Question about using total energy equation or thermal equation

Anna Tian · May 6, 2013, 14:15

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?

JuPa · May 6, 2013, 15:19

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, 17:40

Quote:

Originally Posted by RicochetJ

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, 19:58

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

May 6, 2013, 14:15	Question about using total energy equation or thermal equation	#1
Anna Tian Senior Member Meimei Wang Join Date: Jul 2012 Posts: 494 Rep Power: 16	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? __________________ Best regards, Meimei

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May 6, 2013, 15:19		#2
JuPa Senior Member Mr CFD Join Date: Jun 2012 Location: Britain Posts: 361 Rep Power: 15	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.

May 6, 2013, 19:58		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	The easiest way is to run a model with and without it and you will then see if it makes a difference.