Physical Review Fluids最新文献

{"title":"Rupture of a surfactant-laden draining thin film","authors":"Atul S. Vivek, Ranabir Dey, Harish N. Dixit","doi":"10.1103/physrevfluids.9.074004","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074004","url":null,"abstract":"Surfactant-laden thin liquid films overlaid on solid substrates are encountered in a variety of industrial and biological settings. As these films reach submicron thickness, they tend to become unstable owing to the influence of long-range dispersion forces. In the current study, we investigate how gravitational drainage affects the stability attributes of such thin liquid films. Using scaling arguments, we demonstrate that gravity and dispersion forces can exert their influence simultaneously over a wide range of film thicknesses. In the lubrication limit, we carry out linear stability analysis and nonlinear simulations to understand the evolution of draining thin films. Linear stability indicates the existence of two unstable modes and two cutoff wave numbers, as opposed to a single unstable mode and a unique cutoff wave number observed in stationary films. It is also found that surfactant-laden flowing films are more stable than stationary films with surfactants as well as draining films with clean interfaces. The origin of stabilization is identified as the enhanced surfactant perturbations generated due to drainage. We demonstrate that films exhibiting intermediate levels of surfactant activity and significant drainage exhibit the lowest rates of disturbance growth, leading to extending the time of rupture.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"55 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141775936","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":"Analytical solutions for long-time steady state Boussinesq gravity currents flowing along a horizontal boundary of finite length","authors":"Safir Haddad, Samuel Vaux, Kevin Varrall, Olivier Vauquelin","doi":"10.1103/physrevfluids.9.074803","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074803","url":null,"abstract":"This paper presents analytical solutions for a steady turbulent miscible gravity current flowing along a horizontal rigid boundary of finite length into a quiescent uniform environment. These solutions are obtained from the governing equations (mass, momentum, and buoyancy) originally proposed by Ellison and Turner [<span>J. Fluid Mech.</span> <b>6</b>, 423 (1959)] for a buoyant layer of fluid in the Boussinesq approximation. For a constant drag coefficient <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>C</mi><mi>d</mi></msub></math> and the specific entrainment law <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>E</mi><mo>∝</mo><msup><mtext>Ri</mtext><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow><mo>,</mo><mo> </mo><mtext>Ri</mtext></math> being the local Richardson number, we first derived a system of coupled ordinary differential equations describing the longitudinal evolution of the velocity <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>u</mi></math>, the height <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>h</mi></math>, the density deficit <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>η</mi></math>, and the Richardson number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Ri</mtext></math> of the current. For an initially supercritical flow <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mo>(</mo><msub><mtext>Ri</mtext><mn>0</mn></msub><mrow><mspace width=\"0.16em\"></mspace><mo><</mo><mspace width=\"0.16em\"></mspace></mrow><mn>1</mn><mo>)</mo></mrow></math>, explicit relations are found for <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>u</mi><mo>(</mo><mi>x</mi><mo>)</mo></mrow><mo>,</mo><mo> </mo><mrow><mi>h</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>,</mo></mrow></math> and <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>η</mi><mo>(</mo><mi>x</mi><mo>)</mo></mrow></math> solely as a function of the Richardson number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Ri</mtext><mo>(</mo><mi>x</mi><mo>)</mo></mrow></math>. The longitudinal evolution of the Richardson number is then theoretically obtained from a universal function <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>F</mi></math> which can be tabulated and, as in the present paper, also plotted. The function <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>F</mi></math> allows us to determine (and only from the knowledge of the boundary conditions at the source) whether the flow remains supercritical over the whole length of the rigid boundary, or might transit towards a subcritical state (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Ri</mtext><mrow><mspace width=\"0.16em\"></mspace><mo>></mo><mspace width=\"0.16em\"></mspace></mrow><mn>1</mn></mrow></math>). In this latter case, the mathematical resolution is modified by including a discontinuity similar to a hydraulic jump. The location and amplitude of this discontinuity are calculated from an additional univers","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"41 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141775939","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":"Reactive Rayleigh-Taylor turbulence: Influence of mixing on the growth and displacement of the mixing zone","authors":"Kevin Ley, Olivier Soulard, Jérôme Griffond, Antoine Briard, Serge Simoëns","doi":"10.1103/physrevfluids.9.074609","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074609","url":null,"abstract":"The purpose of this paper is to investigate the effects of molecular mixing on the evolution of a reactive Rayleigh-Taylor turbulent mixing zone. In this regard, we derive algebraic relations showing that an increase in the mixing level leads to a slowing of the growth of the mixing zone width. We also show the existence of a maximum displacement velocity of the mixing zone center. These predictions are assessed using both direct numerical simulations and large eddy simulations.