Typical flow velocities in RCP

[harboe]

This is a second part to my other thread "Need to calculate divergent flow". Using WSPG, I have modeled a single 24-inch line necking down to a single 18-inch with 23 CFS but the velocities become very high, on the order of 30-35 feet per second (Like 20-25MPH!). Is this common in RCP? The slope varies from about 0.0025ft/ft to 0.01ft/ft. The HGL goes to the top of the pipe at the end of the model I would have expected it to go slower but under higher head.

Thanks.

 

[RWF7437]

Are you sure you've modeled this correctly ? What starting water level did you use ? Did you assume normal depth at the downstream end? / Normal depth upstream ? /some other depth?

Did you try modeling it several ways? Which solution required the least energy and which the least momentum ?

 

[cvg]

assuming full flow you would have about 13 fps in the 18" pipe, so it seems that you are supercritical and not flowing full. Doesn't seem reasonable with that much flow and only 1% slope. better check your numbers. add some head loss at the reducer and check your mannings n value. if you really do have 35 fps, you need to reduce this - it is way too high

 

[RWF7437]

Harboe,

In your other thread on this subject you said you were reducing from a 24" dia. to TWO 18" doa. pipes. In this thread you say ONE 18" pipe. Which is it?

This is confusing !

good luck