Pub Date : 2025-12-27DOI: 10.1016/j.euromechflu.2025.204451
Sanjay Kumar Pandey, Kriti Yadav
This study presents an analytical model that extends previous formulations by incorporating axial dependence in all velocity components, thus offering a more realistic representation of dust devil dynamics. We address the limitations of the fundamental model of Vyas and Majdalani (2006), such as unbounded velocity and infinite vortex width, by modifying the stream function, which captures radial and axial variation of velocity. The velocity components are physically bounded and consistent with observed vortex structures. Additionally, the radial pressure distribution is derived, and the flow field is analysed using normalized radial, axial, and azimuthal velocities. The azimuthal velocity is computed from the radial and axial flows using the angular momentum equation. It increases from the centre, peaks near the periphery, and gradually decays to zero toward the axis. This model represents the compact features of dust devils by producing a smooth, confined structure with consistent vertical dependence, unlike alternative models that introduce abrupt transitions or unbounded behaviour. The profile maintains central stability in accordance with the Rayleigh criterion, while peripheral centrifugal instability reflects the transient and dissipative nature of dust devils. The model captures dust lifting and charge separation in dust devils, linking strong updrafts and confined flow to enhanced electrification and particle transport.
{"title":"An analytical model for whirlwinds of finite width rising with bounded velocity and decaying outflow: Application to dust devils","authors":"Sanjay Kumar Pandey, Kriti Yadav","doi":"10.1016/j.euromechflu.2025.204451","DOIUrl":"10.1016/j.euromechflu.2025.204451","url":null,"abstract":"<div><div>This study presents an analytical model that extends previous formulations by incorporating axial dependence in all velocity components, thus offering a more realistic representation of dust devil dynamics. We address the limitations of the fundamental model of Vyas and Majdalani (2006), such as unbounded velocity and infinite vortex width, by modifying the stream function, which captures radial and axial variation of velocity. The velocity components are physically bounded and consistent with observed vortex structures. Additionally, the radial pressure distribution is derived, and the flow field is analysed using normalized radial, axial, and azimuthal velocities. The azimuthal velocity is computed from the radial and axial flows using the angular momentum equation. It increases from the centre, peaks near the periphery, and gradually decays to zero toward the axis. This model represents the compact features of dust devils by producing a smooth, confined structure with consistent vertical dependence, unlike alternative models that introduce abrupt transitions or unbounded behaviour. The profile maintains central stability in accordance with the Rayleigh criterion, while peripheral centrifugal instability reflects the transient and dissipative nature of dust devils. The model captures dust lifting and charge separation in dust devils, linking strong updrafts and confined flow to enhanced electrification and particle transport.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204451"},"PeriodicalIF":2.5,"publicationDate":"2025-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145880202","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 : 2025-12-26DOI: 10.1016/j.euromechflu.2025.204450
Manuel Rubio , Francisco Castro-Ruiz , José Sierra-Pallares , César Barrios-Collado , Joaquín Anatol
This study examines asymmetric pumping in Liebau pumps, a type of valveless pump that generates unidirectional flow through the periodic compression of a flexible (compliant) tube. This pumping has applications in biomedical devices, microfluidics, and organ support. We investigate how the properties of the compliant tube and the operating conditions affect the pump performance, using dimensionless parameters. Experiments were performed with different configurations, varying the tube material (latex and rubber) and the fluid (water and water–glycerine mixture). The results indicate that the flow rate and resonant period depend on the stiffness of the tube and the viscous effects. It was observed that for small values of the Womersley number (), viscous effects significantly reduce the flow rate. In contrast, for large Womersley values, the semiempirical models previously proposed adequately predict the experimental behaviour. Effects such as the compliant tube depression, which were not accounted for in previous models, were also found to influence performance. This work extends the analysis of this type of pump to unexplored conditions, with the aim of expanding knowledge and enabling the use of Liebau pumps in real-world applications.
