检索结果-南通市图书馆

Liutex(vorex)cores in transitional boundary layer with spanwise-wall oscillation

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2019年第6期31卷 1178-1189页

作者： yi-qian wang Chaoqun Liu School of Mathematical Science Soochow UniversitySuzhou 215006China Department of Mathematics University of Texas at ArlingtonArlington 76019USA

The vortex core detection method based on the Liutex vector is utilized to investigate the alternation of vortical structures on a boundary layer transition subjected to spanwise-wall *** with iso-surface based methods,the Liutex core line method is shown to be precise,free of threshold and capable to capture both strong and weak vortices ***-Schlichting(T-S)waves in the linear growth region,A-and hairpin vortices in the transition region and twisted vortices in the turbulent region are all well captured by Liutex core *** cyclic wall movement accelerates the transition process while reducing the turbulent drag by 21.8%with selected *** the wall oscillation case,the development from T・S wave to Avortex is advanced about one T・S wave length in the stream wise *** the transition region,the A-vortex and legs of hairpin vortex are shortened in the wall oscillation case,and the symmetry of the vortical structures is lost in the late transition region since the introduction of asymmetry disturbances by the cyclic wall *** of weak vortices at the edge of boundary layer are found in the turbulent section which is often omitted by iso-surface based vortex identification ***,it is demonstrated that for the transitional boundary layer the Liutex core line method provides a systematic and thresholdvortex definition,which could serve as a powerful tool to understand and guide flow control.

关键词： Liutex vector Liutex core line boundary layer transition spanwise-wall oscillation

A letter for objective Liutex

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2022年第5期34卷 965-969页

作者： yifei Yu yi-qian wang Chaoqun Liu Department of Mathematics University of Texas at ArlingtonArlingtonTexas76019USA School of Mathematical Science Soochow UniversitySuzhou215006China

Vortex structures,detected by the existing popular vortex identification methods,of the same case are generally different if the results are measured by different observers,who are moving with different coordinate *** coordinate systems can be inertial or *** invariance can solve the moving observer problems in different inertial coordinate systems.A variable is invariant under Galilean transformation is called Galilean *** invariant vortex identification methods can provide invariant vortex structures based on different inertial ***,for some situations,the observers are non-inertial,e.g.,the observer is sitting on an aircraft which is accelerating or *** such a situation,it requires to use an objective *** represents a property that one variable is not observer-dependent(the observer’s motion can be either inertial or non-inertial).A strategy based on a zero-vorticity(measured in inertial frame)reference point is proposed in this letter to find the objective vortex *** is chosen as the vortex indicator and two numerical examples are used to test the proposed *** results show that the strategy is effective.

关键词： Objective Liutex vortex structure Galilean invariance

The Stability of the Elliptic Equilibrium of Planar Quasi-periodic Hamiltonian Systems

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2012年第4期28卷 801-816页

作者： Yun Chao WU yi qian wang Department of Mathematics Nanjing University

In this paper, we study the planar Hamiltonian systemwhere where f is real analytic in x and θ,A（θ） is a 2×2real analytic symmetric matrix,J=（1^-1） and w is a Diophantine vector. Under the assumption that the unperturbed systemreducible and stable, we obtain a series of criteria for the stability and instability of the equilibrium of the perturbed system.

关键词： Lyapunov stability elliptic equilibrium Hamiltonian system quasi-periodic system

Liutex-based vortex dynamics:A preliminary study

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2020年第6期32卷 1217-1220页

作者： Hai-dong Yu yi-qian wang School of Aerospace Engineering Tsinghua UniversityBeijing100084China School of Mathematical Science Soochow UniversitySuzhou215006China

Vortex dynamics,with the possibility of efficient flow control,is explored in this study based on the new introduced vortex definition and identification system of *** the six core elements of vortex identification,including(1)absolute strength,(2)relative strength,(3)local rotational axis,(4)global rotational axis,(5)vortex core size and(6)vortex boundary,provided by the Liutex system,it is possible to numerically devise strategies,primarily by introducing additional source terms in Navier-Stokes equations,which we call Liutex force field model here,to control the vortex *** methodologies of centripetal force model and counter-rotation force model are preliminarily investigated in a cavitating flow around two-dimensional Clark-Y *** is found that Liutex based models are capable of illustrating the vortex dynamics and possibly strengthening or weakening the vortices.

关键词： Vortex dynamics Liutex vector flow control

Preliminary control of the air entrainment in bow wave based on the Liutex force method

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2022年第3期34卷 483-490页

作者： yi-ding Hu Jian-wei Wu De-cheng Wan Guo wang yi-qian wang Computational Marine Hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai200240China Wuhan Second Ship Design and Research Institute Wuhan430205China Marine Design and Research Institute of China Shanghai200011China School of Mathematical Science Soochow UniversitySuzhou215006China

Trails induced by air entrainment of bow wave breaking can be observed clearly around an advancing ship,making it prong to be detected and causing reduction in hydrodynamic *** breaking bow wave region,different scale of coherent vortex structures related closely to the air entrainment are *** formation and evolution of bubble clouds can be accounted partly by the swirling vortex flow of the jet *** this work,high-fidelity simulation of the bow wave breaking around a rectangular thin plate is performed with the in-house code BAMR-SJTU.A Liutex force model is constructed to investigate the interaction between the free surface and vortices,and to explore the possibility of alleviating or controlling the air *** study is the first attempt to manipulate vortices corresponding to the air entrainment of the bow wave *** typical vortex structures based on the Liutex vortex identification method and the distribution of the vortex force are *** of the vortex structures and the entrapped bubbles is conducted to illustrate the efficiency of Liutex force model in air entrainment control.

