Pub Date : 2026-01-27DOI: 10.1016/j.euromechflu.2026.204481
Keshav Singh , Y.D. Sharma , Sanjalee Maheshwari
Thermotactic microorganisms are motile organisms that migrate in response to temperature gradients, exhibiting movement toward heat sources. Understanding thermotaxis is vital for advancements in biotechnology, wastewater treatment, and medical microbiology. In this study, the onset of bioconvection in a fluid layer containing thermotactic microorganisms is investigated through both linear and nonlinear stability analysis under free–free boundary conditions. The linear stability analysis is carried out by introducing infinitesimal perturbations and applying the normal mode technique, resulting in an eigenvalue problem. For the nonlinear analysis, an energy method is employed. A variational formulation is developed, which is further used to derive an eigenvalue problem. The obtained eigenvalue problems is finally solved using the Galerkin technique. A comparative study between the linear and nonlinear results is performed to highlight the differences in critical thresholds. The findings indicate that the Péclet number destabilizes the system, and as its value increases, the subcritical region of instability decreases. Furthermore, stronger thermal effects lead to an earlier onset of bioconvection, characterized by a reduction in the critical bioconvection Rayleigh number. These insights can aid in the practical design and control of bioconvective systems in bioengineering, environmental treatment processes, and industrial fluid technologies.
{"title":"Linear and nonlinear stability analysis of thermotactic bioconvection","authors":"Keshav Singh , Y.D. Sharma , Sanjalee Maheshwari","doi":"10.1016/j.euromechflu.2026.204481","DOIUrl":"10.1016/j.euromechflu.2026.204481","url":null,"abstract":"<div><div>Thermotactic microorganisms are motile organisms that migrate in response to temperature gradients, exhibiting movement toward heat sources. Understanding thermotaxis is vital for advancements in biotechnology, wastewater treatment, and medical microbiology. In this study, the onset of bioconvection in a fluid layer containing thermotactic microorganisms is investigated through both linear and nonlinear stability analysis under free–free boundary conditions. The linear stability analysis is carried out by introducing infinitesimal perturbations and applying the normal mode technique, resulting in an eigenvalue problem. For the nonlinear analysis, an energy method is employed. A variational formulation is developed, which is further used to derive an eigenvalue problem. The obtained eigenvalue problems is finally solved using the Galerkin technique. A comparative study between the linear and nonlinear results is performed to highlight the differences in critical thresholds. The findings indicate that the Péclet number destabilizes the system, and as its value increases, the subcritical region of instability decreases. Furthermore, stronger thermal effects lead to an earlier onset of bioconvection, characterized by a reduction in the critical bioconvection Rayleigh number. These insights can aid in the practical design and control of bioconvective systems in bioengineering, environmental treatment processes, and industrial fluid technologies.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204481"},"PeriodicalIF":2.5,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-26DOI: 10.1016/j.euromechflu.2026.204479
Valentin Heller
These Comments address the paper by K. Davey, A. Al-Tarmoom, H. Sadeghi, A two-experiment approach to hydraulic jump scaling, Eur. J. Mech. B Fluids, 111(3) (2025) 215–228 [1], from the perspective of practical hydraulics. The modelling and scaling of complex fluid flows at reduced size, including hydraulic jumps, are explained in more detail. Particular attention is given to the Froude scaling laws, which correspond to some of the scaling relations derived in Ref. [1]. The discussion then extends to alternative theoretical and empirical approaches to address scale effects in hydraulics, in addition to the finite similitude scaling theory [1]. These include precise Froude scaling, one-parameter Lie group point-scaling transformations, Reynolds number invariance, numerical quantification of scale effects and the scale series method. Finally, possible future research paths, building upon the work in Ref. [1], are outlined.