{"title":"Analysis of compliant tube properties and operating conditions in a Liebau pump","authors":"Manuel Rubio , Francisco Castro-Ruiz , José Sierra-Pallares , César Barrios-Collado , Joaquín Anatol","doi":"10.1016/j.euromechflu.2025.204450","DOIUrl":"10.1016/j.euromechflu.2025.204450","url":null,"abstract":"<div><div>This study examines asymmetric pumping in Liebau pumps, a type of valveless pump that generates unidirectional flow through the periodic compression of a flexible (compliant) tube. This pumping has applications in biomedical devices, microfluidics, and organ support. We investigate how the properties of the compliant tube and the operating conditions affect the pump performance, using dimensionless parameters. Experiments were performed with different configurations, varying the tube material (latex and rubber) and the fluid (water and water–glycerine mixture). The results indicate that the flow rate and resonant period depend on the stiffness of the tube and the viscous effects. It was observed that for small values of the Womersley number (<span><math><msup><mrow><mi>W</mi><mi>o</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span>), viscous effects significantly reduce the flow rate. In contrast, for large Womersley values, the semiempirical models previously proposed adequately predict the experimental behaviour. Effects such as the compliant tube depression, which were not accounted for in previous models, were also found to influence performance. This work extends the analysis of this type of pump to unexplored conditions, with the aim of expanding knowledge and enabling the use of Liebau pumps in real-world applications.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204450"},"PeriodicalIF":2.5,"publicationDate":"2025-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837005","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 : 2025-12-23DOI: 10.1016/j.euromechflu.2025.204449
Aakanksha Singh, Punit Kumar
Electron-acoustic solitary waves (EASWs) in quantum plasma comprising stationary ions, cold electrons, hot electrons, and kappa-distributed electrons have been investigated. The generalized Kappa-Fermi distribution has been modified to include electrostatic energy contribution and the number density of Kappa electrons has been obtained using this modified distribution. Utilizing the quantum hydrodynamic (QHD) model, a dispersion relation has been derived for linear EAWs. Employing the standard reductive perturbation technique, a Korteweg–de Vries (KdV) equation governing the dynamics of EAWs have been derived. The quantum mechanical effects of different parameters like kappa index, Mach number and equilibrium kappa electron density have been examined on the profiles of EASWs. It is found that the presence of kappa electrons in quantum plasma leads to new results, including steeper dispersion curves, sharper and more localized solitary waves with lower value of kappa index and stronger plasma interactions with increased kappa electrons density in dense astrophysical environment.
{"title":"Electron acoustic solitary wave in quantum plasmas with Kappa electrons","authors":"Aakanksha Singh, Punit Kumar","doi":"10.1016/j.euromechflu.2025.204449","DOIUrl":"10.1016/j.euromechflu.2025.204449","url":null,"abstract":"<div><div>Electron-acoustic solitary waves (EASWs) in quantum plasma comprising stationary ions, cold electrons, hot electrons, and kappa-distributed electrons have been investigated. The generalized Kappa-Fermi distribution has been modified to include electrostatic energy contribution and the number density of Kappa electrons has been obtained using this modified distribution. Utilizing the quantum hydrodynamic (QHD) model, a dispersion relation has been derived for linear EAWs. Employing the standard reductive perturbation technique, a Korteweg–de Vries (KdV) equation governing the dynamics of EAWs have been derived. The quantum mechanical effects of different parameters like kappa index, Mach number and equilibrium kappa electron density have been examined on the profiles of EASWs. It is found that the presence of kappa electrons in quantum plasma leads to new results, including steeper dispersion curves, sharper and more localized solitary waves with lower value of kappa index and stronger plasma interactions with increased kappa electrons density in dense astrophysical environment.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204449"},"PeriodicalIF":2.5,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837006","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 : 2025-12-23DOI: 10.1016/j.euromechflu.2025.204448
Bruno Thierry Nyatchouba Nsangue , Tang Hao , Mezoue Adiang Cyrille , Liuxiong Xu , Fuxiang Hu , Ruben Mouangue
