RM
Ansys Employee

Hi,

Is it a 1-way or 2-way analysis?

Time Step Size and Number of Time Steps for fluent are controlled by system coupling, so the values specified in fluent are ignored. 

If it is 2-way, refer 42.5. System Coupling Related Settings in Fluent (ansys.com) and System Coupling Related Settings in Mechanical (ansys.com) for settings required as inputs in both participants.