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January 3, 2014, 07:49 
turbulance parameter

#1 
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razieh anari
Join Date: May 2013
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Hi
1 what is the mean of pressure in flow 3d? dynamic or static? 2 what is the mean of turbulent energy? is the same kinetic energy of turbulence? k=0.5(u'2+v'2+w'2) u', v', w' are Average volatility. thanks a lot . 

January 3, 2014, 13:57 

#2 
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Jeff Burnham
Join Date: Apr 2010
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1) p = static pressure.
2) turbulent energy = turbulent kinetic energy, TKE, just as you have guessed: k = 0.5(u'^2+v'^2+w'^2). TKE has units of L^2/t^2 (J/kg in SI). On the Simulation Manager tab (and in Analyze > Probe > General History Data) there is an output called "massaveraged turbulent energy": MTKE = sum(k*mass)/sum(mass). In FLOW3D variables, MTKE = sum(k*rho*f*vf*del)/sum(rho*f*vf*del). Rho is local fluid density, f is local fluid fraction (volume fluid in cell/open volume in cell), and vf is local volume fraction (open volume in cell/total volume in cell), and del is the cell volume dx*dy*dz. The term rho*f*vf*del = mass of fluid in cell. 

April 26, 2014, 15:30 
turbulent dissipation

#3 
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razieh anari
Join Date: May 2013
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hello, thank you for your answers:
please tell me, what is the differences between turbulent energy and turbulent dissipation? turbulent dissipation is reynolds stresses?if not, what's its formula? i need u' , v' , w' , can i have these from out put result? 

July 13, 2014, 07:40 

#4  
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mh
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Quote:
(i need u' , v' , w' , can i have these from out put result?) can you solve this problem? 

July 14, 2014, 12:00 

#5 
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Jeff Burnham
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You can get u', v', w' from LES turbulence modeling. You can't get the velocity fluctuation components separately from RANS turbulence (like ke or kw).


July 14, 2014, 18:11 

#6 
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mh
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July 18, 2014, 14:17 

#7 
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Jeff Burnham
Join Date: Apr 2010
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Use FlowSight (the new postprocessor that comes with v11). It can calculate the timemean velocity values u_, v_, w_ in all cells over a steadystate flow. Then have FlowSight perform an arithmetic operation to subtract: u, v, w  u_, v_, w_ = u', v', w'. From the new fluctuation variables, you can find the max/min, 95th percentile, etc.


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