Estimating velocity fluctuation's component based on Reynolds stress

Mariusz · August 23, 2014, 07:59

Hi,

Can I estimate the value of velocity fluctuation's component based on Reynolds stress tensor?

For example, if I have a simulation that is:
-steady state (simpleFoam)
-constant density
-turbulence is modeled using LRR RSM

and at the end of this simulation I'd like to estimate the values of velocity fluctuation's components in this way (example for z-direction fluctuation):

Code:

so

Code:

Is that correct?

Or are in simpleFoam the Reynolds stress tensor components already divided by density? In case of which it is already:

Code:

Is any of this correct?

huangxianbei · September 12, 2014, 23:19

I don't think so. You'd better use u-umean, considering your simulation is steady, it's impossible to estimate the fluctuation (my opinion)

August 23, 2014, 07:59	Estimating velocity fluctuation's component based on Reynolds stress	#1
Mariusz New Member MP Join Date: Jun 2011 Posts: 4 Rep Power: 15	Hi, Can I estimate the value of velocity fluctuation's component based on Reynolds stress tensor? For example, if I have a simulation that is: -steady state (simpleFoam) -constant density -turbulence is modeled using LRR RSM and at the end of this simulation I'd like to estimate the values of velocity fluctuation's components in this way (example for z-direction fluctuation): Code: $R_{zz}=\rho\overline{u'_z u'_z}=\rho\overline{(u')^2_z}$ so Code: $\overline{u'_z}=\frac{\sqrt{R_{zz}}}{\rho}$ Is that correct? Or are in simpleFoam the Reynolds stress tensor components already divided by density? In case of which it is already: Code: $\overline{u'_z}=\sqrt{R_{zz}}$ Is any of this correct?

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September 12, 2014, 23:19		#2
huangxianbei Senior Member Huang Xianbei Join Date: Sep 2013 Location: Yangzhou,China Posts: 302 Rep Power: 14	I don't think so. You'd better use u-umean, considering your simulation is steady, it's impossible to estimate the fluctuation (my opinion)