A submerged floating tunnel (SFT) is susceptible to significant vibrational responses when subjected to intricate and challenging conditions of the deep-water ocean environment. This is primarily due to the inherent attributes of large flexibility and lower damping exhibited by flexible components of an SFT. To the best of the authors' knowledge, a majority of the current SFT concepts do not completely satisfy the motion-limit values mandated by the relevant standards. In this study, a novel SFT concept is introduced to bolster its vibration suppression capacity through the optimization of the superstructure and substructure by using a three-tube structure and a rigid truss structure, respectively. To evaluate the efficacy of the novel SFT, a comprehensive series of experiments are conducted in a wave-current flume to scrutinize the vibration suppression performance of this novel SFT configuration, juxtaposed against conventional design concepts. The insights are revealed based on a comparative analysis in both the time and frequency domains, encompassing a range of key parameters, and by performing a sensitivity analysis specific to the present model. The results show that the superposition effect of wave and current coupling has a lower impact on the motion response of the proposed SFT with higher mooring stiffness. Despite the increase in cable tension (1–2 times) for the proposed SFT design, the corresponding vibration suppression performance is found to improve by 3–9 times. This experimental investigation holds profound theoretical and engineering significance, as it contributes pivotal knowledge to the field of vibration suppression for the SFT.
{"title":"Experimental study on evaluating hydrodynamic performance of a novel submerged floating tunnel","authors":"Zhiwen Wu, Xiangzhang Meng, Canrong Xie, Yinghong Qin, Ankit Garg, Guoxiong Mei","doi":"10.1063/5.0208351","DOIUrl":"https://doi.org/10.1063/5.0208351","url":null,"abstract":"A submerged floating tunnel (SFT) is susceptible to significant vibrational responses when subjected to intricate and challenging conditions of the deep-water ocean environment. This is primarily due to the inherent attributes of large flexibility and lower damping exhibited by flexible components of an SFT. To the best of the authors' knowledge, a majority of the current SFT concepts do not completely satisfy the motion-limit values mandated by the relevant standards. In this study, a novel SFT concept is introduced to bolster its vibration suppression capacity through the optimization of the superstructure and substructure by using a three-tube structure and a rigid truss structure, respectively. To evaluate the efficacy of the novel SFT, a comprehensive series of experiments are conducted in a wave-current flume to scrutinize the vibration suppression performance of this novel SFT configuration, juxtaposed against conventional design concepts. The insights are revealed based on a comparative analysis in both the time and frequency domains, encompassing a range of key parameters, and by performing a sensitivity analysis specific to the present model. The results show that the superposition effect of wave and current coupling has a lower impact on the motion response of the proposed SFT with higher mooring stiffness. Despite the increase in cable tension (1–2 times) for the proposed SFT design, the corresponding vibration suppression performance is found to improve by 3–9 times. This experimental investigation holds profound theoretical and engineering significance, as it contributes pivotal knowledge to the field of vibration suppression for the SFT.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"196 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141028893","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}
Changliang Ye, Wanru Huang, Hongyeyu Yan, Yuan Zheng, K. Kan, B. V. van Esch
The phenomenon of rotating stall in centrifugal pumps is closely associated with the evolution of the blade boundary layer. Aiming to accurately predict the characteristics of the boundary layer, this study investigates the phenomenon of rotating stall in centrifugal pump impellers using the gamma (γ) transition model. The accuracy of the numerical simulation was confirmed by comparing its conclusions with the results of the testing. In calculations considering transition characteristics, the distribution of low-pressure areas inside the impeller is relatively discontinuous, while the pressure distribution is more uniform. However, in calculations without considering transition, the low-pressure regions in neighboring flow channels exhibit a tendency to be interconnected, resulting in a more variable pressure distribution, and the pressure contour at the outlet is closer to parallel. The dynamic characteristics of the centrifugal pump impeller rotating stall were obtained through the dynamic mode decomposition method, including the frequency, structure, and dynamic evolution process of the stall vortex. Through modal reconstruction, it was discovered that the impeller's rotation causes the stall vortex to undergo periodic fluctuations. The stall vortex is not stationary but moves synchronously with the rotation of the blades. At different time points, the stall vortex exhibits periodic changes. At the blade suction entrance, the stall vortex initially appears. Subsequently, multiple vortex structures resulted in channel blockage. After a period of development, the excess vortex structures merge to generate a typical “8” shaped vortex structure and move toward the exit. Finally, the exit stall vortex disappears, and a new vortex structure is generated at the inlet of the blade suction surface.
