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 CFDST December 11, 2012 03:46

Cinema hall simulation

Hello,

I made a model of a hall in Gambit, meshed it after 1000000 tries, load it into Fluent and start to make a simulation. The project is at the University and it is a ventilation system of a cinema hall. My velocity inlets are at the top,lower top and the front wall,my outlets(outflows) are at the stairs.Velocity of the inlets 2 m/s, 2.3 m/s and 1.4 m/s. My professor told me that I have to get solution converged after about 400 iterations or 600 may be. I made 2100 iterations and I still cannot get solution converged. I set K-e viscous method with RNG. Flow,turbulence and energy equations, the discretization of momentum,turbulence kinetic energy,energy,dissipation rate and energy are second order upwind. I cannot figure out where is the problem, may be :
1.More iterations need
2.I change the steps of the pathlines and it shows a lot more pathlines.
3.I made a sweep surface at the stairs z=2.13 and the velocity is still low.

 CFDST December 11, 2012 03:50

This are the pictures of the vectors,pathlines,the model and sweep surface.

 CFDST December 11, 2012 03:53

http://www.2shared.com/photo/kpbt-MlV/Temperature.html temperature pathlines

 jamesg3373 December 11, 2012 05:54

Have you tried starting with gravity at a lower order of magnitude and increasing it? (say 9.81e-3, then 9.81e-2 etc)

In simulations where gravity is a dependant variable (because of buoyancy etc) it can often struggle to converge with the gravity set at 9.81 right from the start.

 jamesg3373 December 11, 2012 05:56

Also: What are your under-relaxation factors?

 CFDST December 11, 2012 06:17

Quote:
 Originally Posted by jamesg3373 (Post 396863) Have you tried starting with gravity at a lower order of magnitude and increasing it? (say 9.81e-3, then 9.81e-2 etc) In simulations where gravity is a dependant variable (because of buoyancy etc) it can often struggle to converge with the gravity set at 9.81 right from the start.
Thank you for your replies. I'm new to Fluent. Where I can set the order of magnitude of the gravity. And What is under relaxation factors? Thank you.

 jamesg3373 December 11, 2012 07:29

Quote:
 Originally Posted by CFDST (Post 396868) Thank you for your replies. I'm new to Fluent. Where I can set the order of magnitude of the gravity. And What is under relaxation factors? Thank you.
The settings for gravity can be changed under "General" and the under-relaxation factors are under "Solution Controls". They determine the maximum amount any term can change in one iteration. Try reducing your momentum and pressure values in order to converge better.

 CFDST December 11, 2012 10:40

Quote:
 Originally Posted by jamesg3373 (Post 396885) The settings for gravity can be changed under "General" and the under-relaxation factors are under "Solution Controls". They determine the maximum amount any term can change in one iteration. Try reducing your momentum and pressure values in order to converge better.
Pressure = 0.3; Density= 1; Body forces= 1 ; Momentum=0.7; Turbulent kinetic energy=0.7 ; Turbulence dissipation rate=0.7 ; Turbulent viscosity=1; energy=1. So I have to reduce pressure=0.2 and momentum=0.6 may be?
And about gravity I found it at Define>Operating conditions>gravity> to put gravitational acceleration of x,y or z ??

 CFDST December 11, 2012 10:43

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