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

Les jets libres démontrent le comportement du fluide décrit par l'équation de Bernoulli, car le fluide sort d'une buse et s'écoule librement dans l'air.
La vitesse d’écoulement au niveau de la tuyère est déterminée par la hauteur de la colonne de fluide au-dessus d’elle, qui convertit l’énergie potentielle en énergie cinétique.
La pression de sortie du jet correspond à la pression atmosphérique et la vitesse augmente à mesure que le fluide s'écoule d'un grand réservoir.
En raison de l’inertie du fluide, le jet se rétrécit juste à l’extérieur de la buse, formant la plus petite section transversale. Ce phénomène est connu sous le nom de veine contractée.
Le rapport entre la surface du jet au niveau de la veine contractée et la surface de la buse donne le coefficient de contraction.
Diverses formes de buses, telles que les conceptions à tranchant de couteau, bien arrondies, à arêtes vives et rentrantes, ont un impact sur le modèle d’écoulement et le coefficient de contraction.
Lors de la conception de systèmes tels que les déversoirs et les déversoirs, l’effet de la veine contractée est pris en compte pour une mesure précise du débit.
Les jets libres sont cruciaux dans les applications de génie civil pour contrôler l’écoulement des fluides et minimiser l’impact structurel.

jet libre

Les jets libres décrivent l'écoulement d'un liquide sortant d'un réservoir par une ouverture dans l'atmosphère sans résistance. La vitesse (V) du jet de liquide est dérivée à l'aide du principe de Bernoulli et exprimée comme suit:

<img alt="Equation 1" src="/files/ftp_upload/18037/18037_Equation_1.svg" style="text-align: center; height: 15px;">

Où h est la hauteur du liquide au-dessus de l'ouverture. Cette relation suppose une pression atmosphérique à la fois à la surface du réservoir et à la sortie du jet. La hauteur de la colonne de fluide régit la vitesse du fluide au niveau de la buse d'un réservoir, où l'énergie potentielle du fluide se transforme en énergie cinétique pendant l'écoulement.

Le phénomène de vena contracta se produit lorsque le liquide sort par un orifice à arêtes vives, ce qui fait que le diamètre du jet d_j est inférieur au diamètre de la buse d_o. Cela se produit parce que les lignes de courant du fluide ne peuvent pas suivre les bords abrupts, créant une région d'écoulement contractée. Le coefficient de contraction est le rapport entre la surface transversale du jet au niveau de la vena contracta et la surface transversale de la buse, quantifiant le degré de contraction du jet. Ce paramètre est influencé par la géométrie de la buse, avec différentes conceptions telles que les buses à bord tranchant, à bord tranchant, bien arrondies et rentrantes produisant des modèles d'écoulement et des caractéristiques de contraction distinctes. Pour une buse bien arrondie, C_c = 1,0, tandis que les orifices à bord tranchant ou à bord tranchant réduisent C_c à environ 0,61. Les buses rentrantes présentent des valeurs encore plus basses.

Ces caractéristiques d'écoulement et ces effets de contraction sont essentiels dans les applications d'ingénierie impliquant la décharge de liquide, des réservoirs aux buses industrielles.

Jet libre

Les jets libres démontrent le comportement du fluide décrit par l'équation de Bernoulli, car le fluide sort d'une buse et s'écoule librement dans l'air.
La vitesse d’écoulement ...

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

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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free jet

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...

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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

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

Liquid Speed from Reservoir Outlets

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