{"title":"Study on rotating stall characteristics of centrifugal pumps based on gamma transition model","authors":"Changliang Ye, Wanru Huang, Hongyeyu Yan, Yuan Zheng, K. Kan, B. V. van Esch","doi":"10.1063/5.0206916","DOIUrl":"https://doi.org/10.1063/5.0206916","url":null,"abstract":"The phenomenon of rotating stall in centrifugal pumps is closely associated with the evolution of the blade boundary layer. Aiming to accurately predict the characteristics of the boundary layer, this study investigates the phenomenon of rotating stall in centrifugal pump impellers using the gamma (γ) transition model. The accuracy of the numerical simulation was confirmed by comparing its conclusions with the results of the testing. In calculations considering transition characteristics, the distribution of low-pressure areas inside the impeller is relatively discontinuous, while the pressure distribution is more uniform. However, in calculations without considering transition, the low-pressure regions in neighboring flow channels exhibit a tendency to be interconnected, resulting in a more variable pressure distribution, and the pressure contour at the outlet is closer to parallel. The dynamic characteristics of the centrifugal pump impeller rotating stall were obtained through the dynamic mode decomposition method, including the frequency, structure, and dynamic evolution process of the stall vortex. Through modal reconstruction, it was discovered that the impeller's rotation causes the stall vortex to undergo periodic fluctuations. The stall vortex is not stationary but moves synchronously with the rotation of the blades. At different time points, the stall vortex exhibits periodic changes. At the blade suction entrance, the stall vortex initially appears. Subsequently, multiple vortex structures resulted in channel blockage. After a period of development, the excess vortex structures merge to generate a typical “8” shaped vortex structure and move toward the exit. Finally, the exit stall vortex disappears, and a new vortex structure is generated at the inlet of the blade suction surface.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"169 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141039990","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}
P. Valentini, Maninder S. Grover, Nicholas J. Bisek
The alternative interpretation of Stokes' hypothesis provided by Buresti [Acta Mech. 226, 3555–3559 (2015)] is investigated by an analysis of a near-continuum, hypersonic flow of oxygen over a double cone obtained from a large-scale direct simulation Monte Carlo computation. We show that for molecular oxygen, which has comparable bulk and shear viscosity coefficients, the difference between mechanical and thermodynamic pressure is negligible throughout most of the flow. This result justifies neglecting viscous stresses in the normal stress tensor associated with fluid particle dilatation, as is often done in continuum descriptions of compressible flows. The violation of the revisited Stokes' hypothesis was only observed in highly nonequilibrium regions of the flow (shocks and strong expansions) and wherever non-continuum effects become significant. For nonequilibrium flows of gases with large bulk viscosity relative to their shear viscosity, the revisited Stokes' assumption may still breakdown and requires further investigation.
