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 Camilo Costa November 29, 2006 10:35

Analyze Turbulence

Problem Description:

Closed cavity (cilindrical thermal storage tank) with wall hot (16 HORIZONTAL TUBES WITH PRESCRIBED TEMPERATURE) and wall side and wall top cold with prescribed global heat trasfer coeficient. Work fluid is asphalt (variable viscosity).

Formulation:

I simulate this problem whith and without turbulence model (SST). This model of turbulence was used because of strong changes of streamlines. The results was diferents for both cases. With turbulence my mean temperature was 135°C and the wall heat flux was 180000 WATTS. Without turbulence my mean temperaute was 145°C and the wall heat flux was 210000 WATTS. Both cases was converged with 10e-5 and the total imbalance was 1 percent.

Question:

Why occur this diferences of mean temperature and heat flux?

How can i analyze the turbulence of my problem. The turbulence is significative for my problem?

 Glenn Horrocks November 29, 2006 17:10

Re: Analyze Turbulence

Hi,

Assuming your simulation is accurate, the difference could be due to the temperature changing the viscosity, which changes the turbulence field which in turn affects the heat transfer. Have a look at the turbulence kinetic energy in the flow and that may help explain the difference.

Glenn Horrocks

 Camilo Costa November 30, 2006 13:08

Re: Analyze Turbulence

Analyze Turbulence:

Turbulent Kinetic Energy: max: 0.00107 [m^2 s^-2] min: 6.24e-31 [m^2 s^-2] volumeAve(Turbulent Kinetic Energy)@DOMAIN = 5.17754e-005 [J kg^-1]

Eddy Viscosity: max: 2.29 [Pa s] min: 6.11e-34 [Pa s] volumeAve(Eddy Viscosity)@DOMAIN = 0.694581 [Pa s]

Dynamic Viscosity: min: 0.017 [Pa s] max: 30.5 [Pa s] volumeAve(Dynamic Viscosity)@DOMAIN = 0.33397 [Pa s]

Regards!!!

 Glenn Horrocks November 30, 2006 17:19

Re: Analyze Turbulence

Hi,

It is the turbulence and velocity profile near the walls with significant heat transfer which are important, and the difference between the two simulations.

Also: You have a huge range of dynamic viscosities reported, it ranges over a factor of 1000. Are you sure this is physically correct?

Regards, Glenn

 Camilo Costa November 30, 2006 19:47

Re: Analyze Turbulence

The Dynamic Viscosity have much variation because my work fluid is asphalt.

Regards!

 Camilo Costa December 1, 2006 09:04

Re: Analyze Turbulence

But the turbulence have some influence on the flow?

My Turbulence have little Kinetic Energy but the Eddy Viscosity have the same order of the Dinamic Viscosity. So this show me that my turbulence is significative for my problem! Or not?

 Glenn Horrocks December 3, 2006 17:26

Re: Analyze Turbulence

Hi,

Does turbulence affect the flow: yes. Is it significant for your flow: maybe, depends on the the flow. Given the viscosity ratio is low it is possible the turbulence does not significantly affect the flow.

Try running it laminar and compare the results.

Glenn Horrocks

 Camilo Costa December 4, 2006 12:00

Re: Analyze Turbulence

Thank you very much for his contribution in my work.

I start my study in turbulence a little months ago. And if you have some papers or books for recomend to me i appreciate very much.

REGARDS!!

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