Name: fluid head profiles in pipes and channels
Uploaded: 2025-02-13T15:43:14.000Z
Duration: 1 min 27 s
Channel: JoVE

パイプを流れる流体では、エネルギー線は流体の総エネルギーを表し、圧力、速度、および昇降ヘッドを組み合わせています。
対照的に、水理勾配線は、速度を除いて、圧力ヘッドと仰角の合計のみを示します。
これらの線は、流体システム内のエネルギーと圧力の分布を視覚的に表しています。
これらの線の違いは速度ヘッドであり、エネルギー線は流れ中は常に水理勾配線よりも大きくなります。
静止流体では、エネルギーと水理勾配線は一致します。
正圧は、水理勾配線がパイプより上にあるときに発生し、負圧は水圧が下にあるときに発生し、キャビテーションなどの問題を引き起こす可能性があります。
パイプの高さより上の水理勾配を維持することで、空気の巻き込みやパイプラインの構造上の故障などの問題を防ぐことができます。
サイフォンシステムでは、これらのラインを理解することで、途切れることのない流れを維持するための適切な圧力が確保されます。
これらのラインを監視することで、漏れや詰まりを検出し、ウォーターハンマーや逆流を回避するためのシステムを設計することができます。
ピトー管やピエゾメーターなどの機器は、これらのラインを測定し、土木工学における油圧システムの設計と解析を支援します。

エネルギーラインと水力勾配線

Energy Line and Hydraulic Gradient Line

ベルヌーイの方程式に基づき、エネルギーライン (EL) と水力勾配線 (HGL) は、流体フローシステムにおけるエネルギー分布のグラフ表現を提供します。定常、非圧縮、非粘性フローの場合、ベルヌーイの方程式は次のように表されます。

<img alt="Equation 1" src="/files/ftp_upload/18039/18039_Equation_1.svg" style="text-align: center; height: 34px;">

 ここで、H は全水頭、p/γ​ は圧力水頭、V^2/2g​ は速度水頭、z は位置水頭です。

 エネルギーライン (EL) は、フロー内で利用可能な全水頭を表します。これは基準点の上にあり、3 つのエネルギーコンポーネントすべてを含みます。理想的な条件下では、全エネルギーは流線に沿って変化しないため、水平のままです。EL の位置は、よどみ圧力を捕捉して全エネルギー値を提供するピトー管を使用して測定できます。

 水力勾配線 (HGL) は、速度水頭を除いた圧力水頭 (p/γ+ z) を表します。これは EL より垂直距離だけ下にあり、速度水頭 (V^2/2g​) に等しくなります。HGL はシステム内の圧力変動を表します。加圧パイプラインではパイプの上にありますが、開水路流では水面と一致します。

 流体速度またはパイプ径が変化すると、それに応じて HGL 位置が調整されます。圧力水頭はパイプ出口でゼロであるため、HGL は位置水頭と一致します。タンクからの安定した非粘性流の場合、EL と HGL は水平であり、一定の水頭と大気圧の出口圧力を反映しています。

 実際のアプリケーションでは、粘性効果と損失が組み込まれることが多く、EL と HGL が歪められます。これらの概念は、流体システム内の圧力とエネルギー分布を分析するために重要です。

パイプを流れる流体では、エネルギー線は流体の総エネルギーを表し、圧力、速度、および昇降ヘッドを組み合わせています。
で。。。

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

fluid head profiles in pipes and channels

Fluid head profiles in pipes and channels show how pressure, speed, and height change in a flowing fluid. These profiles come from Bernoulli's equation for steady, incompressible, inviscid flow. In that equation, total head includes pressure head, velocity head, and elevation head.

The energy line (EL) shows the total head available in the flow. It sits above the datum and includes all three energy parts. Under ideal conditions, the EL stays horizontal because the total energy does not change along a streamline. A Pitot tube can be used to measure the EL by capturing stagnation pressure and giving the total energy value.

The hydraulic grade line (HGL) shows the piezometric head, which is the pressure head plus the elevation head. It does not include the velocity head. The HGL lies below the EL by a vertical distance equal to the velocity head, V²/2g. It helps show pressure changes in the system.

In a pressurized pipeline, the HGL is usually above the pipe. In open-channel flow, it matches the water surface. If fluid velocity changes or the pipe diameter changes, the HGL position changes too. At a pipe outlet, pressure head is zero, so the HGL meets the elevation head.

For steady, inviscid flow from a tank, both the EL and HGL are horizontal. This reflects constant head and atmospheric pressure at the outlet. In real systems, viscous effects and losses can bend these lines. These ideas are important for reading pressure and energy in fluid systems.

Fluid Head Profiles in Pipes and Channels

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key terms and concepts

Learn how the energy line and hydraulic grade line show total head, pressure changes, and velocity effects in pipes, tanks, and open channels.

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Fluid Head Profiles in Pipes and Channels

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