I use CFX4.3 to calculation transient gas-particle flow in fluidized bed. And the time step is set as 5.0e-4 s or smaller. But predicted time series don't show the fluctuation as expected.

How do you visualize the results? With which software?

The post processor 'Analyze' can read the dump file. Or you can write the data in files by Userfortran.

Both ooptions are possible. But I suppose that the information wasn't saved in time interval that could show the trasient behaviour correctly. You should calculate the time scale of the smallest phenomenum that you want to see in the flow. This time scale will be the time interval to save in dump file. Of course, the time step of the simulation has to be smaller than this time scale.

I hope this helps.