I am simulating an axial turbine, I tried different mesh topologies and all give me almost the same number. In fact, Boundary layer is not captured well, Reynolds number is equal to $4.4 \times 10^5$ and according to mentioned formula in the following link, I computed $y_1$ (First cell height) by using $y^+ = 30$ and $y^+ = 60$.
But in the two cases($y^+=30$ and $y^+=60$), the boundary layer is not captured well (Why?). In the other words, according to the following figure, there is no adjacent wall. And also, I studied the following link:
For this reason, performance parameters are not validated well. In fact, there is a difference with the experimental value. This difference is not big but it is not good! I think that it is difficult to capture BL by using low Re number turbulence model (for example, $k-\epsilon$ turbulence model).