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-   -   creating expresions in cfx build or cfx post (http://www.cfd-online.com/Forums/cfx/19135-creating-expresions-cfx-build-cfx-post.html)

alex August 22, 2002 10:32

creating expresions in cfx build or cfx post
 
hi masters of cfx, i am creating expresions for find the reynolds number in a combustion chamber of gas turbine (it has a varible diameter), this is a problem because i dont know what is the diameter i must take,i know velocity must be mean velocity. I created a expresion in Build and I saw it in the outfile(solver), Where can i see the results of this expresion?, in the Post? or i have to create the expresion in the Post and to do the calculations there?........

please help me, and see you later..

Robin August 22, 2002 13:01

Re: creating expresions in cfx build or cfx post
 
Hi Alex,

The results of expressions are not output by the solver unless you define an additional variable.

The easiest thing to do is create an expression in Post to solve for this and use it to define a variable in Post.

More importantly, the length and velocity (and density for that matter) you use for Reynolds number is really arbitrary and depends on the how you wish to use this information. I suggest looking through the relevant literature for an appropriate length scale. Just remember that a Reynolds number is a way of non-dimensionalizing the flow to use as a similarity criteria. Comparison based on Reynolds number is only meaningful if the Reynolds number was calculated the same way for multiple datasets. There may also be better similarity criteria for combusters.

I don't personally have any combustion experience, so I cannot recommend a lenght to use. Perhaps another keen reader could provide some insight?

Regards, Robin


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