@dheiny - Hi Mr. Heiny. In fact, I planned to perform a supersonic (M = 3) simulation and as you know, in the supersonic flows the region outside the Mach cone does not receive any information from the inside (You can not hear a supersonic airplane before it passes you and you get located within its Mach cone). As because of the sharp nose of this airplane, the airplane is supposed to be located downstream of an oblique shock wave (conical) initiated at the nose, the inlet boundary condition can be started even at the nose. In this way you can save some computational costs as well!
But here the problem is that I can not get a stable solution for the supersonic flows including shock waves. In fact I started with a simple nozzle (https://www.simscale.com/projects/roozbehmousavi/de_laval_nozzle) supposed to make a supersonic flow at the outlet or forming a shock wave at the diverging part. Although the solution was not stable at all using a steady solver, but I could perform a stable simulation using an unsteady solver for the case with no shock wave. But for the higher outlet pressure corresponding to the formation of a shock, the solution does not have a long term stability even with dt = 1e-7s !
So, if I can resolve the nozzle problem, I come back to this airplane for sure. It would be great if I could receive some suggestions from you. Thanks