Journal of Fluid Mechanics最新文献

{"title":"The role of Lagrangian drift in the generation of surface waves by wind.","authors":"L R Seitz, Mara A Freilich, Nick Pizzo","doi":"10.1017/jfm.2026.11348","DOIUrl":"https://doi.org/10.1017/jfm.2026.11348","url":null,"abstract":"<p><p>A nonlinear stability analysis entirely in the Lagrangian frame is conducted, revealing the fundamental role of the wave-induced mean flow in modifying further wave growth and providing new insight into the classic problem of wave generation by wind. The prevailing theory, a critical-layer resonance mechanism proposed by Miles (<i>J. Fluid Mech</i>., 1957, vol. 3, no. 2, pp. 185-204), has seen numerous refinements; yet, the role of Lagrangian drift - the velocity a fluid parcel actually experiences - in wave growth was not understood. Our analysis first recovers the classic Miles growth rate from linear theory before extending it to third order in the wave slope to derive a modified growth rate. The leading-order wave-induced mean flow alters the higher-order instability, manifesting as a suppression of growth with increasing wave steepness for the realistic wind profiles considered. This modified growth rate shows good agreement with experimental observations, explaining the observed steepness-dependent suppression via a single physical mechanism. An integral momentum budget clarifies this mechanism, revealing that the wave-induced current alters the coupling between the total phase speed and the total Lagrangian mean flow at the critical level (as defined in the linear theory), thereby acting to reduce the efficiency of momentum transfer. Notably, this Lagrangian drift is precisely what Doppler-shift-based remote sensing of upper ocean currents measure, providing a direct observational pathway to account for this wave-induced feedback in studies of air-sea coupling. More broadly, this approach can be generalised to analyse other shear instabilities and provides a direct path towards refining wind-stress parametrisations.</p>","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1032 ","pages":"A9"},"PeriodicalIF":3.9,"publicationDate":"2026-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13107201/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147772967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Computational study of the separation of regular sphere clusters in high-Mach-number flow.","authors":"Thomas Whalen, Ralf Deiterding, Stuart Jon Laurence","doi":"10.1017/jfm.2026.11180","DOIUrl":"https://doi.org/10.1017/jfm.2026.11180","url":null,"abstract":"<p><p>A coupled computational-fluid-dynamics/finite-element methodology is implemented to investigate the free aerodynamic separation of clusters of equally sized spheres arranged in regular configurations in Mach-20 flow, representing an idealized meteoroid-fragmentation scenario. The regular nature of the initial agglomeration geometries - touching sphere pairs, tetrahedral four-sphere arrangements and face-centred-cubic 13-sphere configurations - allows a systematic exploration of both individual sphere motions and bulk cluster dynamics as the initial orientation is varied. For sphere pairs, a stable lifting configuration arises when the spheres are in contact in a skewed configuration, a phenomenon that can also emerge in the more populous clusters. In the tetrahedral survey, comprising 38 initial orientations, shock surfing of downstream bodies is found to play a significant role in driving the separation dynamics. Despite substantial variations in detailed sphere motions with initial orientation, the trajectory type and final lateral velocity collapse reasonably well with the initial polar angle of the sphere within the cluster. Indices describing the bluntness and asymmetry of the initial configuration are introduced and correlate well with the collective cluster dynamics, though not always in an intuitive way. For the 13-sphere clusters, the dependency of individual sphere lateral velocities follows a similar trend with initial polar angle to the four-sphere case, suggesting that a simplified separation model may be possible for such configurations. The influence of the initial cluster bluntness on the bulk dynamics is somewhat reduced, however, indicating a tendency towards more homogeneous separation as the cluster population is increased.</p>","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1029 ","pages":"A35"},"PeriodicalIF":3.9,"publicationDate":"2026-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12936463/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147326353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ocean transit times: from basin to planetary scales.","authors":"Paola Cessi","doi":"10.1017/jfm.2025.11047","DOIUrl":"https://doi.org/10.1017/jfm.2025.11047","url":null,"abstract":"<p><p>Lagrangian transit times on basin to planetary scales are controlled by the interplay of multiscale processes. The primary advective time scale is set by throughflow currents, such as interhemispheric western boundary currents. Dispersion by mesoscale eddies introduces fluctuations that erase memory and enhance dispersion, widening the transit-time distribution. The tortuous paths of Lagrangian parcels, particularly within ocean gyres, significantly enhance dispersion beyond the levels attributed to mesoscale eddies alone. Additionally, trapping by ocean gyres leads to multimodal distributions of Lagrangian transit times. These processes are illustrated in three complementary contexts: eddy-permitting ocean state estimates, simplified spatially extended three-dimensional flows and diffusively coupled two-dimensional pipe models.