Low speed wind tunnel testing barlow pdf


    Low speed wind tunnel testing I by Jewel B. Barlow, William H. Rae, Alan . Barlow and Alan Pope wish to acknowledge his early contributions to planning for. 1-John Wiley & Sons ().pdf - Ebook download as PDF File .pdf), Text File . txt) or read Low speed wind tunnel testing I by Jewel B. Barlow, William H. 1% Jewel B. Barlow William H. Rae, Jr. Alan Pope A WILEY-MTERSCIENCE Ed. of: Low-speed wind tunnel testing / WiUiam H. Rae, Jr., Alan Pope. 2nd ed.

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    Low Speed Wind Tunnel Testing Barlow Pdf

    new PDF Low-Speed Wind Tunnel Testing Full Online, new PDF Low -Speed Wind Tunnel Testing Full Page, new PDF Abstract: This paper presents low speed wind tunnel tests of a 2D NACA airfoil Keywords: Aerodynamic balance, Wind tunnel test, Low Reynolds . [2] Barlow J.B., Rae W. H., Pope A.: Low-Speed Wind Tunnel Testing, 3rd. 11, November Book Reviews. Low-Speed Wind Tunnel Testing, Third Edition. Jewel B. Barlow, William H. Rae Jr., and Alan Pope, Wiley, New York,

    Measurement of aerodynamic forces[ edit ] Air velocity and pressures are measured in several ways in wind tunnels. Air velocity through the test section is determined by Bernoulli's principle. Measurement of the dynamic pressure , the static pressure , and for compressible flow only the temperature rise in the airflow. The direction of airflow around a model can be determined by tufts of yarn attached to the aerodynamic surfaces. The direction of airflow approaching a surface can be visualized by mounting threads in the airflow ahead of and aft of the test model. Smoke or bubbles of liquid can be introduced into the airflow upstream of the test model, and their path around the model can be photographed see particle image velocimetry. Aerodynamic forces on the test model are usually measured with beam balances , connected to the test model with beams, strings, or cables. The pressure distributions across the test model have historically been measured by drilling many small holes along the airflow path, and using multi-tube manometers to measure the pressure at each hole. Pressure distributions can more conveniently be measured by the use of pressure-sensitive paint , in which higher local pressure is indicated by lowered fluorescence of the paint at that point.

    First among those is Daniel "Rick" Harris, who drafted the chapter on marine vehicles, with Rui Guterres, who drafted the chapter on ground vehicles, and Molly Simmons, who did yeoman duty in many ways in close array. Robert Ranzenbach, Ahmad Kassaee, and Mark Dresser as leaders of the technical staff along with J une Kirkley as the right-hand person in the office and her able assistant, Zenith Nicholas, have done much to keep the Glenn L.

    Martin Wind Tunnel laboratory on an even keel while allowing J ewel Barlow to focus on preparation of the manuscript. J ewel Barlow also wishes to express his gratitude to the many representatives of member facilities of the SATA with whom he has had the privilege and pleasure of sharing meetings, information, and experiences that have enriched his knowledge of wind tunnel experiments and more.

    Very special thanks from J ewel Barlow are expressed to Diane Barlow, his wife, who has given unwavering support as well as good advice. The concepts to be treated are applicable to higher speed tunnels and to water tunnels as well. However, before launching into the main topics, it is worthwhile to set the stage for wind tunnels in general by asking thequestion: What has motivated the invention, development, and continu- ing uses of wind tunnels?

    Our planet, Earth, is completely enveloped by oceans of air and water. Humans and almost all the other creatures spend their lives immersed in one or the other of these fluids. Naturally produced motions from gentle breezes and currents to storms and tloods have profound impact on human existence. Winds and currents have been harnessed for moving about by boat and sail since before the earliest existing recorded history. And it seems certain that humans throughout their existence have marvelled at the agility of birds and fishes in their expositions of swimming and flying skills.

