Time averaging a product of fluctuations <u'T'>

lavdwall · November 14, 2013, 15:35

Hi everyone,

I would like to calculate turbulent heat fluxes, which are defined as the time averages of the velocity and temperature fluctuations:

<u' T'> where <..> denotes a time averaging operation, and u' and T' are respectively the velocity and temperature fluctuations.

Is there an easy solution to achieve this? I tried with the fieldAverage function in the controlDict but there it is only possible to calculate the prime-squared mean values of 1 field, e.g. <u'u'>. Someone has a solution?

Kind regards,
Laurien

Bernhard · November 15, 2013, 02:18

You can try to create a field U*T somehow, then <u'T'>=<UT>-<U><T>, where I assume you are tracking the mean quantities anyhow.

palmerlee · January 23, 2014, 04:48

Hi, Laurien!

Have you found a solution yet? I want to calculate <u' T'> too. It would be very kind of you to share some information about this problem.

Best regards,
Peter

agustinvo · April 29, 2015, 06:16

Hello

were you able to find a solution for this? I am wondering I have to modify the fieldAverage function, but it's not so easy to understand the code...

November 14, 2013, 15:35	Time averaging a product of fluctuations <u'T'>	#1
lavdwall New Member Laurien Vandewalle Join Date: Jun 2013 Location: Ghent, Belgium Posts: 29 Rep Power: 12	Hi everyone, I would like to calculate turbulent heat fluxes, which are defined as the time averages of the velocity and temperature fluctuations: <u' T'> where <..> denotes a time averaging operation, and u' and T' are respectively the velocity and temperature fluctuations. Is there an easy solution to achieve this? I tried with the fieldAverage function in the controlDict but there it is only possible to calculate the prime-squared mean values of 1 field, e.g. <u'u'>. Someone has a solution? Kind regards, Laurien

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November 15, 2013, 02:18		#2
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 21	You can try to create a field U*T somehow, then <u'T'>=<UT>-<U><T>, where I assume you are tracking the mean quantities anyhow.

January 23, 2014, 04:48		#3
palmerlee Member Peter Join Date: Nov 2011 Posts: 46 Rep Power: 14	Hi, Laurien! Have you found a solution yet? I want to calculate <u' T'> too. It would be very kind of you to share some information about this problem. Best regards, Peter

April 29, 2015, 06:16		#4
agustinvo Senior Member Agustín Villa Join Date: Apr 2013 Location: Alcorcón Posts: 313 Rep Power: 15	Hello were you able to find a solution for this? I am wondering I have to modify the fieldAverage function, but it's not so easy to understand the code...