这些评论针对K. Davey， A. Al-Tarmoom， H. Sadeghi的论文，一个双实验方法的液压跳跃缩放，欧洲。j .机械工程。流体力学，111(3)(2025):215-228[1]。更详细地解释了复杂流体在缩小尺寸时的建模和缩放，包括水力跳跃。特别注意了弗劳德标度律，它对应于参考文献[1]中导出的一些标度关系。讨论然后扩展到替代的理论和经验方法，以解决水力学中的尺度效应，除了有限相似尺度理论[1]。其中包括精确的弗劳德尺度变换、单参数李群点尺度变换、雷诺数不变性、尺度效应的数值量化和尺度级数法。最后，在参考文献b[1]的基础上，概述了未来可能的研究路径。
{"title":"Comments about Davey et al. [1] A two-experiment approach to hydraulic jump scaling","authors":"Valentin Heller","doi":"10.1016/j.euromechflu.2026.204479","DOIUrl":"10.1016/j.euromechflu.2026.204479","url":null,"abstract":"<div><div>These Comments address the paper by K. Davey, A. Al-Tarmoom, H. Sadeghi, A two-experiment approach to hydraulic jump scaling, Eur. J. Mech. B Fluids, 111(3) (2025) 215–228 [1], from the perspective of practical hydraulics. The modelling and scaling of complex fluid flows at reduced size, including hydraulic jumps, are explained in more detail. Particular attention is given to the Froude scaling laws, which correspond to some of the scaling relations derived in Ref. [1]. The discussion then extends to alternative theoretical and empirical approaches to address scale effects in hydraulics, in addition to the finite similitude scaling theory [1]. These include precise Froude scaling, one-parameter Lie group point-scaling transformations, Reynolds number invariance, numerical quantification of scale effects and the scale series method. Finally, possible future research paths, building upon the work in Ref. [1], are outlined.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204479"},"PeriodicalIF":2.5,"publicationDate":"2026-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-23DOI: 10.1016/j.euromechflu.2026.204474
V. Kandavelu , L. Tlau , P.T. Griffiths
The influence of convection in a horizontal channel filled with a porous medium is examined to assess the stability of the fluid flow between the two walls that are held fixed at different temperatures. The flow is described by the Navier–Stokes equations, while heat transfer is captured through the energy equation. A coupled linear stability system is derived and solved using a Chebyshev spectral collocation method. The study focuses on the impact of the relevant nondimensional parameters on the development of the perturbations and the onset of instability within the flow. The onset of convection is advanced as the porous parameter increases, while higher Prandtl numbers and Reynolds numbers delay the onset of convection. The growth rate is unaffected by increases in and the Rayleigh number ; however, it increases as decreases and as increases. The isocontours show that increasing stabilizes temperature variations in the inner flow region.
{"title":"A convective instability analysis of a channel flow within a saturated porous medium","authors":"V. Kandavelu , L. Tlau , P.T. Griffiths","doi":"10.1016/j.euromechflu.2026.204474","DOIUrl":"10.1016/j.euromechflu.2026.204474","url":null,"abstract":"<div><div>The influence of convection in a horizontal channel filled with a porous medium is examined to assess the stability of the fluid flow between the two walls that are held fixed at different temperatures. The flow is described by the Navier–Stokes equations, while heat transfer is captured through the energy equation. A coupled linear stability system is derived and solved using a Chebyshev spectral collocation method. The study focuses on the impact of the relevant nondimensional parameters on the development of the perturbations and the onset of instability within the flow. The onset of convection is advanced as the porous parameter <span><math><mrow><mo>(</mo><mi>M</mi><mo>)</mo></mrow></math></span> increases, while higher Prandtl numbers <span><math><mrow><mo>(</mo><mi>P</mi><mi>r</mi><mo>)</mo></mrow></math></span> and Reynolds numbers <span><math><mrow><mo>(</mo><mi>R</mi><mi>e</mi><mo>)</mo></mrow></math></span> delay the onset of convection. The growth rate is unaffected by increases in <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> and the Rayleigh number <span><math><mrow><mo>(</mo><mi>R</mi><mi>a</mi><mo>)</mo></mrow></math></span>; however, it increases as <span><math><mi>M</mi></math></span> decreases and as <span><math><mrow><mi>R</mi><mi>e</mi></mrow></math></span> increases. The isocontours show that increasing <span><math><mrow><mi>P</mi><mi>r</mi></mrow></math></span> stabilizes temperature variations in the inner flow region.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204474"},"PeriodicalIF":2.5,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-23DOI: 10.1016/j.euromechflu.2026.204478
Oscar Cosserat , Dina Razafindralandy , Can Selçuk
Within the Large Eddy Simulation framework, we propose a methodology based on the Lie theory to derive symmetry-preserving turbulence models. We apply this methodology to the incompressible Navier–Stokes equations. These models explicitly depend on both the filtered strain-rate tensor and the filtered vorticity tensor. Particular emphasis is placed on models that additionally ensure stability.
{"title":"Vorticity-dependent and symmetry-preserving LES models","authors":"Oscar Cosserat , Dina Razafindralandy , Can Selçuk","doi":"10.1016/j.euromechflu.2026.204478","DOIUrl":"10.1016/j.euromechflu.2026.204478","url":null,"abstract":"<div><div>Within the Large Eddy Simulation framework, we propose a methodology based on the Lie theory to derive symmetry-preserving turbulence models. We apply this methodology to the incompressible Navier–Stokes equations. These models explicitly depend on both the filtered strain-rate tensor and the filtered vorticity tensor. Particular emphasis is placed on models that additionally ensure stability.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204478"},"PeriodicalIF":2.5,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-22DOI: 10.1016/j.euromechflu.2026.204475
Untung Surya Dharma , Syaiful Tambah Putra Ahmad , Indarto , Deendarlianto
The bend radius of a T-junction significantly affects local flow dynamics by altering the velocity distribution downstream of the junction. A larger bend radius reduces local vortices, accelerates uniform flow development, and modifies the mechanism of initial gas slug formation. This study investigates the influence of bend radius on initial gas slug formation in a rectangular acrylic T-junction minichannel with a hydraulic diameter (Dh) of 1.6 mm, and three bend radius ratios (r/Dh = 0.5, 0.7, and 1.0). Air and water were used as working fluids. Water superficial velocity (Jl) ranged from 0.626 to 3.186 m·s−1, and air superficial velocity (Jg) from 0.593 to 2.371 m·s−1. Flow formation was analysed using high-speed imaging at 15,000 frames per second, and pressure fluctuations were recorded at 15,000 Hz. Three distinct regimes were identified: shearing (SR), shearing–dripping (SDR), and squeezing (SQR), each characterised by unique stage sequences and pressure fluctuation patterns. In SR and SDR, the formation time (Ts) consists of necking, filling, and pinch-off; in SQR, Ts comprises pressure build-up, filling, and squeezing. Results show that increasing r/Dh enhances gas slug growth velocity (Us) and frequency (fr) while reducing gas slug length (Ls). The proposed non-dimensional Us/Jₗ correlation predicts experimental results with a Mean Absolute Percentage Error (MAPE) of ±5 %. In addition, the fr is generalised using the Strouhal number (St)–Capillary number (Ca) framework, which highlights the combined effects of viscous–capillary dynamics and geometrical control on gas slug formation. Flow pattern maps, constructed from experimental observations and artificial neural network (ANN) predictions, showed up to 91.5 % agreement across all r/Dₕ. This work provides experimental evidence that bend radius governs gas slug initiation dynamics, offering design guidelines for multiphase flow control in chemical and biomedical applications.
