Pub Date : 2024-08-28DOI: 10.1103/physrevfluids.9.084006
Akhil Varma
It is known that, beyond a critical speed, the straight contact line of a partially -wetting liquid destabilizes into a corner. One of the earliest theoretical works exploring this phenomenon [Limat and Stone, Europhys. Lett.65, 365 (2004)] elicited a self-similar conical structure of the interface in the viscous regime. However, noting that inertia is not expected to be negligible at contact line speeds close to and beyond the critical value for many common liquids, we provide the leading-order inertial correction to their solution. In particular, we find the self-similar corrections to the interface shape as well as the flow field, and also determine their scaling with the capillary number. We find that inertia invariably modifies the interface into a cusplike shape with an increased film thickness. Furthermore, when incorporating contact line dynamics into the model, resulting in a narrowing of the corner as the contact line speed increases, we still observe an overall increase in the inertial contribution with speed despite the increased confinement.
众所周知，当速度超过临界值时，部分润湿液体的直线接触线会不稳定地变成拐角。探索这一现象的最早理论著作之一[Limat 和 Stone，Europhys. Lett. 65, 365 (2004)]提出了粘滞状态下界面的自相似锥形结构。然而，我们注意到，对于许多常见液体来说，在接触线速度接近或超过临界值时，惯性是不可忽略的。特别是，我们找到了界面形状和流场的自相似修正，并确定了它们与毛细管数的比例关系。我们发现，随着薄膜厚度的增加，惯性无一例外地将界面修正为尖顶状。此外，当将接触线动力学纳入模型时，随着接触线速度的增加，角会变窄，尽管封闭性增加，我们仍然观察到惯性贡献随速度的总体增加而增加。
{"title":"Weak-inertial effects on destabilized receding contact lines","authors":"Akhil Varma","doi":"10.1103/physrevfluids.9.084006","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084006","url":null,"abstract":"It is known that, beyond a critical speed, the straight contact line of a partially -wetting liquid destabilizes into a corner. One of the earliest theoretical works exploring this phenomenon [Limat and Stone, <span>Europhys. Lett.</span> <b>65</b>, 365 (2004)] elicited a self-similar conical structure of the interface in the viscous regime. However, noting that inertia is not expected to be negligible at contact line speeds close to and beyond the critical value for many common liquids, we provide the leading-order inertial correction to their solution. In particular, we find the self-similar corrections to the interface shape as well as the flow field, and also determine their scaling with the capillary number. We find that inertia invariably modifies the interface into a cusplike shape with an increased film thickness. Furthermore, when incorporating contact line dynamics into the model, resulting in a narrowing of the corner as the contact line speed increases, we still observe an overall increase in the inertial contribution with speed despite the increased confinement.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210844","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 : 2024-08-28DOI: 10.1103/physrevfluids.9.083703
Yu Zhang, Kang Luo, Hongliang Yi, Anjun Liu, Jian Wu
Electroconvection (EC) turbulence is an important branch of electrohydrodynamics (EHD). Because the turbulence model for EHD has not been well studied, in this work we apply the large eddy simulation (LES) to electrohydrodynamic turbulence based on the lattice Boltzmann method (LBM). The eddy-viscosity methods (the Smagorinsky and wall-adapting local eddy-viscosity models) are used to model the momentum equation, and the charge transport equation is modeled with the help of the turbulent Schmidt number. Three EC cases are chosen to test the reliability of the LBM-LES models, including two-dimensional (2D) EC turbulence in square and rectangular cells, and three-dimensional (3D) EC turbulence between two parallel plates. For 2D cases, the LES results are compared to the results of different numerical methods, including direct numerical simulation and LES. The long-time statistics of maximum velocity, charge current and its probability distribution, and flow evolution are used to validate the 2D EC turbulence. We also analyze the flow patterns and average characteristics for 3D cases. The LES results could capture the main flow features of EC turbulence for all cases, and demonstrate a good agreement when compared with references. The mentioned LBM-LES models have demonstrated reliability and high computational speed, making them suitable for further simulations of electrohydrodynamic turbulence.
