First cell-height for aircraft Simulation
 

Hello,

I am trying do a simulation of a small aircraft in order to estimate the drag coefficient.

1.: In order to reduce the number of cells, I want to use standard wall function. So I am trying to set y+ between 30 and 300. My question: which reference length should I use in order to calculate the first cell height?

a) When I use the chord length of the airfoil as reference length I will need a smaller first cell height than using the fuselage as reference length. In order to be sure that y+>30 I should then go for the fuselage first cell height?

b) And what is my free stream velocity? The wing is accelerating the incoming air. So when I set to my farfield boundary Mach=0.7 , is this my free stream velocity (for calculating first cell height) or should I approximate the velocity on the airfoil and use this as free stream velocity (around Mach=0.9) ?


2. Do you think it is important to NOT work with wall functions for solving for drag coefficient of an aircraft (with high angle rudders) ?

Thanks for your thoughts

Best regards
CellZone