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

Dans un fluide s’écoulant dans un tuyau, la ligne d’énergie représente l’énergie totale du fluide, combinant la pression, la vitesse et les hauteurs d’élévation.
En revanche, la ligne de gradient hydraulique ne montre que la somme des charges de pression et d’élévation, à l’exclusion de la vitesse.
Ces lignes représentent visuellement la distribution de l’énergie et de la pression dans un système d’écoulement de fluides.
La différence entre ces lignes est la charge de vitesse ; la ligne d’énergie est toujours supérieure à la ligne de gradient hydraulique pendant l’écoulement.
Dans un fluide stationnaire, les lignes de gradient d’énergie et hydrauliques coïncident.
La pression positive se produit lorsque la ligne de gradient hydraulique se trouve au-dessus du tuyau ; la pression négative se produit lorsqu'elle est en dessous, ce qui peut causer des problèmes tels que la cavitation.
Le maintien de la pente hydraulique au-dessus de l’élévation du tuyau permet d’éviter des problèmes tels que l’entraînement d’air et la défaillance structurelle de la conduite.
Dans les systèmes de siphon, la compréhension de ces conduites garantit une pression adéquate pour maintenir un débit ininterrompu.
La surveillance de ces conduites permet de détecter les fuites ou les blocages et de concevoir des systèmes pour éviter les coups de bélier ou les refoulements.
Des instruments tels que les tubes de Pitot et les piézomètres mesurent ces lignes, ce qui facilite la conception et l’analyse des systèmes hydrauliques en génie civil.

ligne d'énergie et ligne de gradient hydraulique

Energy Line and Hydraulic Gradient Line

Basées sur l'équation de Bernoulli, la ligne d'énergie (EL) et la ligne de pente hydraulique (HGL) fournissent des représentations graphiques de la distribution d'énergie dans un système d'écoulement de fluide. Pour les écoulements stables, incompressibles et non visqueux, l'équation de Bernoulli s'exprime comme suit:

<img alt="Equation 1" src="/files/ftp_upload/18039/18039_Equation_1.svg" style="text-align: center; height: 34px;">

Ici, H est la charge totale, p/γ​ est la charge de pression, V^2/2g​ est la charge de vitesse et z est la charge d'élévation.

La ligne d'énergie (EL) représente la charge totale disponible dans l'écoulement. Elle est située au-dessus du référentiel et comprend les trois composantes énergétiques. Dans des conditions idéales, elle reste horizontale, car l'énergie totale ne varie pas le long d'une ligne de courant. L'élévation de l'EL peut être mesurée à l'aide d'un tube de Pitot, qui capture la pression de stagnation et fournit la valeur d'énergie totale.

La ligne de pente hydraulique (HGL) représente la charge piézométrique (p/γ+ z), qui exclut la charge de vitesse. Elle se situe sous l'EL d'une distance verticale, qui est égale à la hauteur de charge dynamique (V^2/2g​). Le HGL représente les variations de pression au sein du système. Dans les canalisations sous pression, elle se situe au-dessus du tuyau, tandis que dans un écoulement en canal ouvert, elle coïncide avec la surface de l'eau.

Si la vitesse du fluide ou le diamètre du tuyau change, l'élévation du HGL s'ajuste en conséquence. La hauteur de charge est nulle à la sortie du tuyau, ce qui fait que le HGL coïncide avec la hauteur de charge. Pour un écoulement stable et non visqueux d'un réservoir, l'EL et le HGL sont horizontaux, reflétant une hauteur de charge et une pression atmosphérique de sortie constantes.

Les applications pratiques intègrent souvent des effets visqueux et des pertes, qui déforment l'EL et le HGL. Ces concepts sont essentiels pour analyser la pression et les distributions d'énergie dans les systèmes fluides.

Ligne d'énergie et ligne de gradient hydraulique

Dans un fluide s’écoulant dans un tuyau, la ligne d’énergie représente l’énergie totale du fluide, combinant la pression, la vitesse et les hauteurs d’élévation.
Dans...

Education

Enseignement

JoVE Core

Civil Engineering

Génie civil

Unit 1

Unité 1

Fluid Dynamics

Dynamique des fluides

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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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energy line and hydraulic gradient line

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...

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Water slide speed is controlled by Bernoulli's principle and the height of the slide. Engineers use these ideas to keep the ride exciting while making sure the water stays safe for riders. As water moves downhill, gravity makes it speed up. The water at the bottom depends on the height it starts from. A taller slide gives the water more potential energy at the top. That energy changes into kinetic energy as the water descends, so the flow becomes faster. Bernoulli's principle helps describe...

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.

Fluid Head Profiles in Pipes and Channels | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

Fluid Head Profiles in Pipes and Channels

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