    Today, less than years after the first successful airplane, there exists a vast array of aircraft tailored for many specific uses with corresponding variety in their shapes. The shapes of airplanes are determined by considerations of aerodynamics with varying degrees of attention to performance, agility, stealth, procurement cost, operational cost, time to delivery, and any other aspect that a customer may require for intended missions.

    There are millions of automobiles in routine use whose shapes attest to the influence of external aerodynamics on the decisions of the designers. The main focus for production automobiles has been on aerodynamic drag, although lift has recei ved considerable attention as well. Aerodynamic down load is most often the main objective for racing automobiles.

    Automobile companies are also keenly interested in knowing how to choose details of external shapes to reduce exterior and interior noise. Racing yacht keels are the subject of intense investigations in efforts to achieve advantages of a few seconds per mile. Architects routinely require aerodynamic evaluations of any prominent building almost anywhere. Nearly every building component is being subjected to aerodynamic evaluation if it is to be accepted for use in hurricane-prone areas such as Florida.

    The shapes of submarines and the details of their propulsion systems areevaluated asdesigners attempt tomaximize speed, minimize energy requirements, and minimize noise generation. Aerodynamic influences aresubstantial inthedesign of large bridges. Yet the veil covering the secrets of theforces involved inthedynamic interactions of tluids and solid objects has only begun to be lifted and only in relatively recent times and continues to refuse all efforts to tear it cleanly away.

    Low-Speed Wind Tunnel Testing by Jewel B. Barlow

    The great advances in theory and computational capability notwithstanding, experimental explorations remain the mainstay for obtaining data for designers' refined and final decisions across a broad range of applications. A primary tool of experimental aerodynamics is the wind tunnel. Qualitative methods[ edit ] Compilation of images taken during an alpha run starting at 0 degrees alpha ranging to 26 degrees alpha. Images taken at the Kirsten Wind Tunnel using fluorescent mini-tufts.

    Notice how separation starts at the outboard wing and progresses inward. Notice also how there is delayed separation aft of the nacelle.

    Fluorescent mini-tufts attached to a wing in the Kirsten Wind Tunnel showing air flow direction and separation. China clay on a wing in the Kirsten Wind Tunnel showing reverse and span-wise flow Oil flow visible on a straight wing in the Kirsten Wind Tunnel. Trip dots can be seen near the leading edge.

    Tufts can be used to gauge air flow patterns and flow separation. Tufts are sometimes made of fluorescent material and are illuminated under black light to aid in visualization. Evaporating suspensions are simply a mixture of some sort or fine powder, talc, or clay mixed into a liquid with a low latent heat of evaporation. When the wind is turned on the liquid quickly evaporates, leaving behind the clay in a pattern characteristic of the air flow. Oil: When oil is applied to the model surface it can clearly show the transition from laminar to turbulent flow as well as flow separation.

    Tempera Paint: Similar to oil, tempera paint can be applied to the surface of the model by initially applying the paint in spaced out dots. After running the wind tunnel, the flow direction and separation can be identified. An additional strategy in the use of tempera paint is to use blacklights to create a luminous flow pattern with the tempera paint.

    Fog usually from water particles is created with an ultrasonic piezoelectric nebulizer. The fog is transported inside the wind tunnel preferably of the closed circuit and closed test section type. An electrically heated grid is inserted before the test section, which evaporates the water particles at its vicinity, thus forming fog sheets. The fog sheets function as streamlines over the test model when illuminated by a light sheet. Sublimation: If the air movement in the tunnel is sufficiently non-turbulent, a particle stream released into the airflow will not break up as the air moves along, but stay together as a sharp thin line.

    Multiple particle streams released from a grid of many nozzles can provide a dynamic three-dimensional shape of the airflow around a body. As with the force balance, these injection pipes and nozzles need to be shaped in a manner that minimizes the introduction of turbulent airflow into the airstream. Sublimation alternate definition : A flow visualization technique is to coat the model in a sublimatable material where once the wind is turned on in regions where the airflow is laminar, the material will remain attached to the model, while conversely in turbulent areas the material will evaporate off of the model.

