Positive torque definition

jaxk · March 10, 2023, 15:24

Hey, I have a question about the definition of positive torque.

When I make a model of a symmetric airfoil with its nose tilted up as shown in air.jpg, I am expecting to measure a clockwise torque on the airfoil due to what's called the munk moment F1816.15 Munk moment.[rs_590_600_f].jpg.

However, the torque I measure is negative. Does this mean my model is inaccurate, or is it because a positive torque is defined as counter clockwise in CFX?

Thanks for any reply's!

Opaque · March 10, 2023, 16:16

There is only one definition of positive torque anywhere in physics. The rule of the reference frame being used.

That is, Right Handed Frame is positive along the main axes, the same for a left-handed rule. The torque must be consistent with the definition of the cross-product on the frame being used.

jaxk · March 10, 2023, 17:57

Thanks. So you share my expectation of a measured torque in clockwise direction?
And since the z-axis is pointing out of the screen, a positive torque is defined as counter clockwise.
So the negative torque values which I get can be realistic?

March 10, 2023, 15:24	Positive torque definition	#1
jaxk New Member Join Date: Dec 2022 Posts: 29 Rep Power: 3	Hey, I have a question about the definition of positive torque. When I make a model of a symmetric airfoil with its nose tilted up as shown in air.jpg, I am expecting to measure a clockwise torque on the airfoil due to what's called the munk moment F1816.15 Munk moment.[rs_590_600_f].jpg. However, the torque I measure is negative. Does this mean my model is inaccurate, or is it because a positive torque is defined as counter clockwise in CFX? Thanks for any reply's!

March 10, 2023, 16:16		#2
Opaque Senior Member Join Date: Jun 2009 Posts: 1,804 Rep Power: 32	There is only one definition of positive torque anywhere in physics. The rule of the reference frame being used. That is, Right Handed Frame is positive along the main axes, the same for a left-handed rule. The torque must be consistent with the definition of the cross-product on the frame being used. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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March 10, 2023, 17:57		#3
jaxk New Member Join Date: Dec 2022 Posts: 29 Rep Power: 3	Thanks. So you share my expectation of a measured torque in clockwise direction? And since the z-axis is pointing out of the screen, a positive torque is defined as counter clockwise. So the negative torque values which I get can be realistic?