Any world with an atmosphere has wind. Simply put, wind is moving air. Winds can be powerful — which means, in the literal sense, full of power. That's why a dramatic storm’s winds can rip roofs off of houses. When harnessed by turbines, less turbulent winds can electrify cities and towns. Over the long term, steady streams of wind can sculpt landscapes and ecosystems. Three finalists at this year’s Broadcom MASTERS competition each presented findings on various aspects of powerful winds from their personal research.
Broadcom MASTERS brings together 30 U.S. middle-school students each year to tackle team challenges. (MASTERS stands for Math, Applied Science, Technology and Engineering for Rising Stars.) The program was created by Society for Science & the Public, which publishes Science News for Students. Broadcom Foundation, headquartered in Irvine, Calif., sponsored the event.
Unlike most science competitions, only about one-fourth of a finalist’s overall score is based on the qualifying research that he or she had entered at a science fair the previous school year. Sara Kaufman, 12, Cooper City, Fla., analyzed devices that homeowners might use to protect their roofs during hurricanes. This project helped earn her second place in the mathematics category, valued at $2,500. (The overall, first-place winner for this year’s Broadcom MASTERS took home a $25,000 prize.)
The bad kind of wind power
A hurricane can easily cause billions of dollars of damage to homes and businesses. A lot of that damage will be due to storm surges. That’s when powerful winds drive ocean waters onto shore, flooding coastal regions. But a lot of damage also comes from the storm’s winds. These can topple trees onto homes and blow down walls. They also can damage roofs, she notes.
Sometimes the damage will only be minor; the wind may remove just a few roofing shingles. Other times, Sara notes, hurricane winds can rip the entire roof off of a home. In some storm-prone areas, new homes must be built with hurricane straps. These small strips of steel help attach a home’s roof to its walls. But older homes in those areas typically don’t have these.
It’s difficult to add hurricane straps after a home has been built. That’s because layers of plywood and shingles hide the internal structure of the roof. You’d have to remove the roof to install the straps. And while that’s possible, it would be very expensive. So, Sara said, “I decided to see if I could design something to protect strap-free homes from powerful winds.” She figured her additions would need to attach to the outside of the roof.
First, she had to come up with design ideas for these add-ons. They would need to interrupt airflow over the roof and reduce the wind’s lifting power. Sara’s simplest idea was to take long boards and add them along the edge of the roof. Those boards would have a slightly rounded edge. That should smooth out the airflow.
Another idea was to make the shape (in cross-section) of the add-ons resemble an airplane’s wing, or airfoil. She reasoned that this might make the airflow smoother still. It also, however, might create lift, just as an airplane’s wing does. That, in turn, might aid winds in ripping a home’s roof off.
Sara’s third notion was to add chimney-like structures to the corners of the roof. Like the boards she designed for her second idea, their shape (in cross-section) would look like an aircraft wing. But they would stand up vertically like corner posts, not be attached all along the edges of the roof.
Engineers often use large wind tunnels to analyze the flow of air around scale models of objects, such as cars and airplanes. For her tests, Sara built a small-scale wind tunnel. Hers was made from a 1.5-meter (5-foot) section of plastic pipe that was about 15 centimeters (6 inches) in diameter. Sara cut a window in the central section of the pipe. Then she covered it in clear plastic so that she could watch what happened during her tests. Small-scale model homes — with and without her new add-ons — were placed in this zone, which scientists call a test section.
A leaf blower then provided the wind power. To make sure its simulated winds blew through the test section without swirling, each end of her tunnel, both upwind and downwind of the test section, was filled with short lengths of very small pipes. The paths through the small pipes helped straighten the flow and reduced turbulence.
Her leaf blower generated 40-kilometer-per-hour (nearly 25 mile per hour) winds. At the scale of Sara’s wind tunnel, that would be equivalent to the winds in a Category-3 hurricane, she notes. Their winds blow at speeds of at least 178 kph (111 mph).
The model homes Sara tested were actually birdhouses with roofs that could be lifted off. She made and tested four different models of them. “I used balsa wood to make the add-ons,” she said. “It was pretty easy to work with.” She tested all three of her novel designs for roofing add-ons. In addition, she tested one bird house with no changes to its roof. (It was the control for her experiment and represented a regular house.)
