How to estimate blade interference in a propeller or fan?
For a simple 2D approximation, you can do it in a similar way to how you would analyze the effect of wake on a tailplane or any other body, i.e. by solving the flow field around both at the same time.
Since the movement of the  blades is cyclical and the flow is subsonic, each blade affects both the ones ahead and the ones behind it. Therefore, you would would need to solve for an infinite number of blades simultaneously so that the one in the middle would have a realistic airflow, but since the effect of the N-th blade will tend to nill, a good approximation can be had with just a few blades on either side of the studied one.

The process would look like this:


Choose the spanwise station of the blade you are interested in and the operating point (rpm and forward velocity) you want to study. These will give you the effective angle of attack for the blade station.
Knowing the angular blade spacing around the hub, the spanwise station you selected, the rpm and the forward velocity, find out where the first airfoil will be relative to the second one in a 2D representation.
Solve the flow field for an effectively infinite number of airfoils spaced this way. In practice solving for a relatively small number of blade instances will provide a good approximation of the real flow on the central blades in the series, as the ones on the edges are only used to provide boundary conditions resembling the real world case: