# Convergence in Free convection

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 May 4, 2013, 19:02 Convergence in Free convection #1 New Member   Join Date: Oct 2011 Posts: 19 Rep Power: 8 Hi all, I am new user of ANSYS/FLUENT 14.0, sometime i am running simulation of natural convection with boussinesq approximations for density, the simulations is going on with no error, residuals decreases rapidly at start and then constant. so i am confused that either i need to run for more iterations or it will not converge at all. please guide

May 5, 2013, 06:08
#2
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p ding
Join Date: Mar 2009
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Quote:
 Originally Posted by myty Hi all, I am new user of ANSYS/FLUENT 14.0, sometime i am running simulation of natural convection with boussinesq approximations for density, the simulations is going on with no error, residuals decreases rapidly at start and then constant. so i am confused that either i need to run for more iterations or it will not converge at all. please guide
which level of does the residual decreases to.
could you pease upload your mesh system, and what is the Ra number.

 May 5, 2013, 12:00 #3 New Member   Join Date: Oct 2011 Posts: 19 Rep Power: 8 All residuals decreases quickly to value close to convergence but then constant, means no further decrease. The mesh is simple rectangular box, with three walls adiabatic q''=0, and one side heating wall. Is there a role of Ra number to simulate natural convection. Also gravity value at -0.0098 gave convergence but when i increased it to -0.098 or -0.98, -9.8, situation is like i told.

May 5, 2013, 20:04
#4
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p ding
Join Date: Mar 2009
Posts: 324
Rep Power: 11
Quote:
 Originally Posted by myty All residuals decreases quickly to value close to convergence but then constant, means no further decrease. The mesh is simple rectangular box, with three walls adiabatic q''=0, and one side heating wall. Is there a role of Ra number to simulate natural convection. Also gravity value at -0.0098 gave convergence but when i increased it to -0.098 or -0.98, -9.8, situation is like i told.
I high Ra number means a convection intensity, i strongly suggest you to increase the mesh density as the increases of Ra number(increases of gravity).

 May 6, 2013, 17:22 #5 New Member   Join Date: Oct 2011 Posts: 19 Rep Power: 8 Thanks, i decreased the mesh size and now its working, one more thing is that when i am using velocity inlet BC for natural convection flow with very small value 10^-m/s, its working but when i am using pressure inlet BC which is preferred with natural convection flow, its not converging with constant wall T & q''. Do u suggest me something to run it.

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