The surface area that interacts with the working fluid or gas.
In aeronautics, the wetted area is the area which is in contact with the external airflow. This has a direct relationship on the overall aerodynamic drag of the aircraft. See also Wetted aspect ratio.
- Intake Aerodynamics (October 1999) by Seddon and Goldsmith, Blackwell Science and the AIAA Educational Series; 2nd edition