The unsteady turbulent flow, the trawl codend, and the Bycatch reduction device (BRD) are characterized by a complex interaction. A thorough understanding of this interaction is crucial for minimizing bycatch, enhancing the escape probability of non-target species, and improving trawl selectivity. This study analyzes unsteady turbulent flow fields inside and around the bottom trawl codends equipped with BRDs, systematically exploring the reconstruction capabilities of three deep learning algorithms, involving Long Short-Term Memory (LSTM), Echo State Network (ESN), and Convolutional Neural Network-Long Short-Term Memory (CNN-LSTM). Extensive assessment encompasses the predictive reliability of the instantaneous flow fields, velocity ratio profiles, turbulent intensity, turbulent kinetic energy, Reynold stress, time series streamwise flow velocities, and training efficiency. Results indicate a full development of unsteady turbulent flow inside and around the codend without BRD, characterized by instantaneous shear layer instabilities and vortex shedding. In contrast, the codend-BRD system and water flow interaction generates two distinct regions with very low flow velocity fields behind it, characterized by vortex-shedding structures on the unsteady turbulent wake. The flow velocity deficit was greater inside the codend compared to that observed inside the combined codend-BRD system due to free water flow passage through the combined codend-BRD system due to the presence of BRD windows. A higher turbulent kinetic energy, greater momentum flux, and stronger turbulence intensities are observed inside and around the codend without BRD compared to the codend-BRD system. Additionally, the results indicate that ESN and CNN-LSTM exhibit a significant advantage in reconstructing unsteady turbulent flow parameters. The prediction of unsteady turbulent flow parameters indicates that all the three models are substantially consistent with the experimental data. However, LSTM is a judicious choice when solely the time series variables require prediction. These insights significantly advance the development of smart trawl nets, offering a pathway to enhance gear selectivity through data-driven design.
{"title":"Deep learning prediction of unsteady turbulent transformation pattern inside and around the interactions between a sorting grid and a trawl system","authors":"Bruno Thierry Nyatchouba Nsangue , Tang Hao , Mezoue Adiang Cyrille , Liuxiong Xu , Fuxiang Hu , Ruben Mouangue","doi":"10.1016/j.euromechflu.2025.204448","DOIUrl":"10.1016/j.euromechflu.2025.204448","url":null,"abstract":"<div><div>The unsteady turbulent flow, the trawl codend, and the Bycatch reduction device (BRD) are characterized by a complex interaction. A thorough understanding of this interaction is crucial for minimizing bycatch, enhancing the escape probability of non-target species, and improving trawl selectivity. This study analyzes unsteady turbulent flow fields inside and around the bottom trawl codends equipped with BRDs, systematically exploring the reconstruction capabilities of three deep learning algorithms, involving Long Short-Term Memory (LSTM), Echo State Network (ESN), and Convolutional Neural Network-Long Short-Term Memory (CNN-LSTM). Extensive assessment encompasses the predictive reliability of the instantaneous flow fields, velocity ratio profiles, turbulent intensity, turbulent kinetic energy, Reynold stress, time series streamwise flow velocities, and training efficiency. Results indicate a full development of unsteady turbulent flow inside and around the codend without BRD, characterized by instantaneous shear layer instabilities and vortex shedding. In contrast, the codend-BRD system and water flow interaction generates two distinct regions with very low flow velocity fields behind it, characterized by vortex-shedding structures on the unsteady turbulent wake. The flow velocity deficit was greater inside the codend compared to that observed inside the combined codend-BRD system due to free water flow passage through the combined codend-BRD system due to the presence of BRD windows. A higher turbulent kinetic energy, greater momentum flux, and stronger turbulence intensities are observed inside and around the codend without BRD compared to the codend-BRD system. Additionally, the results indicate that ESN and CNN-LSTM exhibit a significant advantage in reconstructing unsteady turbulent flow parameters. The prediction of unsteady turbulent flow parameters indicates that all the three models are substantially consistent with the experimental data. However, LSTM is a judicious choice when solely the time series variables require prediction. These insights significantly advance the development of smart trawl nets, offering a pathway to enhance gear selectivity through data-driven design.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204448"},"PeriodicalIF":2.5,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145880203","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 : 2025-12-22DOI: 10.1016/j.euromechflu.2025.204446
