1 00:00:00,000 --> 00:00:05,720 Why are patterns important in determining drag? 2 00:00:05,720 --> 00:00:09,560 What algebraic relationship shows that a car has drag? 3 00:00:09,560 --> 00:00:14,080 Explain the relationship between pressure and glow. 4 00:00:14,080 --> 00:00:16,360 This is one of NASA Langley's many wind tunnels. 5 00:00:16,360 --> 00:00:19,840 It's called the Basic Aerodynamics Research Tunnel, or BART for short. 6 00:00:19,840 --> 00:00:23,720 Engineers like me use the BART in a technique called flow visualization to try 7 00:00:23,720 --> 00:00:26,120 to understand how the air flows around aircraft. 8 00:00:26,120 --> 00:00:28,340 By looking at or visualizing the airflow, 9 00:00:28,340 --> 00:00:30,540 we can help aircraft designers create new shapes 10 00:00:30,540 --> 00:00:33,220 that are more aerodynamic and produce less drag. 11 00:00:33,220 --> 00:00:35,380 Drag slows down a vehicle or an object, 12 00:00:35,380 --> 00:00:38,340 as you observed in the activity you just conducted. 13 00:00:38,340 --> 00:00:42,900 Recently, NASA Langley used its experience in testing and simulating aircraft 14 00:00:42,900 --> 00:00:48,420 to help a car manufacturer visualize and describe the airflow over one of its automobiles. 15 00:00:48,420 --> 00:00:52,340 What we as engineers would really like to see is the air flowing continuously from the front 16 00:00:52,340 --> 00:00:55,500 of the car to the back of the car, like the flow over this cylinder. 17 00:00:55,500 --> 00:00:58,460 There's no interruption in the airflow and there is no drag. 18 00:00:58,460 --> 00:01:01,420 Unfortunately, this is not how things work in real life, 19 00:01:01,420 --> 00:01:04,100 so we have to make airplanes and cars streamlined. 20 00:01:04,100 --> 00:01:07,340 This particular automobile is streamlined, which means it was designed 21 00:01:07,340 --> 00:01:09,820 to offer minimal resistance to airflow. 22 00:01:09,820 --> 00:01:12,980 Because of its shape, this car has little drag. 23 00:01:12,980 --> 00:01:14,900 You know, that sounds like our activity. 24 00:01:14,900 --> 00:01:17,460 The tetrahedron had the lowest drag because of its shape. 25 00:01:17,460 --> 00:01:18,100 That's right. 26 00:01:18,100 --> 00:01:22,020 The shape of airplanes and cars is mainly determined by aerodynamics and safety. 27 00:01:22,020 --> 00:01:24,980 However, a car has additional factors that may affect its shape. 28 00:01:25,260 --> 00:01:29,380 The vehicle must look good for people to buy it, the passengers must be comfortable, 29 00:01:29,380 --> 00:01:33,260 and the vehicle must be able to transport people, cargo, or both. 30 00:01:33,260 --> 00:01:38,340 With this in mind, automotive engineers used geometry to design cars with one of three shapes, 31 00:01:38,340 --> 00:01:41,540 a hatchback, a squareback, or a notchback. 32 00:01:41,540 --> 00:01:45,420 Which of the three shapes do you think would have the highest drag? 33 00:01:45,420 --> 00:01:47,940 Looks like the notchback has the most drag. 34 00:01:47,940 --> 00:01:48,420 You're right. 35 00:01:48,420 --> 00:01:51,380 After deciding on the shape to test, we created a scale model 36 00:01:51,380 --> 00:01:54,260 of a typical passenger vehicle with a notchback design. 37 00:01:54,300 --> 00:01:58,460 To visualize and measure the airflow around this model, we used the BART and materials 38 00:01:58,460 --> 00:02:03,060 like kerosene and titanium dioxide, a white powdery substance used in paint. 39 00:02:03,060 --> 00:02:07,260 Visualizing the airflow provides a picture of how the air moves around the vehicle. 40 00:02:07,260 --> 00:02:10,140 Okay, so how do you visualize airflow? 41 00:02:10,140 --> 00:02:12,900 You can't really see air, can you? 42 00:02:12,900 --> 00:02:14,540 No, you can, and that's a good question. 43 00:02:14,540 --> 00:02:17,580 Without special materials, you really can't see air flowing. 44 00:02:17,580 --> 00:02:22,260 So we mixed titanium dioxide and kerosene together and applied it to the surface of the model. 45 00:02:22,260 --> 00:02:24,940 We turned on the wind tunnel, and as air flowed over the model, 46 00:02:24,940 --> 00:02:28,140 the kerosene evaporated or turned into a gas. 47 00:02:28,140 --> 00:02:31,940 The titanium dioxide left on the surface shows us an airflow pattern. 48 00:02:31,940 --> 00:02:35,420 This pattern tells us how the air is moving close to the surface. 49 00:02:35,420 --> 00:02:40,140 The measurements we collect allow us to describe the air's properties in motion with numbers. 50 00:02:40,140 --> 00:02:43,100 Luther, that looks really cool, you know, but what does this pattern say 51 00:02:43,100 --> 00:02:45,700 about the shape of the car and the drag it produces? 52 00:02:45,700 --> 00:02:48,940 Well, this pattern tells us that the air is actually traveling in the same direction 53 00:02:48,940 --> 00:02:51,900 as the car, or in other words, towards the back window. 54 00:02:51,940 --> 00:02:53,660 This is called reverse flow. 55 00:02:53,660 --> 00:02:58,220 Reverse flow creates low pressures on the back of the vehicle, which increases drag. 56 00:02:58,220 --> 00:02:59,740 Remember this drawing? 