Boussinsque or incompressible ideal gas

nived · November 26, 2018, 00:25

Iam modelling a 2d natural convection of cylinder. The cylinder is 1 inch in diameter. The heat flux given to cylinder is 800w/m2. Fluid is air.
Should i choose boussinsque or incompressible ideal gas for density??
Please help....

LuckyTran · November 26, 2018, 00:49

Incompressible ideal gas is slightly more general than Bousinesq because it allows the density to vary with temperature. With Boussinesq, you are only adding a body force term which is proportional to temperature difference (i.e. the gravity term only, the density is constant). For small heat fluxes (whatever small is), both should give very similar results.

nived · November 26, 2018, 01:05

Iam taking fluid domain as rectangle. Bottom part taken as inlet and top as outlet. The side walls are adiabatic walls. For natural convection, inlet and outlet , pressure boundary conditions are used. For natural convection, how much velocity should i get at inlet??

LuckyTran · November 26, 2018, 01:54

If you don't know the velocity, why are you trying to impose a velocity boundary condition?

nived · December 1, 2018, 00:47

Which model should i choose for a rotating cylinder in natural convection?? My grashofs number is in the range of 10^6
Please help

November 26, 2018, 00:25	Boussinsque or incompressible ideal gas	#1
nived New Member Nived Sankar Join Date: Mar 2018 Posts: 27 Rep Power: 8	Iam modelling a 2d natural convection of cylinder. The cylinder is 1 inch in diameter. The heat flux given to cylinder is 800w/m2. Fluid is air. Should i choose boussinsque or incompressible ideal gas for density?? Please help....

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November 26, 2018, 00:49		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 66	Incompressible ideal gas is slightly more general than Bousinesq because it allows the density to vary with temperature. With Boussinesq, you are only adding a body force term which is proportional to temperature difference (i.e. the gravity term only, the density is constant). For small heat fluxes (whatever small is), both should give very similar results.

November 26, 2018, 01:05		#3
nived New Member Nived Sankar Join Date: Mar 2018 Posts: 27 Rep Power: 8	Iam taking fluid domain as rectangle. Bottom part taken as inlet and top as outlet. The side walls are adiabatic walls. For natural convection, inlet and outlet , pressure boundary conditions are used. For natural convection, how much velocity should i get at inlet??

November 26, 2018, 01:54		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 66	If you don't know the velocity, why are you trying to impose a velocity boundary condition?

December 1, 2018, 00:47		#5
nived New Member Nived Sankar Join Date: Mar 2018 Posts: 27 Rep Power: 8	Which model should i choose for a rotating cylinder in natural convection?? My grashofs number is in the range of 10^6 Please help