Energetic protons trapped in the radiation belt, as a vital component of the ring current system, are observationally and theoretically modulated by geomagnetic disturbances. Utilizing Van Allen Probe observations, we statistically analyzed their temporal variations at 55–489 keV as well as their pitch angle distributions (PADs) index n (fitted by sinn∂, where ∂ is the pitch angle) in response to geomagnetic storms. It shows that protons at low energies are more easily accelerated during storms. The threshold of accelerations becomes greater for high-energy protons, while a large value of n can persist for a few days to months. Further investigations suggest that one-quarter of the storms increase the proton flux at all energy channels (55–489 keV) both inside and outside the plasmapause location (Lpp). Specifically, more than half of the storms enhance the flux for protons at Ek > 400 keV inside and close to the Lpp as well as protons at Ek < 100 keV deep inside the Lpp. Comparably, protons at larger pitch angles (near 90°) are more easily lost outside the Lpp, which results in more pronounced pancake PADs with larger n. The index n preferentially decreases at L > 5 during 75% of the storms on the dayside, while it decreases at L = ∼4 during 50% of the storms on the nightside, showing significant day–night asymmetry. Further detailed investigations revealed that source and loss processes, including radial diffusion, magnetopause shadowing, and wave–particle interactions, account for the statistical results. The present study provides quantitative information on the overall characteristics of energetic proton fluxes, which can enhance the comprehension of the radiation belts.
作为环流系统的重要组成部分，被困在辐射带中的高能质子在观测和理论上都会受到地磁扰动的影响。利用范艾伦探测器的观测数据，我们统计分析了它们在 55-489 千伏的时间变化以及它们的俯仰角分布（PADs）指数 n（用 sinn∂ 拟合，其中 ∂ 是俯仰角）对地磁暴的响应。它表明，在风暴期间，低能量的质子更容易被加速。高能量质子的加速阈值变得更大，而较大的 n 值可以持续几天到几个月。进一步的研究表明，四分之一的风暴会增加质点位置（Lpp）内外所有能量通道（55-489 keV）的质子通量。具体地说，超过一半的风暴会提高质点位置内部和附近 Ek > 400 千伏的质子通量，以及质点位置深处 Ek < 100 千伏的质子通量。在75%的日侧风暴中，指数n在L > 5时优先减小，而在50%的夜侧风暴中，指数n在L = ∼ 4时减小，表现出明显的昼夜不对称。进一步的详细研究表明，包括径向扩散、磁极阴影和波粒相互作用在内的源和损耗过程是造成统计结果的原因。本研究提供了关于高能质子通量总体特征的定量信息，有助于加深对辐射带的理解。
{"title":"Variability of energetic proton flux and pitch angle distributions in the Earth's radiation belt modulated by geomagnetic storms","authors":"Zhengyang Zou, Wentao Zhou, Jiahui Hu","doi":"10.1063/5.0223947","DOIUrl":"https://doi.org/10.1063/5.0223947","url":null,"abstract":"Energetic protons trapped in the radiation belt, as a vital component of the ring current system, are observationally and theoretically modulated by geomagnetic disturbances. Utilizing Van Allen Probe observations, we statistically analyzed their temporal variations at 55–489 keV as well as their pitch angle distributions (PADs) index n (fitted by sinn∂, where ∂ is the pitch angle) in response to geomagnetic storms. It shows that protons at low energies are more easily accelerated during storms. The threshold of accelerations becomes greater for high-energy protons, while a large value of n can persist for a few days to months. Further investigations suggest that one-quarter of the storms increase the proton flux at all energy channels (55–489 keV) both inside and outside the plasmapause location (Lpp). Specifically, more than half of the storms enhance the flux for protons at Ek &gt; 400 keV inside and close to the Lpp as well as protons at Ek &lt; 100 keV deep inside the Lpp. Comparably, protons at larger pitch angles (near 90°) are more easily lost outside the Lpp, which results in more pronounced pancake PADs with larger n. The index n preferentially decreases at L &gt; 5 during 75% of the storms on the dayside, while it decreases at L = ∼4 during 50% of the storms on the nightside, showing significant day–night asymmetry. Further detailed investigations revealed that source and loss processes, including radial diffusion, magnetopause shadowing, and wave–particle interactions, account for the statistical results. The present study provides quantitative information on the overall characteristics of energetic proton fluxes, which can enhance the comprehension of the radiation belts.