关键词： Bow wave breaking air entrainment coherent vortex structures Liutex force field model

Explicit formula for the Liutex vector and physical meaning of vorticity based on the Liutex-Shear decomposition

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2019年第3期31卷 464-474页

作者： yi-qian wang yi-sheng Gao Jian-ming Liu Chaoqun Liu School of Aerospace Engineering Tsinghua University Beijing 100084 China Department of Mathematics University of Texas at Arlington Arlington 76019 Texas USA School of Mathematics and Statistics Jiangsu Normal University Xuzhou 221116 China

In the present study, the physical meaning of vorticity is revisited based on the Liutex-Shear (RS) decomposition proposed by Liu et al. in the framework of Liutex (previously called Rortex), a vortex vector field with information of both rotation axis and swirling strength (Liu et al. 2018). It is demonstrated that the vorticity in the direction of rotational axis is twice the spatial mean angular velocity in the small neighborhood around the considered point while the imaginary part of the complex eigenvalue (2c.) of the velocity gradient tensor (if exist) is the pseudo-time average angular velocity of a trajectory moving circularly or spirally around the axis. In addition, an explicit expression of the Liutex vector in terms of the eigenvalues and eigenvectors of velocity gradient is obtained for the first time from above understanding, which can further, though mildly, accelerate the calculation and give more physical comprehension of the Liutex vector.

关键词： Vorticity Liutex Liutex-Shear(RS)decomposition explicit formula of Liutex

Galilean invariance of Omega vortex identification method

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2019年第2期31卷 249-255页

作者： Jian-ming Liu yi-qian wang yi-sheng Gao Chaoqun Liu School of Mathematics and Statistics Jiangsu Normal UniversityXuzhou 221116China Department of Mathematics University of Texas at ArlingtonArlington 76019TexasUSA School of Aerospace Engineering Tsinghua UniversityBeijing 100084China

In the new vortex identification method(Liu et al.2016)to represent the rotation level and capture and visualize the vortices,proposed in our previous study,the independence of the reference frame and the Galilean invariant were not *** the present study,the Galilean invariance of the omega vortex identification method is proved and several examples are presented to verify the conclusion.

关键词： Vortex identification Ωmethod.Galilean invariance turbulence visualization

Objective Omega vortex identification method

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2019年第3期31卷 455-463页

作者： Jian-ming Liu yi-sheng Gao yi-qian wang Chaoqun Liu School of Mathematics and Statistics Jiangsu Normal University Xuzhou 221116 China Department of Mathematics University of Texas at Arlington Arlington 76019 Texas USA School of Aerospace Engineering Tsinghua University Beijing 100084 China

A new vortex identification method (Liu et al. 2016) was proposed to represent the rotation relative strength and capture and visualize the vortices in our previous study. The basic idea of the Ω method is that a ratio of the vorticity squared over the summation of the vorticity squared and the deformation squared should be used to measure the relative rotation strength. However, the vorticity tensor norm is not objective. Thus, a moving observer will observe different vortex structures in a moving reference frame, which will make confusions about the real vortex structures. In the present study, by the definitions of the net spin tensor and the net vorticity vector, an objective Ω vortex identification method is presented with examples to verify that the vortex structures retain in a moving reference frame.

关键词： Vortex identification the Ω method objectivity turbulence visualization turbulence

Liutex-based vortex control with implications for cavitation suppression

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2021年第1期33卷 74-85页

作者： yi-qian wang Hai-dong Yu Wei-wen Zhao De-cheng Wan School of Mathematical Science Soochow UniversitySuzhou 215006China School of Aerospace Engineering Tsinghua UniversityBeijing 100084China Computational Marine Hydrodynamics Lab(CMHL) State Key Laboratory of Ocean EngineeringSchool of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China

Viewed as sinews and muscles of fluid motion,coherent vortical structures with their interactions are key to understanding the flow *** upon this observation,we explore the possibility of efficient flow control by directly manipulating vortices numerically inside the flow field based on the vortex definition and identification system of *** objective is twofold:(1)to study the vortex dynamics,for example,by observing the response of the flow to strengthening or weakening of certain vortices,and(2)to obtain efficient vortex-based control strategies which might lead us to practical *** the present numerical study,the manipulating of vortices is achieved by introducing additional source(force)terms to the Navier-Stokes equations,which hereafter will be collectively called Liutex force field *** including controlling the rotation strength and centripetal force of particular vortices are detailed in a flow past a cylinder with different control purposes at Reynolds number of *** examples are provided with a cavitating flow around two-dimensional Clark-Y hydrofoil,with particular interests on cavitation *** is illustrated particular vortex with cavitation encircled could be effectively suppressed.

关键词： Vortex dynamics Liutex vector flow control cavitation Introduction