Sara then measured how long it took a roof to blow off each model home in the wind-tunnel tests. Compared to the control house, all of her add-ons delayed the roof loss. “But some didn’t help that much,” she noted.
It took only 4.19 seconds, on average, for the roof to blow off of the control house. The add-on boards that used only a rounded edge delayed the roof loss by another 0.12 second. The add-ons with an airfoil-shaped cross section worked better. These kept the roof on 72 percent longer (compared to the control house) — an average of 7.22 seconds. The chimney-like structures added to the corners of a home worked best of all. They kept the roof on the model home for nearly 14 seconds.
In the future, Sara says she’d like to try add-ons with different airfoils. She suspects that shapes other than the one she’s already tested might work even better.
Big wind in the big city
Wind turbines that harness the power of moving air are often very large. For some, the distance across their rotor blades is longer than a football field. Never mind that to generate power efficiently they need to stand in an open area stretching at least three times that distance in every direction. So, a large wind turbine has no place in a crowded city.
But Rachel Pizzolato thinks that maybe a lot of small turbines would work.
This 13-year-old from Metairie, La., wouldn’t plop them down in parks and vacant lots, though. She proposes attaching them to buildings, or maybe suspending them between buildings. And she wouldn’t give them long whirling blades. Instead, Rachel would install stretched-out versions of the paddlewheels used to power old-timey steamboats. Finally, the axis of each would be vertical, the opposite of those horizontal riverboat paddlewheels.
Placed on or between skyscrapers, such turbines could take advantage of what researchers often call the “urban street canyon” effect. That’s the relatively narrow area between tall buildings where winds often blow faster than they otherwise would because their air is being funneled into a small area, Rachel explains. Although the winds here speed up, they’re also far more turbulent. And that’s the down side. Turbulence could make it difficult to figure out the best spot to place the turbines, she notes.
For now, Rachel is focusing on coming up with the best design for a single turbine. She built and tested several. For some, the blades were pointed out at a 45-degree angle from the outer rim (that’s half of the angle that makes up the corner of a square). For others, the angle was 60 degrees. Rachel tried these two angles to see which would catch more of the available wind.
Rachel also varied the design of her turbine’s blades. Some had a blunt front edge. Others were rounded. Still others had rear edges that were wavy. That waviness was intended to mimic the bumps on the front edge of a humpback whale’s flippers, the teen explains. Previous studies had shown that those bumps, or tubercles, help guide the flow of water along the flipper’s surface. And that increases lift.
Like Sara, Rachel tested her designs in a handmade wind tunnel. She crafted scale models of her turbines out of balsa wood (which is strong, light and easily carved). Then she tested the turbines at four wind speeds that ranged from 3.9 to 10 meters per second (about 8.7 to 22.4 miles per hour). No big surprise, some of Rachel’s designs generated more power at these speeds than others. In general, blunt-edged turbines performed the worst. Those with rounded front edges on their blades did better. “The devices whose blades had wavy rear edges did the best,” the teen showed. In her tests, the best turbine design generated twice as much power as the worst one.
Rachel plans to continue tweaking her turbines. To help her more quickly come up with a design that produces peak power, she’ll try 3-D printing her blades. By using that technique, she won’t have to slowly carve bits of wood. Instead, she’ll create a computer model of a blade and then have a special printer build it, layer by layer (probably from some sort of plastic). If one design doesn’t work well, she’ll simply change the computer model to print something different.
Winds shape ecosystems
As many hikers do, 14-year-old Kathryn Kümmel (“Koko”, to her friends) pays a lot of attention to her surroundings. While hiking one of her favorite trails near her home, which is in Colorado Springs, Colo., Koko noticed that the tree line had a weird shape. (A tree line is the elevation above which trees can’t grow due to cold or dryness.) At this site, there wasn’t a clear, smooth line dividing the trees below from the grassy areas above. Instead, there were small islands of trees — usually cone-bearing evergreens — well beyond the edges of the larger masses of trees. In some cases, those isolated tree clumps were 20 to 60 meters (yards) upslope from the tree line.
