Biomimetic flow control is being widely applied. In the present study, a biomimetic flow control method, i.e., Kirigami scales, was applied on a 1:2 rectangular cylinder. The effects of scales' shapes and pasting surfaces on the aerodynamics and circumferential flow patterns of a 1:2 rectangular cylinder were studied. Three scale shapes were investigated with different pasting methods, i.e., elliptical, circular, and triangular scales. The Reynolds number (Re) was set at 1.3–3.1 × 104. The surface pressure distributions and the integrated aerodynamic forces were further analyzed at Re = 1.3 × 104. Results show that pasting the elliptical scales on all surfaces performs best, reaching a 2.4% drag reduction and a 76.4% lift reduction. Moreover, the elliptical and triangular scales on the windward and leeward surfaces can significantly reduce the Re effect. To reveal the control mechanism, the particle image velocimetry technique was employed to obtain the circumferential and wake flow fields. The time-averaged and phase-averaged results indicate that the Kirigami scales can push the interactions of shear layers and the shedding vortices further downstream. The Proper orthogonal decomposition analysis and time-averaged turbulent kinetic energy (TKE) results indicate that the wake vortex shedding is significantly suppressed. The spanwise wake flow field was also investigated. Results show that the spanwise TKE values are significantly reduced. This study further deepened the application of Kirigami scales on the common blunt bodies.
仿生流控制技术正在被广泛应用。本研究在一个 1:2 的矩形圆柱体上应用了一种仿生流动控制方法，即桐木鳞片。研究了鳞片的形状和粘贴面对 1:2 矩形圆柱体的空气动力学和圆周流型的影响。用不同的粘贴方法研究了三种鳞片形状，即椭圆形、圆形和三角形鳞片。雷诺数（Re）设定为 1.3-3.1 × 104。进一步分析了 Re = 1.3 × 104 时的表面压力分布和综合空气动力。结果表明，在所有表面粘贴椭圆鳞片的效果最好，阻力减少了 2.4%，升力减少了 76.4%。此外，在迎风面和背风面粘贴椭圆形和三角形鳞片能显著降低 Re 效应。为了揭示控制机制，采用了粒子图像测速技术来获取圆周流场和尾流流场。时间均值和相位均值结果表明，桐神尺度能将剪切层和脱落涡旋的相互作用推向下游。适当正交分解分析和时间平均湍流动能（TKE）结果表明，尾流涡旋脱落被明显抑制。此外，还研究了跨向尾流流场。结果表明，跨向 TKE 值明显降低。这项研究进一步深化了桐神尺度在普通钝体上的应用。
{"title":"Systematical study on the aerodynamic control mechanisms of a 1:2 rectangular cylinder with Kirigami scales","authors":"Haoqi Hu, Wenhan Yang, Hao Meng, Donglai Gao","doi":"10.1063/5.0218442","DOIUrl":"https://doi.org/10.1063/5.0218442","url":null,"abstract":"Biomimetic flow control is being widely applied. In the present study, a biomimetic flow control method, i.e., Kirigami scales, was applied on a 1:2 rectangular cylinder. The effects of scales' shapes and pasting surfaces on the aerodynamics and circumferential flow patterns of a 1:2 rectangular cylinder were studied. Three scale shapes were investigated with different pasting methods, i.e., elliptical, circular, and triangular scales. The Reynolds number (Re) was set at 1.3–3.1 × 104. The surface pressure distributions and the integrated aerodynamic forces were further analyzed at Re = 1.3 × 104. Results show that pasting the elliptical scales on all surfaces performs best, reaching a 2.4% drag reduction and a 76.4% lift reduction. Moreover, the elliptical and triangular scales on the windward and leeward surfaces can significantly reduce the Re effect. To reveal the control mechanism, the particle image velocimetry technique was employed to obtain the circumferential and wake flow fields. The time-averaged and phase-averaged results indicate that the Kirigami scales can push the interactions of shear layers and the shedding vortices further downstream. The Proper orthogonal decomposition analysis and time-averaged turbulent kinetic energy (TKE) results indicate that the wake vortex shedding is significantly suppressed. The spanwise wake flow field was also investigated. Results show that the spanwise TKE values are significantly reduced. This study further deepened the application of Kirigami scales on the common blunt bodies.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141690145","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shuiqing Hu, Zirui Yang, Yiqun Yan, Yiping Ye, Wei Zhang, Zhongchen Ba, Hui He, Daobing Wang
This study delves into the mechanical properties of various rock types found in glutenite reservoirs in the Ma'nan area of the Xinjiang oilfield. It bridges a knowledge gap by exploring the mechanical deformation and failure patterns among different glutenite types. Employing porosity-permeability tests, ultrasonic wave velocity measurements, and triaxial compression tests, this research scrutinizes physical parameters, mechanical properties, deformation, and failure modes of dolomitic sandstone, calcareous coarse sandstone, calcareous fine siltstone, and glutenite. Results highlight a porosity increase from dolomitic sandstone to glutenite, with calcareous coarse sandstone having the lowest permeability and glutenite the highest. Shear wave velocity is greater in dolomitic sandstone and calcareous coarse sandstone compared to calcareous fine siltstone, while longitudinal wave velocity is higher in dolomitic sandstone than in