velocity as function of diameter in turbulent flow ?
velocity as function of diameter in turbulent flow ?
(OP)
Dear all,
In my very old school book I found this equation to describe "velocity as function of diameter in laminar flow":
Vposition = 2 * Vavg * (1-(r^2/R^2)) ; where r = distance from the pipe centre and R = pipe radius. This results in a nice parabolic velocity profile (as can be expected for laminar flow).
My question is: do you have an equation like that for turbulent flow?
Help is much appreciated !
Kind regards,
MVD
In my very old school book I found this equation to describe "velocity as function of diameter in laminar flow":
Vposition = 2 * Vavg * (1-(r^2/R^2)) ; where r = distance from the pipe centre and R = pipe radius. This results in a nice parabolic velocity profile (as can be expected for laminar flow).
My question is: do you have an equation like that for turbulent flow?
Help is much appreciated !
Kind regards,
MVD





RE: velocity as function of diameter in turbulent flow ?
RE: velocity as function of diameter in turbulent flow ?
Not quite, the flow profile will NOT be parabolic, but more flat. Does anybody know the correct equation?
RE: velocity as function of diameter in turbulent flow ?
Correlations do exist the flow profile. Are they any good? It depends on how much straight run you have. That actual profiles will be considerably different depending on the pipe size and the fluid state. You'll have to consult the fluids literature for the recommended exponents.
Ultimately, where the profile is critical, you have to perform a in-situ profile measurement.
RE: velocity as function of diameter in turbulent flow ?
follow this link to see what I mean ->
http://home.hccnet.nl/m.dijk/pressure_drop_calculator/
Please?
RE: velocity as function of diameter in turbulent flow ?
The thickness of the wall laminar layer that offers resistance to heat and mass transfer decreases with increasing Reynolds number, from 0.0043r at Re=10,000 to 0.00055r at Re = 100,000. r is the internal radius of the pipe or circular tube.
RE: velocity as function of diameter in turbulent flow ?
saxon
RE: velocity as function of diameter in turbulent flow ?
A fairly simple equation that isn't too bad is:
Vposition = Vc (1 - r/R)^(1/n)
Vc is centerline velocity. n is a function of the Reynolds number. Varies from about 6 to 10. Specific values: n=7 for Re=10^5, n=9 for Re=10^6. More or less linear variation
on plot of n vs. log Re.
Any comments?
RE: velocity as function of diameter in turbulent flow ?
http://www.care.auckland.ac.nz/~cchr010/courses/adfluids/f2m02.pdf
RE: velocity as function of diameter in turbulent flow ?
Thanks,
Mark