Wind Tunnel

7 Key excerpts on "Wind Tunnel"

• 

  eBook - PDF

  Wind Tunnels

  • Satoru Okamoto(Author)
  • 2011(Publication Date)
  • IntechOpen

    (Publisher)

  Part 1 Wind Tunnel Technologies and Devices 1 Environmental Wind Tunnels Jonathan Merrison Aarhus University, Denmark 1. Introduction Wind Tunnels have been used extensively in industry and research applications over the past 50 years. They vary greatly in scale and geometry, with some large enough to house and test small aircraft (see for example NASA, ATP facilities) and others are miniaturized flow generators used in the calibration of small sensors. However they invariably utilize the same basic technology and design elements. Similarly environmental simulators are also used widely in research, for example in climate and planetary studies. Here again they superficially vary greatly in size and configuration, but basically consist of a hermetic chamber with some form of temperature control [Jensen et al. 2008]. There is therefore a broad array of standard and often commercial technologies and construction techniques which have been successfully applied within the fields of Wind Tunnel and environmental simulator design. Some of these technologies and techniques will be outlined in this chapter to aid researchers or technology developers in their efforts to design or use environmental Wind Tunnels and also serve as an informative guide to those new to these fields of investigation. The fusion of an environmental simulator and a Wind Tunnel is a natural evolution of laboratory based technology to fulfill the need to reproduce specific physical conditions found in nature. Although facilities of this kind are only now being fully developed, they have the potential to expand into a new research field that could substantially contribute to our understanding of climate and mediate growth in advanced sensor technologies. In this chapter many of the challenges in designing and constructing environmental Wind Tunnels will be introduced and possible solutions presented, with some emphasis placed on extreme terrestrial and Martian planetary conditions.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Modelling the Flying Bird

  • C.J. Pennycuick(Author)
  • 2008(Publication Date)
  • Academic Press

    (Publisher)

  It is in the nature of flying birds that they do not stay still to be observed. However, motion is relative, and it is possible for the bird to stay still relative to the observer, while still flying normally, if the air moves. This may happen naturally where the wind blows against a cliff, or it can be made to happen artificially in a Wind Tunnel. A Wind Tunnel is a device that produces a stream of air that flows past the observer at a known speed and in a controlled manner. It is an essential tool in aeronautical research, because a model that remains stationary, with the air moving past it, is physically identical to the same model moving through still air, but much more convenient for observation and measurement.

  14.1 Wind Tunnel Basics

  14.1.1 Required Attributes For A Wind Tunnel

  The air flow in the test section of a Wind Tunnel, where the bird flies, must satisfy the following basic requirements, if measurements made in the tunnel are to have some relevance to the bird's performance in the open air.

  (1) The experimenter must have access to the bird while experiments are in progress. (2) The tunnel must be capable of maintaining a steady wind speed, which is constant over the whole cross section of the test section, and can be accurately set and measured by the experimenter. (3) The direction of flow must be constant throughout the test section, and parallel to the centreline. (4) The level of small‐scale turbulence in the test section must be low. (5) Finally, the facility to tilt the tunnel so as to simulate climb and descent is so useful that it should be considered an essential requirement.

  There is a large volume of published literature, especially in flight physiology, about experiments in Wind Tunnels that do not satisfy any of the above requirements. Before pointing out the advantages and shortcomings of particular Wind Tunnel layouts, I shall first mention a couple of principles that apply to all Wind Tunnels, and then outline the functions of the major components (the fan, settling section, contraction and test section) that are found in all but the most primitive Wind Tunnels. More detailed information can be found in textbooks on low‐speed Wind Tunnel engineering such as Pankhurst and Holder (1965) and Rae and Pope (1984).

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Thermal Measurements in Electronics Cooling

  • Kaveh Azar(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  Wind Tunnels are frequently used to provide a controlled simulation of air flow conditions encountered when forced air cooling is used for electronic systems. Combined with theoretical analysis and increasingly integrated with computational simulations of flow and heat transfer, Wind Tunnel tests often constitute an essential part of the electronic system design cycle. As Bergles explains (Bergles, 1990), the role of experimentation, in this case including Wind Tunnel testing, is not expected to be supplanted by computational simulations in the immediate future. Indeed, new developments in measurement techniques for temperature, heat flux, and air flow elucidated elsewhere in this handbook have made Wind Tunnel tests more effective — and have placed new demands and constraints on Wind Tunnel design. In this Chapter, I will examine the design of Wind Tunnels to be used for simulation of forced air cooling of electronic components and assemblies at the device, board, and system levels, as well as for related fundamental research. The material is aimed at the engineer who has no prior Wind Tunnel design experience, and is intended to be applicable whether selecting a complete, “turn-key” commercial Wind Tunnel system, modifying or evaluating an existing system, or for a “blank page” design of a unique new facility.

