Removing Boundary Layer by Suction
This is a 1927 technical report from the NASA Technical Reports Server, a document in the aerodynamics series, which hands its data and results to aeronautical engineers and researchers. The three pictures are line diagrams of airflow: a slotted suction interpretation with labelled stations, a dimensioned venturi-like duct with a central slot, and a sequence of diffuser profiles showing the boundary layer thinning as suction arrows pull air away from the wall. A designer could borrow the clean arrow-and-dimension language for flow or motion diagrams.
