NACA duct

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Artist's concept picture of a submerged inlet for a jet aircraft

Three intakes on an engine cowling

Numerous ducts on the Ferrari F40

The NACA duct or NACA scoop is a common form of low-drag intake design, originally developed by the National Advisory Committee for Aeronautics (the precursor to NASA) in 1945. When properly implemented, it allows air to be drawn into an internal duct, often for cooling purposes, with a minimal disturbance to the flow. The design was originally called a "submerged inlet," since it consists of a shallow ramp with curved walls recessed into the exposed surface of a streamlined body, such as an aircraft. It is especially favored in racing car design.

Prior submerged inlet experiments showed poor pressure recovery due to the slow-moving boundary layer entering the intake. This design is believed to work because the combination of the gentle ramp angle and the curvature profile of the walls creates counter-rotating vortices which deflect the boundary layer away from the intake and draws in the faster moving air, while avoiding the form drag and flow separation that can occur with protruding inlet designs. This type of flush inlet generally cannot achieve the larger ram pressures and flow volumes of an external design, and so is rarely used for the jet engine intake application for which it was originally designed, (the North American YF-93 and Short Sherpa being exceptions.) It is, however, common for engine and ventilation intakes.

[edit] See also

NACA cowling

[edit] References

Frick, Charles W.; Davis, Wallace F.; Randall, Lauros M.; and Mossman, Emmet A.: An Experimental Investigation of NACA Submerged Duct Entrances NACA ACR 5I20, 1945.
Staniforth. Race and Rally Car Sourcebook. ISBN 1859608469. (Practical guidance on designing and building NACA ducts for motor-racing applications)