Physical Review Fluids最新文献

{"title":"Flooding as a sub-critical instability in open channels","authors":"Serge Mora, Martine Le Berre, Yves Pomeau","doi":"10.1103/physrevfluids.9.084607","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084607","url":null,"abstract":"In flood events caused by a gradual increase in the flow rate of a watercourse, the rise in water level is often abrupt, while the fall in level is delayed. We show that such behavior can be demonstrated by considering stationary flows at a high Reynolds number in a prismatic open channel: Several geometries of the channel cross section lead to a subcritical instability that results in a discontinuous rise in the level when the flow rate exceeds a critical value <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>F</mi><mi>i</mi></msub></math>, and in a fall, also discontinuous, when the flow rate returns below a value <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>F</mi><mi mathvariant=\"script\">o</mi></msub></math> lower than <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>F</mi><mi>i</mi></msub></math>. This hysteretic behavior originates from the interplay between gravity, which drives the flow downstream, and turbulent friction with the channel wall. The potential existence of several solutions arising from this bifurcation requires careful consideration in flood simulations.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"100 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coupling atomization, emulsification, and polymerization steps for creating gel microspheres","authors":"S. Danial Naghib, Matin Mirbaha, Kristina Logushkova, Jérôme Bibette, Nicolas Bremond","doi":"10.1103/physrevfluids.9.083604","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083604","url":null,"abstract":"Calibrated gel microspheres are used in several life-science applications, from embolization to DNA barcoding and drug delivery. Along with selecting or designing specific materials that depend on the application, various processes have been developed to produce such hydrogel particles. Here, we report a high throughput strategy that is based on the controlled fragmentation of an aqueous jet in air that results in droplets of monomer solution, their entry and collection in an oil bath, followed by polymerization of the emulsion droplets which thus turn into gel beads. Each step of the process is detailed and the operating conditions are optimized to obtain homogeneous polyacrylamide gel microspheres. The impact area of the stream of droplets at the free surface, that can be tuned with the help of an electric field, plays a major role in minimizing coalescence of droplets as well as mass transport between the dispersed phase and the continuous phase which is correlated to the sedimentation flow features of the dilute emulsion.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"12 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210859","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Maintenance mechanism of a circular surface wave in a magnetohydrodynamic cell and limits of its existence","authors":"Vladislav Eltishchev, Gennadiy Losev, Peter Frick","doi":"10.1103/physrevfluids.9.083702","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083702","url":null,"abstract":"The circular surface wave (CSW) of a low-temperature gallium alloy in the immovable cell with a central bottom electrode and an upper ring electrode exposed to axial magnetic fields is studied experimentally. It is shown that, depending on the force parameter and geometrical characteristics of the cell [cell radius, height of the liquid metal (LM) layer, and position of the circular electrode], three modes can occur in the cell: rest, CSW, or axial rotation with a deep funnel on the surface providing the circular contact of the LM with the electrode. A mode map showing the boundaries of the CSW existence domain is plotted on the parameter plane. The mechanism which provides the existence of a stable CSW is suggested. It is shown that the CSW is a superposition of two intense large-scale vortices. The main vortex, whose axis coincides with the axis of the cylindrical cell, is generated by the Lorentz force localized near the bottom electrode and arising from the interaction of the divergent electric current with the vertical magnetic field. The intensity of the second vortex is an order of magnitude less, and the axis of rotation is directed to the contact area of the liquid metal with the ring electrode, which appears near the crest of the wave. Similar to the main vortex, it exists due to the interaction of the current converging to the contact area with the superimposed magnetic field. The second vortex provides the lifting of the LM ahead of the incoming wave. The intensity of both vortices is proportional to the product of the external field by the total current, which explains the linear relationship between the relative frequency of surface oscillations and their amplitude.