{"title":"Application of large eddy simulation models to electroconvection turbulence study with lattice Boltzmann method","authors":"Yu Zhang, Kang Luo, Hongliang Yi, Anjun Liu, Jian Wu","doi":"10.1103/physrevfluids.9.083703","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083703","url":null,"abstract":"Electroconvection (EC) turbulence is an important branch of electrohydrodynamics (EHD). Because the turbulence model for EHD has not been well studied, in this work we apply the large eddy simulation (LES) to electrohydrodynamic turbulence based on the lattice Boltzmann method (LBM). The eddy-viscosity methods (the Smagorinsky and wall-adapting local eddy-viscosity models) are used to model the momentum equation, and the charge transport equation is modeled with the help of the turbulent Schmidt number. Three EC cases are chosen to test the reliability of the LBM-LES models, including two-dimensional (2D) EC turbulence in square and rectangular cells, and three-dimensional (3D) EC turbulence between two parallel plates. For 2D cases, the LES results are compared to the results of different numerical methods, including direct numerical simulation and LES. The long-time statistics of maximum velocity, charge current and its probability distribution, and flow evolution are used to validate the 2D EC turbulence. We also analyze the flow patterns and average characteristics for 3D cases. The LES results could capture the main flow features of EC turbulence for all cases, and demonstrate a good agreement when compared with references. The mentioned LBM-LES models have demonstrated reliability and high computational speed, making them suitable for further simulations of electrohydrodynamic turbulence.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210874","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 : 2024-08-28DOI: 10.1103/physrevfluids.9.083501
Rui Yang, Thijs van den Ham, Roberto Verzicco, Detlef Lohse, Sander G. Huisman
We report on the melting dynamics of ice suspended in fresh water and subject to natural convective flows. Using direct numerical simulations we investigate the melt rate of ellipsoidal objects for , where Ra is the Rayleigh number defined with the temperature difference between the ice and the surrounding water. We reveal that the system exhibits nonmonotonic behavior in three control parameters. As a function of the aspect ratio of the ellipsoid, the melting time shows a distinct minimum that is different from a disk which has the minimum perimeter. Furthermore, also with Ra the system shows a nonmonotonic trend, since for large Ra and large aspect ratio the flow separates, leading to distinctly different dynamics. Lastly, since the density of water is nonmonotonic with temperature, the melt rate depends nonmonotonically also on the ambient temperature, as for intermediate temperatures the flow is (partially) reversed. In general, the shape which melts the slowest is quite distinct from that of a disk.
我们报告了悬浮在淡水中并受自然对流影响的冰的融化动力学。通过直接数值模拟，我们研究了椭圆形物体在 2.32×104≤Ra≤7.61×108 条件下的熔化率，其中 Ra 是用冰与周围水的温差定义的瑞利数。我们发现，该系统在三个控制参数中表现出非单调行为。作为椭圆体长宽比的函数，熔化时间显示出明显的最小值，这与具有最小周长的圆盘不同。此外，随着 Ra 的增大，系统也呈现出非单调趋势，因为在 Ra 大和长宽比大的情况下，水流会分离，从而导致截然不同的动力学。最后，由于水的密度随温度的变化是非单调的，因此熔化率也非单调地取决于环境温度，因为在中间温度（4∘C - 7∘C）下，流动（部分）是反向的。一般来说，熔化速度最慢的形状与圆盘形状截然不同。
{"title":"Circular objects do not melt the slowest in water","authors":"Rui Yang, Thijs van den Ham, Roberto Verzicco, Detlef Lohse, Sander G. Huisman","doi":"10.1103/physrevfluids.9.083501","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083501","url":null,"abstract":"We report on the melting dynamics of ice suspended in fresh water and subject to natural convective flows. Using direct numerical simulations we investigate the melt rate of ellipsoidal objects for <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>2.32</mn><mo>×</mo><msup><mn>10</mn><mn>4</mn></msup><mo>≤</mo><mtext>Ra</mtext><mo>≤</mo><mn>7.61</mn><mo>×</mo><msup><mn>10</mn><mn>8</mn></msup></mrow></math>, where Ra is the Rayleigh number defined with the temperature difference between the ice and the surrounding water. We reveal that the system exhibits nonmonotonic behavior in three control parameters. As a function of the aspect ratio of the ellipsoid, the melting time shows a distinct minimum that is different from a disk which has the minimum perimeter. Furthermore, also with Ra the system shows a nonmonotonic trend, since for large Ra and large aspect ratio the flow separates, leading to distinctly different dynamics. Lastly, since the density of water is nonmonotonic with temperature, the melt rate depends nonmonotonically also on the ambient temperature, as for intermediate temperatures <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mo>(</mo><mn>4</mn><msup><mspace width=\"0.16em\"></mspace><mo>∘</mo></msup><mi mathvariant=\"normal\">C</mi><mo> </mo><mo>–</mo><mo> </mo><mn>7</mn><msup><mspace width=\"0.16em\"></mspace><mo>∘</mo></msup><mi mathvariant=\"normal\">C</mi><mo>)</mo></mrow></math> the flow is (partially) reversed. In general, the shape which melts the slowest is quite distinct from that of a disk.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210848","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 : 2024-08-27DOI: 10.1103/physrevfluids.9.083102
