1. Commercial software packages have their y+ value limit but while meshing, how do you choose the minimum size of the element (grid independent study)?
2. For experimentation in turbomachines using hot wire measurements near casing, how do you choose the frequency response?
As you said we need to obtain results which are mesh size independent. This could be done by varying the mesh size until the change in it does not produce any effect on the results. However, I thing the use of adaptive meshing technique could he helpful to avoid such a exhaustive study. We can refine the mesh in key area until the further refinement do not further influence the results.
Dear Harpreet,
The logic behind doing mesh sensitivity is same as u mentioned but when u validate this with experimental result than the mesh size matters..
In the first question you asked about y + criteria actually its depends on which turbulence model choose with enhanced wall ,standard or scalable options in generally for enhance treatment Y + is around 1 to 2 and for standard around range between 30 to 60 .
now in your second question you asked for frequency response so i suggest that you judge this by hit and trial.
The frequency response of the hot - wire probe will be limited by the hardware you are using. It will also depend on the region of flow you are interested in studying. For example free stream turbulence will require a lower frequency response than the boundary layer. The signal should be low pass filtered and acquired at least twice the low pass frequency to avoid aliasing.
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