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Topic: Kelvin Helmholtz instability

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Kelvin-Helmholtz instability - Wikipedia, the free encyclopedia Helmholtz studied the dynamics of two fluids of different densities when a small disturbance such as a wave is introduced at the boundary connecting the fluids. The theory can be used to predict the onset of instability and transition to turbulent flow in fluids of different densities moving at various speeds. The existence of surface tension stabilises the short wavelength instability however, and theory then predicts stability until a velocity threshold is reached. en.wikipedia.org /wiki/Kelvin-Helmholtz_instability   (257 words)

Stability References-Alabduljalil Michalke, A. 1972 The instability of free shear layers. Hooper, A. and Boyd, W. 1987 Shear-flow instability due to a wall and a viscosity discontinuity at the interface. Rangel, R. and Sirignano, W. 1991 The linear and nonlinear shear instability of a fluid sheet. www.4saad.com /Research/ref.htm   (1375 words)

96JA02752.html It is found that a finite north-south field at the center of the neutral sheet inhibits the growth of the Kelvin-Helmholtz instability to some extent. Theory and simulation of Kelvin-Helmholtz instability in the geomagnetic tail In recent nonlocal stability analyses of the cross-field current instability that may operate in the geomagnetic tail, it was found that the instability is suppressed when the cross-field ion flow is uniform, but that the instability is restored only after a substanital velocity shear is introduced. www.agu.org /pubs/abs/nja/96JA02752/96JA02752.html   (202 words)

ANGEO - Abstracts As a Kelvin-Helmholtz instability allows for mass transfer through the magnetopause without any resistivity, we propose it as an alternate process to reconnection for mass transfer through magnetic boundaries. On the other hand, the large mass of H +, He + and O + ions leads to such nonadiabatic motion and we thus propose the Kelvin-Helmholtz instability as a mechanism for either magnetospheric ion leakage into the magnetosheath or solar wind ion entry in the magnetosphere. The crossing regions at the magnetopause are narrow and localized in the vicinity of the instability wave front. www.copernicus.org /EGU/annales/20/757.htm   (288 words)

jet.html The Kelvin-Helmholtz instability is studied in astrophysics in a variety of contexts -- every time there is a flux of material in a quiet environment, for example. This is an instability which develops at the surface that separates two fluids that are in pressure equilibrium and in motion with respect to one another. The jet's surface is perturbed infinitesimally, and as time passes this perturbation grows, giving rise to kinks and bends in the jet, shock waves inside the jet and in the external medium, and a tendency of the jet to expand and finally mix with the ambient medium, slowing down and losing its collimation. www-unix.mcs.anl.gov /~hudson/htmlbase/jet.html   (412 words)

Kelvin helmholtz instability - Wikipedia, the free encyclopedia Look for Kelvin helmholtz instability in the Commons, our repository for free images, music, sound, and video. Check for Kelvin helmholtz instability in the deletion log, or visit its deletion vote page if it exists. Look for Kelvin helmholtz instability in Wiktionary, our sister dictionary project. www.sciencedaily.com /encyclopedia/kelvin_helmholtz_instability   (165 words)

tmp.html In this paper, the effects of magnetic reconnection induced by the Kelvin-Helmholtz (KH) instability are examined in resistive plasmas. Simulation of Kelvin Helmholtz instability in resistive plasmas It is found from the magnetohydrodynamic (MHD) simulations that highly distorted magnetic field lines deformed from the initial parallel configuration by the KH instability become reconnected and flattened when the magnetic field intensity is not strong. www.agu.org /pubs/abs/gl/96GL03476/tmp.html   (149 words)

Water Waves: Heuristic Description of the Kelvin-Helmholtz Instability The standard heuristic explanation of the Kelvin-Helmholtz instability begins with a consideration of a uniform stream blowing over a rigid wavy wall: a sketch of such a wavy wall has been provided at the right. Although this quasi-steady explanation of the instability illustrates the main physical effects in an elementary manner, it is naturally preferable to have a rigorous treatment of the problem. If the wall was not rigid, these aerodynamic perturbations would cause the bumps to grow which in turn would increase the strength of the perturbations, which would cause further growth, and so forth. www.fluidmech.net /tutorials/ocean/khinst.htm   (334 words)

