Help with convergence !
 

i've been doing simulation on an supersonic air intake shown below. residuals can't go below 4e-3 and don't look like a straight line. i started with very low under-relaxation factors and courant number of 0.1. it took me 800000 iteration to get to the residuals shown in attached pictures. i'm using ideal gaz with mach number equals to 2.5
the mesh is hexa, all of it. quality is pretty good. (< 0.5 in 3x3x3 determinant)
Solver is steady density based. I'm using standard k-w for turbulence.
Flux type is AUSM because of presence of shockwaves
Gradient is green-gauss cell based. Second order upwind for the turbulent kinetic energy and specific dissipation rate and first order upwind for the flow.
I'm not sure of the result i'm getting.
Anyone doing same research here ? any suggestion ??

Try starting with a first-order solution. You should consider refining your mesh where the shocks are present. The simulation will be very sensitive in those areas.

it is also possible that flow is transient somewhere.