JESSE: So I want to give you a little bit of time to actually talk about your PhD a little bit. Do you spend any time on Reddit at all? CHRIS: No, not at all. JESSE: Okay. Okay, so -- CHRIS: I'm familiar with Reddit, but I don't use it. JESSE: Okay. That's okay. So there's a subreddit, which is Reddit is just a forum with subforums, basically. So, I say subreddit, the subforum. So, there’s a subforum called Explain Like I'm Five. And it's basically people asking very complicated often science questions and they want it really dumb down for them. So, can you give the Explain Like I'm Five version of what combustion dynamics is and what the heck you're doing? CHRIS: Okay. So, if you've ever sat around the campfire, you'll hear this kind of roaring noise, right? Like this kind of what we'd call it as broadband noise. Basically, there's not like a tone to it. If you sing, you kind of think, okay, you know, there's typically one frequency and we call that frequency a tone. But when you have fire, it tends to-- the wrinkles in the flame tend -- I mean, when gas passes through a flame, it expands that expansion makes sound waves, acoustic waves. And we hear those as different frequencies depending on how the flame is wrinkled. So, generally speaking, a flame excites a wide range of frequencies and so it doesn't have like a particular tone. But if you think of something like a gas turbine on a plane or in a power plant, the kind of like confined geometry of those can busters acts kind of like a trumpet, where it kind of picks a tone. So, you're basically putting in this broadband noise and it's filtering that out and giving you a tone. And so what happens, once you pick a tone like that, that tone tends to resonate in that environment. And then it'll wrinkle the flame, that tone itself will then wrinkle the flame to produce more disturbances at that tone. So, this process kind of continues and it's like a self-excited feedback loop, where wrinkles in the flame excite this tone, this tone then feeds back into whatever's producing the wrinkles in the flame to generate more tones. And this is a huge problem in the gas turbine industry. I think 70% of the costs that like a power plant faces, has to do -- or a gas turbine plant has to do with repairing the hardware that's damaged by instabilities like that. So, that includes employee salaries, that includes any other law or legal expenses or anything like that. So, it does exclude their fuel costs. But like the majority of their expenses has to do with repairing damaged things that occur from these kinds of instabilities. Because, you know, you think of a trumpet, it's not that loud, but what those tones are, are pressure oscillations, and those pressure oscillations actually get so strong that they can cause the flame to move in such a way that it damages the combustion itself. JESSE: Okay. So is it the oscillations that are causing the damage or the effect on the fuel that's -- and the changing of the fuel that’s causing the damage? CHRIS: Yeah, it's complicated and it can be -- It's usually the fact that like, it pushes the flame into somewhere where a flame is not supposed to be. But basically, if you have enough pressure change, you can cause the flow to flow backwards or flow to go away faster than it normally would. So you're just kind of pushing this flame all like if you think of, you know, a candle, you thought about, you know, waving that candle around the room, without blowing out, it would find something that it wasn't supposed to be next to and it would either catch it on fire damage it somehow. So, you can kind of think of it like that, where if you're an engineer and you're designing a combustor, you're going to design a flame to go here, and you're going to design something else to go here and you know, every place, everything has its place, and these instabilities are kind of mixing that all around. And I'm sorry if I'm going -- I think I might not be explaining this as concisely as it would be nice if I could. JESSE: No, I mean, there's -- Well, especially in the like Explain Like I'm Five subreddit, there's only like so far you can dump down. You have to use things like combustor and there are certain words that you need to use. Otherwise, it doesn't even make sense anymore. CHRIS: Yeah, yeah. But basically what I study is you know, this combustion dynamics is a large part of it, but I really study the fluid mechanical part, which basically means I talked about how the flame generates these tones, and then the environment amplifies certain tones. And then I'm really interested in how do those tones then couple back with flow to wrinkle the flame in such a way that those tones are generated in the first place. JESSE: Okay. So, you're interested in essentially the second and subsequent parts of the feedback loop? CHRIS: Yeah. That's called the hydrodynamic part of the feedback loop. So, you basically induce all -- these are called ?? 5:39>, they’re little kind of wrinkles in the flow, basically. And how do those wrinkles in the flow, wrinkled the flame, and then excite those instabilities. JESSE: Okay. So how do you actually study that? Like what kind of instruments, I mean, how do you go about measuring something like that? CHRIS: So, we actually at Georgia Tech, the combustion lab here, it's a really great facility, and I am not an experimentalist, but I look at a lot of experimental data. And basically, the way you do it is you take pictures with really fancy cameras. So, basically, if you think about, if you went out on a snowy day and you took pictures really fast like with a camera, basically, you'd see snowflakes moving, right? And if you looked at two frames between those pictures of snowflakes, you can kind of say, okay, you know, I can see from this first frame, one snowflake moved from here to here. And this