<p>Anyone done any wind tunnel work?</p>
<p>What is it like? Do you enjoy it? Was it interesting or boring?</p>
<p>I am doing wind tunnel work. I love it!</p>
<p>I am a huge fan of the fact that, in working on my wind tunnel, I get a nice healthy dose of theory while also getting my hands dirty doing all the tweaking and upgrades and modifications. I have learned almost as much practical knowledge (like pipefitting and welding and electronics and a gazillion other things) as I have theoretical, fluids-related knowledge. I originally did grad school because after seeing firsthand what jobs with just a B.S. were like, it seemed like you had to either do field/floor work OR you did theoretical/design work, but never both. Seems like I made the right choice.</p>
<p>Right now a typical day for me consists of about half a day of troubleshooting our tunnel (it is currently not starting up because somewhere we must have a leak and it is keeping us from getting the mass flow we need) and half the day either designing/building new equipment for the lab to help us in our endeavor. For a short-duration tunnel like mine, there is a lot more time spent crunching the data than actually running since we can only run for a maximum of 60 seconds, and if we let it run that long, it takes hours to refill our tanks for another run. For that reason we usually keep it to 5 to 10 second runs. Once our tunnel gets working 100% again we will be doing longer runs. Our tunnel is designed to study turbulent transition in hypersonic boundary layers, particularly as it pertains to atmospheric reentry and hypersonic flight. It is a lot more specialized than some of the larger tunnels, so there are only 2 or 3 of us that work on it.</p>
<p>For a long-duration tunnel (like the large, slow ones) you can run continuously, so you often have a larger staff so that you can run and analyze pretty much constantly. For such tunnels, and especially those out in the industrial world (as opposed to academia), the roles of employees are more specialized. It seems like it is more common there to have one guy who specializes in tweaking the force balance and one guy who specializes in PIV rather than a handful of guys who can do it all. For instance, there is a 7’ x 10’ wind tunnel in the adjoining building to my own that runs almost nonstop (except when they have to retool it for different kinds of data-taking) doing contracted commercial work. They have done everything from scale-model testing of the Shuttle Carrier Craft to the aerodynamics of Lance Armstrong (he routinely came in and sat in the tunnel to get data for his bike designer) to anything else in between.</p>
<p>I would imagine that you could find people that could describe the working conditions where they work in just about any different way, but it seems that the common denominator is that you get to do data analysis and theoretical work alongside getting your hands dirty. I haven’t met any engineers who work in a wind tunnel that didn’t do plenty of both.</p>
<p>I don’t really know what else to say. If you have any more specific questions or anything I would be happy to help.</p>
<p>“…we can only run for a maximum of 60 seconds, and if we let it run that long, it takes hours to refill our tanks for another run.”</p>
<p>Haskel pump?</p>
<p>“Our tunnel is designed to study turbulent transition in hypersonic boundary layers, particularly as it pertains to atmospheric reentry and hypersonic flight.”</p>
<p>Cool. There is a recent Phd at my work who did his research in a very similar field at UMich. I’ve never done any viscous effects on compressible/reacting flows. I just finished working with a turbulent water tunnel though. We were more concerned about momentum thickness rather than boundary layers though…</p>
<p>Glad there are real tech-ies on this forum.</p>
<p>Question: What mach numbers are you running at? Are you running a high expansion with an ejector outlet to get a lower reservoir pressure? Don’t you need to have some pretty massive heat exchangers to get your free-stream conditions right (i.e., high stagnation temp)? I’m quite interested…</p>
<p>It takes so long to refill partially because we have two massive compressors but one of them is down right now. I really haven’t worked with the compressors much so I don’t know their specs. I know that they our reservoir is keep at 2400 psi and takes about 60 seconds to fully discharge, but I don’t feel like doing the math to figure out its volume right now, haha.</p>
<p>We run at rought Mach 5.95-ish. We usually just say Mach 6 because it is easier. The tunnel itself draws just a fraction of a kg/s through the nozzle, but we do have a two-stage ejector set up outside that blows about 20 kg/s through it and pulls the diffuser pressure down to about 3 torr give or take. As for the temps, we have some massive heating units out side that we preheat with (again, I don’t really know the specs on them since I haven’t worked with them much) and we preheat the air as well as the settling chamber. We can actually usually get it to start up just fine without any preheating though (when we don’t have a phantom problem like we do now). However, the real value of this tunnel is that it runs quiet. There is 100% laminar flow through the test section, and we CAN’T get that to happen without preheating. When we preheat, we usually bring it up to around 400 C, though we can play around with it.</p>
