Air flow + eye of a needle

[ElViejoEli]

Good Morning Folks:

 

My name is Eli. I'm trying to find some data re the flow of air around and through the eye of a needle. I've spent several hours looking through various links provided by the Google search engine when I input the title into the Google browser window.

 

Most of the results which I've accessed deal with aerodynamics of planes and cars and a "needle" of one kind or another. There seems to be very little or no research into air flow around the eye of a needle or anything remotely resembling the eye of a needle.

 

Any suggestion that can direct me in the right direction would be greatly appreciated. Thanks.

 

 

Eli:shade:

[CraigD]

Hi Eli, and welcome to hypography ;)

My name is Eli. I'm trying to find some data re the flow of air around and through the eye of a needle.

I doubt you’ll find much information about the aerodynamics around the eye of an actual sewing needle, because ... well ... sewing needles don’t fly much.

 

I’m curious – why are you interested in this? :)

 

You might find some information about the aerodynamics of some vaguely needle-eye-shaped objects concerning the circular ducts of fan shrouds, but be warned, aerodynamic data doesn’t “scale” well – that is, data about a large object somewhat resembling a small one often reveals little about the small one.

 

You might have to do direct experiments to answer your needle eye aerodynamics questions. For a sewing needle, you’d need little more to do this than a source of moving air, such as a small fan, a source of smoke, such as a lit cigarette, and perhaps something to optically magnify the image, such as a small binoculars, telescope, or digital still of video camera with a strong light source, such as a flash light.

 

My guess is that you’ll observe little airflow though the eye of the needle, but having never experimented with this, this is only a guess.

[sanctus]

Also just what I vaguely remeber from my "advanced" mechanics course, you might want to look into the reynolds number. If remeber all right, this number is carateristic for an object, in the sense that if you want to study the aerodynamics of a plane you can construct a small thing which has the same reynolds number and do tests in a small lab...so what you would have to do is to find this number of a needle and then look for studies for objects with the same number.

 

What I am not sure is if it is called Reynolds number, but that such a carateristic number exists and can be (and also actually is!) used I am sure.

[ElViejoEli]

I assist in coaching a boys track/field team and was talking to the distance guys once about the effects of running behind someone during a race to benefit from the "drafting effect" that front-runners create for those runners directly behind them. One of the boys commented that the coach he had at the previous school he attended recommended that you follow the runners in the pack in the space directly behind and between two runners that are running side by side. The coach referred to the space between the two runners up front to be similar to "the eye of a needle" while the two runners would make up the side of the needle opening. Supposedly there would be a lower air pressure (?) in that space and the runner trailing the front-runners would benefit from the "drafting effect" that would be produced.

 

My experience has been that the best way to "draft" behind a runner in front of you is to run directly behind a runner and "sit in the low pressure pocket" created by the air that the front runner pushes to either side of him as he runs up front. (This is very similar the drafting that race car drivers exploit in their sport.) If you follow more that 3-4 meters behind the front runner the result is the opposite of the "drafting effect," that is, it is more difficult to run when trailing more than 3-4 meters behind the front runner because said front runner produces "air turbulance" in the space that is > 3-4 meters behind him. It has been explained to me that the air behind the "low pressure pocket" is denser (how so?) than that of the "low pressure pocket" as well as the air in front of the lead runner! I don't know or understand how that could be possible, but I do know from personal experience that running > 3-4 meters behind someone is more difficult than running directly behind them or running by their side or being the front runner.

 

Now, back to the "eye of the needle" aspect of my question. A few nights ago I had a dream that the boys I train were running repeat 400's on the track and were attempting "to feel" the effects of drafting on their fellow training partners. I explained to the runners in the dream that the best way I knew of to benefit from drafting was to follow < 3-4 meters behind the runner in front of you. However, I wanted to experiment with the idea that "eye of the needle" drafting might be better than the traditional approach I used.

 

With six distance runners to work with, I broke up the boys into two groups of three. In each group the slowest of the trio would be the one from running in "the low pressure pocket," the fastest of the trio would run in lane 2 and the other would run in lane 1. Since the fastest of the trio in lane 2 would run a slightly longer distance than 400m while running on the turns, he would be the one most capable of keeping the two sides of "the needle" intact as the two front-runners ran the turns of the 400m interval. The trio would run 6x400m with 4 minutes rest inbetween each 400m as their workout. The instructions to the trio would be that on the 6th and final 400m interval they would sprint for home from the 300m mark, which happens to be at the beginning of the straightaway. The question is can the slowest runner in each trio benefit enough from running the 5 previous 400m intervals in "the low pressure pocket" and beat the other two runners in his trio? In the dream the answer was a resounding YES! since in the first trio the results were as follows: runner A, running in lane 2 ran 62.4; runner B, running in lane 1 ran 63.0; runner C, running in "the low pressure pocket" ran 61.7. The results of the second trio of runners was similar: runner A, 63.8; runner B, 64.1; runner C, 62.9.

