Compressible magnetohydrodynamic Kelvin–Helmholtz instability with vortex pairing in the two-dimensional transverse configuration

1997 ◽  
Vol 4 (8) ◽  
pp. 2871-2885 ◽  
Author(s):  
Akira Miura
Keyword(s):  
Two Dimensional ◽  
Helmholtz Instability ◽  
Vortex Pairing

Phase Effect on Mode Coupling in Kelvin–Helmholtz Instability for Two-Dimensional Incompressible Fluid

2009 ◽  
Vol 52 (4) ◽  
pp. 694-696 ◽  
Author(s):  
Wang Li-Feng ◽  
Teng Ai-Ping ◽  
Ye Wen-Hua ◽  
Xue Chuang ◽  
Fan Zheng-Feng ◽  
...  
Keyword(s):  
Incompressible Fluid ◽  
Mode Coupling ◽  
Two Dimensional ◽  
Helmholtz Instability ◽  
Phase Effect

Passive Manipulation of Separation-Bubble Transition Using Surface Modifications

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Brian R. McAuliffe ◽  
Metin I. Yaras
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Layer ◽  
Separation Bubble ◽  
Surface Modifications ◽  
Small Scale ◽  
Two Dimensional ◽  
Vortex Pairing ◽  
Separated Shear Layer ◽  
Scale Turbulence

Through experiments using two-dimensional particle-image velocimetry (PIV), this paper examines the nature of transition in a separation bubble and manipulations of the resultant breakdown to turbulence through passive means of control. An airfoil was used that provides minimal variation in the separation location over a wide operating range, with various two-dimensional modifications made to the surface for the purpose of manipulating the transition process. The study was conducted under low-freestream-turbulence conditions over a flow Reynolds number range of 28,000–101,000 based on airfoil chord. The spatial nature of the measurements has allowed identification of the dominant flow structures associated with transition in the separated shear layer and the manipulations introduced by the surface modifications. The Kelvin–Helmholtz (K-H) instability is identified as the dominant transition mechanism in the separated shear layer, leading to the roll-up of spanwise vorticity and subsequent breakdown into small-scale turbulence. Similarities with planar free-shear layers are noted, including the frequency of maximum amplification rate for the K-H instability and the vortex-pairing phenomenon initiated by a subharmonic instability. In some cases, secondary pairing events are observed and result in a laminar intervortex region consisting of freestream fluid entrained toward the surface due to the strong circulation of the large-scale vortices. Results of the surface-modification study show that different physical mechanisms can be manipulated to affect the separation, transition, and reattachment processes over the airfoil. These manipulations are also shown to affect the boundary-layer losses observed downstream of reattachment, with all surface-indentation configurations providing decreased losses at the three lowest Reynolds numbers and three of the five configurations providing decreased losses at the highest Reynolds number. The primary mechanisms that provide these manipulations include: suppression of the vortex-pairing phenomenon, which reduces both the shear-layer thickness and the levels of small-scale turbulence; the promotion of smaller-scale turbulence, resulting from the disturbances generated upstream of separation, which provides quicker transition and shorter separation bubbles; the elimination of the separation bubble with transition occurring in an attached boundary layer; and physical disturbance, downstream of separation, of the growing instability waves to manipulate the vortical structures and cause quicker reattachment.

scholarly journals Vortex pairing in two-dimensional Bose gases

2010 ◽  
Vol 81 (2) ◽  
Author(s):  
Christopher J. Foster ◽  
P. Blair Blakie ◽  
Matthew J. Davis
Keyword(s):  
Two Dimensional ◽  
Bose Gases ◽  
Vortex Pairing

scholarly journals Study on the Kelvin-Helmholtz instability in two-dimensional incompressible fluid

2009 ◽  
Vol 58 (7) ◽  
pp. 4787
Author(s):  
Wang Li-Feng ◽  
Ye Wen-Hua ◽  
Fan Zheng-Feng ◽  
Li Ying-Jun
Keyword(s):  
Incompressible Fluid ◽  
Two Dimensional ◽  
Helmholtz Instability

scholarly journals Knudsen Number Effects on Two-Dimensional Rayleigh–Taylor Instability in Compressible Fluid: Based on a Discrete Boltzmann Method

Entropy ◽  
2020 ◽  
Vol 22 (5) ◽  
pp. 500 ◽  
Author(s):  
Haiyan Ye ◽  
Huilin Lai ◽  
Demei Li ◽  
Yanbiao Gan ◽  
Chuandong Lin ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Knudsen Number ◽  
Compressible Fluid ◽  
Two Dimensional ◽  
Helmholtz Instability ◽  
Physical Mechanisms ◽  
Rayleigh Taylor Instability ◽  
Boltzmann Method ◽  
Rt Instability ◽  
Non Equilibrium

