Transient oscillatory flow

yms

Hello everybody,

I am trying now to solve a simplified thermoacoustic problem using Fluent6.1. It is simply an oscillatory flow problem inside a channel, with transient pressure boundry conditons

time:0-->15.71s (period of one cycle is 1.571 s).

I am using the segregated solver with 2nd order implicit unsteady formulation. I got converged solution, with the same trend as the analytical solution but with some differences. If i used a time step of 0.01 s, i noticed that fluent will give me a very good agreement with analytical solution but for a time 0.03 sec earlier than that of the analytical solution. that is analyt sol at t=14.3 is the same as that of fluent but at t=14.27 .

I solved the same problem with Comsol Multiphysics (Femlab 3.2) and it gave me the same results as analyt sol with no time lag.

I also noticed that coupled solver doesnt work for this problem ( iam using viscous incompressible fluid) ??!!

Any suggestions, to solve the problem??!!

Your help is so much appreciated.

Best regards, YMS