Hi,

I am a student trying to investigate the wave making resistance of a submarine traveling just below the surface using CFD.

I am very new to CFD and would greatly appreciate any adivce at all on how to go about modeling the problem.

Thankyou,

Sam

Well... What can one say... I have successfully made this calculations for a surface hull. My learning period was about 4 months full time before I could successfully generate a solution, and I now use 20 CPU cores w 20GB RAM to run for about 100hrs to get one solution.

It is a difficult problem. So don't fool yourself into thinking you can do it in a week or two...

The mesh is the key, as usual. Once you have a good mesh everything is easy. But you need about 10mm vertical resolution at the water surface, more than 5xhull size domain in all dimensions, and very good Y+ values around the hull.

I don't think you can do it with unstructured tet's, either you get too little vertical resolution at the surface or your element count will blow through the celing. I use fully structured mesh with 6M elements, 10mm vertical res at surface up to 0.4 m res at domain boundary, Y+ = 20 around the hull, SST turbulence model.

There is a very good section of how to set up the free surface model in the CFX manuals.

Thanks very much,

I appreciate the advice its good to get a starting point. Luckily I have all year to work on the project and a few decent clusters at my use.

I have read in a few places that VOF modeling is the best way to tackle a free surface do you believe this would be applicable for my model?

Yes, certainly.

Ansys CFX-Solver Modeling Guide, pages 196-ff