[Mirage]

I am trying to understand how to calculate the non-dimensional cell size Δx⁺.
According to many books and papers, you calculate with the following formula :

Δx⁺=U_tau*Δx/nu, with nu is the dynamic viscosity and Δx is the streamwise cell size.

My question is how can we define Δx in case of complex geometry or even for simple cases like ribbed channel.

I tried to define for each block the value of Δx⁺. I took the ratio between the length of the block and the number of cells (L/Nr_cells) as Δx. Unfortunately I a getting very low values for Δx⁺, so I was wondering, if someone could explain what I am doing wrong and how can calculate Δx⁺ and Δx correctly.

[FMDenaro]

Δx⁺=U_tau*Δx*(L/L)/nu = Re_tau* Δx/L

Therefore, multiply the Re_tau value for all your non-dimensional grid sizes

[Mirage]

Originally Posted by FMDenaro

Δx⁺=U_tau*Δx*(L/L)/nu = Re_tau* Δx/L

Therefore, multiply the Re_tau value for all your non-dimensional grid sizes

Thank you !

How can we calculate Δx? is Δx a global mesh variable or should I define Δx for each block?

[FMDenaro]

is the local mesh size in each direction