Anupam M. Hiremath , Harunori N. Yoshikawa , Innocent Mutabazi
Liquid Metal Battery (LMB) is a recent technology proposed to store the energy produced by intermittent sources such as solar cells, wind turbines or tidal power plants. The liquid metal batteries operate with large current densities but with very low open circuit voltages (OCV). A LMB consists of superimposed three layers of immiscible liquids in a stable stratification: the top layer made of light liquid metal and the bottom one made of dense liquid metal alloy sandwich the electrolyte layer (often a molten salt). Each layer has its own specific fluid properties and due to large difference in thermal and electrical conductivities between the liquid metals and the electrolyte, the application of a large current density can generate thermoconvective instabilities. The present works presents, in the framework of the linear stability analysis, the effects of the physical properties and thicknesses of liquid layers on the critical parameters on thermoconvective flows induced by Joule heating in a LMB of rectangular cross-section. The thermal coupling of the LMB with its environment described by the mixed thermal boundary conditions through the Biot number modifies the temperature profiles of the conduction state and reduces the threshold of all thermoconvective flows.
{"title":"Threshold of thermoconvective flows in a liquid metal battery with thermal coupling with its environment","authors":"Anupam M. Hiremath , Harunori N. Yoshikawa , Innocent Mutabazi","doi":"10.1016/j.euromechflu.2025.204446","DOIUrl":"10.1016/j.euromechflu.2025.204446","url":null,"abstract":"<div><div>Liquid Metal Battery (LMB) is a recent technology proposed to store the energy produced by intermittent sources such as solar cells, wind turbines or tidal power plants. The liquid metal batteries operate with large current densities but with very low open circuit voltages (OCV). A LMB consists of superimposed three layers of immiscible liquids in a stable stratification: the top layer made of light liquid metal and the bottom one made of dense liquid metal alloy sandwich the electrolyte layer (often a molten salt). Each layer has its own specific fluid properties and due to large difference in thermal and electrical conductivities between the liquid metals and the electrolyte, the application of a large current density can generate thermoconvective instabilities. The present works presents, in the framework of the linear stability analysis, the effects of the physical properties and thicknesses of liquid layers on the critical parameters on thermoconvective flows induced by Joule heating in a LMB of rectangular cross-section. The thermal coupling of the LMB with its environment described by the mixed thermal boundary conditions through the Biot number modifies the temperature profiles of the conduction state and reduces the threshold of all thermoconvective flows.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204446"},"PeriodicalIF":2.5,"publicationDate":"2025-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145921070","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 : 2025-12-18DOI: 10.1016/j.euromechflu.2025.204447
Yupeng Liao , Changjun Li , Wenlong Jia , Juncheng Mu , Jie He , Fan Yang , Qiaojing Huang
This paper proposes a new segregated algorithm named SIMPLE-Revised with Residual Coupling (SIMPLER*) for simulating the two-phase flow of gas-condensate in pipelines. The full coupling of velocity and pressure is ensured by introducing the momentum equation residual and the double inner iteration, which improves the computational efficiency while solving the issues of velocity-pressure decoupling and pressure overcorrection in the traditional Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. The adaptive time-stepping method is employed to reduce computational costs in transient simulations. The performance of SIMPLE, SIMPLE-Revised-Revised (SIMPLERR), and SIMPLER* algorithms is comprehensively compared. Validation across four classical benchmark tests confirms the superior robustness and numerical stability of SIMPLER*, which exhibits lower numerical diffusion and remains oscillation-free under strong pressure discontinuities. Subsequent steady-state and transient engineering cases demonstrate that the computational efficiency of the SIMPLER* algorithm is significantly better than that of the SIMPLE and SIMPLERR algorithms, both in coarse and fine grids. The proposed "adaptive time-stepping + SIMPLER* algorithm" combination method greatly reduces the computational overhead while ensuring the accuracy of the solution, providing an efficient and reliable solution for the transient simulation of complex two-phase flow with phase change.
