|October 21, 2013, 06:52||
[Help!] impeller torque calculation: pressure and viscous moments
Join Date: Oct 2010
Posts: 992Rep Power: 17
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:
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)
Impeller 007 zone (all in N*m)
Impeller 007-shadow zone (all in N*m)
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.
|March 27, 2014, 03:37||
Join Date: Feb 2012
Posts: 77Rep Power: 6
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.
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