{"title":"Effect of radius ratio on the sheared annular centrifugal turbulent convection","authors":"Jun Zhong, Junyi Li, Chao Sun","doi":"10.1017/jfm.2024.543","DOIUrl":"https://doi.org/10.1017/jfm.2024.543","url":null,"abstract":"We perform linear stability analysis and direct numerical simulations to study the effect of the radius ratio on the instability and flow characteristics of the sheared annular centrifugal Rayleigh–Bénard convection, where the cold inner cylinder and the hot outer cylinder rotate with a small angular velocity difference. With the shear enhancement, the thermal convection is suppressed and finally becomes stable for different radius ratios <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005433_inline1.png\"/> <jats:tex-math>${eta in mathbb {R}|0.2leqslant eta le 0.95}$</jats:tex-math> </jats:alternatives> </jats:inline-formula>. Considering the inhomogeneous distribution of shear stresses in the base flow, a new global Richardson number <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005433_inline2.png\"/> <jats:tex-math>$Ri_g$</jats:tex-math> </jats:alternatives> </jats:inline-formula> is defined and the marginal-state curves for different radius ratios are successfully unified in the parameter domain of <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005433_inline3.png\"/> <jats:tex-math>$Ri_g$</jats:tex-math> </jats:alternatives> </jats:inline-formula> and the Rayleigh number <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005433_inline4.png\"/> <jats:tex-math>$Ra$</jats:tex-math> </jats:alternatives> </jats:inline-formula>. The results are consistent with the marginal-state curve of the wall-sheared classical Rayleigh–Bénard convection in the streamwise direction, demonstrating that the basic stabilization mechanisms are identical. Moreover, systems with small radius ratios exhibit greater geometric asymmetry. On the one hand, this results in a smaller equivalent aspect ratio for the system, accommodating fewer convection roll pairs; fewer roll pairs are more likely to cause a transition in the flow structure during shear enhancement. On the other hand, the shear distribution is more inhomogeneous, allowing for an outward shift of the convection region and the elevation of bulk temperature under strong shear.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"23 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256262","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}
{"title":"Decay rate of homogeneous isotropic turbulence laden with finite-size particles","authors":"Qichao Sun, Cheng Peng, Lian-Ping Wang, Songying Chen, Zuchao Zhu","doi":"10.1017/jfm.2024.698","DOIUrl":"https://doi.org/10.1017/jfm.2024.698","url":null,"abstract":"This study conducts particle-resolved direct numerical simulations to analyse how finite-size spherical particles affect the decay rate of turbulent kinetic energy in non-sustained homogeneous isotropic turbulence. The decaying particle-laden homogeneous isotropic turbulence is generated with two set-ups, i.e. (1) releasing particles into a single-phase decaying homogeneous isotropic turbulence and (2) switching off the driving force of a sustained particle-laden homogeneous isotropic turbulence. With both set-ups, the decay of turbulent kinetic energy follows a power-law when the flow is fully relaxed, similar to their single-phase counterparts. The dependence of the power-law decay exponent <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024006980_inline1.png\"/> <jats:tex-math>$n$</jats:tex-math> </jats:alternatives> </jats:inline-formula> on the particle-to-fluid density ratio, particle size and volume fraction is also investigated, and a predictive model is developed. We find that the presence of heavier particles slows down the long-time power-law decay exponent.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"203 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256278","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}
{"title":"Experimental investigation on magneto-convective flows around two differentially heated horizontal cylinders","authors":"Cyril Courtessole, H.-J. Brinkmann, L. Bühler","doi":"10.1017/jfm.2024.591","DOIUrl":"https://doi.org/10.1017/jfm.2024.591","url":null,"abstract":"Liquid metal buoyant flow around two differentially heated horizontal cylinders in the presence of a uniform vertical magnetic field is investigated experimentally. While magneto-convection in pipes or ducts has been studied theoretically and experimentally in recent years, data for heat transfer at immersed obstacles are rare and, to our knowledge, detailed experimental investigations on this fundamental magnetohydrodynamic problem do not exist. In the present work, two horizontal cylinders inserted into an adiabatic rectangular cavity filled with gallium–indium–tin are kept at constant temperatures to establish a driving temperature gradient in the surrounding liquid metal. The buoyancy-driven flow, quantified by the Grashof number <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005913_inline1.png\"/> <jats:tex-math>$Gr$</jats:tex-math> </jats:alternatives> </jats:inline-formula>, is varied in the range <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005913_inline2.png\"/> <jats:tex-math>${10^{6} leq Gr leq ~5times 10^{7}}$</jats:tex-math> </jats:alternatives> </jats:inline-formula>. With increasing magnetic field, expressed via the Hartmann number <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005913_inline3.png\"/> <jats:tex-math>$Ha$</jats:tex-math> </jats:alternatives> </jats:inline-formula>, different flow regimes are identified from measurements for <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005913_inline4.png\"/> <jats:tex-math>$0 leq Ha leq ~3000$</jats:tex-math> </jats:alternatives> </jats:inline-formula>. The effect of the electromagnetic force primarily consists in suppressing turbulence and damping the convective flow. The heat transfer is quantified in terms of the non-dimensional Nusselt number <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005913_inline5.png\"/> <jats:tex-math>$Nu$</jats:tex-math> </jats:alternatives> </jats:inline-formula>, and its dependence on <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S0022112024005913_inline6.png\"/> <jats:tex-math>$Gr/{Ha}^{2}$</jats:tex-math> </jats:alternatives> </jats:inline-formula>, which is identified as the important group governing the flow, is discussed.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"13 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256279","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}
{"title":"Magnetohydrodynamic flow control in Hele-Shaw cells","authors":"Kyle I. McKee","doi":"10.1017/jfm.2024.618","DOIUrl":"https://doi.org/10.1017/jfm.2024.618","url":null,"abstract":"Consider the motion of a thin layer of electrically conducting fluid, between two closely spaced parallel plates, in a classical Hele-Shaw geometry. Furthermore, let the system be immersed in a uniform external magnetic field (normal to the plates) and let electrical current be driven between conducting probes immersed in the fluid layer. In the present paper, we analyse the ensuing fluid flow at low Hartmann numbers. Physically, the system is particularly interesting because it allows for circulation in the flow, which is not possible in the standard pressure-driven Hele-Shaw cell. We first elucidate the mechanism of flow generation both physically and mathematically. After formulating the problem using complex variables, we present mathematical solutions for a class of canonical multiply connected geometries in terms of the prime function framework developed by Crowdy (<jats:italic>Solving Problems in Multiply Connected Domains</jats:italic>, SIAM, 2020). We then demonstrate how recently developed fast numerical methods may be applied to accurately determine the flow field in arbitrary geometries.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"54 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256256","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}
{"title":"Relative dispersion in free-surface turbulence","authors":"Yaxing Li, Yifan Wang, Yinghe Qi, Filippo Coletti","doi":"10.1017/jfm.2024.637","DOIUrl":"https://doi.org/10.1017/jfm.2024.637","url":null,"abstract":"We report on an experimental study in which Lagrangian tracking is applied to millions of microscopic particles floating on the free surface of turbulent water. We leverage a large jet-stirred zero-mean-flow apparatus, where the Reynolds number is sufficiently high for an inertial range to emerge while the surface deformation remains minimal. Two-point statistics reveal specific features of the flow, deviating from the classic description derived for incompressible turbulence. The magnitude of the relative velocity is strongly intermittent, especially at small separations, leading to anomalous scaling of the second-order structure functions in the dissipative range. This is driven by the divergent component of the flow, leading to fast approaching/separation rates of nearby particles. The Lagrangian relative velocity shows strong persistence of the initial state, such that the ballistic pair separation extends to the inertial range of time delays. Based on these observations, we propose a classification of particle pairs based on their initial separation rate. When this is much smaller than the relative velocity prescribed by inertial scaling (which is the case for the majority of the observed particle pairs), the relative velocity transitions to a diffusive growth and the Richardson–Obukhov super-diffusive dispersion is recovered.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"16 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256261","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}