Nora Caroline Wild, Kartik V. Bulusu, Michael W. Plesniak
Carotid artery atherosclerosis is a significant contributor to mortality in the United States. While it is recognized that low wall-shear stresses trigger plaque formation, there is a limited comprehension of the internal vortical structures that impact these stresses and how they differ between a healthy and a disease-prone, high-risk patient cohort. Our objective is to determine which driving factors, such as anatomical features (artery geometry) and mass-flow split, govern vortex behavior. Physiological pulsatile flow computational fluid dynamics simulations were performed on a “healthy” and a “disease-prone” carotid artery bifurcation model. Geometry and flow effects are investigated separately by simulating a third hybrid model having a healthy geometry with outlet boundary conditions imposing disease-prone flow conditions. This “unhealthy ” model recreated disease-prone mass-flow split and internal carotid artery sinus axial pressure gradient conditions in a healthy carotid artery bifurcation geometry. The results of our study revealed that the main vortex's time of formation is primarily dictated by carotid artery bifurcation geometry, whereas its lifespan is determined by the flow conditions. The main vortex's spatial expansion, as well as its circulation decay rate, are dictated by the geometry, not the flow conditions. We conclude that a high internal carotid artery mass flow rate and a higher favorable pressure gradient maximum magnitude occurring near peak systole are strong indicators of a high predisposition towards atherogenesis.
{"title":"Vortex dynamics in healthy and pro-atherogenic carotid artery bifurcation models","authors":"Nora Caroline Wild, Kartik V. Bulusu, Michael W. Plesniak","doi":"10.1103/physrevfluids.9.083102","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083102","url":null,"abstract":"Carotid artery atherosclerosis is a significant contributor to mortality in the United States. While it is recognized that low wall-shear stresses trigger plaque formation, there is a limited comprehension of the internal vortical structures that impact these stresses and how they differ between a healthy and a disease-prone, high-risk patient cohort. Our objective is to determine which driving factors, such as anatomical features (artery geometry) and mass-flow split, govern vortex behavior. Physiological pulsatile flow computational fluid dynamics simulations were performed on a “healthy” and a “disease-prone” carotid artery bifurcation model. Geometry and flow effects are investigated separately by simulating a third hybrid model having a healthy geometry with outlet boundary conditions imposing disease-prone flow conditions. This “unhealthy <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi mathvariant=\"normal\">Δ</mi><mi mathvariant=\"normal\">P</mi></mrow></math>” model recreated disease-prone mass-flow split and internal carotid artery sinus axial pressure gradient conditions in a healthy carotid artery bifurcation geometry. The results of our study revealed that the main vortex's time of formation is primarily dictated by carotid artery bifurcation geometry, whereas its lifespan is determined by the flow conditions. The main vortex's spatial expansion, as well as its circulation decay rate, are dictated by the geometry, not the flow conditions. We conclude that a high internal carotid artery mass flow rate and a higher favorable pressure gradient maximum magnitude occurring near peak systole are strong indicators of a high predisposition towards atherogenesis.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227806","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 : 2024-08-26DOI: 10.1103/physrevfluids.9.084609
Soju Maejima, Kazuki Tanino, Soshi Kawai
This study proposes a physics-informed machine learning to enable using the erroneous flow data at near-wall grid points as the input to the wall model in a wall-modeled large-eddy simulation (LES). The proposed neural network predicts the amount of numerical error in the near-wall grid-point data and inputs the physically correct flow variables into the wall model by correcting the near-wall error. The input and output features of the neural networks are selected based on the physical relations of the turbulent boundary layer for robustness against various Reynolds and Mach number conditions. The proposed neural networks allow the wall model to accurately predict the wall shear stress from the erroneous near-wall information and yields accurate predictions of the turbulence statistics. Additionally, the proposed physics-informed machine-learning approach reproduces the asymmetry in the probability density functions of the predicted wall shear stress observed in direct numerical simulations, while the conventional wall model with input away from the wall does not. The results suggest that using the near-wall information for wall modeling may increase the fidelity of the wall-modeled LES.
