Calculation of Reynolds Number In CFX
 

Hi all

I simulated a steady flow in a pipe. Mean velocity at inlet of pipe is 0.02 [m/s]. The pipe diameter is 20 [mm]. The following data has been taken from CFX solver output file.

Global Length = 5.4614E-02
Minimum Extent = 1.9994E-02
Maximum Extent = 5.4000E-01
Density = 1.0600E+03
Dynamic Viscosity = 3.7100E-03
Velocity = 2.0012E-02
Advection Time = 2.7290E+00
Reynolds Number = 3.1227E+02

When I calculate the Reynolds number with above information. It becomes 114 while as it shown above, CFX calculated 312 for Reynolds number. Does anybody know how CFX calculated the Reynolds Number?

regards
Ashtonj

CFX use Volume^(1/3) to calculate the length scale, that why you dont get the same Reynolds number.

From your data:
((0.02^2*pi/4)*(5.4e-1-2e-2))^(1/3)*1060*2e-2/3.7e-3 = 313

mean Velocity at Inlet
 

Hi,


In my output file the Velocity is shown to be 70 but if i caluculate it in CFD -Post as ave(Velocity)@Inlet then it is much higher than that.It is 129.Can anyone please tell me what is the problem.I want to know this to calculate Reynolds number manualy in CFD-Post.

Have you tried areaAve(Velocity)@inlet ?

yup...Its showing 150.659 which is more higher

Does anyone know how to calculate Reynolds number manually in CFD-Post using an expression??

If you want to calculate the Reynolds number you are comparing against literature values, you need to use the same definition of Reynolds Number.

These are my guesses:
Velocity scale = areaAve(Velocity)@inlet
Length scale = the diameter of the cylinder or chord length or whatever the geometry is
density scale = areaAve(Density)@inlet
Viscosity scale = areaAve(Viscosity)@inlet

Then you can define Re number using these numbers.