{"title":"Insight into the numerical efficiency and stability of a residual-coupled segregated solver for gas-condensate two-phase flow in pipelines: An algorithmic study","authors":"Yupeng Liao , Changjun Li , Wenlong Jia , Juncheng Mu , Jie He , Fan Yang , Qiaojing Huang","doi":"10.1016/j.euromechflu.2025.204447","DOIUrl":"10.1016/j.euromechflu.2025.204447","url":null,"abstract":"<div><div>This paper proposes a new segregated algorithm named SIMPLE-Revised with Residual Coupling (SIMPLER*) for simulating the two-phase flow of gas-condensate in pipelines. The full coupling of velocity and pressure is ensured by introducing the momentum equation residual and the double inner iteration, which improves the computational efficiency while solving the issues of velocity-pressure decoupling and pressure overcorrection in the traditional Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. The adaptive time-stepping method is employed to reduce computational costs in transient simulations. The performance of SIMPLE, SIMPLE-Revised-Revised (SIMPLERR), and SIMPLER* algorithms is comprehensively compared. Validation across four classical benchmark tests confirms the superior robustness and numerical stability of SIMPLER*, which exhibits lower numerical diffusion and remains oscillation-free under strong pressure discontinuities. Subsequent steady-state and transient engineering cases demonstrate that the computational efficiency of the SIMPLER* algorithm is significantly better than that of the SIMPLE and SIMPLERR algorithms, both in coarse and fine grids. The proposed \"adaptive time-stepping + SIMPLER* algorithm\" combination method greatly reduces the computational overhead while ensuring the accuracy of the solution, providing an efficient and reliable solution for the transient simulation of complex two-phase flow with phase change.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204447"},"PeriodicalIF":2.5,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837007","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 : 2025-12-16DOI: 10.1016/j.euromechflu.2025.204440
Siyi Li , Zihao Zhu , Lei Xie , Yaguang Xie , Ruonan Wang , Qiang Du , Junqiang Zhu
Instabilities in rotor–stator cavities significantly influence flow dynamics and heat transfer processes within aerospace propulsion systems. Among these instabilities, the circular waves manifests within the stator boundary layer and exhibits transient behavior highly sensitive to disturbances in the basic state. To elucidate the underlying mechanisms driving this transient phenomenon, through direct numerical simulation (DNS), we systematically imposed impulsive changes and harmonic modulations on the rotation speed of the rotor, thereby inducing various types of disturbances. Our findings reveal that the emergence of circular waves is triggered by these disturbances, with the waves’ characteristics displaying marked sensitivity to the nature of the disturbances. Specifically, increasing the disturbance frequency leads to an upward migration of the circular waves’ radial position. The energy and radial extent of the circular waves exhibit a trend of first increasing and then decreasing as the disturbance frequency increases. Moreover, as the disturbance amplitude increases, the radial extent occupied by the circular waves expands, while the midpoint of their radial position remains unaltered. We further identified that when a hub rotating with the rotor, circular waves can become self-sustaining under certain conditions. Specifically, when the gap ratio (, where is the radius of the hub, is the radius of the shroud, is the half of the gap between the rotor and stator) and rotational Reynolds number (, where refers to the rotational speed of the rotor, and refers to the kinematic viscosity) are sufficiently large, disturbances on the stator side can migrate through the hub, amplify, and form disturbances on the rotor side, subsequently re-exciting circular waves on the stator. Through linear stability analysis, we determined the boundary in the parameter domain that delineates conditions for self-sustaining circular waves. This study provides a comprehensive investigation into the behavior of circular waves, shedding new light on their complex dynamics within rotor–stator cavities.
