Average torque in transient vawt simulation

FeveR · March 29, 2018, 05:53

Dear users,
I'm simulating flow around 3 blades, vertical axis wind turbine (2D) for my master thesis using sliding mesh method. I have done 200 timesteps with 0,005s time step size which give 5s of real time simulation. My results looks really fine, but I need to know average torque over rotation axis (Z) on all blades of the turbine in that 5 seconds and I don't know how to calculate it. Value of torque is different in every timestep. Is it possible to export torque from all timesteps to excel and then calculate average of it ?
I tried to plot Momentum during the simulation (Solution -> Report Definitions -> Force Report -> Moment), and than select blades and Z axis, but values on that plot is always less than 1, so it looks like Cm, not really torque. When i calculate torque using CFD-Post calculator the values at any timestep looks fine. Thanks for help. Sorry for my english..

FeveR · March 30, 2018, 07:33

Please help. I'm stuck here because I can't compare my cases

FeveR · March 31, 2018, 11:04

Ok, problem solved.. if anybody else facing it, there is a solution :
You need to print a Cm plot (like I wrote in 1st post) and write this values to a file. Then export this file to excel and count torque using this formula for every timestep :

$Cm = \frac{M}{\frac{1}{2}\rho v^{2}AL}$

where M - torque, V - stream velocity, A - Area, L - lenght (rho, A, L in 'reference Value tab')
Finally, just do the average of all torque values.

AerospaceVN · December 20, 2019, 11:03

dear feveR
I am simulating a VAWT like you. Can I ask some question about moment and moment coefficient
When you set up the solution, did you set the reference value? what reference values you set?
I set Area = wing area, lenght = radius, velocity = wind speed
the moment coefficient is very low according to my calculations.
hope you share your experience
thank you

March 29, 2018, 05:53	Average torque in transient vawt simulation	#1
FeveR New Member Patryk Join Date: Apr 2016 Location: Poland Posts: 11 Rep Power: 10	Dear users, I'm simulating flow around 3 blades, vertical axis wind turbine (2D) for my master thesis using sliding mesh method. I have done 200 timesteps with 0,005s time step size which give 5s of real time simulation. My results looks really fine, but I need to know average torque over rotation axis (Z) on all blades of the turbine in that 5 seconds and I don't know how to calculate it. Value of torque is different in every timestep. Is it possible to export torque from all timesteps to excel and then calculate average of it ? I tried to plot Momentum during the simulation (Solution -> Report Definitions -> Force Report -> Moment), and than select blades and Z axis, but values on that plot is always less than 1, so it looks like Cm, not really torque. When i calculate torque using CFD-Post calculator the values at any timestep looks fine. Thanks for help. Sorry for my english..

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March 30, 2018, 07:33		#2
FeveR New Member Patryk Join Date: Apr 2016 Location: Poland Posts: 11 Rep Power: 10	Please help. I'm stuck here because I can't compare my cases

March 31, 2018, 11:04		#3
FeveR New Member Patryk Join Date: Apr 2016 Location: Poland Posts: 11 Rep Power: 10	Ok, problem solved.. if anybody else facing it, there is a solution : You need to print a Cm plot (like I wrote in 1st post) and write this values to a file. Then export this file to excel and count torque using this formula for every timestep : $Cm = \frac{M}{\frac{1}{2}\rho v^{2}AL}$ where M - torque, V - stream velocity, A - Area, L - lenght (rho, A, L in 'reference Value tab') Finally, just do the average of all torque values.

December 20, 2019, 11:03		#4
AerospaceVN New Member Nguyễn Tài Đức Join Date: Dec 2019 Posts: 1 Rep Power: 0	dear feveR I am simulating a VAWT like you. Can I ask some question about moment and moment coefficient When you set up the solution, did you set the reference value? what reference values you set? I set Area = wing area, lenght = radius, velocity = wind speed the moment coefficient is very low according to my calculations. hope you share your experience thank you