Low Speed Wind Tunnel Testing By Barlow Rae And Pope Pdf
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- J. B. Barlow, W. H. Rae, Jr, A. Pope-Low Speed Wind Tunnel Testing. 1-John Wiley & Sons (1999).pdf
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Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft will fly. NASA uses wind tunnels to test scale models of aircraft and spacecraft. Some wind tunnels are large enough to contain full-size versions of vehicles.
The wind tunnel moves air around an object, making it seem as if the object is flying. Most of the time, large powerful fans blow air through the tube. The object being tested is held securely inside the tunnel so that it remains stationary and does not move. The object can be an aerodynamic test object such as a cylinder or an airfoil, an individual component, a small model of the vehicle, or a full-sized vehicle. The air moving around the stationary object shows what would happen if the object was moving through the air.
The motion of the air can be studied in different ways; smoke or dye can be placed in the air and can be seen as it moves around the object. Coloured threads can also be attached to the object to show how the air moves around it. Special instruments can often be used to measure the force of the air exerted against the object. The earliest wind tunnels were invented towards the end of the 19th century, in the early days of aeronautic research, when many attempted to develop successful heavier-than-air flying machines.
The wind tunnel was envisioned as a means of reversing the usual paradigm: instead of the air standing still and an object moving at speed through it, the same effect would be obtained if the object stood still and the air moved at speed past it. In that way a stationary observer could study the flying object in action, and could measure the aerodynamic forces being imposed on it.
The development of wind tunnels accompanied the development of the airplane. Large wind tunnels were built during World War II.
Wind tunnel testing was considered of strategic importance during the Cold War development of supersonic aircraft and missiles. Later, wind tunnel study came into its own: the effects of wind on man-made structures or objects needed to be studied when buildings became tall enough to present large surfaces to the wind, and the resulting forces had to be resisted by the building's internal structure.
Determining such forces was required before building codes could specify the required strength of such buildings and such tests continue to be used for large or unusual buildings.
Circa the s,  wind tunnel testing was applied to automobiles , not so much to determine aerodynamic forces per se but more to determine ways to reduce the power required to move the vehicle on roadways at a given speed. In these studies, the interaction between the road and the vehicle plays a significant role, and this interaction must be taken into consideration when interpreting the test results. In an actual situation the roadway is moving relative to the vehicle but the air is stationary relative to the roadway, but in the wind tunnel the air is moving relative to the roadway, while the roadway is stationary relative to the test vehicle.
Some automotive-test wind tunnels have incorporated moving belts under the test vehicle in an effort to approximate the actual condition, and very similar devices are used in wind tunnel testing of aircraft take-off and landing configurations.
Wind tunnel testing of sporting equipment has also been prevalent over the years, including golf clubs, golf balls, Olympic bobsleds, Olympic cyclists, and race car helmets. Helmet aerodynamics is particularly important in open cockpit race cars Indycar, Formula One. Excessive lift forces on the helmet can cause considerable neck strain on the driver, and flow separation on the back side of the helmet can cause turbulent buffeting and thus blurred vision for the driver at high speeds.
The advances in computational fluid dynamics CFD modelling on high-speed digital computers has reduced the demand for wind tunnel testing. 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.
Pressure distributions can also be conveniently measured by the use of pressure-sensitive pressure belts , a recent development in which multiple ultra-miniaturized pressure sensor modules are integrated into a flexible strip.
The strip is attached to the aerodynamic surface with tape, and it sends signals depicting the pressure distribution along its surface. Pressure distributions on a test model can also be determined by performing a wake survey , in which either a single pitot tube is used to obtain multiple readings downstream of the test model, or a multiple-tube manometer is mounted downstream and all its readings are taken.
The aerodynamic properties of an object can not all remain the same for a scaled model. The choice of similarity parameters depends on the purpose of the test, but the most important conditions to satisfy are usually:. In certain particular test cases, other similarity parameters must be satisfied, such as e. Froude number.
