Particle image velocimetry (PIV) and tracer lag problem

29:37>> It's kind of like when you put the the dye in animal testing to make the things show up when you look at it different areas. >> Exly. Yeah. Yeah. Because the fluid is just moving around on its own. >> But you need to be able to visualize it somehow. >> But you need to visualize it somehow. So, you're going to put some tracer thingy that's going to track where the fluid is moving. Okay? >> And it's going to be seated with these microscopic tracer particles. >> But here's here's the problem. Those tracer particles are quite big compared to the air itself. >> Okay? >> Right? The air is made out of nitrogen and oxygen. These are single molecules. The particles are made out of let's say

30:1810 the 5 10 the 10 something like that number of these. So there's going to be a particle lag. >> There's going to be the air is going to be pushing this particle and then the particle is going to move and then I'm going to image it and create this velocity field. Right? >> So there's a delta between the thing we're tracking and the thing we actually care about. >> Yes. >> Because of this scale difference. >> Yes. That's not going to matter at low low speeds. >> Matters a lot. But at Mach 5, Mach 6 now all of a sudden maybe it matters. >> That's the question. Does it matter? Right? Does at high speeds the fact that my tracer, my dust particle or whatever

30:58>> is so much larger than the fluid particles themselves, does that matter? >> Yes. >> And here's what they did. They they said "Okay >> instead of having tracer particles, I'm going to use something called krypton tagging velocytry. >> They're going to use krypton gas." Okay? and the krypton atom which is a monatomic gas because it's a noble gas it doesn't make molecules that's going