Negative power and torque(Axial Turbine analysis)

Far · December 20, 2011, 22:16

it seems that the blade is not following the flow or vice versa. Did you use the reference equal to zero or 101325?
On pressure contour plot, scale shows the pressure from 3e+06 to -1e+07, looks strange?

mak86 · December 22, 2011, 10:29

Well things are getting stranger...In the Passages and Alignment section the Passages per Mesh, Passages to Model and Passages per 360 change automatically to 27,27 and 108!
Every time I change them to 1,1 and 4 but as soon as I close CFX-Pre and reopen it they are changed. I am modelling a quarter of a 4 blade turbine so why CFX is changing these parameters?

Far · December 22, 2011, 10:48

should not happen, could you please past the snapshot of cfx pre witht the stated problem

mak86 · December 22, 2011, 11:23

Here it is.

Far · December 22, 2011, 11:27

make the passage per mesh equal to 1

mak86 · December 22, 2011, 11:30

Quote:

Originally Posted by Far

make the passage per mesh equal to 1

I did this more than 10 times but as soon as I close CFX-Pre it changes again

Far · December 22, 2011, 11:43

it is not possible !!!!

coolguys · March 27, 2012, 12:48

Dear one,

I also get this type of problem in Cfx-post.

While i initialize the stator and rotor in Turbo mode.
By default the number of passage in 360 degree is 12 i got, if i change it to 52 in stator and 58 in rotor, but the report generate for turbine shows the mass flow rate as per 12 passage rather than 58 passage for moving bled outlet

bluessoulman · January 23, 2013, 08:20

Hi,
I'm simulating a Wind Turbine but I don't know the Cp vs lambda curve. I read your post about the net torque procedure. In fluent (ANSYS CFD) I can know the momentum Z (rotation axes) for every blade. This momentum is always positive at different angular velocity:
wind speed = 6 m/s,
angular velocity 10-50-100-150 rad/s
Mz= 0.23 - 4.18 - 6.17 - 6.73 Nm
Is this the net torque?
regards

deii · July 2, 2018, 05:09

can i ask if compressor torque negative, which means that is rotor run too fast too?

ghorrocks · July 2, 2018, 06:55

You have to be careful about your definition of positive and negative. But assuming your comment means that a compressor is producing a negative torque (ie a torque in the direction of rotation), that means the compressor is running too slowly and will speed up. So the steady state speed of this compressor is faster than you have modelled.

January 23, 2013, 08:20	NET TORQUE - Fluent	#29
bluessoulman New Member AG Join Date: Jan 2013 Posts: 1 Rep Power: 0	Hi, I'm simulating a Wind Turbine but I don't know the Cp vs lambda curve. I read your post about the net torque procedure. In fluent (ANSYS CFD) I can know the momentum Z (rotation axes) for every blade. This momentum is always positive at different angular velocity: wind speed = 6 m/s, angular velocity 10-50-100-150 rad/s Mz= 0.23 - 4.18 - 6.17 - 6.73 Nm Is this the net torque? regards israa likes this.

July 2, 2018, 06:55		#31
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,708 Rep Power: 143	You have to be careful about your definition of positive and negative. But assuming your comment means that a compressor is producing a negative torque (ie a torque in the direction of rotation), that means the compressor is running too slowly and will speed up. So the steady state speed of this compressor is faster than you have modelled. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

December 20, 2011, 22:16		#21
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	it seems that the blade is not following the flow or vice versa. Did you use the reference equal to zero or 101325? On pressure contour plot, scale shows the pressure from 3e+06 to -1e+07, looks strange?

December 22, 2011, 10:29		#22
mak86 New Member Join Date: Jul 2010 Posts: 23 Rep Power: 15	Well things are getting stranger...In the Passages and Alignment section the Passages per Mesh, Passages to Model and Passages per 360 change automatically to 27,27 and 108! Every time I change them to 1,1 and 4 but as soon as I close CFX-Pre and reopen it they are changed. I am modelling a quarter of a 4 blade turbine so why CFX is changing these parameters?

December 22, 2011, 10:48		#23
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	should not happen, could you please past the snapshot of cfx pre witht the stated problem

December 22, 2011, 11:27		#25
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	make the passage per mesh equal to 1

December 22, 2011, 11:43		#27
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	it is not possible !!!!

March 27, 2012, 12:48		#28
coolguys New Member smith Join Date: Feb 2012 Posts: 2 Rep Power: 0	Dear one, I also get this type of problem in Cfx-post. While i initialize the stator and rotor in Turbo mode. By default the number of passage in 360 degree is 12 i got, if i change it to 52 in stator and 58 in rotor, but the report generate for turbine shows the mass flow rate as per 12 passage rather than 58 passage for moving bled outlet

July 2, 2018, 05:09		#30
deii New Member limlibin Join Date: Jun 2018 Posts: 11 Rep Power: 7	can i ask if compressor torque negative, which means that is rotor run too fast too?