Journal of Fluid Mechanics最新文献_第3页

Negative available potential energy dissipation as the fundamental criterion for double diffusive instabilities 负可用势能耗散是双重扩散不稳定性的基本标准

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-18 DOI: 10.1017/jfm.2024.647

R. Tailleux

{"title":"Negative available potential energy dissipation as the fundamental criterion for double diffusive instabilities","authors":"R. Tailleux","doi":"10.1017/jfm.2024.647","DOIUrl":"https://doi.org/10.1017/jfm.2024.647","url":null,"abstract":"The background potential energy (BPE) is the only reservoir that double diffusive instabilities can tap their energy from when developing from an unforced motionless state with no available potential energy (APE). Recently, Middleton and Taylor linked the extraction of BPE into APE to the sign of the diapycnal component of the buoyancy flux, but their criterion can predict only diffusive convection instability, not salt finger instability. Here, we show that the problem can be corrected if the sign of the APE dissipation rate is used instead, making it emerge as the most fundamental criterion for double diffusive instabilities. A theory for the APE dissipation rate for a two-component fluid relative to its single-component counterpart is developed as a function of three parameters: the diffusivity ratio, the density ratio, and a spiciness parameter. The theory correctly predicts the occurrence of both salt finger and diffusive convection instabilities in the laminar unforced regime, while more generally predicting that the APE dissipation rate for a two-component fluid can be enhanced, suppressed, or even have the opposite sign compared to that for a single-component fluid, with important implications for the study of ocean mixing. Because negative APE dissipation can also occur in stably stratified single-component and doubly stable two-component stratified fluids, we speculate that only the thermodynamic theory of exergy can explain its physics; however, this necessitates accepting that APE dissipation is a conversion between APE and the internal energy component of BPE, in contrast to prevailing assumptions.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"16 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256215","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}

引用次数: 0

Influence of outer large-scale motions on near-wall structures in compressible turbulent channel flows 外层大尺度运动对可压缩湍流通道流近壁结构的影响

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-18 DOI: 10.1017/jfm.2024.755

Zisong Zhou, Yixiao Wang, Shuohan Zhang, Wei-Xi Huang, Chun-Xiao Xu

{"title":"Influence of outer large-scale motions on near-wall structures in compressible turbulent channel flows","authors":"Zisong Zhou, Yixiao Wang, Shuohan Zhang, Wei-Xi Huang, Chun-Xiao Xu","doi":"10.1017/jfm.2024.755","DOIUrl":"https://doi.org/10.1017/jfm.2024.755","url":null,"abstract":"The influence of outer large-scale motions (LSMs) on near-wall structures in compressible turbulent channel flows is investigated. To separate the compressibility effects, velocity fluctuations are decomposed into solenoidal and dilatational components using the Helmholtz decomposition method. Solenoidal velocity fluctuations manifest as near-wall streaks and outer large-scale structures. The spanwise drifting of near-wall solenoidal streaks is found to be driven by the outer LSMs, while LSMs have a trivial influence on the spanwise density of solenoidal streaks, consistent with the outer LSM impacts found in incompressible flows (Zhou et al., J. Fluid Mech., vol. 940, 2022, p. A23). Dilatational motions are characterized by the near-wall small-scale travelling-wave packets and the large-scale parts in the outer region. The streamwise advection velocity of the near-wall structures remains at $16 sim 18u_{tau }$ , hardly influenced by Mach numbers, Reynolds numbers and wall temperatures. The spanwise drifting of near-wall dilatational structures, quantified by the particle image velocimetry method, follows a mechanism distinct from solenoidal streaks. This drifting velocity is notably larger than those of the solenoidal streaks, and the influence of outer LSMs is not the primary trigger for this drifting.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"16 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256225","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}

引用次数: 0

Resurrection of a superhydrophobic cylinder impacting onto liquid bath 超疏水性圆柱体撞击液槽后复活

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-18 DOI: 10.1017/jfm.2024.691

