Shouldn't the fan get rid of the flies? When I used a fan to dry lemon peels and pulp, it prevented all fruit flies from proliferating. However, for meat flies, maybe you need a more powerful fan? Since the type of fly that likes meat (house fly) is much bigger and can probably resist milder air flows. Another option might be to use a sort of net or mesh over the top that prevents larger flies from accessing the meat, but allows the air to flow.
Keep in mind that once a thin crust of dried meat has formed on the surface, I don't think flies can do anything about it at that point, since they only feed or lay eggs in fresh, wet meat, and they prefer liquids only (they use their saliva to liquify meats before ingesting it)