English military engineer and mathematician Benjamin Robins — invented a whirling arm apparatus to determine drag  and did some of the first experiments in aviation theory. Sir George Cayley — also used a whirling arm to measure the drag and lift of various airfoils. Otto Lilienthal used a rotating arm to accurately measure wing airfoils with varying angles of attack , establishing their lift-to-drag ratio polar diagrams, but was lacking the notions of induced drag and Reynolds numbers.
However, the whirling arm does not produce a reliable flow of air impacting the test shape at a normal incidence. Centrifugal forces and the fact that the object is moving in its own wake mean that detailed examination of the airflow is difficult. Francis Herbert Wenham — , a Council Member of the Aeronautical Society of Great Britain , addressed these issues by inventing, designing and operating the first enclosed wind tunnel in Konstantin Tsiolkovsky built an open-section wind tunnel with a centrifugal blower in , and determined the drag coefficients of flat plates, cylinders and spheres.
Danish inventor Poul la Cour applied wind tunnels in his process of developing and refining the technology of wind turbines in the early s. Carl Rickard Nyberg used a wind tunnel when designing his Flugan from and onwards. In a classic set of experiments, the Englishman Osborne Reynolds — of the University of Manchester demonstrated that the airflow pattern over a scale model would be the same for the full-scale vehicle if a certain flow parameter were the same in both cases.
This factor, now known as the Reynolds number , is a basic parameter in the description of all fluid-flow situations, including the shapes of flow patterns, the ease of heat transfer, and the onset of turbulence. This comprises the central scientific justification for the use of models in wind tunnels to simulate real-life phenomena. However, there are limitations on conditions in which dynamic similarity is based upon the Reynolds number alone.
The Wright brothers ' use of a simple wind tunnel in to study the effects of airflow over various shapes while developing their Wright Flyer was in some ways revolutionary. Between and Eiffel ran about 4, tests in his wind tunnel, and his systematic experimentation set new standards for aeronautical research.
In Eiffel's laboratory was moved to Auteuil, a suburb of Paris, where his wind tunnel with a two-metre test section is still operational today. Subsequent use of wind tunnels proliferated as the science of aerodynamics and discipline of aeronautical engineering were established and air travel and power were developed. The inlet was almost 11 feet 3. The layout was a double-return, closed-loop format and could accommodate many full-size real aircraft as well as scale models. The tunnel was eventually closed and, even though it was declared a National Historic Landmark in , demolition began in It was designed to test full-size aircraft and had six large fans driven by high powered electric motors.
Today, this wind tunnel is preserved as a national monument. It was completed in and used for Northrop Alpha testing. It used some large natural caves which were increased in size by excavation and then sealed to store large volumes of air which could then be routed through the wind tunnels.
This innovative approach allowed lab research in high-speed regimes and greatly accelerated the rate of advance of Germany's aeronautical engineering efforts.
By the end of the war, Germany had at least three different supersonic wind tunnels, with one capable of Mach 4. A large wind tunnel under construction near Oetztal , Austria would have had two fans directly driven by two 50, horsepower hydraulic turbines. The installation was not completed by the end of the war and the dismantled equipment was shipped to Modane , France in where it was re-erected and is still operated there by the ONERA.
With its 8m test section and airspeed up to Mach 1 it is the largest transonic wind tunnel facility in the world. On 22 June Curtiss-Wright financed construction of one of the nation's largest subsonic wind tunnels in Buffalo, N. The first concrete for building was poured on 22 June on a site that eventually would become Calspan, where the largest independently owned wind tunnel in the United States still operates. Later research into airflows near or above the speed of sound used a related approach.
Metal pressure chambers were used to store high-pressure air which was then accelerated through a nozzle designed to provide supersonic flow. The observation or instrumentation chamber "test section" was then placed at the proper location in the throat or nozzle for the desired airspeed. In the United States, concern over the lagging of American research facilities compared to those built by the Germans led to the Unitary Wind Tunnel Plan Act of , which authorized expenditure to construct new wind tunnels at universities and at military sites.
