A fan, No, but...
For airplanes which have low speed performance requirements there is a concept called ventialted slots or blown flaps. In this case a blower, not a fan, blows air across the leading edge of the wing or flap. THis is done to insure the air flow stays attached -- preventing stalling -- and allowing the aircraft to fly much more slowly and land in shorter distances.
This concept has been experimented with on sailboats. Rigid sail catamrans in particular.
The issue is power requirements. Such a blower on a sailboat would have energy requirements that would be at least as demanding as a motorsailors.
However, boat's such as Cousteau's Alcyone did consider spinning their rigs using power until natural forces took over.