Eulerian Model HELP!!!

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 June 24, 2004, 13:24 Eulerian Model HELP!!! #1 Nicholas Wood Guest   Posts: n/a Hey, I've been trying top model granular phase flow and I cannot get the equations to converge. I keep getting unstable residuals that oscillate. I've tried calculating intial solutions by turning off the volume fraction calculator. Initial conditions are calculated well, but once I turn on the volume fraction calcualtor I get oscillations and instability again. PLEASE HELP

 June 28, 2004, 08:16 Re: Eulerian Model HELP!!! #2 ap Guest   Posts: n/a What kind of system do you want to simulate? What equations do not converge? As general suggestions: 1) Use an hexaedral mesh, if possible. 2) Use the second order upwind or the QUICK discretization scheme for the convective term of transport equations. 3) Set the under-relaxation factors as follows: Pressure 0.6 Momentum 0.4 Turbulence (both k and eps) 0.8 Leave the other values unchanged. 4) If you do an unsteady calculation, try to reduce the size of the time step. Hi ap

 July 5, 2004, 13:48 Re: Eulerian Model HELP!!! #3 Nicholas Wood Guest   Posts: n/a Thank you, I will try those methods. I'm having especial difficulty in converging the contiuum and air velocity equations. I also have a lot of turbulent viscosities limited. I've heard this can be caused by an unstable problem.

 July 5, 2004, 14:49 Re: Eulerian Model HELP!!! #4 ap Guest   Posts: n/a Turbulent viscosity limitation usually is due to a too coarse grid or to bad boundary conditions for turbulence variables. Hi ap

 July 5, 2004, 16:47 Re: Eulerian Model HELP!!! #5 Nicholas Wood Guest   Posts: n/a The basic shape Im working with is a recatngular box with air blowing in one end and out the other. Along hte bottom of the box is another box where there is a bed of 'granular phase'. It reflects two 'zones' representing the air and the granular phase(the granular phase on the bottom). I have a velocity inlet on one end and a pressure outlet on the other and walls every where else. I've tried many different mesh sizes with the same result: very unstable solutions with oscillation, especially in velocities and continuity equation. Thanks for your help.

 July 6, 2004, 15:45 Re: Eulerian Model HELP!!! #6 ap Guest   Posts: n/a With the granular model of FLUENT I always have the turbulent viscosity limitation. For convergence, what kind of drag factor are you using? I obtained good results using Syamlal and O'Brien formulation both for the drag factor and the viscosity of the granular phase. Hi ap

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