snowflake moved from here to here, just by looking at the difference between the two frames, right. And so if you do that on with super precise cameras and scientific instruments, you can basically do the same thing in this combustion environment where you see it with these tiny little particles, and then take really good pictures really fast, I’m talking nanosecond type speeds. And from that, you're able to, like, infer a velocity field. And so you can study how, you know, if I -- basically you just put a speaker next to it, and you turn on the speaker at different tones. And you look at how the flow behaves with different forcing, you know, like styles, different attitudes, that sort of thing. And you're able to explicitly kind of gauge this flow response. JESSE: Okay. So, this is just a curiosity, it's really a side note, it doesn't delve too deep in anything, but I'm curious like are the pictures being taken the visible spectrum or you’re working in like infrared because you're going with combustibles? Or what are you working with as far as like actually taking those snapshots? CHRIS: Yeah, so these are visible spectrum snapshots. You can change -- So typically, these are done with green lasers. Basically, if you just take really fast, high-speed pictures, there's not enough exposure for your - camera to like, see the particles. So, to generate the kind of exposure we need, we shine a really bright laser on the particles. And so those lasers are typically green for the experiments that we've been doing. I say we, but again, I'm not the one doing these experiments, I’m reading the data. JESSE: You're the figurehead right now. So I mean, it's okay. CHRIS: Right, right. Yeah, so you shine a really bright green laser at them and then you look at how those tiny particles kind of dance around in response to the different tones, you play them. JESSE: Okay. So, the particles, you know, obviously, I'm coming at this from like, I know absolutely nothing. So just treat me as a ?? 8:54>. Are the particles actually, like pre-combustion particles or post-combustion or a mixture of both or, you know, like -- CHRIS: That's a good question. They're solid particles that we kind of -- So, we kind of mix, fuel and oxidizer ?? 9:12> and those are both gaseous. And then, in addition to that sort of gaseous thing, which is actually what burns, we inject all these tiny little micrometer-sized particles or several millimeter size particles and those are what we actually see… scatters out those particles and -- JESSE: Okay. So, it’s an indicator, not the -- CHRIS: Not the - itself. Yeah, that's actually a really good point. You have to do your analysis correctly to make sure that you're using the right size and weight particles to accurately, kind of represents what the flow is doing. JESSE: Right. Because it reminds me of this British quote, it says, “It's the finger pointing to the moon, not the moon itself.” And basically like, you're not actually staring at the thing that you're studying. You're staring at the thing that's pointing to the thing. CHRIS: Yes. JESSE: Yeah. So, you can't get confused between the two because it's not exactly the same thing. CHRIS: Right. JESSE: So, it's always curious to me, like how people get to where they are. So, how do you get from being a, you know kindergartener to working on combustion dynamics? Like, you know, obviously, a truncated timeline. But I mean, how did you get interested in what you're doing? CHRIS: So an undergrad, I had an awesome professor who pulled me aside after class one day, I think sophomore year, and basically said, “What are you going to do after college?” And you know, kind of said, what I thought I was supposed to say, “Oh, you know, I'm looking for an internship now. And then I'll get a job and, you know, whatever, I'll be an engineer.” And that's that, you know, I didn't really have like a -- this was not like a lifelong goal for me. But I had that conversation with him and he invited me to join his research group and to kind of see what I thought about research. At that point, I also worked at two years for Caterpillar in my undergrad, kind of got the big company and industry experience in engineering. And I didn't really like that. So, I kind of knew I didn't really want to go on that route. But I had a really great experience working in this research environment. It's really fun. You ask questions, and you kind of -- You ask hard questions and questions that hopefully, no one else has ever asked and trying to figure out a way to answer them. And basically, I've spent the last almost five years trying to ask questions and figure out how to answer them. So, it's a really kind of cool and frustrating sometimes process, but it can be really rewarding. And I had, I guess, enough rewarding experiences in that first exposure to it to kind of convince me that this is something I'd like to do more of. And then from there, it's just a matter of writing applications. And I never really had my eye on combustion dynamics. I liked math, I did a minor in math in addition to mechanical engineering, and this is a very math heavy research area. So, that kind of set me up for it and I knew I wanted to do something where I could kind of exploit my background in math to get a head start. So, this kind of seemed like a good way to do that. But really, when I came here, I was looking at, I talked to professors who are doing modeling of brains, you know, nonlinear networks, and stuff like that. And I talked to, you know, all sorts of other people from different backgrounds. The really cool thing about science is it's a process, and you develop an expertise in the field, but what you're really working on is the process of like, how do I ask intelligent questions and design experiments that answer those questions and that sort of thing? It's problem-solving. If