{"title":"Direct numerical simulation and linear stability analysis of circular waves in the stator boundary layer of rotor–stator cavity","authors":"Siyi Li , Zihao Zhu , Lei Xie , Yaguang Xie , Ruonan Wang , Qiang Du , Junqiang Zhu","doi":"10.1016/j.euromechflu.2025.204440","DOIUrl":"10.1016/j.euromechflu.2025.204440","url":null,"abstract":"<div><div>Instabilities in rotor–stator cavities significantly influence flow dynamics and heat transfer processes within aerospace propulsion systems. Among these instabilities, the circular waves manifests within the stator boundary layer and exhibits transient behavior highly sensitive to disturbances in the basic state. To elucidate the underlying mechanisms driving this transient phenomenon, through direct numerical simulation (DNS), we systematically imposed impulsive changes and harmonic modulations on the rotation speed of the rotor, thereby inducing various types of disturbances. Our findings reveal that the emergence of circular waves is triggered by these disturbances, with the waves’ characteristics displaying marked sensitivity to the nature of the disturbances. Specifically, increasing the disturbance frequency leads to an upward migration of the circular waves’ radial position. The energy and radial extent of the circular waves exhibit a trend of first increasing and then decreasing as the disturbance frequency increases. Moreover, as the disturbance amplitude increases, the radial extent occupied by the circular waves expands, while the midpoint of their radial position remains unaltered. We further identified that when a hub rotating with the rotor, circular waves can become self-sustaining under certain conditions. Specifically, when the gap ratio (<span><math><mrow><mi>γ</mi><mo>=</mo><mrow><mo>(</mo><mi>b</mi><mo>−</mo><mi>a</mi><mo>)</mo></mrow><mo>/</mo><mi>H</mi></mrow></math></span>, where <span><math><mi>a</mi></math></span> is the radius of the hub, <span><math><mi>b</mi></math></span> is the radius of the shroud, <span><math><mi>H</mi></math></span> is the half of the gap between the rotor and stator) and rotational Reynolds number (<span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mi>Ω</mi><msup><mrow><mi>b</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>ν</mi></mrow></math></span>, where <span><math><mi>Ω</mi></math></span> refers to the rotational speed of the rotor, and <span><math><mi>ν</mi></math></span> refers to the kinematic viscosity) are sufficiently large, disturbances on the stator side can migrate through the hub, amplify, and form disturbances on the rotor side, subsequently re-exciting circular waves on the stator. Through linear stability analysis, we determined the boundary in the <span><math><mrow><mo>(</mo><mi>R</mi><mi>e</mi><mo>,</mo><mi>γ</mi><mo>)</mo></mrow></math></span> parameter domain that delineates conditions for self-sustaining circular waves. This study provides a comprehensive investigation into the behavior of circular waves, shedding new light on their complex dynamics within rotor–stator cavities.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204440"},"PeriodicalIF":2.5,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837011","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 : 2025-12-15DOI: 10.1016/j.euromechflu.2025.204445
Valerio Lupi , Filippo Caruso Lombardi , Martino Andrea Scarpolini , Roberto Verzicco , Francesco Viola
Although blood exhibits non-Newtonian properties, it is often modelled as a Newtonian fluid in numerical studies. However, the impact of this assumption on the accuracy of the predictions of computational models is not thoroughly assessed. For this reason, in this work, we compare the effect of Newtonian and shear-thinning blood rheological models on computational haemodynamics in the left heart. The analysis is based on the fluid–structure-electrophysiology interaction (FSEI) within a patient-specific anatomy of an individual with low ejection fraction to better highlight viscosity changes at low strain rates. Owing to the pulsatile nature of the flow, considerable spatio-temporal variations of the kinematic viscosity are observed for the non-Newtonian case. Integral quantities as well as blood pressure within the cardiac chambers are found to be weakly affected by the rheological model. Substantial differences are reported, instead, between the Newtonian and non-Newtonian cases, for the wall shear stress and local haemolysis index since they are sensitive to the local kinematic viscosity, which decreases within the shear layers of the systolic and diastolic jets, as well as in the near-wall regions.