本研究提出了一种物理信息机器学习方法，可将近壁网格点的错误流量数据作为壁模型大涡流模拟（LES）中壁模型的输入。所提出的神经网络可预测近壁网格点数据的数值误差量，并通过修正近壁误差将物理上正确的流动变量输入壁模型。神经网络的输入和输出特性是根据湍流边界层的物理关系选择的，以确保在各种雷诺数和马赫数条件下的鲁棒性。所提出的神经网络允许壁面模型从错误的近壁信息中准确预测壁面切应力，并产生准确的湍流统计预测。此外，所提出的物理信息机器学习方法再现了直接数值模拟中观察到的壁面剪应力预测概率密度函数的不对称性，而使用远离壁面输入的传统壁面模型则没有这种不对称性。结果表明，使用近壁信息进行壁面建模可提高壁面建模 LES 的保真度。
{"title":"Physics-informed machine-learning solution to log-layer mismatch in wall-modeled large-eddy simulation","authors":"Soju Maejima, Kazuki Tanino, Soshi Kawai","doi":"10.1103/physrevfluids.9.084609","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084609","url":null,"abstract":"This study proposes a physics-informed machine learning to enable using the erroneous flow data at near-wall grid points as the input to the wall model in a wall-modeled large-eddy simulation (LES). The proposed neural network predicts the amount of numerical error in the near-wall grid-point data and inputs the physically correct flow variables into the wall model by correcting the near-wall error. The input and output features of the neural networks are selected based on the physical relations of the turbulent boundary layer for robustness against various Reynolds and Mach number conditions. The proposed neural networks allow the wall model to accurately predict the wall shear stress from the erroneous near-wall information and yields accurate predictions of the turbulence statistics. Additionally, the proposed physics-informed machine-learning approach reproduces the asymmetry in the probability density functions of the predicted wall shear stress observed in direct numerical simulations, while the conventional wall model with input away from the wall does not. The results suggest that using the near-wall information for wall modeling may increase the fidelity of the wall-modeled LES.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210849","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 : 2024-08-26DOI: 10.1103/physrevfluids.9.084610
Wei Zhao
Momentum-scalar coupling turbulence, a phenomenon observed in both natural and engineering contexts, involves the intricate interaction between multicomponent scalars and multiscale forces (i.e., multiple coupling mechanisms), resulting in a wide array of manifestations. Despite its importance, limited research has been conducted to comprehend the influence of these multicomponent and multiple coupling mechanisms on turbulence cascades. Hence, this study aims to provide a preliminary and theoretical exploration into how these multiple coupling mechanisms govern the cascades of turbulent kinetic energy and multicomponent scalars. To simplify the mathematical analysis, homogeneous and isotropic hypotheses of flow field have been applied. The key findings of this study can be summarized as follows. The first is validation of quad-cascade processes. The second is an examination of various cases involving single scalar components but multiple coupling mechanisms. Of particular interest is the coexistence of buoyancy-driven turbulence and electrokinetic turbulence, which introduces a new variable flux (VF) subrange resulting from their nonlinear interaction. Another extension considers an exponential modulation function, equivalent to the coexistence of multiple coupling mechanisms acting on a single scalar. The study identifies two new VF subranges. Third, binary scalar components and coupling mechanisms are investigated, indicating coupling mechanisms with significantly different strengths that can also induce complex interactions and new VF subranges. Fourth is the complexity when three or more different scalar components and coupling mechanisms coexist simultaneously: with the exception of certain special cases, closure of the problem becomes unattainable. This highlights the challenges inherent in addressing the simultaneous presence of multiple scalar components and coupling mechanisms. This research endeavor illuminates the theoretical understanding of the diverse scaling properties observed in momentum-scalar coupling turbulence across different scenarios.
