Blowing machine

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Tunborough
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Re: Blowing machine

Post by Tunborough »

Terry McGee wrote: Sat Mar 25, 2023 10:18 pm I concentrated on looking directly down the windway, seeing equal amounts of ceiling and floor. And made easier by placing something of contrasting colour beyond the head.

Mellow D: All ramp
Feadog Mk 1: All ramp
Killarney: All ramp

Old Gen: 2/3 ramp, 1/3 through.
Newer (but probably still fairly old) Gen: 1/3 ramp, 2/3 through.

The Killarney, being of Sindt design, is easy to confirm, as, once you have pulled the pin, you can push the stopper forward until it passes under the ramp.
The comparison I was making was not windway relative to blade (which is an important consideration for voicing in its own right), but windway and blade relative to the centre-line of the tube. Looking up the head of a Generation, from the open end toward the windway, I see a fairly sizable circle segment above the bottom of the blade and the windway exit. The blade hangs lower into the bore than it does on a Feadog Mk 1. Interestingly, the head of a Freeman Mellow Dog, which I gather is a newer Feadog head, lines up more with the Generation head than it does with the Feadog Mk 1 head.
Terry McGee wrote: Sun Mar 26, 2023 5:26 am Sigh, if only we still had Neville (Fletcher), he would love to have been involved in our discussion. Neville learned flute when he was a boy in Armidale in rural NSW, starting on a conical band flute (they were cheap!). He went on to be a leading voice in musical acoustics internationally. And of great help to me whenever asked.
Yes, I still have the text he wrote with Thomas Rossing close to hand. I'm sure there's at least one academic paper in this, if only we had an academic to take notice.
trill
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Re: Blowing machine

Post by trill »

Tunborough wrote: Thu Mar 23, 2023 9:46 am . . .
I don't see any way to blame that drop in pressure on the flowmeter. . . . Yes, we are seeing anomalies when we try to switch among the 5 L/min meter, the 20 L/min meter, and two meters in parallel
david_h wrote: Thu Mar 23, 2023 10:17 am . . . Neither do I. . .

Well, this is embarrassing . . .
So, I re-read the passage where the 35mm and 130mm tubes were added on to the calibrator. For what its worth, I had a totally different mental picture of what was taking place. For this case, of course, the flowmeter is not the problem. My statements were erroneous.

I am totally embarrassed at being so sloppy. I sincerely apologize for injecting noise to the thread.

Electrical Analog
I was puzzling over why, if pressure was changing when adding the tubes, the flow was not (remaining at 20). I resorted to considering an electrical analog and came to the following understanding:

1) the regulator acts as a constant voltage
2) the resistor and flowmeter act as resistors, whose resistance is *much much* greater than the calibrator + tubes.
3) The key idea is the those 2 resistors are *much* greater than the calibrator + small contribution (ε).
4) Thus, with Ohm's law, I = E/R, where R = (R+R+r+ε), the epsilon is so small compared to the rest, the change in current (flow) will be so small it wouldn't be visible on the flowmeter.

"adding the tube" = "less resistance".
I haven't figured that out for myself. I'm sure there's an analysis that shows it. I simply haven't done it. One thing's for sure, the repeated + systematic measurements made by Terry are conclusive.

Flowmeter
Yes, there are "anomalies" arising from 5, 20, 20+20 lpm floweters and the tubing+valves that go with. Even with those anomalies, large trends have been tractable + amenable to model-checking. However, it is my belief that the flowmeters being used were never intended for lab-grade measurements. I really think that any analysis and model-checking would be better served (quicker, more accurate, less cluttered) with a better flowmeter. What puzzles me the reluctance. The price of a better meter is less than a good Low-D. Even less when shared.

(yes, I'm a dog with a bone . . .)
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Terry McGee
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Re: Blowing machine

Post by Terry McGee »

Tunborough wrote: Sun Mar 26, 2023 8:02 am The comparison I was making was not windway relative to blade (which is an important consideration for voicing in its own right), but windway and blade relative to the centre-line of the tube. Looking up the head of a Generation, from the open end toward the windway, I see a fairly sizable circle segment above the bottom of the blade and the windway exit.
OK, starting there, I've tried various approaches to get a good view. The Zoom microscope doesn't do much as the ring of LEDs that are used for illumination are shaded by the socket walls. Ditto the Maggy Lamp, for the same reason. Best viewing seems to be using a strong bench lamp.

