开尔文-亥姆霍兹不稳定性：修订间差异
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{{Translating |time=2013-8-12}} |
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|G1=物理學 |
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[[File:Kelvin Helmholz wave clouds.jpg|thumb|250px|在舊金山上空的开尔文-亥姆霍兹波雲]] |
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'''開爾文-亥姆霍茲不穩定性'''（{{lang-en|'''Kelvin–Helmholtz instability'''}}，名稱來自[[威廉·汤姆森，第一代开尔文男爵|開爾文男爵]]和[[赫尔曼·冯·亥姆霍兹]]）是在有{{link-en|剪力速度|Shear velocity}}的[[连续介质力学|連續流體]]內部或有速度差的兩個不同流體的介面之間發生的不穩定現象。 |
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一個例子是風吹過水面時，在水面上表面的波的不穩定。而這種不穩定狀況更常見於雲、海洋、[[土星]]的雲帶、[[木星]]的[[大紅斑]]、[[太陽]]的[[日冕]]中<ref>{{cite web|last=Fox|first=Karen C.|title=NASA's Solar Dynamics Observatory Catches "Surfer" Waves on the Sun|url=http://www.nasa.gov/mission_pages/sunearth/news/sun-surfing.html|work=NASA-The Sun-Earth Connection: Heliophysics|publisher=NASA|access-date=2013-08-12|archive-date=2021-11-20|archive-url=https://web.archive.org/web/20211120110428/https://www.nasa.gov/mission_pages/sunearth/news/sun-surfing.html|dead-url=no}}</ref>。 |
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== 理論 == |
== 理論 == |
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本理論可預測不同密度的流體在不同的運動速度下的不穩定狀態發生，並且層流變成[[湍流]]的界限。亥姆霍兹研究兩種不同密度流體的[[動力學]]，並發現小規模的擾動，例如波發生時在不同流體間邊界的反應。 |
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The theory predicts the onset of instability and transition to [[turbulent flow]] in [[fluid]]s of different [[density|densities]] moving at various speeds. Helmholtz studied the [[Dynamics (mechanics)|dynamics]] of two fluids of different densities when a small disturbance, such as a wave, was introduced at the boundary connecting the fluids. |
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[[File:Wavecloudsduval.jpg|thumb|left|在澳大利亞出現的因為开尔文-亥姆霍兹不稳定性所產生的雲。]] |
[[File:Wavecloudsduval.jpg|thumb|left|在澳大利亞出現的因為开尔文-亥姆霍兹不稳定性所產生的雲。]] |
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For some short enough wavelengths, if surface tension is ignored, two fluids in parallel motion with different velocities and densities yield an interface that is unstable for all speeds. [[Surface tension]] stabilises the short wavelength instability however, and theory predicts stability until a velocity threshold is reached. The theory with surface tension included broadly predicts the onset of wave formation in the important case of wind over water.{{Citation needed|date=June 2013}} |
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在一些波長短到一定程度的狀態下，如果忽略表面張力，以不同速度平行運動的兩種不同密度流體的介面下，在所有速度時都會不穩定。然而，[[表面張力]]可抵消短波長的不穩定狀態，而理論預測直到達到速度閾值以前都是穩定的。包含表面張力的理論可大致預測在風吹過水面時產生波的界限{{Citation needed|date=June 2013}}。 |
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[[File:Saturn Kelvin Helmholtz.jpg|thumb|right|300px|在[[土星大氣層]]內因為兩條雲帶交互作用發生的开尔文-亥姆霍兹不稳定性現象。]] |
[[File:Saturn Kelvin Helmholtz.jpg|thumb|right|300px|在[[土星大氣層]]內因為兩條雲帶交互作用發生的开尔文-亥姆霍兹不稳定性現象。]] |
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[[File:Deep Oceanic Kelvin-Helmholtz billows.jpg|thumb|left|大西洋深500公尺處因為开尔文-亥姆霍兹不稳定性產生的波浪。]] |
[[File:Deep Oceanic Kelvin-Helmholtz billows.jpg|thumb|left|大西洋深500公尺處因為开尔文-亥姆霍兹不稳定性產生的波浪。]] |
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在重力作用下，連續變化的密度和速度分布（較輕的層在上方，所以流體是[[瑞利－泰勒不穩定性|瑞利－泰勒穩定]]）使开尔文-亥姆霍兹不稳定性的動力學是以{{link-en|泰勒－戈德斯坦方程|Taylor–Goldstein equation}}描述。而不穩定性開端可由[[理查逊数]]（Richardson number，Ri）得知。通常情況下Ri<0.25就會不穩定。這些效應常在雲層中出現。對於不穩定性的研究也可應用在[[電漿]]物理學中，例如[[慣性局限融合]]和電漿－[[铍]]的介面。 |
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In gravity, for a continuously varying distribution of density and velocity (with the lighter layers uppermost, so that the fluid is [[Rayleigh–Taylor instability|RT-stable]]), the dynamics of the KH instability is described by the [[Taylor–Goldstein equation]] and its onset is given by a [[Richardson number]], Ri. Typically the layer is unstable for Ri<0.25. These effects are common in cloud layers. The study of this instability is applicable in plasma physics, for example in [[inertial confinement fusion]] and the [[Plasma (physics)|plasma]]–[[beryllium]] interface. |