glutenite. Deformation behavior varies: dolomitic sandstone is primarily elastic, and calcareous sandstone and glutenite show elastoplastic characteristics. Dolomitic sandstone boasts the highest compressive strength, elastic modulus, and Poisson's ratio. Calcareous fine siltstone's compressive strength and elastic modulus fall below dolomitic sandstone, while the Poisson's ratio of calcareous coarse sandstone is three-quarters that of dolomitic sandstone. Main failure modes observed are shear failure in dolomitic sandstone, calcareous coarse sandstone, and glutenite, and axial splitting failure in calcareous fine siltstone. Microscopic analyses, including environmental scanning electron microscopy and mineral composition, shed light on the mechanical differences among the rocks. In sum, this research yields crucial insights into the mechanical traits of glutenite reservoir rocks, essential for optimizing hydraulic fracturing strategies in such reservoirs.
{"title":"Experimental study on the comparison of mechanical properties of different types of glutenite in the Ma'nan area","authors":"Shuiqing Hu, Zirui Yang, Yiqun Yan, Yiping Ye, Wei Zhang, Zhongchen Ba, Hui He, Daobing Wang","doi":"10.1063/5.0218642","DOIUrl":"https://doi.org/10.1063/5.0218642","url":null,"abstract":"This study delves into the mechanical properties of various rock types found in glutenite reservoirs in the Ma'nan area of the Xinjiang oilfield. It bridges a knowledge gap by exploring the mechanical deformation and failure patterns among different glutenite types. Employing porosity-permeability tests, ultrasonic wave velocity measurements, and triaxial compression tests, this research scrutinizes physical parameters, mechanical properties, deformation, and failure modes of dolomitic sandstone, calcareous coarse sandstone, calcareous fine siltstone, and glutenite. Results highlight a porosity increase from dolomitic sandstone to glutenite, with calcareous coarse sandstone having the lowest permeability and glutenite the highest. Shear wave velocity is greater in dolomitic sandstone and calcareous coarse sandstone compared to calcareous fine siltstone, while longitudinal wave velocity is higher in dolomitic sandstone than in glutenite. Deformation behavior varies: dolomitic sandstone is primarily elastic, and calcareous sandstone and glutenite show elastoplastic characteristics. Dolomitic sandstone boasts the highest compressive strength, elastic modulus, and Poisson's ratio. Calcareous fine siltstone's compressive strength and elastic modulus fall below dolomitic sandstone, while the Poisson's ratio of calcareous coarse sandstone is three-quarters that of dolomitic sandstone. Main failure modes observed are shear failure in dolomitic sandstone, calcareous coarse sandstone, and glutenite, and axial splitting failure in calcareous fine siltstone. Microscopic analyses, including environmental scanning electron microscopy and mineral composition, shed light on the mechanical differences among the rocks. In sum, this research yields crucial insights into the mechanical traits of glutenite reservoir rocks, essential for optimizing hydraulic fracturing strategies in such reservoirs.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141698821","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jia Ning, Qing-Yun Huang, Chen-Hui Gai, Yi-Zhan Ding, Bing Zhang, Yu-Lin Lei, Yang Wu, Hong Hu
The rapid development of microfluidics has significantly highlighted the role of surface acoustic waves (SAWs) in microfluidic actuation. SAW influences droplet manipulation, inducing interface instability and processes such as droplet splitting, jetting, and atomization, which have been key research focal points. Previous studies have identified a close correlation between these instability mechanisms and three critical parameters: the Marangoni number (Ma), associated with piezoelectric substrate thermal effects; the slip coefficient (β0), related to piezoelectric substrate slip; and the acoustic capillary number (C). Given the intimate link between the aspect ratio (H/L, where H is the characteristic height, and L is the characteristic width of droplets) and atomization size, this study comprehensively investigates the combined effects of these factors on the droplet aspect ratio H/L. Specifically, increases in the acoustic capillary number C and slip coefficient β0 promote reductions in droplet height (H) and outward expansion (L), while the Marangoni number Ma counteracts this expansion, maintaining larger H/L values. This inhibitory effect is particularly pronounced when C and β0 are small but diminishes as their values increase. Additionally, higher values of C and β0 accelerate the convergence of the H/L ratio, whereas Ma decreases the rate of this convergence. Through the coordinated interplay of Ma, β0, and C, multidimensional and fine-tuned adjustments of the droplet aspect ratio H/L over a wide range can be achieved.