Wanqiu Zhang, Yaochen Mei, Chenyu Fu, Xinping Zhou

{"title":"Resurrection of a superhydrophobic cylinder impacting onto liquid bath","authors":"Wanqiu Zhang, Yaochen Mei, Chenyu Fu, Xinping Zhou","doi":"10.1017/jfm.2024.691","DOIUrl":"https://doi.org/10.1017/jfm.2024.691","url":null,"abstract":"An interesting resurrection phenomenon (including the initial complete submersion, subsequent resurfacing and final rebounding) of a superhydrophobic sphere impacting onto a liquid bath was observed in experiments and direct numerical simulations by Galeano-Rios et al. (J. Fluid Mech., vol. 912, 2021, A17). We investigate the mechanisms of the liquid entry for a superhydrophobic cylinder in this paper. The superhydrophobic cylinder, commonly employed as supporting legs for insects and robots at the liquid surface, can exhibit liquid-entry mechanisms different from those observed with the sphere. The direct numerical simulation method is applied to the impact of a two-dimensional (2-D) superhydrophobic cylinder (modelled as a pseudo-solid) onto a liquid bath. We find that for the impacting cylinder the resurrection phenomenon can also exist, and the cylinder can either rebound (get detached from the liquid surface) or stay afloat after resurfacing. The cylinder impact behaviour is classified into four regimes, i.e. floating, bouncing, resurrecting (resurrecting-floating and resurrecting-bouncing) and sinking, dependent on the Weber number and the density ratio of the cylinder to the liquid. For the regimes of floating and bouncing, the force analysis indicates that the form drag dominates the motion of the cylinder in the very beginning of the impact, while subsequently the surface tension force also plays a role with the contact line pinning on the horizontal midline of the cylinder. For the critical states of the highlighted resurrecting regime, our numerical results show that the rising height for the completely submerged cylinder of different density ratios remains nearly unchanged. Accordingly, a relation between the maximum ascending velocity and the density ratio is derived to predict whether the completely submerged cylinder can resurface.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"22 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142269809","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}

引用次数: 0

Modon solutions in an N-layer quasi-geostrophic model N 层准地转模型中的模子解法

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-18 DOI: 10.1017/jfm.2024.619

Matthew N. Crowe, Edward R. Johnson

引用次数: 0

On the three-dimensional structure of instabilities beneath shallow-shoaling internal waves 浅层翔泳内波下不稳定性的三维结构

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-18 DOI: 10.1017/jfm.2024.703

Nicolas Castro-Folker, Marek Stastna

引用次数: 0

Coupled unsteady actuator disc and linear theory of an oscillating foil propulsor 振荡箔推进器的耦合非稳态致动器圆盘和线性理论

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-18 DOI: 10.1017/jfm.2024.624

Amanda S.M. Smyth, Takafumi Nishino, Andhini N. Zurman-Nasution

引用次数: 0

Reactive experimental control of turbulent jets 湍流喷射的反应性实验控制

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-18 DOI: 10.1017/jfm.2024.569

Diego B.S. Audiffred, André V.G. Cavalieri, Igor A. Maia, Eduardo Martini, Peter Jordan

{"title":"Reactive experimental control of turbulent jets","authors":"Diego B.S. Audiffred, André V.G. Cavalieri, Igor A. Maia, Eduardo Martini, Peter Jordan","doi":"10.1017/jfm.2024.569","DOIUrl":"https://doi.org/10.1017/jfm.2024.569","url":null,"abstract":"We present an experimental study of reactive control of turbulent jets, in which we target axisymmetric coherent structures, known to play a key role in the generation of sound. We first consider a forced jet, in which coherent structures are amplified above background levels, facilitating their detection, estimation and control. We then consider the more challenging case of an unforced jet. The linear control targets coherent structures in the region just downstream of the nozzle exit plane, where linear models are known to be appropriate for description of the lowest-order azimuthal modes of the turbulence. The control law is constructed in frequency space, based on empirically determined transfer functions. And the Wiener–Hopf formalism is used to enforce causality and to provide an optimal controller, as opposed to the sub-optimal control laws provided by simpler wave-cancellation methods. Significant improvements are demonstrated in the control of both forced and unforced jets. In the former case, order-of-magnitude reductions are achieved; and in the latter, turbulence levels are reduced by up to 60 %. The results open new perspectives for the control of turbulent flow at high Reynolds number.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"106 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142269427","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}

引用次数: 0

An experimental study of a quasi-impulsive backwards wave force associated with the secondary load cycle on a vertical cylinder 与垂直气缸二次载荷循环相关的准脉冲后向波力的实验研究