{"title":"Swimming efficiently by wrapping","authors":"H. Gidituri, M. Ellero, F. Balboa Usabiaga","doi":"10.1017/jfm.2024.594","DOIUrl":"https://doi.org/10.1017/jfm.2024.594","url":null,"abstract":"Single-flagellated bacteria are ubiquitous in nature. They exhibit various swimming modes using their flagella to explore complex surroundings such as soil and porous polymer networks. Some single-flagellated bacteria swim with two distinct modes, one with the flagellum extended away from its body and another with the flagellum wrapped around it. The wrapped mode has been observed when bacteria swim under tight confinements or in highly viscous polymeric melts. In this study we investigate the hydrodynamics of these two modes inside a circular pipe. We find that the wrapped mode is slower than the extended mode in bulk but more efficient under strong confinement due to a hydrodynamic increase of its flagellum translation–rotation coupling and an Archimedes’ screw-like configuration that helps to move the fluid along the pipe.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"31 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256282","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}
Lei Ren, Xin Tao, Lu Zhang, Ke-Qing Xia, Yi-Chao Xie
{"title":"Heat transport in liquid metal convection from onset to turbulence: the effect of small aspect ratio","authors":"Lei Ren, Xin Tao, Lu Zhang, Ke-Qing Xia, Yi-Chao Xie","doi":"10.1017/jfm.2024.630","DOIUrl":"https://doi.org/10.1017/jfm.2024.630","url":null,"abstract":"We present a systematic study on the effects of small aspect ratios <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline1.png\"/> <jats:tex-math>$varGamma$</jats:tex-math> </jats:alternatives> </jats:inline-formula> on heat transport in liquid metal convection with a Prandtl number of <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline2.png\"/> <jats:tex-math>$Pr=0.029$</jats:tex-math> </jats:alternatives> </jats:inline-formula>. The study covers <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline3.png\"/> <jats:tex-math>$1/20le varGamma le 1$</jats:tex-math> </jats:alternatives> </jats:inline-formula> experimentally and <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline4.png\"/> <jats:tex-math>$1/50le varGamma le 1$</jats:tex-math> </jats:alternatives> </jats:inline-formula> numerically, and a Rayleigh number <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline5.png\"/> <jats:tex-math>$Ra$</jats:tex-math> </jats:alternatives> </jats:inline-formula> range of <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline6.png\"/> <jats:tex-math>$4times 10^3 le Ra le 7times 10^{9}$</jats:tex-math> </jats:alternatives> </jats:inline-formula>. It is found experimentally that the local effective heat transport scaling exponent <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline7.png\"/> <jats:tex-math>$gamma$</jats:tex-math> </jats:alternatives> </jats:inline-formula> changes with both <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline8.png\"/> <jats:tex-math>$Ra$</jats:tex-math> </jats:alternatives> </jats:inline-formula> and <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline9.png\"/> <jats:tex-math>$varGamma$</jats:tex-math> </jats:alternatives> </jats:inline-formula>, attaining a <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S002211202400630X_inline10.png\"/> <jats:tex-math>$varGamma$</jats:tex-math> </jats:alternatives> </jats:inline-formula>-dependent maximum value before transition-to-turbulence and appro","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"75 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256255","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}
{"title":"Multiple stable postures of a falling object in fluids","authors":"Shuyue Sun, Xinliang Tian, Yakun Zhao, Xing Chen, Binrong Wen, Xiantao Zhang, Xin Li","doi":"10.1017/jfm.2024.557","DOIUrl":"https://doi.org/10.1017/jfm.2024.557","url":null,"abstract":"We present evidence revealing that an object with specific properties can exhibit multiple stable falling postures at low Reynolds numbers. By scrutinizing the force equilibrium relationship of a fixed object at various attack angles and Reynolds numbers, we introduce a methodology that can obtain the stable falling postures of the object. This method saves computational resources and more intuitively presents the results in the full parameter domain. Our findings are substantiated by free-fall tests conducted through both physical experiments and numerical simulations, which validate the existence of multiple stable solutions in accordance with the interpolation results obtained with fixed objects. Additionally, we quantify the abundance and distribution patterns of stable falling postures for a diverse range of representative shapes. This discovery highlights the existence of multiple stable solutions that are universally present across objects of different shapes. The implications of this research extend to the design, stability control and trajectory prediction of all free and controlled flights in both air and water.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"8 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256264","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}