Froude Number

[305Gurl]

I have solved several different geometry type problems using the Froude Number equations provided in CERM, but this question pops up in my head just now and I am freaking out, because of uncertainty (and also since the exam is drawing near). I just realized that I have not solved a problems; I have only done this for partial flows and for square and trapezoid.

Could someone please confirm that for a pipe flowing full, the value for Dh in the Froude equation would actually be the pipe diameter.

For example: Given a 6-ft diameter pipe, and velocity is 100 ft/sec. the Fr # = 6/[sqrt (32.2 * 6ft)] = 0.432, which is a sub critical flow regime.

Thank you!

 

[civilized_naah]

Could someone please confirm that for a pipe flowing full, the value for Dh in the Froude equation would actually be the pipe diameter.

For example: Given a 6-ft diameter pipe, and velocity is 100 ft/sec. the Fr # = 6/[sqrt (32.2 * 6ft)] = 0.432, which is a sub critical flow regime.

Thank you!

Answering the second question first, why are you putting the diameter (6 ft) in the numerator? It should be the velocity (100 ft/sec), which will yields Fr = 7.2 (supercritical)

As far as the first question is concerned, the hydraulic depth is defined as the "area of flow/width at the free surface". When the pipe flows full, the free surface disappears. Also, for a pipe flowing full the Froude number is not that relevant because it is not a free surface flow.

 

[305Gurl]

Could someone please confirm that for a pipe flowing full, the value for Dh in the Froude equation would actually be the pipe diameter.

For example: Given a 6-ft diameter pipe, and velocity is 100 ft/sec. the Fr # = 6/[sqrt (32.2 * 6ft)] = 0.432, which is a sub critical flow regime.

Thank you!

Answering the second question first, why are you putting the diameter (6 ft) in the numerator? It should be the velocity (100 ft/sec), which will yields Fr = 7.2 (supercritical)

As far as the first question is concerned, the hydraulic depth is defined as the "area of flow/width at the free surface". When the pipe flows full, the free surface disappears. Also, for a pipe flowing full the Froude number is not that relevant because it is not a free surface flow.

Civilized Thanks for your response....That was definitely a typo on my part.