Rocket Engine Starting/Stopping Simulation
 

Hello!

I need to simulate a flow in CD nozzle where pressure and temperature at inlet changes from 0 to some level and then from this level to 0. Is it possible to simulate such a process it CFX? If possible, then what kind of boundary conditions at outlet and relative pressure should I specify?

CFX cannot model plasmas or explosions, but has a chemistry model. It also has all the normal Navier Stokes solver stuff like compressible flow, heat transfer etc.

So if your flow can be described with a chemistry model then probably yes. But if you need plasma or explosion models then no.

I don't need to model plasma and reactions. All I need is to model transient flow in CD nozzle where chamber pressure changes from 0 to 7 atm (nozzle start) and then from 7 atm to 0 (nozzle shut down). Outside pressure is 0 (vacuum). Since outlet velocity changes from subsonic to supersonic and vice versa, what BC should I specify there? I tried to specify opening and outlet with pressure 0 and near 0 (taking into account the Reference Pressure). As the Ref. Pressure I tried to specify 7 atm and 0. CFX failed in both cases.

CFX cant handle mixed BCs like this at the outlet. Try modeling more of the domain in the nozzle exit region in order to get a fully subsonic exit, regardless of time during the transient.