Name: liquid speed from reservoir outlets
Uploaded: 2026-01-30T03:08:28.000Z
Duration: 1 min 14 s
Channel: JoVE

フリージェットは、ベルヌーイの方程式で表される流体の挙動を示し、流体がノズルを出て自由に空気中に流れ込みます。
ノズルの流速は、その上の流体柱の高さによって決定され、位置エネルギーを運動エネルギーに変換します。
ジェットの出口圧力は大気圧と一致し、流体が大きな貯留層から流れるにつれて速度が増加します。
流体の慣性により、ジェットはノズルのすぐ外側で狭くなり、最小の断面積を形成します。この現象は、大静脈収縮として知られています。
大静脈収縮部でのジェットの面積とノズルの面積の比が収縮係数を与えます。
ナイフエッジ、丸みを帯びた、シャープエッジ、リエントラント設計など、さまざまなノズル形状がフローパターンと収縮係数に影響を与えます。
余水吐や堰などのシステムを設計する際には、正確な流量測定のために大静脈収縮効果が考慮されます。
フリージェットは、流体の流れを制御し、構造的影響を最小限に抑えるために、土木工学用途で非常に重要です。

自由噴流

自由噴流は、液体が貯留槽から開口部を通じて抵抗なく大気中に流れ出る流れを表します。液体噴流の速度 (V) はベルヌーイの定理を使用して導き出され、次のように表されます:

<img alt="Equation 1" src="/files/ftp_upload/18037/18037_Equation_1.svg" style="text-align: center; height: 15px;">

 ここで、h は開口部より上の液体の高さです。この関係は、貯留槽の表面と噴流出口の両方に大気圧があることを前提としています。流体柱の高さは、貯留槽内のノズルでの流体の速度を制御します。ノズルでは、流体の位置エネルギーが流れ中に運動エネルギーに変換されます。

 縮流現象は、液体が鋭いエッジのオリフィスから出るときに発生し、ジェットの直径 d_j がノズルの直径よりも小さくなります。これは、流体の流線が急なエッジに沿うことができず、縮流領域が形成されるために発生します。縮流係数は、縮流におけるジェットの断面積とノズルの断面積の比であり、ジェットの縮流の程度を定量化します。このパラメータはノズルの形状によって影響を受け、ナイフエッジ、鋭いエッジ、丸みを帯びたノズル、凹みのあるノズルなど、さまざまな設計によって、明確な流れパターンと収縮特性が生成されます。丸みを帯びたノズルの場合、C_c = 1.0 ですが、鋭いエッジまたはナイフエッジのオリフィスでは C_c が約 0.61 に低下します。凹みのあるノズルでは、さらに低い値を示します。

 これらの流れ特性と収縮効果は、貯留槽から工業用ノズルまで、液体排出を伴う工学応用で重要です。

フリージェットは、ベルヌーイの方程式で表される流体の挙動を示し、流体がノズルを出て自由に空気中に流れ込みます。
流速...

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

Fluid Dynamics

流体力学

KEY TERMS AND CONCEPTS

主要用語と概念

Free Jet

liquid speed from reservoir outlets

Free jets show how liquid moves after leaving a reservoir through an opening and flowing into the air without resistance. The jet speed is found with Bernoulli’s principle, and it depends on the height of liquid above the opening. This relationship assumes atmospheric pressure at both the reservoir surface and the jet exit.

The liquid column’s height controls the speed at the nozzle because the fluid’s potential energy changes into kinetic energy during flow. As the liquid leaves the reservoir, its motion reflects this energy conversion. This is why a deeper liquid level can produce a faster jet.

A sharp-edged orifice can also cause vena contracta, which is the narrowed region where the jet becomes smaller than the nozzle opening. This happens because the streamlines cannot follow the abrupt edge smoothly. The contraction coefficient measures this narrowing by comparing the jet area at vena contracta with the nozzle area.

Nozzle shape changes the flow pattern and the amount of contraction. Knife-edge, sharp-edge, well-rounded, and re-entrant nozzles each produce different results. For a well-rounded nozzle, the contraction coefficient is 1.0, while sharp or knife-edged openings reduce it to about 0.61, and re-entrant nozzles produce even lower values. These effects matter in engineering systems that discharge liquid from reservoirs and industrial nozzles.

Liquid Speed from Reservoir Outlets

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key terms and concepts

Learn how liquid speed from a reservoir depends on height, Bernoulli’s principle, and nozzle shape, including vena contracta and contraction coefficient.

Liquid Speed from Reservoir Outlets | JoVE K12

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Liquid Speed from Reservoir Outlets

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