[velan]

Hi,
I am newbie to OpenFOAM, got started a week before. I started a ramjet simulation with M=2. Everything goes fine when i used the outlet as supersonic bc's(extrapolated). But when i applied Exit back pressure, the simulation starts blowing up. I am using standard RNG k-epsilon model. I am using sonicTurbFoam. Please help me to sort it out.

- Velan

[kaleekun]

With or without combustion ??

[velan]

Its without combustion. We are simulating from forebody to cowl portion(which ends before combustion starts). So in the vicinity of cowl, i am getting cowl shock and it reflects(where i am getting separation bubble).
I ran the different case using openFOAM.
* Fully supersonic flow (Extrapolation at exit)
* Fully subsonic flow
* Restarted the simulation with Fully developed supersonic flow and applied exit pressure condition at the exit, but Normal shock was not formed.

So my problem is, i need to get a weak normal shock inside the cowl by applying exit pressure condition. Can you please suggest me how can i do it. If you have any idea please share with me.

- Velan

[dmoroian]

Hello Velan,
In my experience, it is very hard to find the right value of the backpressure for a certain position of the normal shock (see for example lambda shockwave), but it will always be a normal shock wave somewhere in your domain (or a strong oblique one). Even if you want to avoid the formation of a normal shock wave, it is impossible if you apply such a boundary condition, because you block one of the 5 outgoing characteristics which gives you a subsonic type of flow.
So my suggestion is to look closely, maybe you have a too low backpressure and your normal shockwave is exactly at the outlet, which means you have to increase a little its value.

I hope this is helpful,
Dragos