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-18 DOI: 10.1017/jfm.2024.648

Tianning Tang, Haoyu Ding, Saishuai Dai, Paul H. Taylor, Jun Zang, Thomas A.A. Adcock

{"title":"An experimental study of a quasi-impulsive backwards wave force associated with the secondary load cycle on a vertical cylinder","authors":"Tianning Tang, Haoyu Ding, Saishuai Dai, Paul H. Taylor, Jun Zang, Thomas A.A. Adcock","doi":"10.1017/jfm.2024.648","DOIUrl":"https://doi.org/10.1017/jfm.2024.648","url":null,"abstract":"Steep wave breaking on a vertical cylinder (a typical foundation supporting offshore wind turbines) will induce slam loads. Many questions on the important violent wave loading and the associated secondary load cycle remain unanswered. We use laboratory experiments with unidirectional waves to investigate the fluid loading on vertical cylinders. We use a novel three-phase decomposition approach that allows us to separate different types of nonlinearity. Our findings reveal the existence of an additional quasi-impulsive loading component that is associated with the secondary load cycle and occurs in the backwards direction against that of the incoming waves. This quasi-impulsive force occurs at the end of the secondary load cycle and close to the passage of the downward zero-crossing point of the undisturbed wave. Wavelet analysis showed that the impulsive force exhibits superficially similar behaviour to a typical wave-slamming event but in the reverse direction. To monitor the scattered wave field and extract run-up on the cylinder, we installed a four-camera synchronised video system and found a strong temporal correlation between the arrival time of the Type-II scattered wave onto the cylinder and the occurrence of this quasi-impulsive force. The temporal characteristics of this quasi-impulsive force can be approximated by the Goda wave impact model, taking the collision of the Type-II scattered waves at the rear stagnation point as the impact source.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"17 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256216","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}

引用次数: 0

Particle motion in a bed under a rigid plate, submerged and oscillated over its surface, and bed morphologies induced by flexible plates 颗粒在刚性板下的床面运动、浸没和在其表面摆动，以及柔性板诱导的床面形态

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-13 DOI: 10.1017/jfm.2024.705

Anna Prati, Michele Larcher, James T. Jenkins, Luigi La Ragione

{"title":"Particle motion in a bed under a rigid plate, submerged and oscillated over its surface, and bed morphologies induced by flexible plates","authors":"Anna Prati, Michele Larcher, James T. Jenkins, Luigi La Ragione","doi":"10.1017/jfm.2024.705","DOIUrl":"https://doi.org/10.1017/jfm.2024.705","url":null,"abstract":"We study the behaviour of a particle bed immersed in water when a flow generated by an oscillating plate is induced above it. We first consider a rigid plate submerged and oscillated over a particle bed. During upward motion of the plate, a portion of the bed fails, allowing particle displacement, and the bed surface to deform into a heap. We have already determined the flow of the fluid above and within the bed. This work describes the particle motion within the failed region of the bed: when the particles are mobile, they follow the fluid. We depth average the balance of mass and obtain an evolution equation for the displacement of the bed surface. We solve this equation and compare the predictions with the measurements of surface displacement in earlier experiments on rigid square plates. We carry out new experiments to measure the surface displacements under elongated plates. Elongated rigid plates behave similarly to the rigid square ones. Flexible plates produce multiple heaps. We determine that the peaks of these heaps are correlated with the flexural modes of the plates and occur at points along the bed at which the fluid pressure has its extreme values. Different plate flexural modes, resulting in different numbers of heaps, are produced by driving the plate at different frequencies. The particle motion within the bed and heap evolution under a flexible plate can be roughly described by regarding it as two or more rigid plates. We test the predictions of the theory against experiments.","PeriodicalId":15853,"journal":{"name":"Journal of Fluid Mechanics","volume":"4 1","pages":""},"PeriodicalIF":3.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142256253","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}

引用次数: 0

The instability of non-monotonic drag laws 非单调阻力定律的不稳定性

IF 3.7 2区工程技术

Journal of Fluid Mechanics Pub Date : 2024-09-13 DOI: 10.1017/jfm.2024.635

Timour Radko

引用次数: 0