Jump
The alternating jump (also water jump or hydraulic jump ) is a term from the hydromechanics of open channels . It is an abrupt change in flow from very fast to very slowly flowing water. A hydraulic jump is z. B. the water roller .
The reverse case (see section on delimitation below ) is also a flow change, but takes place continuously.
Discharge velocities related to the water depth
If the runoff in a channel is faster than the speed of propagation of disturbances ( waves ), then this is called torrential or supercritical runoff ( ).
If the runoff is slower than the speed of propagation of disturbances, then this is called flowing or subcritical runoff ( ).
The Froude number is used to differentiate :
With
- v = mean speed,
- g = acceleration due to gravity ,
- h = water depth.
Jump
An alternating jump (hydraulic jump) occurs at the flow transition from the shooting to the flowing discharge:
- Transition occurs suddenly (discontinuously)
- significant energy losses when shooting from the upper water into the lower water
- The water depth is greater than the water limit
- Speed is less than the speed limit
- if the inflow is increasing with Fr <1.7, an undulating or undulating alternating jump occurs
An analogous phenomenon are shock waves in gas flows. The Mach number in gases corresponds to the Froude number in channel flows.
The mechanism of energy conversion in the hydraulic jump is to that in the breaking of breakers used.
Demarcation
A second type of flow transition (no jump) occurs from flowing to flowing drainage:
- The prerequisite is the channel discontinuity
- Change in water depth is continuous
- Speed is greater than the speed limit.
See also
- Compression shock - analogous phenomenon in gases that behave as a compressible fluid
- hydraulic jump in the foehn weather phenomenon
literature
- Gerhard H. Jirka, Cornelia Lang: Introduction to Channel Hydraulics , Universitätsverlag, Karlsruhe 2009, ISBN 978-3-86644-363-1
Web links
- M. Koch: Technical hydraulics (PDF; 205 kB) , script, University of Kassel
- Gerhard H. Jirka, Cornelia Lang: Introduction to channel hydraulics. (PDF) Archived from the original on March 1, 2014 ; accessed on March 17, 2015 (8400 kB).
Individual evidence
- ↑ Wolfgang Schröder : Fluid Mechanics. Wissenschaftsverlag Mainz in Aachen 2004 , ISBN 3-86130-371-X , p. 125.