BC in closed box simulation

Miky1020 · March 30, 2009, 19:58

Hi,

I am simulating free convection inside a closed box. I have set heat flux at the bottom and insulated walls at the others surfaces. Also, I have set no slip at all the surfaces. However, I have problems with convergence and I think (after read cfx documentation) they are in BCs, since I haven't set pressure nor temperature levels at any BC. Could this be true? if so, how can I set pressure and temperature in a closed and insulated box?

Thanks

Miguel

ghorrocks · March 31, 2009, 17:55

Hi,

I assume you are running a transient simulation - it has to be as you have a hot wall on the bottom and everything else adiabatic so it is going to heat up over time. These type of buoyancy simulations invariably have big transient flow instabilities. You often have to run much smaller timesteps than you would expect to resolve these transient features.

Just set the reference pressure and temperature at the initial temp and pressure, that should be OK.

Glenn Horrocks

Miky1020 · March 31, 2009, 20:16

Thanks Glenn,

I will try smaller timesteps.

March 30, 2009, 19:58	BC in closed box simulation	#1
Miky1020 New Member Miguel Baritto Join Date: Mar 2009 Location: Caracas,Venezuela Posts: 16 Rep Power: 17	Hi, I am simulating free convection inside a closed box. I have set heat flux at the bottom and insulated walls at the others surfaces. Also, I have set no slip at all the surfaces. However, I have problems with convergence and I think (after read cfx documentation) they are in BCs, since I haven't set pressure nor temperature levels at any BC. Could this be true? if so, how can I set pressure and temperature in a closed and insulated box? Thanks Miguel

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March 31, 2009, 17:55		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Hi, I assume you are running a transient simulation - it has to be as you have a hot wall on the bottom and everything else adiabatic so it is going to heat up over time. These type of buoyancy simulations invariably have big transient flow instabilities. You often have to run much smaller timesteps than you would expect to resolve these transient features. Just set the reference pressure and temperature at the initial temp and pressure, that should be OK. Glenn Horrocks

March 31, 2009, 20:16		#3
Miky1020 New Member Miguel Baritto Join Date: Mar 2009 Location: Caracas,Venezuela Posts: 16 Rep Power: 17	Thanks Glenn, I will try smaller timesteps.