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-   -   natural convection equations in non-dimensional form (http://www.cfd-online.com/Forums/fluent/86992-natural-convection-equations-non-dimensional-form.html)

Ehsan Khalili April 8, 2011 04:18

natural convection equations in non-dimensional form
 
Hi guys
I am trying to simulate a natural convection flow inside a triangular..... by fluent. How i can solve natural convection equations in non-dimensional form? How i can estimate modified material properties based only on two input parameters Pr and Ra?

studen April 25, 2012 22:21

natural convection equations in non-dimensional form
 
1. in fluent you can not solve non-dimensional, everything is dimensional .

2. regarding the pr and ra, you cant give direct input, as your know
http://upload.wikimedia.org/wikipedi...87fc9a41a4.png it depends on viscosity, and specific heat.http://upload.wikimedia.org/wikipedi...96a1ecdaef.png depends on volumetric co-efficeint, viscosity, length of the cavity, and temperature difference,you have to entre these properties in materials section and intialize, set the boundary conditions and u can see the prandtl number in contour--->contour of properties--->molecular prandtl number.

t.krishnamohan April 27, 2012 01:50

You can solve in non dimensional form in Fluent. Go to units and set every properties you encounter in your problem as non dimensional (user specified). From non dimensional equations, plug in values for coefficient of viscosity and thermal diffusivity, in your case its 1 and 1/Pr.(for forced convection problems its 1/Re). Develop a UDF for the source terms.

LuckyTran April 27, 2012 01:57

Quote:

Originally Posted by t.krishnamohan (Post 357356)
You can solve in non dimensional form in Fluent. Go to units and set every properties you encounter in your problem as non dimensional (user specified). From non dimensional equations, plug in values for coefficient of viscosity and thermal diffusivity, in your case its 1 and 1/Pr.(for forced convection problems its 1/Re). Develop a UDF for the source terms.

This is merely an equation without units, it is not a non-dimensional equation. If the equations are non-dimensional, you would never need to know the dimensional quantities (visocisty, diffusivity).

t.krishnamohan April 27, 2012 02:10

What I mean to say is compare the dimensional and non dimensional equations and in place of coefficient of viscosity and thermal conductivity in Fluent put the resp. coefficients 1 and 1/Pr. It is possible to solve in non dimensional form in Fluent.

LuckyTran April 27, 2012 02:12

Quote:

Originally Posted by t.krishnamohan (Post 357370)
What I mean to say is compare the dimensional and non dimensional equations and in place of coefficient of viscosity and thermal conductivity in Fluent put the resp. coefficients 1 and 1/Pr. It is possible to solve in non dimensional form in Fluent.

That still isn't non-dimensional form or non-dimensional equations. They're definitely dimensional, you just took away the units.

studen April 27, 2012 02:48

non dimensional form
 
i have used fluent 6.3.26 you can not change to non-dimensional form in this version their is no option available, the available options are british, si and cgs. i think they might have included non dimensional form from ansys fluent 12.1, which version are you using.

t.krishnamohan April 29, 2012 21:06

Select new and add a name say non dimen to it. You have to make all the properties as non dimensional like Length, mass, time, velocity, acceleration, temperature, viscosity, thermal conductivity,..................
Also need to specify the limits of the properties like temperature between 0 to 1.


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