# Reynolds Number Calculation

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 January 17, 2011, 20:33 Reynolds Number Calculation #1 Senior Member   Ashkan Javadzadegan Join Date: Sep 2010 Posts: 245 Rep Power: 9 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? Regards Ashtonj

 January 18, 2011, 03:52 #2 Senior Member   Lance Join Date: Mar 2009 Posts: 598 Rep Power: 12

 February 16, 2011, 06:36 #3 New Member   Join Date: Feb 2011 Posts: 3 Rep Power: 7 hi, 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

 February 16, 2011, 06:44 #4 Senior Member   Lance Join Date: Mar 2009 Posts: 598 Rep Power: 12 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?

 February 16, 2011, 06:53 #5 New Member   Join Date: Feb 2011 Posts: 3 Rep Power: 7 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 ?

 February 16, 2011, 12:08 #6 Senior Member   Lance Join Date: Mar 2009 Posts: 598 Rep Power: 12 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.

 October 14, 2013, 10:50 Calculatin Re number in complex Geometries #7 New Member   Ali Join Date: Dec 2012 Posts: 9 Rep Power: 5 Hi Foamer do you know if it is possible to calculate the Re number in different parts of a complex geometry using openFoam?

 October 14, 2013, 17:26 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,709 Rep Power: 98 Try the openfoam forum.

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