    This technique is primarily employed to verify that trip dots placed at the leading edge in order to force a transition are successfully achieving the intended goal. High-speed turbulence and vortices can be difficult to see directly, but strobe lights and film cameras or high-speed digital cameras can help to capture events that are a blur to the naked eye.

    High-speed cameras are also required when the subject of the test is itself moving at high speed, such as an airplane propeller. The camera can capture stop-motion images of how the blade cuts through the particulate streams and how vortices are generated along the trailing edges of the moving blade.

    Quantitative methods[ edit ] Pressure Sensitive Paint PSP : PSP is a technique whereby a model is spray coated with a paint that reacts to variations in pressure by changing color. In conjunction with this technique, cameras are usually positioned at strategic viewing angles through the walls, ceiling, and floor of the wind tunnel to photograph the model while the wind is on.

    The photographic results can be digitized to create a full distribution of the external pressures acting on the model, and subsequently mapped onto a computational geometric mesh for direct comparison with CFD results. PSP measurements can be effective at capturing pressure variations across the model however often require supplemental pressure taps on the surface of the model to verify the absolute magnitude of the pressure coefficients.

    An important property of well behaved PSP paints is they also should be insensitive to temperature effects since the temperature inside the wind tunnel could vary considerably after continuously running. Common difficulties encountered when using PSP include the inability to accurately measure the leading and trailing edge effects in areas where there is high curvature due to limitations in the cameras ability to gain an advantageous viewing angle.

    Additionally application of PSP on the leading edge is sometimes avoided because it introduces a finite thickness that could cause early flow separation thus corrupting results. Since the pressure variations at the leading edge is typically of primary interest, the lack of accurate results in that region is very problematic. Once a model is painted with pressure sensitive paint, certain paints have been known to adhere and continue to perform for a matter of months after initially applied.

    Finally PSP paints have been known to have certain frequency characteristics where some require a few moments to stabilize before achieving accurate results while others converge rapidly. In the latter instance paints that have ability to reflect rapid changes in pressure can be used for Dynamic PSP applications where the intent is to measure unsteady flow characteristics.

    Particle Image Velocimetry PIV : PIV is a technique in which a laser sheet is emitted through a slit in the wall of the tunnel where an imaging device is able to track the local velocity direction of particles in the plane of the laser sheet. Sometimes this technique involves seeding the airflow with observable material. This technique allows for the quantitative measurement of the velocity and direction of the flow across the areas captured in the plane of the laser.

    Model Deformation Measurement MDM : MDM works by placing markers at known geometric locations on the wind tunnel model and taking photographs of the change in the marker's location as the wind in the tunnel is applied. By analyzing the change in marker positions from different camera viewing angles, the translational change in location of the marker can be calculated.

    By collecting results from a few markers, the degree to which the model is flexibily yielding due to the air load can be calculated. Classification[ edit ] There are many different kinds of wind tunnels. They are typically classified by the range of speeds that are achieved in the test section, as follows:. They are typically very heavily scheduled for their environmental purposes. The auto industry frequently refers to wind tunnels.

    Control Room An example of such a wind tunnel is shown in Figure 2. Steam Lances Lamps Section Courtyard Cooling Tower 7. The use of a wide-angle diffuser to permit a contraction ratio of Wind tunnels for automotive experiments are increasingly required to have low-flow noise levels so that wind noise associated with flow around the vehicle can be measured with sufficient accuracy to allow assessment of proposed design variations.

    This permitted the length needed for the fan noise suppressors. A major point concerning wind tunnel experiments on automobiles is the question of ground simulation. Most automobiles are considered to be aerodynamically bluff bodies. This and other issues will be addressed in more detail later in the book. To provide a strict simulation. A considerable amount of work has been carried out to address thequestionof when this is necessaryand when this conditioncan be relaxed.