In some regions, climate change has been causing tree lines to migrate to higher elevations. (As temperatures grow warmer at high elevations, cold-sensitive plants and animals can more readily survive and thrive.) But Koko suspected that winds also might have played a role in sculpting the oddly shaped tree line in her area. So, she did some lab tests and also collected data in the field.
Instead of using a wind tunnel, as Sara and Rachel had, Koko made some models and dragged them through a tank of water. Those tiny model trees were “planted” in a slab of Styrofoam and then turned upside down and submerged in the tank. She released droplets of ink into the water to highlight the flow patterns (her model for wind patterns) that were moving past her tiny models of clumped trees.
These data indicate that winds don’t just flow over and past trees, then move on. Instead, some swirl back into the protected area downwind of the clump. Koko suspects that such wind patterns could affect the buildup of snowdrifts and the scattering of seeds, among other things.
To check this out in the real world, she installed a couple of sophisticated weather stations near one tree island along her favorite hiking route. Those instruments measured things such as temperature, humidity and the wind speeds at two different heights above ground. She placed one station a few meters (yards) upwind of the tree island. She put the other just downwind of the clump.
Data from these field sites backed up the results of her water-tank tests. On the upwind side of the clump, wind speeds were higher than on the downwind — or protected — side of the tree island. “That dramatically affected how the trees were shaped,” says Koko. On wind-blasted sides of the trees, especially those along the edge of the clump, branches were shorter and weirdly shaped.
Trees along the upwind edge of the clump weren’t taller than the others. But based on the appearance of their bark, they were older than other trees in the island.
That, in turn, suggests that the older trees’ seeds had been carried downwind. Yet the tree island that Koko studied included only mature trees and not any seedlings. The teen plans to further study the issue. Even though the downwind sides of tree islands are protected from the wind, it’s possible that any snowdrifts that accumulate and persist there may stifle the growth of seedlings.
If you’ve ever watched a weather vane (or simply stood outside on a breezy day), you know that winds are fickle. They arrive from one direction in one moment and then a different one soon after. Not only that, but their speed changes from one moment to the next. Computer models of airflow are either way too crude to give good results, or they’re so complicated they seemingly take forever to run. So, for the near future, scientists and engineers everywhere — including researchers like Sara, Rachel and Koko — will be using wind tunnels and water tanks to make sure that their experiments give consistent results.
(for more about Power Words, click here)
3-D printing A means of producing physical items — including toys, foods and even body parts — using a machine that takes instructions from a computer program. That program tells the machine how and where to lay down successive layers of some raw material (the “ink”) to create a three-dimensional object.
airfoil (in aeronautics) The surface of a wing, aileron or other structure that has been designed to help lift or control an aircraft by making use of natural air currents.
angle The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.
atmosphere The envelope of gases surrounding Earth or another planet.
average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
axis The line about which something rotates. On a wheel, the axis would go straight through the center and stick out on either side.
balsa Trees of the Ochroma genus that grow in the tropical Americas. Their wood is extremely lightweight, easy to cut and buoyant. That’s why it’s often used to make rafts, model airplanes and other projects that may require light weight and the ability for someone to sculpt parts easily.
Broadcom MASTERS Created in 2011 by the Society for Science & the Public, Broadcom MASTERS (Math, Applied Science, Technology and Engineering Rising Stars) is the premier middle school science and engineering fair competition. Broadcom MASTERS International gives select middle school students from around the world a unique opportunity to attend the Intel International Science & Engineering Fair.
climate The weather conditions that typically exist in one area, in general, or over a long period.
climate change Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.
computer model A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.
control A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered. For example, if scientists were testing different types of fertilizer in a garden, they would want one section of it to remain unfertilized, as the control. Its area would show how plants in this garden grow under normal conditions. And that gives scientists something against which they can compare their experimental data.
cross-section A term for the view of some three-dimensional solid as it would appear if a knife had cut through the structure, separated it in two, and then one of those pieces was now looked at edge-on from the cut side.
diameter The length of a straight line that runs through the center of a circle or spherical object, starting at the edge on one side and ending at the edge on the far side.
ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.
elevation The height or altitude at which something exists.
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
field An area of study, as in: Her field of research was biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory.
football field The field on which athletes play American football. Owing to its size and familiarity, many people use this field as a measure of how big something is. A regulation field (including its end zones) runs 360 feet (almost 110 meters) long and 160 feet (almost 49 meters) wide.
humidity A measure of the amount of water vapor in the atmosphere. (Air with a lot of water vapor in it is known as humid.)
humpback A species of baleen whale (Megaptera novaeangliae), perhaps best known for its novel “songs” that travel great distances underwater. Huge animals, they can grow up to more than 15 meters (or around 50 feet) long and weigh more than 35 metric tons.
hurricane A tropical cyclone that occurs in the Atlantic Ocean and has winds of 119 kilometers (74 miles) per hour or greater. When such a storm occurs in the Pacific Ocean, people refer to it as a typhoon.
lift An upward force on an object. It may occur when an object (such as a balloon) is filled with a gas that weighs less than air; it can also result when a low-pressure area occurs above an object (such as an airplane wing).
mature (adj.) Connoting an adult individual or full-grown and fully developed (non-juvenile) form of something. (verb) To develop toward — or into — a more complex and full-grown form of some individual, be it a plant, animal or microbe.
migrate To move long distances (often across many countries) in search of a new home.
model A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.
novel Something that is clever or unusual and new, as in never seen before.
plywood An “engineered” product made by gluing thin layers of wood together into big sheets using high heat, strong pressure and glue. Because each layer — or ply — is laid down with its grain running in a different direction, plywood is usually stronger and less likely to warp than an equally thick board made from a single sheet of wood.
-scape A suffix borrowed from “landscape” that refers to an expansive view of some scenic vista (or a picture of that). Examples: moonscape, seascape, treescape.
seedling The initial plant that sprouts leaves and roots after emerging from a seed.
skyscraper A very tall building.
sophisticated A term for something that is advanced, complex and/or elegant.
square (in geometry) A rectangle with four sides of equal length. (In mathematics) A number multiplied by itself, or the verb meaning to multiply a number by itself. The square of 2 is 4; the square of 10 is 100.
storm surge A storm-generated rise in water above normal tidal level. In most cases, the largest cause of storm surge is strong onshore winds in a hurricane or tropical storm.
Styrofoam A trademarked name for a type of rigid foam made from light-weight polystyrene plastic. It is used for everything from home craft projects to decorative ornaments and building insulation.
technology The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.
tree line On a mountain, this is the height above which trees can’t grow because the environment is generally too cold or dry.
tubercle A tiny knobby projection — a prominent bump — that occurs naturally on some part of a plant or animal. It might be a protruding nodule on a bone or the surface of the skin, for instance.
turbine A device with extended arm-like blades (often curved) to catch a moving fluid — anything from a gas or steam to water — and then convert the energy in that movement into rotary motion. Often that rotary motion will drive a system to generate electricity.
turbulent (n. turbulence) An adjective for the unpredictable fluctuation of a fluid (including air) in which its velocity varies irregularly instead of maintaining a steady or calm flow.
upslope The designation of a direction, one at some upward elevation on a slope (such as a mountain or hillside). Or a term for any slope that rises (ascends upward with distance).
upwind A designation for the direction from which winds are blowing.
urban Of or related to cities, especially densely populated ones or regions where lots of traffic and industrial activity occurs. The development or buildup of urban areas is a phenomenon known as urbanization.
vertical A term for the direction of a line or plane that runs up and down, as the vertical post for a streetlight does. It’s the opposite of horizontal, which would run parallel to the ground.
weather Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.
whale A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.
wind tunnel A facility used to study the effects of air moving past solid objects, which often are scale models of real-size items such as airplanes and rockets. The objects typically are covered with sensors that measure aerodynamic forces like lift and drag. Also, sometimes engineers inject tiny streams of smoke into the wind tunnel so that airflow past the object is made visible.
wind turbine A wind-powered device — similar to the type used to mill grain