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940617","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study investigates the modulating effect of the pycnocline thickness in two-dimensional stratified flow on a cylinder. It encompasses three typical flow regimes identified by Boyer in experiments conducted within the Reynolds number range of Re = 260–2000. Quantitative control of the modulation effect of internal interface waves on the cylinder wake is achieved by varying the thickness of the pycnocline. Under appropriate thickness of the pycnocline, a multiple-centerline-structure can transition to isolated-mixed-structure flow regimes and Double-Eddy-Wavy-Wake flow regimes. Similar modulation patterns are also observed in isolated-mixed flow regimes. Normalized pressure distribution and velocity fields indicate that in low Reynolds number flow regimes (Re < 600), downstream isolated mixed regions generate dynamic pressure that periodically cascades upstream. This periodic reverse energy transfer provides favorable adverse pressure gradients, cyclically reducing the drag force on the cylinder. The cyclic period is, for the first time, classified into four stages: dynamic pressure storage stage, dynamic pressure transfer stage, dynamic pressure consumption stage, and dynamic pressure exhaustion stage. Despite the highly nonlinear modulation effect of internal interface waves in low Reynolds number conditions, the linear predictive theory of lee waves based on streamline equations remains instructive in predicting the trend of lee waves wavelength variation with pycnocline thickness. Drawing upon the modulation study results concerning the pycnocline thickness on lee waves, a regime map is constructed, illustrating the directional evolution of lee waves flow patterns based on variations in pycnocline thickness.
本研究探讨了在圆柱体上的二维分层流中，pycnocline 厚度的调节作用。它包括 Boyer 在 Re = 260-2000 雷诺数范围内进行的实验中确定的三种典型流动状态。通过改变pycnocline的厚度，可以定量控制内界面波对圆柱体尾流的调制效应。在适当的pycnocline厚度下，多中心线结构可过渡到孤立-混合结构流态和双-Eddy-Wave-Wake流态。在孤立混合流态中也观察到类似的调制模式。归一化压力分布和速度场表明，在低雷诺数流态（Re < 600）中，下游孤立混合区产生的动态压力会周期性地向上游串联。这种周期性的反向能量传递提供了有利的逆向压力梯度，周期性地降低了气缸上的阻力。循环周期首次被划分为四个阶段：动压储存阶段、动压传递阶段、动压消耗阶段和动压耗尽阶段。尽管内界面波在低雷诺数条件下具有高度非线性的调制效应，但基于流线方程的利波线性预测理论对预测利波波长随pycnocline厚度的变化趋势仍具有指导意义。借鉴有关跃层厚度对利波的调制研究结果，构建了一个波形图，说明了基于跃层厚度变化的利波流动模式的方向性演变。
{"title":"Modulation of the wake of a horizontal cylinder by pycnocline thickness in stratified flow","authors":"Min-min Zheng, Ya-dong Liu, Wei-huang Liu, Yu-ying Tang, You-jiang Wang, Yan-ping He","doi":"10.1063/5.0217927","DOIUrl":"https://doi.org/10.1063/5.0217927","url":null,"abstract":"This study investigates the modulating effect of the pycnocline thickness in two-dimensional stratified flow on a cylinder. It encompasses three typical flow regimes identified by Boyer in experiments conducted within the Reynolds number range of Re = 260–2000. Quantitative control of the modulation effect of internal interface waves on the cylinder wake is achieved by varying the thickness of the pycnocline. Under appropriate thickness of the pycnocline, a multiple-centerline-structure can transition to isolated-mixed-structure flow regimes and Double-Eddy-Wavy-Wake flow regimes. Similar modulation patterns are also observed in isolated-mixed flow regimes. Normalized pressure distribution and velocity fields indicate that in low Reynolds number flow regimes (Re &lt; 600), downstream isolated mixed regions generate dynamic pressure that periodically cascades upstream. This periodic reverse energy transfer provides favorable adverse pressure gradients, cyclically reducing the drag force on the cylinder. The cyclic period is, for the first time, classified into four stages: dynamic pressure storage stage, dynamic pressure transfer stage, dynamic pressure consumption stage, and dynamic pressure exhaustion stage. Despite the highly nonlinear modulation effect of internal interface waves in low Reynolds number conditions, the linear predictive theory of lee waves based on streamline equations remains instructive in predicting the trend of lee waves wavelength variation with pycnocline thickness. Drawing upon the modulation study results concerning the pycnocline thickness on lee waves, a regime map is constructed, illustrating the directional evolution of lee waves flow patterns based on variations in pycnocline thickness.