# Variable non-dimensional CFX

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 October 15, 2009, 17:13 Variable non-dimensional CFX #1 New Member   Juan Lorenzo Join Date: Jul 2009 Posts: 19 Rep Power: 9 I want to compare the results obtained in the CFX with another study but in this, they standardized the continuity and the Navier-Stokes equations it is possible to make non-diemnsional the equations in the CFX??? I understand that using one cell I can work the equations that I create I pleasure. what I want to know if the variables of the program (the continuity and the Navier-Stokes equations) can be standardized (non-adimensional) and since it becomes? if the answer is negative as I compare a study of simulation in CFX with another non-dimensional?

 October 15, 2009, 18:41 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,456 Rep Power: 104 CFX is a dimensional solver. As long as you give it a consistent set of input units to work in then it is fine. You can define a unit system which is non-dimensional if you like. Obviously you can compare a dimensional and non-dimensional solution. The non-dimensional result can be made dimensional by assuming a length, time and any other necessary scales and scaling the results to give a dimensional result. Alternately you can non-dimensionalise the CFX result. Either is fine.

October 15, 2009, 22:18
#3
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Juan Lorenzo
Join Date: Jul 2009
Posts: 19
Rep Power: 9
Quote:
 Originally Posted by ghorrocks Alternately you can non-dimensionalise the CFX result. Either is fine.
As I can non-dimensionalise the cfx result? I must establish to unit non-dimensional system which is before the simulation or after finished the simulation I can pass non-dimensionale the result?

 October 18, 2009, 07:07 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,456 Rep Power: 104 No, you can use the same non-dimensional system (eg U*=U/Uref where U* is the non dimensional velocity, U is the dimensional velcoity and Uref is the reference velocity) used to define to define the non-dimensional system in the first place to the CFX results.

October 18, 2009, 10:50
#5
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Juan Lorenzo
Join Date: Jul 2009
Posts: 19
Rep Power: 9
thanks Glenn... understand.

Now, already like establishing my non-dimensional system, but like I can cause that the CFX recognizes my non-dimensional variables to me. I explain myself:

Quote:
 Originally Posted by ghorrocks (eg U*=U/Uref where U* is the non dimensional velocity, U is the dimensional velcoity and Uref is the reference velocity).
Taking your example I podria to write something thus:

Velocity u (non-dimensional) = Velocity u/Free Stream.
Velocity u = Velocity that calculates the CFX

Free Stream = Velocity of reference (I define)

Q: Since I do so that the CFX works with my new variable (non-dimensional Velocity or) instead of velocity u?

reading HELP CFX consegui this: (Example)
EXPRESSIONS:
Re = 4.29E6 []
Bel = 60 [m s^-1]
L=1.044 [m]
Visc=areaAve (density) @in*Vel*L/Re

PROPERTIES:
Option = Ideal Gas
Molar Mass = 2.896E1 [kg kmol^-1]
Dynamic Viscosity = Visc
Specific Heat Capacity = 1.E3 [J kg^-1 K^-1]
Thermal Conductivity = 2.52E-2 [W m^-1 K^-1]

In theory it could make this but parameters like the Velocity u, v, w or distance x, y, z or density where not to look for them to change them by my expressions non-dimensional.

I would want to settle down this non-dimensional system this way:

Velocity u (non-dimensional) = Velocity u/Free Stream.
Velocity v (non-dimensional) = Velocity v/Free Stream.
Velocity w (non-dimensional) = Velocity w/Free Stream.

X (non-dimensional) = X/Diam.
Y (non-dimensional) = Y/Diam.
Z (non-dimensional) = Z/Diam.

t (non-dimensional) = (t*Free Stream) /Diam.

same question, since I do so that the CFX works with my new variables and not with which it has by defect?

excuses by my English… are very bad

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