<p>The quiet flow itself is generated through the combination of that preheating and a few unique design features. Just before the throat, we have an annular slot that can be adjusted for size that bleeds off the existing turbulent boundary layer just before the expansion and lets a brand new, laminar layer form. The nozzle itself is highly polished nickel that was electroplated onto a mandrel to get a near perfect finish and is shaped so as to minimize a lot of the noise generated at the wall. You end up with a quiet flow core that is something like 6 inches in diameter and shaped like two cones butted up to each other end to end ( <> ). Because of all that, we can’t run PIV or LDV or anything like that so we have to do everything with hot wires, which is kind of a pain, but there are some very interesting results that we can get once we get it up and running again.</p>
<p>Just to add, you can find a lot more detail here:
[NASA</a> Langley Mach 6 Quiet Tunnel | The National Center for Hypersonic Laminar-Turbulent Transition](<a href=“http://hypersonics.tamu.edu/facilities/info/nasa-langley_mach_6_quiet_tunnel/]NASA”>http://hypersonics.tamu.edu/facilities/info/nasa-langley_mach_6_quiet_tunnel/)</p>
<p>I should have thought of that before.</p>
<p>Working with wind tunnels can be fun. They come in all shapes and sizes and are used for a lot of stuff. Some industrial application, some academics, but its tough to just generalize all wind tunnels since they are so very different from each other. </p>
<p>I’m in a lab that has continuous 4 wind tunnels for basic turbulence experiments, 1 for really high Reynolds number turbulence, a couple supersonic tunnels and a hypersonic tunnels. If you have any specific questions feel free to ask</p>
<p>But, why would you want to work in a wind tunnel when you can work in a water channel? :)</p>
<p>haha, vienna, I find it funny how you have the very high Re tunnel while I have a tunnel that strives to get as low of a Re as possible.</p>
<p>Thanks guys.</p>
<p>While I’m working tons of overtime on the program that I’m currently on, the program will be wrapping up at the end of the year and I’ll have to do some internal job hunting to find a new program. One of the common ones that my coworkers move to is our wind tunnel and I’m trying to see what it’s like. Bonehead answered my questions pretty well.</p>
<p>Basically, I’d be the engineer that represents the lab to the aerodynamics engineer. I’d work with them to plan and coordinate the various wind tunnel experiments and also design necessary tooling and fixturing needed to create the right test conditions. Because it’s at a industry setting rather than academic, the tests are large scale and involve lots of people so it’s not like I’d actually play around with the tunnel. I’d do test planning and coordination. Still, it’s wind tunnel work and might be interesting.</p>
<p>Is the low Re number for your hypersonic tunnel or another one? We really have tunnels to cover all spectrums of the regime. We actually do some really low Re stuff in tanks of oil as well. We’re down in the Re = 0.001 range for those.</p>
<p>We are trying to keep low Re (relatively speaking) in addition to quiet flow in one of our hypersonic tunnels so as to avoid transition. it is still a ridiculously high Re given that it is moving at Mach 6, but we do everything we can to keep it from transitioning as long as possible. We want it to transition on the model, not before it.</p>
<p>Gotcha. I saw you said you were doing hot-wire stuff so I realized it couldn’t be too low. I think about 75% of our lab does hot-wire work and the rest do PIV, some do both.</p>
<p>Yeah, the finish on our nozzle is so imperative to its functioning that sending PIV seed particles through it would potentially scratch it up, and even a 50 nm scratch is enough to create tiny vortices that will get magnified at such high Mach numbers and completely destroy what we are trying to do. Hot wires and IR thermography are our only options.</p>
<p>Well good luck! I know the guys doing work in our hypersonic facilities are constantly fighting with the compressors, so I feel your frustration</p>
<p>I wish we knew what we were fighting with right now. We just upgraded our infrastructure and now the tunnel magically doesn’t start, so we’ve spent the last 2 1/2 months walking step by step through the possible causes. We have fixed some problems only to find more. We got so frustrated we even welded a hammer union shut to stop a leak, knowing that that wasn’t the problem, haha. There are only a few things left that it could be though…</p>