basic fluid dynamics question: Flow though time
 

Hello,

let we think we simulate air flow on an airfoil. The length of airfoil is 1 m.

And the CFD-Domain has 30 m in the direction of the flow.

Velocity is 30 m/s.

then in this case, my flow though time is...

1. 1 s? or
2. 1/30 s?

I think 1/30 s is right...

I'd say that is completely up to you, if you want it to be a complete domain flow-through or an airfoil flow-through. For my work on channel flows we define a flow-through as the time it takes from the domain inlet to the domain outlet, but your problem is different.
Also, if such accuracy would be desired, remember that the flow-through time for the suction surface of the airfoil will be shorter than for the pressure surface, but I doubt that level of accuracy is what you're looking for!

Flow thru time is 1 s. 1/30 seconds isn't the right answer, it's wishful thinking.

It's the same as channel flow, the initial condition needs to get washed out completely