Blowing machine
- Terry McGee
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Re: Blowing machine
I reckon I can get to less than 1mm readability on the analog manometer, but it is tricky. You are aware of the top of the meniscus, the bottom of the meniscus and a bit of a blur in the middle. I think precision in the comparison will be limited by
- readability of the analog manometer (about 1mm, but remember it gets multiplied by two)
- possible remnant stickability of the liquid
- the 1mm minimum increment on the digital instrument
- any non-linearity in the digital instrument
And once we bring the flow back in
- the readability and precision of the analog flow meters.
The notion of moving the flow meter to after the item_under_test is interesting, although I'm not sure what it gains us. And yes, very tricky to achieve with a whistle!
- readability of the analog manometer (about 1mm, but remember it gets multiplied by two)
- possible remnant stickability of the liquid
- the 1mm minimum increment on the digital instrument
- any non-linearity in the digital instrument
And once we bring the flow back in
- the readability and precision of the analog flow meters.
The notion of moving the flow meter to after the item_under_test is interesting, although I'm not sure what it gains us. And yes, very tricky to achieve with a whistle!
- Terry McGee
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Re: Blowing machine
Tunborough, on turbulence: "It hasn't been established ... That was idle speculation on my part. It doesn't sound relevant, so I won't attach any more significance to it."
But a good concept for us to keep our antennae up about. I am aware, listening to my various whistles as I play, that there are pretty big differences in tonality and clarity that I'd like to get to the bottom of. Bit by bit, we are alerting ourselves to the differences in these whistles. Hopefully some pennies will drop as we proceed....
But a good concept for us to keep our antennae up about. I am aware, listening to my various whistles as I play, that there are pretty big differences in tonality and clarity that I'd like to get to the bottom of. Bit by bit, we are alerting ourselves to the differences in these whistles. Hopefully some pennies will drop as we proceed....
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Re: Blowing machine
The pressure of the air in the flow meter - and hence its density - would then stay almost the same throughout.Terry McGee wrote: ↑Thu Feb 23, 2023 6:10 am The notion of moving the flow meter to after the item_under_test is interesting, although I'm not sure what it gains us.
The issue is related to what trill has pointed out - what gas is the flow meter calibrated for? My hunch would be that the physics of the flow round the bead that lifts it is described by equations involving density - probably similar to the ones Tunborough is modelling at the same applied pressure and flow rate.
Ah yes Tunborough, my mistake about the water density. I had much earlier had a quick look and decided it was not worth bringing up in the context of workshop temperature changes. Haven't done the same regarding temperature in the flow meter.
Re: Blowing machine
Indeed it is: Fdrag = 1/2*Cdrag*rho*v^2*Sref
I used that relation in trying to estimate the effects of density (air vs. oxygen). My current guess is that using air (instead of oxygen) in the flowmeter will yield an "indicated" flow rate ~10% lower than the actual. I ordered a flowmeter to check.
Test results pending.
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Re: Blowing machine
So drag varies directly with density. Gas density varies directly with pressure. If Terry' workshop were at average atmospheric pressure (a little more than 10m of water) 0 to 360mm of water is roughly 3.5% variation in density. That may be all that would be gained by moving the flow meter, though that variation in scale spacing indicates something complicated is going on in the flow meter. I guess flow changes as the space the air is going into gets shorter.
Question to Tunborough. If a really simple test sample was made - hole in a thin plate maybe - is the modelling then simple enough to calibrate the flow meter? Or at least get a handle on any idiosyncrasies.
Question to Tunborough. If a really simple test sample was made - hole in a thin plate maybe - is the modelling then simple enough to calibrate the flow meter? Or at least get a handle on any idiosyncrasies.
Re: Blowing machine
Excellent idea !
That would take care of density uncertainties due to both pressure + chemistry !
My guess is that the mfr simply tailors the curvature of the flowmeter channel to give greater resolution for flows ranges of interest. Just a guess.
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Re: Blowing machine
If one had two simple samples, maybe slightly different size holes, it might show if odd things were related to flow rate rather than the thing under investigation.
- stringbed
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Re: Blowing machine
It means that I'm a poor proofreader. It should read "laminar." I've corrected the original post.
- DrPhill
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Re: Blowing machine
IIRC and I hope I am not teaching my grandmother.... but can you not float a small object on the liquid? Said small object can have a clear line marked on it. There will be a constant offset from meniscus to the line, and a slight distortion (liquid needs to support weight of object). Re-calibration may be required for absolute measurements.Terry McGee wrote: ↑Thu Feb 23, 2023 6:10 am I reckon I can get to less than 1mm readability on the analog manometer, but it is tricky. You are aware of the top of the meniscus, the bottom of the meniscus and a bit of a blur in the middle. I think precision in the comparison will be limited by
......