{"title":"Effect of bend radius on gas slug formation mechanisms in air–water two-phase flow within a horizontal minichannel T-junction","authors":"Untung Surya Dharma , Syaiful Tambah Putra Ahmad , Indarto , Deendarlianto","doi":"10.1016/j.euromechflu.2026.204475","DOIUrl":"10.1016/j.euromechflu.2026.204475","url":null,"abstract":"<div><div>The bend radius of a T-junction significantly affects local flow dynamics by altering the velocity distribution downstream of the junction. A larger bend radius reduces local vortices, accelerates uniform flow development, and modifies the mechanism of initial gas slug formation. This study investigates the influence of bend radius on initial gas slug formation in a rectangular acrylic T-junction minichannel with a hydraulic diameter (<em>D</em><sub><em>h</em></sub>) of 1.6 mm, and three bend radius ratios (<em>r/D</em><sub><em>h</em></sub> = 0.5, 0.7, and 1.0). Air and water were used as working fluids. Water superficial velocity (<em>J</em><sub><em>l</em></sub>) ranged from 0.626 to 3.186 m·s<sup>−1</sup>, and air superficial velocity (<em>J</em><sub><em>g</em></sub>) from 0.593 to 2.371 m·s<sup>−1</sup>. Flow formation was analysed using high-speed imaging at 15,000 frames per second, and pressure fluctuations were recorded at 15,000 Hz. Three distinct regimes were identified: shearing (SR), shearing–dripping (SDR), and squeezing (SQR), each characterised by unique stage sequences and pressure fluctuation patterns. In SR and SDR, the formation time (<em>T</em><sub><em>s</em></sub>) consists of necking, filling, and pinch-off; in SQR, <em>T</em><sub><em>s</em></sub> comprises pressure build-up, filling, and squeezing. Results show that increasing <em>r/D</em><sub><em>h</em></sub> enhances gas slug growth velocity (<em>U</em><sub><em>s</em></sub>) and frequency (<em>f</em><sub><em>r</em></sub>) while reducing gas slug length (<em>L</em><sub><em>s</em></sub>). The proposed non-dimensional <em>U</em><sub><em>s</em></sub><em>/Jₗ</em> correlation predicts experimental results with a Mean Absolute Percentage Error (MAPE) of ±5 %. In addition, the <em>f</em><sub><em>r</em></sub> is generalised using the Strouhal number (<em>St</em>)–Capillary number (<em>Ca</em>) framework, which highlights the combined effects of viscous–capillary dynamics and geometrical control on gas slug formation. Flow pattern maps, constructed from experimental observations and artificial neural network (ANN) predictions, showed up to 91.5 % agreement across all <em>r/Dₕ</em>. This work provides experimental evidence that bend radius governs gas slug initiation dynamics, offering design guidelines for multiphase flow control in chemical and biomedical applications.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204475"},"PeriodicalIF":2.5,"publicationDate":"2026-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-21DOI: 10.1016/j.euromechflu.2026.204468
Arda Cetiner , Mete Budakli
The spreading dynamics of droplet impact on a solid surface is of great importance in applications such as printing, spray cooling, coating process and anti-icing. These phenomena have been studied in several investigations and aspects such as the effect of critical Weber number on droplet break-up or the air bubble entrainment phenomenon as well as the influence of surface roughness. While experimental studies using surface roughness values ranging from to were conducted, a few analytical approaches are available taking into account roughness effects in correlations. Contrary to this, considering roughness physically in simulations requires large calculation capability, time for geometry preparation as well as the reconstruction of varying topographical combinations is rather difficult and needs to be elaborated broadly. Therefore, the present study recommends a time-saving approach in OpenFOAM in which surface roughness is not represented physically in the domain, rather taken into account in a wall function term. The results of the study are in good agreement of with the experimental data and mathematical models found in literature. Single drop impact simulations were carried out over a range of Weber number from 106 to 298 indicate that as We number increases, the effect of the surface roughness on the spreading process diminishes.