 

I was so excited from the dream that I woke up at about 6:15 AM and went directly to the computer to begin searching for data about air flow around and through "the eye of a needle." Now I know that it was the dream that really got me to think seriously about this idea of "the eye of the needle" being a better drafting technique than the traditional approach of running <3-4m behind the runner in front of you. But this is the source of my curiosity. In order to find out, I posted my question.

[Boerseun]

Well, if that's the case, I don't think you should look at a needle for aerodynamic properties.

 

Like Craig said, aerodynamics don't scale very well, but apart from that, remember that a needle closes on top - it forms a full loop that constricts the airflow from both the sides, the bottom and the top. The constriction you're proposing (forget about scale and detail for a second) constricts air from only the sides.

 

I think a much better proposal for what you're attempting to simulate would be a flat board with round pegs inserted into the board in the same layout as what you have in mind with your team. Then get a smoke source, and a fan with a grid in front to even out the airflow and minimize turbulence. You can then photograph the results for later analysis, and play around with different layouts of the pegs on your board to better understand the process.

 

Calling your particular player arrangement an "eye of a needle" is purely a metaphor, and won't have much to do with the aerodynamics of a needle, at all.

[ElViejoEli]

Thanks for your input. Because the bodies of the guys in the front of the pack might more resemble the shape of a rectangle or trapezoid than a peg, might I be better off using these instead of pegs in the layout and "...then get a smoke source, and a fan with a grid in front to even out the airflow and minimize turbulence." Also, for the grid, would I use something like chickewire or do I need something more substantial in girth, say furring strips?

 

Eli

[ElViejoEli]

To Boerseun:

 

I've tried to determine to no avail the meaning of your quote at the bottom of your reply to my post, namely, "Ecce bos taurus justitia." What language is it (Latin?) and what does it mean?

 

Eli

[GAHD]

Everything fron "hypography science moderator" to "Ecce bos taurus justitia." is a footnote that gets appended to all his messages, much like there is one at the bottom of my post.

 

If you can get access to a copy of SolidWorks I think it has built in aerodynamic simulators. Failing that, I've heard of people doing similar simulations with an autodesk product and cleverly coded particle arrays.

 

How fast are you guys running that you get a noticeable 4m wake in air? o.0

[ElViejoEli]

It comes out to about 16 mph for someone like myself. I ran an 800m race in 1 min. 52.0 seconds in college and remember struggling behind another athlete (who ran 1:51.0) running about 7 meters in front of me for the last 300m of the race. No matter how hard I tried to close the gap on him, I couldn't seem to make any headway. My college coach explained to me that the problem was the turbulance that guy created as I ran behind him. Coach told me that if I stayed closer to him earlier on in the race and drafted off of him that I would find the running easier. Three weeks later we met again and indeed the running was easier when I drafted off him by staying within 3-4m directly him. I didn't beat the guy but I was able to close the gap to only 0.1 seconds, losing 1:50.8 to 1:50.9. As a student of science I know that I was relying only on empirical evidence that lacked a control. At the time it seemed to me to be a reasonable explanation for my improved performance which was achieved with seemingly less effort because I didn't feel I struggled as much as I did three weeks prior. To boot, I ran 1.1 seconds faster.

[CraigD]

I assist in coaching a boys track/field team and was talking to the distance guys once about the effects of running behind someone during a race to benefit from the "drafting effect" that front-runners create for those runners directly behind them.

When I ran on a coached team, drafting was discouraged, because our coaches were of the opinion that the distraction and possibility of spiking/tripping the runner you’re following outweighs any reduction in effort that could be gained.

 

Tactically, a good argument can be made that for 400 and 800 m (in my day, 440 and 880 yards) distances without lanes or with a lane break, you want to get ahead and stay there - otherwise a crafty runner who’s a bit slower than you can get you running off his shoulder in the corners, or even run you out an extra lane, then break back inside. I actually had someone add about 0.3 sec to my 600 yd time on a 160 yd square indoor track using this trick – and made it a point to never get beaten to the first corner by him again!