Phill
One does not equal two. Not even for very large values of one.
One does not equal two. Not even for very large values of one.
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Re: Blowing machine
You would be talking about an orifice plate. It would have to be installed in a long stretch of pipe, with pressure taps at specific distances above and below the plate. Once we have a discharge coefficient, we can calculate flow rate from the pressure differential across the plate. (The formula they give for discharge coefficient depends on Reynolds number, which depends on flow rate, so I've no idea how you calculate that, but I think there's a reasonable approximation for our purposes.)
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Re: Blowing machine
Looking at the equation I think the critical thing is that we are back to Bernoulli's equation. If a hole is a simple enough thing that the flow regime doesn't change over the range of pressures we are interested then a plate in Terry's sample holder should give flow proportional to sqrt(pressure). Done with two hole sizes should give an indication if departures from a theoretical curve shape are related to measured flow rates.
That would allow a correction for unevenness in the flow metre scale (but not a full calibration) so the the shape of a Flow - Pressure curve would be more related to the thing
under test.
There is chance everything may then get simpler to model and attention could get beyond the windway. Or, of course, that it may suggest a change of flow regime in the windway so harder to model but more interesting.
That would allow a correction for unevenness in the flow metre scale (but not a full calibration) so the the shape of a Flow - Pressure curve would be more related to the thing
under test.
There is chance everything may then get simpler to model and attention could get beyond the windway. Or, of course, that it may suggest a change of flow regime in the windway so harder to model but more interesting.
- Terry McGee
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Re: Blowing machine
OK, trill, here you go:
Notes:
Excuse the truncated column headings - needed to keep in line with figures when transferred to this forum
I put in the fingerings so I could show what worked for D7 (I didn't seem to like oxx ooo). Would also be handy for c-naturals if added.
The cents column shows I couldn't make it up to 0 in some cases. Arguably should have shortened the Blade-to-foot length. Regard the ones that made it to 0 as very close to breaking! The whistle would probably benefit from touching up the tuning, but who's going to bother with such an old whistle!
Flow as shown on 20L/Min flow meter up to G6, adding second meter in parallel from then on.
Pressure as shown on Digital Manometer. It is much easier to read!
Resistance as calculated by my dodgy simplistic method (until we agree on something better)! Left to 3 decimal places though of course data doesn't support that!
Code: Select all
Old Generation Blade to foot: 271mm
Holes Note Cents Flow mm(H2O) Res.
xxx xxx D5 0 7.7 1.6 0.164
xxx xxo E5 0 8.3 1.8 0.162
xxx xoo F#5 -20 9 2.3 0.169
xxx ooo G5 0 9.6 2.6 0.168
xxo ooo A5 -15 10.3 3 0.168
xoo ooo B5 0 10.8 3.3 0.168
ooo ooo C#6 0 12.5 4.4 0.168
xxx xxx D6 0 13.3 5 0.168
xxx xxo E6 0 15.5 7.1 0.172
xxx xoo F#6 -25 16.4 7.6 0.168
xxx ooo G6 -10 18.3 9.15 0.165
xxo ooo A6 -15 22 13.5 0.167
xoo ooo B6 0 24.2 15.35 0.162
ooo ooo C#7 -10 26.3 19.8 0.169
oxx xxx D7 0 25.4 16.9 0.162
Excuse the truncated column headings - needed to keep in line with figures when transferred to this forum
I put in the fingerings so I could show what worked for D7 (I didn't seem to like oxx ooo). Would also be handy for c-naturals if added.
The cents column shows I couldn't make it up to 0 in some cases. Arguably should have shortened the Blade-to-foot length. Regard the ones that made it to 0 as very close to breaking! The whistle would probably benefit from touching up the tuning, but who's going to bother with such an old whistle!
Flow as shown on 20L/Min flow meter up to G6, adding second meter in parallel from then on.
Pressure as shown on Digital Manometer. It is much easier to read!
Resistance as calculated by my dodgy simplistic method (until we agree on something better)! Left to 3 decimal places though of course data doesn't support that!
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Re: Blowing machine
Something's off with those numbers, Terry. In the first batch of measurements on that whistle, it took 27 mm H2O to get 10 L/min of flow, which was a bit less than I expected. This time it took only 3 mm H2O to get that much flow, which is much less than I would expect. I realize the first batch was on the manometer without dish soap, but that doesn't explain that much difference.