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在數值模式下，开尔文-亥姆霍兹不稳定性是以時間发展或空間发展方式模擬。時間发展方式下采用周期边界条件进行模拟。空間发展方式则采用实际中的入口和出口條件。 |
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Numerically, the KH instability is simulated in a temporal or a spatial approach. In the temporal approach, experimenters consider the flow in a periodic (cyclic) box "moving" at mean speed (absolute instability). In the spatial approach, experimenters simulate a lab experiment with natural inlet and outlet conditions (convective instability). |
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== 參見 == |
== 參見 == |
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* [[瑞利－泰勒不穩定性]] |
* [[瑞利－泰勒不穩定性]] |
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* [[ |
* [[里克特迈耶－梅什科夫不稳定性]] |
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* [[蘑菇雲]] |
* [[蘑菇雲]] |
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* |
* {{link-en|普拉托－瑞利不稳定性|Plateau–Rayleigh instability}} |
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* [[卡门涡街]] |
* [[卡门涡街]] |
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* [[泰勒－庫埃特流]] |
* [[泰勒－庫埃特流]] |
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|url=http://www.nytimes.com/2010/04/20/science/20waves.html?src=sch&pagewanted=all |
|url=http://www.nytimes.com/2010/04/20/science/20waves.html?src=sch&pagewanted=all |
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|title=In Deep Sea, Waves With a Familiar Curl |
|title=In Deep Sea, Waves With a Familiar Curl |
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|first=William J. |
|first=William J. |
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|last=Broad |
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|publisher=[[New York Times]] |
|publisher=[[New York Times]] |
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|date=April 19, 2010 |
|date=April 19, 2010 |
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|accessdate=April |
|accessdate=April 2010 |
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|archive-date=2022-02-12 |
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|archive-url=https://web.archive.org/web/20220212015801/https://www.nytimes.com/2010/04/20/science/20waves.html?src=sch&pagewanted=all |
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|dead-url=no |
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== 外部連結 == |
== 外部連結 == |
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* {{cite journal |last = Hwang |first = K.-J. |coauthors = Goldstein, Kuznetsova, Wang, Viñas, Sibeck |title = The first in situ observation of Kelvin-Helmholtz waves at high-latitude magnetopause during strongly dawnward interplanetary magnetic field conditions |journal = J. Geophys. Res. |volume = 117 |issue = A08233 |pages = |year = 2012 |url = |doi = 10.1029/2011JA017256 |bibcode = 2012JGRA..117.8233H }} |
* {{cite journal |last = Hwang |first = K.-J. |coauthors = Goldstein, Kuznetsova, Wang, Viñas, Sibeck |title = The first in situ observation of Kelvin-Helmholtz waves at high-latitude magnetopause during strongly dawnward interplanetary magnetic field conditions |journal = J. Geophys. Res. |volume = 117 |issue = A08233 |pages = |year = 2012 |url = |doi = 10.1029/2011JA017256 |bibcode = 2012JGRA..117.8233H }} |
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* [http://news.yahoo.com/giant-tsunami-shape-clouds-roll-across-alabama-sky-192102289.html Giant Tsunami-Shaped Clouds Roll Across Alabama Sky] - Natalie Wolchover, [[Livescience]] via Yahoo.com |
