overtaking process
 

Good day,
I'm making an analysis of the overtaking process between two ahmed body(288*389*1044).
The problem is that the results obtained in the case of different discrete fixed position of the overtaking vehicle(stationary steady for different value of deltax/L) are the same, except for the negative peak(that dynamic is greater), as the dynamic case simulated with rigid body motion. Another words, the transient effect associated with the ovetaking process don't show themself. I changed the time step decreasing to 0.01 s, I maked finer the mesh and I selected the compressible option but nothing changed
Do you have any idea from where my error can result?
thank you very much:)