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Leo April 6, 2002 07:09

Mixed Convection Problem
Hi all! Does anyone tell me where can I find some graphical(Fluent contours picture)analysis documents about the convection problem?? otherwise, can I set inlet be "Velocity inlet" and and outlet be "outflow" on Fluent boundary condition to solve laminar flow convection problem?

Chetan Kadakia April 8, 2002 02:32

Re: Mixed Convection Problem
The Fluent manual (a CD can be purchased from Fluent) has topics on convection.

Yes a velocity inlet and outflow can be used as you said. Once you run your solution, check out the boundary layer near the wall surface with the use or contours or vectors.

Leo April 9, 2002 13:10

Re: Mixed Convection Problem
Thks Chetan Kadakia Actually, I still have other porblems, I want to ask which turbulence model is best for "mixed convection" under turbulence flow? RNG? ot others? and then what is the function of "turbulence kinetic energy" and "turbulence dissipation rate" in "velocity inlet" setting? Can I get buoyancy parameter on Fluent calculation directly?? Thks all of your help!

Chetan Kadakia April 9, 2002 13:44

Re: Mixed Convection Problem
The questions you ask cannot be answered unless you give more detail.

And which turbulence model is best depends on several factors. Grid size and computational power, 2d vs. 3d flow, amount time you need to complete your simulation in, accuracy required, complications of flow, is the flow fully turbulent, etc.

As for you turbulent parameters at the inlet, the ideal would be to obtain experimental data that can give you these values. That takes some research, and have to consider the inlet you are simulating.

The manual also has some guidelines on turbulent parameters for the B.C.'s.

You can also r

Rajeev Kumar Singh April 15, 2002 07:28

Re: Mixed Convection Problem
Dear Leo,

Here is the simple method given by fluent to calculate turbulent kinetic energy and dissipation rate for any inlet or outlet consideration.

Consider this for a circular opening. For opening of any other shape use hydraulic diameter concept.

1. Calculate Reynolds number (Re) = rho x d(sub)inlet x v(sub) inlet / mu

2. Calculate turbulent intensity (Tu %) = 0.16 x Re (sup) (-1/8)

3. K = 1.5 x v (sub)inlet (sup)2 x Tu (sup) 2 4. epsilon = (0.09 sup 0.75 x k sup 1.5)/(0.07 x d (sub) inlet

5. sub stands for subscript and sup stands for superscript.

6. 0.07 is the length scale multiplication factor for a circular pipe. Use fluent manual if inlet is of any other cross section.

Hope this solves your problem.


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