NACA Vent

Plastics 4 Performance NACA vent 

High quality vacuum formed Naca vent for optimal air intake, Can be fitted in windows or bodywork as an air inlet. 

Specifications for Large Naca Vent:

- 235 mm long
- 175 mm wide
- 40 mm high (from window surface)

Specifications for Small Naca Vent:

- 170 mm long
- 150 mm wide
- 30 mm high (from window surface)

Specifications for Mini Naca Vent:

- 135 mm long
- 120 mm wide
- 20 mm high (from window surface)

The purpose of a NACA vent is to increase the flow rate of air through it while not disturbing the vehicles boundary layer of air. When the cross-sectional flow area of the duct is increased, you decrease the static pressure and make the duct into a kind of 'vacuum cleaner' that sucks air in, but without the drag effects of a plain protruding scoop. The reason why the duct is narrow, then suddenly widens in a graceful arc is to increase the cross-sectional area slowly so that airflow does separate and cause turbulence (and drag).

NACA vents are useful when air needs to be drawn into an area which isn't exposed to the direct air flow like a protruding air scoop has access to. Quite often you will see NACA vents along the sides of a car,engine bonnet or in polycarbonate side windows. The NACA vent takes advantage of the boundary layer, a layer of slow moving air that "clings" to the bodywork of the car, especially where the bodywork flattens, or does not accelerate or decelerate the air flow. Areas like the roof and side body & window panels are good examples. The longer the roof or body panels, the thicker the boundary layer becomes (a source of drag that grows as the layer thickens too).

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 like our NACA ducts with additional air scoops attached. However it is common for engine and cockpit ventilation intakes.

More technical info can be found on wikipedia here