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Old   July 31, 2001, 05:07
Default pressure problem
  #1
joseph
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hey all,

can any body explain to me the references pressure in CFX 5.4.1.

like all pressures in CFX in the BC are relative to the ref pressure.

so if my reference pressure is 10 psi and my totat pressre for solving is to be 15 and from my calculation my staic pressure is 11psi

so should my total pressure at the BC GUI be 5 or 4 0r 15 psi

I think it should be 4 is this right.

and my flow is compressible.

I have gone through the manuals very well. it looks kind of straight forward but the results are not so, the results I am getting is different from what I should be getting

please put in your comments

thanks for your time

regards,

joseph
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Old   July 31, 2001, 14:20
Default Re: pressure problem
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John C. Chien
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(1). As I have said many times recently that a cfd code does not do analysis by itself yet. So, you need to learn how to do analysis in fluid mechanics first. (2). At the same time, there is only one absolute static pressure (p). You can pick a pressure and call it a reference pressure (p,ref). Then p,g= p - p,ref. and p= p,g + p,ref. This is just algebra. There is nothing to it. (3). The total pressure(PT) is something else, which is derived from other flow variables including the static pressure. It has the unit of pressure. So, PT,g= PT - p,ref, and PT=PT,g + p,ref.
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Old   August 1, 2001, 00:12
Default Re: pressure problem
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Dan Williams
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Your total pressure boundary condition should be set to 5 psi "relative pressure" if you have set the reference pressure to 10 psi.

As for your results not looking right, well, that's another story. There could be a dozen things that you didn't do quite right. Did you use a decent timestep, is the solution converged, did you type any properties in wrong, is the mesh OK, etc....

Dan.
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