Physical Review Fluids最新文献

{"title":"Investigating the effect of turbulence on hemolysis through cell-resolved fluid-structure interaction simulations of individual red blood cells","authors":"Grant Rydquist, Mahdi Esmaily","doi":"10.1103/physrevfluids.9.073102","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.073102","url":null,"abstract":"Existing hemolysis algorithms are often constructed for laminar flows that expose red blood cells (RBCs) to a constant rate of shear. It remains an open question whether such models are applicable to turbulent flows, where there is a significant variation in shear rate along cell trajectories. To evaluate the effect of turbulence on hemolysis, we perform cell-resolved simulations of isolated RBCs in turbulent channel flow at <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> and 360 and compare them against the results obtained from laminar flow simulations at an equivalent wall shear stress. The RBCs are modeled as isolated cells in an unbounded domain with the viscosity of the bulk fluid used for the surrounding fluid. This comparison shows that, while the laminar flow generally induces greater stretch in the cell in a time-averaged sense, cells experience an overall larger deformation in turbulence. This difference is attributed to extreme events in turbulence that occasionally create bursts of high shear conditions, which, consequently, induce a large deformation in the cells. Associating damage with the most extreme deformation regimes, we observe that, in the worst case, the turbulent flow can produce deformation in the cell that is higher than the absolute maximum value in the analogous laminar case approximately <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>14</mn><mo>%</mo></mrow></math> of the time. Additionally, the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>Re</mi><mi>τ</mi></msub><mo>=</mo><mn>180</mn></mrow></math> universally induced greater deformation in the cells than the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>Re</mi><mi>τ</mi></msub><mo>=</mo><mn>360</mn></mrow></math> case, suggesting that increasing the range of scales in the flow does not necessarily yield greater deformation when all other parameters are kept constant. A strong direct correlation (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>R</mi><mo>&gt;</mo><mn>0.8</mn></mrow></math>) between shear rate and deformation metrics was observed in turbulence. The correlation against <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>Q</mi></math>-criterion is inverse and weaker (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>R</mi><mo>≈</mo><mo>−</mo><mn>0.26</mn></mrow></math>), but once the shear contribution is subtracted, it improves in terms of areal dilatation (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>R</mi><mo>≈</mo><mo>−</mo><mn>0.6</mn></mrow></math>).","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"9 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141785246","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":"Evolution of turbulence using a random jet array","authors":"Arefe Ghazi Nezami, Blair Anne Johnson","doi":"10.1103/physrevfluids.9.074610","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074610","url":null,"abstract":"Random jet arrays (RJAs) have been shown to be effective in generating zero mean flow homogeneous isotropic turbulence. While many laboratory studies have investigated the flow in these facilities, there are several remaining questions regarding the evolution of turbulence, from the development of turbulence to where it decays, along with understanding how input energy from the jet array transfers into different turbulent flow characteristics. To address these questions, we perform a series of laboratory experiments in which we alter the parameters of the randomized algorithm, along with the jet spacing and outlet velocity of the jets. We first determine the location where turbulence transitions to a fully developed state and show that it is a function of jet penetration length, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi mathvariant=\"script\">L</mi><mi mathvariant=\"script\">J</mi></msub></math>, and effective jet spacing, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>S</mi><mi>e</mi></msub></math>. We identify three distinct regions for the spatial decay of turbulence in RJA facilities and notably, we find different decay rates, unlike previous studies that report only one spatial decay rate using similar facilities. These regions are shown to depend on the variations of input parameters yet independent of the strength of the mean flow. We also find the strength of the mean flow does not affect the homogeneity, nor the production, transport, or advection terms of the turbulent kinetic energy budget equation. Finally, we address a longstanding question toward estimating turbulence metrics with an RJA based on the input parameters. We define an efficiency parameter that provides insight into the transfer rate of input power to the dissipation rate of the generated turbulence.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"31 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141785441","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":"Dynamics of a magnetic particle in an oscillating magnetic field","authors":"I. Misra, V. Kumaran","doi":"10.1103/physrevfluids.9.074303","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074303","url":null,"abstract":"The orientation dynamics of and the torque fluctuations due to a spheroidal magnetic particle in an oscillating magnetic field are analyzed in the Stokes flow regime. For a permanent dipole, the dynamics depends on <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msup><mi>ω</mi><mo>†</mo></msup></math>, the ratio of the magnetic field frequency, and the viscous relaxation rate. For <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msup><mi>ω</mi><mo>†</mo></msup><mo>≫</mo><mn>1</mn></mrow></math>, the particle executes oscillations with amplitude <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mo>∼</mo><msup><mrow><mo>(</mo><msup><mi>ω</mi><mo>†</mo></msup><mo>)</mo></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> about its initial orientation. The average torque is zero because the particle does not execute complete rotations, and the root mean square of the torque fluctuations scaled by the characteristic magnetic torque tends to a constant in this limit. For <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msup><mi>ω</mi><mo>†</mo></msup><mo>≪</mo><mn>1</mn></mrow></math>, the orientation is close to the magnetic field direction for most of the oscillation period, and it rapidly rotates when the field passes through extrema. The scaled root mean square of the torque fluctuations is proportional to <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msup><mrow><mo>(</mo><msup><mi>ω</mi><mo>†</mo></msup><mo>)</mo></mrow><mrow><mo>−</mo><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup></math> in this limit. The particle orientation aligns along the magnetic field direction for different models of induced dipoles if the magnetization is nonhysteretic. For the hysteretic Stoner-Wohlfarth model, the dynamics also depends on the parameter <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>h</mi><mn>0</mn></msub></math>, the ratio of the Zeeman energy, and the anisotropy energy. For <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>h</mi><mn>0</mn></msub><mo>≪</mo><mn>1</mn></mrow></math>, the magnetic moment oscillates about one pole of the orientation vector, and the orientation vector rapidly rotates when the field passes through extrema in a manner similar to that for a permanent dipole. For <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>h</mi><mn>0</mn></msub><mo>≫</mo><mn>1</mn></mrow></math>, the magnetic moment switches between the two poles of the orientation vector, and the orientation vector executes small amplitude oscillations about the field direction. There is a discontinuous transition between the oscillating and switching magnetic moment which depends on <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>h</mi><mn>0</mn></msub></math> and the initial orientation.