Implicit steger warming fvs

pooja · May 18, 2011, 17:05

Hiiii, i am writing code for the implicit steger warming flux vector splitting for 1d cd nozzle case. i am using gmres method to solve Ax = b.
One strange thing is happening with in the code, as all of us know that for implicit there is no restriction on CFL number, First point is that if i start with CFL value 0.1 and max CFL value 2, with incrementation in CFL given by CFL*1.1 my code is converging nicely upto log rss value -7.034528 and results are matching.
But if i am taking max CFL number more than 2 say 4 the its blow up and go for log rss value -1.234 so on or if further increase in max CFL say upto 10 i will get nan after some iteration. I am really getting fed up with it from last one month then one of my friend told that u can put your problem in cfd forum surely you will get nice ideas. All ideas are welcome and thanks in advance plz help me

praveen · May 19, 2011, 00:10

gmres is not easy to get working for flows with shocks.

From your description I assume you are solving a steady state problem.

You do need to use a smaller cfl to begin with. You can slowly increase this as your residual decreases. So you can try something like

$cfl^n = cfl^{n-1} \frac{Res^{n-1}}{Res^n}$

You can also put an upper bound on the cfl.

Note that without good preconditioner, gmres will not work.

pooja · May 19, 2011, 05:34

Thanx parveen for reply, but for 1d cd nozzle case as i said earlier i am starting with a low value of CFl 0.1 and incrementing with CFL*1.01 .
Shall i have to change the iterative method ?

pooja · May 19, 2011, 06:48

Hey only, one reply from this forum not expected

I am really in very much trouble help me plzzzzzzzzzzz

May 18, 2011, 17:05	Implicit steger warming fvs	#1
pooja New Member dushyant Join Date: May 2011 Posts: 6 Rep Power: 14	Hiiii, i am writing code for the implicit steger warming flux vector splitting for 1d cd nozzle case. i am using gmres method to solve Ax = b. One strange thing is happening with in the code, as all of us know that for implicit there is no restriction on CFL number, First point is that if i start with CFL value 0.1 and max CFL value 2, with incrementation in CFL given by CFL*1.1 my code is converging nicely upto log rss value -7.034528 and results are matching. But if i am taking max CFL number more than 2 say 4 the its blow up and go for log rss value -1.234 so on or if further increase in max CFL say upto 10 i will get nan after some iteration. I am really getting fed up with it from last one month then one of my friend told that u can put your problem in cfd forum surely you will get nice ideas. All ideas are welcome and thanks in advance plz help me

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May 19, 2011, 00:10		#2
praveen Super Moderator Praveen. C Join Date: Mar 2009 Location: Bangalore Posts: 342 Blog Entries: 6 Rep Power: 18	gmres is not easy to get working for flows with shocks. From your description I assume you are solving a steady state problem. You do need to use a smaller cfl to begin with. You can slowly increase this as your residual decreases. So you can try something like $cfl^n = cfl^{n-1} \frac{Res^{n-1}}{Res^n}$ You can also put an upper bound on the cfl. Note that without good preconditioner, gmres will not work.

May 19, 2011, 05:34		#3
pooja New Member dushyant Join Date: May 2011 Posts: 6 Rep Power: 14	Thanx parveen for reply, but for 1d cd nozzle case as i said earlier i am starting with a low value of CFl 0.1 and incrementing with CFL*1.01 . Shall i have to change the iterative method ?

May 19, 2011, 06:48		#4
pooja New Member dushyant Join Date: May 2011 Posts: 6 Rep Power: 14	Hey only, one reply from this forum not expected I am really in very much trouble help me plzzzzzzzzzzz