# Nondimensionalising and Reynolds number

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 May 23, 2014, 13:28 Nondimensionalising and Reynolds number #1 New Member   nilesh Join Date: Mar 2014 Location: Kanpur / Mumbai, India Posts: 27 Rep Power: 4 Hi, I am using incompressible flow solver (ROE MUSCL) to solve flow over NACA 0018. In the physical problem: density=1.2256, dynamic viscosity=1.789*10^-5, velocity=7.8 m/s, chord=0.2 m. So the Reynolds number based on chord turns out to be approx 10^5. In computation: density=1.2256, dynamic viscosity=1.789*10^-5, velocity=7.8 m/s, but I have a mesh with chod=1. I tried setting MESH_SCALE_CHANGE=0.2 but the Reynolds number is being considered as 5*10^5 as if the chord is still being considered as 1. What is it that is going wrong? Thanks.

 June 5, 2014, 02:49 #2 Senior Member   Heather Kline Join Date: Jun 2013 Posts: 241 Rep Power: 6 Thank you for your question. You need to set the REYNOLDS_LENGTH. By default it is 1.0 I am not familiar with the scale setting you mention - we used to have a convert_to_meter setting, however I think that been discontinued in favor of requiring meshes to be defined in meters. However that will not affect the Reynolds length - it will always be 1.0 unless set otherwise.

June 5, 2014, 14:50
#3
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Thomas D. Economon
Join Date: Jan 2013
Location: Stanford, CA
Posts: 270
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Quote:
 Originally Posted by nilesh In computation: density=1.2256, dynamic viscosity=1.789*10^-5, velocity=7.8 m/s, but I have a mesh with chod=1. I tried setting MESH_SCALE_CHANGE=0.2 but the Reynolds number is being considered as 5*10^5 as if the chord is still being considered as 1. What is it that is going wrong? Thanks.
Hi,

For the incompressible solver in SU2, we assume that the Reynolds length is always 1.0 m. In order to define your flow conditions correctly, please supply a Reynolds number per meter in the config file. However, it should be noted that for the compressible solver, we do indeed use the Reynolds length in meters within the config file.

Hope this helps,
Tom

 June 13, 2014, 15:10 #4 New Member   nilesh Join Date: Mar 2014 Location: Kanpur / Mumbai, India Posts: 27 Rep Power: 4 Thanks. I got it.

 July 31, 2014, 12:45 Nondimensionalising and Reynolds number #5 New Member   Amit Join Date: Jul 2014 Posts: 11 Rep Power: 4 i dont know how is reynolds number per metre is exactly to be mentioned in the cfg file, please guide.

July 31, 2014, 20:37
#6
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Heather Kline
Join Date: Jun 2013
Posts: 241
Rep Power: 6
Quote:
 Originally Posted by Amit_Pawarpawar i dont know how is reynolds number per metre is exactly to be mentioned in the cfg file, please guide.
Set it with REYNOLDS_NUMBER - when the reynolds length is set to 1.0 they are equivalent.

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