Some German war-time wind tunnels were dismantled for shipment to the United States as part of the plan to exploit German technology developments. For limited applications, Computational fluid dynamics CFD can supplement or possibly replace the use of wind tunnels. For example, the experimental rocket plane SpaceShipOne was designed without any use of wind tunnels. However, on one test, flight threads were attached to the surface of the wings, performing a wind tunnel type of test during an actual flight in order to refine the computational model.
Where external turbulent flow is present, CFD is not practical due to limitations in present-day computing resources. For example, an area that is still much too complex for the use of CFD is determining the effects of flow on and around structures, bridges, terrain, etc. The most effective way to simulative external turbulent flow is through the use of a boundary layer wind tunnel. There are many applications for boundary layer wind tunnel modeling.
For example, understanding the impact of wind on high-rise buildings, factories, bridges, etc. Another significant application for boundary layer wind tunnel modeling is for understanding exhaust gas dispersion patterns for hospitals, laboratories, and other emitting sources. Other examples of boundary layer wind tunnel applications are assessments of pedestrian comfort and snow drifting. Wind tunnel modeling is accepted as a method for aiding in Green building design. For instance, the use of boundary layer wind tunnel modeling can be used as a credit for Leadership in Energy and Environmental Design LEED certification through the U.
Green Building Council. Wind tunnel tests in a boundary layer wind tunnel allow for the natural drag of the Earth's surface to be simulated. For accuracy, it is important to simulate the mean wind speed profile and turbulence effects within the atmospheric boundary layer.
Most codes and standards recognize that wind tunnel testing can produce reliable information for designers, especially when their projects are in complex terrain or on exposed sites. In the United States, many wind tunnels have been decommissioned in the last 20 years, including some historic facilities. Pressure is brought to bear on remaining wind tunnels due to declining or erratic usage, high electricity costs, and in some cases the high value of the real estate upon which the facility sits.
On the other hand, CFD validation still requires wind-tunnel data, and this is likely to be the case for the foreseeable future. Studies have been done and others are underway to assess future military and commercial wind tunnel needs, but the outcome remains uncertain.
J. B. Barlow, W. H. Rae, Jr, A. Pope-Low Speed Wind Tunnel Testing. 1-John Wiley & Sons (1999).pdf
Barlow, William H. Rae, Alan Pope. A brand-new edition of the classic guide on low-speed wind tunnel testing While great advances in theoretical and computational methods have been made in recent years. Martin Wind Tunnel. Biblio is a marketplace for book collectors comprised of thousands of independent, professional booksellers, located all over the world, who list their books for sale online so that customers like you can find them! When you place your order through Biblio, the seller will ship it directly to you. Bookseller Completion RateThis reflects the percentage of orders the seller has received and filled.
Concessao , Jaimon Quadros. All Rights Reserved. Low speed wind tunnel testing has evolved over the last century and has become a cornerstone in the development of aviation vehicles. Study of the effects of aerodynamics and its influence are substantial in the design of aircrafts and much fluid effect based engineering machines. The forces involved in the dynamic interactions of fluids and solids have only begun to be lifted, therefore the study of wind behavior is necessary to design large Airplanes. A conditioning circuit was also developed in order to record the CL and CD values which gave smooth output data values.
They may be of open-return type also known as the Eiffel type, see figure , or closed-return flow also known as the Prandtl type, see figure with air moved by a propulsion system usually consisting of large axial fans that increase the dynamic pressure to overcome the viscous losses. The working principle is based on the continuity and Bernoulli's equation :. In a return-flow wind tunnel the return duct must be properly designed to reduce the pressure losses and to ensure smooth flow in the test section. The compressible flow regime: Again with the continuity law, but now for isentropic flow gives:. High subsonic wind tunnels 0.
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