ANACA duct,[1] also sometimes called a NACA scoop or NACA inlet, is a common form of low-dragair inlet design, originally developed by the U.S.National Advisory Committee for Aeronautics (NACA), the precursor toNASA, in 1945.[2][3]
Prior submerged inlet experiments showed poorpressure recovery due to the slow-movingboundary layer entering the inlet. The NACA design is believed to work because the combination of the gentle ramp angle and the curvature profile of the walls creates counter-rotatingvortices which deflect the boundary layer away from the inlet and draws in the faster moving air, while avoiding theform drag andflow separation that can occur with protruding scoop designs.
When properly implemented, a NACA duct allows air to flow 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 anaircraft.
This type of flush inlet generally cannot achieve the greater ram pressures and flow volumes of an external design, and so is rarely used for thejet engine intake application for which it was originally designed, such as theNorth American YF-93 andShort SB.4 Sherpa. It is commonly used for piston engine and ventilation intakes.
It is especially favored inracing car design.[4][5]Sports cars featuring prominent NACA ducts include theFerrari F40 andF80, theLamborghini Countach, the 1996–2002Dodge Viper, the 1971–1973Ford Mustang, the 1973Pontiac GTO, the 1979Porsche 924 Turbo, theMaserati Biturbo, theNissan S130, and thePorsche 911 GT2. It is also prevalent in some motorcycle designs, such as the 1994–1997Honda VFR750F or the 1994-1998Ducati 916.
NACA-ACR-5I20
Practical experience of fabricating simple NACA ducts for ventilation of aHPV