NACA Duct size?

[nissin]

I work at a high-performance off-shore boat company and I have been asked to do research on "NACA ducts". We need an opening of almost 200 sq. in. above our engines intake (200 for each one, and there are two engines in the boat) and I'm having trouble finding information on how to design one of this size. Is a NACA duct of this size even feasible? Any links to websites or online documents that have formulas for dimensions or flow rates would be very helpful.

Thanks for the help in advance,

Tom

 

[40818]

Hi, try the following address (Nasa Tech report archive).

http://www.ntrs.nasa.gov

Also;

http://naca.central.cranfield.ac.uk/report.php?NID=2176

These should help you hopefully.

Also, the following thread stepped briefly into that field.

thread1-186104

 

[tbuelna]

nissin,

200 sq.in. per engine? That sounds like quite a bit of duct, so your engines must be huge. Just how much airflow do you think you need and how did you come about that figure? As an example, a 200 mph, 800 hp F1 car uses less than 50 sq. in. for its intake duct.

NACA ducts are not typically used for engine air intakes. Engine air intakes are usually forward facing "scoops" with an "S" shaped diffuser duct behind it, so that the engine intake sees high pressure, turbulence-free airflow. The increased intake pressure and higher engine power, due to the ram effect, more than offsets the drag produced by the protruding duct.

A drawback with NACA ducts is that, while they can be very efficient aero-wise, they must be on a forward sloping surface to function properly. If you plan to use one on a pitching and heaving boat hull, make sure the surface you put it on never experiences a negative slope with respect to the direction of airflow. Otherwise it will not function well.

 

[thruthefence]

Yeah, but it will look "cool"

 

[evelrod]

Just FYI stuff...We did some engine air intake ducting experiments over a period of several months on several SCCA race cars and sedans in the early 80's at Riverside (RIR) and concluded that any ram effect at speeds below 125/130 mph were negligible, at best.

Rod