Pub Date : 2024-07-29DOI: 10.1103/physrevfluids.9.l071101
Midhun Puthumana Melepattu, Guillaume Maîtrejean, Thomas Podgorski
Blood rheology and microcirculation are strongly influenced by red blood cell aggregation. We investigate the dissociation rates of red cell aggregates in extensional flow using hyperbolic microfluidic constrictions and image analysis by a convolutional neural network (CNN). Our findings reveal that aggregate dissociation increases sharply when a critical extension rate is reached which falls within the range of microcirculatory conditions, suggesting that large variations of aggregate sizes should be expected in vivo. This work contributes to a deeper understanding of the behavior of red blood cell aggregates in response to extensional stress in microcirculatory networks, provides crucial experimental data to validate theoretical and numerical models, and constitutes the basis for improved evaluation of blood aggregability in clinical contexts.
{"title":"Dissociation of red blood cell aggregates in extensional flow","authors":"Midhun Puthumana Melepattu, Guillaume Maîtrejean, Thomas Podgorski","doi":"10.1103/physrevfluids.9.l071101","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.l071101","url":null,"abstract":"Blood rheology and microcirculation are strongly influenced by red blood cell aggregation. We investigate the dissociation rates of red cell aggregates in extensional flow using hyperbolic microfluidic constrictions and image analysis by a convolutional neural network (CNN). Our findings reveal that aggregate dissociation increases sharply when a critical extension rate is reached which falls within the range of microcirculatory conditions, suggesting that large variations of aggregate sizes should be expected <i>in vivo</i>. This work contributes to a deeper understanding of the behavior of red blood cell aggregates in response to extensional stress in microcirculatory networks, provides crucial experimental data to validate theoretical and numerical models, and constitutes the basis for improved evaluation of blood aggregability in clinical contexts.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141869063","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}
Pub Date : 2024-07-26DOI: 10.1103/physrevfluids.9.074201
Shubhra Sahu, Bapan Mondal, Somnath Bhattacharyya
Atomistic and coarse-grained simulations show the formation of a condensed layer of counterions near a charged surface in contact with multivalent or monovalent electrolytes of high concentration. This condensed layer may overscreen the surface charge, and eventually a coion-dominated region may arise within the electric double layer, which again draws a layer of counterions and so on till the charge density approaches zero. Such a type of overscreening and charge density oscillation cannot be predicted through the mean-field based models as it does not account for the correlations between discrete charges. In the present study the mean-field-based model has been extended to consider the many-body interactions to analyze the electro-osmosis and ion transport of multivalent electrolytes in a highly charged nanopore. The ions are considered to be finite-sized, which is accounted for by considering the hydrodynamic steric interactions and modification of the suspension medium viscosity. Consideration of the electrostatic correlation leads to a fourth-order Poisson-Fermi equation for an electric field. Such a type of continuum model is easy to handle and to use to predict the layered structure of the EDL. Our model captures the existing experimental and molecular dynamics simulation correctly. Based on the modified model, we have analyzed the volume flow rate, current density, and ion selectivity of the pore in multivalent electrolytes for different electrostatic conditions. The present model shows that the counterion size has an impact on the condensed layer and hence overscreening. We demonstrate that the EOF reversal of multivalent electrolytes can be suppressed by mixing with monovalent slats.
