ENDLESS PROCRASTINATION
My last post entitled “a cool picture” is an image of a bullet moving through some fluid medium at somewhat high velocity. I took the liberty of doing a reasonable simulation of this event. I did this for almost no reason other than as a challenge to myself and as what can only be described as my ability to endlessly procrastinate my OP. I show images of said simulation below.
For those of you that are interested, this simulation was done in Fluent (which I loathe but it makes simulations like this really simple). Done with a density based 2D implicit solver formulation with steady time steps. Energy equation included, base temperature is 300K. K-epsilon “Realizable” 2 equation model of turbulence with standard model constants and wall functions. No treatment of surface roughness. Far field boundaries were used to constrain the simulation, though they are not visible here. I assumed a 9mm bullet. The dimensions of the bullet I roughly approxiated by looking at the original picture.
Here we see the velocity profile of a the flow in air, max velocity (and mean speed of the bullet) is about 1000 m/s, which is somewhere between mach 2 and 3 (closer to 3). There wasn’t much of a reason for me to look at this type of bullet moving this fast, but I did it anyway. Certainly this velocity is possible depending on the gun.
Here is a turbulent intensity plot which, when you compare to the original image, is pretty interesting. Note this simulation here is done at lower velocity (just over mach 1) from the previous image. I won’t explain why, but the idealized description of air used here doesn’t translate particularly well to a dense fluid like water, and would require a lot more work than I’m willing to put in to get right. So, just believe me when I tell you this is (sort of) legit. Note that in air, the turbulent intensity wouldn’t look at all like this at 1000 m/s.
seriously… I would be amazed but I know this is what you do for fun.
most impressive form of procrastination I have seen from you yet. But honestly, what kind of a scientist are you if you don’t even make the numbers in your figures legible?
they’re scaled images for the width of the site … click on them.
Hello, Anthony.
I think you have been watching too much “Numbers” about the mathematical sleuthing team.
Come down to Indianapolis sometime to see the exhibit at the Indianapolis Museum of Art (IMA) from the Louvre. I think it is mostly Roman and Greek antiquities, but I have not been yet. We will buy you a dinner at Puck’s, the restaurant in the museum. Miss you.
Mrs. Fisch
Definitely will come down to Indy as soon as I finish my OP on the 2nd of November. I have, in fact, seen a bunch of numbers. The CSI of math, really. It’s suprisingly entertaining … Most chemists can’t watch CSI and most mathematicians can’t watch numbers. I appear to be able to watch both. Maybe I’m neither. I definitely enjoy mocking the show when (numerous) inaccuracies or completely misleading scenes appear in each episode.
Sorry to post like this, I couldn’t find an email contact
I was excited to find your blog. It looks like you are based in Chicago. I am part of a new radio station called vocalo.org. It airs radio live on 89.5 in Northwest Indiana and streams off the website. We are building a strong listenership. We would love podcasters and bloggers like you to add their stories, original music, and audio to the site. I would advise doing it in smaller clips, instead of entire shows, because it makes it easier for our host to put it on air. It’s a great way to get new people to hear your voice, and possibly start visiting your podcast. You can also just type text or read text for broadcasting.
Once you have a clip on the site, be sure to direct your friends and listeners there to hear you. You retain all ownership of the material you post (unlike some social networking sites).
I look forward to hearing your work on vocalo.org. Please email me at shannon@vocalo.org if you have any questions.
Shannon
So I looked around a bit and it turns out that 1000m/s is about 3 times faster than a normal 9mm bullet travels coming out of the muzzle. That is more the speed of a rifle bullet like a .223 or a .30-06.
Also your bullet has a completely flat bottom. Which apparently creates a lot of drag lowering the “ballistic coefficient.” The answer to that is “boat tailing” the bullet. Or adding a slope back in after the “tail.” This can be seen here with these high accuracy bullets. It makes sense looking at your turbulent intensity plot. Do you have a second to run it with a “boat tail” projectile?
i know it’s too fast … i noted that. however the original experiment was done in a liquid, which is WAY harder to do this kind of simulation with (damn near impossible). i can run a boat tail at some point. it’ll be interesting …
i definitely don’t think that was a 9mm bullet. there is no reason for that type of shock structure unless the bullet was moving a LOT faster, especially in water.
ac;
Fair enough I just wanted to see how much the boat tail changed things (especially at the high speed). Thats probably most interesting from the engineering side of things.