</p>","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1026 ","pages":"A31"},"PeriodicalIF":3.9,"publicationDate":"2026-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12926746/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147284102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Behaviour of finite-size floating particles in free-surface turbulence.","authors":"Henri Sanness Salmon, Kelken Chang, Claudio Mucignat, Filippo Coletti","doi":"10.1017/jfm.2025.10648","DOIUrl":"10.1017/jfm.2025.10648","url":null,"abstract":"<p><p>Motivated by the need for a better understanding of marine plastic transport, we experimentally investigate finite-size particles floating in free-surface turbulence. Using particle tracking velocimetry, we study the motion of spheres and discs along the quasi-flat free-surface above homogeneous isotropic grid turbulence in open channel flows. The focus is on the effect of the particle diameter, which varies from the Kolmogorov scale to the integral scale of the turbulence. We find that particles of size up to approximately one-tenth of the integral scale display motion statistics indistinguishable from surface flow tracers. For larger sizes, the particle fluctuating energy and acceleration variance decrease, the correlation times of their velocity and acceleration increase, and the particle diffusivity is weakly dependent on their diameter. Unlike in three-dimensional turbulence, the acceleration of finite-size floating particles becomes less intermittent with increasing size, recovering a Gaussian distribution for diameters in the inertial subrange. These results are used to assess the applicability of two distinct frameworks: <i>temporal filtering</i> and <i>spatial filtering</i>. Neglecting preferential sampling and assuming an empirical linear relation between the particle size and its response time, the temporal filtering approach is found to correctly predict the main trends, though with quantitative discrepancies. On the other hand, the spatial filtering approach, based on the spatial autocorrelation of the free-surface turbulence, accurately reproduces the decay of the fluctuating energy with increasing diameter. Although the scale separation is limited, power-law scaling relations for the particle acceleration variance based on spatial filtering are compatible with the observations.</p>","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1019 ","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7618314/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145431851","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Complex transition pathways in boiling and cavitation.","authors":"M Gallo, F Occhioni, F Magaletti, C M Casciola","doi":"10.1017/jfm.2025.10591","DOIUrl":"10.1017/jfm.2025.10591","url":null,"abstract":"<p><p>This work combines Navier-Stokes-Korteweg dynamics and rare event techniques to investigate the transition pathways and times of vapour bubble nucleation in metastable liquids under homogeneous and heterogeneous conditions. The nucleation pathways deviate from classical theory, showing that bubble volume alone is an inadequate reaction coordinate. The nucleation mechanism is driven by long-wavelength fluctuations with densities slightly different from the metastable liquid. We propose a new strategy to evaluate the typical nucleation times by inferring the diffusion coefficients from hydrodynamics. The methodology is validated against state-of-the-art nucleation theories in homogeneous conditions, revealing non-trivial, significant effects of surface wettability on heterogeneous nucleation. Notably, homogeneous nucleation is detected at moderate hydrophilic wettabilities despite the presence of a wall, an effect not captured by classical theories but consistent with atomistic simulations. Hydrophobic surfaces, instead, anticipate the spinodal.The proposed approach is fairly general and, despite the paper discussing results for a prototypical fluid, it can be easily extended, also in complex geometries, to any real fluid provided the equation of state is available, paving the way to model complex nucleation problems in real systems.</p>","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1019 ","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7618312/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145431829","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coastal wave refraction in variable currents over a varying bathymetry.","authors":"Trygve Halsne, Yan Li","doi":"10.1017/jfm.2025.10573","DOIUrl":"10.1017/jfm.2025.10573","url":null,"abstract":"<p><p>Refraction is the predominant mechanism causing spatially inhomogeneous surface gravity wave fields. However, the complex interplay between depth- and current-induced wave refraction remains poorly understood. Assuming weak currents and slowly varying bathymetry, we derive an analytical approximation to the wave ray curvature, which is validated by an open-source ray tracing framework. The approximation has the form of linear superposition of a current- and a depth-induced component, each depending on the gradients in the ambient fields. This separation enables quantification of their individual and combined contributions to refraction. Through analysis of a few limiting cases, we demonstrate how the sign and magnitude of these components influence the wave refraction, and identify conditions where they either amplify or counteract each other. We also identify which of the two plays a dominant role. These findings provide physically resolved insights into the influence of current and depth gradients on wave propagation, and are relevant for applications related to remote sensing and coastal wave forecasting services.</p>","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1019 ","pages":"A6"},"PeriodicalIF":3.9,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7618210/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145251129","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The joint effects of planetary <i>β</i>, topography and friction on baroclinic instability in a two-layer QG model.","authors":"Miriam F Sterl, André Palóczy, Sjoerd Groeskamp, Michiel L J Baatsen, Joseph H LaCasce, Pål E Isachsen","doi":"10.1017/jfm.2025.10172","DOIUrl":"10.1017/jfm.2025.10172","url":null,"abstract":"<p><p>The quasi-geostrophic two-layer model is a widely used tool to study baroclinic instability in the ocean. One instability criterion for the inviscid two-layer model is that the potential vorticity (PV) gradient must change sign between the layers. This has a well-known implication if the model includes a linear bottom slope: for sufficiently steep retrograde slopes, instability is suppressed for a flow parallel to the isobaths. This changes in the presence of bottom friction as well as when the PV gradients in the layers are not aligned. We derive the generalised instability condition for the two-layer model with nonzero friction and arbitrary mean flow orientation. This condition involves neither the friction coefficient nor the bottom slope; even infinitesimally weak bottom friction destabilises the system regardless of the bottom slope. We then examine the instability characteristics as a function of varying slope orientation and magnitude. The system is stable across all wavenumbers only if friction is absent and if the planetary, topographic and stretching PV gradients are aligned. Strong bottom friction decreases the growth rates but also alters the dependence on bottom slope. Thus the often mentioned stabilisation by steep bottom slopes in the two-layer model only holds in very specific circumstances and thus probably plays only a limited role in the ocean.