Looking into the Old Gen, I see first the reduction from tube outside diameter (about 12.7mm) to tube inside diameter (about 11.5mm) that stops the tube from inserting too far. Excepting that it's D-shaped, not a full circle concentric with the socket - the spine of the D being a platform underneath the ramp. I can get a Telescoping T-gauge into that area. It suggests a horizontal width of 11.45mm, but a vertical width (if we take the window side of the head as "up") reduces to about 10.4mm. So the platform drops about 1mm. If I then push further in so I'm seeing the T-gauge tips about to enter the window, the vertical diameter drops a little to around 10.2, but the horizontal diameter drops a little to, to about 11.35. These are probably not acoustically significant details, being more about some tapering to be able to get the head out of the mold!

And beyond that, I can see the end of the windway and the cavity below it. But finding a way to measure how it relates to the platform or circle isn't easy. I took a 9.5mm brass rod and faced it off cleanly, offered that up the head socket until it reached the end of the windway. I could rock the head until I was confident that the platform was sitting on the rod. At that point the outer circumference of the rod came up to the bottom of the windway exit.

And yet, when I look down the windway, I can see some through as well as mostly ramp. But it's possible that the windway isn't parallel to the rest of the whistle, isn't it! So, while inconclusive at this point, there may be some scope there for measurement systems.
The blade hangs lower into the bore than it does on a Feadog Mk 1.
Agreed. Using the same approach on the Feadog Mk 1, the horizontal head bore after the socket is 11.9mm, while the vertical is about the same. And I couldn't get a good sense of a platform to try the brass rod test. I just got the sense that the head was rocking on the bottom of the blade.

A more recent Generation looks the same as Old Gen, but when I get to the brass rod test, I reckon about 5mm width of the circumference of the end of the rod passes above the floor of the windway. That's consistent with seeing more "through" when looking from the beak. But again, perhaps we're getting more into voicing here than what you're looking for.

The Mellow D shows a small platform, but again I have difficulty assessing its relationship with the windway exit.

And the Killarney as I mentioned previously is no mystery. All you see up there is the perfect circle that forms the bottom of the tube socket. The stopper and bottom of the ramp are all at that reduced diameter.
I'm sure there's at least one academic paper in this, if only we had an academic to take notice.
Hmmm, does this take us back to my University of Limerick Physics Department quip? Anyone aware of anyone working in this field these days?
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Terry McGee
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Re: Blowing machine

Post by Terry McGee »

And responding to trill above, don't beat yourself up too much! This stuff is pretty tricky which is why I'm leaving the heavy thinking to those who have delved further into the physics than I have. That doesn't mean I don't have a role. I raise the quibbles, they knock them on the head. Hopefully!

I have learned that electrical analogies only get you so far in this more dimensional world. That's why I was surprised to find that adding some tubing (resistance) after the calibrator didn't increase the pressure (voltage) as I expected. Because it allowed the partial vacuum to form in that tubing, pulling down the measured pressure on both sides of the calibrator. I can't think of an electrical analogy for that one! Negative resistance?

And in regard to the flow meters, yes, the current ones leave a lot to be desired, but are good enough to let us prove we can deal with the weird stuff, like the tubing added to calibrators (whistle bodies added to whistle heads), before we lash out on better metering!
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Re: Blowing machine

Post by david_h »

Tunborough wrote: Fri Mar 24, 2023 9:56 am I'd say the pressure doesn't vary consistently with air speed squared until above 200 Pa (20 mm H2O), and when it does, there's an offset of 60 to 100 Pa, depending on the recorder: P = m * v^2 + offset.
That's puzzling me. Bernoulli's equation doesn't have a constant. Even if the the pressure doesn't vary with air speed squared at low pressures when it starts doing so wouldn't the graph still trend to v=0 when P=0? Not doing so indicates that whatever creates the offset is still happening at higher pressures and flow rates.
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Terry McGee
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Re: Blowing machine

Post by Terry McGee »

You see what I mean, trill? These guys talk in tongues!

