Advection Vs Convergence

saisanthoshm88 · July 5, 2012, 05:27

My simulation runs fine with a high resolution (or) a upwind advection scheme but the run crashes when I use a second order (Blend = 1) and also when I use a specified blend factor = 0.5

What does this indicate ?

flotus1 · July 5, 2012, 05:55

This behaviour might indicate a poor mesh quality or a "difficult" setup in general.
An Upwind advection scheme acts as a damping function to the numerical solution and thus supresses instabilities of the solver at the cost of lower accuracy.

Try achieving a converged flow field with the first order upwind scheme first.
Then use this flow field as the initial condition for the next run where you use a higher order scheme.

Far · July 5, 2012, 06:13

try to plot the contours of blending factor to see where you get the problems and what is the min value of it.

July 5, 2012, 05:27	Advection Vs Convergence	#1
saisanthoshm88 Senior Member --------- Join Date: Oct 2010 Posts: 303 Rep Power: 17	My simulation runs fine with a high resolution (or) a upwind advection scheme but the run crashes when I use a second order (Blend = 1) and also when I use a specified blend factor = 0.5 What does this indicate ? __________________ Best regards, Santhosh.

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July 5, 2012, 05:55		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	This behaviour might indicate a poor mesh quality or a "difficult" setup in general. An Upwind advection scheme acts as a damping function to the numerical solution and thus supresses instabilities of the solver at the cost of lower accuracy. Try achieving a converged flow field with the first order upwind scheme first. Then use this flow field as the initial condition for the next run where you use a higher order scheme.

July 5, 2012, 06:13		#3
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	try to plot the contours of blending factor to see where you get the problems and what is the min value of it.