微流控技术的快速发展极大地凸显了表面声波（SAW）在微流控中的作用。声表面波影响液滴操作，诱发界面不稳定性以及液滴分裂、喷射和雾化等过程，这些一直是研究的重点。以往的研究发现，这些不稳定机制与三个关键参数密切相关：与压电基底热效应相关的马兰戈尼数 (Ma)；与压电基底滑移相关的滑移系数 (β0)；以及声毛细管数 (C)。鉴于高宽比（H/L，其中 H 是液滴的特征高度，L 是特征宽度）与雾化尺寸之间的密切联系，本研究全面探讨了这些因素对液滴高宽比 H/L 的综合影响。具体来说，声学毛细管数 C 和滑移系数 β0 的增加会促进液滴高度（H）的降低和向外扩展（L），而马兰戈尼数 Ma 则会抵消这种扩展，使 H/L 值保持较大。当 C 和 β0 值较小时，这种抑制作用尤为明显，但随着 C 和 β0 值的增加，这种抑制作用会逐渐减弱。此外，C 和 β0 值越大，H/L 比值的收敛速度越快，而 Ma 值则会降低这种收敛速度。通过 Ma、β0 和 C 的协调相互作用，可以在很大范围内实现液滴长宽比 H/L 的多维微调。
{"title":"Numerical study of thermocapillary and slip effects on interfacial destabilization under surface acoustic waves","authors":"Jia Ning, Qing-Yun Huang, Chen-Hui Gai, Yi-Zhan Ding, Bing Zhang, Yu-Lin Lei, Yang Wu, Hong Hu","doi":"10.1063/5.0215087","DOIUrl":"https://doi.org/10.1063/5.0215087","url":null,"abstract":"The rapid development of microfluidics has significantly highlighted the role of surface acoustic waves (SAWs) in microfluidic actuation. SAW influences droplet manipulation, inducing interface instability and processes such as droplet splitting, jetting, and atomization, which have been key research focal points. Previous studies have identified a close correlation between these instability mechanisms and three critical parameters: the Marangoni number (Ma), associated with piezoelectric substrate thermal effects; the slip coefficient (β0), related to piezoelectric substrate slip; and the acoustic capillary number (C). Given the intimate link between the aspect ratio (H/L, where H is the characteristic height, and L is the characteristic width of droplets) and atomization size, this study comprehensively investigates the combined effects of these factors on the droplet aspect ratio H/L. Specifically, increases in the acoustic capillary number C and slip coefficient β0 promote reductions in droplet height (H) and outward expansion (L), while the Marangoni number Ma counteracts this expansion, maintaining larger H/L values. This inhibitory effect is particularly pronounced when C and β0 are small but diminishes as their values increase. Additionally, higher values of C and β0 accelerate the convergence of the H/L ratio, whereas Ma decreases the rate of this convergence. Through the coordinated interplay of Ma, β0, and C, multidimensional and fine-tuned adjustments of the droplet aspect ratio H/L over a wide range can be achieved.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141716611","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Haotian Cong, Minli Bai, Xuecheng Lv, Yubai Li, Yongchen Song
Hydrophilic-hydrophobic hybrid surfaces are developed to solve the flow and heat transfer performance contradiction. However, hybrid surfaces often have micro- or nano-scale featured sizes and are used in phase change heat transfer because hydrophilic regions contribute to droplet nucleation, and hydrophobic regions contribute to bubble nucleation. In this study, large eddy simulation is used to investigate the forced convection on macroscopic hydrophilic-hydrophobic hybrid surfaces where only the surface local wettability is changed. Three hybrid surfaces with different hydrophilic-hydrophobic ratios and two homogeneous wettability surfaces are designed, and representative flow Reynolds numbers of 4000, 6000, 10 000, and 40 000 are explored to achieve different turbulent styles. The transient parameters of kinematics, vorticity, and boundary layer are analyzed to clarify the mechanism of turbulence change and eddy generation and explain the causes of variations in flow and heat transfer performances. It proves that macroscopic hydrophilic-hydrophobic hybrid surfaces are suitable for forced convection due to the drag reduction on hydrophobic regions, backflows at hydrophilic-hydrophobic interfaces, and eddies at hydrophobic-hydrophilic interfaces, which can enhance the internal disturbance and harmonize the flow and heat transfer performances. The mechanism has a profound significance in broadening the application of hydrophilic-hydrophobic hybrid surfaces and designing the arrangement of hydrophobic regions.