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"351 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141775937","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":"Analysis of a turbulent round jet based on direct numerical simulation data at large box and high Reynolds number","authors":"Cat Tuong Nguyen, Martin Oberlack","doi":"10.1103/physrevfluids.9.074608","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074608","url":null,"abstract":"We have conducted a direct numerical simulation of a turbulent round jet at a previously unattained Reynolds number of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Re</mtext><mo>=</mo><mn>3500</mn></mrow></math> based on the jet diameter <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>D</mi></math> and jet-inlet bulk velocity <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>U</mi><mtext>b</mtext></msub></math> in a particularly long box of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>75</mn><mi>D</mi></mrow></math>. To achieve very fast convergence to self-similarity, we used a turbulent pipe flow at the same Reynolds number and length <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>5</mn><mi>D</mi></mrow></math> as the upstream inflow boundary condition. This indeed results in a very rapid emergence of self-similarity already at very small axial distances <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>z</mi></math> compared to all turbulent jet data published so far. Not only for the mean velocities and the Reynolds stresses as well as the budgets of the Reynolds stress tensor and the turbulent kinetic energy, a nearly perfect classical scaling based on the normalized radius <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>η</mi><mo>=</mo><mi>r</mi><mo>/</mo><mi>z</mi></mrow></math> in the range <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>z</mi><mo>/</mo><mi>D</mi><mo>=</mo><mn>25</mn><mo>−</mo><mn>65</mn></mrow></math> is shown, but also for the probability density function (PDF) of the axial velocity <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>U</mi><mi>z</mi></msub></math> as well as the associated skewness and kurtosis. All budget terms have been calculated directly, resulting in a marginal error in the balance. An almost completely Gaussian behavior of the PDF for the axial velocity is observed on the jet axis, while a clear deviation with increasingly heavy tails is evident with increasing distance from the axis.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"12 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141785443","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":"Heat transport in three-layer turbulent thermal convection","authors":"Xiao-Zheng Zhao, Can Qiu, Sheng-Qi Zhou, Yi-Zhen Li, Heng-Dong Xi, Ke-Qing Xia","doi":"10.1103/physrevfluids.9.073501","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.073501","url":null,"abstract":"We report an experimental study of heat transport in a three-layer turbulent Rayleigh-Bénard convection. The experiments were conducted in a cylindrical cell (with diameter <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>D</mi></math>) filled with a FC77 layer with height <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>H</mi><mo>=</mo><mi>D</mi></mrow></math>. A very thin layer of water and a very thin layer of mercury were introduced to the top and bottom of the FC77 layer to provide slippery boundary conditions. We performed high spatial resolution temperature measurements across the water-FC77 and FC77-mercury interfaces, determined the temperatures at the two interfaces, the Rayleigh number (Ra) and the Nusselt number (Nu) across the FC77 layer. The experiments were conducted in the Ra range of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>2.81</mn><mo>×</mo><msup><mn>10</mn><mn>9</mn></msup></mrow></math> to <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>1.24</mn><mo>×</mo><msup><mn>10</mn><mn>11</mn></msup></mrow></math> for the FC77 layer. It is found that not only the amplitude but also the scaling exponent (with Ra) of Nu is greatly enhanced in this three-layer system compared to the canonical single-layer system, especially in the high Ra range. In particular, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Nu</mtext></math> first scales as <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msup><mtext>Ra</mtext><mrow><mn>0.31</mn></mrow></msup></math> and then <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msup><mtext>Ra</mtext><mrow><mn>0.38</mn></mrow></msup></math> when Ra exceeds a transitional Rayleigh number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mtext>Ra</mtext><mi>t</mi></msub><mo>=</mo><mn>2.52</mn><mo>×</mo><msup><mn>10</mn><mn>10</mn></msup></mrow></math>, whereas in the canonical single-layer FC77 case, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Nu</mtext></math> is found to scale as <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msup><mtext>Ra</mtext><mrow><mn>0.26</mn></mrow></msup></math>. Temperature measurements show that the boundary condition above and below the FC77 layer is asymmetric especially when <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Ra</mtext><mo>&gt;</mo><msub><mtext>Ra</mtext><mi>t</mi></msub></mrow></math>: the temperature drop across the top half (in contact with the water layer) of the FC77 layer is smaller than that across the bottom half (in contact with the mercury layer), and the top thermal boundary layer (TBL) becomes thinner and follows a steeper scaling with <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Ra</mtext></math> compared to the bottom TBL. We consider a hypothetical experiment where the top and the bottom boundary conditions are symmetric, denoted as a “water-FC77-water” three-layer system, in which the temperature drop across the bottom boundary layer <math xmlns=\"h","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"27 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141775938","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":"Modeling a spheroidal squirmer through a complex fluid","authors":"Zhenyu Ouyang, Chen Liu, Zhaowu Lin, Jianzhong Lin","doi":"10.1103/physrevfluids.9.073303","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.073303","url":null,"abstract":"We simulate a spheroidal swimmer through a complex fluid, modeled by the Giesekus constitutive equation incorporating fluid inertia. We develop a spheroidal swimmer model and exert it in a direct-forcing fictitious domain method framework. This model extends the conventional spherical “squirmer,” representing a microswimmer generating self-propulsion through tangential surface waves at its boundaries. We vary the swimmer's aspect ratio (AR) and Weissenberg number (Wi; the ratio of fluid elastic force to viscous force), respectively, in the range of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>1.5</mn><mo>≤</mo><mi>AR</mi><mo>≤</mo><mn>8</mn></mrow></math> and <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>0.5</mn><mo>≤</mo><mi>Wi</mi><mo>≤</mo><mn>10</mn></mrow></math>. Our results show that, an inertial spheroidal puller with a small <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mo>|</mo><mi>β</mi><mo>|</mo></mrow></math> (a swimming intensity parameter) swims faster than the counterpart subjected to the Stokes flow regime—a departure from the observed pattern in spherical pullers. Within the Giesekus fluid medium, an augmented mobility factor <i>α</i> correlates with an increased squirmer velocity, while a larger AR contributes significantly to the speed enhancement of a neutral squirmer in the presence of fluid inertia. Meanwhile, we explore the squirmer's energy expenditure and hydrodynamic efficiency, finding that a slenderer, inertial squirmer with a vigorous swimming intensity expends more energy, contrasting with the reduced energy expenditure associated with a smaller intensity. Notably, a larger AR positively correlates with squirmer efficiency, displaying an advantageous relationship with swimming speed.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"38 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141754059","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":"Coarsening effects on the liquid permeability in foam-filled porous media","authors":"Margaux Ceccaldi, Vincent Langlois, Olivier Pitois, Marielle Guéguen, Daniel Grande, S. Vincent-Bonnieu","doi":"10.1103/physrevfluids.9.074003","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074003","url":null,"abstract":"Injection of liquid foam through soils is increasingly used in applications such as soil remediation or soil improvement, where it is also crucial to control the liquid relative permeability through the foam-filled soil. We have measured the time dependence of the liquid permeability of granular packings initially filled with liquid foam for different values of the liquid saturation. It is shown that, systematically, permeability increases significantly over time before reaching saturation. We have demonstrated that this evolution is directly related to the coarsening of the liquid foam confined in the pore space. We have shown how the evolution of the liquid permeability can be predicted from the knowledge of the bubble size evolution.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"31 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141754062","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":"Impact dynamics of nanodroplets on pillared surfaces","authors":"Yi-Feng Wang, Yi-Bo Wang, Ling-Zhe Zhang, Xin He, Yan-Ru Yang, Xiao-Dong Wang, Duu-Jong Lee","doi":"10.1103/physrevfluids.9.073602","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.073602","url":null,"abstract":"This work investigates impacting nanodroplets on pillared surfaces via molecular dynamics (MD) simulations, especially to understand the intrusion effect of liquid in pillar gaps at the nanoscale, by comprehensively revealing outcome regimes and modeling the maximum spreading factor <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mo>(</mo><msub><mi>β</mi><mi>max</mi></msub><mo>)</mo></mrow></math>. A total of six outcomes, including first sticky (1S), second sticky (2S), first nonbouncing (1NB), second nonbouncing (2NB), first bouncing (1B), and second bouncing (2B), are identified. The 1S, 2S, and 2B regimes take place on monostable Wenzel surfaces with the Wenzel-to-Cassie dewetting