  9.1.1      Historical backgound

  Any introduction to Wind Tunnel design must acknowledge that the present understanding of the art has been developed primarily from aeronautical needs. Wind Tunnels have been used widely to simulate air flow about complete aircraft, specific aircraft components, and to conduct fundamental research concerning flow phenomena related to flight for over a century (Prandtl and Tietjens, 1934; Baals and Corliss, 1981). The effectiveness of the Wind Tunnel was demonstrated by the Wright brothers, who developed their early wing designs using subscale tests in a small, low-cost tunnel. More recently, Wind Tunnel testing has become an integral part of the automobile design and development cycle (Hucho and Sovran, 1993), and has become routine for such applications as testing of atmospheric wind erosive effects and building-wind interactions. Some of the largest, most complex Wind Tunnel facilities operated by government, universities, and industry are catalogued by Pẽnaranda and Freda (1985); a list of some larger, low-speed facilities is provided by Rae and Pope (1984). Still, the vast majority of the literature concerning Wind Tunnel system and individual part design — as well as the commercially available Wind Tunnel apparatus — has been developed with a view to the particular needs of aeronautical research and testing.

  But aeronautical applications pose very different requirements than does the simulation of forced air cooling. Considering subsonic aircraft as an example, the full-scale Reynolds number (and Mach number) of flight conditions is to be simulated as closely as possible, and the forces experienced by the aircraft are generally of primary concern. Subscale models are preferred because of their low cost, although the need to simultaneously simulate both Reynolds and Mach numbers generally limits the ability to reduce model size. Aeronautical facilities which employ increased pressure and/or lowered air temperature compared to standard ambient conditions can achieve closer matches in Reynolds and Mach numbers for subscale testing. But inevitably, aeronautical Wind Tunnels will employ much higher air speeds than are common in electronics cooling simulations, wherein the test model is frequently full size or simply an actual component or system.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Wind Forces in Engineering

  • Peter Sachs(Author)
  • 2013(Publication Date)
  • Pergamon

    (Publisher)

  CHAPTER* Wind-tunnel Techniques WIND-TUNNEL tests on a structural model are needed when the full-scale structure cannot be tested or analysed. Very few industrial structures can be analysed accurately, particularly when they have solid and not lattice faces, and objects of tunnel tests include bridges, chimneys, vehicles, buildings, radars. Normally, forces, moments and pressures are found on rigid models, but deflections and oscillatory effects can be determined on flexible or spring-mounted scaled models. Although the major industrial (non-aerodynamic) use of wind-tunnels is to deter-mine the response of a structure to wind forces, a second important application is to ascertain the pattern of wind flow to leeward of a structure. Research is carried out on the eddy formation behind bluff bodies to find the frequency and strength of oscil-latory forces; on the structure of a turbulent air-stream, and on the simulation of natural boundary layer effects. 4.1. Wind-tunnels In general the wind-tunnels developed for aircraft work are suitable for bluff models ; they are basically of two types—open jet and closed jet (Fig. 4.1a, b). In the open-jet tunnel the working section, where the model is situated, has no side walls, so that the air-stream is spilled out by the model, and the force and pressure readings are artificially low. The closed-jet tunnel, with side walls, constrains the air-flow past the model, so that forces and pressures are artificially high. Measurements are made by conventional instrumen-tation, such as force and moment balances and pressure manometers, and the stiffness and damping of flexible structures is either simulated in the model, or by mounting a rigid model on springs with eddy-current damping. The main differences between aircraft and industrial testing lie in model manufacture and the calculation of test results. For bluff models, the effect of air-flow separation at sharp edges swamps the effects of small detail or surface roughness.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Wind Loading of Structures

  • John D. Holmes, Seifu Bekele(Authors)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 7 Laboratory simulation of strong winds and wind loads

  7.1 Introduction

  Practising structural engineers will not generally themselves operate Wind Tunnels, or other laboratory equipment, for simulation of strong wind effects on structures, but they may be clients of specialist groups who will provide wind loading information for new or existing structures, usually by means of model tests. For this reason, this chapter will not attempt to describe in detail Wind Tunnel, or other simulation, techniques. There are detailed references, guide books and manuals of practice available which perform this function (e.g. Cermak, 1977; Reinhold, 1982; Australasian Wind Engineering Society, 2019; American Society of Civil Engineers, 2012). However, sufficient detail is given here to enable the educated client to be able to ‘ask the right questions’ of their wind-tunnel contractors.

