Some questions after learning the MFiX User Manual

MFiX
#1

Hi everyone,

I am a new MFiX user. I have read in chapters 4 and 8 of the MFiX User Manual, hoping that I could ask some questions here.

(1) If I want to add a Basset force, a kind of lift force, into gas momentum equations, which files should I focus on and edit?

(2) If I have to change the forces acted on the particle, which files should be edited?

(3) NORM_G is a “factor to normalize the gas continuity equation residual”. How to understand it more clear or from the perspective of formula?

(4) PPG_DEM is a “denominator used to scale initial solids volume fraction correction equation residual when Norm_g=0. Default value is 10. Increase to tighten tolerance, decrease to loosen”. How to understand tighten/ loosen tolerance? What is tolerance refer to?

(5) In ANSYS Fluent or OpenFOAM, users usually decrease the maximum to 1.0e-5 or 1.0e-6. Is it necessary to decrease the default residuals?

(6) LEQ_METHOD represents the LEQ solver; LEQ_TOL is the linear equation tolerance; LEQ_PC refers to the linear preconditioner. These nouns LEQ solver, linear equation tolerance, and linear preconditioner are abstract and how to understand them much clearer? What are they used for?

(7) What is the scheme for pressure-velocity coupling, SIMPLE or PISO?

(8) For TFM, RDF_TYPE represents the “Radial distribution function (RDF) at contact”. Is it the RDF for particles? It also needs to be selected from its list even for particles with fixed diameters. I am confused about this selection.

(9) In a time step for the fluid field, the maximum number of iteration is 50. What is the maximum number of iteration in a DEM time step?

(10) DES_ETAT_FAC is “Ratio of the tangential damping factor to the normal damping factor for inter-particle collisions”. How to understand the damping factor? What are the differences between the damping factor and the restitution coefficient or the friction coefficient? I feel the effects of restitution and friction are similar to damping.

(11) DES_NEIGHBOR_SEARCH means a “flag to set the neighbor search algorithm”. How to understand the neighbor search? Why it is needed?

(12) FLPC is “fluid lens proportionality constant used to calculate the radius of the fluid lens that surrounds a particle”. How to understand the radius of the fluid lens?

Kindly regards

#2

Hello Fei -

We appreciate your interest in MFiX. You may find that you get better replies here on the help forum (and on forums in general) if you limit yourself to one question per posting, with a descriptive title, rather than “Some questions” - this makes it easier for us to keep track of which questions have been answered, and for others to search the forums.

– Charles

#3

Thanks for your kind remind. I will re-analyse these questions and re-question them one by one with a descriptive title.

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