* [http://news.yahoo.com/giant-tsunami-shape-clouds-roll-across-alabama-sky-192102289.html Giant Tsunami-Shaped Clouds Roll Across Alabama Sky] {{Wayback|url=http://news.yahoo.com/giant-tsunami-shape-clouds-roll-across-alabama-sky-192102289.html |date=20220212190851 }} - Natalie Wolchover, [[Livescience]] via Yahoo.com |
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* [http://uk.news.yahoo.com/amazing-%E2%80%98tsunami-cloud%E2%80%99-hits-florida-coastline.html Tsunami Cloud Hits Florida Coastline] |
* [http://uk.news.yahoo.com/amazing-%E2%80%98tsunami-cloud%E2%80%99-hits-florida-coastline.html Tsunami Cloud Hits Florida Coastline] {{Wayback|url=http://uk.news.yahoo.com/amazing-%E2%80%98tsunami-cloud%E2%80%99-hits-florida-coastline.html |date=20210615114801 }} |
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* [http://www.youtube.com/watch?v=ELaZ2x42dkU&hd=1 Vortex formation in free jet] - YouTube video showing Kelvin Helmholz waves on the edge of a fre jet visualised in a scientific experiment. |
* [http://www.youtube.com/watch?v=ELaZ2x42dkU&hd=1 Vortex formation in free jet] {{Wayback|url=http://www.youtube.com/watch?v=ELaZ2x42dkU&hd=1 |date=20160609063942 }} - YouTube video showing Kelvin Helmholz waves on the edge of a fre jet visualised in a scientific experiment. |
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{{DEFAULTSORT:Kelvin-Helmholtz instability}} |
{{DEFAULTSORT:Kelvin-Helmholtz instability}} |
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[[Category:流體動力學]] |
[[Category:流體動力學]] |
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[[Category:云、雾与降水]] |
[[Category:云、雾与降水]] |
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[[Category:流体动力学的不穩定性]] |
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2022年2月24日 (四) 04:25的最新版本
開爾文-亥姆霍茲不穩定性（英語：Kelvin–Helmholtz instability，名稱來自開爾文男爵和赫尔曼·冯·亥姆霍兹）是在有剪力速度的連續流體內部或有速度差的兩個不同流體的介面之間發生的不穩定現象。
一個例子是風吹過水面時，在水面上表面的波的不穩定。而這種不穩定狀況更常見於雲、海洋、土星的雲帶、木星的大紅斑、太陽的日冕中[1]。
理論
[编辑]本理論可預測不同密度的流體在不同的運動速度下的不穩定狀態發生，並且層流變成湍流的界限。亥姆霍兹研究兩種不同密度流體的動力學，並發現小規模的擾動，例如波發生時在不同流體間邊界的反應。
在一些波長短到一定程度的狀態下，如果忽略表面張力，以不同速度平行運動的兩種不同密度流體的介面下，在所有速度時都會不穩定。然而，表面張力可抵消短波長的不穩定狀態，而理論預測直到達到速度閾值以前都是穩定的。包含表面張力的理論可大致預測在風吹過水面時產生波的界限[來源請求]。
在重力作用下，連續變化的密度和速度分布（較輕的層在上方，所以流體是瑞利－泰勒穩定）使开尔文-亥姆霍兹不稳定性的動力學是以泰勒－戈德斯坦方程描述。而不穩定性開端可由理查逊数（Richardson number，Ri）得知。通常情況下Ri<0.25就會不穩定。這些效應常在雲層中出現。對於不穩定性的研究也可應用在電漿物理學中，例如慣性局限融合和電漿－铍的介面。
在數值模式下，开尔文-亥姆霍兹不稳定性是以時間发展或空間发展方式模擬。時間发展方式下采用周期边界条件进行模拟。空間发展方式则采用实际中的入口和出口條件。
參見
[编辑]註釋
[编辑]- ^ Fox, Karen C. NASA's Solar Dynamics Observatory Catches "Surfer" Waves on the Sun. NASA-The Sun-Earth Connection: Heliophysics. NASA. [2013-08-12]. （原始内容存档于2021-11-20）.
參考資料
[编辑]
维基共享资源上的相关多媒体资源：开尔文-亥姆霍兹不稳定性
- Lord Kelvin (William Thomson). Hydrokinetic solutions and observations. Philosophical Magazine. 1871, 42: 362–377.
- Hermann von Helmholtz. Über discontinuierliche Flüssigkeits-Bewegungen [On the discontinuous movements of fluids]. Monatsberichte der Königlichen Preussische Akademie der Wissenschaften zu Berlin [Monthly Reports of the Royal Prussian Academy of Philosophy in Berlin]. 1868, 23: 215–228.
- Article describing discovery of K-H waves in deep ocean: Broad, William J. In Deep Sea, Waves With a Familiar Curl. New York Times. April 19, 2010 [April 2010]. （原始内容存档于2022-02-12）.
外部連結
[编辑]- Hwang, K.-J.; Goldstein, Kuznetsova, Wang, Viñas, Sibeck. The first in situ observation of Kelvin-Helmholtz waves at high-latitude magnetopause during strongly dawnward interplanetary magnetic field conditions. J. Geophys. Res. 2012, 117 (A08233). Bibcode:2012JGRA..117.8233H. doi:10.1029/2011JA017256.
- Giant Tsunami-Shaped Clouds Roll Across Alabama Sky （页面存档备份，存于互联网档案馆） - Natalie Wolchover, Livescience via Yahoo.com
- Tsunami Cloud Hits Florida Coastline （页面存档备份，存于互联网档案馆）
- Vortex formation in free jet （页面存档备份，存于互联网档案馆） - YouTube video showing Kelvin Helmholz waves on the edge of a fre jet visualised in a scientific experiment.