{"title":"Application of wall functions for investigating surface roughness effects on spreading of an impacting droplet","authors":"Arda Cetiner , Mete Budakli","doi":"10.1016/j.euromechflu.2026.204468","DOIUrl":"10.1016/j.euromechflu.2026.204468","url":null,"abstract":"<div><div>The spreading dynamics of droplet impact on a solid surface is of great importance in applications such as printing, spray cooling, coating process and anti-icing. These phenomena have been studied in several investigations and aspects such as the effect of critical Weber number on droplet break-up or the air bubble entrainment phenomenon as well as the influence of surface roughness. While experimental studies using surface roughness values ranging from <span><math><mrow><msub><mrow><mi>R</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>003</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span> to <span><math><mrow><mn>25</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span> were conducted, a few analytical approaches are available taking into account roughness effects in correlations. Contrary to this, considering roughness physically in simulations requires large calculation capability, time for geometry preparation as well as the reconstruction of varying topographical combinations is rather difficult and needs to be elaborated broadly. Therefore, the present study recommends a time-saving approach in OpenFOAM in which surface roughness is not represented physically in the domain, rather taken into account in a wall function term. The results of the study are in good agreement of <span><math><mrow><mo>±</mo><mn>10</mn><mtext>%</mtext></mrow></math></span> with the experimental data and mathematical models found in literature. Single drop impact simulations were carried out over a range of Weber number from 106 to 298 indicate that as <em>We</em> number increases, the effect of the surface roughness on the spreading process diminishes.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204468"},"PeriodicalIF":2.5,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-20DOI: 10.1016/j.euromechflu.2026.204476
Xiaojin Fu , Da Xu , Junxiong Zeng , Guangtao Zhai
Wettability-confined tracks enable rapid spontaneous droplet transport, providing an effective manipulation platform for open-surface microfluidic systems. In this study, a series of combined wettability-confined tracks is designed to achieve complex droplet manipulation, including long-distance transport, merging and splitting. The lattice Boltzmann method is used to study the droplet dynamic behaviors. First, the validity of the model has been verified by simulating the dynamic partial wetting process and coalescence of adjacent stationary droplets. Then, the droplet spreading behaviors on the designed surfaces are systematically investigated. Serial tracks enable the long-distance transportation of droplets, and the constriction ratio at the junction regions serves as the critical factor determining the feasibility of sustained long-range transport. Both T-shaped tracks and combined parallel tracks are designed to achieve droplet merging effectively, and the morphological evolution of droplets during the merging process is revealed. The centrally symmetrical track pattern can realize the droplet splitting in equal volumes to eliminate the cross-contamination of reagents. These designs offer a versatile strategy for advanced droplet-based operations.
{"title":"Droplet transport, merging and splitting based on combined wettability-confined tracks","authors":"Xiaojin Fu , Da Xu , Junxiong Zeng , Guangtao Zhai","doi":"10.1016/j.euromechflu.2026.204476","DOIUrl":"10.1016/j.euromechflu.2026.204476","url":null,"abstract":"<div><div>Wettability-confined tracks enable rapid spontaneous droplet transport, providing an effective manipulation platform for open-surface microfluidic systems. In this study, a series of combined wettability-confined tracks is designed to achieve complex droplet manipulation, including long-distance transport, merging and splitting. The lattice Boltzmann method is used to study the droplet dynamic behaviors. First, the validity of the model has been verified by simulating the dynamic partial wetting process and coalescence of adjacent stationary droplets. Then, the droplet spreading behaviors on the designed surfaces are systematically investigated. Serial tracks enable the long-distance transportation of droplets, and the constriction ratio at the junction regions serves as the critical factor determining the feasibility of sustained long-range transport. Both T-shaped tracks and combined parallel tracks are designed to achieve droplet merging effectively, and the morphological evolution of droplets during the merging process is revealed. The centrally symmetrical track pattern can realize the droplet splitting in equal volumes to eliminate the cross-contamination of reagents. These designs offer a versatile strategy for advanced droplet-based operations.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204476"},"PeriodicalIF":2.5,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-20DOI: 10.1016/j.euromechflu.2026.204467
Mac Lee , Stefan G. Llewellyn Smith
Quasi-geostrophic flow is an asymptotic theory for flows in rotating systems that are in geostrophic balance to leading order. It is characterised by the conservation of (quasi-geostrophic) potential vorticity and weak vertical flows. Surface quasigeostrophy (SQG) is the special case when the flow is driven by temperature anomalies at a horizontal boundary. The next-order correction to QG, QG+, takes into account ageostrophic effects. We investigate point vortex dynamics in SQG+, building on the work of Weiss (2022). The conservation laws for SQG point vortices that parallel the 2D Euler case no longer exist when ageostrophic effects are included. The trajectories of point vortices are obtained explicitly for the general two-vortex case in SQG and SQG+. For the three-vortex case, exact solutions are found for rigidly rotating and stationary equilibria consisting of regular polygons and collinear configurations. As in the 2D case, only certain collinear vortex configurations are rigid equilibria. Trajectories of passive tracers advected by point vortex systems are studied numerically, in particular their vertical excursions, which are non-zero because of ageostrophic effects. Surface trajectories can manifest local horizontal divergence even though the underlying fluid equations are incompressible.
