RE: [Harp-L] Waxing Rivets for Overbends [plus!]

["MLeFree" <mlefree@xxxxxxxxxxxxxxxxxxxxxx>]

Bobbie Giordano wrote:
> I finally relocated that link to the image I sent yesterday, BTW... It's
> provided by the Institute of Computational Fluid Dynamics in Tokyo, Japan.
>
> Here's the URL:  http://www2.icfd.co.jp/examples/karman/kr2.htm
>
> For another link, go here to see the mpeg movie which I couldn't manage to
> add to my small weblink... Storm hit my server, I think.  [I really should
> get packing for SPAH anyway!]  <major clip>

Then she shared this additonal info and movie:
> Additionally, though, here is the website's explanation of their
> movie image:
> >The periodic nature of the Von Karman vortex street is best
> >illustrated in the third example, which shows the vortex street
> >created by a flat plate.  This movie only includes a single cycle
> >of the phenomenon, therefore for best viewing, configure your
> >MPEG viewer to play the movie in a continuous loop.
>
> [For example in WinAmp, click Toggle Repeat to loop the short movie.]
>
> http://www.itsc.com/movies/vort.mpg
>
> =====================================================
>
> In this example, it's shown affecting a plate-shaped object [more
harmonica
> reed shaped] in the air stream.  More akin to a harmonica reed shape, I
> figure.
>
> Interesting to me is that the induced vibration of the "plate" seems to be
> crosswise... from one side to the other, not in typical reed fashion as we
> think of it as being lengthwise, waving up and down.  <more clippage>

Those are great web pages, Bobbie!  The moving images are even more
interesting than they are beautiful.  I love scientific visualization.  What
complex air currents there are around a free reed (well, a flat plate at
least :)!  It's easy to see how this Von Karman vortex effect (a new term
and concept for me--thanks) induces torsional forces that impart the
"sideways" vibration that you attribute to causing the whining overblowers
report when using asian harmonicas.

The question of the day is, "Why don't ~all~ harmonicas have this problem?".
It would seem intuitively obvious that the clearance between the reed and
the reedplate would have direct impact on the amount  of air that could
escape around the side of the reed to contribute to the formation of Von
Karman vortices (VKV).  Also, the thickness of the reedplate, given a
certain amount of reed deflection, would similarly impact the amount of air
made available to cause the VKV effect, as would the length of the reed.
These are a but few of the many factors that it would seem could influence
the VKV effect in different harmonicas of different keys from different
manufacturers.  I'm sure you could list another dozen or more.

There are some obvious questions that arise from an inquisitive
non-overblower thinking about all this.  Can you speculate why instruments
from some manufacturers have the squealing problem while others don't?  Why
don't reeds played with non-overblow technique whine--or do they?  Do all
reeds exhibit the same problem regardless of tone (and hence length)?  What
is it about overblowing that changes the nature of the vibration of the
"active" reed?  I understand that, with overblows, one reed is choked while
the other is induced to vibrate.  Maybe choking the opposing reed changes
the air flow through the reed chamber significantly enough to make the VKV
effect more prominent than under "normal" conditions where both reeds are
allowed to vibrate?  Perhaps the two vibrating reed system has some
"cancellation" of the VKV effect from the opposing reeds?  Or maybe laminar
flow turns into turbulent flow (or vice-versa) when the opposing reed chokes
under overblow conditions?  Those moving images of the VKV effect looked
like they were depicting a pretty laminar-looking flow to me.

One quick question for Jonathan, too (I always have more questions than
answers, it seems...  ;).  I know there are commercially available FEA
software environments that are fairly easy to use (heh, heh...), though they
aren't cheap.  By "easy to use" I mean you can input a 2- or 3-D
mathematical model and some relevant boundary conditions and the program
will make a wire frame and do the FEA calculations for you.  Is there such a
commercially available progam environment for computational fluid dynamics?
Might you have acces to it?

What secrets this amazing little instrument holds!

BTW, I'm sure Vern would have chimed in here, but I think he's at Rob't
Bonfiglio's chromatic class.  Maybe we'll hear from him when he returns
home.  I hope so, 'cuz he always has valued input on engineering topics like
this.

Thanks,

Michelle