{"title":"Impact of blood rheology on left heart haemodynamics: Newtonian vs. non-Newtonian modelling","authors":"Valerio Lupi , Filippo Caruso Lombardi , Martino Andrea Scarpolini , Roberto Verzicco , Francesco Viola","doi":"10.1016/j.euromechflu.2025.204445","DOIUrl":"10.1016/j.euromechflu.2025.204445","url":null,"abstract":"<div><div>Although blood exhibits non-Newtonian properties, it is often modelled as a Newtonian fluid in numerical studies. However, the impact of this assumption on the accuracy of the predictions of computational models is not thoroughly assessed. For this reason, in this work, we compare the effect of Newtonian and shear-thinning blood rheological models on computational haemodynamics in the left heart. The analysis is based on the fluid–structure-electrophysiology interaction (FSEI) within a patient-specific anatomy of an individual with low ejection fraction to better highlight viscosity changes at low strain rates. Owing to the pulsatile nature of the flow, considerable spatio-temporal variations of the kinematic viscosity are observed for the non-Newtonian case. Integral quantities as well as blood pressure within the cardiac chambers are found to be weakly affected by the rheological model. Substantial differences are reported, instead, between the Newtonian and non-Newtonian cases, for the wall shear stress and local haemolysis index since they are sensitive to the local kinematic viscosity, which decreases within the shear layers of the systolic and diastolic jets, as well as in the near-wall regions.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204445"},"PeriodicalIF":2.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837008","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 : 2025-12-12DOI: 10.1016/j.euromechflu.2025.204429
Zhongying Feng , Ye Wang , Chenghao Fu , Ruipeng Li , Kun Zheng , Zhan Wang
The phase-resolved wave prediction is of vital importance for improving the safety and operations of structures in ocean engineering, such as floating wind turbines and wave energy converters. However, it is challenging for traditional physical methods to predict wave elevation accurately and efficiently in high sea states where the nonlinearity plays an important role. Inspired by the capability of the Koopman theory in solving nonlinear problems, a phase-resolved wave prediction model by combining deep learning with Koopman operator, referred to as DKWP, is designed. The high-order spectral method is employed for providing training and test data. To illustrate the effectiveness of the proposed method, we compare it with another four phase-resolved wave prediction models, including the models based on artificial neural network, long short-term memory, U-Net and linear wave theory. The models are trained under the sea states 3–5 with wide ranges of significant height, peak period and peak factor. Comparisons between the predicted wave elevation and true wave elevation indicate that DKWP outperforms the other models in terms of accuracy. The generalization of the DKWP is validated when it predicts the wave elevation under the sea states 6–7. In addition, to improve the interpretability of the DKWP, the eigenvalues of the Koopman operator in the proposed model are further analyzed.
{"title":"A unidirectional phase-resolved wave prediction model based on deep Koopman embeddings","authors":"Zhongying Feng , Ye Wang , Chenghao Fu , Ruipeng Li , Kun Zheng , Zhan Wang","doi":"10.1016/j.euromechflu.2025.204429","DOIUrl":"10.1016/j.euromechflu.2025.204429","url":null,"abstract":"<div><div>The phase-resolved wave prediction is of vital importance for improving the safety and operations of structures in ocean engineering, such as floating wind turbines and wave energy converters. However, it is challenging for traditional physical methods to predict wave elevation accurately and efficiently in high sea states where the nonlinearity plays an important role. Inspired by the capability of the Koopman theory in solving nonlinear problems, a phase-resolved wave prediction model by combining deep learning with Koopman operator, referred to as DKWP, is designed. The high-order spectral method is employed for providing training and test data. To illustrate the effectiveness of the proposed method, we compare it with another four phase-resolved wave prediction models, including the models based on artificial neural network, long short-term memory, U-Net and linear wave theory. The models are trained under the sea states 3–5 with wide ranges of significant height, peak period and peak factor. Comparisons between the predicted wave elevation and true wave elevation indicate that DKWP outperforms the other models in terms of accuracy. The generalization of the DKWP is validated when it predicts the wave elevation under the sea states 6–7. In addition, to improve the interpretability of the DKWP, the eigenvalues of the Koopman operator in the proposed model are further analyzed.