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HMR July 31, 2011 04:38

Time series of max plume height
Hi CFX users,

I am doing transient simulation of negatively buoyancy flow discharging into a confined enclosure with CFX. Every thing is working good and I successfully get the final transient results but now I am unable to export results of Time versus Max plume Height or Time Versus Froude number of the negatively buoyancy flow. I tried it several time but I failed to do it.

Could anybody please assist me to figure out this problem.



singer1812 August 1, 2011 10:48

How did you try? Max plume height would be a user generated data point. CFX isnt going to know what that is unless you tell it. Once you define it, export it as you would all other data.

HMR August 1, 2011 21:56

Hi Edmund,

Thanks for your reply. I didn't define anything for plume height, as before doing any simulation I don't know in which location it will be finally reached and if plume shape is not symmetrical may be the peak of the plume will be deviate from the middle.So after simulation in CFX post I considered one line along the bottom of the jet inlet and peak point of temparature contour and I tried to export data of time vs max plume height from chart xy transient plot, but I can't get what I want.

According to your advice, I think I need to write User define function/expression/variable, but I don't understand that how can I proceed, and another thing around me there is not a single person to whom I can discuss and get some advice or clue.

Would you able to please help in this regards.



singer1812 August 2, 2011 09:54

I meant how did you tell CFX what max plume height is (it can be moving with time as a function of results). What you describe with the line sounds like it will just give you the max inlet temp, not the plume height.

There needs to be a scaler definition for plume height. When you define that, what you describe will work (h vs t on a chart).

If you are going to use temperature for a definition, I dont think you can use peak temperature (unless your plume starts off at a lower temperature than ambient). Regardless, using temp, you probably will have to make sum judgement that the plume ends when the plume reachs x% of the ambient temperature (I have never done this, and I am only guessing at ways to mark a plume). In addition perhaps you could use velocity in the same way, it might give better results.

Either way, you need to make sure the value is scaler if you want to plot it the way you describe.

HMR August 2, 2011 22:00

Hi Edmund,

Thanks for your reply. I understand what you mean, but could you please tell me how can I define plume height in CFX. What I know that the downflow and the ambient interface is 1% of the difference between jut inlet temperature and ambient temperature. Based on that I already write programme on Fortran which is working well and I got very good Plume height VS Time plot. In Fortran coding I uses location of mesh and considered plume is asymmetric.

I don't know, how can I can prepare user define code in CFX. Could you please help me in this regards


singer1812 August 3, 2011 07:46

Off the top of my head, I would think you could create an isosurface based on your definition, then create an expression of maxVal(X)@isosurface (or Y or Z) for each time step. Then plot that expression versus time.

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