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-   -   HELP-Combustion, convergence (http://www.cfd-online.com/Forums/fluent/66375-help-combustion-convergence.html)

eseller July 13, 2009 16:48

HELP-Combustion, convergence
 
Hi Everyone!

I have been working in Fluent the past couple weeks to model LOX/methane propellant combustion inside a rocket motor to predict temperature and oxygen consumption. I have worked my way up to large geometry containing multiple injector elements. However, I have run into numerous problems as of late ...

1) I don't seem to have convergence ... residuals oscillate near 1e+00.

2) Contours of species O2 show total consumption throughout the chamber and then trace amounts coming at the outlet (does not make sense).

3) Velocity contour shows zero velocity throughout chamber --> no flow? if so, why would it show reactants and products in chamber when looking at species contour?

4) also there are repeated signals of backflow during iteration

I am asking for advice on how to judge the mesh and sort out this convergence issue. My selection of parameters are outlined below ... look at these and if you have tackled similar problems or have any experience with combustion modeling, please reply with help.

Pressure-based --> Steady (time) --> Standard k-omega --> P1 (radiation model) --> non-premixed combustion

My objective is to model the propellants as high-density gases rather than liquids b/c I'm working with limited memory. I generated a PDF table, and inputed constant densities at their cryogenic states ... I am also working at cryogenic temperatures (~200 R). I understand that this goal may be far in advance from where I am presently ... I would like to just get flow through my mesh and convergence first, then worry about likening my setup to the REAL problem.

Thank you for your help, I truly appreciate it!

--E


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