Name: flow regimes and energy in hydraulic jumps
Uploaded: 2025-03-26T15:04:31.000Z
Duration: 1 min 29 s
Channel: JoVE

A hydraulic jump is a sudden rise in fluid depth that occurs when high-velocity water transitions to a slower flow.&nbsp;This only happens in supercritical flow, where the Froude number exceeds 1. In subcritical flow (a Froude number less than 1), hydraulic jumps cannot form because the flow lacks the excess energy needed for the transition.Hydraulic jumps are classified by their upstream Froude number, each with distinct features. These types include Jump Impossible, Standing Wave or Undulant Jumps, Weak Jumps, Oscillating Jumps, Stable Jumps, and Strong Jumps.&nbsp;The depth ratio across the jump and energy dissipation, or head loss, depend on the upstream Froude number. As the Froude number increases, the depth ratio also rises, signifying a more significant change in depth through the jump.In engineering, hydraulic jumps are essential for dissipating energy in structures like dam spillways.&nbsp;High-speed water from a spillway can erode downstream channels, but a hydraulic jump helps slow the water, converting it to subcritical flow and protecting these areas. Hydraulic jumps can also appear in various configurations, such as submerged jumps, depending on channel slope or obstacles.

hydraulic jump

Hydraulic Jump

A hydraulic jump is a sudden rise in fluid depth in open channels, occurring when high-velocity (supercritical) flow transitions to low-velocity (subcritical) flow. This phenomenon requires an upstream Froude number greater than 1, as flows with Fr1&lt;1 remain subcritical, making a hydraulic jump impossible due to the need for negative head loss, which violates thermodynamic principles.The characteristics of a hydraulic jump depend on the upstream Froude number and are classified as follows:<ol><li>Jump Impossible (Fr1&lt;1): Subcritical flow prevents a hydraulic jump from forming.</li><li>Standing Wave or Undulant Jump (Fr1​=1 to 1.7): Barely supercritical flow causes minimal depth changes, forming a standing wave.</li><li>Weak Jump (Fr1​=1.7 to 2.5): A mild increase in depth occurs with low energy dissipation.</li><li>Oscillating Jump (Fr1=2.5 to 4.5): Unstable with regular oscillations, this jump moderately dissipates energy.</li><li>Stable Jump (Fr1​=4.5 to 9.0): Steady and well-balanced, this jump causes significant energy loss.</li><li>Strong Jump (Fr1​&gt;9.0): Highly turbulent with substantial energy dissipation.</li></ol>The depth ratio and head loss across the jump depend on the Froude number​. Higher Froude number​ values result in considerable depth changes and greater energy dissipation.Hydraulic jumps are vital in engineering for dissipating energy in structures like dam spillways. High-speed water exiting spillways can damage downstream channels, but hydraulic jumps convert supercritical flow to subcritical flow, reducing energy and protecting structures.In sloped or obstructed channels, hydraulic jumps, such as submerged jumps or standing waves, can adapt to channel conditions in unique ways. Submerged jumps occur when downstream depth is artificially raised by structures like weirs or gates, dissipating energy over a longer distance. On the other hand, standing waves form with minimal depth changes, offering localized energy dissipation in steep or constricted sections. These types are tailored solutions for specific engineering needs, differing in behavior, efficiency, and spatial requirements.

A hydraulic jump is a sudden rise in fluid depth in open channels, occurring when high-velocity (supercritical) flow transitions to low-velocity ...

Education

JoVE Core

Civil Engineering

Unit 1

Open Channel Flow

KEY TERMS AND CONCEPTS

flow regimes and energy in hydraulic jumps

Hydraulic jumps happen in open channels when fast, shallow water changes into slower, deeper water. This sudden rise in depth depends on the upstream Froude number, which compares flow speed to wave speed. A hydraulic jump can form only when the upstream flow is supercritical, with Fr greater than 1.

If Fr is less than 1, the flow is already subcritical, and a jump cannot form. That is because the jump would require a negative head loss, which is not possible under thermodynamic principles. When Fr is close to 1, the flow may form a standing wave or an undulant jump instead of a strong depth change.

The jump type changes with the upstream Froude number. A weak jump occurs for Fr from 1.7 to 2.5, with only a small rise in depth and little energy loss. An oscillating jump appears for Fr from 2.5 to 4.5 and is less stable, with regular surface motion and moderate energy dissipation.

A stable jump forms for Fr from 4.5 to 9.0. It is steady and balanced, and it removes a large amount of flow energy. A strong jump occurs when Fr is greater than 9.0, and it is highly turbulent with major energy dissipation. In every case, the depth ratio and head loss across the jump depend on the Froude number, and higher values produce larger depth changes.

Hydraulic jumps are important in engineering because they help protect structures by dissipating energy. They are often used in dam spillways, where fast water leaving the spillway could damage downstream channels. By changing supercritical flow to subcritical flow, the jump reduces that danger.

Some channel conditions create special forms of hydraulic jumps. A submerged jump happens when a weir or gate raises the downstream depth, so the energy is dissipated over a longer distance. Standing waves can also form in steep or constricted sections, where the depth change is small and the energy loss stays localized. These patterns are useful because they fit different channel shapes, spatial limits, and engineering needs.

Flow Regimes and Energy in Hydraulic Jumps

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Hydraulic jumps happen in open channels when fast, shallow water changes into slower, deeper water. This sudden rise in depth depends on the upstream Froude number, which compares flow speed to wave speed. A hydraulic jump can form only when the upstream flow is supercritical, with Fr greater than 1. If Fr is less than 1, the flow is already subcritical, and a jump cannot form. That is because the jump would require a negative head loss, which is not possible under thermodynamic principles.

hydraulic jump: problem solving

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key terms and concepts

Learn how hydraulic jumps form, why the Froude number matters, and how spillways and channel structures use them to reduce flow energy.

Flow Regimes and Energy in Hydraulic Jumps | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

civil engineering

Flow Regimes and Energy in Hydraulic Jumps

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