    This leads tointeractions between the flow about the model and the wind tunnel walls or free jet boundary that are somewhat more complex than is the case for bodies with fully attached flow. Generally speaking. Realizing the advantages of holding the model and the measuring instrumentation still and letting the fluid move.

    Special features include: The principal difference is the clearance between the bottom of the car and the ground. And the flow quality is generally less than is thought proper for external aerodynamic studies.

    One result is that understanding these types of flow in wind tunnels continues to engage research personnel. While basically a singlereturn wind tunnel with a closed test section upstream of an open one.

    A sketch of the tunnel is shown in Figure 2. The wedges used for reflection cancellation are evident in the background.

    Increased understanding of aeroacoustic principles. Section isolation is practiced throughout. An example of a general-purpose facility that has received extensive acoustic treatment is the National Full Scale Facility. Many general-purpose wind tunnels have been modified to include noise absorption materials and other features to. Extremely heavy concrete constructions plus the use of noise suppression materials on walls.

    An anechoic chamber surrounding the open test section to yield by far the lowest noise levels achieved in a wind tunnel. Water tunnels tend to be physically smaller than wind tunnels for achieving the same Reynolds numbers. Small water tunnels have been widely used for flow visualization studies. Water tunnels support direct investigation of cavitation phenomena that cannot be done in a wind tunnel.

    This tunnel is used for underwater vehicle development. There are few "large" water tunnels. There is a in. It has been possible to achieve low dispersion of die streaks. Courtesy Naval Surface Warfare Center. For many purposes they are simply the most cost effective at carrying out exploratory investigations when no fully satisfactory capability is available. A selection of subjects of aerodynamic experiments not previously mentioned is added here to further emphasize the broad range of applications that arise for lowspeed wind tunnels.

    Martin wind tunnel at the University of Maryland. Navy has two. Air Force has one. Many of these tunnels have been closed and some have been destroyed as work that had its origin in these tunnels moved more specialized facilities spawned by increasing understanding of particular problems.

    The most common of these is the 7 X ft class wind tunnel that have those approximate dimensions of their test sections. People Attention has been paid to people-drag of the type encountered by bike racers and skiers. These facilities continue to be very good for a wide range of vehicle-related experiments and continue to be the best available for a range of special-purpose experiments that have not spawned their own specially designed aerodynamic facilities.

    The U. Its layout is shown in Figure 2. Experiments are usually run at low tunnel speeds. Live insects have been somewhat more cooperative than live birds and have flown more extensively in tunnels for close observation. It would be preferable to evaluate windmills in the wind gradient that they will eventually see. A programmed computation in real time can also be presented so the skier or biker can be shown how much each change helps in terms of race time or distance results.

    The tunnel engineer should encourage the windmill promoter to have siting experiments PTior made in an environmental wind tunnel to get the best results in the field. Wind tunnel entries have proven beneficial for showing bike riders their lowest drag posture.

    For skiers. Airborne troops have been trained in vertical wind tunnels so that they are familiar with the condition they will experience when jumping from aircraft. Substantial improvements in clothing have resulted from such programs. Initially experimenters were seeking mysterious and incredibly efficient devices that nature's creatures were supposed to have.

    Differences that remain are of small magnitude and are within the uncertainty of experiments to date. Experiments will probably encompass runs under various power loadings and at different Reynolds numbers.

    Bird fat turns out to have a similar energy content to jet fuel. In some cases clothing has been evaluated to seek increases in drag when it is to be worn by an athlete seeking to increase load during training.

    No such things have been found. Birds and Insects Over the years a number of wind tunnel experiments have been made of natural fliers. Wind Power Devices Currently. Experiments have shown a change of drag with the number of wheel spokes and other details. The high landing angles of some buds have been duplicated with highly latticed wings.

