[Tosbaga]

Hello Everyone,

I am currently trying to simulate a wind tunnel experiment with a Delta wing inside it. The problem is with the mass residual which i cannot drop it below an order of E-4. The other residuals are converging nicely.

I have used an adequate mesh with the following qualities,

Max Skewness : 0.86,
Max Aspect Ratio : 56,
Min Orthogonal Quality : 0.13

I am confident that the element size is suitable for my simulation. I am using PBCS with a SST k-w turbulence model, Inflations layers are produced with a first layer thickness which will produce a y+ value of ~1.

Computational domain consist of a Velocity inlet, Pressure outlet,Symmetry, Wind tunnel walls and delta wing as wall also.

I have tried to lower the relaxation factors as well but it didnt cause any significant effect on the mass residual.

I am also monitoring the Cl and Cd coefficients and after 2000 iterations they do not change. I also checked the mass flux difference between inlet and outlet an its of order E-9 close to zero too but I feel like I cannot rely on the solution because of the mass residual.

Do i miss something i dont know. Help would be much appreciated.

Thanks in advance.
Regards,

[MKuhn]

Why you would like to reach a residual for the mass lower than 1E-3, which is the default value and for the most cases fully sufficient, as you can see on your mass flux balance?
Keep in mind that the flow in your steady state case could have a little transient, time dependent character, that could be the reasen for not lowering the mass residual further.

[Tosbaga]

Originally Posted by MKuhn

Why you would like to reach a residual for the mass lower than 1E-3, which is the default value and for the most cases fully sufficient, as you can see on your mass flux balance?
Keep in mind that the flow in your steady state case could have a little transient, time dependent character, that could be the reasen for not lowering the mass residual further.

Thanks for the answer, I am not an expert in CFD area however, in most of the cases I have seen, I learned that the mass flow residual should at least be under E-5 and the same recommendation is also available in FLUENT best practices document too.

I have considered unsteadiness but there is none in my case. Could you recommend some other suggestion ?

Regards.

[MKuhn]

Sorry no more hints. It depends also what for a precision do yo need. Normally I have with 1E-3 for the mass residual good consonance betwenn simulation and reality.

Moritz