How can I control the aspect ratio of my mesh in CFX-mesher?I need of an inflated boundary to obtain y+ values for k-epsilon turbolence model: how high aspect ratio must be to optimize my analisys? Thanks!

Hi,

If you are referring to the inflation layers at the boundaries: You can control them with the properties tab. Have a look at the documentation.

Optimum aspect ratio: There is no general optimum, it problem dependant. You should do a sensitivity analysis and determine what the best aspect ratio to use for your simulation.

Glenn Horrocks

Thank you Glenn. I tried several discretization by forcing either y+ value and first element high.The problem is that I obtained very small elements that are not suitable for k epsilon turbulence model.Calculation fails with a "fatal overflow error".Now I'm trying with k omega and double precision: calculation goes, but it is very very slow! Do you think this problems could be related? Do you haev some hint about this? Thanks again!

Hi,

Your error does not mean your elements are too small for the k-epsilon turbulence model. It means the solution has diverged. You would have to describe what you are modelling better if you want us to help you.

Glenn Horrocks

Carrying out a mesh dependency test will give you lots of insight about the discretisation error. A balancing approach is always needed. Is it worth the effort to gain the 1% accuracy if it takes a month to produce a solution? Errors such as assumptions made in turbulence model could easily overwhelm the discretisation error, as the mesh is refining.

Ok I'll describe my problem. I have to calculate a multiphase flow field. My domain is entirely closed and contains 60% in volume fraction of liquid and 40% of compressible fluid (Air Ideal Gas). Domain oscillates around a stable position so calculation is unsteady calculation with a time step of about 10E-5. How can I set the problem?How can I fix the pressure level for the compressible fluid since the domain is closed? Last calculation failed and gave a fatal bounds error (Absolute Pressure). Have you some hint?

Thank you!