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Pressure Term in GENTRA

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Old   June 12, 2003, 12:06
Default Pressure Term in GENTRA
  #1
Pedro Lavinas
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Hello everybody,

I am experiencing a problem with GENTRA and would like to get some help.

I am trying to simulate the flow of water with small particles in a 180 curve. Particles that are lighter than water (rho<1000 kg/m3) surprisingly do not drive inwards, and the heavier ones do flow outwards as expected, but with larger curvature radii than one could expect. So, it seems that the pressure gradient term, which should act as a centripetal force to the particle, is not implemented, or at least not correctly.

I have tried to activate the variable GSURPR, but PHOENICS surprisingly turns it automatically back to False. Is there any other variable that I must activate prior to setting GSURPR=T?

Furthermore, the documentation of GENTRA (TR211) about this term is quite misleading (please see eq. 6.3 - there is a pressure term; see eq. 6.32 - there is no pressure term!)

Has anybody already experienced such a problem and could give me some advice on how to handle it?

Thanks for your attention, and sorry for the loooong message and for the bad English.

Pedro Lavinas

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Old   June 17, 2003, 06:50
Default Re: Pressure Term in GENTRA
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ronghua
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"GSURPR=T" can not be set by VR-Editor now.

If you want to use GSURPR=T,you must edit Q1 file directly, and save Q1,then you can double click the EAREXE file,which should have been in your working directory(by copying or recompiling)

It is true that -Vp/mp*grad(p) is lost in the eq. (6.32) ,but I can tell you it is not lost in GENTRA's code.

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Old   June 17, 2003, 15:48
Default Re: Pressure Term in GENTRA
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Pedro Lavinas
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Dear Ronghua,

thank you for your reply. It has now worked to set GSURPR=T, but i still get unphysical results.

Example: the viscous-dominated flow between two cylinders, where the inner cylinder is stationary and the outer rotates with constant angular velocity. Particles that are less dense than the fluid should move inwards since their smaller inertia cannot balance the pressure force, which points to the center. However, GENTRA shows trajectories that slowly drive outwards.

This test case has an exact solution, so that i can calculate the pressure and drag forces acting on the particle, and then numerically integrate the equation of motion of the particle. Lighter particles do drive inwards, what does not happen in GENTRA. Furthermore, if i neglect the pressure forces in my exact calculations, the agreement with GENTRA results is very good. So it really seems that GENTRA fails to calculate the pressure forces on the particle.

Do you agree with my argumentation? I can send you the q1 file if necessary.

Thank you once more.

Pedro Lavinas
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Old   June 20, 2003, 08:59
Default Re: Pressure Term in GENTRA
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ronghua
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Please send me your case, let me check it.
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Old   July 9, 2003, 04:25
Default Re: Pressure Term in GENTRA
  #5
CHAM Support
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The problem in the pressure term of the particle momentum equation has now been corrected by CHAM Japan. The corrected gentra source files for PHOENICS V3.5.0 can be obtained from CHAM UK.
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