Abrasive flow finishing

[Gordon Couger]

It's been a while but I set in on a PhD level course on turbulant
flow in open channels. By introducing small projections into the
surface you force the flow to become turbulant at a lower speed
and therefor forming a smaller bubble of turbulance. The small 
turbulant bubbles act very much like ball bearings between the
in coming air and the skin. 

Every thing I studied was for water. So it my be a little different
for air.

I would expect that the most benifit would be at the flow rates that
just started into turbulance.

Gordon
Gordon Couger 
624 Cheyenne
Stillwater, OK 74075
405/624-2855   gcouger at ionet.net    
Time Zone GMT-6


>I read an article recently in Design News concerning skin
>friction drag reductions.  They quote another article in
>Nature where skin friction drag was reduced by 13% on
>aerodynamic surfaces by adding random small bumps to 
>the surface (vs a smooth surface).  Design News was considering
>the fuel reduction costs possible for typical commercial aircraft.
>A 13% skin friction drag equates to about a 6.5% overall
>drag reduction.  Big numbers when a 1% drag reduction saves
>a typical commercial aircraft about $100,000 annually in fuel
>costs.
>
>The idea is similar to the dimples used on golf balls which
>enable the golf balls to fly farther than undimpled
>balls.  I wonder what this might mean for engine intakes and
>exhausts?  Maybe an extrude honing type smooth surface is
>not the ideal surface even when injectors are near the valves.
>
>The dimples have to be in a random pattern, else you increase
>drag.  The theory is that random dimples (or chevrons) reduce
>bursting near an aerodynamic surface.  Busting is caused by
>low speed air streaks near the wall and is believed to be
>responsible for creating intense turbulence.
>
>Comments?
>
>Dan L
>