Force of water out of a vertical pipe

[mehr27]

Hello. I have water on a bridge deck flowing into a gutter and into an 8 inch pipe that runs down the length of a 90 foot column. The pipe has a 90 degree bend at the bottom just before the water expels out of the column.

The water is flowing out too quickly and onto a nearby street. I am attempting to stop the water by using a steel plate approximately 6 inches in front of the pipe. (The client does not want to use an elbow.)

In order to design the steel plate, how can I calculate the force of water expelled from the pipe?

Thanks,
Glenn

 

[rconner]

This design/situation sounds a little strange, but per your inquiry if you have access to Lindeburgh's "Civil Engineering Reference Manual" there is a calculation procedure "40." shown therein (e.g. pg 17-32 of the 7th ed.) for the force "Fx" of an "Open Jet on a Vertical Flat Plate".
I guess it must be remembered however, that the water must go somewhere from there once it is dissipated around the plate; also, I suspect some folks instead/also use flare or bell mouth outlets, I suspect to more widely disperse the flow/reduce force (from discharge points) than from a straight ell constriction etc.

 

[JStephen]

I doubt a flared section would affect the outflow much.

Basically, treat the flat plate as though it were an ell, assume it changes the direction of the water by 90 degrees. Force is derived from Reynold's Transport Theorem using momentum as the property in question.

 

[rconner]

You may be interested in checking out some of the interesting products I happened to see that among other things minimize erosion damage in hydrant/pipeline flushing operations at

http://pollardwater.com/

(including the interesting "Hose Monster" device).

 

[mflam]

Sounds pretty tacky.
Clearly, we're talking about storm water here.
Have you considered removing the offending elbow and inserting the end of the pipe in a prefabbed concrete box. That would dissipate the energy without the "open shower" effect.