{"title":"Validity of Stokes' hypothesis for near-continuum hypersonic flows","authors":"P. Valentini, Maninder S. Grover, Nicholas J. Bisek","doi":"10.1063/5.0206817","DOIUrl":"https://doi.org/10.1063/5.0206817","url":null,"abstract":"The alternative interpretation of Stokes' hypothesis provided by Buresti [Acta Mech. 226, 3555–3559 (2015)] is investigated by an analysis of a near-continuum, hypersonic flow of oxygen over a double cone obtained from a large-scale direct simulation Monte Carlo computation. We show that for molecular oxygen, which has comparable bulk and shear viscosity coefficients, the difference between mechanical and thermodynamic pressure is negligible throughout most of the flow. This result justifies neglecting viscous stresses in the normal stress tensor associated with fluid particle dilatation, as is often done in continuum descriptions of compressible flows. The violation of the revisited Stokes' hypothesis was only observed in highly nonequilibrium regions of the flow (shocks and strong expansions) and wherever non-continuum effects become significant. For nonequilibrium flows of gases with large bulk viscosity relative to their shear viscosity, the revisited Stokes' assumption may still breakdown and requires further investigation.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"70 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141045679","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}
Hydraulic fracturing enables effective exploitation of deep coalbed methane. During the hydraulic fracturing process, high salinity flowback fluid is generated, and this poses a significant challenge for water treatment. Therefore, we investigate the effect of hydraulic fracturing on ion migration in deep coal seams and its underlying mechanisms. In this study, nuclear magnetic resonance, inductively coupled plasma mass spectrometry, scanning electron microscopy, and energy dispersive x-ray spectroscopy were utilized to systematically study the diffusion behavior of ions and its correlation with water imbibition. Our results show that imbibition equilibrium was reached before ion diffusion finished. Ion diffusion displays three linear stages followed by a plateau part, and the second segment is the fastest one. The water–coal interactions result in the diffusion of ions into solution, with the most significant increases in Ca2+, Mg2+, Na+, K+, Li+, Cu2+, V5+, Hg2+, Pb2+, B3+, Mo6+, Cr3+, Sn4+, Cd2+, Cs+, Sr2+, and Ba2+. The dissolution of calcite, sodium feldspar, and kaolinite are the main contributions for ion migration. In addition, these reactions not only cause the release of ions into the solution but also lead to the formation of secondary pore-fractures and secondary precipitation. The results of this work help to understand better the ion migration induced by the water–coal interaction and to evaluate the fluid properties in deep coal formations.
水力压裂法能够有效开采深层煤层气。在水力压裂过程中会产生高盐度的回流液，这给水处理带来了巨大挑战。因此，我们研究了水力压裂对深部煤层离子迁移的影响及其内在机制。本研究利用核磁共振、电感耦合等离子体质谱法、扫描电子显微镜和能量色散 X 射线光谱法系统研究了离子的扩散行为及其与水浸润的相关性。研究结果表明，在离子扩散完成之前，水的浸润已达到平衡。离子扩散表现为三个线性阶段，之后是一个高原部分，第二段扩散速度最快。水-煤相互作用导致离子扩散到溶液中，其中以 Ca2+、Mg2+、Na+、K+、Li+、Cu2+、V5+、Hg2+、Pb2+、B3+、Mo6+、Cr3+、Sn4+、Cd2+、Cs+、Sr2+ 和 Ba2+ 的增加最为显著。方解石、钠长石和高岭石的溶解是离子迁移的主要原因。此外，这些反应不仅会导致离子释放到溶液中，还会形成二次孔隙裂缝和二次沉淀。这项工作的结果有助于更好地理解水煤相互作用引起的离子迁移，并评估深部煤层的流体性质。
{"title":"Ion migration effects during hydro-fracturing of deep high salinity coal seam","authors":"Ruying Ma, Yanbin Yao, Dong Feng, Hao Wu, Veerle Vandeginste, Zefan Wang, Xiaona Zhang","doi":"10.1063/5.0206794","DOIUrl":"https://doi.org/10.1063/5.0206794","url":null,"abstract":"Hydraulic fracturing enables effective exploitation of deep coalbed methane. During the hydraulic fracturing process, high salinity flowback fluid is generated, and this poses a significant challenge for water treatment. Therefore, we investigate the effect of hydraulic fracturing on ion migration in deep coal seams and its underlying mechanisms. In this study, nuclear magnetic resonance, inductively coupled plasma mass spectrometry, scanning electron microscopy, and energy dispersive x-ray spectroscopy were utilized to systematically study the diffusion behavior of ions and its correlation with water imbibition. Our results show that imbibition equilibrium was reached before ion diffusion finished. Ion diffusion displays three linear stages followed by a plateau part, and the second segment is the fastest one. The water–coal interactions result in the diffusion of ions into solution, with the most significant increases in Ca2+, Mg2+, Na+, K+, Li+, Cu2+, V5+, Hg2+, Pb2+, B3+, Mo6+, Cr3+, Sn4+, Cd2+, Cs+, Sr2+, and Ba2+. The dissolution of calcite, sodium feldspar, and kaolinite are the main contributions for ion migration. In addition, these reactions not only cause the release of ions into the solution but also lead to the formation of secondary pore-fractures and secondary precipitation. The results of this work help to understand better the ion migration induced by the water–coal interaction and to evaluate the fluid properties in deep coal formations.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"56 19","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141043041","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}
Yunzhen Zhang, Miao Cheng, Xiangyang Liu, Guangyao Rong, Zhaohua Sheng, D. Shen, Kewen Wu, Jianping Wang
