Here it is:
On 2002-10-24 13:16, dkehoe wrote:
Isn’t the air stream perturbed anyway? A rough calculation indicated that the air in the windway is turbulant (Reynolds no. > 2000), so the air stream in the windway is not laminar. As soon as it leaves the windway, the jet that forms is turbulent too, so the idea that the air stream somehow retains the shape of the windway is probably not the case. If I can figure out how, I’ll post a animated gif of the air stream exiting the windway, forming turbulant eddies and hitting the edge.
Most of the newer 3D rendering packages (3D Studio Max, Lightwave, Maya, Strata, Bryce) have particle systems that should allow for this. Look at the lovely turbulent flames that issue from the elevator in “The Matrix”. One of my brothers is a 3D animator for architectural firms. I’ll ask him and get back.
Cheers,
Bill Whedon
On 2002-10-24 13:55, dkehoe wrote:
Here it is:
Nifty! What’d you use to do it? Can you slow it down?
Bill Whedon
dkehoe:
That is way cool!!!
My bro is gonna try it in two packages - Lightwave and Maya, and see which works best. I asked him to do it inside a whistle cutaway…
More to follow,
Bill Whedon
On 2002-10-24 12:37, wizzy wrote:
On 2002-10-24 10:05, markv wrote:
Which is why it is important to when tuning your pipes sharper to add a material that doesn’t cause the air to be “perturbed”.
Mark V.So Mark.
What shape is best for the bottom of the tube, Flat or domed or coned?
Wizzy
Slightly cup shaped base I believe. I wonder what a cone or small spike would do. If I remember correctly some flutes andor recorders do this on the block. There is a name for the spike that eludes me at the moment.
Mark V
You folks give me way too much credit. I actually got that gif from a website in Japan. I did a Google search on “edge tone” and came up with this. As for slowing it down, I haven’t a clue. The thing I like about it is that it really shows what is happening in a fipple. We talk about the air “flipping” in and out of the whistle, but without explaining why. The series of votexes that form are called a “Von Karman street”, and form whenever a turbulent jet is formed in a stagnant fluid (air). The size and frequency of these is determined by something called the Strouhal number, and it also determines, for example, the frequency of flag waving. As you can see on the underside of the edge, this results in pulses into the tube (the whistle). The edgetone, by itself, is much higher in frequency than the note that the pipe makes (just take the pipe off of the fipple and blow, you’ll see), but the pipe can only oscillate at certain frequencies, and so it does. There is a guy named Wade Blocker who has a whole website on edgetone oscillators.
dkehoe wrote (in part):
There is a guy named Wade Blocker who has a whole website on edgetone oscillators.
… got an URL? This is some very cool stuff, indeed!
Cheers, thanks!
Bill Whedon
On 2002-10-24 13:55, dkehoe wrote:
Here it is:
This is great! but what about the diffrant pressure that we blow at, ie; to jump the octave?
Wizzy
Also What about vortex sheding!
[ This Message was edited by: wizzy on 2002-10-25 03:13 ]
I think the model depicts an airstream in free air, not in a resonant tube. That would add some serious physics effects (air column vibration (compression, rarefaction on longitudinal and radial axes), among others) to the mix, which is the situation my bro is trying to overcome with Maya or whatever. I don’t know that there’s visualization S/W available, at the moment, to depict that level of complex interaction, short of by comping. I’m still of a mind that an actual video would have to be made, perhaps of a glass whistle, in a smoke stream, to actually see the totality. (“Grok the fullness” for you elderly Heinlein readers 
)
Cheers,
Bill Whedon
When you blow harder, the windsheet (that’s what organ makers call it) gets thicker. If you have a metal whistle, put in in the refridgerator and after it gets cold, you can see a fog trail of the windsheet.
Making the air laminar coming out of the duct is important as it must focus on the blade. I’ve seen it come out shooting to one side or another in early prototypes, sometimes if there’s a dent in the block, the windway will split in two.
