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Old   April 12, 2006, 08:00
Default Problem with DES model
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mehul
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Hi to all. I have done DES transient analysis of a surge chamber(just like pressure vessel).I have used DES because inlet is fluctuating.The pressure at inlet is fluctuating sinusodially.I have to also do harmonic structutal analysis for that I resuire pressure vs frequency data.so I am getting pressure vs time in cfx and converting into ps vs freq.but after doing transient analysis using DES I am getting same results as RANS model.Actually Actually I a msupplying pr at inlet which is varying sinusodially.In RANS model I am getting same nature at any point inside the pressure.I want some peaks for freq so that I can apply it into structural analysis.That's why I am doing DES .but I am getting same results .Only peaks are coming at upto 0.0165 sec.My total time was 0.075 sec.From 0.0165 to 0.075 sec the nature is same as RANS model. (1) Second thing is that when I have observed residuals of momentum ,mass,velocity then they are also fluctuating after 100 iteration.(Upto 100 ietration it was steady state).and upto end of solution i.e. upto 1000 th iteration it remains same.(I have taken 1000 time steps). (2) My courant no is 0.03 to 0.16.Earlier I was getting 200 and beyond and so I have refined mesh. So what should I do?Should I reduce time step?Or should I use another model.Only thing I require is that I should get some peaks of pressure. Other thing is that can courant no be zero?and DES can only applied to open flows.Because in my case it is closed flow.why I have chosen DES is that it is also applicable to fluctuating inlet.so I have chosen it.Pls help me if anybody can. Thanks all.

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