Re: NACA ducts - how do they work?

26/10/2003 21:34:47, "Nigel Marston" <[email protected]> 
wrote:

>Anyone know how a NACA duct works and what it is supposed to 
do? 

Where they're particularly useful is in a flat sheet with a laminar 
(smooth) flow over the surface. In that regime, you run them with 
the narrow end pointing into the airflow - the sharp edges allow 
little vortices to start, dropping down into the of the duct. As the 
duct widens, the vortex grows (and vice versa - that's why the 
ducts are the shape they are). By the end of the duct, you've got 2 
countra-rotating vortices, without patrticularly disturbing the 
airflow over the rest of the sheet, and those vortices can be routed 
into a duct nice & easily. 

It all goes to pot when you're not dealing with nice laminar flows, 
though, at which point you could cut a teletubby-shaped slot in 
your bonnet and get equally good / bad results - but NACA ducts 
look the part...  Testing with wool tufts should show whether teh 
duct's doing the right thing. 

Same goes for using them as outlets - it's just a hole :)

Steve
-------------------------------------------------
To manage your subscription options visit :-
http://mailman.se7ens.net/mailman/listinfo/sevens