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}
Pub Date : 2026-01-17DOI: 10.1016/j.euromechflu.2026.204465
Michael Gerard Connolly, Alojz Ivankovic, Malachy J. O’Rourke
This paper presents a novel on-road method for determining a vehicle’s aerodynamic drag coefficient using a constant power approach with a towbar-mounted drag plate. The technique involves fixing the throttle pedal and measuring the vehicle’s equilibrium speeds in two configurations: baseline and with the added drag plate. From these speeds, the vehicle’s baseline drag coefficient can be calculated. Two formulations are introduced — one for an idealised plate with negligible self and interference drag, and another for practical setups where the support structure introduces additional self-drag and interference. The method was applied to a Citroen Berlingo van using an aluminium plate and stand, yielding a measured drag coefficient of 0.416. Validation against traditional coastdown testing showed a close agreement, with only a 6.1% difference. A sensitivity analysis demonstrated that the new method is less dependent on variables such as vehicle mass, air density and rolling resistance compared to coastdown testing. The potential to extend the method to estimate a vehicle’s rolling resistance is discussed, though limited by current GPS accuracy. Overall, the new constant power plate method offers a simple, robust alternative to coastdown testing and demonstrates strong potential for its usage in future aerodynamic assessment and vehicle development.
{"title":"On road determination of vehicle drag coefficient using the new constant power plate method","authors":"Michael Gerard Connolly, Alojz Ivankovic, Malachy J. O’Rourke","doi":"10.1016/j.euromechflu.2026.204465","DOIUrl":"10.1016/j.euromechflu.2026.204465","url":null,"abstract":"<div><div>This paper presents a novel on-road method for determining a vehicle’s aerodynamic drag coefficient using a constant power approach with a towbar-mounted drag plate. The technique involves fixing the throttle pedal and measuring the vehicle’s equilibrium speeds in two configurations: baseline and with the added drag plate. From these speeds, the vehicle’s baseline drag coefficient can be calculated. Two formulations are introduced — one for an idealised plate with negligible self and interference drag, and another for practical setups where the support structure introduces additional self-drag and interference. The method was applied to a Citroen Berlingo van using an aluminium plate and stand, yielding a measured drag coefficient of 0.416. Validation against traditional coastdown testing showed a close agreement, with only a 6.1% difference. A sensitivity analysis demonstrated that the new method is less dependent on variables such as vehicle mass, air density and rolling resistance compared to coastdown testing. The potential to extend the method to estimate a vehicle’s rolling resistance is discussed, though limited by current GPS accuracy. Overall, the new constant power plate method offers a simple, robust alternative to coastdown testing and demonstrates strong potential for its usage in future aerodynamic assessment and vehicle development.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204465"},"PeriodicalIF":2.5,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035443","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 : 2026-01-17DOI: 10.1016/j.euromechflu.2026.204472
Tian Bao , Ya Zhang , Qiaogao Huang
Mantas exhibit significant deformation at the fin tip during swimming, which results in remarkable hydrodynamic performance. To investigate the wake characteristics at the streamwise tip cross-section of a manta robot, we have developed an experimental platform that utilizes a Particle Image Velocimetry (PIV) system. The physical and geometric characteristics of the wake vortex at the fin tip are analyzed when varying motion parameters and flow velocity conditions. Results indicate that the vortex flux in the wake decreases over time, with attenuation exceeding 50 % by the fifth vortex, while the vortex core area initially increases, reaching a peak at a characteristic length of 3.0 with a 35 % increase before subsequently decreasing. Moreover, only the first two vortices contribute to propulsion momentum. Similarly, the propulsion performance of the single-bone fins is comparable to that of the double-bone designs. Furthermore, the Strouhal number (St) significantly influences the wake dynamics: when St is within [0.2, 0.4], effective wake jets develop, and efficient propulsion appears with St located in [0.37, 0.44], where the jet angle and momentum angle align, thus optimizing hydrodynamic performance. Sensitivity analysis further confirms that amplitude and frequency are the most influential parameters on vortex momentum, while phase difference plays a key role on propulsion efficiency.
{"title":"Wake characteristics at the fin tip streamwise cross-section of a manta robot","authors":"Tian Bao , Ya Zhang , Qiaogao Huang","doi":"10.1016/j.euromechflu.2026.204472","DOIUrl":"10.1016/j.euromechflu.2026.204472","url":null,"abstract":"<div><div>Mantas exhibit significant deformation at the fin tip during swimming, which results in remarkable hydrodynamic performance. To investigate the wake characteristics at the streamwise tip cross-section of a manta robot, we have developed an experimental platform that utilizes a Particle Image Velocimetry (PIV) system. The physical and geometric characteristics of the wake vortex at the fin tip are analyzed when varying motion parameters and flow velocity conditions. Results indicate that the vortex flux in the wake decreases over time, with attenuation exceeding 50 % by the fifth vortex, while the vortex core area initially increases, reaching a peak at a characteristic length of 3.0 with a 35 % increase before subsequently decreasing. Moreover, only the first two vortices contribute to propulsion momentum. Similarly, the propulsion performance of the single-bone fins is comparable to that of the double-bone designs. Furthermore, the Strouhal number (St) significantly influences the wake dynamics: when St is within [0.2, 0.4], effective wake jets develop, and efficient propulsion appears with St located in [0.37, 0.44], where the jet angle and momentum angle align, thus optimizing hydrodynamic performance. Sensitivity analysis further confirms that amplitude and frequency are the most influential parameters on vortex momentum, while phase difference plays a key role on propulsion efficiency.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204472"},"PeriodicalIF":2.5,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035435","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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