</p>","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1012 ","pages":""},"PeriodicalIF":3.6,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7617829/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144584099","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reverse capillary trapping and self-removal of non-aqueous fluid from dead-end structures by nanoparticle suspension","authors":"Wenhai Lei, Xukang Lu, Guang Yang, Shervin Bagheri, Moran Wang","doi":"10.1017/jfm.2025.53","DOIUrl":"https://doi.org/10.1017/jfm.2025.53","url":null,"abstract":"We report an anomalous capillary phenomenon that reverses typical capillary trapping via nanoparticle suspension and leads to a counterintuitive self-removal of non-aqueous fluid from dead-end structures under weakly hydrophilic conditions. Fluid interfacial energy drives the trapped liquid out by multiscale surfaces: the nanoscopic structure formed by nanoparticle adsorption transfers the molecular-level adsorption film to hydrodynamic film by capillary condensation, and maintains its robust connectivity, then the capillary pressure gradient in the dead-end structures drives trapped fluid motion out of the pore continuously. The developed mathematical models agree well with the measured evolution dynamics of the released fluid. This reversing capillary trapping phenomenon via nanoparticle suspension can be a general event in a random porous medium and could dramatically increase displacement efficiency. Our findings have implications for manipulating capillary pressure gradient direction via nanoparticle suspensions to trap or release the trapped fluid from complex geometries, especially for site-specific delivery, self-cleaning, or self-recover systems.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1009 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147332300","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pulsatile flow in a thin-walled viscoelastic tube.","authors":"Oleksander Krul, Prosenjit Bagchi","doi":"10.1017/jfm.2025.150","DOIUrl":"10.1017/jfm.2025.150","url":null,"abstract":"<p><p>Low inertia, pulsatile flows in highly distensible, viscoelastic vessels exist in many biological and engineering systems. However, many existing works focus on inertial, pulsatile flows in vessels with small deformations. As such, here we study the dynamics of a viscoelastic tube at large deformation conveying low Reynolds number, oscillatory flow using a fully-coupled fluid/structure interaction computational model. We focus on a detailed study on the effect of wall (solid) viscosity and oscillation frequency on the tube deformation, flow rate, phase shift and hysteresis, and the underlying flow physics. We find that the general behavior is dominated by an elastic flow surge during inflation and a squeezing effect during deflation. When increasing the oscillation frequency, the maximum inlet flow rate increases and tube distention decreases, whereas increasing solid viscosity causes both to decrease. As the oscillation frequency approaches either 0 (quasi-steady inflation cycle) or ∞ (steady flow), the behaviors of tubes with different solid viscosities converge. Our results suggest that deformation and flow rate are most affected in the intermediate range of solid viscosity and oscillation frequency. Phase shifts of deformation and flow rate with respect to the imposed pressure are analyzed. We predict that the phase shifts vary throughout the oscillation; while the deformation always lags the imposed pressure, the flow rate may either lead or lag depending on the parameter values. As such, the flow rate shows hysteresis behavior that traces either a clockwise or counterclockwise curve, or a mix of both, in the pressure-flow rate space. This directional change in hysteresis is fully characterized here in the appropriate parameter space. Furthermore, the hysteresis direction is shown to be predicted by the signs of the flow rate phase shifts at the crest and trough of the oscillation. A distinct change in the tube dynamics is also observed at high solid viscosity which leads to global or \"whole-tube\" motion that is absent in purely elastic tubes.</p>","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1007 ","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12360716/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144956867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Topology of shallow-water waves on a rotating sphere.","authors":"Nicolas Perez, Armand Leclerc, Guillaume Laibe, Pierre Delplace","doi":"10.1017/jfm.2024.1228","DOIUrl":"10.1017/jfm.2024.1228","url":null,"abstract":"<p><p>Topological properties of the spectrum of shallow-water waves on a rotating spherical body are established. Particular attention is paid to spectral flow, i.e. the modes whose frequencies transit between the Rossby and inertia-gravity wavebands as the zonal wavenumber is varied. Organising the modes according to the number of zeros of their meridional velocity, we conclude that the net number of modes transiting between the shallow-water wavebands on the sphere is null, in contrast to the Matsuno spectrum. This difference can be explained by a miscount of zeros under the <i>β</i>-plane approximation. We corroborate this result with the analysis of Delplace <i>et al</i>. (<i>Science</i>, vol. 358, 2017, pp. 1075-1077) by showing that the curved metric discloses a pair of degeneracy points in the Weyl symbol of the wave operator, non-existent under the <i>β</i>-plane approximation, each of them bearing a Chern number of -1.</p>","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"1003 ","pages":""},"PeriodicalIF":3.6,"publicationDate":"2025-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7617373/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143382591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}