Vena contracta

Japanese: 縮流 - しゅくりゅう（英語表記）vena contracta

Also called contraction or constriction. When a fluid leaves a container's outlet, the cross-sectional area of the flow that is in contact with the atmosphere asymptotically approaches a value S∞ _that is smaller _than the cross-sectional area of the outlet S0 ₍ Figure). The ratio k = S∞ / S _of S∞ to S0 is called _the coefficient of contraction, and has a theoretical minimum value between 0.5 and 1. If the hole is too thin, the phenomenon becomes complicated due to viscosity and surface tension. [Hashimoto Hidenori]

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

縮脈，くびれともいう。流体が容器の流出口から出ていくとき，大気に接する流れの断面積が出口の断面積S₀よりも小さい値S_∞に漸近する現象(図)。S_∞とS₀との比k＝S_∞/Sはくびれの係数coefficient of contractionと呼ばれ，理論的な最小値0.5と1の間の値をとる。孔が細すぎると，粘性や表面張力のために現象が複雑になる。【橋本英典】

出典　株式会社平凡社世界大百科事典第２版について　情報

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