Although I did see some pretty weird data coming in at low flow rates. But let's not humour them, eh? Let's make them work for their keep!

I'll go quiet for a day or so. I have to go up to Canberra tomorrow and play some music at a funeral for an old Irish box player up there. It will be an honour...
trill
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Re: Blowing machine

Post by trill »

Terry McGee wrote: Sun Mar 26, 2023 7:47 pm . . . Because it allowed the partial vacuum to form in that tubing, pulling down the measured pressure on both sides of the calibrator . . .
Food for thought.
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Re: Blowing machine

Post by trill »

Terry McGee wrote: Mon Mar 27, 2023 5:32 am . . . You see what I mean, trill? These guys talk in tongues! . . .
Ouch, ouch, ouch ! !
Tunborough
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Re: Blowing machine

Post by Tunborough »

david_h wrote: Mon Mar 27, 2023 4:45 am
Tunborough wrote: Fri Mar 24, 2023 9:56 am I'd say the pressure doesn't vary consistently with air speed squared until above 200 Pa (20 mm H2O), and when it does, there's an offset of 60 to 100 Pa, depending on the recorder: P = m * v^2 + offset.
That's puzzling me. Bernoulli's equation doesn't have a constant. Even if the the pressure doesn't vary with air speed squared at low pressures when it starts doing so wouldn't the graph still trend to v=0 when P=0? Not doing so indicates that whatever creates the offset is still happening at higher pressures and flow rates.
I agree ... at high enough pressures, both Bernoulli and Darcy-Weisbach have pressure varying with air speed squared with no offset. I was disappointed that Blanc, Fabre, et al., who I must emphasize are all dedicated and respected researchers, would collect data that didn't agree with this, and not investigate why. We're not in a position to explain it after the fact, so we can't really use their data for much.

I wondered how laminar flow at low pressures might influence the relationship. I calculated pressure as a function of air speed (squared) for a wide range of speeds, assuming laminar flow at low speeds and turbulent flow at higher speeds. At the low air speeds, laminar flow does add an offset that starts at zero for v = 0, rises to around 20 Pa (that's 2 mm H2O), and drops back down to zero pretty quickly as the air speed increases. If you like, I can post the numbers when I get to my other computer.
Terry McGee wrote: Mon Mar 27, 2023 5:32 am You see what I mean, trill? These guys talk in tongues!
You ain't seen nothing yet, Terry. When you get around to the frequency-flow-pressure study on the Feadog + tube, I'll start talking Strouhal numbers and Z = R + iX. :wink:
Last edited by Tunborough on Mon Mar 27, 2023 2:44 pm, edited 1 time in total.
Tunborough
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Re: Blowing machine

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Terry McGee wrote: Sun Mar 26, 2023 7:47 pm I have learned that electrical analogies only get you so far in this more dimensional world. That's why I was surprised to find that adding some tubing (resistance) after the calibrator didn't increase the pressure (voltage) as I expected. Because it allowed the partial vacuum to form in that tubing, pulling down the measured pressure on both sides of the calibrator. I can't think of an electrical analogy for that one! Negative resistance?

And in regard to the flow meters, yes, the current ones leave a lot to be desired, but are good enough to let us prove we can deal with the weird stuff, like the tubing added to calibrators (whistle bodies added to whistle heads), before we lash out on better metering!
Agree on both counts. trill's original analogy holds: the pressure loss across the calibrator is small relative to that across the flow meter, so changing it a little isn't going to noticeably affect the flow. But the influence of that added tubing still has me scratching my head.
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Re: Blowing machine

Post by david_h »

@Tunborough. Sorry I wasn't clear, I was meaning what I think you are saying. Whatever happens at low pressures can't change the relationship at higher pressures, just give a kink and maybe a discontinuity in a graph 'before' that. A plot of Q v. sqrt(P) once Bernoulli and Darcy-Weisbach describe the flow should go through the origin. So when the authors mention that the data are consistent with Bernoulli at the higher pressures but not say more than that they could be fudging round a small flowmeter zero offset (which would not spoil their overall treatment) rather than neglecting (or not noticing) something. In places it reads as if they are either writing in a second language or have used a translator.

