natural convection in stratifeid zone

cfdlame · November 14, 2011, 11:14

The problem is: For different solver setting I'm experiencing natural convection in zone, where initialized temperature gradient is less than the lapse rate - convection should't occure.

I'm investigating convection in closed cube 3kmx3kmx2km with adiabatic boundary condition (hex grid 150000 elements). Initialized temperature gradient is decreasing 0,5K/100m (adiabatic lapse rate is 1K/100m). I've tried: boussinesq, ideal gas, and real gas for a density model, for both solvers: density, and pressure based (presto, second order for everything). I don't even know solver type matters, probably not. UDF is written fine. In every case convection occured. Somebody have any idea?

TomeK

cfdlame · November 15, 2011, 09:21

what you say?

zhangwei632 · November 30, 2011, 23:01

Where did you set temperature gradient? In the "patch" or others?

cfdlame · December 1, 2011, 04:37

Yeah I did it, using UDF. I've also set the pressure gradient, to show the hydrostatic gradient, but it was all wrong, because Fleunt do this by himself.

I know that was the main reason for the problem: bad boundary conditions. Now it's working more less, but Fluent equations for convection are very simplyfied, so some effects cannot be shown.

November 14, 2011, 11:14	natural convection in stratifeid zone	#1
cfdlame New Member Join Date: Nov 2011 Location: Poland Posts: 7 Rep Power: 15	The problem is: For different solver setting I'm experiencing natural convection in zone, where initialized temperature gradient is less than the lapse rate - convection should't occure. I'm investigating convection in closed cube 3kmx3kmx2km with adiabatic boundary condition (hex grid 150000 elements). Initialized temperature gradient is decreasing 0,5K/100m (adiabatic lapse rate is 1K/100m). I've tried: boussinesq, ideal gas, and real gas for a density model, for both solvers: density, and pressure based (presto, second order for everything). I don't even know solver type matters, probably not. UDF is written fine. In every case convection occured. Somebody have any idea? TomeK

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November 15, 2011, 09:21		#2
cfdlame New Member Join Date: Nov 2011 Location: Poland Posts: 7 Rep Power: 15	what you say?

November 30, 2011, 23:01		#3
zhangwei632 New Member zhangwei Join Date: Sep 2011 Posts: 1 Rep Power: 0	Where did you set temperature gradient? In the "patch" or others?

December 1, 2011, 04:37		#4
cfdlame New Member Join Date: Nov 2011 Location: Poland Posts: 7 Rep Power: 15	Yeah I did it, using UDF. I've also set the pressure gradient, to show the hydrostatic gradient, but it was all wrong, because Fleunt do this by himself. I know that was the main reason for the problem: bad boundary conditions. Now it's working more less, but Fluent equations for convection are very simplyfied, so some effects cannot be shown.