I am simulating the rotating motion of a fan (a physical and real geometric model) using COMSOL. I'm using the moving mesh component and applying the rotating domain condition. Also, I'm calculating the net force (using "spf.T_stressx" variable) applied on the surface of the fan blades and use that force to calculate the velocity of the flow passing through the fan. Then I want to apply this velocity to my inlet boundary so that I can simulate the transient behavior of the fluid flow passing through the fan until it reaches a steady state. I created a cylindrical domain inside my main block, I used form assembly, I created identity pairs and in fact, I think I set everything up in the right order! Even the rotating domain starts to rotate correctly. However, when it comes to calculating the total force exerted on the surface of blades, the extracted values are not correct (technically speaking, a drag force and a thrust force are defined for a fan and therefore, the total force must have a periodic change around the zero Newton), instead the value of the total force nears a constant positive value. Also, this wasn't the end! Even though the extracted force has a positive value, I get zero for the calculated velocity at each iteration.

I'd appreciate it if anybody could help me with this.