    Position changes are shown on frontal and side TV projectors. In some cases. The fascinating part of these experiments. Courtesy Verdian-Calspan Operations. A long-term record cannot be established for the mountain location. For estimating the maximum power coefficient one should use.

    Measurement of side force is not normally made but should be. The lower maximum power coefficient for the Savonius type is offset in practice by its lower manufacturing cost. At the moment. Besides needing loads for strength and preservation of the proper focal distance. It turns out that a maximum of An example of an installation to evaluate the effect of wind screens is shown in Figure 2.

    Radar Antennas and Satellite Television Receivers The same type of experiments described above for solar collectors may be made for radar antennas or other dish-type receivers. The collector pitch angle is varied from. Loads are reduced substantially by being shielded by a nearly solid fence around the array or other collectors.

    In particular. As local winds may be quite high. Windmills have. Natural winds have many times the total power needed for the entire electrical needs of humans.

    Since winds come from all directions. The experimental program usually consists of force. Large installations seem to suffer from making a disturbing buzzing sound.

    Solar Collectors Interest in solar energy has spawned a need for wind loads and moments on the various solar collectors.

    Yawing moments and roll moments are measured but are usually of lesser import. The tunnel speed range is chosen based on historical wind records at the proposed site. Pressure data are needed for limiting local deflections of the reflector itself. Runs at several air speeds usually establish that there is little variation with Reynolds number.

    A major difference is that one would not expect to find them in arrays. Array spacing and distance above ground are additional variables.

    Windmills should never be put on a rooftop. If there is any question at all about structural integrity. Ship experiments have been somewhat more extensive.

    For wind tunnel experiments on exposed antennas the model should be mounted in the tunnel on top of the same structure it will see in the field-trailer. Sails and Above-Water Parts of Ships The performance of sails have been evaluated in wind tunnels in limited numbers over the years.

    Aeroacoustic Phased Array Testing in Low Speed Wind Tunnels

    These usually embrace a floor or ground plane model cut off at the waterline. Material roughness and porosity will probably be out of scale. Sail material should be varied during an experiment to see what effect. Radar antennas are common on ships that may expect to encounter high-wind conditions and at those very times may be dependent on the radar for safety.

    Measurements of drag. It is quite common to evaluate the actual hardware in the wind tunnel to obtain the actual structural integrity and the capability of the drive motors to operate the antenna in the specified wind conditions. Here the model is set at a range of pitch angles about the stem. Four types of experiments have been tried: There has been at least one case in which aerodynamic excitation at quite low wind speed led to fatigue cracking of high aspect ratio I beams in a bridge superstructure.

    The models should be kept small enough so that at a yaw angle of 90" bow and stem remain no less than half a ship length from the tunnel walls. Martin Wind Tunnel. Extreme care to duplicate model detail. Experiments on speed boats are primarily to find a body shape that has minimum nose-up characteristics. A relatively recent problem that arises with tankers carrying liquid natural gas is ascertaining that the vents needed as the gas boils off do not constitute a fire hazard.

    Bridges The effect of natural winds is important to the proper design of long or even intermediate bridge spans. The current wide. Courtesy Glenn L. Both sail and ship model experiments should have their data corrected for wake and solid blockage. To be most useful. Full models in turbulent air are the best. Drag component includes support drag. When evaluated in smooth air. Section models would of course be desirable for ease of construction. It is wind engineering. They are used to determine wind loads on buildings.

    Experimental methods for environmental studies were done first in generalpurpose wind tunnels. This area includes buffet. These problems are concerned with forces. The Boundary Layer Wind Tunnel Facility at the University of Western Ontario even has an extended water pool to help in simulating flow in the marine boundary layer. Dynamics of Structures. In general four separate areas are studied: Wind Forces on Buildings and Structures. This is accomplished by having adjustable roughness elements along the floor of the tunnel for as much as test-section widths upstream of the zone in which the model is positioned.

