The yPlus value is an important index to consider when choosing the grid size for the near-wall region. How about the outer region?

The Rule-of-Thumb Estimation

There is a rule-of-thumb estimation for outer region flows using the ratio of integral length scale to grid length scale,
$$R_l = \frac{l_0}{\Delta} , $$
where
$$l_0 = \frac{k^{1.5}}{\varepsilon}, \quad \mathrm{or} \quad l_0 = \frac{k^{0.5}}{C_{\mu}\omega} \quad \mathrm{where} \quad{}C_{\mu} = 0.09, \\\Delta \approx{}\sqrt[3]{\mathrm{Cell \, \,Volume}}\quad \mathrm{for \,\,modest\,\,aspect\,\,ratios.}$$

It is recommended that $R_l > 5-10$, where 5 is the lower limit for RANS/URANS/VLES simulations and 10 for LES/DES.

How to Check the Resolution of a Simulation in ParaView

Use two filters, Cell Volume and Calculator.

• First, use the Cell Volume filter to get the Volume scalar field.
• Then use the Calculator filter to calculate the $R_l$ field, e. g. k^0.5 / 0.09 / omega / (Volume)^0.3333
• Plot the contour of the $R_l$ field, and use the clapping tool, the Threshold filter, to show only the region where $0 < R_l < 5$, which is under-resolved.