Kelvin-Helmholtz Instability In the evolved stages of KH instability, cyclonic 'cat-eye' structures are formed. When combined with RT instabilities, KH tends to form 'mushroom caps' on the end of RT fingers. Since the growth rate of these fingers is proportional to their cross section, KH tends to slow down finger growth. casa.colorado.edu /~danforth/science/cloudshock/node5.html   (174 words)

2-D Simulation of Kelvin-Helmholtz Instability The simulation was able to very nicely reproduce--at least qualitatively--a Kelvin-Helmholtz instability. An Instability is an unstable response to a small perturbation. Once this small perturbation to the initial equilibrium is applied, the instability will grow in amplitude in non-equilibrium stages---fed by the sources of free energy. ffden-2.phys.uaf.edu /645fall2003_web.dir/John_Styers/GFD_PAGE.html   (400 words)

IWF: News Therefore, the stability of the Martian ionopause is analyzed with respect to the Kelvin-Helmholtz instability. In a recent study, the Kelvin-Helmholtz instability in the frame of Hall-MHD is considered, showing that the inclusion of Hall effects can lead to an unstable ionopause even near the subsolar point. For the full paper see Penz et al., Ion loss on Mars caused by the Kelvin-Helmholtz instability, Planet. www.iwf.oeaw.ac.at /german/news/newsionlossonmars_11_04_d.html   (271 words)

Double helix in the quasar 3C273 The MPIfR scientists have shown that this double helical structure is consistent with Kelvin-Helmholtz (K-H) instability developing in a light jet with Lorentz factor of 2 and Mach number of 3.5. This instability originates from transverse velocity gradients or discontinuities due to interaction between the relativistic plasma of the outflow and (typically) sub-relativistic surrounding material. They conclude that the instability in the jet of 3C273 is developing in a plasma with moderate Lorentz factor and Mach number and a much lower density than that of the surrounding material. www.mpifr-bonn.mpg.de /staff/alobanov/3C273-Science   (1105 words)

KH Instability Test Page To seed the instability, we add random numbers to both the x- and y-components of the velocity with peak-to-peak amplitude of 0.01. At late times, once the instability has gone fully nonlinear, it is difficult to make quantitative comparisons. Sections 101 considers the stability of a slip surfce between two fluids of different densities, section 106 considers the effect of a magnetic field on the problem. www.astro.princeton.edu /~jstone/tests/kh/kh.html   (487 words)

Rao and Fuelberg Kelvin-Helmholtz instability, evident as billows or vorticies, is seen to initiate at the head of the sea breeze and propagate backwards relative to the front. Furthermore, they are evident only on the 100 m grid, thus confirming previous results indicating the high resolution that is necessary for resolving Kelvin-Helmholtz instability. A Numerical Modeling Study to Investigate the Role of Kelvin-Helmholtz Instability on Convection Near the Cape Canaveral Sea Breeze Front www.nssl.noaa.gov /users/brooks/public_html/sls19/abstracts/raofuelberg.html   (224 words)

Kelvin-Helmholtz instability [Bat67][DR81][Ge98] For two-dimensional parallel shear flows, the purely mechanical (inviscid) Kelvin-Helmholtz instability is connected with the presence of an inflection point in the velocity profile (in contrast to e.g. In the framework of the linear instability theory one may distinguish between amplifiers, the dynamics of which are sensitive to inflow perturbations, and oscillators, which sustain intrinsic global modes tuned at a well defined frequency. Within the linear instability analysis, the vorticity is indeed transported by the basic flow. lmhwww.epfl.ch /Publications/Theses/Mauri/thesis_html/node112.html   (502 words)