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940621","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hemodynamic parameters can provide surveillance for the risk of complication of abdominal aortic aneurysms following endovascular aneurysm repair (EVAR). However, obtaining hemodynamic parameters through computational fluid dynamics (CFD) has disadvantages of complex operation and high computational costs. Recently proposed physics-informed neural networks offer novel solutions to solve these issues by leveraging fundamental physical conservation principles of fluid dynamics. Based on cardiovascular point datasets, we further propose an integration algorithm combining physics-informed PointNet and quadratic residual networks (PIPN-QN) that is capable of mapping sparse point clouds to four-dimensional hemodynamic parameters. The implemented workflow includes generating point cloud datasets through CFD simulation and dynamically reproducing the three-dimensional flow field in the spatial and temporal dimensions through deep learning. Compared with physics-informed PointNet (PIPN), the PIPN-QN reduces the mean square error of pressure and wall shear stress by around 32.1% and 33.1% and anticipates hemodynamic parameters in less than 2 s (14 400 times faster than CFD). To address the challenge of big data requirements, we quantify the universal flow field using a reduced number of supervision points, as opposed to the large number of point clouds generated from the CFD simulation. The PIPN-QN can meet the real-time hemodynamic parameters obtained from patients with abdominal aortic aneurysms following EVAR with higher accuracy, faster speed, and lower training costs.
{"title":"Four-dimensional hemodynamic prediction of abdominal aortic aneurysms following endovascular aneurysm repair combining physics-informed PointNet and quadratic residual networks","authors":"Jiaheng Kang, Gaoyang Li, Yue Che, Xiran Cao, Mingyu Wan, Jing Zhu, Mingyao Luo, Xuelan Zhang","doi":"10.1063/5.0220173","DOIUrl":"https://doi.org/10.1063/5.0220173","url":null,"abstract":"Hemodynamic parameters can provide surveillance for the risk of complication of abdominal aortic aneurysms following endovascular aneurysm repair (EVAR). However, obtaining hemodynamic parameters through computational fluid dynamics (CFD) has disadvantages of complex operation and high computational costs. Recently proposed physics-informed neural networks offer novel solutions to solve these issues by leveraging fundamental physical conservation principles of fluid dynamics. Based on cardiovascular point datasets, we further propose an integration algorithm combining physics-informed PointNet and quadratic residual networks (PIPN-QN) that is capable of mapping sparse point clouds to four-dimensional hemodynamic parameters. The implemented workflow includes generating point cloud datasets through CFD simulation and dynamically reproducing the three-dimensional flow field in the spatial and temporal dimensions through deep learning. Compared with physics-informed PointNet (PIPN), the PIPN-QN reduces the mean square error of pressure and wall shear stress by around 32.1% and 33.1% and anticipates hemodynamic parameters in less than 2 s (14 400 times faster than CFD). To address the challenge of big data requirements, we quantify the universal flow field using a reduced number of supervision points, as opposed to the large number of point clouds generated from the CFD simulation. The PIPN-QN can meet the real-time hemodynamic parameters obtained from patients with abdominal aortic aneurysms following EVAR with higher accuracy, faster speed, and lower training costs.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We investigate the effect of liquid elasticity on the transient cavitation bubbles confined in a tube both experimentally and theoretically. In experiments, the tube-arrest apparatus is used to generate cavitation bubbles near the tube bottom with various polyethylene oxide solutions. Our experiments show that bubble dynamics, particularly the maximum bubble length, are significantly influenced by liquid elasticity. We establish a double oscillator model for the liquid column to explain the experimental results and predict the bubble dynamics over a broader range. Finally, we propose that the reciprocal of the cavitation number Ca2 and prR/k determine the regimes of the liquid column separation, where pr is the reference pressure, R is tube radius, and k is the “stiffness coefficient” of the liquid column. Our work provides a quantitative scaling of the dynamics of large cylindrical cavitation bubbles in viscoelastic liquids during the transient process.
