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Old   April 20, 2007, 04:10
Default negative pressure
  #1
sijin james
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i have given atmospheric pressure as reference pressure and i m doing an diesel engine combustion analysis.. In the starting of analysis i m getting a negative pressure always and then it slowly increasing. Why its like that? In motoring analysis also i m getting the same.. Any input error?? awaiting ur valuable response..
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Old   April 20, 2007, 09:37
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Kasper Skriver
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Star-CD or Star-CCM?
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Old   April 20, 2007, 12:57
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Ben
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Where are you getting the pressure value from? You are probably looking at relative pressure in which case negative pressure is entirely plausible if your reference is atmospheric, especially if the cylinder is on the expansion stroke.
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Old   April 20, 2007, 22:11
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sijin james
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i m using STAR CD and getting pressure drop to negative in compression stroke, means starting of compression.. Actually it should not be like that. my reference pressure is atmospheric. at the initial stages it showing negative pressures which means below atmospheric.After 5 iterations it become positive.. i want to know how can i eliminate initial negative pressure.. surely its not vacuum pressure. its below atm.
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Old   April 21, 2007, 06:16
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Ben
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Of course you can have pressure before atmosphere, get yourself a book on physics
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Old   April 21, 2007, 21:16
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sijin james
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i m accepting that.. pressure can be less than atm in an engine.. but in compression the pressure should be always increasing and in my analysis its fluctuating tendency.. first decreasin then increasin then again decreasin.. y its like that???
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Old   April 25, 2007, 04:16
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Ben
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Which pressure are you talking about? Mass averaged, instantaneous in one cell, volume averaged, total......?
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