Academic literature on the topic 'Rectangular wind tunnels'

Portable wind erosion tunnels must satisfy several aerodynamic criteria to ensure that the flow within them acceptably reproduces the atmospheric flow causing natural wind erosion. We define these criteria and use them to assess the flow and turbulence in two alternative designs of portable wind erosion tunnel: the first has a working section with an approximately triangular, 'tent-shaped' cross section, while the second has a conventional, rectangular working section. The measurements were made with Pitot-static tubes and X-configuration hot-wire anemometers, over stable (non-eroding) rough surfaces, mainly mowed grass of height 1 cm. We found that, with careful attention to flow conditioning elements such as honeycombs and tripping fences, an acceptable flow can be achieved in the rectangular tunnel. The flow in the tent-shaped tunnel is less satisfactory, exhibiting departures from the logarithmic wind profile law which depend on the surface roughness.

Analytical solutions for the three-dimensional inhomogeneous wave equation with flow in a hardwall rectangular wind tunnel and in the free field are presented for a stationary monopole noise source. Dipole noise sources are calculated by combining two monopoles 180 deg out of phase. Numerical calculations for the modal content, spectral response and directivity for both monopole and dipole sources are presented. In addition, the effect of tunnel alterations, such as the addition of a mounting plate, on the tunnels reverberant response are considered. In the frequency range of practical importance for the turboprop response, important features of the free field directivity can be approximated in a hardwall wind tunnel with flow if the major lobe of the noise source is not directed upstream. However, for an omnidirectional source, such as a monopole, the hardwall wind tunnel and free field response will not be comparable.

This study describes the start/unstart characteristics of a finite and rectangular supersonic biplane wing. Two wing models were tested in wind tunnels with aspect ratios of 0.75 (model A) and 2.5 (model B). The models were composed of a Busemann biplane section. The tests were carried out using supersonic and transonic wind tunnels over a Mach number range of0.3≤M∞≤2.3with angles of attack of 0°, 2°, and 4°. The Schlieren system was used to observe the flow characteristics around the models. The experimental results showed that these models had start/unstart characteristics that differed from those of the Busemann biplane (two dimensional) owing to three-dimensional effects. Models A and B started at lower Mach numbers than the Busemann biplane. The characteristics also varied with aspect ratio: model A (1.3<M∞<1.5) started at a lower Mach number than model B (1.6<M∞<1.8) owing to the lower aspect ratio. Model B was located in the double solution domain for the start/unstart characteristics atM∞=1.7, and model B was in either the start or unstart state atM∞=1.7. Once the state was determined, either state was stable.

The approach to problems of wall interference in wind tunnel testing is generally based on the so-called classical method, which covers the wall interference experienced by a simple small model or the neo-classical method that contains some improvements as such that it can be applied to larger models. Both methods are analytical techniques offering solutions of the subsonic potential equation of the wall interference flow field. Since an accurate description of wind tunnel test data is only possible if the wall interference phenomena are fully understood, uncounted subsequent efforts have been spent by many researchers to improve the limitation of the classical methods by applying new techniques and advanced methods. However, the problem of wall interference has remained a lasting concern to aerodynamicists and it continues to be a field of active research until the present. The main objective of this paper is to present an improved classical method of the wall interference assessment in rectangular subsonic wind tunnel with solid-walls.

Our understanding of animal flight benefits greatly from specialized wind tunnels designed for flying animals. Existing facilities can simulate laminar flow during straight, ascending and descending flight, as well as at different altitudes. However, the atmosphere in which animals fly is even more complex. Flow can be laminar and quiet at high altitudes but highly turbulent near the ground, and gusts can rapidly change wind speed. To study flight in both laminar and turbulent environments, a multi-purpose wind tunnel for studying animal and small vehicle flight was built at Stanford University. The tunnel is closed-circuit and can produce airspeeds up to 50 m s −1 in a rectangular test section that is 1.0 m wide, 0.82 m tall and 1.73 m long. Seamless honeycomb and screens in the airline together with a carefully designed contraction reduce centreline turbulence intensities to less than or equal to 0.030% at all operating speeds. A large diameter fan and specialized acoustic treatment allow the tunnel to operate at low noise levels of 76.4 dB at 20 m s −1 . To simulate high turbulence, an active turbulence grid can increase turbulence intensities up to 45%. Finally, an open jet configuration enables stereo high-speed fluoroscopy for studying musculoskeletal control in turbulent flow.