{"title":"Effect of liquid elasticity on transient cavitation bubbles in the tube","authors":"Zhichao Wang, Peng Xu, Zhigang Zuo, Shuhong Liu","doi":"10.1063/5.0223705","DOIUrl":"https://doi.org/10.1063/5.0223705","url":null,"abstract":"We investigate the effect of liquid elasticity on the transient cavitation bubbles confined in a tube both experimentally and theoretically. In experiments, the tube-arrest apparatus is used to generate cavitation bubbles near the tube bottom with various polyethylene oxide solutions. Our experiments show that bubble dynamics, particularly the maximum bubble length, are significantly influenced by liquid elasticity. We establish a double oscillator model for the liquid column to explain the experimental results and predict the bubble dynamics over a broader range. Finally, we propose that the reciprocal of the cavitation number Ca2 and prR/k determine the regimes of the liquid column separation, where pr is the reference pressure, R is tube radius, and k is the “stiffness coefficient” of the liquid column. Our work provides a quantitative scaling of the dynamics of large cylindrical cavitation bubbles in viscoelastic liquids during the transient process.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
From Phan-Thien and Giacomin [“Growth-adjusted impact factor,” Phys. Fluids 36, 050402 (2024)], we learn that journal growth decreases impact factor (all else being held equal). In this Editorial, we apply the teachings of Phan-Thien and Giacomin [“Growth-adjusted impact factor,” Phys. Fluids 36, 050402 (2024)] to growth-adjust the impact factors of the journal Physics of Fluids. We do so for the years for which the data are available, 2001–2023. We find that, over the course of its history, the growth of Physics of Fluids often suppressed its impact factor.
{"title":"The growth-adjusted impact factors of Physics of Fluids","authors":"M. Zatloukal, A. J. Giacomin, N. Phan-Thien","doi":"10.1063/5.0224881","DOIUrl":"https://doi.org/10.1063/5.0224881","url":null,"abstract":"From Phan-Thien and Giacomin [“Growth-adjusted impact factor,” Phys. Fluids 36, 050402 (2024)], we learn that journal growth decreases impact factor (all else being held equal). In this Editorial, we apply the teachings of Phan-Thien and Giacomin [“Growth-adjusted impact factor,” Phys. Fluids 36, 050402 (2024)] to growth-adjust the impact factors of the journal Physics of Fluids. We do so for the years for which the data are available, 2001–2023. We find that, over the course of its history, the growth of Physics of Fluids often suppressed its impact factor.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940629","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Abdelsayed, J. Hasslberger, M. Ertl, B. Weigand, M. Klein
While direct numerical simulation (DNS) of multiphase flows has been the focus of many research investigations in recent years, large eddy simulation (LES) of multiphase flows remains a challenge. There is no standardized set of governing equations for multiphase LES. Different approaches and formulations have been discussed in the literature, each with its own advantages and disadvantages. In this paper, the conventional (non-weighted) filtering approach is compared with the density-weighted Favre filtering method by evaluating the subgrid scale (SGS) energy transfer for a simple test case of a shear-thinning droplet in air. The findings reveal that, unlike the Favre filtering approach, the conventional filtering method results in a notable amount of nonphysical backward scatter in the flow. Based on these results, the Favre filtering method appears preferable and is applied to the a priori analysis of shear-thinning liquid jets, where the viscosity has been modeled using the Carreau–Yasuda model. First, by explicitly filtering existing DNS data of shear-thinning jet breakup into stagnant air, the order of magnitude of different SGS terms is evaluated using the Favre filtering method. Consistent with earlier studies on Newtonian jets, the present study indicates that the diffusive term remains negligible, while the convective term plays a dominant role. Functional and structural models for the closure of the convective SGS term are assessed by means of a correlation analysis and an order of magnitude study. Existing structural models provide good results for both Newtonian and shear-thinning cases. Promising a posteriori model candidates are discussed.
