Forces on a rotating aerofoil

usr0830 · December 14, 2021, 10:17

Hello all,

I know the topic of lift and drag for rotating aerofoils has been discussed many times on the forum. But I have a specific question and would really appreciate the help.

I am trying to extract the lift and drag forces on a rotating airfoil of a vertical axis wind turbine. But to my best understanding, in Fluent when you monitor the lift and drag forces on a rotating object it basically monitors the forces in the X and Y direction. Where X corresponds to drag (parallel to inflow velocity) and Y corresponds to lift(perpendicular to inflow velocity).

Could any of you please help me with going from these force values to the actual aerofoil lift and drag values(perpendicular and parallel to the relative flow velocity at the aerofoil)?
It is essentially like going from a global reference frame to a local reference frame, I think.

Thanks in advance!

AlexanderZ · December 15, 2021, 00:26

when you are creating monitor for lift/drag you should specify vector.
this is what you are looking for

same approach when you are obtaining lift/drag through reports panel

usr0830 · December 15, 2021, 08:35

Hi Alexander,
Thank you for your response. If I want to specify the vector as you suggest, I would need to do that at every timestep during the rotation, right? I would also need to know the direction of the relative velocity at the quarter chord to determine this vector at every timestep if I understand correctly.

So far, I see the same values when I visualise both velocity magnitude and absolute velocity magnitude. Could you please help me with some suggestions on how to find the correct relative velocity components from Fluent?
Thanks again!

December 14, 2021, 10:17	Forces on a rotating aerofoil	#1
usr0830 New Member Join Date: Jul 2019 Posts: 14 Rep Power: 7	Hello all, I know the topic of lift and drag for rotating aerofoils has been discussed many times on the forum. But I have a specific question and would really appreciate the help. I am trying to extract the lift and drag forces on a rotating airfoil of a vertical axis wind turbine. But to my best understanding, in Fluent when you monitor the lift and drag forces on a rotating object it basically monitors the forces in the X and Y direction. Where X corresponds to drag (parallel to inflow velocity) and Y corresponds to lift(perpendicular to inflow velocity). Could any of you please help me with going from these force values to the actual aerofoil lift and drag values(perpendicular and parallel to the relative flow velocity at the aerofoil)? It is essentially like going from a global reference frame to a local reference frame, I think. Thanks in advance!

December 15, 2021, 00:26		#2
AlexanderZ Senior Member Alexander Join Date: Apr 2013 Posts: 2,363 Rep Power: 34	when you are creating monitor for lift/drag you should specify vector. this is what you are looking for same approach when you are obtaining lift/drag through reports panel __________________ best regards ****************************** press LIKE if this message was helpful

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December 15, 2021, 08:35		#3
usr0830 New Member Join Date: Jul 2019 Posts: 14 Rep Power: 7	Hi Alexander, Thank you for your response. If I want to specify the vector as you suggest, I would need to do that at every timestep during the rotation, right? I would also need to know the direction of the relative velocity at the quarter chord to determine this vector at every timestep if I understand correctly. So far, I see the same values when I visualise both velocity magnitude and absolute velocity magnitude. Could you please help me with some suggestions on how to find the correct relative velocity components from Fluent? Thanks again!