Neat experiements involving arrows and liquid nitrogen

[James Park]

Check out:
http://www.anu.edu.au/Physics/aldir/publications/Houwing_JSWS_1999.pdf
This covers investigation of boundary layer separation of an arrow in flight (that is: where does the flow change from laminar to turbulent, and other rather neat things). To investigate the effect of temperature, the investigators cooled some of the arrows down using liquid nitrogen prior to shooting them. While the paper has quite an amount of maths, it also has some real neat pictures of arrows in flight.

[CMB50]

There were lots of pretty colors on page 5 :Fade-color ....and a flat zebra on page 2, but other than that..... i didn't understand a damn thing! :infinity:

[Clare Barnes]

There were lots of pretty colors on page 5 :Fade-color ....and a flat zebra on page 2, but other than that..... i didn't understand a damn thing! :infinity:

Or you could just create a great pink zebra by combining your page 2 flat zebra with the colour from Figure 4 on page 4 .... :D

[CMB50]

Yeah, i probably could, but that would require opening photoshop, and we know how tedious that can be!
I'm just going to sit here and appreciate the big pink flat zebra in my head. :D

[James Park]

A useful thing from my point of view is that the Reynold's Numbers they calculate match up with my modelling quite well (which helps in the drag calculations for arrows).

[Flehrad]

You know what Jim?
I actually thought of that idea myself early last year when I was playing with LN02 at uni, but my friends thought I was nuts using liquid nitro on arrows, they figured they'd shatter on impact or something :D

Having a good grounding in physics, I thought that cooling them down would have made a difference on flight, as well as heat damage from friction in the target, and prevent rubbish being "burnt" on the arrows :P

[James Park]

It was in fact an astute observation by the ever-alert Zoe that brought this paper to my attention.

[2Dogs]

I knew she was a nerd........ :lol: but that really is into "Super" nerd status :o

[James Park]

It strikes me that being the archer in these experiments would have its interesting side:
- how do you load an arrow that has been cooled to liquid Nitrogen temperatures? Wear gloves I guess.
- do you get any material property changes in Aluminium at that temperature? For example, does its brittleness change and could they become dangerous to shoot? Maybe DrRalph or Flehrad would know this?

[Marcus]

Good question. To find out I propose that Siemens provide us for testing:
4 doz X7's
4 doz Cartels
4 doz X10's with Tungstun points
4 dox CXL's
1 Hoyt ProElite
1 PSE Primos
1 Mathews Ovation
1 Hooter Shooter

It is vital that we do the testing to make sure this research is indead correct and repeatable.

[Flehrad]

It's quite easy to load an arrow that has been submerged into liquid nitrogen, as you only have to hold it by the nock. But it's not the part that you freezing your fingers on the arrow that you have to worry about, but with body temp on the arrows warming it back up. The contact of +37C with something at -170C might stick your finger on for a short time, but, it'd more likely warm it quickly.

The properties of Alum would be expected to be definately a lot more brittle, but most likely not to a shatter point, more likely to be a snap point.
However, concerns would then arise in the spine. If the alum becomes stiffer due to the temp change, then the spine rating would go out of whack....

Though I have no idea what it would do to carbon fibres.

[DrRalph]

A useful thing from my point of view is that the Reynold's Numbers they calculate match up with my modelling quite well (which helps in the drag calculations for arrows).

They quote a unit Reynolds number of 2.73x10^6, and then go on to assume the critical dimension is the arrow diameter (8mm), giving a Re of only 2.19x10^4, much lower than the transition of ~3x10^5, ie laminar flow should result. They observe the layer is likely to be turbulent everywhere despite this, even in the first 100mm or so where even taking the shaft length as the critical dimension it should still be laminar.

They suggest the tip is the culprit for flow separation, but I wonder if the LN cooled arrow became covered in tiny ice crystals that encouraged a flow separation, effectively roughening the surface.

BTW I suspect that the matrix in carbon fibre arrows would become very brittle if cooled to LN temps. I also agree with Flehrad, in any case it should affect the spine.