{"title":"Analysis of interfacial effect and boundary layer for forced convection on the macroscopic hydrophilic-hydrophobic hybrid surface: A large eddy simulation","authors":"Haotian Cong, Minli Bai, Xuecheng Lv, Yubai Li, Yongchen Song","doi":"10.1063/5.0215005","DOIUrl":"https://doi.org/10.1063/5.0215005","url":null,"abstract":"Hydrophilic-hydrophobic hybrid surfaces are developed to solve the flow and heat transfer performance contradiction. However, hybrid surfaces often have micro- or nano-scale featured sizes and are used in phase change heat transfer because hydrophilic regions contribute to droplet nucleation, and hydrophobic regions contribute to bubble nucleation. In this study, large eddy simulation is used to investigate the forced convection on macroscopic hydrophilic-hydrophobic hybrid surfaces where only the surface local wettability is changed. Three hybrid surfaces with different hydrophilic-hydrophobic ratios and two homogeneous wettability surfaces are designed, and representative flow Reynolds numbers of 4000, 6000, 10 000, and 40 000 are explored to achieve different turbulent styles. The transient parameters of kinematics, vorticity, and boundary layer are analyzed to clarify the mechanism of turbulence change and eddy generation and explain the causes of variations in flow and heat transfer performances. It proves that macroscopic hydrophilic-hydrophobic hybrid surfaces are suitable for forced convection due to the drag reduction on hydrophobic regions, backflows at hydrophilic-hydrophobic interfaces, and eddies at hydrophobic-hydrophilic interfaces, which can enhance the internal disturbance and harmonize the flow and heat transfer performances. The mechanism has a profound significance in broadening the application of hydrophilic-hydrophobic hybrid surfaces and designing the arrangement of hydrophobic regions.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141697394","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The present work investigates the creeping peristaltic propulsion of viscid fluid in an annular gap between sinusoidally deforming permeable and impermeable curved tubes of similar shape under the influence of an externally imposed electric and magnetic field. In this model, the outer tube with a permeable wall surface is supposed to satisfy the Saffman slip condition. The flow equations are simplified by the estimation of a large wavelength in comparison with the radius of the external tube. An analytical solution for the axial velocity is obtained in the computational software MATHEMATICA. Graphical analyses are conducted to explore the variations in wall shear stress, velocity, pressure rise, frictional force, and stream function with respect to different emergent parameters, providing insight into the underlying physics of the flow phenomena. An investigation of the effects of the Hartmann number and electric field strength on the flow through a gap between deformable tubes with curved structures has important implications for a variety of engineering applications, including mechanical and biomedical engineering. The streamlines are plotted to discuss fluid trapping and visualize the flow pattern of the viscid fluid inside the curved annular domain. A comparative analysis of fluid transport induced by sinusoidal, triangular, trapezoidal, and square wave shapes is encountered with the help of streamlined contour diagrams. The comparison of pressure gradients in three different models is also discussed to gain insight due to fluid–structure interaction. A gap in the body of recently published literature is filled by the results discussed in this paper.
{"title":"Mathematical modeling of creeping electromagnetohydrodynamic peristaltic propulsion in an annular gap between sinusoidally deforming permeable and impermeable curved tubes","authors":"P. Yadav, Muhammad Roshan","doi":"10.1063/5.0217370","DOIUrl":"https://doi.org/10.1063/5.0217370","url":null,"abstract":"The present work investigates the creeping peristaltic propulsion of viscid fluid in an annular gap between sinusoidally deforming permeable and impermeable curved tubes of similar shape under the influence of an externally imposed electric and magnetic field. In this model, the outer tube with a permeable wall surface is supposed to satisfy the Saffman slip condition. The flow equations are simplified by the estimation of a large wavelength in comparison with the radius of the external tube. An analytical solution for the axial velocity is obtained in the computational software MATHEMATICA. Graphical analyses are conducted to explore the variations in wall shear stress, velocity, pressure rise, frictional force, and stream function with respect to different emergent parameters, providing insight into the underlying physics of the flow phenomena. An investigation of the effects of the Hartmann number and electric field strength on the flow through a gap between deformable tubes with curved structures has important implications for a variety of engineering applications, including mechanical and biomedical engineering. The streamlines are plotted to discuss fluid trapping and visualize the flow pattern of the viscid fluid inside the curved annular domain. A comparative analysis of fluid transport induced by sinusoidal, triangular, trapezoidal, and square wave shapes is encountered with the help of streamlined contour diagrams. The comparison of pressure gradients in three different models is also discussed to gain insight due to fluid–structure interaction. A gap in the body of recently published literature is filled by the results discussed in this paper.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141690227","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A fluid–structure interaction numerical investigation was conducted on the flow past a circular cylinder with a detached flexible plate at a low Reynolds number Re = 160. A broad gap ratio range of 0–6.0 is examined at three plate lengths. Numerical results indicated that the vortex formation is closely related to the position of the plate with respect to the recirculation region behind the cylinder. Three wake interference regimes are identified, including the extended-body, continuous reattachment (CR), and alternate reattachment (AR). Taking into account the wake interference and vortex shedding modes and the response order, six wake flow patterns are observed. The CR regime shifts to AR at a critical gap G/D = 3, where both the vibration amplitude and frequency sharply increase. The sizes of vortex spacing and plate length determine the response mode of the flexible plate. Compared to an isolated cylinder, the optimal reduction percentages in drag and lift coefficients are around 90% and 20%, respectively.
