At the stage of meshing - while doing a CFD analysis - what is the appropriate size of the elements according to the properties of the analysis. I know that the size is not costant but it varies (most of the time) but I don't now is for example close to the airfoil what is the "corect size and also what is the rate of change of the size while moving away from the arifoil? Thanks in advance Dimitris Tavernarakis

(1). The mesh size and distribution depend on your solution requirement, so you can change your mesh (refine it) in your own way until your solution becomes mesh independent. (2). The rule is "mesh independent solution". So, you will have to look at your solution to see whether it changes with mesh or not.