CFD Online URL
[Sponsors]
Home > Forums > Main CFD Forum

[Help!] impeller torque calculation: pressure and viscous moments

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 21, 2013, 07:52
Default [Help!] impeller torque calculation: pressure and viscous moments
  #1
Senior Member
 
ghost82's Avatar
 
Daniele
Join Date: Oct 2010
Location: Italy
Posts: 760
Rep Power: 14
ghost82 will become famous soon enough
Hi all!
I simulated a vessel+impeller with multiple reference frame and I want to calculate the power needed to drive the impeller: as I know the power P is:

P [Watt]=2*pigreco*N*Torque

N=revolution per seconds (12 rpm)
Torque in N*m

Impeller axis rotation is Z and the vessel is centered in X,Y; the domain is in +Z.
Impeller rotates counterclockwise.

Rotating frame is all the cylinder zone, which rotates at 12 rpm, because impeller 007/impeller 007-shadow are very closed to the wall. Bottom conical zone is stationary zone.
Vessel walls have absolute 0 rotational velocity.
Impeller/impeller 007/impeller 007-shadow have relative velocity to adjacent fluid zone of 0.

If I calculate the pressure and viscous moments (moment center: 0,0,0 moment axis 0,0,1) I have:

Impeller zone (all in N*m)
Pressure: -225
Viscous: +103
Total: -122

Impeller 007 zone (all in N*m)
Pressure: -109
Viscous: -8
Total: -117

Impeller 007-shadow zone (all in N*m)
Pressure: -107
Viscous: -8
Total: -115

So total moment is: -354

and P should be:
P=abs(total moment)*N*2*pigreco=354*12/60*2*pigreco=445 W

Is it right?

What I don't understand is why in the impeller zone viscous moment has opposite sign in respect to pressure moment.
Can anybody explain to me please?

I'm attaching some pictures.

Thank you
Daniele
Attached Images
File Type: jpg Agitatore+vessel.jpg (25.7 KB, 28 views)
File Type: jpg Vettori-velocita-SST.jpg (33.4 KB, 25 views)
ghost82 is offline   Reply With Quote

Old   March 27, 2014, 04:37
Default
  #2
Member
 
Pekka Pasanen
Join Date: Feb 2012
Location: Finland
Posts: 34
Rep Power: 4
zordiack is on a distinguished road
Did you ever figure this out? I'm having the same problem with my turbomachinery case, the pressure moment seems to be in the right direction but the viscous moment has opposite sign, which doesn't make any sense to me.
zordiack is offline   Reply With Quote

Reply

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
CFD-Post: Pressure and Viscous Drag on Isosurface Shirock CFX 4 June 4, 2012 02:02
how does Fluent calculate the pressure and viscous force ? e30.lsb FLUENT 7 June 27, 2011 22:31
how does Fluent calculate the pressure and viscous force vector? Ralf Schmidt FLUENT 2 May 17, 2010 16:49
what the result is negatif pressure at inlet chong chee nan FLUENT 0 December 29, 2001 06:13
How to obtain correct viscous pressure drag using CFX? Ketut Utama Main CFD Forum 1 January 25, 1999 06:05


All times are GMT -4. The time now is 04:56.