[Vino]

Hi,

I am bit confused with the parameter Reynolds Length, mainly for Incompressible flows. Let us say, I would like to simulate flow over cylinder at Re=100.

If I keep my cylinder diameter as 1 unit in mesh file, then keeping Reynolds Length as 1 , it will give me Reynolds no of 100 for the following parameters (rho=1,u=1,mu=0.01)

If I keep my cylinder diameter as 10 unit in mesh file, then keeping Reynolds Length as 1, will it give me Reynolds no of 100?(other parameters are same as above) or Do I need to specify Reynolds Length as 10?

[hlk]

Thank you for your interest in SU2.

For the incompressible solver, the Reynolds number is not used to specify the freestream flow, rather it is specified with something like below (copied from one of the test cases in the github su2code/testcases folder). In general the test cases folder is a good resource for identifying which parameters are needed for different types of simulations.


% -------------------- INCOMPRESSIBLE FREE-STREAM DEFINITION ------------------%
%
% Free-stream density (1.2886 Kg/m^3 (air), 998.2 Kg/m^3 (water))
FREESTREAM_DENSITY= 2.13163
%
% Free-stream velocity (m/s)
FREESTREAM_VELOCITY= ( 52.1572, 0.00, 0.00 )
%
% Free-stream viscosity (1.853E-5 Ns/m^2 (air), 0.798E-3 Ns/m^2 (water))
FREESTREAM_VISCOSITY= 1.853e-05

[Vino]

Thank you for your answer.

I am clear with the config setting for incompressible flow. I have a bit confusion on setting Reynolds Length, not on Reynolds Number. I found that changing Reynolds Length is changing my Reynolds number, time & time step (printed in console output at the beginning of the simulation). I hope the above question is clear.

Thanks once again.!!

[hlk]

Originally Posted by Vino

Thank you for your answer.

I am clear with the config setting for incompressible flow. I have a bit confusion on setting Reynolds Length, not on Reynolds Number. I found that changing Reynolds Length is changing my Reynolds number, time & time step (printed in console output at the beginning of the simulation). I hope the above question is clear.

Thanks once again.!!

The incompressible solver was written with the assumption of a Reynolds Length of 1.0. The Reynolds length config option should only be used with a compressible solver.

The Reynolds number (which uses the reynolds length in its calculation) is used in determining the solver time step. Changing the Reynolds length in the incompressible solver is inadvisable, because that may do unexpected things to the solution. For the incompressible solver, it does not matter what the characteristic length of your geometry is, only that the mesh is in meters.

[Vino]

Thank you.!!!

What I understood is that, whether cylinder dia is 1 m or 10 m in the mesh file, keep Reynolds length as always 1 and modify other parameters to get the required Reynolds number.

I set (rho=1, v=1, mu=0.01)to achieve Re=100. It hold true irrespective of what cylinder dia I am using in mesh file(1m or 10m).

[Vino]

plz ignore this Least Square solution algorithm post here.!