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Old   March 17, 2008, 09:31
Default opposed buoyancy__ required help
  #1
haris
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i am working on opposed buoyancy effect on a heated cylinder at Re 100.i have done a steady state simulation at Richarson Number -1 (negative one). the residuals start increasing significantly after 1000 Iterations and becomes constant there after.the solution does not get converged .but lift coefficient varies sinusoidally with no. of iteration showing good vortex shedding .i want to know 1)will i get correct results even if the solution is not converged.2)if no then how to get the solution converged.
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Old   March 19, 2008, 00:31
Default Re: opposed buoyancy__ required help
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Hirdesh
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As you are doing steady state study, solution should converged. If not, the residual should be well below than zero and do not change with time or periodically same. Try with reducing under relaxation factor of Momentum, Pressure, energy.
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Old   March 20, 2008, 08:10
Default Re: opposed buoyancy__ required help
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jamal
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hi! Hirdesh,

i tried that ....it did converged for very low value of residuals( 0.01). will that not effect the accuracy of results......

thanks

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Old   March 20, 2008, 10:22
Default Re: opposed buoyancy__ required help
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Isaac
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I think that just because the residual values for say continuity goes below 1E-04 does not mean the solution is converged. In most cases when this happens, you have to monitor the difference in flow rates between inlet and outlet. If this is not steadily decreasing, and you see an oscillating trend (which you are in your lift), I think the problem may be inherently time dependent. It would be incorrect to model this as a steady state problem.

Ofcourse the issue may just be that you do not have a good enough grid and the solution is steady state. You will have to do some checks to confirm. Hope this helps.
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Old   March 23, 2008, 22:02
Default Re: opposed buoyancy__ required help
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Hirdesh
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Low value of under ralaxation method means you are reducing the increment of values par time step. It will not effect solution. Only thing is that solution will take more time to converge. but you should check grid independence.
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