I'm having trouble with measuring the torque created by a fluid drag force over a surface, so I create a simple model to try to understand what is going on. In the below picture, here are the results I get for my 3 goals (using the global coordinate system) :
Top Face -0.042Nm
Bottom Face 0.013Nm
Both Faces -.0.29NM
I expected both values to be negative, but the bottom face is positive. Why is this? Also, this causes the total torque to be less (because one face is subtracted instead of added).
For the more complicated version, I am trying to measure power = rpm * torque off a shaft, and my torque value is based on two faces which are giving me opposite (+ and -) values, which cancel out to give me much smaller torque than expected. I am wondering if there is a "face normal" in the reported result somehow?
I'm not too sure if this might help but, I see that you have Inlet and an Environmental Pressure defined. You may need to define an outlet of some sort. You can probably make a Flow Trajectory plot to see what the air is doing and why it may be giving you that negative value.