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Old   June 8, 2007, 05:59
Default Target Mass Flow Rate
  #1
Brian Tang
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Does anyone know if there is any real difference between using a pressure outlet with target mass flow rate specified and using a mass-flow inlet, but with the velocity specified in a direction that takes it out of the domain? As far as I can tell, both will merely adjust the static pressure each iteration to match the targetted mass flux.

Thanks! Brian
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Old   June 11, 2007, 09:11
Default Re: Target Mass Flow Rate
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Xiana
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Hi Brian, I have the same question!!! I donīt know why using a pressure outlet with target mass flow should adjust the static pressure to match the targeted mass flux.I did it and I saw that in the solution the outlet pressure is different as what I defined. What happens exactly in this boundary condition: pressure outlet + target mass flow???

Thank you very much

Xiana
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Old   June 20, 2007, 19:05
Default Re: Target Mass Flow Rate
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red lemon
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target mass flow rate dynamically adjusts downstream static pressure to meet the summed mass flux specified and the defined pressure is ignored. Fluent doesnt allow negative mass flow inlets (try it) so dont use with negative vector. Negative velocity inlets for outlets are ok for incompressible flow though. Always keep a bc as pressure to prevent overconstraining solution.
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Old   June 21, 2007, 02:51
Default Re: Target Mass Flow Rate
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Xiana
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Thank you for your advice "red lemon", I will try with negative velocity inlet. I have another problem with the pressure outlet too. I used it without target mass flow and I noticed that the static pressure that Fluent achieved is not exactly what I defined (0 Gauge Pressure). It differs in some punts in a range of -1000 Pa. Does anybody know why?

Kind regards

Xiana
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Old   June 21, 2007, 07:11
Default Re: Target Mass Flow Rate
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red lemon
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So you are specifying a 0Pa gauge pressure but youre seeing -1kPa. Could be that : - you have reverse flow and static is treated as total - you are reporting total instead of absolute

If target mass flow rate is used though, the pressure condition is ignored as it cannot to conform to both a constant static pressure AND a fixed mass flux. Enabling one disables the other.

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