Defining a Wind Tunnel and Sizing Considerations

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