在低雷诺数 Re = 160 条件下，对流经带有分离式柔性板的圆筒的流体进行了流固耦合数值研究。研究了三个板长的 0-6.0 宽间隙比范围。数值结果表明，涡流的形成与柔性板相对于圆柱体后方再循环区域的位置密切相关。研究确定了三种唤醒干扰机制，包括扩展体、连续再附着（CR）和交替再附着（AR）。考虑到唤醒干扰和涡流脱落模式以及响应顺序，观察到六种唤醒流动模式。在临界间隙 G/D = 3 时，CR 模式转变为 AR 模式，此时振动幅度和频率都急剧增加。涡流间距和板长的大小决定了柔性板的响应模式。与孤立的圆柱体相比，阻力系数和升力系数的最佳降低率分别约为 90% 和 20%。
{"title":"Wake-induced response of a flexible splitter plate detachedly placed downstream of a circular cylinder","authors":"Hongjun Zhu, Quanyu Chen, Jiawen Zhong, Wenxiang Zhang, Tongming Zhou","doi":"10.1063/5.0217046","DOIUrl":"https://doi.org/10.1063/5.0217046","url":null,"abstract":"A fluid–structure interaction numerical investigation was conducted on the flow past a circular cylinder with a detached flexible plate at a low Reynolds number Re = 160. A broad gap ratio range of 0–6.0 is examined at three plate lengths. Numerical results indicated that the vortex formation is closely related to the position of the plate with respect to the recirculation region behind the cylinder. Three wake interference regimes are identified, including the extended-body, continuous reattachment (CR), and alternate reattachment (AR). Taking into account the wake interference and vortex shedding modes and the response order, six wake flow patterns are observed. The CR regime shifts to AR at a critical gap G/D = 3, where both the vibration amplitude and frequency sharply increase. The sizes of vortex spacing and plate length determine the response mode of the flexible plate. Compared to an isolated cylinder, the optimal reduction percentages in drag and lift coefficients are around 90% and 20%, respectively.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141705102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Experimental investigations were conducted on a single vortex ring impinging on a concave hemi-cylindrical shell with Dm/De = 2 at different Reynolds numbers. Vortex rings with five different Reynolds numbers were generated for experimental studies, i.e., Re = 750, 1500, 3000, 5000, and 7000. The planar laser-induced fluorescence visualizations and two-dimensional particle image velocimetry measurements were used in the experiment. The vorticity field based on the Eulerian framework and the finite-time Lyapunov exponent (FTLE) field based on the Lagrangian framework were used to identify the dynamic processes of vortex rings, respectively. The results show that as the vortex rings impinge on concave surfaces from Re = 750 to Re = 7000, the extension of the main vortex ring in the straight-edged direction is larger than that in the concave direction, and the instability of the vortex ring is promoted. While the Reynolds number is increasing, the vortex ring deformation becomes larger, and the overall vortex ring cross section becomes smaller, leading to a larger attenuation of the vortex ring rotation. Calculations performed by the FTLE field were used to derive the Lagrangian coherent structure to analyze the boundaries of the vortex ring motion process, clearly observe the shape of the secondary vortex connecting segments, and verify the speculation by the vortex ring trajectory identification results. Finally, a dynamic model of vortex rings impinging a concave surface was proposed, and the inference of the experimental process was explained by the model.