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204429"},"PeriodicalIF":2.5,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837009","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 study presents a comprehensive numerical investigation of the melting behavior of a phase change material during heat transfer and storage. This material is located in an inclined enclosure filled with nanofluid, under non-uniform wall heating conditions. For the nanofluid medium, the influence of natural convection and volumetric thermal radiation is considered using real radiative properties of nanoparticles. The Lattice Boltzmann Method is utilized to simulate the coupled heat transfer and phase change processes. The effects of Planck numbers ( = 0.01–1), Rayleigh numbers ( = 104 and 105), and inclination angles ( = 0°–90°) are examined at different times to assess temperature distribution, melting front propagation, velocity profile, liquid fraction, and total heat transfer performance. The results show that at the highest Planck number ( = 1), natural convection dominates, with melting starting from boundaries aligned with the heated nanofluid flow. However, at Planck numbers less than 0.1, radiation significantly enhances the temperature distribution and melting rate, resulting in up to 8.3 and 7.5 times increases in the liquid fraction and total Nusselt number, respectively. At = 1, the inclination angle of 0° yielded the highest melting performance with a liquid fraction of 31 % and 22 % for = 104 and 105, respectively. While at = 0.01, the inclination angle of 45° achieved the maximum melting with values exceeding 60 % due to the intensified radiative heat transfer and enhancement of the total Nusselt number by about 8 times. The interplay between radiation intensity and enclosure angle offers an influential mechanism for enhancing thermal performance. These findings provide valuable insights into the optimized design of advanced latent heat storage systems under multi-mode heat transfers.
{"title":"PCM energy storage considering nanofluid volumetric radiation and natural convection in an inclined non-uniformly heated enclosure: LBM simulation","authors":"Masoud Sobhani , Javad Abolfazli Esfahani , Hashem Ahmadi Tighchi","doi":"10.1016/j.euromechflu.2025.204444","DOIUrl":"10.1016/j.euromechflu.2025.204444","url":null,"abstract":"<div><div>This study presents a comprehensive numerical investigation of the melting behavior of a phase change material during heat transfer and storage. This material is located in an inclined enclosure filled with nanofluid, under non-uniform wall heating conditions. For the nanofluid medium, the influence of natural convection and volumetric thermal radiation is considered using real radiative properties of nanoparticles. The Lattice Boltzmann Method is utilized to simulate the coupled heat transfer and phase change processes. The effects of Planck numbers (<span><math><mi>Pl</mi></math></span> = 0.01–1), Rayleigh numbers (<span><math><mi>Ra</mi></math></span> = 10<sup>4</sup> and 10<sup>5</sup>), and inclination angles (<span><math><mi>γ</mi></math></span> = 0°–90°) are examined at different times to assess temperature distribution, melting front propagation, velocity profile, liquid fraction, and total heat transfer performance. The results show that at the highest Planck number (<span><math><mi>Pl</mi></math></span> = 1), natural convection dominates, with melting starting from boundaries aligned with the heated nanofluid flow. However, at Planck numbers less than 0.1, radiation significantly enhances the temperature distribution and melting rate, resulting in up to 8.3 and 7.5 times increases in the liquid fraction and total Nusselt number, respectively. At <span><math><mi>Pl</mi></math></span> = 1, the inclination angle of 0° yielded the highest melting performance with a liquid fraction of 31 % and 22 % for <span><math><mi>Ra</mi></math></span>= 10<sup>4</sup> and 10<sup>5</sup>, respectively. While at <span><math><mi>Pl</mi></math></span> = 0.01, the inclination angle of 45° achieved the maximum melting with values exceeding 60 % due to the intensified radiative heat transfer and enhancement of the total Nusselt number by about 8 times. The interplay between radiation intensity and enclosure angle offers an influential mechanism for enhancing thermal performance. These findings provide valuable insights into the optimized design of advanced latent heat storage systems under multi-mode heat transfers.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204444"},"PeriodicalIF":2.5,"publicationDate":"2025-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145837012","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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