{"title":"Ion steric interactions and electrostatic correlations on electro-osmotic flow in charged nanopores with multivalent electrolytes","authors":"Shubhra Sahu, Bapan Mondal, Somnath Bhattacharyya","doi":"10.1103/physrevfluids.9.074201","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074201","url":null,"abstract":"Atomistic and coarse-grained simulations show the formation of a condensed layer of counterions near a charged surface in contact with multivalent or monovalent electrolytes of high concentration. This condensed layer may overscreen the surface charge, and eventually a coion-dominated region may arise within the electric double layer, which again draws a layer of counterions and so on till the charge density approaches zero. Such a type of overscreening and charge density oscillation cannot be predicted through the mean-field based models as it does not account for the correlations between discrete charges. In the present study the mean-field-based model has been extended to consider the many-body interactions to analyze the electro-osmosis and ion transport of multivalent electrolytes in a highly charged nanopore. The ions are considered to be finite-sized, which is accounted for by considering the hydrodynamic steric interactions and modification of the suspension medium viscosity. Consideration of the electrostatic correlation leads to a fourth-order Poisson-Fermi equation for an electric field. Such a type of continuum model is easy to handle and to use to predict the layered structure of the EDL. Our model captures the existing experimental and molecular dynamics simulation correctly. Based on the modified model, we have analyzed the volume flow rate, current density, and ion selectivity of the pore in multivalent electrolytes for different electrostatic conditions. The present model shows that the counterion size has an impact on the condensed layer and hence overscreening. We demonstrate that the EOF reversal of multivalent electrolytes can be suppressed by mixing with monovalent slats.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141775933","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}
Pub Date : 2024-07-26DOI: 10.1103/physrevfluids.9.073102
Grant Rydquist, Mahdi Esmaily
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 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 of the time. Additionally, the universally induced greater deformation in the cells than the 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 () between shear rate and deformation metrics was observed in turbulence. The correlation against -criterion is inverse and weaker (), but once the shear contribution is subtracted, it improves in terms of areal dilatation ().
{"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>></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":null,"pages":null},"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}
Pub Date : 2024-07-26DOI: 10.1103/physrevfluids.9.074610
Arefe Ghazi Nezami, Blair Anne Johnson
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, , and effective jet spacing, . 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.
随机射流阵列（RJAs）已被证明可以有效地产生零平均流均质各向同性湍流。虽然许多实验室研究已经对这些设施中的流动进行了调查，但关于湍流的演变，从湍流的发展到湍流的衰减，以及了解射流阵列的输入能量如何转移到不同的湍流特性等，还存在一些问题。为了解决这些问题，我们进行了一系列实验室实验，在实验中我们改变了随机算法的参数以及射流间距和射流出口速度。我们首先确定了湍流过渡到充分发展状态的位置，并证明它是射流穿透长度 LJ 和有效射流间距 Se 的函数。我们确定了 RJA 设备中湍流空间衰减的三个不同区域，值得注意的是，我们发现了不同的衰减速率，这与之前使用类似设备只报告一种空间衰减速率的研究不同。研究表明，这些区域取决于输入参数的变化，但与平均流的强度无关。我们还发现，平均流的强度不会影响均质性，也不会影响湍流动能预算方程中的生成、传输或平流项。最后，我们解决了一个长期存在的问题，即根据输入参数用 RJA 估算湍流度量。我们定义了一个效率参数，该参数可帮助我们了解输入功率向所产生湍流的耗散率的转移率。
{"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":null,"pages":null},"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}
Pub Date : 2024-07-26DOI: 10.1103/physrevfluids.9.074303
I. Misra, V. Kumaran
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 , the ratio of the magnetic field frequency, and the viscous relaxation rate. For , the particle executes oscillations with amplitude 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 , 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 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 , the ratio of the Zeeman energy, and the anisotropy energy. For , 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 , 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 and the initial orientation.
{"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":null,"pages":null},"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}
Pub Date : 2024-07-26DOI: 10.1103/physrevfluids.9.074402
Tristan Aurégan, Sylvain Courrech du Pont, Benjamin Thiria
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.
{"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":null,"pages":null},"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}
Pub Date : 2024-07-25DOI: 10.1103/physrevfluids.9.074004
Atul S. Vivek, Ranabir Dey, Harish N. Dixit
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.