在不同的雷诺数下，对单个涡环撞击到 Dm/De = 2 的凹半圆柱形壳上进行了实验研究。实验研究生成了五个不同雷诺数的涡环，即 Re = 750、1500、3000、5000 和 7000。实验中使用了平面激光诱导荧光可视化和二维粒子图像测速仪测量。基于欧拉框架的涡度场和基于拉格朗日框架的有限时间李亚普诺夫指数（FTLE）场分别用于识别涡环的动态过程。结果表明，从 Re = 750 到 Re = 7000，当涡旋环撞击凹面时，主涡旋环在直角方向的延伸大于在凹面方向的延伸，促进了涡旋环的不稳定性。当雷诺数增大时，涡环变形变大，整体涡环截面变小，导致涡环旋转衰减变大。利用 FTLE 场进行计算，得出拉格朗日相干结构，分析涡环运动过程的边界，清晰观察次级涡连接段的形状，并通过涡环轨迹识别结果验证推测。最后，提出了涡环撞击凹面的动力学模型，并用该模型解释了实验过程的推理。
{"title":"Reynolds number effect of a vortex ring impinging on a concave hemi-cylindrical shell","authors":"Liangquan Zhang, Guangtao Li, Wen-li Chen, Donglai Gao","doi":"10.1063/5.0214319","DOIUrl":"https://doi.org/10.1063/5.0214319","url":null,"abstract":"Experimental investigations were conducted on a single vortex ring impinging on a concave hemi-cylindrical shell with Dm/De = 2 at different Reynolds numbers. Vortex rings with five different Reynolds numbers were generated for experimental studies, i.e., Re = 750, 1500, 3000, 5000, and 7000. The planar laser-induced fluorescence visualizations and two-dimensional particle image velocimetry measurements were used in the experiment. The vorticity field based on the Eulerian framework and the finite-time Lyapunov exponent (FTLE) field based on the Lagrangian framework were used to identify the dynamic processes of vortex rings, respectively. The results show that as the vortex rings impinge on concave surfaces from Re = 750 to Re = 7000, the extension of the main vortex ring in the straight-edged direction is larger than that in the concave direction, and the instability of the vortex ring is promoted. While the Reynolds number is increasing, the vortex ring deformation becomes larger, and the overall vortex ring cross section becomes smaller, leading to a larger attenuation of the vortex ring rotation. Calculations performed by the FTLE field were used to derive the Lagrangian coherent structure to analyze the boundaries of the vortex ring motion process, clearly observe the shape of the secondary vortex connecting segments, and verify the speculation by the vortex ring trajectory identification results. Finally, a dynamic model of vortex rings impinging a concave surface was proposed, and the inference of the experimental process was explained by the model.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141716168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Combustion instability has been widely reported in several combustion types; however, there is limited information on different fuel/air mixing distances in non-premixed combustion. Setting different distances between air tube and fuel tubes, the fuel/air mixing distances (δ) are changed by structural variations of nozzles. Keeping the heat load and equivalence ratios constant, the present work aims to examine the effects of fuel/air mixing distances on combustion instability in non-premixed combustion. Experimental observations suggest that combustion oscillations occur in non-premixed combustion with flame ignited outside the nozzle rather than other types of non-premixed combustion. Quasiperiodic oscillations, limit cycle modes, and intermittency modes are found in three fuel/air mixing distances in non-premixed combustion. The calculation methods of convection time for non-premixed combustion are established in the present work. The convection time of the limit cycle oscillations is then calculated, which is further found to trigger the second resonance modes of the combustion system. The further analysis reveals that varying fuel/air mixing distances can cause influences on local equivalence ratio distributions, and the convection time are correspondingly varied. The changes in convection time affects the coupling characteristics between heat release rate fluctuations and the acoustic modes in the combustion chamber. When the thermoacoustic coupling occurs, combustion instabilities appear. This work establishes a link between combustion instability and fuel/air mixing distances in non-premixed combustion and highlights the influences on spatial distributions of local equivalence ratios and then convection time, which can provide technical guidance for actual applications in various fuel/air mixing types.
