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-   -   Oscillating Residuals (http://www.cfd-online.com/Forums/fluent/41865-oscillating-residuals.html)

Cairol July 27, 2006 08:34

Oscillating Residuals
 
Hi all

I'm calculating a flow arround a Turbofans nacelle with mixing of core and bypass massflow using a 6 million nodes large grid. I have a converged solution for a freestream velocity of 50m/s and I now want to simulate the flow at different freestream velocities. Unfortunately the residuals for the velocities, energie and continuity are beginning to oscillate after 100 Iterations in between 1e-1 and 2e-1 with an amplitude of around 1e-1 and no convergence is reached.

My Simulation parameters are: Solver: Coupled explicit parallel on 8 cpus Gas: Ideal Gas Law for Compressible Flows Turbulence: Realizable k-eps CFL: 0.2

Maybe a multigrid can solve the problem??? Thanks for any suggestions.

Cairol

Cairol July 27, 2006 08:35

Re: Oscillating Residuals
 
ups ...

esteve July 27, 2006 10:13

Re: Oscillating Residuals
 
What about changing the underelaxation parametres for velocity , If I were you I would decrease underrelax parametre 0.1 point and then see what happens

Cairol July 31, 2006 04:14

Re: Oscillating Residuals
 
Thanks for your Answers

I changed the under-relaxation parameter as well as the CFL-Number to 0.1 and used the coupled implicit solver instead of the explicit like Razvan suggested.

Unfortunately, the same oscillation appears after a 100 iterations.

Again, my simulation parameters are:

Solver: Coupled implicit parallel on 8 cpus

Gas: Ideal Gas Law for Compressible Flows

Turbulence: Realizable k-eps - first order upwind

CFL: 0.1

Massflows on inlets and outlets are more or less steady during the run, that is no oscillation appears in Massflow!

Cheers Cairol

Cairol July 31, 2006 09:34

Re: Oscillating Residuals
 
I took the segregated solver and .................................................. .................................................. ............... it is going to converge

Cheers

Cairol


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