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Peter Lemtis December 17, 2002 12:13

combustion models
 
Hello again!

I am trying to model combustion within a cylindre. The problem is that ignition occurs near the walls due to the k/e ratio. Wall functions don't help. My next approach is to write a UDF, but I would have to implement the whole EBU-combustion-model again (from my point of view). Is there anybody who has experienced the same problems and has worked out possible solutions? Please contact me!

Thank you!

Regards,

Peter

Peter Lemtis December 17, 2002 13:32

Re: combustion models
 
Appendix:

At www.rz.unibw-muenchen.de/~j9lp0407/ one can see 2 tiffs of my problem. Ignition shall only take place in the area on the lower left. There I patched with a higher temperature and higher product mass fractions. The problem is that the eddy dissipation model does not work correct in the laminar sub-layer near the wall. Instead, there is a high reaction rate.

Regards,

Peter

David Huckaby December 19, 2002 10:31

Re: combustion models
 
Peter,

Are you using the finite-rate/eddy-dissipation model or standard eddy-dissipation model ? Also, could you give more information about the problem you are trying to model ?

Dave

Peter Lemtis December 19, 2002 10:50

Re: combustion models
 
OK. I am modelling premixed combustion (2d) of n-octane/air in a cylindre. Ignition shall take place in the lower left corner. I initialised with T=786K, p=922400 Pa. The material settings are piecewise polynomial for the cps, except n-octane (no data in the database), sutherland-theory for viscosity. The I marked the ignition area and patched with T=2600K and mass fractions representing fully burned mixture. Due to the k/e-Viscosity-model ignition takes place near the wall after about 10exp-4 seconds. I have also used a boundary-layer like grid and the k-w-model for viscosity, but achieved the same results. My idea now is to write a UDF that avarages the turbulent timescale. I think I would have to re-program the whole combustion model for that purpose, so I asked whether someone has already written a UDF modifying the combustion model. Other hints for solving this weired problem are also welcomed. I hope, this describes my problem. If you need more detailed information, please write again.

Regards,

Peter


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