With the rotating detonation engine's (RDE) development to engineering applications, the selection and optimization of nozzle is garnering great concerns, with the aim to maximize the performance benefits of this pressure gain propulsion system. The present study represents the first effort to explore the distinct impacts of two commonly used nozzles in RDE, namely, the plug nozzle and the Laval nozzle, on the internal flow and performance within the combustion chamber. Three-dimensional numerical simulations are conducted on non-premixed annular RDEs with plug nozzles and Laval nozzles. It is found that the Laval nozzle induces a forward-leaning wavefront structure in the combustion chamber. Furthermore, the overall pressure gain of the RDE is divided into the injection pressure loss, the average pressure gain at the chamber bottom, and the flow losses downstream, by combining the wavefront coordinate averaged flow field, which is proposed and applied in this study, and laboratory coordinate averaged flow field. The results show that, for the performance of the combustion chamber, while Laval nozzles enhance pressure gains at the chamber bottom and reduce exit flow non-uniformity, they also increase downstream losses. By comparing the RDE performance with the ideal performance of deflagration-based combustors, it is found that the premixed control group exceeded the deflagration ideal performance by 30%. Despite lower combustion efficiency, non-premixed configurations nearly match the ideal deflagration performance, underscoring the inherent advantages of RDEs.
{"title":"The influence of plug nozzle and Laval nozzle on the flow field and performance of non-premixed rotating detonation combustor","authors":"Yunzhen Zhang, Miao Cheng, Xiangyang Liu, Guangyao Rong, Zhaohua Sheng, D. Shen, Kewen Wu, Jianping Wang","doi":"10.1063/5.0207508","DOIUrl":"https://doi.org/10.1063/5.0207508","url":null,"abstract":"With the rotating detonation engine's (RDE) development to engineering applications, the selection and optimization of nozzle is garnering great concerns, with the aim to maximize the performance benefits of this pressure gain propulsion system. The present study represents the first effort to explore the distinct impacts of two commonly used nozzles in RDE, namely, the plug nozzle and the Laval nozzle, on the internal flow and performance within the combustion chamber. Three-dimensional numerical simulations are conducted on non-premixed annular RDEs with plug nozzles and Laval nozzles. It is found that the Laval nozzle induces a forward-leaning wavefront structure in the combustion chamber. Furthermore, the overall pressure gain of the RDE is divided into the injection pressure loss, the average pressure gain at the chamber bottom, and the flow losses downstream, by combining the wavefront coordinate averaged flow field, which is proposed and applied in this study, and laboratory coordinate averaged flow field. The results show that, for the performance of the combustion chamber, while Laval nozzles enhance pressure gains at the chamber bottom and reduce exit flow non-uniformity, they also increase downstream losses. By comparing the RDE performance with the ideal performance of deflagration-based combustors, it is found that the premixed control group exceeded the deflagration ideal performance by 30%. Despite lower combustion efficiency, non-premixed configurations nearly match the ideal deflagration performance, underscoring the inherent advantages of RDEs.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"10 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141048219","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}
We investigate the influence of streamwise-elongated and spanwise-periodic roughness arrays on the supersonic boundary-layer instability under the assumption of a high Reynolds number. The main focus is on the lower-branch viscous instability modes, and the spanwise spacing of the roughness arrays is taken to be comparable to the characteristic wavelength of the modes (which is on the triple-deck scale), so that most significant effects can be generated. The streamwise length scale of the elements is much greater than the spanwise length scale. The roughness height is determined by requiring the change of the wall shear to be O(1). The equations governing the nonlinear roughness-induced streaky flow are deduced from the standard triple-deck theory. These equations are parabolic in the streamwise direction and are solved using a streamwise marching method to characterize the evolution of streaky structures. The linear stability of the streaky flow is analyzed. By exploiting the asymptotic structure, the bi-global eigenvalue problem is reduced to a one-dimensional one, where the stability is found to be controlled by the spanwise-dependent wall shear. The reduced eigenvalue problem is solved numerically. The results show that roughness arrays inhibit instability modes with moderate frequencies but promote high-frequency modes. Roughness elements of greater height have stronger effects on the linear stability. The shape of roughness elements plays an important role. A significant feature, different from the subsonic case, is that fundamental and superharmonic resonance modes radiate sound waves spontaneously into the far field.