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"44 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141775932","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":"Shape reconfiguration for underwater propeller efficiency improvement","authors":"Tristan Aurégan, Sylvain Courrech du Pont, Benjamin Thiria","doi":"10.1103/physrevfluids.9.074402","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074402","url":null,"abstract":"We investigate experimentally the propulsive efficiency of a propeller in water with chordwise flexible blades that deform under the action of fluid loading. Using a scale model experiment, we record the deformation of the blades as well as the thrust and torque generated by the rotor. The use of flexible materials can improve the resilience to changing external conditions: with optimal flexibility, the blades deform and remain efficient under off-design conditions. We derive a theoretical law for blade tip deformation and show good agreement with experiments. Our results suggest that, using only the blade flexibility alone, we are able to program the blade deformation to passively adopt an optimized shape for efficient propulsion within a given parameter range.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"51 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141775935","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":"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 [&lt;span&gt;J. Fluid Mech.&lt;/span&gt; &lt;b&gt;6&lt;/b&gt;, 423 (1959)] for a buoyant layer of fluid in the Boussinesq approximation. For a constant drag coefficient &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;msub&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt; and the specific entrainment law &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mi&gt;E&lt;/mi&gt;&lt;mo&gt;∝&lt;/mo&gt;&lt;msup&gt;&lt;mtext&gt;Ri&lt;/mtext&gt;&lt;mrow&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mo&gt; &lt;/mo&gt;&lt;mtext&gt;Ri&lt;/mtext&gt;&lt;/math&gt; being the local Richardson number, we first derived a system of coupled ordinary differential equations describing the longitudinal evolution of the velocity &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mi&gt;u&lt;/mi&gt;&lt;/math&gt;, the height &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mi&gt;h&lt;/mi&gt;&lt;/math&gt;, the density deficit &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mi&gt;η&lt;/mi&gt;&lt;/math&gt;, and the Richardson number &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mtext&gt;Ri&lt;/mtext&gt;&lt;/math&gt; of the current. For an initially supercritical flow &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;msub&gt;&lt;mtext&gt;Ri&lt;/mtext&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/msub&gt;&lt;mrow&gt;&lt;mspace width=\"0.16em\"&gt;&lt;/mspace&gt;&lt;mo&gt;&lt;&lt;/mo&gt;&lt;mspace width=\"0.16em\"&gt;&lt;/mspace&gt;&lt;/mrow&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;, explicit relations are found for &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mi&gt;u&lt;/mi&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mo&gt; &lt;/mo&gt;&lt;mrow&gt;&lt;mi&gt;h&lt;/mi&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt; and &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mi&gt;η&lt;/mi&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt; solely as a function of the Richardson number &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mtext&gt;Ri&lt;/mtext&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;. The longitudinal evolution of the Richardson number is then theoretically obtained from a universal function &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mi&gt;F&lt;/mi&gt;&lt;/math&gt; which can be tabulated and, as in the present paper, also plotted. The function &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mi&gt;F&lt;/mi&gt;&lt;/math&gt; 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 (&lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mtext&gt;Ri&lt;/mtext&gt;&lt;mrow&gt;&lt;mspace width=\"0.16em\"&gt;&lt;/mspace&gt;&lt;mo&gt;&gt;&lt;/mo&gt;&lt;mspace width=\"0.16em\"&gt;&lt;/mspace&gt;&lt;/mrow&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;). 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 &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/math&gt;) filled with a FC77 layer with height &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mi&gt;H&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;. 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 &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mn&gt;2.81&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mn&gt;9&lt;/mn&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;/math&gt; to &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mn&gt;1.24&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mn&gt;11&lt;/mn&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;/math&gt; 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, &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mtext&gt;Nu&lt;/mtext&gt;&lt;/math&gt; first scales as &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;msup&gt;&lt;mtext&gt;Ra&lt;/mtext&gt;&lt;mrow&gt;&lt;mn&gt;0.31&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt; and then &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;msup&gt;&lt;mtext&gt;Ra&lt;/mtext&gt;&lt;mrow&gt;&lt;mn&gt;0.38&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt; when Ra exceeds a transitional Rayleigh number &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mtext&gt;Ra&lt;/mtext&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;2.52&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;msup&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;/math&gt;, whereas in the canonical single-layer FC77 case, &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mtext&gt;Nu&lt;/mtext&gt;&lt;/math&gt; is found to scale as &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;msup&gt;&lt;mtext&gt;Ra&lt;/mtext&gt;&lt;mrow&gt;&lt;mn&gt;0.26&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;. Temperature measurements show that the boundary condition above and below the FC77 layer is asymmetric especially when &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mrow&gt;&lt;mtext&gt;Ra&lt;/mtext&gt;&lt;mo&gt;&gt;&lt;/mo&gt;&lt;msub&gt;&lt;mtext&gt;Ra&lt;/mtext&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;: 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 &lt;math xmlns=\"http://www.w3.org/1998/Math/MathML\"&gt;&lt;mtext&gt;Ra&lt;/mtext&gt;&lt;/math&gt; 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 &lt;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}