# How to compute Reynolds number from information in inv_NACA0012.cfg ?

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April 7, 2021, 13:55
How to compute Reynolds number from information in inv_NACA0012.cfg ?
#1
New Member

Harry Kim
Join Date: Sep 2015
Posts: 6
Rep Power: 10
I'm struggling about calculating Reynolds number based on the flow conditions given in "inv_NACA0012.cfg" file. (txt file attached)

According to the free-stream definition in the .cfg file,
Mach number = 0.8 and Freestream Temperature = 273.15

I could calculate Reynolds number using

Re = (Freestream vel* Length of Airfoil)/Kinematic viscosity
= (Mach number*Speed of Sound @ 273K * Length of Airfoil)/Kinematic vis

How to know "Length of the Airfoil" to calculate Free-stream Reynolds Number based on information in the .cfg file?

If I have something wrong for Re calculation, please correct me.

FYI, this is the simplest test case for SU2 in the QuickStart tutorial.

Attached Files
 inv_NACA0012.txt (14.0 KB, 3 views)

 April 9, 2021, 00:35 #2 Member   Amit Join Date: May 2013 Posts: 85 Rep Power: 12 You need not input the Reynolds number for inviscid flow calculations. Adequate information is supplied in the file you have attached (M, P, T). Also reference length is mentioned here in file for this case as - REF_LENGTH= 1.0. Anyways, you can work out Reynolds number as - Re=Rho*V*Lref/mu Get Rho from P, T. Obtain V=Mach*sqrt(Gamma*R*T), Lref is specified and mu can be computed from Sutherland's formula.

April 9, 2021, 00:53
#3
New Member

Harry Kim
Join Date: Sep 2015
Posts: 6
Rep Power: 10
Quote:
 Originally Posted by aero_amit You need not input the Reynolds number for inviscid flow calculations. Adequate information is supplied in the file you have attached (M, P, T). Also reference length is mentioned here in file for this case as - REF_LENGTH= 1.0. Anyways, you can work out Reynolds number as - Re=Rho*V*Lref/mu Get Rho from P, T. Obtain V=Mach*sqrt(Gamma*R*T), Lref is specified and mu can be computed from Sutherland's formula.
Oh, you are right. Reynolds number in inviscid flow is theoretically infinite. I was just stupid being confused with viscous flow. Thanks for reminding me that!

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