{"title":"Effects of streamwise-elongated and spanwise-periodic surface roughness arrays on supersonic boundary-layer instability","authors":"Jianing Zheng, Xuesong Wu","doi":"10.1063/5.0203025","DOIUrl":"https://doi.org/10.1063/5.0203025","url":null,"abstract":"We investigate the influence of streamwise-elongated and spanwise-periodic roughness arrays on the supersonic boundary-layer instability under the assumption of a high Reynolds number. The main focus is on the lower-branch viscous instability modes, and the spanwise spacing of the roughness arrays is taken to be comparable to the characteristic wavelength of the modes (which is on the triple-deck scale), so that most significant effects can be generated. The streamwise length scale of the elements is much greater than the spanwise length scale. The roughness height is determined by requiring the change of the wall shear to be O(1). The equations governing the nonlinear roughness-induced streaky flow are deduced from the standard triple-deck theory. These equations are parabolic in the streamwise direction and are solved using a streamwise marching method to characterize the evolution of streaky structures. The linear stability of the streaky flow is analyzed. By exploiting the asymptotic structure, the bi-global eigenvalue problem is reduced to a one-dimensional one, where the stability is found to be controlled by the spanwise-dependent wall shear. The reduced eigenvalue problem is solved numerically. The results show that roughness arrays inhibit instability modes with moderate frequencies but promote high-frequency modes. Roughness elements of greater height have stronger effects on the linear stability. The shape of roughness elements plays an important role. A significant feature, different from the subsonic case, is that fundamental and superharmonic resonance modes radiate sound waves spontaneously into the far field.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"5 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141034632","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}
Wuguang Chen, Guangyuan Huang, Yu Song, Junlian Yin, Dezhong Wang
The mechanism of turbulence modulation by bubbles is crucial for understanding and predicting turbulent bubbly flow. In this study, we conducted an experimental investigation of turbulence modulation by bubbles of different sizes in homogeneous isotropic turbulence using two-phase stereo-particle image velocimetry measurement techniques. Two bubble generation methods, electrolysis and porous medium, were employed to generate bubbles in micrometer and millimeter sizes, respectively. The oscillating grid system was utilized to generate homogeneous isotropic turbulence, allowing precise control of turbulent boundary conditions. The ratio of the fluctuating velocities and the comparison between turbulent kinetic energy and average kinetic energy indicated that the generated turbulence was nearly homogeneous and isotropic. With increasing turbulence intensity, micron-sized bubbles transition from suppressing turbulence to enhancing it, while millimeter-sized bubbles exhibit the opposite behavior. Turbulence modulation by millimeter-sized bubbles appears to be nearly isotropic, whereas micrometer-sized bubbles do not exhibit isotropy.
