How Does A NASCAR Wind Tunnel ACTUALLY Work? Behind The Scenes in an Official Testing Facility!

If you're a gear head like me, you probably heard a lot about wind tunnels. It comes up in conversation all the time, whether it's race teams or OEM manufacturers doing fuel mileage testing. Well, have you ever wondered how they actually work? How do you build one? What's inside them? How do they measure these things that are so important? I realized the other day that I had all these questions and no answers to them. So, we found a wind tunnel and we're going to go check it out. My name is Gary Akre and I am the designer and owner of the Aerodine wind tunnel here in Morsville, North Carolina. uh where we do almost exclusively NASCAR testing both NASCAR the organization and also the individual teams that race for NASCAR. Behind me is is the machine itself uh which is an open style open return as in an Eiffel style wind tunnel uh which means that the important part is the red the blue and the red and then the huge warehouse simply allows the air to recirculate back into the front. When you say what is a wind tunnel? Uh it is essentially just a machine that blows air on an object and very very accurately measures the effect of that air. So you say okay how do I design a wind tunnel? Well first you tell me what it is you want to test. If it's an airplane it's going to be a very very large wind tunnel and it's going to have very high speeds. If it's a golf ball it can be a very small wind tunnel and perhaps the speeds can be a little lower. Uh in this case, since we're designing for a NASCAR car, uh the center section, which is the test section, is the most critical part. So, you design the test section to be the right size. It's got to be small enough to allow a lot of speed as the air accelerates in, but it's got to be large enough that these walls don't restrict the air flow as it's flowing around the car. So, it's a balancing act. So once you've done that, once you've got the right shape of the test section and you've got a car parked in there, you have to have that air entering smoothly. That's the function of the contraction, which is the blue portion. It starts off with a 4:1 contraction and smoothly accelerates the air flow to get it up to about, in our case, 130 mph. And then as it goes through the test section and it empties out in the diffuser, that diffuser is slowing down the air in a very uniform manner. So it's not about quality of the air flow, but it's about recovering all that energy that you've put into the air because we've got 2400 horsepower that we're putting into that air. And we would like to recover as much of that as possible. If we don't, we would have to have 5 or 6,000 horsepower to do the same job. The other thing is you don't see any fans in the front. The fans are all at the rear for a very simple reason. Air coming off the fans is really a turbulent mess. You don't want a turbulent mess coming into the test section for this car. You want the air to be very smooth and very uniform. So, if you put the fans in the back, you're sucking the air through the honeycomb and then it is very smooth and very well defined when it hits the car. And that's how you can measure it with that precision. The turbulence doesn't really do you a lot of good when you're in the testing phase. Yes, there is turbulence out on the racetrack and that's unavoidable, but the turbulence is a big variable. We don't want large scale turbulence because you never get the same answer twice. This kind of works like a carburetor. Was that the venturi effect? How it in a sense? Although it's interesting you say that. Yes, you could kind of describe it as a ventury, but it's ex it's exactly the opposite reason that we have a ventury in a carburetor. A ventury is designed to generate a low pressure to suck the fuel up into the carburetor. We're not about uh generating low pressures, but we are about generating high velocities. Now, the two are related. As the velocity goes up, the pressure goes down, but we really aren't designing it to get a low pressure. We're designing it to get a very high speed. So it's kind of opposite ends of of getting the same effect. But yes, it is a contraction, a small section, and then an expansion. So in that regard, it is similar to a venturi, just not the same function. So that stuff is interesting to me. Like all the we're going to get in all the like boundary layers and you know those kinds of things. That's kind of stuff that I want to learn about and how you measure it, I guess. Sure. Well, we could start off. We could just walk around here and talk about the uh the contraction. It it looks very uh solid until you're actually looking into it. It's really just very thick metal honeycomb. And of course, the honeycomb is here to straighten up the air as it's turning this corner and making a 180° turn. Uh it's coming into here. And we want all the air to be very uniform. If you look at the shape, it's got kind of