initiate pressure step at inlet to do dynamic response
 

I wanna analyze dynamic response of pressure measurement and get transfer function from Fluent. What i do is to initiate a total pressure step at pressure inlet when simulation becomes periodic and to see how long it takes to reach another periodic level. Then export data and use Matlab to post-process. Is this the correct method to initiate step response and then do fft or bode of the time domain?

Yes. More or less. Usually you do it with a stationary system, but if the periodic state is the equilibrium state then it makes sense.

Thank you. Because I have vortex shedding behind, it's a periodic convergence..