    These problems require measuring mean wind velocities. Wind engineering combines the fields of meteorology. Mass Transport by Winds. This covers soil erosion. The material in this section is complementary to material in Chapter 16 on wind engineering. These are sometimes referred to as "meteorological wind tunnels. A new term has entered the technological lexicon. Local Winds. Instead it is manipulated to obtain a flow distribution that is nonuniform in time and space to represent the atmospheric boundary layer.

    The velocity distributions in the natural boundary layer should be simulated as completely as possible. There is a small error in that the boundary layer and turbulence in the real world may be different according to the approach direction.

    It accounts for a change of wind direction of perhaps 5" in ft. Nor does the atmosphere have only one temperature gradient as both daily and seasonal changes occur. The Rossby number is concerned with the effect of the rotation of Earth on its winds.

    While it is necessary to provide cooled or heated air and test-section floor areas for some types of experiments on pollution. For these experiments simulating the boundary layer structure and turbulence is adequate. If problems show up. The longitudinal pressure gradient normally found in a wind tunnel and exacerbated by the very thick boundary layer needed can be made negligible by providing an adjustable test-section roof that may be adjusted to provide the extra crosssectional area needed.

    The boundary layer velocity distribution and turbulence can be well duplicated by an installation of spires in the entrance cone followed by a roughness run of test-section heights often made with small cubes on the floor. This is of little significance and would be hard to simulate if it were necessary. The boundary layer must be matched to at least 3 ft high.

    Reynolds number effects are usually small due to the sharp edges of most objects under study. The building or locale to be evaluated and its environs are placed on a turntable. Ground conditions influence the boundary layer [see Eq. Reynolds numbers for buildings are commonly based on width w. For example. This can lead to a variety of unexpected intake problems.

    Detailed smoke studies after force experiments have been made and the model painted a dull red to make the smoke show up better are used to convince the architect and his or her backers that the suggested changes are needed. Current practice is to use transducers that have a flat frequency response. Static wind loads. A direct-current drive motor plus a variable-pitch propeller is the best arrangement for this. A full building experiment program encompasses the following: Static Loads and Associated Experiments on Buildings Wind tunnel engineers may be called upon to help correct buildings already built and in trouble or to guide the architect in a new design.

    These include smoke. On proposed designs it is less costly to make changes. Adjusting tunnel speed by rpm is less necessary with thick boundary layer flow because the flow pattern is adjusted by the spires and roughness. Preliminary smoke experiments to search for possible trouble spots where pressure ports are needed. The high wind velocities near the top of a building result in a higher total pressure near the top and wind blowing downward.

    These experiments are more tense than those on proposed buildings because the architect is usually very defensive. Ventilation intake studies with smoke being emitted by nearby factories or efflux from the proposed building itself. Air pollution experiments sometimes require that the tunnel be run at very low velocities. Local high-velocity areas that might cause problems for people. An elastic model can be built and actual accelerations and displacements measured for the various wind speeds and wind directions.

    Some typical cases are indicated. A special case of wind loading occurs when one tall building is adjacent to another. Locations for pressure ports are from item 1 above and from the tunnel engineer's experience. Unsteady Aerodynamics in Wind Engineering The wind can produce structural oscillations and other phenomena in several ways.

    The model had 21 degrees of freedom. If not. The natural frequencies of many items trees. It must be defined or the data are useless. The building structural engineer knows the natural frequencies of the building. Buffeting from adjacent cylindrical or hexagonal structures can be reduced by fixing transition through added roughness. There are two approaches to solving this problem: Experiments using a rigid model on a highresponse balance can obtain the needed information.

    Simple Oscillations All natural and man-made structures have one or more natural frequencies at which they will readily oscillate unless critically or over damped. Usually this produces shielding from winds in some directions and more serious buffeting in others. Dynamic Loads on Buildings Buildings with more than a 6: The dynamic pressure used for reducing the forces and moments to coefficient form may be taken as an average value over the model.