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"406 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Confinement induced three-dimensional trajectories of microswimmers in rectangular channels","authors":"Byjesh N. Radhakrishnan, Ahana Purushothaman, Ranabir Dey, Sumesh P. Thampi","doi":"10.1103/physrevfluids.9.083302","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083302","url":null,"abstract":"We study the trajectories of a model microorganism inside three-dimensional channels with square and rectangular cross sections. Using (1) numerical simulations based on the lattice-Boltzmann method and (2) analytical expressions using far-field hydrodynamic approximations and the method of images we systematically investigate the role of the strength and finite-size of the squirmer, confinement dimensions, and initial conditions in determining the three-dimensional trajectories of microswimmers. Our results indicate that the hydrodynamic interactions with the confining walls of the channel significantly affect the swimming speed and trajectory of the model microswimmer. Specifically, pullers always display sliding motion inside the channel: weak pullers slide through the channel center line, while strong pullers slide through a path close to any of the walls. Pushers generally follow helical motion in a square channel. Unlike pullers and pushers, the trajectories of neutral swimmers are not easy to generalize and are sensitive to the initial conditions. Despite this diversity in the trajectories, the far-field expressions capture the essential features of channel-confined swimmers. Finally, we propose a method based on the principle of superposition to understand the origin of the three-dimensional trajectories of channel confined swimmers. Such construction allows us to predict and justify the origin of apparently complex three-dimensional trajectories generated by different types of swimmers in channels with square and rectangular cross sections.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"19 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210865","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical investigation on the heat transfer in wind turbulence over breaking waves","authors":"Min Lu, Zixuan Yang, Guowei He, Lian Shen","doi":"10.1103/physrevfluids.9.084606","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084606","url":null,"abstract":"Heat transfer in wind turbulence over breaking waves is studied through direct numerical simulations. The air-water system is simulated on an Eulerian grid with the interface between the two phases captured by a coupled level set and volume-of-fluid method. To examine the effect of wave age, different cases representing slow, intermediate, and fast waves are considered for the scenario of air temperature being higher than the water temperature. The results show that the evolution of mean temperature profile responds nonmonotonically to the increasing wave age. At a small wave age, the mean temperature near the water surface increases after wave breaking. At intermediate and large wave ages, however, the temperature decreases after wave breaking, while the decrement magnitude is larger at the intermediate wave age. An investigation of the temperature fluctuation flux indicates that a combined effect of wave-coherent flux and turbulence-induced flux leads to a large magnitude of temperature decrement at the intermediate wave age. A further analysis of the production term in the transport equation of the turbulence-induced temperature flux elucidates the mechanism underlying the generation of the turbulence-induced flux at the intermediate wave age. The findings of the present study suggest that temperature responds in a more complex manner to wave age than velocity does and this phenomenon should be considered in models for air-sea interaction and weather forecasting.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"3 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227808","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Droplet breakup and size distribution in an airstream: Effect of inertia","authors":"Someshwar Sanjay Ade, Pavan Kumar Kirar, Lakshmana Dora Chandrala, Kirti Chandra Sahu","doi":"10.1103/physrevfluids.9.084004","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084004","url":null,"abstract":"We experimentally investigate the morphology and breakup of a droplet as it descends freely from a height and encounters an airstream. The size distributions of the child droplets are analyzed using high-speed shadowgraphy and in-line holography techniques. We find that a droplet falling from various heights exhibits shape oscillations due to the intricate interplay between inertia and surface tension forces, leading to significant variations in the radial deformation of the droplet, influencing the breakup dynamics under an identical airstream condition. Specifically, the droplet undergoes vibrational breakup when introduced at a location slightly above the air nozzle. In contrast, as the release height of the droplet increases, keeping the Weber number defined based on the velocity of the airstream fixed, a dynamic interplay between the inertia of the droplet and the aerodynamic flow field comes into play, resulting in a sequence of breakup modes transitioning from vibrational breakup to retracting bag breakup, bag breakup, bag-stamen breakup, retracting bag-stamen breakup, and eventually returning to vibrational breakup. Our experiments also reveal that the size distribution resulting from retracting bag breakup primarily arises from rim and node fragmentation, leading to a bimodal distribution. In contrast, bag and bag-stamen breakups yield a trimodal size distribution due to the combined contributions of bag, rim, and node breakup mechanisms. Furthermore, we utilize a theoretical model that incorporates the effective Weber number, considering different release heights. This model accurately predicts the size distribution of the child droplets resulting from the various breakup modes observed in our experiments.