57 00:02:59,740 --> 00:03:03,980 See how the air flows smoothly over the cylinder and comes together again in the back? 58 00:03:03,980 --> 00:03:08,180 Although this isn't how things work in the real world, the air pressure in the front, 59 00:03:08,180 --> 00:03:12,780 PF, is the same or equal to the pressure in the back, PB. 60 00:03:12,780 --> 00:03:16,980 When the pressure in the front is equal to the pressure in the back, then there is no drag. 61 00:03:16,980 --> 00:03:19,300 However, look at our notchback model. 62 00:03:19,300 --> 00:03:23,020 See how the air flow separates at the back of the vehicle and the air actually begins 63 00:03:23,020 --> 00:03:24,860 to flow in the reverse direction? 64 00:03:24,860 --> 00:03:27,020 This is reverse flow, and the pressure in the front 65 00:03:27,020 --> 00:03:29,900 of the model is greater than the pressure in the back. 66 00:03:29,900 --> 00:03:34,620 When the pressure in the front is greater than the pressure in the back, you have drag. 67 00:03:34,620 --> 00:03:38,060 Flow visualization helps us understand how the air flows over the model, 68 00:03:38,060 --> 00:03:41,740 but in order to measure the pressures on the surface, we had to use additional techniques. 69 00:03:41,740 --> 00:03:44,660 The most exciting is probably pressure-sensitive paint. 70 00:03:44,660 --> 00:03:48,420 In addition to NASA Langley, NASA Glenn Research Center in Ohio, 71 00:03:48,420 --> 00:03:52,700 and NASA Ames Research Center in California use pressure-sensitive paint 72 00:03:52,700 --> 00:03:54,220 in their wind tunnel tests. 73 00:03:54,220 --> 00:04:00,060 Pressure-sensitive paint, or PSP, is a special paint that glows when exposed to blue light. 74 00:04:00,060 --> 00:04:05,100 The glow is really due to special molecules embedded in the paint called luminophores. 75 00:04:05,100 --> 00:04:06,540 Luminophores. 76 00:04:06,540 --> 00:04:09,020 Sounds like a word that comes from illuminate. 77 00:04:09,020 --> 00:04:09,580 That's right. 78 00:04:09,580 --> 00:04:13,300 These luminophores are excited or given excess energy by the blue light. 79 00:04:13,300 --> 00:04:17,620 The luminophores don't like to have excess energy, so they get rid of it by either glowing 80 00:04:17,620 --> 00:04:20,420 or by bumping into nearby oxygen molecules. 81 00:04:20,420 --> 00:04:24,300 The behavior of the luminophores allows us to see a relationship between the brightness 82 00:04:24,300 --> 00:04:27,740 of their glow and the pressure on the surface. 83 00:04:27,740 --> 00:04:29,380 A relationship. 84 00:04:29,380 --> 00:04:30,580 Sounds like algebra. 85 00:04:30,580 --> 00:04:31,220 That's right. 86 00:04:31,220 --> 00:04:33,060 I use algebra in my work every day. 87 00:04:33,060 --> 00:04:34,020 Let me show you. 88 00:04:34,020 --> 00:04:37,780 Remember when I said that the behavior of the luminophores allows us to relate the brightness 89 00:04:37,780 --> 00:04:40,140 of the glow to the pressure on the surface? 90 00:04:40,140 --> 00:04:42,580 This is done using a graph like this. 91 00:04:42,580 --> 00:04:46,900 The curve on the graph shows an inverse relationship between pressure and glow. 92 00:04:46,940 --> 00:04:49,980 When glow increases, we know the pressure has decreased. 93 00:04:49,980 --> 00:04:53,540 But when glow decreases, we know the pressure has increased. 94 00:04:53,540 --> 00:04:58,060 This inverse relationship can be represented with the following algebraic equation. 95 00:04:58,060 --> 00:05:03,140 Pressure equals quantity glow minus one divided by the slope of the curve. 96 00:05:03,140 --> 00:05:07,060 Using the graph in this algebraic equation, we solve for pressure. 97 00:05:07,060 --> 00:05:11,060 The pressures we calculate can be displayed using different colors like this. 98 00:05:11,060 --> 00:05:14,620 The red regions show where the pressures are high, and the blue regions show where the 99 00:05:14,620 --> 00:05:15,860 pressures are low. 100 00:05:15,860 --> 00:05:19,660 As you can see, the pressures in the front of the car are higher than the pressures in 101 00:05:19,660 --> 00:05:20,660 the back. 102 00:05:20,660 --> 00:05:24,980 As we calculated earlier, this difference determines the vehicle's drag. 103 00:05:24,980 --> 00:05:28,700 This information is used by car designers to decide if the shape or geometry of a car 104 00:05:28,700 --> 00:05:29,700 needs to be changed. 105 00:05:29,700 --> 00:05:33,860 If I were a car designer, I'd change the notchback shape of the car. 106 00:05:33,860 --> 00:05:35,340 It creates too much drag. 107 00:05:35,340 --> 00:05:39,380 Well, Van, the research conducted here at the NASA Langley Research Center can be used 108 00:05:39,380 --> 00:05:44,100 by automotive engineers and designers to create new designs and shapes with reduced drag and 109 00:05:44,100 --> 00:05:45,660 better fuel efficiency. 110 00:05:45,660 --> 00:05:49,660 This allows drivers like us to save money and protect the environment. 111 00:05:49,660 --> 00:05:53,940 Okay, we've seen how different shapes affect drag. 112 00:05:53,940 --> 00:05:59,420 Now, let's head back to First Flight Middle School and see what would happen if we changed 113 00:05:59,420 --> 00:06:02,220 the frontal surface area of an object. 114 00:06:02,220 --> 00:06:02,900 Are you ready, guys?