Yplus value as an indicator of mesh convergence
 

Hello,

I am trying to simulate breaking waves interactions with structures such as monopiles. I had made a convergence study and my results are close to the experimental results. Although, because I am using a turbulence model ( k- omega SST ) and wall functions are activated near the walls the maximum yplus value during the wave breaking is very big (around 5000) and the average is 500 and minimum around 0.2 . What should I do with the results? Are the results correct? why I have very close results with the experiment despite of the high value of Yplus?

Thanks you very much,

Kind regards,

Renos

The Wall Y plus is an indication of your first cell distance from the wall. Usually you need it to decide whether to use wall-function to resolve the boundary layer of the turbulence flow or to use a low y+ value to fully resolve the boundary layer.

The solution convergence is dependent on the residuals levels of your simulation. You can set the criteria in the drop down tree.

To ensure that you flow has reach steady-state, monitor a variable with respect to iteration, once it stop changing, your solution has reach a final converged solution. The accuracy of your solution is dependent on your mesh resolution (how dense). If the information near the wall is important then wise to use low y+ such as y+ = 1 and use near-wall-treatment (fully resolve BL), if only core value is important use y+ > 30 (ANSYS Fluent guideline)

Overly simplified: wall-normal resolution is more important to model the impact of wall shear stress. If wall shear stress has little impact on the physical phenomenon you are trying to simulate, wall-normal resolution is less important. So it is at least plausible that you can get reasonable results, even with very high y+ values.