# Oscillating Residuals

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 July 27, 2006, 08:34 Oscillating Residuals #1 Cairol Guest   Posts: n/a 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

 July 27, 2006, 08:35 Re: Oscillating Residuals #2 Cairol Guest   Posts: n/a ups ...

 July 27, 2006, 10:13 Re: Oscillating Residuals #3 esteve Guest   Posts: n/a 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

 July 31, 2006, 04:14 Re: Oscillating Residuals #4 Cairol Guest   Posts: n/a 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

 July 31, 2006, 09:34 Re: Oscillating Residuals #5 Cairol Guest   Posts: n/a I took the segregated solver and .................................................. .................................................. ............... it is going to converge Cheers Cairol

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