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-   -   Transient vs Steady State (http://www.cfd-online.com/Forums/cfx/23849-transient-vs-steady-state.html)

Adam April 12, 2007 10:46

Transient vs Steady State
 
What are the main differences between running transient and steady state?

I have a fourier series inlet velocity profile at my inlet that changes with time. When I run transient, the profile changes and settles into a different profile (peaks and troughs become smaller).

I have ran it with up to 1000 timesteps for a total time of 0.117s, and on a couple of grids (fairly coarse), but it makes little difference.

When I alter the profile so that the time is manually changed, and run it steady state at different time values on the same coarse grid, the profile is replicated perfectly.

Any ideas as to what is happening with the transient case? Can i run steady state using appropriate time values to manually alter the velocity profile instead of running transient and writing results at thos timesteps? The transient behaviour in the domain is due to the transient inlet velocity profile.

Many thanks

Adam

Juan Martin Catelén April 12, 2007 11:34

Re: Transient vs Steady State
 
I don't know how is changing your inlet velocity profile, but in transient, the profile may be doesn't have time to settle as in steady state because the inlet profile is changing at the same time. So, by running it in steady state your are not seeing the dynamics of the system. The results should be equal if the time for reaching the steady state is significantly smaller than the time that takes to the inlet profile to change. Bye.


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