Rocket Engine Starting/Stopping Simulation

Antanas · September 30, 2012, 11:27

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?

ghorrocks · October 1, 2012, 08:30

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.

Antanas · October 22, 2012, 06:16

Quote:

Originally Posted by ghorrocks

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.

singer1812 · October 23, 2012, 17:59

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.

September 30, 2012, 11:27	Rocket Engine Starting/Stopping Simulation	#1
Antanas Senior Member Join Date: Feb 2011 Posts: 496 Rep Power: 18	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?

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October 1, 2012, 08:30		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	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.

October 23, 2012, 17:59		#4
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	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.