CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

inlet velocity profiles

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 13, 2002, 15:50
Default inlet velocity profiles
  #1
cfxuser
Guest
 
Posts: n/a
hi,

I want to calculate a swirling pipe flow with a specified inlet velocity profile of the type

U_ax=f(r)

W_tan=f(r)

The profile is not an expression but stored in a file in cylindrical coordinates:

r_1 u_1 w_1

r_2 u_2 w_2 etc.

The geometry is set up so that that the x-axis is the axis of rotation. So the radius would be calculated as r=sqrt(y^2 + z^2). Now my problem is:

Is it sufficient to define a new variable "rad" with CEL so that the solver "knows" that the tabulated values are cylindrical ?

Thanks for your comments
  Reply With Quote

Old   August 14, 2002, 18:07
Default Re: inlet velocity profiles
  #2
Neale
Guest
 
Posts: n/a
You will need to define u, v and w velocity components from your radial and axial components. This requires transforming your cylindrical components into Cartesian in CEL. You could do this with 1D interpolation functions and the following:


CEL:
EXPRESSIONS:
r = sqrt(x^2+y^2)
theta = atan(y,x)
Vrad = Vradf(r)
Vaxial = Vaxialf(r)
Vtheta = Vthetaf(r)
Ucomp = Vaxial
Vcomp = Vradial*cos(theta) + r*Vtheta*sin(theta)
Wcomp = Vradial*sin(theta) - r*Vtheta*cos(theta)
END
END


where Vradf, Vaxialf, and Vthetaf are 1D interpolation functions for each of your velocity components. Looks like you might need to split your text files up. Hopefully I got my sin() and cos() correct!
  Reply With Quote

Old   August 17, 2002, 07:18
Default Re: inlet velocity profiles
  #3
cfxuser
Guest
 
Posts: n/a
Neale,

thanks a lot for your help! Unfortunately I still get the following error message:

Error processing expression: U = Ucomp

Obviously something is wrong with the boundary condition definition. As you suggested I defined the CEL expressions, declared the functions and defined the junction box routines (which I derived from the CFX documentation for user subroutines). Maybe you can see the mistake in the CCL file below ... ?

Best regards and many thanks in advance.

1. EXPRESSIONS:

(..)

rad = sqrt(z^2+y^2)

phi = atan(y,z)

Vrad = Vradf(rad)

Vaxial = Vaxialf(rad)

Vtang = Vtangf(rad)

Ucomp = Vaxial

Vcomp = Vrad*cos(phi) + rad*Vtang*sin(phi)

Wcomp = Vrad*sin(phi) - rad*Vtang*cos(phi)

(..)

2. FUNCTIONS:

(..)

FUNCTION : Vaxial

Option = User Function

Argument List = [m]

Result Units = [m s^-1]

(..)

FUNCTION : Ucomp

Option = User Function

Argument List = [m s^-1]

Result Units = [m s^-1]

(..)

3. USER ROUTINE DEFINITIONS

(..)

USER ROUTINE : Load Inlet Profiles

Option = Junction Box Routine

Junction Box Location = User Input

Calling Name = user_input_rad

Library Name = user_input_rad

Library Path = /home/cfxuser/Testcase

(..)

USER ROUTINE : Vaxial

Option = Junction Box Routine

Junction Box Location = User Input

Calling Name = vaxialf

Library Name = user_input_rad

Library Path = /home/cfxuser/Testcase

(..)

3. BOUNDARY CONDITIONS :

(..)

MASS AND MOMENTUM :

Option = Cartesian Velocity Components

U = Ucomp

V = Vcomp

W = Wcomp

END (..)
  Reply With Quote

Old   August 26, 2002, 15:13
Default Re: inlet velocity profiles
  #4
Neale
Guest
 
Posts: n/a
From this I can't tell. Is there any more output in the output file which is more descriptive than what you have?

One thing you should be able to do is set Ucomp = Vaxiaf(rad) directly, rather than through another expression variable.

I'm also not sure why you have created a user function called "Ucomp". This should not be necessary. All you should need is to define three user functions: Vradialf, Vaxialf and Vthetaf and set Ucomp, Vcomp and Wcomp accordingly. Maybe this is/was the problem?

Neale
  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Problem with assigned inlet velocity profile as a boundary condition Ozgur_ FLUENT 5 August 25, 2015 05:58
Steady pipe flow mean velocity higher than inlet velocity anita OpenFOAM Running, Solving & CFD 7 September 25, 2012 06:35
FSI- Pipe- uniform velocity profile inlet Absy Main CFD Forum 0 April 6, 2010 04:01
commit velocity outlet to velocity inlet chelvistero OpenFOAM 0 March 27, 2010 04:46
inlet velocity profiles? khelila FLUENT 0 February 6, 2006 11:28


All times are GMT -4. The time now is 18:04.