多相流的直接数值模拟（DNS）是近年来许多研究调查的重点，但多相流的大涡度模拟（LES）仍然是一项挑战。多相流 LES 没有一套标准化的控制方程。文献中讨论了不同的方法和公式，各有利弊。本文通过评估空气中剪切稀化液滴这一简单测试案例的子网格尺度（SGS）能量传递，将传统（非加权）滤波方法与密度加权法弗尔滤波方法进行了比较。研究结果表明，与法弗尔滤波法不同，传统滤波法会在流动中产生大量非物理的后向散射。基于这些结果，Favre 滤波方法显得更为可取，并被应用于剪切稀化液体射流的先验分析，其中粘度已使用 Carreau-Yasuda 模型建模。首先，通过明确过滤剪切稀化射流破裂进入停滞空气的现有 DNS 数据，使用 Favre 滤波法评估了不同 SGS 项的数量级。与早期对牛顿喷流的研究一致，本研究表明扩散项仍然可以忽略不计，而对流项则起主导作用。通过相关分析和数量级研究，评估了对流 SGS 项闭合的功能模型和结构模型。现有的结构模型为牛顿和剪切稀化情况提供了良好的结果。讨论了有希望的后验模型候选者。
{"title":"Toward large eddy simulation of shear-thinning liquid jets: A priori analysis of subgrid scale closures for multiphase flows","authors":"M. Abdelsayed, J. Hasslberger, M. Ertl, B. Weigand, M. Klein","doi":"10.1063/5.0219269","DOIUrl":"https://doi.org/10.1063/5.0219269","url":null,"abstract":"While direct numerical simulation (DNS) of multiphase flows has been the focus of many research investigations in recent years, large eddy simulation (LES) of multiphase flows remains a challenge. There is no standardized set of governing equations for multiphase LES. Different approaches and formulations have been discussed in the literature, each with its own advantages and disadvantages. In this paper, the conventional (non-weighted) filtering approach is compared with the density-weighted Favre filtering method by evaluating the subgrid scale (SGS) energy transfer for a simple test case of a shear-thinning droplet in air. The findings reveal that, unlike the Favre filtering approach, the conventional filtering method results in a notable amount of nonphysical backward scatter in the flow. Based on these results, the Favre filtering method appears preferable and is applied to the a priori analysis of shear-thinning liquid jets, where the viscosity has been modeled using the Carreau–Yasuda model. First, by explicitly filtering existing DNS data of shear-thinning jet breakup into stagnant air, the order of magnitude of different SGS terms is evaluated using the Favre filtering method. Consistent with earlier studies on Newtonian jets, the present study indicates that the diffusive term remains negligible, while the convective term plays a dominant role. Functional and structural models for the closure of the convective SGS term are assessed by means of a correlation analysis and an order of magnitude study. Existing structural models provide good results for both Newtonian and shear-thinning cases. Promising a posteriori model candidates are discussed.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940489","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Heat transfer and phase change phenomena, particularly diffusion-driven droplet evaporation, play pivotal roles in various industrial applications and natural processes. Despite advancements in computational fluid dynamics, modeling multiphase flows with large density ratios remains challenging. In this study, we developed a robust and stable conservative Allen–Cahn-based phase-field lattice Boltzmann method to solve the flow field equations. This method is coupled with the finite difference discretization of vapor species transport equation and the energy equation. The coupling between the vapor concentration and temperature field at the interface is modeled by the well-known Clausius–Clapeyron correlation. Our approach is capable of simulations under real physical conditions and is compatible with graphics processing unit architecture, making it ideal for large-scale industrial simulations. Three validation test cases are conducted to demonstrate the consistency of the presented model, including simulations of Stefan flow, the evaporation of suspended droplets containing water, acetone, and ethanol in the air, and the evaporation of a water sessile droplet on a flat surface. The results show that the model is able to predict the behavior and characteristics of each case accurately. Notably, our numerical results exhibit a maximum relative error of approximately 1% in simulations of Stefan flow. In the case of suspended droplet evaporation, the observed maximum difference between the calculated wet bulb temperatures and those derived from psychrometric charts is approximately 0.9 K. Moreover, our analysis of the sessile droplet reveals a good agreement between the results obtained by our model for the evaporative mass flux and those obtained from the existing models in the literature for different contact angles.