  In the following sections, a brief description of Wind Tunnel layouts is given, and methods of simulation of natural wind flow and experimental measurement techniques are discussed.

  7.2 Wind-tunnel history and layouts

  7.2.1 Historical

  The first use of a Wind Tunnel to measure wind forces on buildings is believed to have been made by W. C. Kernot in Melbourne, Australia (1893). A sketch of the apparatus, which he called a ‘blowing machine’, is given in Figure 7.1 (Aynsley et al. , 1977). This would now be described as an “open-circuit, open test-section” arrangement. With this equipment, Kernot studied wind forces on a variety of bluff bodies – cubes, pyramids, cylinders, etc. – and on roofs of various pitches.

  Figure 7.1

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Wind Effects on Cable-Supported Bridges

  • You-Lin Xu(Author)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  7 Wind Tunnel Studies

  7.1 Preview

  As can be seen from earlier chapters, wind-induced response analyses of long-span cable-supported bridges or coupled vehicle-bridge systems require some basic aerodynamic parameters or functions such as force coefficients, flutter derivatives and aerodynamic admittance functions. At present, these parameters and functions are obtained mainly from Wind Tunnel section model tests. To ensure the functionality and safety of long-span cable-supported bridges under strong wind conditions, full aeroelastic model tests are often carried out in Wind Tunnels to observe and quantify their aeroelastic behavior. Wind Tunnel studies are also performed to explore some new aerodynamic or aeroelastic phenomena, such as rain-wind-induced cable vibration. There are also many situations in which the wind load and the wind-induced responses of bridges and vehicles cannot be predicted with sufficient accuracy, either to assure functionality and safety or to avoid using uneconomically large safety factors. In such situations, it may be desirable to conduct Wind Tunnel tests of structural models. This is particularly true when seeking aerodynamic measures to mitigate vortex shedding-induced vibration or increase critical flutter velocity, as will be discussed in Chapter 12.

  Techniques for the modeling of wind effects on bridge structures have improved considerably in the past with the advent of several large Wind Tunnels designed to produce turbulent boundary layer models of the natural wind. New measurement techniques used in Wind Tunnel tests have also been developed to significantly improve the measurement accuracy.

  This chapter first introduces the common types of boundary-layer Wind Tunnels used for bridge wind engineering, followed by a general discussion for model scaling requirements and boundary wind simulation. The most common types of Wind Tunnel tests for bridge wind engineering are then presented, and the methods for identifying aerodynamic parameters and functions are introduced. Special Wind Tunnel tests for rain-wind-induced cable vibration and wind-vehicle-bridge interaction are finally described. Since not all of the model scaling requirements and boundary wind simulation requirement can be satisfied in most Wind Tunnel tests, the validation of Wind Tunnel tests by field measurements is sometimes necessary.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Wind Tunnel Designs and Their Diverse Engineering Applications

  • N. A. Ahmed(Author)
  • 2013(Publication Date)
  • IntechOpen

    (Publisher)

  Although stationary Wind Tunnels have great utility, they are limited to testing disturbed soil surfaces that have been removed from their natural setting. The development of field portable Wind Tunnels has greatly expanded our ability to investigate aeolian processes in the field under controlled conditions. 2. Portable Wind Tunnels Over the last six decades, portable Wind Tunnels have been developed and used on natural soil surfaces to measure the effects of soil surface characteristics and protective cover on soil erodibility and dust emissions [24]. In their simplest form, portable field Wind Tunnels must have at least three components: 1.) a self contained or at least portable power source such as an internal combustion engine, 2.) a fan or blower to induce air movement and create an ar‐ tificial wind, and 3.) a working section that trains the wind from the blower over a finite area of soil surface. Portable Wind Tunnels in which the fan or blower pushes air through the working section are called pusher-type tunnels and if the fan or blower pulls the air through the working section they are called suction-type Wind Tunnels. Other components may in‐ clude transition sections between the blower and the working section including a flow con‐ ditioning section and instrumentation to measure the wind speed in the working section and/or to capture sediment at the mouth of the working section. A typical portable field Wind Tunnel is presented in Figure 1. The use of portable field Wind Tunnels has been traced back as far as the early 1940s, but the designers and builders did not publish retrievable documentation of their efforts. Austin Zingg, a mechanical engineer with the US Department of Agriculture, was the first to docu‐ ment the design and construction of a portable Wind Tunnel [25].

  Sign up to read

  Learn more about book