Why does hydraulic jump occur

Remember Me! Don't have account, Join Here. Forgot Password Lost your password? Ask A Question. What Is Hydraulic Jump? Types and Characteristics of Hydraulic Jump. Undular Hydraulic Jump — Froude Number 1 to 3 : 2. Weak Jump — Froude Number 3 to 6 3. Oscillating Hydraulic Jump — Froude Number 4. In FishXing a hydraulic jump can only occur if the following two conditions are satisfied:. If both of these conditions exist FishXing checks for the possibility of a jump occurring within the culvert.

FishXing solves the Gradually Varied Flow equations in the downstream direction frontwater calculations starting from critical depth at the inlet. This gives a supercritical water surface profile. Next, FishXing performs backwater calculations starting at the outlet with the water depth equal to the tailwater depth.

Proceeding upstream, the backwater calculations produces a subcritical water surface profile. At any given point in the culvert there is now both a supercritical and subcritical depth. In fluid dynamics , the equation of continuity is effectively an equation of conservation of mass. Considering any fixed closed surface within an incompressible moving fluid, the fluid flows into a given volume at some points and flows out at other points along the surface with no net change in mass within the space since the density is constant.

Its differential form the equation of continuity is:. Since the density is constant and we are considering only a 2-dimensional case, this integrates to:. Negative answers do not yield meaningful physical solutions, so this reduces to:.

The greater that the flow is supercritical, the more pronounced the jump will be. Practically this means that water accelerated by large drops can create stronger standing waves in the form of hydraulic jumps as it decelerates at the base of the drop.

Such standing waves, when found downstream of a weir or natural rock ledge, can form an extremely dangerous "keeper" with a water wall that "keeps" floating objects e. A similar analysis, reaching exactly the same results, derives the same results starting with the impulse-momentum principle. This equation yields the same overall relationship between jump height and Froude number. One of the most important engineering applications of the hydraulic jump is to dissipate energy in canals, dam spillways, and similar structures so that the excess kinetic energy does not damage these structures.

The energy dissipation or head loss across a hydraulic jump is a function of the magnitude of the jump. The larger the jump as expressed in the fraction of final height to initial height, the greater the head loss. Analytically using the model developed by R. McDonald [4] , the fractional energy loss FEL can be expressed in terms of the Froude number F r 0 for the incident flow as:.

Since this is equivalent to concluding the energy loss can be predicted by predicting or measuring the speed and depth of the entering water. In the design of a dam the energy of the fast-flowing stream over a spillway must be partially dissipated to prevent erosion of the streambed downstream, which could ultimately lead to failure of the dam.

This can be done by arranging for the formation of an hydraulic jump to dissipate energy. To limit damage, this hydraulic jump normally occurs on an apron engineered to withstand hydraulic forces and to prevent local cavitation and other phenomena which accelerate erosion.

In the design of a spillway and apron, the engineers select the point at which a hydraulic jump will occur. Obstructions such as a lip or slope changes are routinely designed into the apron to force a jump as a specific location — obstructions are unnecessary as the slope change alone is normally sufficient. To trigger the hydraulic jump without obstacles, an apron is designed such that the flat slope of the apron retards the rapidly flowing water from the face of the dam.

If the apron slope is insufficient to maintain the original high velocity, a jump will occur. In both cases, the final depth of the water is determined by the downstream characteristics.

The jump will occur if and only if the level of inflowing supercritical water level h 0 satisfies the condition:. In fluid dynamics , gravity waves are waves generated in a fluid which has as the restoring force, gravity. Gravity waves on an air-water interface are called surface gravity waves or surface waves. Hydraulic jumps, ocean waves and tsunamis can all be treated as examples of gravity waves.

The wave speed or celerity speed of individual waves, as opposed to the speed of a group of waves of gravity waves in shallow water is given by:. The constraints on the approximation for the speed of a gravity wave as for shallow depths are:. A hydraulic jump can be viewed as discontinuous waves of all frequencies wavelengths , which are generated and propagate from a point near the jump.

The waves propagate both upstream and downstream. Since a large fraction of the waves fall in a wavelength range where they are shallow water gravity waves that move at the same speed for a given depth, they move upstream at the same rate; however as the water shallows upstream, their speed drops quickly, limiting the rate at which they can propagate upstream to.

Shorter wavelengths, which propagate more slowly than the speed of the wave in the deeper downstream water, are swept away downstream. Still, a fairly wide range of wavelengths and frequencies are present, so Fourier Analysis would suggest that a relatively abrupt wave front can be formed; this is indeed observed. Viewing the hydraulic jump from a wave perspective provides another insight into the phenomena.

When the incoming water speed is slow enough, a number of the longer wavelength waves propagate faster than the incoming flow, and can disperse upstream as well as downstream.