hi , thank you so much Rob for your answer
I really want to say sorry that I miss the notification, unfortunately, I haven't solved it.
the Mach number will be unity in the throat and will increase up to 1300m/s at the nozzle outlet (based on paper). so the density-based model will be sufficient for this (based on paper)
I don't really know why, but if my mesh is coarse (2000 element) the simulation goes well.
but when I increase up until 40000 like the paper said, the hot spot "excessive temperature" occur
would you like to give me an advice, thank you so much