I am thinking you need to make this an external simulation so you can have free air (domain) about 30x the nozzle diameters after the nozzle and expand the domain around the nozzle.
For parameters at the nozzle exit:
Create a disk at the nozzle exit.
Assign Goals to the disk surface.
Use Component Control to 'not include' the disk in the solution.
With a nozzle with that wide of an angle you will re-circulation in the nozzle expansion area.
You can use CFD analysis
Your questions are clear, but uploading your model would be more helpful as you have faced with some technical issues as well.