{"title":"A novel phase-field lattice Boltzmann framework for diffusion-driven multiphase evaporation","authors":"Masoumeh Mirhoseini, Alireza Banaee, Alireza Jalali","doi":"10.1063/5.0218145","DOIUrl":"https://doi.org/10.1063/5.0218145","url":null,"abstract":"Heat transfer and phase change phenomena, particularly diffusion-driven droplet evaporation, play pivotal roles in various industrial applications and natural processes. Despite advancements in computational fluid dynamics, modeling multiphase flows with large density ratios remains challenging. In this study, we developed a robust and stable conservative Allen–Cahn-based phase-field lattice Boltzmann method to solve the flow field equations. This method is coupled with the finite difference discretization of vapor species transport equation and the energy equation. The coupling between the vapor concentration and temperature field at the interface is modeled by the well-known Clausius–Clapeyron correlation. Our approach is capable of simulations under real physical conditions and is compatible with graphics processing unit architecture, making it ideal for large-scale industrial simulations. Three validation test cases are conducted to demonstrate the consistency of the presented model, including simulations of Stefan flow, the evaporation of suspended droplets containing water, acetone, and ethanol in the air, and the evaporation of a water sessile droplet on a flat surface. The results show that the model is able to predict the behavior and characteristics of each case accurately. Notably, our numerical results exhibit a maximum relative error of approximately 1% in simulations of Stefan flow. In the case of suspended droplet evaporation, the observed maximum difference between the calculated wet bulb temperatures and those derived from psychrometric charts is approximately 0.9 K. Moreover, our analysis of the sessile droplet reveals a good agreement between the results obtained by our model for the evaporative mass flux and those obtained from the existing models in the literature for different contact angles.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940555","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
There are occurrences of crude oil emulsification following the fracturing shut-in wells in the Jimushar, but the emulsification characteristics and mechanism remain unclear. In this study, the low-field nuclear magnetic resonance technique and visual microdisplacement tests are employed to investigate the emulsification characteristics of crude oil, along with its emulsification mechanism in porous media. Experimental results revealed that the heavy components (asphaltene and resin) enhance crude oil emulsification by increasing the viscous force of water droplets in the oil phase, affecting the size and stability of small water droplets in the oil phase. In the process of flowing through pore throats, emulsions are formed primarily by stretching and snap-off action, with stretching preferring to form smaller droplet-size emulsions, while snap-off results in the division of larger oil droplets into two smaller ones. The primary factors causing a large oil droplet to be stretched into smaller droplets include changes in the composition of the oil droplet, external tension, and the duration of these forces acting on the droplet. Capillary forces can emulsify crude oil and water at the pore scale, resulting in a reduction of the absorption rate. However, this rate can be restored when the capillary forces are strong enough for the water phase to penetrate and break through the emulsified layer. This study offers valuable insights into understanding the adaptability of the emulsification flooding mechanism.