{"title":"Experimental study on modulation of homogeneous isotropic turbulence by bubbles of different sizes","authors":"Wuguang Chen, Guangyuan Huang, Yu Song, Junlian Yin, Dezhong Wang","doi":"10.1063/5.0208461","DOIUrl":"https://doi.org/10.1063/5.0208461","url":null,"abstract":"The mechanism of turbulence modulation by bubbles is crucial for understanding and predicting turbulent bubbly flow. In this study, we conducted an experimental investigation of turbulence modulation by bubbles of different sizes in homogeneous isotropic turbulence using two-phase stereo-particle image velocimetry measurement techniques. Two bubble generation methods, electrolysis and porous medium, were employed to generate bubbles in micrometer and millimeter sizes, respectively. The oscillating grid system was utilized to generate homogeneous isotropic turbulence, allowing precise control of turbulent boundary conditions. The ratio of the fluctuating velocities and the comparison between turbulent kinetic energy and average kinetic energy indicated that the generated turbulence was nearly homogeneous and isotropic. With increasing turbulence intensity, micron-sized bubbles transition from suppressing turbulence to enhancing it, while millimeter-sized bubbles exhibit the opposite behavior. Turbulence modulation by millimeter-sized bubbles appears to be nearly isotropic, whereas micrometer-sized bubbles do not exhibit isotropy.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"65 s254","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141134079","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}
New exact solutions of the Charney–Obukhov equation for the ocean are obtained in the form of a partial superposition of elementary solutions with different wave numbers. The boundary conditions for the ocean are satisfied due to the presence of a carrier zonal flow in the solution. The existing arbitrariness in the choice of wave numbers and other solution parameters makes it possible to simulate an arbitrary stream function profile at a fixed ocean depth on an interval of a fixed length using a Fourier series or in a circle of a fixed radius using a Fourier–Bessel series. An example of modeling a Gaussian stream function profile on the ocean surface in the presence of circular symmetry is considered.
{"title":"Modeling ocean eddies using exact solutions of the Charney–Obukhov equation","authors":"A. Kudryavtsev, N. Myagkov","doi":"10.1063/5.0213276","DOIUrl":"https://doi.org/10.1063/5.0213276","url":null,"abstract":"New exact solutions of the Charney–Obukhov equation for the ocean are obtained in the form of a partial superposition of elementary solutions with different wave numbers. The boundary conditions for the ocean are satisfied due to the presence of a carrier zonal flow in the solution. The existing arbitrariness in the choice of wave numbers and other solution parameters makes it possible to simulate an arbitrary stream function profile at a fixed ocean depth on an interval of a fixed length using a Fourier series or in a circle of a fixed radius using a Fourier–Bessel series. An example of modeling a Gaussian stream function profile on the ocean surface in the presence of circular symmetry is considered.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":" 45","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141131568","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}
Unsteady three-dimensional simulations are performed to elucidate the hidden transitional flow dynamics and Hopf bifurcations along the topological corelines of the created von Kármán streets behind a pair of square cylinders positioned in tandem. Our simulations provide significant new insight into the three-dimensional wake evolution and governing flow physics. We explain how pressure, velocity, and vorticity fluctuation along the Kármán vortex corelines in the increasingly unstable wake amplify, facilitating the growth of various modal instability patterns. The existing knowledge of wake transition through the intertwining of modes A, B, and C instabilities and associated linear stability analysis helped to gain some insight into the overall wake feature. The current study explains how exactly the transitional disturbances physically spread behind a pair of inline and tandem cylinders through the self-excited spanwise-periodic oscillation of the wake and created a sequence of variable length scaled Hopf bifurcations and their swapping for varied gaps between the cylinders and Reynolds number. The growth of a slow mode of the spectral frequency at the bifurcation points seemed crucial in initiating the near-transitional flow irregularity.
