[xisluke]

Hi guys!

I'm trying to simulate a .50 BMG travelling at supersonic speed using Fluent, but I'm experiencing some problems. Basically I have a 2D domain (not incredibly large, I'm using the student version) and I'm simulating only a half of the bullet in steady state. These are my boundary conditions:

INLET: velocity inlet, 514.65 m/s (more or less 1.5 Mach @ 293.15 K)
OUTLET: pressure outlet (gauge pressure 0 Pa @ 293.15 K))
UP: pressure farfield (gauge pressure 0 Pa, 1.5 Mach @ 293.15 K)
DOWN: axis boundary condition (2D space axisymmetric)
BULLET: wall, no slip

As a first guess, I decided to use a k-epsilon realizable model and scalable wall functions, energy equation obviously ON, with ideal gas law and sutherland formulation for viscosity (the fluid is air). I leave some images of my mesh below.

As I was mentioning above, I'm experiencing some issues, in particular:

1 - using a Pressure-Based solver I'm able to run the case reaching a sensible result, but the continuity residuals have problems dropping down and they remain pretty high. I'm also monitoring y+ max, min and average on the wall, in addition I'm plotting the drag coefficient of the bullet; all these values remain constant at a given point of the iterative process.

2 - using a Density-Based solver, I'm not able to run the simulation at all (all the residuals diverge except for the turbulence related ones), and this makes me think of boundary conditions mistakes maybe...

With respect to point 1, I have also doubts in regards the mesh quality in one particular point (showed in two of the images below), which can represent a sort of "singularity" where the solver is not able to predict correctly the flow, since the cell should be somehow adjacent to the wall, but this does not happen due to the block construction in use (please, let me know if there is a way to do better without increase too much skewness and non-orthogonality!)

Thank you so much!