I'm trying to simulate some kind of gas combustion with EDM/Methane Air WD1 in CFX5. I have some questions: 1. Sometimes, I can't get it burn with transient simulations. Now what I'm doing is: running a few steps with steady state, as init file for transient. Is it OK by this way and is there a simpler/better way? Is there an option somewhere for ignition? 2. I simulated a case which Methane+O2 is burning in air, with buoyancy model, BCs are inlet(burner), floor, the others are opening. It converged to RMS<10^-4, the flame looks like "_/". But if I continue this run, the flame type changes into "_)". Is there something wrong? If not, how can I explain this?

Thanks.

I do not have experience with combustion simulations in CFX5, but I would like to add a comment to your question.

I guess you could set a initial guess of the temperature to a high value that should secure the ignition.

If it does not ignite in your case, could it be that it is physical. (depends highly on what you are calculating, but some times it does not burn in the real world to

If you are calculation the combustion as transient - why should it not shift around, have you seen a flame for real! What kind of burner/combustion are you simulating, the phenomenen depends on you burner but the transient behaviour of a flame is desribed in the litterature.

Jan, thank you for your reply.

> I guess you could set a initial guess of the temperature to a high value that should secure the ignition.

But I intend to simulate the heating process of a reactor. Maybe I should set a high temperature point or small area close to the inlets?

HI we found that for a transient release of Methane / ethane mix in CFX5.5, burning using the eddy dissipation model that we needed to include the following command in the CCL file under the Fluid Model section. COMBUSTION MODEL : Option = Eddy Dissipation Eddy Dissipation Model Coefficient B = -1 END

this activated ignition.

Hope this helps Bob

Bob, thank you very much. It really works!

No worries, I think it may be a small over sight in the online help mannual or something like that. Bob

[siddharthpandey]

i am using edm model to solve a detonation problem i have a cylinder meshed geometry with one end closed and the other an opening, with fluid material as methane air, i want to ignite at at the closed end since detonation phenomena occurs when we have ignition at the closed end, how do i do that in CFX v11? i cant give the condition like a patch is given in fluent or the source point , i have also learnt that a patch cannot ignite mixture in EDM model, since ignition is reaction rate based, but giving initial rates of products in initialised values or high initial temperature will not be the same as ensuring the ignition takes place at the closed end, please if someone could help me out!