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-   -   turbulance parameter (http://www.cfd-online.com/Forums/flow-3d/128098-turbulance-parameter.html)

razieh anari January 3, 2014 07:49

turbulance parameter
 
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 .

JBurnham January 3, 2014 13:57

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 "mass-averaged turbulent energy":

MTKE = sum(k*mass)/sum(mass). In FLOW-3D 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.

razieh anari April 26, 2014 14:30

turbulent dissipation
 
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?

Milad h July 13, 2014 06:40

Quote:

Originally Posted by razieh anari (Post 488412)
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?

hi razieh
(i need u' , v' , w' , can i have these from out put result?)
can you solve this problem?

JBurnham July 14, 2014 11:00

You can get u', v', w' from LES turbulence modeling. You can't get the velocity fluctuation components separately from RANS turbulence (like k-e or k-w).

Milad h July 14, 2014 17:11

Quote:

Originally Posted by JBurnham (Post 501438)
You can get u', v', w' from LES turbulence modeling. You can't get the velocity fluctuation components separately from RANS turbulence (like k-e or k-w).

Hi JBurnham
thank u
but, How do i get u', v', w' from output??

JBurnham July 18, 2014 13:17

Use FlowSight (the new post-processor that comes with v11). It can calculate the time-mean velocity values u_, v_, w_ in all cells over a steady-state 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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