a hemispherical design to it. And that is because each one of these planes of honeycomb are pointed at where the front of the car would be. Think of it like a lens that is focusing the light. In this case, you can think of this as kind of a aerodynamic lens. It's focusing the air to get it all to come in at the right angles. This is kind of like the stuff that you find in intake tubes of cars in front of the mass air flow sensor. Yes. Yes. For the same reason. Yes. You want to straighten out the air and make it as uniform as you can. In our case, you know, a vector has length and direction. So, every particle of air is a vector. So, if you looked at this thing as a field, you'd want every molecule of air to be coming in at the right angle and at the right speed. And this uh honeycomb controls the angle. Um the fact that we've got the 4:1 contraction ratio that helps unify the speed as it's accelerating coming downstream from the face of this to the uh test area. Now since it's a 4:1 contraction, the air flow here is running at around 35 m an hour. So you could stand in front of it and you'd feel a pretty good suction, but it's not uncontrolled. And then as soon as you get into there, obviously it speeds up. The last thing I want to mention is you've heard several times now about 130 mph. You say, "Well, gee, these cars are capable of running over 200, but you have to be very careful. Sure, we can build a wind tunnel and other people have built wind tunnels that run 180 to 200 mph, and that's great. The issue is that it takes a tremendous amount more power and more capital to build a big wind tunnel that does that. The question is, do you really need that?" Well, that depends. uh in most cases when you're trying to measure the aerodynamics of a certain object as the speeds are too low, it's not really a legitimate it's not qualitatively the same air flow. But once you get up to a certain number, uh a certain percentage of the full speed, uh all of the uh qualities of the air tend to straighten out. It's called the Reynolds number. And so, um, essentially we've determined experimentally that the shape of the car, a full-sized car, probably has all these qualifying or quality air flow issues pretty well sorted out once you get on the north side of 100 miles an hour. And so, from there, it's simply scaling the the numbers up and down. So, we take the 130 mph air and scale it up in force to what it would be at 200 mph like you were running at Tallaladega. And it usually works pretty well. Horsepower required goes up with the cube of velocity. So, if you are running twice as fast, it requires eight times as much horsepower to generate that speed. So again, that's a big uh emphasis of why you really don't want to run any faster than you need to for testing purposes to try to save energy, save money, and even the forces and everything. You're going to have to have a wind tunnel that is got more reinforcements in it and everything to generate that 200 mph. When you built this, did you have to calculate the size of the building that it was being put in as a part of the airflow measure inside? Let me tell you, uh the when you have an engineering staff of one, that's me. Uh it's amazing the number of things you have to go through. Uh I have always used Excel uh the the spread sheet program Excel uh as a tool as a as a screwdriver, a hammer, and a wrench on how to calculate things. It's very powerful. And so I went through and I had a spreadsheet that said, "Okay, here's the expansion or contraction ratio. Uh here's the test section speed. Here are how many fans. Here's the fan performance map. Here's the diffuser angle. And here's the efficiencies and all this stuff went into a rather large spreadsheet so that every time you change one number say what if I use 12 fans instead of 24 fans blah blah blah everything changes. And when I got all done and I said okay this is a design that meets the requirements for air speed and energy and so on and so forth. I wound up with the design. Now it's not magic. I had to put all these parameters into the Excel spreadsheet. But when it was all done, the XEL Excel spreadsheet had an entire map of the dimensions of this tunnel. I mean, as in dots really, uh, three-dimensional dots. And so this I do not have a single CAD drawing of this wind tunnel. I have an Excel spreadsheet that has an entire cloud of 3D dots that essentially shaped what this wind tunnel was going to be designed. Remember that the computer did not design that or shape it. It simply was marching to my orders of of the parameters and everything. But the bottom line was I have all these three-dimensional points in space. You connect the dots just like you did when you're a little kid with the coloring book. And that's the size and shape of the wind tunnel. And that included how big this outer building had to be, what the velocities were going to be because the recirculation velocities are only 10 to 15 m an hour. That's what allows the building