Hello, I am sorry if this a too basic question, but I am trying to understand what each parameter in the twoSpheresGlow... tutorial does and I am having some problems. Basically if I remove gravity in the DEM part particles start to go up instead of going down and that has sense because lift force. But, DEM is in "si" units and CFD is too. I added a rho file to CFD/0 folder and rho is equal to the density of the DEM particles but particles still move up. So, my questions are: Is there other field affecting the system? does rho internal field equal 1.5 mean fluid density equal 1.5? what is phiIB?
I also found that gravity is -980 is CFD/constant folder. but if I set this to be zero or to be 9.8 (with ligggths gravity set to 0 already) particles do not move any more. why is this for?
thank you very much in advance to anybody that could help me with that.
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alice | Mon, 02/06/2017 - 14:07
Hello Paul,
Hello Paul,
you are right, if you remove the gravity the particles only experience the lift force exceeded bythe fluid and thus start moving upwards. The solver is written for incompressible fluids, which allows to "normalize" the eqation with the density. So in reality, p is pressure divided by density (which also explains the unis in the p-file). The case "looks" as if it was si, but in reality it was a cgs case. As all the units scale nicely and the conversion was taken over by the user, thus the results are correct, even though the the keyword si is used (see the hight gravity values as well as the values in the transportProperties file).
Best regards,
Alice
paulaalejandrayo | Tue, 03/21/2017 - 18:32
Hello Alice,
Thank you for your answer. I came back to this tutorial because I am having some problems with cfdemSolverIB and I am trying to isolate these (pressure increases when OF time-step decreases) . I have removed all forceModels in this tutorial (leaving just a noDrag force model). DEM part has gravity so the particles fell down (if g=0 everything stays static). But this movement in the particles affect the pressure in the fluid, is it possible to remove this interaction in the same way I removed the fluid interaction on the particles? Thank you very much in advance.
Best regards,
Paula
luisjau8967 | Thu, 04/02/2020 - 16:20
What is phiIB?
Hello,
For my master thesis I'm using Immersed Boundary Method, thus cfdemSolverIB. In order to compute drag force/coefficient, I'm using the tutorial case twoSpheresGlowinski as a starting point to construct a simple model of flow past a stationary sphere. Therefore, I'm trying to understand everything contained in the aforementioned case. I still don't have a concrete definition of phiIB. Can somebody please provide me with a resource or an explanation to understand what is phiIB?
Thank you in advance!
Regards,
Luis