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Peter Lemtis November 22, 2002 05:49

temperature too high in eddy dissipation

I am modeling a SI-engine. Within the cylinder a n-octane-air-mixture shall ignite. I am using the eddy dissipation model. I adapted for every species the cp-terms, so that tey are temperature dependent (piecewise polynomial). I also reduced the underrelaxation factors for density and energy to values of about 0.3 .... 0.5. Ignition is modeled by defining a patch on the lower left corner of the cylinder wherein the temperature is 1700K and the share of products is 100%. Turbulence values are 18 m2/s2 for the energy and 5900 m2/s3 for the dissipation rate. The problem now is that even after the first iteration the temperature rises near the outer wall (!?) to values of >3000K and after a few iterations more reaches values above the 5000K margin. In other cases using the premixed model with the same parameters, no reaction takes place. There is only a convective heat transport visible (patch is with c=1 in patched area).

I would be very relieved if someone could help me. Thank you in advance.


Peter Lemtis

Nick November 22, 2002 06:45

Re: temperature too high in eddy dissipation

You will find with the eddy dissipation model you will have to alter the A and B constants to adjust the rate of each reaction that takes place, which in effect shall allow you to calibrate the model. This can be time consuming however. You will probably find that after you have patched in a temperature for ignition that the temperaure will rise, however I have found this to be quite normal and the temperature should re-adjust itself after further iterations.

Regards Nick

ravi varma November 22, 2002 09:38

Re: temperature too high in eddy dissipation
with reaction problems, i have had similar problems. initially there is high temperature. i have used the two-step method. initialise flow and solve and then initialise cold flow solution. run a few iterations. finally, select the energy and reaction products equations to solve.

mahdi saniee nezhad November 24, 2002 01:45

Re: temperature too high in eddy dissipation
Dear sir I have a problem with this title. If it's possible for you please send me your received responses. Very thanks for your attention to my request. With the best regards. Mahdi saniee nezhad

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