我们进行了非稳态三维模拟，以阐明隐藏的过渡流动力学和沿一对串联放置的方形圆柱体后方所形成的 von Kármán 街道拓扑核心线的霍普夫分岔。我们的模拟对三维尾流演化和流动物理学提供了重要的新见解。我们解释了在越来越不稳定的尾流中，沿着卡曼涡旋核心线的压力、速度和涡度波动是如何放大的，从而促进了各种模态不稳定模式的增长。现有的关于通过模式 A、B 和 C 不稳定性交织实现唤醒过渡的知识以及相关的线性稳定性分析有助于深入了解唤醒的整体特征。目前的研究解释了过渡扰动如何通过唤醒的自激跨度周期振荡在一对直列和串联气缸后面进行物理扩散，并在气缸之间的间隙和雷诺数不同的情况下产生一系列长度可变的霍普夫分岔及其交换。分岔点频谱频率慢模的增长似乎是引发近过渡流不规则现象的关键。
{"title":"The onset of instability and bifurcations in the transitional wake of two tandem square cylinders","authors":"Kai Dong, A. Sau","doi":"10.1063/5.0189711","DOIUrl":"https://doi.org/10.1063/5.0189711","url":null,"abstract":"Unsteady three-dimensional simulations are performed to elucidate the hidden transitional flow dynamics and Hopf bifurcations along the topological corelines of the created von Kármán streets behind a pair of square cylinders positioned in tandem. Our simulations provide significant new insight into the three-dimensional wake evolution and governing flow physics. We explain how pressure, velocity, and vorticity fluctuation along the Kármán vortex corelines in the increasingly unstable wake amplify, facilitating the growth of various modal instability patterns. The existing knowledge of wake transition through the intertwining of modes A, B, and C instabilities and associated linear stability analysis helped to gain some insight into the overall wake feature. The current study explains how exactly the transitional disturbances physically spread behind a pair of inline and tandem cylinders through the self-excited spanwise-periodic oscillation of the wake and created a sequence of variable length scaled Hopf bifurcations and their swapping for varied gaps between the cylinders and Reynolds number. The growth of a slow mode of the spectral frequency at the bifurcation points seemed crucial in initiating the near-transitional flow irregularity.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"44 34","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141142405","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}
Jiale Liu, Bosheng Pang, Teng Wang, Lijun Yang, Jingxuan Li
Thermoacoustic instability typically presents in the operation of various engines and is harmful. It is thus necessary to investigate the influence mechanisms on it. When the effect of natural convection caused by buoyancy is equivalent to that of forced convection, the buoyancy effect will have a significant effect on the thermoacoustic instability. In order to study these effects, an electrically heated Rijke tube with adjustable pitch angle was designed. By adjusting the pitch angle under different operating conditions, the instability map as the functions of flow rates and heating powers was obtained. As the temperature field within the Rijke tube varies greatly at different pitch angles, its effect was also investigated associated with the numerical simulation. The results showed that the growth rates of the thermoacoustic instability exhibited a sinusoidal-like dependence on the pitch angle under certain operating conditions. This variation relationship only occurs when the Richardson number is sufficiently large.
{"title":"Investigation of the buoyancy effect on the thermoacoustic instability in an electrically heated Rijke tube","authors":"Jiale Liu, Bosheng Pang, Teng Wang, Lijun Yang, Jingxuan Li","doi":"10.1063/5.0207217","DOIUrl":"https://doi.org/10.1063/5.0207217","url":null,"abstract":"Thermoacoustic instability typically presents in the operation of various engines and is harmful. It is thus necessary to investigate the influence mechanisms on it. When the effect of natural convection caused by buoyancy is equivalent to that of forced convection, the buoyancy effect will have a significant effect on the thermoacoustic instability. In order to study these effects, an electrically heated Rijke tube with adjustable pitch angle was designed. By adjusting the pitch angle under different operating conditions, the instability map as the functions of flow rates and heating powers was obtained. As the temperature field within the Rijke tube varies greatly at different pitch angles, its effect was also investigated associated with the numerical simulation. The results showed that the growth rates of the thermoacoustic instability exhibited a sinusoidal-like dependence on the pitch angle under certain operating conditions. This variation relationship only occurs when the Richardson number is sufficiently large.","PeriodicalId":509470,"journal":{"name":"Physics of Fluids","volume":"48 21","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141142302","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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