to be, if you pardon the expression, kind of crude. You see exposed I-beams and everything. But when the air is only flowing 10 m an hour, you don't have to be particularly careful about streamlining everything. When it's running 130 mph, you better be very careful about how you streamline things. What is it actually made out of? berserk cuz there's not like a you can't just go on Google like how to build a wind tunnel. What What did you choose to Okay. Well, let me start. Let me let me do Let's do this right here. When you're building a race car, an airplane, or a rocket, it better be very, very lightweight. It better be made out of whatever materials you have at your disposal, carbon fiber, titanium, etc., etc. Wind tunnels are great big machines bolted to the earth. And even though there have been examples of people using high tech materials and once in a while it may be necessary but mo for the most part this wind tunnel is just a very big channel that's controlling the airflow. So using a lot of very expensive materials is not only unnecessary but you have to remember we did not have a big budget and uh it took us a while to get the financing even with all the money we brought up front and all the people the grassroots level people who were helpful in in making this thing happen. It still came down to we had to be absolutely as economical as possible. We didn't build this thing out of high-tech materials um for a very specific reason. It's the reason that your car is not built out of titanium. Uh it would cost 200,000, half a million, I don't know what, but you build it out of the materials you need to to get the job done. So, we actually had some of the race teams laugh and say, "Gee, it looks like you went to to Lowe's home improvement uh to to get your building materials." And the answer is, well, actually, we did some of our materials. The floor is concrete. That probably doesn't surprise you. The I-beams are all steel because whether they weigh 1 ton or 10 tons makes no difference whatsoever. So the the the bigger skeleton is all I beams and then the smaller skeleton within the I-beams is all wooden spars. You know, this construction is really no different than than say the floor of your house where you have all of the runners and you apply the floor. In this case, we had to cut all of the ply or all of the uh 2 by six's at a with a curve built into it. And then we laid the plywood onto the curved spars of wood and that shaped not only the contraction, but the diffuser as well. Now, inside the wind tunnel, we'll get into the test section. That is a little bit different material. I wouldn't say it's high tech, but it's a it's a different uh design and a different material than what you might expect. It's not using a lot of wood or even metal in this case. Where did you learn all this stuff? Well, I went to General Motors Institute. I'm a gear head. I actually uh got my degree in engine design and thermodynamics. So, I thought I was going to spend my whole career building engines and uh understanding crankshafts and cams and heads and all that. Uh, one year out of school I got the opportunity to get into aerodynamics. I said, "Well, gee, at General Motors, there probably have to be a thousand engineers that are working on engines. There were only seven that were working on aerodynamics." So, I said, "I think I like my odds there." So, uh, I joined the Aerrow Group in 1977. Uh, the GM wind tunnel at the tech center in Warren, Michigan was finished in 1980. Uh before that I had traveled to the Lockheed wind tunnel, to the Caltech wind tunnel in Pasadena, to the NRC wind tunnel up in Ottawa, Canada. Um so here I am at GM and in 1981 um a funny looking uh production car which was really just a stock car from NASCAR came in and so I got the opportunity to start testing that. That was 81. So I became the uh stock car specialist for General Motors for all of the brands. Um, and so I did that through 1994. And in 94, Hendrickk was looking for a full-time arrow guy. And nobody in in the NASCAR business had had a full-time arrow guy yet. So they came and asked me if I was interested in moving down from uh Metro Detroit to Charlotte to work in uh as an aerodynamicist for him. Now he asked me where I where I got the information and all my education from. I had a good strong very excellent engineering background. I had one introductory course in fluid mechanics, which is not going to be enough to get you where you're going. But between what I was learning, just being self-taught, just reading books and learning things and being interested in airplanes, and then of course having a whole lot of experience in the wind tunnel and doing airplanes and the GM wind tunnel is a fantastic machine, but it's so much bigger and so much different. And it's designed for production cars, not for race cars. So I I just being an engineering geek, I'd say, gee, if I ever built a wind tunnel, it would look like this. It would do like this. It doesn't