detonation problem
 

hello friends,
i am trying to simulate a 2d rectangular model(0.2X0.02m) for detonation with fluent 6.3.initially i am filling the model with premixed mixture of hydrogen and air/oxygen and kept temperature and pressure at ambient conditions(300K&1atm) and progress variable as 0(no burnt gases).then i am patching a small rectangular part with dimensions 0.002X0.02m to pressure value of 30bar, temperature of 3000K and progress variable as 1(full combustion).my turbulence model is k-epsilon.when i am trying to run this model for 10^-9sec, i am getting a very high pressure values in range of 5000atm even in patched region(wic is impossible).i dont know where i am making the mistake..can anyone help to find where i am making a mistake.i also dont have tutorials for premixed combustion models.if u have, kindly send it to my email id:sudhir86@ymail.com

sudhir

Hey,

Currently I´m working on my dissertation on a Pulse Detonation Engine, I´m studying a simple 2D design straight tube, closed at one end and opened at the other where I will join nozzles with different geometrys and simulate it on Ansys Fluent to study nozzle effects. Although I´m having some troubles achieving detonation.

How do I define a high pressure and temperature and fully combusted zone as you said? I dont have an inlet zone, should i define as inlet conditions?

Which species model should I use? partial premixed combustion?

How do I make sure that the flow travels and get CJ speed through the outlet zone?

Thank you for your help

Hey,
Btw whats your fuel and oxidiser. It would be better and simpler if you use species transport model..Use patching option in FLUENT for creating high pressure and temperature zone. Follow the paper i mentioned. Do the analysis for their A/F and then yours..
Hope it helps :cool::)
Sudhir

Now I am trying with Hydrogen and Oxygen so I can get the detonation easily. After I´ll maybe do it with air.

I am following the paper but I still dont get how do you Patch something (defining temperature and pressure) to the geometry that I did.

Thanks

You can find patching in user guide of FLUENT

Ok I understand patch now but I cant define where to patch. How do I create a different zone where I will define the initial pressure and temperature? Is it on the geometry? because I cant create two surfaces together.

hi Sacosi,
For this type of problems, you have to create a Rectangular iso-surface inside the fluid domain and patch only that domain with high temperature and pressure values. Dont forget to change the mass fraction of species also inside this zone.
Sudhir

Single Shot Detonation
 

Hello there,

Have either of you gentlemen been successful at creating a CJ detonation for stoichiometric H2/O2? I am having a rather difficult time attempting this. I am using a 18 step mechanism developed by Petersen and Hanson for ram accelerator combustion. Likewise, I am patching a thin region of 30 atm and 3500 K at the thrust wall to initiate a shock induced detonation (note the region also consist of the mass fraction of the species in a post detonation equilibrium state as predicted by NASA CEA). It seems that no matter how fine my grid is (10 micro meters with level 3 adaptive mesh refinement), or how small my time step is (1.0e-8~1.0e-11) the solution will not converge. It appears that that the chemical kinetics are too stiff for fluent. Can any light be shed on this matter? It would be greatly appreciated.

Thanks,

I have the same problem. My temperature and pressure sky-rocket and don't come down. Has anyone found a solution to this in fluent?