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Old   October 7, 2004, 07:30
Default pressure outlet condition
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Hello Fluent Users

I am user user of fluent and i am modelling two phase, air-water flow in vertcial pipe. i am using mixture model and boundary conditions are two velocity inlets at the bottom, one for water other for air and the outlet boundary condition is pressure outlet. I am defining opertaing pressure at atmospheric at refernce location on the top of the pipe.

Although i did manage to get some results but i think they are not correct as there is mass imbalance, residuals of continuity being too high, k-e residuals going too high (spikes) and most importantly the velocity of air although defined at 4.4. m/s at inlet show a value of 4.4 m/s at start of inlet and and than shows patch values of 10 m/s in core and when it enters the main pipe it shows 2.55 to 3.55 m/s. I can't understand whether its the boundary conditions that making this probelm or using refernce pressure location at the top of the pipe.

any suggestions..............???

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Old   October 9, 2004, 00:07
Default Re: pressure outlet condition
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There are two things which you can do here. One, the atmospheric pressure defined as default in Fluent is zero gauge pressure, meaning all B.C's have to defined with the gauge pressure. Two, in the menu's under the Report menu, look for reference values, change that according to your conditions and geometry, sometimes this might affect your results. Three, try using a different solver scheme, you can use the Quick scheme, instead of first order upwind or second order upwind. hope this helps, Aravind
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