Accurate monitoring of the tunnel wind speed plays a key role in achieving intelligent mine ventilation. Based on the difficulty faced in precise reflection of the average tunnel wind speed by point wind speed monitoring, this paper puts forward a method for accurate monitoring the tunnel wind speed by large-span ultrasonic linear wind speed sensor based on the method of the time difference. Besides, as to the core problem of representing the average section wind speed by section-linear wind speed, the distribution rules of section wind speed in rectangular tunnel with various support forms is studied through combing theoretical analysis and experimental verification. The results could be well applied to rapid determination of ventilation parameters in other coal mines, which is better for the ventilation management of mines.

This paper describes the wind tunnel testing of a Blended Wing Body (BWB) with rectangular canards and twisted wing (Baseline II E2 configuration) developed in Universiti Teknologi MARA (UiTM). The experiment work was carried out in UiTM low speed wind tunnel using 1:6 scaled model of BWB at Mach 0.1. The testing is conducted for canard’s deflection angle between 0° to +20. The results show by adding the canard surface to the BWB’s body, at 12 degree and higher angles of attack,α there will be a slight increment in lift. Maximum lift-to-drag ratio decreases with increasing canard surface deflection. Also, by adding the canard surface, the value of moment at zero lift,CM,0 is increased.

Flow structure is a crucial point for the conceptual design of Wing-in-Ground effect (WIG) crafts. In this study, pressure distributions around a compound wing, velocity and the turbulent intensity distribution in the wake area after trailing of the wing, have been investigated numerically. Computational simulations were completed regarding various angles of attack in-ground-effect. Two parts made up the compound wing: The first composed by one rectangular wing in the center, the second composed by a reverse taper wing, consisting of an anhedral angle at the side. A realizable k-ε turbulent model exhibited the flow field in the physical domain about the wing surface. The numerical results of the compound wing were validated using the data provided by wind tunnel tests. The flow structures around the compound wing were compared with that of a rectangular wing for different conditions. It was found that the pressure distribution on the rectangular wing was weaker than at the lower surface for the compound wing. However, the suction effect on the upper surface of the rectangular wing was higher. Also, the velocity defect and the turbulence level in the wake area was greater behind the compound wing.

The paper deals with the wind action on flat roofs of rectangular shapes which can be considered for medium-rise and high-rise buildings. Distributions of mean pressure coefficient Cp on flat roofs were measured. All analyses were based on model measurements which had been performed in the boundary layer wind tunnel in Wind Engineering Laboratory of Cracow University of Technology. Vertical, fixed in the floor of the wind tunnel on the turn table rectangular prisms of the ratio of cross-section dimensions 1:2 and 1:4 were investigated. Measurements were carried out for the angle of wind attack in the range 0°-90°, every 15°. The influence of the wind structure on pressures was investigated in six different cases of the approaching wind.