Fluent NEWS - Fall 2004 - Computational Cloud Dynamics A published nonlinear calculation of a Kelvin-Helmholtz instability using two fluids of equal density indicates that a wave of this scale should break between 63 and 72 seconds if the surface is initially perturbed [1, 2]. The cloud formation of interest is named for the Kelvin-Helmholtz instability, which is well known to scientists, since it appears in so many forms in nature and laboratory applications. Since Kelvin- Helmholtz cloud formations are normally observed on the upper, rather than the lower boundary of a cloud, a case was considered with the cloud density greater than that of air. www.fluent.com /about/news/newsletters/04v13i2/a6.htm   (597 words)

Instability in the Ionosphere A two-dimensional theoretical model is used to describe the Kelvin Helmholtz Instability in the ionosphere. In the longwavelength regime, the mechanism is the well known Kelvin Helmholtz Instability which has been extensively studied in fluid dynamics. Note the development of vortices during the nonlinear phase of the instability. www.sv.vt.edu /research/scales/scales.html   (368 words)

tmp.html A linear analysis of the Kelvin-Helmholtz instability is performed by assuming that one of the plasma regimes (magnetosphere) separated by a velocity shear layer of zero thickness is spatially nonuniform. In contrast, the present analysis reveals that the Kelvin-Helmholtz instability generates global-scale monochromatic waves when the magnetosphere is nonuniform and the magnetosheath flow speed is quite fast. The previous theories based on the semi-infinite uniform model with infinitesimally thin magnetopause showed that wave growth due to the Kelvin-Helmholtz instability exhibits monotonic increase for shorter frequency. www.agu.org /pubs/abs/ja/96JA02676/tmp.html   (174 words)

Theory and Simulation of the Kelvin-Helmholtz Instability: Finite Larmor Radius Magnetohydrodynamics Physically, the asymmetry occurs because the FLR effects introduce the diamagnetic drift velocity in the direction B\times \nabla n; however, the phase velocity of the wave associated with the Kelvin-Helmholtz instability in an inhomogenous plasma depends on the vorticity Ømega and density gradient. A preliminary theoretical and computational study of the Kelvin-Helmholtz instability in an inhomogeneous plasma is presented using finite Larmor radius magnetohydrodynamic (FLR MHD) theory. Thus, depending on the relative directions of the diamagnetic drift velocity and the phase velocity of the wave, the behavior of the instability is affected differently. flux.aps.org /meetings/BAPSDPP96/abs/S730001.html   (230 words)

Geomagnetism and Aeronomy A linear theory of the Kelvin-Helmholtz instability in a compressible plasma with a magnetic field is discussed. The Kelvin-Helmholtz instability for a velocity profile with a sharp bend It is shown that for a plasma velocity profile with a sharp bend (a sharp maximum of the velocity second derivative), it is possible to obtain an approximate analytical solution for the growth rate, phase velocity, and wavelength of the oscillations. eos.wdcb.rssi.ru /transl/gma/9501/pap05.htm   (153 words)

Kelvin Helmholtz instabilities- Theory, links and various ressources... This part summarizes some information on the theory and the mathematical modeling of the Kelvin Helmholtz instabilities. The further evoltion of the instability (step 3) in particular the rolling up process can not be described by these equations. On the other side the gravity has a stabilization effect for long wavelength (when the wave number k is small) and that surface tension stabilizes short wavelength (when k is big). wn7.enseeiht.fr /hmf/travaux/CD0001/travaux/optmfn/gpfmho/00-01/grp5/theo.htm   (452 words)

Kelvin--Helmholtz instability in a rotating ideally conducting inhomogeneous plasma The Kelvin--Helmholtz instability in sheared magnetohydrodynamic flow of an ideally conducting rotating inhomogeneous compressible plasma is investigated. The asymptotic behaviour in $x$ of the Kelvin--Helmholtz eigenfunctions for the case of finite compressibility in the presence of rotation is discussed and instability condition is derived. Kelvin--Helmholtz instability in a rotating ideally conducting inhomogeneous plasma www.iisc.ernet.in /pramana/v62/p899/abs.htm   (122 words)

