer subsystems are integrated into a single ‘head’) has been undertaken. In the present study, we demonstrate the use of OWCh rheometry using combined motor transducer/single-head rheometers using a stress-controlled operating principle, thus avoiding the reliance on complicated and instrument-specific feedback control systems that would be required to perform strain-controlled experiments. The use of stress-controlled chirps requires a modification to the established OWCh analysis protocol such that the complex viscosity <span><math><mrow><msup><mrow><mi>η</mi></mrow><mrow><mo>∗</mo></mrow></msup><mrow><mo>(</mo><mi>ω</mi><mo>)</mo></mrow></mrow></math></span> is used as an intermediate proxy function for ultimately computing the complex modulus <span><math><mrow><msup><mrow><mi>G</mi></mrow><mrow><mo>∗</mo></mrow></msup><mrow><mo>(</mo><mi>ω</mi><mo>)</mo></mrow></mrow></math></span>. This approach negates the effect of the strain offset that is inherent to stress-controlled oscillatory rheometry. Secondly, a correction algorithm and operational criteria for identifying inertial artefacts is established before we consider the impact of chirp digitisation on data acquisition. The use of stress-controlled OWCh rheometry (which we term Stress-OWCh, i.e. <span><math><mi>σ</mi></math></span>OWCh) is demonstrated for a diverse range of material classes including, Newtonian calibration fluids (silicone oil), polymer solutions (polyethylene oxide in water), an entangled polymer melt (polydimethylsiloxane), worm-like micellar systems (cetylpyridinium chloride/sodium salicylate), time-evolving critical gels (gelatin) and aging elastoviscoplastic materials (Laponite®). This novel implementation of chirp waveforms using a single-head rheometer will facilitate the wider adoption of OWCh rheometry and allow the benefits of frequency-modulation techniques to be exploited where separate motor transducer instruments are unavailable/unsuitable.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"333 ","pages":"Article 105307"},"PeriodicalIF":2.7,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S037702572400123X/pdfft?md5=8699673a8af80917a3a3c894395db0a9&pid=1-s2.0-S037702572400123X-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142274444","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oscillatory one-roll and two-roll solutions in laminar viscoelastic Rayleigh-Bénard convection in a square cavity","authors":"Govind Maurya,&nbsp;Suneet Singh,&nbsp;Lalit Kumar","doi":"10.1016/j.jnnfm.2024.105308","DOIUrl":"10.1016/j.jnnfm.2024.105308","url":null,"abstract":"<div><p>Rayleigh-Bénard convection in square closed cavities filled with Oldroyd-B fluid was studied using OpenFOAM-based RheoTool. For the RBC in Newtonian fluids, the transition always occurs from conduction to steady state convection with increasing Rayleigh number (<em>Ra</em>). On the other hand, the viscoelastic fluids may also show the transition from conduction to oscillatory convection. Further increase in <em>Ra</em> may result in a steady state convective solutions. It is further noted that the behavior is similar to Newtonian fluids for larger values of viscosity ratio (<em>B</em>). Considering the abovementioned different flow behavior at different values of the parameters, it is noted that there are five different types of solutions possible for the viscoelastic fluids viz. pure conduction (PC), one roll periodic oscillations (ORPO), one roll steady state (ORSS) convection, two roll periodic oscillations (TRPO), simultaneous one and two roll steady state convection. Therefore, a bifurcation diagram in the parametric space of <em>Ra</em> and <em>B</em> is presented, depicting these five regions corresponding to each type of solution. The boundaries of these regions have been identified by numerical simulation. Note that all these regions exist in the laminar flow regime, and the transition to turbulence is not considered here. Interestingly, at low values of <em>B</em>, as one increases <em>Ra</em>, it is seen that the ORSS region is sandwiched between ORPO and TRPO. The likely reason for this interesting behavior is explained. Moreover, representative solutions in each region in terms of isotherms, streamlines, and vector plots have been included to demonstrate the dynamics of each delineated region.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"332 ","pages":"Article 105308"},"PeriodicalIF":2.7,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142136315","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}