you enjoy solving problems, then I think it's something you can enjoy. You just got to learn how to enjoy it. JESSE: Yeah, and see that thought, like enjoying problem-solving is how I ended up being a math major. Like I decided after calculus in high school, I was like, no more math. And then I was like, oh, it's only 15 hours for math minor. And then I was like, well, it's only one more class per semester for math majors. So, I just continued for -- Like, I enjoyed the problem-solving. So, I definitely can like, empathize. I don't know that I was interested in the math just for math sake. But I definitely love the journey of like, figuring out how to do proofs and like understanding the logic behind those, you know, all these different, I'll call them systems, but different fields. It's definitely like, easy to sympathize with you. CHRIS: It’s got a parallel with triathlon too and now your goal is something that you've spent very little time achieving your goal in triathlon and in science. Most of it is in the kind of nitty-gritty daily grind. And if you're able to find a way to enjoy that, you know, daily struggle, then you can find a way. I mean, then you enjoy the whole process. JESSE: So, you're looking at, once you finish your thesis, as we're talking about before we got started, you've finished everything up, you just have your thesis to write, correct? CHRIS: Yeah, yeah, yeah. JESSE: So after you're done, you're looking at postdoctoral work to do more research in academic field, like in an institution? CHRIS: That is something that appeals to me, that is not something that I have a direct track on to at this point. Like, I mean, it very well could happen, but I've not, you know, really narrowed it down to exactly that, exactly a specific position. I don’t know. So, this semester, this past semester, I taught my first course. And that was something I really enjoyed doing. And I'd always kind of wondered if I would, I thought I would, and I did. And so I've, you know, think that an academic setting could be something I enjoy, maybe not right away, but you know, either much later on or soon later on. I think my biggest focus is going to be on getting something kind of close to home in Atlanta here because my girlfriend is going to be another two or so years in her PhD. So, I'd like to stay local. And there are a couple of prospects in this area, but nothing is set in stone yet. JESSE: Okay. I'm going to go off the deep end and this is just as a curiosity. I think I saw, I always look at people's Instagram, social media kind of stuff. I think I saw you had taken a trip to India a couple years ago? CHRIS: Yeah, I did. JESSE: So, I'm just curious, you know, I think our generation is everybody's interested in travel, but it seems like almost hyper-focused in our generation, like, we don't care about buying stuff, we just want to go places. So, I'm curious, like, why did you go to India? Like, how did you end up on India, you know, of all the places you could go instead of, you know, going and partying somewhere like ?? 16:19> ended up there? CHRIS: It was not a vacation. It was a really cool trip...ike enjoyed it a lot. But it was for my research, we have a collaborator at the Indian Institute of Science in Mangalore. And so I spent roughly three weeks I think, in his lab there working with one of his senior grad students who kind of mentored me and taught me so much. It was a great experience where it was more than 12 hours in the lab every day, just trying to soak up everything I could. But in addition to that, I got to get out and take some pictures for Instagram. So, that was fun. Went to a Hindu temple, which was interesting and got to go around and try different foods. And one of the cool things about being a triathlon, when you travel or being in triathlon when you travel is you get to go run around or try to -- I ended up not swimming or biking at all, but just to run around the city and kind of explore and that was really cool. It's so different than here. But at the same time, there's so much commonality. I think travel is a really good way to see that. And it sounds super cliche, but you go around the world expecting to see a lot of different stuff. And you know, you get there at first you think, wow, this is so different. And then you stay there a week longer and you think, wow, we're really the same. So that was my ?? 17:44> in a nutshell. JESSE: I always like if I'm anywhere new, whether I'm walking or running, I always feel like that's the best way to like explore city. Like if you're in a car things go by so quickly. You don't really get to absorb everything. So, like I definitely like to be on foot whether I'm you know, depending on how fast I'm moving, but I rather to be on foot to actually see things. CHRIS: When I was in a car in Bangalore, I was more scared to look out the window than I think -- I didn't have time to think about sightseeing or looking around. JESSE: Fair enough. So, I got one last question for you and I asked this of everybody because it's always different, and I’d love to hear what it is. So, if you only get to eat one thing for recovery for the rest of your life, what do you choose? CHRIS: It's Taco Tuesday. I gotta go tacos. JESSE: See as like Todd chose peanut butter jelly sandwich. I was like -- CHRIS: He didn't go cinnamon roll? I would have sworn -- JESSE: He did not. He did not go cinnamon roll. I gave him a hard time about that. So, you’re really eating tacos after like you go do a hard set and then you’re really eating tacos afterwards? CHRIS: I love tacos. Yeah, I'm going to go home and have tacos after this. JESSE: Great. Hey, I'm glad you're consistent, Chris. I appreciate your time today. I'll let you go and you can go get some tacos. CHRIS: Thank you very much. JESSE: Thanks for coming on. Go to Part 1Go to Part 2