{"title":"Effects of fuel/air mixing distances on combustion instabilities in non-premixed combustion","authors":"Jiaying Cheng, Bofan Liu, Tong Zhu","doi":"10.1063/5.0220095","DOIUrl":"https://doi.org/10.1063/5.0220095","url":null,"abstract":"Combustion instability has been widely reported in several combustion types; however, there is limited information on different fuel/air mixing distances in non-premixed combustion. Setting different distances between air tube and fuel tubes, the fuel/air mixing distances (δ) are changed by structural variations of nozzles. Keeping the heat load and equivalence ratios constant, the present work aims to examine the effects of fuel/air mixing distances on combustion instability in non-premixed combustion. Experimental observations suggest that combustion oscillations occur in non-premixed combustion with flame ignited outside the nozzle rather than other types of non-premixed combustion. Quasiperiodic oscillations, limit cycle modes, and intermittency modes are found in three fuel/air mixing distances in non-premixed combustion. The calculation methods of convection time for non-premixed combustion are established in the present work. The convection time of the limit cycle oscillations is then calculated, which is further found to trigger the second resonance modes of the combustion system. The further analysis reveals that varying fuel/air mixing distances can cause influences on local equivalence ratio distributions, and the convection time are correspondingly varied. The changes in convection time affects the coupling characteristics between heat release rate fluctuations and the acoustic modes in the combustion chamber. When the thermoacoustic coupling occurs, combustion instabilities appear. This work establishes a link between combustion instability and fuel/air mixing distances in non-premixed combustion and highlights the influences on spatial distributions of local equivalence ratios and then convection time, which can provide technical guidance for actual applications in various fuel/air mixing types.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141703227","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
While the opposing jet technique has the potential to achieve efficient drag and heat reduction, it can be severely affected by the incoming angle of attack. To analyze the angle-of-attack characteristics of opposing jet for improving drag and heat reduction, a three-dimensional blunt model was studied under various jet stagnation pressure ratios and angles of attack using the verified numerical method. The results showed that the enhanced reattachment shock on the windward side resulted in a higher pressure and temperature rise, which led to the deterioration of drag and heat reduction. Under the influence of the incoming angle of attack, the recirculation vortex transformed into a longitudinal vortex, resulting in a slanted U-shaped distribution of the surface pressure coefficient and Stanton number. Increasing the jet stagnation pressure ratio widened the coverage of the recirculation vortex on both the windward and leeward sides, which brought an improvement in drag and heat reduction. The interaction between the incoming angle of attack and the opposing jet caused a double-peak distribution of Stanton number due to the recirculation vortex reattachment and the compression of the incoming flow. The inclined opposing jet could reduce the peak values of pressure coefficient and Stanton number when subjected to the incoming flow with an angle of attack by spreading the recirculation vortex along the windward side. There should exist an optimal inclination angle that can effectively reduce the peak caused by the compression of the incoming flow without generating an excessive peak due to the recirculation vortex reattachment.
虽然对向射流技术具有实现高效减阻和减热的潜力，但它会受到射流攻角的严重影响。为了分析对向射流的攻角特性以改善阻力和热量的减少，使用验证的数值方法研究了不同射流停滞压力比和攻角下的三维钝模型。结果表明，迎风侧的再附着冲击增强导致压力和温升升高，从而导致阻力和减热效果恶化。在来流攻角的影响下，再循环漩涡转变为纵向漩涡，导致表面压力系数和斯坦顿数呈斜 U 形分布。增大喷流滞压比扩大了再循环漩涡在迎风面和背风面的覆盖范围，从而改善了阻力和热量的减少。由于再循环漩涡的重新附着和入流的压缩，入流攻角与对向射流之间的相互作用导致斯坦顿数出现双峰分布。倾斜的对向射流可以通过沿迎风面扩散再循环漩涡来降低带攻击角的入流的压力系数和斯坦顿数峰值。应该存在一个最佳倾角，既能有效降低来流压缩造成的峰值，又不会因再循环漩涡重新附着而产生过高的峰值。
{"title":"Angle-of-attack characteristics of opposing jet for improving drag and heat reduction","authors":"Haonan Xu, Xueying Li, Jing Ren","doi":"10.1063/5.0219134","DOIUrl":"https://doi.org/10.1063/5.0219134","url":null,"abstract":"While the opposing jet technique has the potential to achieve efficient drag and heat reduction, it can be severely affected by the incoming angle of attack. To analyze the angle-of-attack characteristics of opposing jet for improving drag and heat reduction, a three-dimensional blunt model was studied under various jet stagnation pressure ratios and angles of attack using the verified numerical method. The results showed that the enhanced reattachment shock on the windward side resulted in a higher pressure and temperature rise, which led to the deterioration of drag and heat reduction. Under the influence of the incoming angle of attack, the recirculation vortex transformed into a longitudinal vortex, resulting in a