[ekraft]

So the wall function I'm using requires a y+ value to be as close to 1 as possible. If my max y+ after simulation is around .02, does that change my results significantly than if my max y+ was lets say 0.9? Does the closer max y+ is to 1, the better the results, or as long as my max y+ is less than one, I'm good to go? Thank you.

[jsb12136]

Your results will not be accurate considering your y+ is .02. You should make it around 1 as possible as you can. Y+ is a function describing the distance of first node from the wall. The y+ value is a non-dimensional distance (based on local cell fluid velocity) from the wall to the first mesh node. To ensure that y+ values are not so large that the first node falls outside the boundary layer region. If this happens, then the Wall Functions used by our turbulence model may incorrectly calculate the flow properties at this first calculation point which will introduce errors into our pressure drop and velocity results.In addition to the concern about having a mesh with y+ values that are too large, you need to be aware that if the y+ value is too low then the first calculation point will be placed in the viscous sublayer flow region and the Wall Functions will also be outside their validity. To be short just make it around 1.

[ggulgulia]

Hi Edward,

as far as I remember, the y+ values should be selected based on the flow regime. If your flow is laminar throughout, then you must make sure that the y+ values lies within 1 to 10 and if the flow is turbulent, then it should be in the range of 10 to 300. You need to tune the mesh accordingly for each case.

In each case you can select the All Wall model for turbulent schemes when you select the models. This is a hybrid model that takes care of the near wall flow resolution.

Thanks

[lcarasik]

Originally Posted by ekraft

So the wall function I'm using requires a y+ value to be as close to 1 as possible. If my max y+ after simulation is around .02, does that change my results significantly than if my max y+ was lets say 0.9? Does the closer max y+ is to 1, the better the results, or as long as my max y+ is less than one, I'm good to go? Thank you.

I'd highly recommend taking some time and research wall functions for turbulence models and how to apply them properly. The specific thing I believe is relevant to research is "integrating to the wall" for turbulence models.

as far as I remember, the y+ values should be selected based on the flow regime. If your flow is laminar throughout, then you must make sure that the y+ values lies within 1 to 10 and if the flow is turbulent, then it should be in the range of 10 to 300. You need to tune the mesh accordingly for each case.

In each case you can select the All Wall model for turbulent schemes when you select the models. This is a hybrid model that takes care of the near wall flow resolution.

Please be very careful applying the all wall y+ model. It still has it's own range of acceptable y+ values for your near wall region cells. Additionally, a lot of models in Star-CCM+ do not have the functionality of the all wall y+ model..