{"title":"Cascades of turbulent kinetic energy and multicomponent scalars in a momentum-scalar coupling turbulence driven by multiple mechanisms under homogeneous and isotropic hypotheses","authors":"Wei Zhao","doi":"10.1103/physrevfluids.9.084610","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084610","url":null,"abstract":"Momentum-scalar coupling turbulence, a phenomenon observed in both natural and engineering contexts, involves the intricate interaction between multicomponent scalars and multiscale forces (i.e., multiple coupling mechanisms), resulting in a wide array of manifestations. Despite its importance, limited research has been conducted to comprehend the influence of these multicomponent and multiple coupling mechanisms on turbulence cascades. Hence, this study aims to provide a preliminary and theoretical exploration into how these multiple coupling mechanisms govern the cascades of turbulent kinetic energy and multicomponent scalars. To simplify the mathematical analysis, homogeneous and isotropic hypotheses of flow field have been applied. The key findings of this study can be summarized as follows. The first is validation of quad-cascade processes. The second is an examination of various cases involving single scalar components but multiple coupling mechanisms. Of particular interest is the coexistence of buoyancy-driven turbulence and electrokinetic turbulence, which introduces a new variable flux (VF) subrange resulting from their nonlinear interaction. Another extension considers an exponential modulation function, equivalent to the coexistence of multiple coupling mechanisms acting on a single scalar. The study identifies two new VF subranges. Third, binary scalar components and coupling mechanisms are investigated, indicating coupling mechanisms with significantly different strengths that can also induce complex interactions and new VF subranges. Fourth is the complexity when three or more different scalar components and coupling mechanisms coexist simultaneously: with the exception of certain special cases, closure of the problem becomes unattainable. This highlights the challenges inherent in addressing the simultaneous presence of multiple scalar components and coupling mechanisms. This research endeavor illuminates the theoretical understanding of the diverse scaling properties observed in momentum-scalar coupling turbulence across different scenarios.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227807","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 : 2024-08-26DOI: 10.1103/physrevfluids.9.083905
J. Mak, N. Harnik, E. Heifetz, G. Kumar, E. Q. Y. Ong
One mechanistic interpretation of baroclinic instability is that of mutual constructive interference of Rossby edge waves. The suppression of baroclinic instability over slopes has been widely established, where previous research argues that a sloping boundary modifies the properties of these Rossby edge waves, but does not provide a mechanistic explanation for the suppression that is valid over all parameter space. In the context of an Eady problem modified by the presence of a sloping boundary, we provide a mechanistic rationalization for baroclinic instability in the presence of slopes that is valid over all parameter space, via an equivalent formulation explicitly in terms of Rossby edge waves. We also highlight the differences between edge-wave phase shifts and normal-mode phase tilts, showing that the edge-wave phase shifts should be the ones that are mechanistically relevant, and normal-mode phase tilt is a potentially misleading quantity to use. Further, we present evidence that the edge-wave phase shifts but not normal-mode phase tilts are well correlated with geometric quantities diagnosed from an analysis framework based on eddy variance ellipses. The result is noteworthy in that the geometric framework makes no explicit reference to the edge-wave structures in its construction, and the correlation suggests the geometric framework can be used in problems where edge-wave structures are not so well defined or readily available. Some implications for parametrization of baroclinic instability and relevant eddy-mean feedbacks are discussed. For completeness, we also provide an explicit demonstration that the linear instability problem of the present modified Eady problem is parity-time symmetric, and speculate about some suggestive links between parity-time symmetry, shear instability, and the edge-wave interaction mechanism.
