Definition of NACA Duct Help

[RDelaCourt513]

Hi all, just looking for some help and advice on a NACA duct that i modelling up on CAD.

I am in the process of building a closed-wheel time-attack race car, I had a NACA duct intake that feeds air directly into the radiators and oil coolers. Unfortunately the carbon fibre moulded NACA duct I had before has been damaged on track and has destroyed the part.

I know I could just go out and buy the same spec duct but I want to practice creating carbon fibre components and this is the perfect opportunity before I progress onto larger (and more expensive)components.

I have populated the respected intersections derived primarily from the total width, depth and length of the duct profile.

I have attached some images of the 3D scanned geometry of the current damaged duct. as well as the excel spreadsheet populating the respected dimensions.

I realise that i'm probably going to do a terrible job trying to explain this, but basically im having difficulty defining the depth profile of the duct. as you can see in the attached excel spreadsheet, I have populated a profile. The starting point of the depth sweep is tangent to the flat A-surface (top) however on my 3d scanned model (and others i have seen online) the depth profile appears to run off in a different fashion as to the depth profile I have generated towards the end point. I need to ensure that the sweep is as per the data provided as i want to ensure that I have sufficient volume in the void.


How should I taper off the end of the duct that assumes the 75mm od profile.

Again apologies for the crude explanation, I really would appreciate any help

Thank you

Ryan

 

[RDelaCourt513]

Naca profile Excel Spreadsheet

 

[RDelaCourt513]

Naca 3d scan #1

 

[RDelaCourt513]

Naca 3d scan #2

 

[RDelaCourt513]

Or should I be aiming for something with a sweep more like this?

 

[GregLocock]

I'm not going to look at your stuff, but I suspect that any reasonably smooth profile that obeys the normal rules will work

Here's the original work on them so you can understand what you are playing with.

https://ntrs.nasa.gov/search.jsp?R=20090012113

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[RDelaCourt513]

Thanks for the input Greg,

Im happy with the x and y coordinates. My concern is the depth z profile) the part that i have and that has been 3 scanned appears to be considerably deeper than most naca duct profiles.

 

[Tmoose]

"My concern is the depth z profile) the part that i have and that has been 3 scanned appears to be considerably deeper than most naca duct profiles."
What is the angle of the "ramp" ( Z profile ?) ?

The original 1945 NACA paper linked by Greg L is pretty specific in that regard.

 

[Sparweb]

About that report (not so much about the poster's question, which has already been answered) I notice they've replaced the PDF. It's a better scan of the same print with all the mark-ups as it always was. Also in the PDF is somebody's hand-written note which I always found funny but couldn't read. In the new scan, I can now read it. Barely. I think it says this:

p.16
Should note that airplane model had no survey rake in inlet, hence press. recovery in diffuser can be used quantitatively.
Shows "a" need for basic tests without inlet rake in order to compare recovery ratios for simple and applied cases.​

For those who care to download copies of these PDF's, you can annotate the PDF with a Comment box so that you don't have to struggle to read the handwriting.

Edit: I believe the comment means that the rake in the wind tunnel would pose an obstruction in the model that wouldn't exist in a real aircraft. A rake has tubes that disturb the flow, while the pressure taps used on the wind tunnel model would not cause such an obstruction. The note may be been added after a discussion among engineers about application of the test results to actual aircraft installation.

http://www.sparweb.ca