Overflow coefficient
The discharge coefficient is a μ in hydraulic common dimensionless coefficient for calculating the amount of water during storage of a body of water by a fixed weir or a movable closure member coat (in response to the overflow height ).
use
The weir flow ( volume flow ) with the SI unit is determined according to the mathematical relationship often referred to as the Poleni formula:
With
- Acceleration due to gravity (= at the surface of the earth)
- Width of the raid
- Overflow height ( measured at least away from the overflow edge in the direction of the headwater , better further).
Because the flow increases disproportionately with the overflow height, overflows are suitable structures for flood or emergency relief .
Conversely, the spill height increases only disproportionately with increasing spill volume:
This is why raids are ideal for regulating the water level when the outflows change .
values
The overflow coefficient is primarily a function of the transition shape and thus takes into account the shape of the beam deflection. For an initial pre-dimensioning , it is sufficient to assume the overflow coefficient for a weir or overflow structure that is straight in the floor plan according to the following information:
number | Training of the military crown | Overflow coefficient |
---|---|---|
1. | wide, sharp-edged, horizontal | 0.49-0.51 |
2. | wide, well rounded edges, horizontal | 0.50-0.55 |
3. | wide, completely rounded weir crown, reaches z. B. by a deflected storage flap | 0.65-0.73 |
4th | sharp-edged, ventilated overflow jet | ~ 0.64 |
5. | Round crown, vertical upstream and sloping downstream side | 0.73-0.75 |
6th | Roof-shaped, rounded weir crown | 0.75-0.79 |
Secondly, the overflow coefficient is also a function of the flow velocity and the amount of overflow water or the overflow height itself.
literature
- Gerhard Bollrich, G. Preißler: Technical hydromechanics. 5th edition. Volume 1, Verlag für Bauwesen, 2000, ISBN 3-345-00744-4 .