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-   -   Question about using total energy equation or thermal equation (http://www.cfd-online.com/Forums/cfx/117315-question-about-using-total-energy-equation-thermal-equation.html)

 Anna Tian May 6, 2013 13:15

Question about using total energy equation or thermal equation

HI,

The tutorial tell that, for low-speed flow, thermal equation could be used instead of total energy equation to accelerate the computation. But how to know whether my case is 'low-speed' or not?

By the way, I'm simulating water. How to know whether the viscous term has to be included or not?

 RicochetJ May 6, 2013 14:19

Only use the total energy equation related to high speed flow if compressibility is important. I think (I invite anyone to correct me here) it's a speed around mach 0.3 and above.

If you're using water, and your flow is subsonic you won't have heat generation due to viscous work, so I wouldn't worry about it.

 Anna Tian May 6, 2013 16:40

Quote:
 Originally Posted by RicochetJ (Post 425634) Only use the total energy equation related to high speed flow if compressibility is important. I think (I invite anyone to correct me here) it's a speed around mach 0.3 and above. If you're using water, and your flow is subsonic you won't have heat generation due to viscous work, so I wouldn't worry about it.

My flow speed is not that high. Is there is a way (or criteria) to detect whether viscous term need to be included or not?

 ghorrocks May 6, 2013 18:58

The easiest way is to run a model with and without it and you will then see if it makes a difference.

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