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ashtonJ January 17, 2011 20:33

Reynolds Number Calculation
Hi all

I am confused about value of Reynolds Number shown in CFX-Solver Output file.

I simulated a laminar flow in a constricted pipe which diameter of the non-constricted section is 20 mm. At Inlet of pipe, streamwise and spiral velocity profiles are applied as Inlet boundary condition as below:

Streamwise Velocity Profile: 2*0.0875 [m/s]*(1-(r/R)^2)
Spiral Velocity Profile: 1.46 [1/s]*r

Density and Viscosity are 1060 [kg/m^3]and 0.00371 [pa.s].

When I calculate Reynolds number at Inlet, it becomes 500 while in CFX-Solver Output text file, Reynolds number is mentioned as 1900.

Does anybody know how CFX calculate Reynolds number?


Lance January 18, 2011 03:52


jvr February 16, 2011 06:36

i want to calculate the Reynolds number of exhaust gas with a given temperature(c) and massflow(g/s).
What is the fastest way?
thanks in advance

Lance February 16, 2011 06:44

um... the fastest way? Why not use the definition of Reynolds number?
Re = density scale*length scale*velocity scale/viscosity scale
Or are you comparing against some other definition of Re?

jvr February 16, 2011 06:53

thanks for the reply man.

isn't it density * velocity * diameter of the pipe / viscosity ?

but then the next problem is that i don't know how to calculate the density of the exhaust gas and the viscosity ?

Lance February 16, 2011 12:08

So you are modeling pipe flow? Then the length scale is usually the diameter of the (circular) pipe.

To get the density and viscosity you could use areaAve(density)@outlet and areaAve(viscosity)@outlet, but again, it depends on what you are comparing with.

ali.ghaemi October 14, 2013 10:50

Calculatin Re number in complex Geometries
Hi Foamer

do you know if it is possible to calculate the Re number in different parts of a complex geometry using openFoam?

ghorrocks October 14, 2013 17:26

Try the openfoam forum.

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