Good article how any slot works.
Popular misconception is that air increase velocity in slot,this is not case.Same apply for slotted flap.
(A.M.O. Smith High lift aerodynamics),
page 518, chapter 5.3 Multi element Airfoils-General
quote from text:
"There are two things wrong with these statements.First of all,the slat does not give the air in the slot ...