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Riaan September 14, 2005 11:41

Modeling engine effects
 
My question is about modeling the effect of a gas turbine on the flow through an intake duct.

I have an intake duct, turbine and exhaust duct in a standard configuration:

Intake Duct volume --> Boundary Condition Face --> Turbine Volume (empty, not meshed) --> Boundary Condition Face --> Exhaust Duct volume

What B.C should I use at the end of the Intake duct volume - I know the massflow that the turbine requires, but not the Static Pressure or Total Pressure at this face.

What B.C for the inlet face of the Exhaust Duct?

-Thanks Riaan

Razvan September 15, 2005 03:20

Re: Modeling engine effects
 
Do you want to MODEL the turbine, not actually calculate it (I mean you do not want to insert real turbine geometry in the middle volume and take its effects into account by simply imposing BC on the two faces)?

Razvan

Riaan September 15, 2005 07:44

Re: Modeling engine effects
 
No, I don't want to model the turbine, just have a "black box" with inlet and exit b.c. similar to what a turbine would generate.

Razvan September 15, 2005 14:00

Re: Modeling engine effects
 
Let me explain myself:

- MODELING = taking into account the possible effects of a certain geometry by analitical means, approximating it with a mathematical model, actually deliberately imposing not calculating its properties;

- SIMULATING = considering real geometry, calculating effects by imposing conditions on boundaries away from actual object.

So, what you're trying to do is MODEL the turbine, not SIMULATE it!

Concerning your problem, the only way I can imagine solving it is this:

- eliminate first and second volume and keep only exhaust pipe with turbine exit as inlet condition

- calculate by hand or using a mathematical program the radial distribution of fluid's thermodynamic properties based on specific turbomachinery relations

- input these radial profiles as BC at the inlet boundary

- obtain solution. Of course, you will have to repeat steps 2-4 for every mass flow you need to consider.

Best wishes, Razvan

Riaan September 19, 2005 08:24

Re: Modeling engine effects
 
Found easier way. Set Mass-flow inlet B.C. at the turbine inlet face, with the mass-flow vector pointing "into" the turbine. Since this is a subsonic case, pressure values on the b.c. face will be interpolated from the cells next to the b.c.

Anycase, agree on difference between modeling and simulating. Quick and dirty forum post - sorry.

Riaan September 20, 2005 17:45

Re: Modeling engine effects
 
Running into problems - seems the Mass-flow inlet creates a local strong shock in the exit plane...M>2...don't know why yet?


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