APPM 8100 Seminar: Mathew Tearl he Kelvin-Helmholtz (KH) instability is one important source of turbulence in stably stratified fluids (such as the atmosphere). This can then be further reduced to a simple problem in linear algebra: finding the eigenvectors of an Hermitian matrix. Attempting to characterize the turbulence that results from KH events forces us to consider the problem of finding "optimal perturbations" to KH flow. amath.colorado.edu /courses/8100/2002Spr/tearle.html   (82 words)

penzetal2004 Title: Ion loss on Mars caused by the Kelvin-Helmholtz instability Thus, atmospheric loss caused by the Kelvin-Helmholtz instability should be comparable with other non-thermal loss processes. We investigate the instability growth rate at the Martian ionopause resulting from the flow of the solar wind for the case where the interplanetary magnetic field is oriented normal to the flow direction. lep694.gsfc.nasa.gov /gunther/gunther/penzetal2004.html   (382 words)

The MHD Kelvin-Helmholtz Instability: Oblique Field 2\frac12D Simulations We extend recently published numerical simulations of the nonlinear evolution of the MHD Kelvin-Helmholtz instability (Frank etal, ApJ, 460, 777 (1996)). The MHD Kelvin-Helmholtz Instability: Oblique Field 2\frac12D Simulations All of the runs extend well beyond the initial saturation of the instability. www.aas.org /publications/baas/v28n2/aas188/abs/S007016.html   (272 words)

Kelvin-Helmholtz instability This instability is known as the Kelvin-Helmholtz instability (Helmholtz 1868; Kelvin 1871) and causes an interface between two fluids to wrinkle if the fluids on the two sides are moving with different speeds. The most common example of the Kelvin-Helmholtz instability is provided by the observation that a wind blowing over a water surface causes the water surface to undulate. Hence the instability occurs when the expression within the square root in Eq (10.121) is negative, i.e. astron.berkeley.edu /~jrg/ay202/node145.html   (265 words)

Publications The occurrence of different magnetohydrodynamic instabilities, namely the Kelvin-Helmholtz instability, the Kelvin-Helmholtz instability in Hall-MHD, the Rayleigh-Taylor instability, and the interchange instability, are discussed. Because of the velocity difference between the solar wind and the ionospheric plasma, it is likely that the Kelvin-Helmholtz instability occurs at the Martian ionopause. Penz, I. Arshukova, N. Terada, H. Shinagawa, N. Erkaev, H. Biernat, and H. Lammer, A comparison of magnetohydrodynamic instabilities at the Martian ionopause, Adv. physik.kfunigraz.ac.at /~thp/pub.htm   (3022 words)

New theory unravels magnetic instability The Newsbulletin December 9, 2002 The theory is based on a 19th century mathematical observation called Kelvin-Helmholtz instability. Researchers at the Laboratory now have a new theory that may explain the instability and advance the understanding of these phenomena. Reconnection, the merging of magnetic field lines of opposite polarity near the surface of the sun, Earth and some black holes, is believed to be the root cause of many spectacular astronomical events such as solar flares and coronal mass ejections, but the reason for this is not well understood. www.lanl.gov /orgs/pa/newsbulletin/2002/12/09/text02.shtml   (440 words)

3D MHD Simulations of the Nonlinear Kelvin-Helmholtz Instability We have studied new 3D simulations of the MHD Kelvin-Helmholtz instability in a periodic section of a strongly sheared flow. 3D MHD Simulations of the Nonlinear Kelvin-Helmholtz Instability [40.17] 3D MHD Simulations of the Nonlinear Kelvin-Helmholtz Instability www.aas.org /publications/baas/v30n2/aas192/abs/S040017.html   (298 words)

Univ of MN Space Physics Research Group Abstracts The Kelvin-Helmholtz instability is a mechanism for transport at the magnetopause. Simulation of the Kelvin-Helmholtz Instability With a Magnetic Shear The results from a two-dimensional MHD simulation using the total variation scheme will be presented. ham.spa.umn.edu /spacephys/abstracts/kkeller1.html   (112 words)

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