natural convection equations in non-dimensional form

Ehsan Khalili · April 8, 2011, 05:18

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, 23:21

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

it depends on viscosity, and specific heat.

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, 02:50

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, 02:57

Quote:

Originally Posted by t.krishnamohan

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, 03:10

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, 03:12

Quote:

Originally Posted by t.krishnamohan

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, 03:48

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, 22:06

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.

April 8, 2011, 05:18	natural convection equations in non-dimensional form	#1
Ehsan Khalili New Member Ehsan Join Date: Mar 2011 Posts: 4 Rep Power: 15	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?

April 25, 2012, 23:21	natural convection equations in non-dimensional form	#2
studen New Member studen Join Date: Jan 2012 Posts: 12 Rep Power: 14	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 it depends on viscosity, and specific heat. 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.

April 27, 2012, 03:48	non dimensional form	#7
studen New Member studen Join Date: Jan 2012 Posts: 12 Rep Power: 14	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.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Coupled vs Seg - Natural vs. Forced Convection	Alex	Siemens	5	December 12, 2007 05:58
natural convection at high Rayleigh	mauricio	FLUENT	2	February 23, 2005 20:43
Approximate Mixing due to Natural Convection	Greg Perkins	Main CFD Forum	0	February 12, 2003 19:43
Mixing By Natural Convection Processes	Greg Perkins	FLUENT	0	February 12, 2003 19:40
natural convection in a sealed enclosure	James	Main CFD Forum	4	April 2, 2001 16:48

April 27, 2012, 02:50		#3
t.krishnamohan Member Krishna Join Date: Oct 2009 Posts: 34 Rep Power: 17	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.

April 27, 2012, 03:10		#5
t.krishnamohan Member Krishna Join Date: Oct 2009 Posts: 34 Rep Power: 17	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.

April 29, 2012, 22:06		#8
t.krishnamohan Member Krishna Join Date: Oct 2009 Posts: 34 Rep Power: 17	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.