{"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":null,"pages":null},"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}
Pub Date : 2024-07-25DOI: 10.1103/physrevfluids.9.074803
Safir Haddad, Samuel Vaux, Kevin Varrall, Olivier Vauquelin
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 [J. Fluid Mech.6, 423 (1959)] for a buoyant layer of fluid in the Boussinesq approximation. For a constant drag coefficient and the specific entrainment law being the local Richardson number, we first derived a system of coupled ordinary differential equations describing the longitudinal evolution of the velocity , the height , the density deficit , and the Richardson number of the current. For an initially supercritical flow , explicit relations are found for and solely as a function of the Richardson number . The longitudinal evolution of the Richardson number is then theoretically obtained from a universal function which can be tabulated and, as in the present paper, also plotted. The function 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 (). 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
本文提出了沿有限长度水平刚性边界流向静态均匀环境的稳定湍流混杂重力流的解析解。这些解法来自 Ellison 和 Turner [J. Fluid Mech. 6, 423 (1959)]最初提出的布森斯克近似浮力层流体的控制方程（质量、动量和浮力）。对于恒定的阻力系数 Cd 和特定的夹带定律 E∝Ri-1（Ri 是当地的理查德森数），我们首先导出了一个耦合常微分方程系统，描述了水流的速度 u、高度 h、密度亏损 η 和理查德森数 Ri 的纵向演变。对于初始超临界流（Ri0<1），可以发现 u(x)、h(x) 和 η(x) 完全是理查森数 Ri(x) 的函数。理查德森数的纵向演化可以通过一个通用函数 F 从理论上得到，该函数可以制表，在本文中还可以绘制成图。通过函数 F，我们可以确定（而且只能根据对源头边界条件的了解）流动是在刚性边界的整个长度上保持超临界状态，还是可能向亚临界状态（Ri>1）过渡。在后一种情况下，通过加入一个类似于水力跃迁的不连续性来修改数学分辨率。这种不连续性的位置和振幅是通过附加的通用函数 G 和注入条件计算得出的。该方法最后扩展到为其他经典夹带定律提供解析解。
{"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":null,"pages":null},"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}
Pub Date : 2024-07-25DOI: 10.1103/physrevfluids.9.074609
Kevin Ley, Olivier Soulard, Jérôme Griffond, Antoine Briard, Serge Simoëns
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.
{"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":null,"pages":null},"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}
Pub Date : 2024-07-25DOI: 10.1103/physrevfluids.9.074608
Cat Tuong Nguyen, Martin Oberlack
We have conducted a direct numerical simulation of a turbulent round jet at a previously unattained Reynolds number of based on the jet diameter and jet-inlet bulk velocity in a particularly long box of . To achieve very fast convergence to self-similarity, we used a turbulent pipe flow at the same Reynolds number and length as the upstream inflow boundary condition. This indeed results in a very rapid emergence of self-similarity already at very small axial distances 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 in the range is shown, but also for the probability density function (PDF) of the axial velocity 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.
我们在一个 75D 的特长箱中，根据射流直径 D 和射流入口体积速度 Ub，在 Re=3500 的雷诺数条件下对湍流圆形射流进行了直接数值模拟。为了实现自相似性的快速收敛，我们使用了相同雷诺数和长度为 5D 的湍流管道流作为上游流入边界条件。与迄今为止公布的所有湍流射流数据相比，这确实导致在非常小的轴向距离 z 时就已经非常快速地出现了自相似性。在 z/D=25-65 范围内，不仅平均速度和雷诺应力以及雷诺应力张量和湍流动能的预算显示了基于归一化半径 η=r/z 的近乎完美的经典缩放，而且轴向速度 Uz 的概率密度函数（PDF）以及相关的偏度和峰度也显示了近乎完美的经典缩放。所有预算项都是直接计算得出的，因此平衡中存在边际误差。在射流轴上可以观察到轴向速度的概率密度函数几乎完全呈高斯分布，而随着与轴线距离的增加，明显出现了尾部越来越大的偏差。
{"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":null,"pages":null},"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}
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