Modelling effect of a really simple turbojet in Fluent
 

Heyho,

I am trying to describe the effect of a turbojet engine on an aircraft in Ansys. So I do not want to simulate a rotating fan etc. , solely the thrust effect of the engine.

What I know from my engine: mass flow rate, inlet and outlet surface, produced thrust, exhaust velocity and exhaust temperature.

So my geometry has an intake and an outlet of the engine. Which boundaries should I choose?


Engine Outlet Surface:

1. Exhaust Fan Boundary: here I can specify Gauge Pressure, Total Temperature and pressure Jump -- > i do not know the pressure jump
2. Mass flow inlet: here I can specify mass flow rate, total temperature and Gauge pressure (static pressure) --> this might work

Engine Inlet Surface:

1. Mass flow outlet -- > requires only mass flow rate -- given value -- > this might work
2. Intake fan: Gauge Total Pressure, Supersonic Gauge pressure, Pressure jump -- > i do not know pressure jump
3. Pressure outlet: I can play with the pressure as long as I have the correct mass flow rate

I found some hints on cfd-online but not really what is the best way to do this.
Anyone with some advices?

Thanks so much!

The Effect
 

An important aspect is the objective here. What kind of effects of the engine do you want to study on the aircraft? Everything is driven by that.

Use a mass flow outlet for the engine intake (technically a pressure outlet with the targeted mass flow rate option).

Mass flow inlet for the engine exhaust is probably the way to go. Specify the total temperature corresponding to match the exhaust velocity and temperature. Then specify the total pressure to match the stream thrust. The other option is to go for a stagnation inlet, but here you won't be able to specify the mass flowrate (which you need in order to match the massflow and thrust). If it's supersonic then you specify the total and static pressure.


The Fan boundary conditions are just derived from pressure inlets/outlets but allows you to specify a pressure jump. If you don't want a jump, you can just use the more primitive pressure inlet/outlet.

Thank you for your help.

@LuckyTran: If I specify total temperature, mass flow rate AND pressure , my System will be overdetermined. For mass flow inlet, my pressure is normally automatically calculated at the inlet.

But if the pressure is automatically determined, how can I reach my necessary thrust:
F=m*(c_exit) with m=A*rho*c_exit (c_exit = velocity)
Because in mass flow rate the density will be calculated from pressure and temperature. Then I will get a correspondening c_exit velocity