hydraulic jump


What's a hydraulic jump?

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Determining the loss of specific energy in a hydraulic jump

At the hydraulic jump a supercritical discharge Q becomes subcritical again. The discharge depth h rises rapidly and increases after the hydraulic jump. Energy is dissipated at the hydraulic jump due to the resulting turbulence. However, the momentum is retained, which means that there are two sequent depths h for the same specific force F. The ratio of the sequent depths h1 and h2 is described by the following formula:

Using the given specifi c energy diagram and an analogue specifi c force diagram, it is a simple matter to determine the resulting specific energy loss ΔE graphically:

The discharge depth h1 is entered in the specific energy diagram and the specific force diagram (points 1 and 2). To determine the discharge depth h2 after the hydraulic jump, the sequent depth to h1 is determined graphically in the specific force diagram (point 3). The specific forces F1 in point 2 and F2 in point 3 are equal (conservation of momentum). Then the discharge depth h2 is entered in the specific energy diagram (point 4). The specific energies E1 and E2 are read in the diagram. The specific energy loss ΔE that occurs in the hydraulic jump is equal to the difference between the specific energies.

The resulting specific energy loss ΔE can also be calculated using the following formula: