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-   -   time averaged results as initial conditions in CFX (http://www.cfd-online.com/Forums/cfx/23926-time-averaged-results-initial-conditions-cfx.html)

mike May 2, 2007 16:37

time averaged results as initial conditions in CFX
 
Hi Everybody, I am using CFX 11 package. I have time averaged results of a case and I want to use this "time averaged results" as initial condition for my other run (same mesh). I tried couple of things but could not succeed. Any advice would be greatly appreciated. Thanks, Mike

Robin May 2, 2007 16:59

Re: time averaged results as initial conditions in
 
Hi Mike,

Open your results file in Post and replace the Velocity, Temperature and Pressure variables with expressions equating them to the time averaged equivalents (you can do this by selecting the appropriate variable under the Variables tab in Post and checking the box next to "Replace with expression").

Note that the original results are never lost, to recover them just go back to the variable and uncheck the "Replace with expression" box.

Interpolate the results of this modified results file onto new analysis.

Regards, Robin

Dr. FLow Squad May 3, 2007 01:31

Re: time averaged results as initial conditions in
 
I've always just use the interpolation function in the solver to have the steady state results as a start value. Is that wrong then?

Just ignore the Pre warning when saving a def file.

mike May 3, 2007 08:15

Re: time averaged results as initial conditions in
 
Hi Robin, Thank you very much. I did as you said, and it worked out great. Thanks again for you help. Mike

mike May 3, 2007 08:19

Re: time averaged results as initial conditions in
 
Dr Flow, To have steady state results as a start condition, you can do as you said. However in my case, I have time averaged results of transient run. and I want to use time averaged results as initial condition (not steady state solution). Mike

Gert-Jan May 4, 2007 17:14

Re: time averaged results as initial conditions in
 
Hi Mike,

I wonder what your application is. Why do you need time averaged results as an initial guess? Is it for a structural calculation?

Just trying to understand for what kind of application I could use this.......

Gert-Jan

mike May 5, 2007 20:33

Re: time averaged results as initial conditions in
 
Hi Gert-Jan, I have convergence problems mostly due to the transient effects. Thus, in order to get the best prediction, I run transient and take the time averaged of the field. That is good enough for our application. In addition, I wanted to get the temperature distribution (uncoupled with flow). So I shut the fluid and turbulence solvers off from expert parameters and just wanted to solve heat transfer equation.However I had to define velocity distribution for the domain. For the best prediction, I wanted to use the time averaged velocity field. Thats why I needed time averaged velocity field for initials conditions. Mike

Robin May 7, 2007 09:46

Re: time averaged results as initial conditions in
 
Hi Mike,

If that is the case, you should probably adjust the Eddy Viscosity to reflect the diffusion effect of turbulence. Otherwise you will combine the instantaneous turbulence field with the time averaged velocity field.

Interesting idea though.

Regards, Robin

mike May 7, 2007 14:54

Re: time averaged results as initial conditions in
 
Thanks Robin, I had never thought about it. I need to figure out something for this. Regards, Mike


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