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"55 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210868","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Platelet margination dynamics in blood flow: The role of lift forces and red blood cells aggregation","authors":"Mariam Dynar, Hamid Ez-Zahraouy, Chaouqi Misbah, Mehdi Abbasi","doi":"10.1103/physrevfluids.9.083603","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083603","url":null,"abstract":"Homeostasis plays a critical role in maintaining the delicate balance between preventing excessive bleeding and enabling clot formation during injuries. One pivotal aspect of homeostasis involves the development of platelet clots. In this study, we analyze numerically the behavior of platelet margination as a function of the adhesion energy between red blood cells (RBCs), driven by the presence of plasma proteins. We examine scenarios encompassing both physiological conditions and pathological states, such as those seen in patients with diabetes. Employing a two-dimensional simulation, we utilize rigid particles and a vesicle model to simulate platelets and RBCs, respectively. We employ the lattice Boltzmann method to solve the underlying model equations. We first demonstrate that platelet margination is primarily determined by lift forces and is not notably affected by whether the cells undergo tank-treading (TT) or tumbling (TB) behavior, as often reported. Specifically, we unveil instances where cells exhibit TT or TB behavior, yet their platelet concentration profiles closely resemble each other. Furthermore, we present a striking result concerning the impact of RBC adhesion. In microcirculation the hematocrit is in the range <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>5</mn><mo>–</mo><mn>20</mn><mo>%</mo></mrow></math>. A moderate adhesion energy (falling within the physiological range) boosts platelet margination in microcirculation. However, this effect becomes small for larger hematocrit encountered in macrocirculation (e.g., <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>40</mn><mo>%</mo></mrow></math>). This boost is more significant for a viscosity contrast (viscosity of cytoplasm over that the suspending fluid) equal to a known value for RBCs, as compared to the case without viscosity contrast. As we increase the adhesion energy (the pathological range), a noteworthy decline in platelet margination is found, albeit that for some flow strength the platelet margination reaches a minimum and increases again at higher adhesion energy. These results can be attributed to a combination of lift generated by the bounding walls and the formation of RBC clusters. Notably, our study sheds light on a critical consequence of excessive adhesion, typically observed in pathological conditions like diabetes mellitus.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"13 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227810","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Subcritical axisymmetric solutions in rotor-stator flow","authors":"Artur Gesla, Yohann Duguet, Patrick Le Quéré, Laurent Martin Witkowski","doi":"10.1103/physrevfluids.9.083903","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083903","url":null,"abstract":"Rotor-stator cavity flows are known to exhibit unsteady flow structures in the form of circular and spiral rolls. While the origin of the spirals is well understood, that of the circular rolls is not. In the present study the axisymmetric flow in an aspect ratio <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>R</mi><mo>/</mo><mi>H</mi><mo>=</mo><mn>10</mn></mrow></math> cavity is revisited numerically using recent concepts and tools from bifurcation theory. It is confirmed that a linear instability takes place at a finite critical Reynolds number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Re</mtext><mo>=</mo><msub><mtext>Re</mtext><mi>c</mi></msub></mrow></math> and that there exists a subcritical branch of large amplitude chaotic solutions. This motivates the search for subcritical finite-amplitude solutions. The branch of periodic states born in a Hopf bifurcation at <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Re</mtext><mo>=</mo><msub><mtext>Re</mtext><mi>c</mi></msub></mrow></math>, identified using a self-consistent method (SCM) and arclength continuation, is found to be supercritical. The associated solutions only exist, however, in a very narrow range of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Re</mtext></math> and do not explain the subcritical chaotic rolls. Another subcritical branch of periodic solutions is found using the harmonic balance method with an initial guess obtained by SCM. In addition, edge states separating the steady laminar and chaotic regimes are identified using a bisection algorithm. These edge states are biperiodic in time for most values of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Re</mtext></math>, where their dynamics is analyzed in detail. Both solution branches fold around at approximately the same value of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Re</mtext></math>, which is lower than <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mtext>Re</mtext><mi>c</mi></msub></math> yet still larger than the values reported in experiments. This suggests that, at least in the absence of external forcing, sustained chaotic rolls have their origin in the bifurcations from these unstable solutions.