{"title":"SQG point vortex dynamics with order Rossby corrections","authors":"Mac Lee , Stefan G. Llewellyn Smith","doi":"10.1016/j.euromechflu.2026.204467","DOIUrl":"10.1016/j.euromechflu.2026.204467","url":null,"abstract":"<div><div>Quasi-geostrophic flow is an asymptotic theory for flows in rotating systems that are in geostrophic balance to leading order. It is characterised by the conservation of (quasi-geostrophic) potential vorticity and weak vertical flows. Surface quasigeostrophy (SQG) is the special case when the flow is driven by temperature anomalies at a horizontal boundary. The next-order correction to QG, QG+, takes into account ageostrophic effects. We investigate point vortex dynamics in SQG+, building on the work of Weiss (2022). The conservation laws for SQG point vortices that parallel the 2D Euler case no longer exist when ageostrophic effects are included. The trajectories of point vortices are obtained explicitly for the general two-vortex case in SQG and SQG+. For the three-vortex case, exact solutions are found for rigidly rotating and stationary equilibria consisting of regular polygons and collinear configurations. As in the 2D case, only certain collinear vortex configurations are rigid equilibria. Trajectories of passive tracers advected by point vortex systems are studied numerically, in particular their vertical excursions, which are non-zero because of ageostrophic effects. Surface trajectories can manifest local horizontal divergence even though the underlying fluid equations are incompressible.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204467"},"PeriodicalIF":2.5,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035437","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-19DOI: 10.1016/j.euromechflu.2026.204473
Lei Yu, Xiaobin Zhan, Tielin Shi
This paper is aimed to study the energy dissipation mechanism of the three-degree-of-freedom (three-DOF) acoustic vibration system due to high-viscosity fluid motion. A simulation model describing the dynamic interaction between a three-DOF acoustic vibration system and the fluid is established using computational fluid dynamics (CFD) and fluid-structure interaction (FSI) methods. The simulation results show that under acoustic vibration excitation, the fluid inside the vessel rapidly transitions from a relatively stationary state to violent motion behavior. The key factor in the energy dissipation of the fluid is caused by the phase difference between the fluid force as the fluid impacts on the wall and the motion imposed on the vessel. The energy input to the system is primarily dissipated by the fluid and the structural damping of the system. The effects of excitation amplitude, excitation frequency, filling ratio, and fluid viscosity on the energy dissipation of the system are also analyzed in this study. An increase in the excitation amplitude as well as an increase in the excitation frequency within a certain frequency range, results in an enhancement of the systems' dynamic response, which leads to a significant increase in the energy input to the system and the energy dissipated by the fluid. In the range of filling ratios investigated in this study, the total input energy and fluid dissipation energy are minimized at the filling ratio of 50 %. Furthermore, an increase in fluid viscosity results in higher fluid energy dissipation and input energy.
{"title":"Study on the energy dissipation mechanism of three-degree-of-freedom acoustic vibration system due to high-viscosity fluid motion","authors":"Lei Yu, Xiaobin Zhan, Tielin Shi","doi":"10.1016/j.euromechflu.2026.204473","DOIUrl":"10.1016/j.euromechflu.2026.204473","url":null,"abstract":"<div><div>This paper is aimed to study the energy dissipation mechanism of the three-degree-of-freedom (three-DOF) acoustic vibration system due to high-viscosity fluid motion. A simulation model describing the dynamic interaction between a three-DOF acoustic vibration system and the fluid is established using computational fluid dynamics (CFD) and fluid-structure interaction (FSI) methods. The simulation results show that under acoustic vibration excitation, the fluid inside the vessel rapidly transitions from a relatively stationary state to violent motion behavior. The key factor in the energy dissipation of the fluid is caused by the phase difference between the fluid force as the fluid impacts on the wall and the motion imposed on the vessel. The energy input to the system is primarily dissipated by the fluid and the structural damping of the system. The effects of excitation amplitude, excitation frequency, filling ratio, and fluid viscosity on the energy dissipation of the system are also analyzed in this study. An increase in the excitation amplitude as well as an increase in the excitation frequency within a certain frequency range, results in an enhancement of the systems' dynamic response, which leads to a significant increase in the energy input to the system and the energy dissipated by the fluid. In the range of filling ratios investigated in this study, the total input energy and fluid dissipation energy are minimized at the filling ratio of 50 %. Furthermore, an increase in fluid viscosity results in higher fluid energy dissipation and input energy.