{"title":"Edge-wave phase shifts versus normal-mode phase tilts in an Eady problem with a sloping boundary","authors":"J. Mak, N. Harnik, E. Heifetz, G. Kumar, E. Q. Y. Ong","doi":"10.1103/physrevfluids.9.083905","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083905","url":null,"abstract":"One mechanistic interpretation of baroclinic instability is that of mutual constructive interference of Rossby edge waves. The suppression of baroclinic instability over slopes has been widely established, where previous research argues that a sloping boundary modifies the properties of these Rossby edge waves, but does not provide a mechanistic explanation for the suppression that is valid over all parameter space. In the context of an Eady problem modified by the presence of a sloping boundary, we provide a mechanistic rationalization for baroclinic instability in the presence of slopes that is valid over all parameter space, via an equivalent formulation explicitly in terms of Rossby edge waves. We also highlight the differences between edge-wave phase shifts and normal-mode phase tilts, showing that the edge-wave phase shifts should be the ones that are mechanistically relevant, and normal-mode phase tilt is a potentially misleading quantity to use. Further, we present evidence that the edge-wave phase shifts but not normal-mode phase tilts are well correlated with geometric quantities diagnosed from an analysis framework based on eddy variance ellipses. The result is noteworthy in that the geometric framework makes no explicit reference to the edge-wave structures in its construction, and the correlation suggests the geometric framework can be used in problems where edge-wave structures are not so well defined or readily available. Some implications for parametrization of baroclinic instability and relevant eddy-mean feedbacks are discussed. For completeness, we also provide an explicit demonstration that the linear instability problem of the present modified Eady problem is parity-time symmetric, and speculate about some suggestive links between parity-time symmetry, shear instability, and the edge-wave interaction mechanism.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210845","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}
Impulsively generated focused jets play a significant role in various applications, including inkjet printing, needle-free drug delivery, and microfluidic devices. As the demand for generating jets and droplets from medium to highly viscous liquids increases, understanding the role of viscosity in jetting dynamics becomes crucial. While previous studies have examined the viscous effects on walls, the impact on free surfaces has not been thoroughly understood. This study aims to bridge this gap by integrating experiments with numerical simulations to investigate the viscous effects on focused jet formation. We demonstrate that mass and momentum transfer along the tangential direction of the free surface contribute to focused jet formation, and viscosity plays a key role in this transfer process. The viscosity-induced diffusion of the shear flow and vorticity near the free surface reduces the jet speed. Based on experimental observations and simulation results, we propose an equation to predict the viscous jet velocity. These findings offer new perspectives on viscous interface dynamics in advanced manufacturing and biomedical applications.
{"title":"Viscous influences on impulsively generated focused jets","authors":"Xianggang Cheng, Xiao-Peng Chen, Hang Ding, Chun-Yu Zhang, Haibao Hu, Laibing Jia","doi":"10.1103/physrevfluids.9.l082001","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.l082001","url":null,"abstract":"Impulsively generated focused jets play a significant role in various applications, including inkjet printing, needle-free drug delivery, and microfluidic devices. As the demand for generating jets and droplets from medium to highly viscous liquids increases, understanding the role of viscosity in jetting dynamics becomes crucial. While previous studies have examined the viscous effects on walls, the impact on free surfaces has not been thoroughly understood. This study aims to bridge this gap by integrating experiments with numerical simulations to investigate the viscous effects on focused jet formation. We demonstrate that mass and momentum transfer along the tangential direction of the free surface contribute to focused jet formation, and viscosity plays a key role in this transfer process. The viscosity-induced diffusion of the shear flow and vorticity near the free surface reduces the jet speed. Based on experimental observations and simulation results, we propose an equation to predict the viscous jet velocity. These findings offer new perspectives on viscous interface dynamics in advanced manufacturing and biomedical applications.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210876","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 : 2024-08-22DOI: 10.1103/physrevfluids.9.083606
P. Pico, L. Kahouadji, S. Shin, J. Chergui, D. Juric, O. K. Matar
We present a numerical study of the main substages preceding aerosol formation via bursting bubbles: capillary wave propagation along the bubble, convergence at the bubble's apex, and the ascent of a Worthington jet and its breakup to release liquid drops. We focus on two crucial yet overlooked aspects of the system: the presence of surface-active agents and dynamics driven by non-negligible gravitational effects, quantified by the Bond number. Our results propose a mechanism explaining capillary wave retardation in the presence of surfactants, involving the transition from bi- to unidirectional Marangoni stresses, which pull the interface upwards, countering the motion of the waves. We also quantitatively elucidate the variable nature of the waves' velocity with various surfactant parameters, including surfactant solubility and elasticity, a departure from the constant behavior well documented in clean interfaces.
