I especially liked the comment in the report where it says that the
higher the pressure drop across the core, the higher the diffuser
efficiency.   I interpret this as 'thicker core is better than
thinner!'   Of course there is a point of diminishing returns where
flow is simply too low as Ed has pointed out but in an application
where diffuser efficiency is such an important factor, this pushes
that point in the direction of 'thick'.

Tracy (back from the dragon and sorry to bring up the thick vs thin
thing again :>)


On Nov 7, 2007 3:54 PM, Ed Anderson <eanderson@carolina.rr.com> wrote:
>
> Here are two of the charts from the Naca report.  The one on the left shows
> diffuser resistance without a resistance (radiator) behind it and the one on
> the right shows the diffuser with a radiator core behind it.
>
>  Note the considerably increase in diffuser efficiency with a core. It
> appears that the while the  pressure that builds up in front of a core
> eventually leads to boundary layer separation due to the adverse pressure
> gradient,.
>
> It  in fact actually helps the resistance diffuser pressure recovery
> efficiency over the open diffuser by preventing the separation until much
> later.  The one on the right also shows that a shorter length L/D also helps
> efficiency as that apparently causes the expansion before the boundary layer
> has grown too thick with the tendency to separate.
>
> Of course you could always get the report and do your own interpretation
> {:>)
>
>
> Ed Anderson
> Rv-6A N494BW Rotary Powered
> Matthews, NC
> eanderson@carolina.rr.com
> http://www.andersonee.com
> http://members.cox.net/rogersda/rotary/configs.htm#N494BW
> http://www.dmack.net/mazda/index.html
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