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-   -   Nondimensionalising and Reynolds number (http://www.cfd-online.com/Forums/su2/136172-nondimensionalising-reynolds-number.html)

nilesh May 23, 2014 13:28

Nondimensionalising and Reynolds number
 
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.

hlk June 5, 2014 02:49

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.

economon June 5, 2014 14:50

Quote:

Originally Posted by nilesh (Post 493844)
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

nilesh June 13, 2014 15:10

Thanks. I got it.

Amit_Pawarpawar July 31, 2014 12:45

Nondimensionalising and Reynolds number
 
i dont know how is reynolds number per metre is exactly to be mentioned in the cfg file, please guide.

hlk July 31, 2014 20:37

Quote:

Originally Posted by Amit_Pawarpawar (Post 503957)
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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