[acon18]

I didn't take convergent results whatever i tried in eulerian multi-phase flow. Mesh quality is enough in terms of skewness and orthogonal qualities. I have problem about continuity eqn convergence. If any possible advice such as time step, under relaxation or scheme, i will be appreciated greatly.

[vinerm]

The description of your case is rather vague and very generic. Assuming the mesh is good, the problem could be in physical setup. Numerics, such as, URF or time-step would help only if the physical setup is correct. Otherwise, doesn't matter what time-step or URF you use, the case will keep on diverging. You need to share more details of the setup, such as, material properties, boundary conditions, phase interactions, etc.

[acon18]

Model: Eularian Granular Multi-Phase
Phases: Air and Sand
Inlet B.C: Velocity Inlet
Outlet: Pressure Outlet
Wall: Specularity Coefficient as 0,6
Laminar 2-D
Implicit phase coupled
Pressure: Tried PRESTO and second order
Volume Fraction: First Order
Least Square based
I tried initiliazation from fluent user guide tips
Time Steps: 0,001, 0,0001, 0,00001
URF: I tried different urf for momentum and pressure. Not exact convergent results
I tried variable time steps so i had floating point.
I have always floating point exception after some iteration while changing time step.
Geometry has conical section at the bottom.
Drag Model: Gidaspow

[vinerm]

Why is the flow laminar? Air cannot even move sand if laminar.

[acon18]

I tried turbulence and i had same error. There are a lots of laminar cases in multiphase simulation while simulating sand and air. But i will try again for turbulence.

[sam_cfdd]

Hi,

apply k-epsilon model then follow the below procedures 1, 2 and 3:

1-model>multhiphase>phases>secondary phase (solid phase)>

Diameter: [your desire size]
granular viscosity: Gidespaw or syamlal O'brian
granular bulk viscosity: lun et al.
frictional voscosity: Schaefer
Angle of internal friction: leave it by default
frictional pressure: based-ktgf
fractional modulus: derived
frictional packing limit: by default
granular temp: algebraic
solid pressure: lun et al.
radial distribution: lun et al.
elasticity modulus: derived
packing limit: 0.63 [packing limit can be increased or decreased by yourself. maximum packing limit can be 0.74 also. the high packing limit prevent particles to jump and leave the bed immediately]

2- model>multhiphase>phases>phase interaction> drag

choose: Gidespow or syamlal O'brien. [if you choose Gidespow on granular viscosity then you must choose Gidespow for drag also. these two must be same]

3- solution methods

scheme: phase couple simple
gradient: least squred...
momentum: second order upwind
volume fraction: Quick
turbuetn kinetoc: first order
turbulent diss: first order
transient formulation: second order implicit

Good luck

Originally Posted by acon18

Model: Eularian Granular Multi-Phase
Phases: Air and Sand
Inlet B.C: Velocity Inlet
Outlet: Pressure Outlet
Wall: Specularity Coefficient as 0,6
Laminar 2-D
Implicit phase coupled
Pressure: Tried PRESTO and second order
Volume Fraction: First Order
Least Square based
I tried initiliazation from fluent user guide tips
Time Steps: 0,001, 0,0001, 0,00001
URF: I tried different urf for momentum and pressure. Not exact convergent results
I tried variable time steps so i had floating point.
I have always floating point exception after some iteration while changing time step.
Geometry has conical section at the bottom.
Drag Model: Gidaspow