,CFD Simulation of Delta Wing: Questions & Guidance

[rahman1019]

I am trying to perform a CFD simulation of a 70 degree sweep Delta Wing at different angles of attack (aoa = 20, 25, 30, 35 degrees). The inlet flow is at 25m/s. I have made a spherical Far-field boundary with the sphere radius of 5 times the root chord length of the delta wing. Because of the symmetrical shape only half of the delta wing and spherical far-field boundary is considered for meshing. I have made 10 inflation layers on the delta wing surface to capture the boundary layer and an unstructured mesh in the far-field using ICEM-CFD. A mesh with 0.7 million cells has been created. Since the Mach no. is low, I have run a steady state Pressure based simulation using SA turbulence model in Fluent. Density of air is taken as constant. The hemi-spherical boundary is taken as velocity inlet and the symmetry is applied at the symmetrical face. My y+ lies in the range of 0.1 - 0.6.

I want to know, have i made any mistake in the case setup?

what turbulence conditions i need to mention at the inlet velocity boundary condition?

I also want to perform simulations with k-w SST and k-epsilon turbulence models. Is my y+ enough for the simulations with the above mentioned turbulence models? Among all which is a relatively better turbulence model for subsonic CFD simulations of delta wings at high angles of attack?

Do i need to make a structured mesh?

Your guidance will be appreciated.

Best regards

 

[AIR&SPACE]

You'll probably be better off on a different forum site.

Try www.cfd-online.com/Forums/

 

[Vadar2012]

It'd be nice to see a picture of the mesh. It's kind of hard to imagine. That should be enough cells for the turbulence models, but the mesh has to be constructed well. A picture of it would help a lot.

 

[bigfooted]

What makes you think there is a mistake?

There is a lot of information on turbulence modeling in the ANSYS theory manuals, especially for fluent (you didn't mention which solver you use). They also give guidelines for the y+ values, depending on your near-wall treatment. If you use some 'law-of-the-wall' kind of wall function, y+ actually needs to be large (>30), if you are resolving the boundary layer, y+ needs to be small (<1).

You might also want to take a look at some NASA papers on their online NASA Technical Reports database. Some papers give a lot of details on settings, model comparison etc.

If your solver knows about structured meshes, it's better because it can be solved faster. Also, structured meshes tend to have higher quality cells.

 

[alphy]

,

Dear researcher,

Thank you for sharing your simulation setup for the delta wing. It seems that you have followed a sound approach in setting up the case and mesh. However, without further details or access to your simulation files, it is difficult to determine if any mistakes have been made. It would be helpful to provide more information on the geometry, boundary conditions, and solver settings.

In terms of turbulence conditions at the inlet velocity boundary, this may depend on the specific flow conditions and the turbulence model being used. Generally, for subsonic flows, it is recommended to use a low turbulence intensity and a turbulent kinetic energy (k) value of around 1% of the freestream velocity. The turbulence length scale (l) can also be set to 0.07 times the characteristic length of the geometry.

Your y+ values seem appropriate for the SA turbulence model, which is commonly used for low Mach number flows. However, for more accurate predictions, it may be beneficial to also consider the k-w SST or k-epsilon models, which are known to perform well for complex flows like delta wings. In this case, your y+ values may be too low and may need to be adjusted to fall within the recommended range (5-50 for k-w SST and 30-300 for k-epsilon).

Regarding the use of a structured mesh, it may not be necessary for your current setup as unstructured meshes can often provide good results. However, it may be worth exploring the use of both types of meshes to see which one performs better for your specific case.

I hope this guidance helps in your simulations. As always, it is recommended to validate your results against experimental data or other reliable sources to ensure accuracy. Best of luck with your research.

Sincerely,