We are often told that wing sweep causes the airflow to be deflected outwards. I can understand this for the underside, but for the upper surface it seems inconsistent with other effects.
For example on a sharply-swept delta, sideways flow out from below, up around the leading edge and back in again over the upper surface becomes dominant. It feeds the vortices employed by Concorde to enhance lift at low speeds. The sharper the sweep, the more the air over the upper wing flows inwards. The same effect is seen in miniature with tip vortices on a straight wing. This makes sense to me because the pressure above the wing is low, so that would naturally attract air in towards that zone.
So, does sweeping a straight wing really reverse such effects, or do say wing fences on the upper surface actually stop the air flowing inwards?