transition and bouncing boundaries separating them; the 1NB, 2NB, 1B, and 2B regimes occur on monostable Cassie surfaces, distinguished by the Cassie-to-Wenzel wetting transition and bouncing boundaries. By establishing criteria of all boundaries, a universal phase diagram of impacting nanodroplets on pillared surfaces is constructed. Besides, to understand the altered spreading dynamics by the liquid intrusion effect, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>β</mi><mi>max</mi></msub></math> is modeled. The bulk droplet above pillared surfaces is found to have the same spreading dynamics as a nanodroplet on flat surfaces, which decouples the effects of the bulk droplet and the liquid intruding into pillar gaps. Subsequently, two intrusion regimes are classified based on different intrusion morphology of the liquid front, and the scalings for intrusion volume in different intrusion regimes are obtained with the corresponding transition criterion being proposed. Eventually, scaling laws of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>β</mi><mi>max</mi></msub></math> for impacting nanodroplets on pillared surfaces are established by incorporating the volume term of the bulk droplet, and are in good agreement with all available MD data of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>β</mi><mi>max</mi></msub></math>, showing their strong robustness and universality.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"37 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141754061","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":"Hidden mechanism of dynamic large-eddy simulation models","authors":"Xiaohan Hu, Keshav Vedula, George Ilhwan Park","doi":"10.1103/physrevfluids.9.074607","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074607","url":null,"abstract":"The dynamic model is one of the most successful inventions in subgrid-scale (SGS) modeling as it alleviates many drawbacks of the static coefficient SGS stress models. The model coefficient is often calculated dynamically through the minimization of the Germano-identity error (GIE). However, the driving mechanism behind the dynamic model's success is still not well understood. In wall-bounded flows, we postulate that the principal directions of the resolved rate-of-strain tensor play an important role in the dynamic models. Specifically, we find that minimization of the GIE along only the three principal directions (or less), in lieu of the nine components in its original formulation, produces equally comparable results as the original model when examined in canonical turbulent channel flows, a three-dimensional turbulent boundary layer, and a separating flow over periodic hills. This suggests that not all components of the Germano identity are equally important for the success of the dynamic model, and that there might be dynamically more important directions for modeling the subgrid dynamics.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"38 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141744364","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":"Critical charges for droplet collisions","authors":"A. Dubey, G. P. Bewley, K. Gustavsson, B. Mehlig","doi":"10.1103/physrevfluids.9.074302","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074302","url":null,"abstract":"Two micron-sized water droplets approaching each other do not always coalesce due to the cushioning effect of the air between them. When the droplets do not carry any electrical charges, one needs to consider the breakdown of hydrodynamics at very small scales to decide whether the droplets collide and coalesce or not. In contrast, two approaching droplets that are oppositely charged always coalesce if the charges are large enough. To find the charge for which the transition to charge-dominated collisions occurs, we computed the collision efficiency of charged, hydrodynamically interacting droplets settling in quiescent air, including the noncontinuum regime at small interfacial distances. For oppositely charged droplets, we find that the transition occurs when a saddle point of the relative droplet dynamics exits the region within which the continuum hydrodynamics breaks down. For cloud droplets with radii 16 and <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>20</mn><mspace width=\"0.16em\"></mspace><mi>µ</mi><mi mathvariant=\"normal\">m</mi></mrow></math>, we observe that the transition occurs at <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mo>∼</mo><msup><mn>10</mn><mn>3</mn></msup></mrow></math> elementary charges <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>e</mi></math>. For charges smaller than this, we predict that the coalescence rate depends primarily upon the Knudsen number (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>Kn</mi></math>, the ratio of the mean-free-path of air to the mean droplet radius), whereas coalescence for much larger charges does not depend upon <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>Kn</mi></math>. For droplets charged with the same polarity, we find the critical charge to be substantially larger (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mo>∼</mo><msup><mn>10</mn><mn>4</mn></msup><mspace width=\"0.16em\"></mspace><mi>e</mi></mrow></math> for the above radii) for reasons that we discuss.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"52 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141744365","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}