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"2 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Prediction of turbulent channel flow using Fourier neural operator-based machine-learning strategy","authors":"Yunpeng Wang, Zhijie Li, Zelong Yuan, Wenhui Peng, Tianyuan Liu, Jianchun Wang","doi":"10.1103/physrevfluids.9.084604","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084604","url":null,"abstract":"Fast and accurate predictions of turbulent flows are of great importance in the science and engineering field. In this paper, we investigate the implicit U-Net enhanced Fourier neural operator (IUFNO) in the stable prediction of long-time dynamics of three-dimensional (3D) turbulent channel flows. The trained IUFNO models are tested in the large-eddy simulations (LES) at coarse grids for three friction Reynolds numbers: <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mtext>Re</mtext><mi>τ</mi></msub><mo>≈</mo><mn>180</mn></mrow></math>, 395, and 590. The adopted near-wall mesh grids are tangibly coarser than the general requirements for wall-resolved LES. Compared to the original Fourier neural operator (FNO), the implicit FNO (IFNO), and U-Net enhanced FNO (UFNO), the IUFNO model has a much better long-term predictive ability. The numerical experiments show that the IUFNO framework outperforms the traditional dynamic Smagorinsky model and the wall-adapted local eddy-viscosity model in the predictions of a variety of flow statistics and structures, including the mean and fluctuating velocities, the probability density functions (PDFs) and joint PDF of velocity fluctuations, the Reynolds stress profile, the kinetic energy spectrum, and the Q-criterion (vortex structures). Meanwhile, the trained IUFNO models are computationally much faster than the traditional LES models. Thus, the IUFNO model is a promising approach for the fast prediction of wall-bounded turbulent flow.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"24 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Self-sustained oscillations in a low-viscosity round jet","authors":"V. Srinivasan, X. Tan, E. Whitely, I. Wright, A. Dhotre, J. Yang","doi":"10.1103/physrevfluids.9.083902","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083902","url":null,"abstract":"The effect of viscosity contrast between a jet and its surroundings is experimentally investigated using density-matched fluids. A gravity-driven flow is established with a jet of saltwater emerging into an ambient medium composed of high-viscosity propylene glycol. Jet Reynolds numbers, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>Re</mi></math>, ranging from 1600 to 3400 were studied for an ambient-to-jet viscosity ratio, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>M</mi></math>, between 1 and 50. Visualization suggests that at low values of the viscosity ratio, the jet breakdown mode is axisymmetric, while helical modes develop at high values of viscosity ratio. The transition between these two modes is attempted to be delineated using a variety of diagnostic tools. Hot-film anemometry measurements indicate that the onset of the helical mode is accompanied by the appearance of a discrete peak in the frequency spectrum of velocity fluctuations, which exhibits little spatial variation for the first several diameters in the downstream direction. Laser-induced fluorescence (LIF) is used to identify the jet boundary against the background. An analysis of high-speed images acquired using the LIF technique enables identification of the spatial growth rate of waves on the jet boundary, as well as the frequency of oscillation of the weakly diffusive interface. Temporal fluctuations of fluorescence intensity are found to be spatially invariant in the jet near field, further attesting to behavior consistent with that of a self-sustained oscillation whose frequency depends on the viscosity ratio. The observed frequencies show trends similar to those of absolutely unstable modes calculated from spatiotemporal linear stability theory presented in a companion paper. Spectral proper orthogonal decomposition was used to analyze the images and identify the various spatial modes, and suggests the existence of a single dominant mode. Together, these observations provide strong circumstantial evidence for the existence of a global mode that arises from the absolute instability of velocity and viscosity profiles in a region close to the nozzle exit plane.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"46 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}