Based on the framework of our previous work [H.L. Lai et al., Phys. Rev. E, 94, 023106 (2016)], we continue to study the effects of Knudsen number on two-dimensional Rayleigh–Taylor (RT) instability in compressible fluid via the discrete Boltzmann method. It is found that the Knudsen number effects strongly inhibit the RT instability but always enormously strengthen both the global hydrodynamic non-equilibrium (HNE) and thermodynamic non-equilibrium (TNE) effects. Moreover, when Knudsen number increases, the Kelvin–Helmholtz instability induced by the development of the RT instability is difficult to sufficiently develop in the later stage. Different from the traditional computational fluid dynamics, the discrete Boltzmann method further presents a wealth of non-equilibrium information. Specifically, the two-dimensional TNE quantities demonstrate that, far from the disturbance interface, the value of TNE strength is basically zero; the TNE effects are mainly concentrated on both sides of the interface, which is closely related to the gradient of macroscopic quantities. The global TNE first decreases then increases with evolution. The relevant physical mechanisms are analyzed and discussed.

Influence of vortex-pairing location on the three-dimensional evolution of plane mixing layers

2002 ◽  
Vol 462 ◽  
pp. 43-77 ◽  
Author(s):  
JORDI ESTEVADEORDAL ◽  
STANLEY J. KLEIS
Keyword(s):  
Time Evolution ◽  
Dimensional Space ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Secondary Structures ◽  
Two Dimensional ◽  
Vortex Pairing ◽  
Instability Modes ◽  
Dimensional Measurements ◽  
Large Plane

Detailed three-dimensional measurements of the first vortex pairing of a large plane mixing layer reveal excitation of several three-dimensional instability modes. Time evolution in three-dimensional space (x, y, z, t) shows how the two-dimensional rollers become three-dimensional as they approach each other and that the linear growth of at least two instability waves leads to a spanwise periodic pairing. The results are based on phase-locked measurements made in three-dimensional spatial grids, with a mesh spacing of 8.5% of the fundamental instability wavelength. Spanwise-uniform, periodic acoustic excitation stabilizes the most probable two-dimensional natural features – roll-up and first pairing. The second subharmonic is added to study the effect of alternate streamwise pairing locations on the three-dimensional characteristics of vortex pairing. Velocities are measured using hot-wire anemometry, and the coherent structures are reconstructed from the ensemble-averaged vorticity field.Vortex pairing is shown to initiate through local ‘bridging’ at the maxima of periodic spanwise undulations. The undulations result from linear amplification of various instability modes on pairing rollers having different strengths. Bridging results from the change of the relative phase between the spanwise undulations of the pairing rollers from in-phase (due to the initial translative mode) to out-of-phase (due to the amplification of bulging-like and non-axisymmetric modes). It is found that when pairing occurs sufficiently far upstream, only axisymmetric waves are amplified and the evolution results in axisymmetric merging. In contrast, when pairing occurs sufficiently far downstream, both axisymmetric and non-axisymmetric waves are amplified and the evolution results in non-axisymmetric merging.The results indicate that vortex pairing is accompanied by the counter-rotating pairs of secondary structures (‘streamwise vortices’ or ‘ribs’) located in the mixing-layer braids and residing in the valleys of the spanwise-roller waves. Time evolution of these secondary structures shows that they move in the transverse direction, following the rollers.

Numerical Simulation of Mixing Enhancement and Suppression in Two-Dimensional Mixing Layer

2011 ◽  
Author(s):  
Masayuki Kawagoe ◽  
Koji Fukagata
Keyword(s):  
Numerical Simulation ◽  
Mixing Layer ◽  
Mixing Enhancement ◽  
Computational Domain ◽  
Momentum Thickness ◽  
Two Dimensional ◽  
Control Effect ◽  
Chemical Product ◽  
Vortex Pairing ◽  
Time Periodic

Direct numerical simulation of two-dimensional mixing layer with time-periodic forcing mimicking the input of piezofilm actuator is performed. Three different forcing frequencies (i.e., the natural frequency, its first subharmonic and second subharmonic frequencies) are examined. Simplified chemical reactions are also taken into account. We investigate whether mixing is promoted or suppressed using two indices: the momentum thickness and the concentration of chemical product. The momentum thickness indicates that the forcing enhances the development of mixing layer near the inlet and suppresses it in the region right downstream. Instantaneous vorticity fields show that the location where the vortex pairing starts depend on the forcing frequency. The effect of forcing on the mixing layer development strongly depends on its frequency: in particular, the forcing at the second subharmonic frequency is found to suppress the development of mixing layer in a wide region. On the other hand, from the chemical product concentration, mixing is found to be promoted regardless of the forcing frequency. We also investigate how far the control effect lasts. It is revealed that in the downstream region the mixing layer thickness develops linearly regardless of the forcing frequency, which in turn suggests that the present numerical simulation is performed in a computational domain large enough to examine the control effect.

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