In aeronautical research, they are minute grooves on an aircraft's surface that reduce skin friction by smoothing the turbulent airllow next to the skin.
(they; are; minute grooves on an aircraft's surface that reduce skin friction by smoothing the turbulent airllow next to the skin; L:In aeronautical research) (minute grooves on an aircraft's surface; reduce; skin friction; by smoothing the turbulent airllow next to the skin)
they minute grooves on an aircraft's surface
are reduce
minute grooves on an aircraft's surface that reduce skin friction by smoothing the turbulent airllow next to the skin L:In aeronautical research
skin friction by smoothing the turbulent airllow next to the skin