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204473"},"PeriodicalIF":2.5,"publicationDate":"2026-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This work investigates the behavior of dust-acoustic waves (DAWs) in cometary plasmas including opposite-polarity dust grains, Maxwellian ions, and suprathermal electrons. We derived the modified Korteweg–de Vries (mKdV) equation to define periodic, superperiodic, and solitary wave solutions. Bifurcation analysis uncovers supernonlinear periodic waves (SPOs), a novel class of coherent structures sustained under extreme nonlinearity through precise nonlinear-dispersive balance. The phase velocity of DAWs is shown to rise with increasing positive-to-negative dust charge ratio, , and negative-to-positive dust temperature ratio, , while nonlinear coefficients decline, contrasting the dispersive term’s enhancement. Sagdeev potential analysis reveals dual energy minima governing compressive/rarefactive solitary waves, with thermal gradients modulating amplitude and width. Numerical simulations, benchmarked against laboratory parameters, demonstrate that heightened thermal contrast amplifies nonlinear coupling, driving larger-amplitude periodic waves. SPOs, distinguished by concentrated energy and potential turbulence onset, highlight efficient energy transport mechanisms critical to astrophysical plasmas. These findings advance predictive models for wave behavior in cometary tails, planetary rings, and laboratory experiments, offering insights into energy transfer, instability thresholds, and applications in space physics and industrial plasmas. The study bridges theoretical and observational gaps, underscoring the role of dust charge asymmetry and thermal gradients in shaping nonlinear wave dynamics.
{"title":"Nonlinear dynamics of dust-acoustic waves in cometary plasmas: Supernonlinear periodic waves, charge asymmetry, and thermal gradients bridging astrophysical and industrial applications","authors":"M.A. El-Borie , Reem Altuijri , Abdel-Haleem Abdel-Aty , A. Atteya , Pralay Kumar Karmakar , Kottakkaran Sooppy Nisar , Nadia Alsaeed Saad","doi":"10.1016/j.euromechflu.2026.204469","DOIUrl":"10.1016/j.euromechflu.2026.204469","url":null,"abstract":"<div><div>This work investigates the behavior of dust-acoustic waves (DAWs) in cometary plasmas including opposite-polarity dust grains, Maxwellian ions, and suprathermal electrons. We derived the modified Korteweg–de Vries (mKdV) equation to define periodic, superperiodic, and solitary wave solutions. Bifurcation analysis uncovers supernonlinear periodic waves (SPOs), a novel class of coherent structures sustained under extreme nonlinearity through precise nonlinear-dispersive balance. The phase velocity of DAWs is shown to rise with increasing positive-to-negative dust charge ratio, <span><math><msub><mrow><mi>α</mi></mrow><mrow><mi>d</mi></mrow></msub></math></span>, and negative-to-positive dust temperature ratio, <span><math><msub><mrow><mi>δ</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>, while nonlinear coefficients decline, contrasting the dispersive term’s enhancement. Sagdeev potential analysis reveals dual energy minima governing compressive/rarefactive solitary waves, with thermal gradients <span><math><msub><mrow><mi>δ</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> modulating amplitude and width. Numerical simulations, benchmarked against laboratory parameters, demonstrate that heightened thermal contrast amplifies nonlinear coupling, driving larger-amplitude periodic waves. SPOs, distinguished by concentrated energy and potential turbulence onset, highlight efficient energy transport mechanisms critical to astrophysical plasmas. These findings advance predictive models for wave behavior in cometary tails, planetary rings, and laboratory experiments, offering insights into energy transfer, instability thresholds, and applications in space physics and industrial plasmas. The study bridges theoretical and observational gaps, underscoring the role of dust charge asymmetry and thermal gradients in shaping nonlinear wave dynamics.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204469"},"PeriodicalIF":2.5,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035436","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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