need this. It needs extra that. And so I kind of had some theories of what would make for a good wind tunnel. Like I said, when I got to Hendrickk and uh they were interested. And by the way, um I think Rick would have loved to have a wind tunnel on site. They had so many projects uh coming down the pike that the wind tunnel was simply way down the timeline. And I could see that it was going to be years before this wind tunnel was built. And I was hearing rumblings uh from other race teams about um if we didn't build a wind tunnel, maybe they should. So that was enough stimulus for me to say, "Okay, my contract's up in 01. I got to build this thing before somebody else does." So that's when I went off on my own. And uh I'd had several years of design of what would the Hendrickk wind tunnel look like. And so this was just a tweak. Uh I had to save a few more bucks because I didn't have Rick Hendrick's budget. So a lot of the things in here are different. And in fact, that could have been a problem because uh when you're not building things the way most people build things, um you have to prove that that works. And that was the beautiful thing about having racers and technical people to come and to test in our tunnel because they don't care about mirrored glass and marble floors. All they care about is the function. If the wind tunnel works, they will come back. If the wind tunnel doesn't work, they're not coming back. And I said, "Fair enough." So they came in, they tested, they liked the numbers compared to the non race car wind tunnel at Lockheed. That was in time for aircraft. The GM wind tunnel in Warren, Michigan, that was designed for production cars. The NRC wind tunnel up in Ottawa was kind of an all-purpose tunnel. Uh those tunnels are a great design, exactly what they're designed for, but their one weakness was that a good race car wind tunnel has to have very good boundary layer simulation along the floor because the race cars are very close to the ground and they depend upon this airflow under the car for a significant portion of their aerodynamics and the other wind tunnels just really weren't designed for that. So I said, "Well, I've got an advantage right there. Not because I'm smarter, but because I'm designing this for race cars. They didn't design theirs for race cars. That is interesting. We're going to get in there and see that. But I got a question about this. You got air to air intercoolers for Absolutely. What is this doing? Okay. Well, um, you know, along the way, we've had several different um modifications. The main principle for the boundary layer control has always been the same, but the details, it's kind of like the next model car that has more features than the last. So, we're on our third generation of floor. The principle always being the same. You'll see it when we get in there, but basically, we have jets of air keeping the air moving cuz the air wants to slow down and stall. That's what that's what a boundary layer is. We don't want a boundary layer, so we keep energizing it and blowing the air along there. This is the latest uh I guess you could say Gen 3 that we have a compressor in here that is uh blowing air into the floor in just a certain area which we'll look at when we get into there. This compressor uh as you probably know, anybody knows anything about turbochargers, they always add heat to the air. Always. And we don't want hot air being injected into this. So this small compressor uh and you can see these are silicone boots and everything. They're they're simply blowing the air into this. This is no different than an airto-air intercooler in a turbo. The only difference is we have the the luxury of making it big and not worrying about how big it is. So, we have these four intercoolers. We have this fan which looks like a unit that would come off the top of an AC unit outside your home. And so by having this airto-air intercooler, we're able to inject the air within 2° of ambient temperature, which means now we don't have to worry about temperature differences uh spoiling the effect of our of our jets. Is that your main air conditioning unit right there? That is one half. The other half is on the other side. That's half. Yes. How many tons is that? Uh you talking about cooling capacity? Yes. Yes. Your typical home has a four or five ton uh air conditioner. Our wind tunnel, remember this is cooling capacity, not the weight of the machine. Um our air conditioner is 250 tons of capacity. And in case you didn't know, a ton of refrigeration capacity is exactly the reason they named it that is you take one ton of ice and melt it over a 24-hour period of time. The amount of heat that it absorbs is one ton of refrigeration. 12,000 BTUs per hour. I did not know that it came from an measurement of ice melting. That is interesting. That is some serious man. Well, let me tell you, when you got 2400 horsepower plus we've got more this stuff that's all going into the floor. So, alto together we have…