Also the tragectory of this windway, the profile of the block can send the air too much above the blade or below and make a ‘chiffy’ or ‘airy’ whistle. Think of the windsheet as a three dimensional conduit of air that comes out of the duct and once it’s free it begins to scatter.
We’re dealing with subsonic flow - it’s very picky.
It’s also amazing to note the end correction on a whistle. The tone column exceeds the length of the whistle as it meets resistance with the atmosphere. Tape all the holes shut and play the bell note. Feel around the bottom of the whistle for the jet of vibrating air column and how far out it moves (more obvious on low whistles because of the diameter).
Serpent, you are right - the gif showed a free jet, not one in a tube. The frequency of the tube oscillations does feed back to the frequency of the eddies, but I’m a little loose on the physics here.
Some of the stuff I’ve seen indicates that the octave jump occurs at a Strouhal number of about 0.2. I actually did some measurements of some commercial fipples, and one I built, and calcuated what the Strouhal numbers were at the bell frequency of the whistle. To do this, I had to make an assumption of the air volumetric flow rate. The numbers I got for this were consistant with some rough estimates of lung volume and blowing time, so I think the Strouhal number approach is in the right ballpark.
To do this, I had to make an assumption of the air volumetric flow rate. The numbers I got for this were consistant with some rough estimates of lung volume and blowing time, so I think the Strouhal number approach is in the right ballpark.
So just how do you come up with the pressure,lung volume,and blowing time.
The problem I sometimes find is, that of tuning low D’s all one day. Then the next going to sop. D’s, it often takes a while to
get the right pressure back.
What’s the average blowing presure, maybe the drink driving cop’s would know!
:roll:
Wizzy
The Strouhal number uses the velocity of the air stream. if you figure that the air has to go through the windway, then the velocity times the area area is the volumetric flow rate. I took a Gen D, took a reasonable breath, and blew D 'till I couldn’t anymore. That gave me a time. I then did some research on lung volume, and said that my lungs were average for an adult male, and figured I’d exhausted that many liters in that period of time - a volumetric flow rate. They weren’t exact, but in the same order of magnitude anyway, and all I was looking for was a sanity check on the theory.
Dave
Finally got a .AVI file from my brother, but it’s obvious he doesn’t have the right tools, and perhaps not the skillset for this sort of raw-physics work. He did get a smoke-stream going down a tube in Lightwave, but it behaves more like a turbulent ball than a laminar flow. Next, we try it with particles.
… just an update …
Bill Whedon
Anybody got access to a supercomputer? My bro tells me that the collision calculations for using particles are causing his Pentium IV 2GHz to come to a grinding crawl. I guess he’s talking hours per frame.
TIA
Bill Whedon
Nope, but I thought I’d post this to add to the discussion.
http://www.acoustics.org/press/132nd/5pmu9.html
It’s about organ pipes, but in my mind they’re a close analogy to whistles.
[quote]
On 2002-10-26 12:19, dkehoe wrote:
Nope, but I thought I’d post this to add to the discussion.
http://www.acoustics.org/press/132nd/5pmu9.html
Well well Dekhoe.
This should give Serpent a bit of food for thought.
Ofcouse, I knew all this all ready its just the sort of bed time reading I like!
:roll:
Wizzy
What can I say? Wow! I guess what this all means is, we’re not having totally original thoughts here! What a concept!
That photo series is most impressive, and from the look of that cross-section, I’d bet that the same or very similar results would be achieved in a whistle. I’ve had very close looks at organ pipes, and yep, they’re much more like a whistle than not.
Too bad the article didn’t include an AVI or QuickTime with it - that’d have been fun to watch!
BTW, Wizzy, I printed it off and put it in the bathroom to entertain visitors. 
Next, we must find a site with photomicrograms of edge turbulence within a Susato and a Gen. Search! Find! Run! Run like the wind, my children! Run fast! Run far! (ROFL)
Back to the shop…
Cheers,
Bill Whedon