    Here some galloping has been developed. The Aeolian singing is understood. Aeolian Wbrations Long. Transmission lines exhibit both Aeolian and galloping oscillations.

    There is a range of Reynolds numbers over which there is an alternating shedding with corresponding unsteady side force and drag. When such a coincidence occurs. This is not unusual for buff bodies whose in-wind side becomes unstalled with a small angle of attack. Galloping produced by wind loads is reasonably well understood. Such an oscillation is called Aeolian.

    Vortex shedding from circular cylinders is one of the most studied problems in fluid dynamics. Bredhing Sometimes large-diameter stacks and other structures will distort at some natural frequency such that the flow pattern is changed toward that frequency. Galloping oscillations are usually violent and must be eliminated through design changes. As can be seen. These are cases of forced response at a resonant frequency. This is different from motion of the body in the absence of distortion.

    Such oscillations are the source of the tones in an "Aeolian Harp" produced by the wind. Experiments have been made on springmounted sections employing a bare wire. Over a wide range of conditions the shedding frequency corresponds to a Strouhal number. Galloping A second type of motion arises when a body has a negative slope of the lift curve. This phenomena is a result of the combination of the structural tendency to vibrate at a natural frequency and aerodynamic phenomena of slender bodies shedding vortex streets.

    For instance. Trees near the edge of the fields may need to be cut to improve the natural winds. Another type of erosion is the determination of the wind speed at which gravel begins to be eroded from the roof of a damaging the roof. Much of the correlation with full scale is encouraging. Pollination for many agricultural products is by the wind.

    AgriculturaVSoil Erosion Soil erosion caused by wind is of interest to the agronomist from the standpoint of losing topsoil.

    Instrumentation downstream of the windbreak should continue for at least six times its height. Snow Drifting Many people in warmer regions do not realize the yearly cost of snow removal.

    Drifting snow can block doorways and roads and may even inactivate a facility completely. The basic parameters of snowdrift and erosion problems are discussed below. On the other hand. Another facet of soil erosion is the damage done to car windshields and paint by windbome particles.

    A second and important use is to reduce winter heating loads by reducing the convective cooling of a house. Snow patterns that might take years in the Arctic to accumulate may be duplicated in a few hours. Fundamental studies of large-scale grain loads have been made using strain-gage-mounted grains. The area of wind engineering as applied to agriculture is only in its infancy. The road engineer. Data for snow experiments are obtained in the form of photographs and depth contours.

    One substantial contribution from tunnel experiments is the technique of reducing drifting by erecting a building on piles with a free space beneath. This has been applied in Arctic buildings with good results. Electric lights or other heaters are used for temperature control. This process is called "saltation" and is responsible for most of the motion and end deposits that form snowdrifts or soil erosion. Evaporation and Related Issues The growing need for studying transpiration from plants and evaporation from open bodies of water has resulted in the construction of wind tunnels in which the moisture content of the air and its temperature may be controlled.

    Selecting a model scale of h. Modeling to match this phenomenon is by the following ratios: Scale factor dlL. Transpiration experiments are full scale in that the weight of moisture removed from actual plants is studied. Tunnels of this type are in Japan. This concerns the rebound distanceldrop distance and is 0. The fall ratio may be maintained by using borax NaZB2O7.

    Coefficient of restitution e. They are all low-speed tunnels employing controlled air exchange. Particle Froude number VZlgd. Here we have one of the rare instances where we may "scale gravity"-at least to the extent that the fall velocity may be varied by changes in the particle density. Particle velocity VJY where V.

    When the wind velocity exceeds about five times the threshold speed. In a tunnel saltation has been found for the above-simulated snow to occur at 11 mph without snow falling and at lower velocities when snow is falling. Note the effect of tower at left rear. Pollution Dispersion For all of the various types of pollutants being discharged into the air. This last term is the "catch. Evaporation is of interest both to agronomists who are concerned with the loss of water from storage areas and channels and to process engineers who have drying problems.

