CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

Angular momentum

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

LinkBack Thread Tools Display Modes
Old   July 30, 2003, 12:55
Default Angular momentum
Posts: n/a
I have done some steady viscous calculations of a turbine stage with a cell centered multigrid code using Jameson scheme and Baldwin Lomax turbulence model. After doing these calculations, I have found the power produced by the rotor with an enthalpy balance, that is:

Power=(ro cx h)_in - (ro cx h)_out

Then I have calculated it using the angular momentum, that is:

Power=(ro cx r cth w)_in -(ro cx r cth w)_out

with :

ro = density

cx = axial velocity

h = total enthalpy

r = radius

cth = tangential velocity

w = angular speed of the rotor

_in = inlet of the rotor

_out= outlet of the rotor

I have obtained different values (differences are greater than 1%); then I have calculated, and included in the balance, the torque due to the endwall boundaries and I have also changed the grid but ... nothing.

Can you help me?

Best regards,

  Reply With Quote

Old   July 30, 2003, 13:28
Default Re: Angular momentum
Posts: n/a
Try repeating your prediction with a coarser grid and/or a finer grid. I suspect you will find that you have simply derived an indirect way of demonstrating numerical error in you solution (probably not particually useful one because of postive errors cancelling negative ones). A code can only strictly conserve a small number of physical quantities, the rest have to suffer the effects of truncation errors.

  Reply With Quote

Old   July 31, 2003, 11:09
Default Re: Angular momentum
Posts: n/a
Since you have a mass flow term in your calculations, the level of mass flow convergence enters into this. How well is your solution converged? Also, as you have a density term, you have to consider how accurately density is calculated. Your final comment regarding torque brings in another source of error.
  Reply With Quote

Old   July 31, 2003, 12:31
Default Re: Angular momentum
Posts: n/a
Mass flow error is 0.4% between inlet and outlet sections and I think solution is converged.

>Your final comment regarding torque brings in another source of error

Can you explain?

  Reply With Quote


Thread Tools
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 On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Angular momentum flux through faceZone askjak OpenFOAM Programming & Development 1 March 5, 2010 15:42
Derivation of Momentum Equation in Integral Form Demonwolf Main CFD Forum 2 October 29, 2009 20:53
angular momentum in swirling flows Roberto CFX 3 October 22, 2007 07:05
angular momentum with swirling flow Roberto FLUENT 0 October 20, 2007 11:18
Angular momentum conservation? Barry Main CFD Forum 19 April 11, 2002 10:37

All times are GMT -4. The time now is 17:47.