Stale air in house with windows
Fans move air. If you need to move air in this apartment then fans will be your friend. Putting fans in windows will be the most sure way to get air to flow in or out without it just circulating around inside. 

There are downsides of using portable fans:


Fans make noise.
Fans in windows project some of the noise outside which may annoy neighbors.
You will have to deal with cords strung over to an outlet to power the fan(s).
Fans consume electrical power so will have some impact on your utility bill. 
Some types of fans may represent a safety hazard unless they are equipped with proper grills and screens to keep body parts away from spinning fan blades.
Fans in windows may obscure views or light coming in.


Some advantages:


Portable fans are for the most part are relatively cheap.
You can position the fans experimentally to achieve the result you need.
Moving air will feel cooler than stagnant air. 
There may be seasons where the fans are not needed and it is easy to store a portable fan away till needed again.