I think their data tells us that something not explained may be happening but that above the lowest pressures the overall relationship is fairly simple. That is not all that different to our situation with Terry's data - being unsure if intercepts in a Q-sqrt(P) plot are flowmeter errors or some flow process to be understood.
Tunborough wrote: Mon Mar 27, 2023 11:48 am But the influence of that added tubing still has me scratching my head.
If you mean the lower pressure with the tube added than without I don't think that's a problem** if it is a lower energy-loss configuration for the space just beyond an orifice. Hard to think about maybe, but I find the Bernoulli grip hard to think about and it obviously works.

** but I don't have to model it!
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Re: Blowing machine

Post by Tunborough »

david_h wrote: Mon Mar 27, 2023 1:50 pm @Tunborough. Sorry I wasn't clear, I was meaning what I think you are saying.
And I wasn't clear. I was absolutely agreeing with you that Bernoulli, etc. didn't explain an offset. Edited to make that explicit.

Their graph did bend to go through the origin, but at higher pressures it looked more like m * v^2 + offset.
david_h wrote: Mon Mar 27, 2023 1:50 pm In places it reads as if they are either writing in a second language or have used a translator.
Their native language is French, and mine isn't, so I'm not going to hold any translation issues against them.
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Re: Blowing machine

Post by david_h »

Tunborough wrote: Mon Mar 27, 2023 2:45 pm Their native language is French, and mine isn't, so I'm not going to hold any translation issues against them.
It wasn't a criticism but a recognition that some of the flow of the presentation derives from a language with different means of expression and sequencing of information. Which for me requires more careful reading.
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Re: Blowing machine

Post by Terry McGee »

OK, back from Canberra. The funeral and wake went well. Joe's casket had the Irish flag on one side and the Eureka miners' rebellion flag on the other! A bit of a rebel.
And his accordion, and a cross that had been hand carved from bog oak in his youth back in Sligo.

And we learned that apart from the box that we often saw him play, he also played the whistle. And so here was Mark and me to send him off, playing box and whistle.

But back to business. The question of the effect of the extra tubing overhanging after the calibrator still bothered me, so I thought to delve a little deeper. I added 120mm of extra tubing, and put some masking tape on it, with markers reading every 20mm. My plan was to cut them off every 20mm to chart the effect. As I proceeded though, I saw the more interesting stuff was happening as we got closer, so I dropped to 10mm increments. Here are the results:

Code: Select all

4 x 30mm Calibrators plus variable lengths of 13.3mm tubing, 29 March 2023			
+ Length	Flow	MM(H20)	Resistance
120	20	69	0.42
100	20	69	0.42
80	20	67	0.41
60	20	66.5	0.41
40	20	69	0.42
30	20	71	0.42
20	20	73.5	0.43
10	20	75.5	0.43
0	20	76	0.44
			
Average Resistance	0.42
So, reading from the bottom of the table upwards, we see that the apparent pressure drops more and more as we add the extra tubing, until we reach 60mm, after which (*) it starts to increase again and then stabilises. At about the 8 diameter point! But note it stabilises at a different pressure than with no extra tubing.

(*) Interesting that I originally typed "whereafter it starts...". Must have been the sermon at the funeral.
Last edited by Terry McGee on Wed Mar 29, 2023 5:31 pm, edited 1 time in total.
trill
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Re: Blowing machine

Post by trill »

Terry McGee wrote: Tue Mar 28, 2023 10:50 pm . . . The question of the effect of the extra tubing overhanging after the calibrator still bothered me . . .
Honestly, I've been scratching my head about the same question in "spare moments" for the past several days . . .
Terry McGee wrote: Tue Mar 28, 2023 10:50 pm . . . So, reading from the bottom of the table upwards . . .
Image

Looks very systematic.

Any chance you could run it out another 100 or 200 mm ? Out to 220 or 320 ? Big increments (25 or 50mm) should be fine.

I ask in the the interest of observing the effect of "skin friction".
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