    They include industrial smoke. The number and types of pollution problems are astounding. Both types of experiments have been explored in wind tunnels. They argue that 1 the dominant feature of plume. Skinner and L u d w i p 3made a great contribution to methods for experimenting on dispersal in wind tunnels. Evaporation experiments employ open bodies of water. Figure shows how smoke or pollutants can blanket an entire factory under inversion conditions.

    They also note that there is a minimum Reynolds number below which there will be a laminar sublayer in the tunnel that cannot be tolerated. Environmental Protection Agency reserves the right to require fluid modeling or field experiments for proposed installations.

    A few examples are given of smoke visualizations from pollution dispersal studies. Their conclusion. Efflux velocity is equal to wind speed and stack height is 1. Building is downstream of stack. Having the plume in the tunnel. Courtesy National Physical Laboratory. Thus hot stack gases are not necessary for this type of experiment. The objective is to keep the stack gases from impinging on the containers. Another type of pollution experiment employs a pollutant distributed at various locations to see how the dispersal is affected by changing conditions.

    In addition to a need for studies of the above problems for engineering purposes. Courtesy VerdianCalspan Operations. Panama City. A Review. Including a Summary of Ailfoil Data. Cambridge University Press. April Applied Analysis of the Navier-Stokes Equations.. Viscous Flow. Theory of Wng Sections. San Diego. New York.

    Courtesy Colorado State University. CER Techniques to Maximize Sail Power. Report No. Energy Research and Development Adrnin. Adlard Coles Nautical and Intemational Marine.. Aero-Hydrodynamics of Sailing. Windmills and Wind Characteristics. The use of the term environmental wind tunnel by the automotive industry indicates a very different type of facility from that described later in the section on Environmental Wind Tunnels.

    Local ground winds can be as much as four times those aloft. Los Angeles. Description and Characteristics.. Colorado Springs. June Washington DC. Aero Machi wind tunnel. Adlard Coles Nautical and Intemational Marine. Sail Performance.. If Candlestick Park had been built one playing field to the north.. Science Year: World Book Annual.

    Field Enterprise Education Corp.

    J. B. Barlow, W. H. Rae, Jr, A. Pope-Low Speed Wind Tunnel Testing. 1-John Wiley & Sons (1999).pdf

    Institute of Low Temperature Science. Atmospheric Environment. Aeolus was the Greek God of the wind. Army Snow. Report A Sections of this book addressing instrumentation bill.

    The principles are the same for other types of tunnels. These tunnels are equipped with mounting systems and instrumentation that can be readily adapted for many types of tests of air. The first step in the design of a tunnel is to determine the size and shape of the test section based on the intended uses of the facility. In this chapter. This type of arrangement leads to some compromises but is being found to be an overall advantage in some cases.

    Tunnels with smaller size test sections are mostly used for research and instructional purposes. A study of the basic aspects of wind tunnel design is useful to those who may be users or potential users of wind tunnels as well as those who may consider acquiring a wind tunnel. A number of special-purpose wind tunnels were mentioned in Chapter 2. A growing number of tunnels have multiple test areas so that a wider range of tests can be readily accommodated.

    In the medium-size tunnels with test-section area around ft2 large amounts of both research and vehicle development testing are accomplished. The test-section size.

    The material in this chapter will assist readers to gain an understanding of principal features of wind tunnels. It is also assumed that a major part of the testing will be force testing. These included spin tunnels. It is axiomatic that economics indicates that any given project should be carried out in the smallest size tunnel that will provide the needed simulation with the proviso that data from an improper and misunderstood simulation can be much worse than no data at all.

    A major part of the following discussions address tunnels for which the primary use is vehicle and vehicle component testing. Many low-speed tunnels. The cross-sectional area of the test section basically determines the overall size of the facility. Although the major cost of operation is the salaries of the tunnel personnel.

    The requirement for a facility to be a useful aeroacoustic facility is that the background noise level be sufficiently low.

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