Dear Yinping Yang,
See my previous post for reasons why FAST may generate nonzero yaw moments: Shear force(x) at the tower base (Bladed may not treat all these the same).
It is difficult to answer your questions regarding FAST and Bladed comparisons because we do not offer support for Bladed at NREL. May I ask why you’re comparing FAST and Bladed? Have you also contacted GH for support?
In his post, Marshall offered very useful advice for code-to-code comparisons. I suggest you follow his guidance before posting more questions on this forum.
Best regards,