Well, I forgot to say that we have done that before but my friend said the result is not satisfactory or, in another word, completely wrong. Since we are doing an impulse turbine propelled by four cd nozzles, we assume that, if we use sliding mesh method (I read the tutorial on ansys website), we have to assign a fixed angular velocity for our turbine. However, the project requires us to determine the angular velocity of the turbine when the four nozzles are working, meaning that we have to use Fluent to calculate how much the angular velocity is. So that is why we considered dynamic mesh and we encountered this problem. I apologize for making you confused.