 

I was and still am skeptical of the “drafting’s more trouble than it’s worth” opinion, as accurate testing with track bicycles has show that drafting can reduce pedaling power by around 30%, and drafting’s very important even among youth and amateur bike racers, and bikes and runners are in similar speed and aerodynamic domains. Also, some time-correction calculators (the underlying physics of which I’ve not seen) indicate that a 10 m/s tailwind (about running speed) reduces a 100 m time of about 12 s by about 0.5 s, suggesting that effective drafting might have a similar impact. Of course, you can’t draft forever and win, but if it keeps you rested enough to out kick the lead runner by a few meters in the last 50 m, it mean a win over someone as much as a sec or more faster than you in a the same race in lanes.

 

I can imagine some pretty cool experimenting – rather than traditional smoke and cameras, I think you could get some good data running or biking behind a runner with a handheld anemometer (something like this http://www.amazon.com/Crosse-Technology-EA-3010U-Handheld-Anemometer/dp/B0002WZRKE), or perhaps a more accurate device, either held by its grip, or with an extension stick. You should be able to pretty quickly build a map of apparent windspeeds behind a runner, from which you could get an “effective tailwind” for different running speeds, wind speeds, and following distances, that could be used to calculate the power saving for a runner drafting at different distances and positions.

 

I might try this myself, as I'm always on the lookout for an excuse to buy a new gadget, and have long wanted a handheld anemometer. :shrug:

How fast are you guys running that you get a noticeable 4m wake in air? o.0

A top male high school 400 m runner can usually break 50 s. A world-class male these days is under 44 s, female, under 49. These equate to speeds from 8 to 9 m/s (18 to 20 MPH)

It comes out to about 16 mph for someone like myself. I ran an 800m race in 1 min. 52.0 seconds in college and remember struggling behind another athlete (who ran 1:51.0) running about 7 meters in front of me for the last 300m of the race.

You’re 800 m times are about the same as my 880 yd (804.67 m) times as a high school senior.

 

Because I ran all seasons (x-country, indoor track, outdoor track), I was cursed in high school by my coaches’ impression that I was some sort of distance runner, so my senior year (18 years old), the shortest distance I ran was the 880 – despite a 440 time of 48.2 as a junior (17). It only got worse as the years went on – my most recent races are all marathons, not my strong suite, as I have the body of a sprinter. Unfortunately, I now have the body of a poorly trained 49 year-old sprinter, and a couple dozen extra kg of mass that does me no good at all :phones:

[ElViejoEli]

Those are quite impressive times for a high schooler CraigD. Congratulations! Like you, I also ran yards, not meters like today. In trying to keep up with the times I converted my yards times into meters. Unfortunately, like you, Father Time has been unkind to my figure and I now tip the scales at 209 lbs., compared to the 142 lbs. while competing 44 years ago. I've developed osteoarthritis in my left ankle which prevents me from jogging anymore, never mind running. Hence the upward spiral of weight.

 

Thanks for the tips about determining the tailwinds using a hand-held anemometer. The drafting would not be of any value in races below 800m since they (the 100, 200 & 400) are now run only in lanes. Also, the longer the race, the more important the use of drafting becomes as a technique to "save energy" for the final kick in one's race. In high school, they are only the 800, 1500, 3000 and 5,000 runs that would involve using drafting. I won't be able to do those studies until after the season is over. I'll post any results I get if I can find volunteers over the summer to do the studies. Thanks again.

 

Eli

[Jay-qu]

Drafting is not actually allowed in the races I have done (triathlons - in the biking leg) you can be disqualified after 1 warning - you have to be careful to pass quickly!

 

Also drafting can also have the opposite effect - but sitting in the right spot behind someone you can actually reduce the turbulence they create and hence reduce the drag they experience.

 

Reverse Drafting - Why Sometimes The Leader Of The Pack Has Less Drag

[CraigD]

Also drafting can also have the opposite effect - but sitting in the right spot behind someone you can actually reduce the turbulence they create and hence reduce the drag they experience.

 

Reverse Drafting - Why Sometimes The Leader Of The Pack Has Less Drag

Interesting link! ;)

 

However, the article is about the drag of very small poles with flapping flags attached to them, which are dominated by unusual, “flappy”, drag, not mostly rigid bodies like cars, bicycles and bicyclists, or runners, which are dominated by drag due to their cross-sectional area. For these latter kinds of objects, all the data I’ve read indicates that the body being drafted always requires more power to maintain speed than the body drafting it, although the lead body may experience a slight reduction in drag due to a reduction in turbulent airflow behind it.

 

There is a maneuver, ”bump drafting”, to the best of my knowledge unique to close-wheeled car racing, where the drafting car physically pushes the lead car, allowing both vehicles to go faster than possible alone or with touch-free drafting, but this isn’t due to aerodynamics, but due to the two cars forming in effect a single vehicle with a higher power-to-drag ratio than separate.