How to simulate flow of vortex generator on sedan?

kian

Hi, I am trying to run simulation of flow around a sedan car with vortex generators. The problem I faced is the VG not really generate vortices at the rear part of the car and the effect of the VG on the drag and lift is not obvious...

I didn't apply boundary layer on the car body. Is it the main reason of the problem?I heard that the mesh density should be very high. May I know how 'high' the density should be?

I use edge mesh of 0.001m on the VG, 0.02m edge mesh on other edges on the car, then mesh the car faces, then apply sizing function with growth rate 1.1 and size limit 6m and mesh the volume. My car size is 4.2mx1.4m and 0.7m half width. The outer domain size is L60xH15xW10.

Thanks in advance!