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This study presents a methodology focusing on the use of computational model and experimental data fusion to improve the Spalart-Allmaras (SA) closure model for Reynolds-averaged Navier-Stokes solutions. In particular, our goal is to develop a technique that not only assimilates sparse experimental data to improve turbulence model performance, but also preserves generalization for unseen cases by recovering classical SA behavior. We achieve our goals using data assimilation, namely the ensemble Kalman filtering approach, to calibrate the coefficients of the SA model for separated flows. A holistic calibration strategy is implemented via the parametrization of the production, diffusion, and destruction terms. This calibration relies on the assimilation of experimental data collected in the form of velocity profiles, skin friction, and pressure coefficients. Despite using observational data from a single flow condition around a backward-facing step (BFS), the recalibrated SA model demonstrates generalization to other separated flows, including cases such as the two-dimensional (2D) NASA wall mounted hump and the modified BFS. Significant improvement is observed in the quantities of interest, i.e., the skin friction coefficient and the pressure coefficient , for each flow tested. Finally, it is also demonstrated that the newly proposed model recovers SA proficiency for flows, such as a NACA-0012 airfoil and axisymmetric jet, and that the individually calibrated terms in the SA model target specific flow-physics wherein the calibrated production term improves the recirculation zone while destruction improves the recovery zone.
本研究提出了一种方法，重点是利用计算模型和实验数据融合来改进雷诺平均纳维-斯托克斯解的斯帕拉特-阿勒马拉斯（SA）闭合模型。特别是，我们的目标是开发一种技术，它不仅能同化稀疏的实验数据以提高湍流模型的性能，还能通过恢复经典的 SA 行为来保留未见案例的通用性。我们利用数据同化（即集合卡尔曼滤波方法）来校准分离流的 SA 模型系数，从而实现我们的目标。通过对生产、扩散和破坏项进行参数化，实施了整体校准策略。这种校准依赖于以速度剖面、表皮摩擦和压力系数形式收集的实验数据的同化。尽管使用的是后向阶梯（BFS）周围单一流动条件的观测数据，但重新校准的 SA 模型显示出对其他分离流动的普适性，包括二维（2D）NASA 壁装驼峰和改进的 BFS 等情况。在所测试的每种流体中，都能观察到相关量（即表皮摩擦系数 (Cf) 和压力系数 (Cp)）的显著改善。最后，还证明了新提出的模型能够熟练地恢复 NACA-0012 机翼和轴对称射流等流动的 SA，而且 SA 模型中的单独校准项针对的是特定的流动物理，其中校准的生产项改善了再循环区，而破坏项改善了恢复区。
{"title":"Robust experimental data assimilation for the Spalart-Allmaras turbulence model","authors":"Deepinder Jot Singh Aulakh, Xiang Yang, Romit Maulik","doi":"10.1103/physrevfluids.9.084608","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084608","url":null,"abstract":"This study presents a methodology focusing on the use of computational model and experimental data fusion to improve the Spalart-Allmaras (SA) closure model for Reynolds-averaged Navier-Stokes solutions. In particular, our goal is to develop a technique that not only assimilates sparse experimental data to improve turbulence model performance, but also preserves generalization for unseen cases by recovering classical SA behavior. We achieve our goals using data assimilation, namely the ensemble Kalman filtering approach, to calibrate the coefficients of the SA model for separated flows. A holistic calibration strategy is implemented via the parametrization of the production, diffusion, and destruction terms. This calibration relies on the assimilation of experimental data collected in the form of velocity profiles, skin friction, and pressure coefficients. Despite using observational data from a single flow condition around a backward-facing step (BFS), the recalibrated SA model demonstrates generalization to other separated flows, including cases such as the two-dimensional (2D) NASA wall mounted hump and the modified BFS. Significant improvement is observed in the quantities of interest, i.e., the skin friction coefficient <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mo>(</mo><msub><mi>C</mi><mi>f</mi></msub><mo>)</mo></math> and the pressure coefficient <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mo>(</mo><msub><mi>C</mi><mi>p</mi></msub><mo>)</mo></math>, for each flow tested. Finally, it is also demonstrated that the newly proposed model recovers SA proficiency for flows, such as a NACA-0012 airfoil and axisymmetric jet, and that the individually calibrated terms in the SA model target specific flow-physics wherein the calibrated production term improves the recirculation zone while destruction improves the recovery zone.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210852","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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