Question

For Broad crested weir Experiment:

i. Does the magnitude of the flow-rate affect the discharge coefficient Cd?

ii. Does Cd increase or decrease with increasing flow-rate?
iii. What is the pattern of the water as it passes over the weir?
iv. Would you expect the length of the weir crest to affect the discharge coefficient Cd?
v. What is the effect of drowning the weir (increasing the downstream depth)?

Answer 1

1) Magnitude of Flow Rate and Effect on Discharge Coefficient Cd

It was found that as the magnitude of the flow rate increased, so did the discharge coefficient. This may have been due to the shape of the weir which had a rectangular control section. Since the height of the water increased with increased flow, more friction loosed may have occurred.

2)Relationship Between Cd and Flow Rate

Experimental data showed that Cdincreased with increasing flow rate.

3) pattern of Flow of water is attached a image- It's for reference only.

4) Basic experiments were conducted on rectangular broad-crested . It was found that the discharge coefficient of a rectangular broad-crested weir is related to upstream total head above the crest, length of weir and Channel breadth. So As the length increases, Cd also increases..

5) The effects of varying upstream and downstream slope coefficients on discharge coefficients
of rectangular short-crested weirs were studied systemically by the combination of laboratory
experiments and numerical simulation. A calculation formula was proposed by using the dimensional
analysis between hydraulic parameters and geometrical parameters: height of weir, length of weir,
upstream overflow total energy head, and upstream and downstream slope coefficients.