Mesh Motion reference frame directions
 

Hello everyone,

I'm simulating pitching motion of a 3D wing. The model has 2 O-blocks, communicating via mesh interface. The whole inner block, containing the wing, rotates according to UDF that defines the angular velocity which is the input of the block Mesh Motion (pitching is about Y axis).

The simulation is converging, but I get some strange values of the coefficients. Moment coefficient is as expected, also Lift coefficient shows reasonable values. As for drag coefficient I get negative values that are the opposite of the expected values. I obtain forces coefficients by projecting X and Z coefficients with respect to the angle of attack at each time step. I get X and Z forces by setting directions as (1 0 0) and (0 0 1) respectively, but I'm not sure whether these directions are inertial to the body, so "rotating" together with the block, or rather fixed with the absolute reference frame.

Can anybody help me?

Thank you in advance.