{"title":"Emulsification characteristics of crude oil with a high content of heavy components and its emulsification mechanism in porous media","authors":"Leilei Jia, Liguo Zhong, Jiachang Zhu, Yuhao Liu, Hao Liu, Wenqi Feng, Heng Liang","doi":"10.1063/5.0215374","DOIUrl":"https://doi.org/10.1063/5.0215374","url":null,"abstract":"There are occurrences of crude oil emulsification following the fracturing shut-in wells in the Jimushar, but the emulsification characteristics and mechanism remain unclear. In this study, the low-field nuclear magnetic resonance technique and visual microdisplacement tests are employed to investigate the emulsification characteristics of crude oil, along with its emulsification mechanism in porous media. Experimental results revealed that the heavy components (asphaltene and resin) enhance crude oil emulsification by increasing the viscous force of water droplets in the oil phase, affecting the size and stability of small water droplets in the oil phase. In the process of flowing through pore throats, emulsions are formed primarily by stretching and snap-off action, with stretching preferring to form smaller droplet-size emulsions, while snap-off results in the division of larger oil droplets into two smaller ones. The primary factors causing a large oil droplet to be stretched into smaller droplets include changes in the composition of the oil droplet, external tension, and the duration of these forces acting on the droplet. Capillary forces can emulsify crude oil and water at the pore scale, resulting in a reduction of the absorption rate. However, this rate can be restored when the capillary forces are strong enough for the water phase to penetrate and break through the emulsified layer. This study offers valuable insights into understanding the adaptability of the emulsification flooding mechanism.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Niloofar Hosseini, Mehran Tadjfar, Mohammad Saeedi, Antonella Abbà
In this study, the interaction of vortices generated from an oscillating airfoil with a hindfoil placed downstream of the oscillating forefoil at low-Reynolds-number flow was investigated numerically. The forefoil entered a deep dynamic stall induced by large-amplitude pitching oscillation. The dynamic stall process is characterized by unsteady separation and the formation of a strong clockwise vortex. A wall-resolved large-eddy simulation approach was applied to compute the flowfield. The numerical measurements were performed for an incompressible flow at a Reynolds number of Re = 30 000 based on chord length with a pitching reduced frequency of K= 0.5, and amplitude of A = 14.1° over Selig–Donovan 7003 airfoils. A single-airfoil case was validated against numerical and experimental measurements. In the present study, we investigated the flowfield and aerodynamic coefficients resulting from the deep dynamic stall of the pitching forefoil and the vortex interaction in tandem-airfoil configuration related to micro-air vehicle applications by employing large-eddy simulation approach. Large-eddy simulation was also compared to two-dimensional unsteady Reynolds-averaged Navier–Stokes simulation to determine the accuracy and validity of the low-fidelity approach in prediction of deep dynamic stall and vortex interaction at low-Reynolds-number flow.
本研究采用数值方法研究了在低雷诺数流动条件下，摆动机翼产生的涡流与置于摆动前翼下游的后翼之间的相互作用。前翼在大振幅俯仰振荡的诱导下进入深度动态失速。动态失速过程的特点是不稳定分离和形成强烈的顺时针旋涡。计算流场时采用了壁面分辨大涡流模拟方法。对不可压缩流进行了数值测量，其雷诺数为 Re = 30 000，基于弦长，俯仰降低频率为 K=0.5，在 Selig-Donovan 7003 机翼上的振幅为 A=14.1°。根据数值和实验测量结果对单翼面情况进行了验证。在本研究中，我们采用大涡流模拟方法研究了与微型空气飞行器应用相关的串联翼面配置中俯仰前翼的深度动态失速和涡流相互作用产生的流场和气动系数。大涡流模拟还与二维非稳态雷诺平均纳维-斯托克斯模拟进行了比较，以确定低保真方法在预测低雷诺数流动的深度动态失速和涡流相互作用时的准确性和有效性。
{"title":"Large-eddy simulation of vortex interaction in pitching-fixed tandem airfoils","authors":"Niloofar Hosseini, Mehran Tadjfar, Mohammad Saeedi, Antonella Abbà","doi":"10.1063/5.0218556","DOIUrl":"https://doi.org/10.1063/5.0218556","url":null,"abstract":"In this study, the interaction of vortices generated from an oscillating airfoil with a hindfoil placed downstream of the oscillating forefoil at low-Reynolds-number flow was investigated numerically. The forefoil entered a deep dynamic stall induced by large-amplitude pitching oscillation. The dynamic stall process is characterized by unsteady separation and the formation of a strong clockwise vortex. A wall-resolved large-eddy simulation approach was applied to compute the flowfield. The numerical measurements were performed for an