slanted U-shaped distribution of the surface pressure coefficient and Stanton number. Increasing the jet stagnation pressure ratio widened the coverage of the recirculation vortex on both the windward and leeward sides, which brought an improvement in drag and heat reduction. The interaction between the incoming angle of attack and the opposing jet caused a double-peak distribution of Stanton number due to the recirculation vortex reattachment and the compression of the incoming flow. The inclined opposing jet could reduce the peak values of pressure coefficient and Stanton number when subjected to the incoming flow with an angle of attack by spreading the recirculation vortex along the windward side. There should exist an optimal inclination angle that can effectively reduce the peak caused by the compression of the incoming flow without generating an excessive peak due to the recirculation vortex reattachment.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141706286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Joung-Sook Hong, L. Palodhi, Manoranjan Mishra, Min Chan Kim
We investigate the onset and growth of viscous fingering (VF) of miscible annulus in a radial Hele-Shaw cell. Systematic numerical study on a finite annulus domain is performed by employing finite element method solver in COMSOL Multiphysics software. We justify that concentration field analysis is not a good choice for dynamic study in radial flows. Instead, velocity magnitude is a better tool to understand the dynamics. Therefore, we propose velocity field analysis to better differentiate the stable and unstable states and present a new stability criterion using the velocity field method. Most interestingly, using the velocity field analysis and the new stability criterion, we show a restabilization of the VF at a critical time when the system becomes diffusion dominant and able to provide both the onset time, τon (time at which instability develops), and the time at which the interface returns to the stable state, τd. Furthermore, the study successfully suggests the critical values for several dimensionless parameters, the Péclet number (Pe), log-viscosity ratio (R), and volumetric ratio (ra) and time (τ), to induce instability. When Pe is higher than 103, the evolution of VF instability is no longer enhanced by Pe, and Rc converges to a certain value. In particular, for the transiently unstable system of low Pe, the restabilization of VF instability is identified even though R is higher than Rc. The unstable system (τ>τon) returns to the stable state as injection time increases further. Moreover, we obtained a critical value of the volumetric ratio (rc,a).
我们研究了径向 Hele-Shaw 单元中混溶环的粘性指状（VF）的发生和增长。通过使用 COMSOL Multiphysics 软件中的有限元法求解器，对有限环形域进行了系统的数值研究。我们证明，浓度场分析不是径向流动态研究的最佳选择。相反，速度大小是了解动态的更好工具。因此，我们建议采用速度场分析来更好地区分稳定和不稳定状态，并利用速度场方法提出了一种新的稳定准则。最有趣的是，利用速度场分析和新的稳定性标准，我们显示了 VF 在临界时间的重新稳定，此时系统变得以扩散为主，并能提供起始时间 τon（不稳定状态出现的时间）和界面恢复到稳定状态的时间 τd。此外，研究还成功地提出了几个无量纲参数的临界值，即佩克莱特数（Pe）、对数粘度比（R）、体积比（ra）和时间（τ），以诱发不稳定性。当 Pe 大于 103 时，VF 不稳定性的演变不再受 Pe 的影响，Rc 收敛到一定值。特别是对于低 Pe 的瞬态不稳定系统，即使 R 大于 Rc，也能发现 VF 不稳定的再稳定。随着注入时间的进一步增加，不稳定系统（τ>τon）会恢复到稳定状态。此外，我们还获得了体积比 (rc,a) 的临界值。
{"title":"Onset and growth of viscous fingering in miscible annular ring","authors":"Joung-Sook Hong, L. Palodhi, Manoranjan Mishra, Min Chan Kim","doi":"10.1063/5.0216418","DOIUrl":"https://doi.org/10.1063/5.0216418","url":null,"abstract":"We investigate the onset and growth of viscous fingering (VF) of miscible annulus in a radial Hele-Shaw cell. Systematic numerical study on a finite annulus domain is performed by employing finite element method solver in COMSOL Multiphysics software. We justify that concentration field analysis is not a good choice for dynamic study in radial flows. Instead, velocity magnitude is a better tool to understand the dynamics. Therefore, we propose velocity field analysis to better differentiate the stable and unstable states and present a new stability criterion using the velocity field method. Most interestingly, using the velocity field analysis and the new stability criterion, we show a restabilization of the VF at a critical time when the system becomes diffusion dominant and able to provide both the onset time, τon (time at which instability develops), and the time at which the interface returns to the stable state, τd. Furthermore, the study successfully suggests the critical values for several dimensionless parameters, the Péclet number (Pe), log-viscosity ratio (R), and volumetric ratio (ra) and time (τ), to induce instability. When Pe is higher than 103, the evolution of VF instability is no longer enhanced by Pe, and Rc converges to a certain value. In particular, for the transiently unstable system of low Pe, the restabilization of VF instability is identified even though R is higher than Rc. The unstable system (τ>τon) returns to the stable state as injection time increases further. Moreover, we obtained a critical value of the volumetric ratio (rc,a).","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141694951","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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