incompressible flow at a Reynolds number of Re = 30 000 based on chord length with a pitching reduced frequency of K= 0.5, and amplitude of A = 14.1° over Selig–Donovan 7003 airfoils. A single-airfoil case was validated against numerical and experimental measurements. In the present study, we investigated the flowfield and aerodynamic coefficients resulting from the deep dynamic stall of the pitching forefoil and the vortex interaction in tandem-airfoil configuration related to micro-air vehicle applications by employing large-eddy simulation approach. Large-eddy simulation was also compared to two-dimensional unsteady Reynolds-averaged Navier–Stokes simulation to determine the accuracy and validity of the low-fidelity approach in prediction of deep dynamic stall and vortex interaction at low-Reynolds-number flow.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940558","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A novel formulation of the electron energy relaxation terms is presented here, which is applicable to plasma flows and discharges wherein the electron temperature could be higher or lower than the gas temperature. It is demonstrated that the electron energy losses due to inelastic collisions can be expressed as a function of only two species-dependent parameters: the reduced electric field and the reduced electron mobility. This formulation is advantageous over previous ones, being simpler to implement and more accurate when experimental data of the reduced electric field and reduced mobility are available. Curve fits to empirical data of these two properties are outlined here for all important air molecular species. The approach accounts for all inelastic electron energy relaxation processes without needing individual cross sections or rates, reducing potential errors associated with independently handling each process. Several test cases are presented to validate the proposed electron energy source terms including reentry plasma flows for which the electron temperature is less than the gas temperature, as well as discharges in which the electron temperature reaches values in excess of 30 eV. In all cases, the agreement with experimental data is observed to be very good to excellent, significantly surpassing prior electron energy models for plasma flows.
本文提出了一种新的电子能量弛豫项公式，适用于电子温度高于或低于气体温度的等离子体流和放电。研究表明，非弹性碰撞导致的电子能量损失可以表示为两个依赖于物种的参数的函数：降低的电场和降低的电子迁移率。与之前的公式相比，这种公式的优点是实现起来更简单，而且在有还原电场和还原迁移率实验数据的情况下更精确。这里概述了所有重要空气分子种类的这两个特性与经验数据的曲线拟合。该方法考虑了所有非弹性电子能量弛豫过程，不需要单独的截面或速率，从而减少了独立处理每个过程可能产生的误差。本文提出了几个测试案例来验证所提出的电子能量源术语，包括电子温度低于气体温度的再入等离子体流，以及电子温度超过 30 eV 的放电。在所有情况下，与实验数据的一致性都非常好，甚至非常出色，大大超过了之前的等离子体流电子能量模型。
{"title":"Progress in electron energy modeling for plasma flows and discharges","authors":"Bernard Parent, Felipe Martin Rodriguez Fuentes","doi":"10.1063/5.0219552","DOIUrl":"https://doi.org/10.1063/5.0219552","url":null,"abstract":"A novel formulation of the electron energy relaxation terms is presented here, which is applicable to plasma flows and discharges wherein the electron temperature could be higher or lower than the gas temperature. It is demonstrated that the electron energy losses due to inelastic collisions can be expressed as a function of only two species-dependent parameters: the reduced electric field and the reduced electron mobility. This formulation is advantageous over previous ones, being simpler to implement and more accurate when experimental data of the reduced electric field and reduced mobility are available. Curve fits to empirical data of these two properties are outlined here for all important air molecular species. The approach accounts for all inelastic electron energy relaxation processes without needing individual cross sections or rates, reducing potential errors associated with independently handling each process. Several test cases are presented to validate the proposed electron energy source terms including reentry plasma flows for which the electron temperature is less than the gas temperature, as well as discharges in which the electron temperature reaches values in excess of 30 eV. In all cases, the agreement with experimental data is observed to be very good to excellent, significantly surpassing prior electron energy models for plasma flows.","PeriodicalId":20066,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":4.6,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141940624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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