碩士
淡江大學
土木工程學系
85
Due to slenderness and less rigidity of modern building, wind loads become the dominate lateral force for highrise building design . The fluctuating wind loads acting on hig-rise building consist of drag force , periodic acrosswind force due to vortex shedding and torsional force due to load asymmetry. The paper studies torsional force on a rectangular prism with various cross sectional length -to-width ratio in two simulated atmospheric boundary layer flows .The experiments were performed by a new pressure-measured system. Through this system ,pressures at four side of rectangular prisms can be measured simultaneously, and then relationship between torsion and drag force ,lift force can be obtained. The results indicate that torsion will increase with length -to- width ratio .when length - to-width ratio less then critical value , 70%~90% of torque comes from asymmetries pressure distributions on the leeward side . If length -to-width ratio greater then critical value ,50%~90% of torque comes from the side face ,,the contributions increase with length -to-width ratio. The contributions to the torque from the two half forces of each side are opposite to each other and tend to cancel out .Therefore , the vortex shedding peak in the pressure spectrum on side face doesn''t appear in the torque spectrum .However , the contributions to the torque from the two leeward half faces are the same , the effects tend to add up .So the vortex shedding peak will appear in the torque spectrum .

Tese de doutoramento em Engenharia Mecânica, no ramo de Aerodinâmica Industrial e Engenharia do Vento, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
The transport of soil particles by wind is of enormous relevance in a wide range of events from those related to agriculture (e.g., seed transport) to the formation and modification of the landscape. A classic example is sand dunes, which can be formed, moved, or entirely eroded due to aeolian processes. Still, aeolian transport of particles may cause serious damage in transportation, communications and severe environmental problems, such as the degradation of air quality due to dispersion of pollutants from stockpiles. The wind exposure will lead to the particles movement through several mechanisms, such as, suspension, creeping, saltation, and saltation bombardment. Consequently, the free surface will change over time due to entrainment and deposition phenomena. The main objective of this study is assessing the airflow characteristics over and around granular material complex three-dimensional piles when subjected to the wind erosion and its influence in the behavior of the free surface, as well as, in the sand emission rate. A literature review was made over the main subjects of interest to the present work, from the basics, such as granular material and aeolian transport mechanisms, to the key magnitudes involved in the wind erosion phenomena. Studies performed to calculate the dust emission from stockpiles are presented and reviewed along with the widely applied methodology from United States Environmental Protection Agency (USEPA). This methodology estimates the emission of particles from stockpiles only during specific erosion events, such as bursts, when in reality emissions occur in many other occasions. The present work offers the possibility of conducting the determination of emissions from stockpiles along time; this approach makes viable to follow the time-dependent evolution of the free surface enhancing in this way the accuracy of the predictions. Therefore, studies that are related to free surface progress are also reviewed. The present work has a significant experimental component, and the thesis describes in considerable detail the experimental apparatus and procedures, including wind tunnel, granular material, tested pile configurations and performed tests – in particular, erosion and shear stress (with Irwin probes) measurements. In addition, the use of Computational Fluid Dynamics (CFD) plays an important role in the present study; therefore, for completeness, key concepts related to CFD are included in this thesis along with a brief survey of studies that employ CFD methodology to evaluate aeolian erosion. The present CFD studies were conducted by using an open source CFD code – OpenFOAM (OF). The motivation for the selection of OF, as the CFD tool, is related to its wide acceptance in the scientific community; moreover, its application to the prediction and study of wind erosion is an original contribution to this field of research. Full description of the numerical model and its implementation are given along with the methodology used in the model validation. Two different pile configurations were studied - a two-dimensional triangular pile and a three-dimensional oblong pile. The increasing geometrical complexity of the piles allowed gaining gradual experience with the procedures and methodologies involved. The experimental and numerical studies for these cases and their results are analyzed and discussed. In what concerns the oblong piles, the numerical results are correlated with the registered free surface deformation of the piles and compared against other study available in the literature, in which oil film visualization tests were conducted and a different CFD tool was used. Considering that the model validation is partly performed against experimental results, particular attention was given to their accuracy. For the triangular piles, the comparison is primarily against the wall shear stress results obtained using the Irwin probes, which were built and calibrated for this work. The study of these probes was extensive and it led to an innovative and significant contribution to this field of research, which justifies an integrated, but autonomous Part B of this thesis. Due to the versatility of experimental apparatus built to assist the calibration of the Irwin probes, a more in-depth study was also carried out on the flow through rectangular ducts with a constant and variable cross-section. Finally, the main findings resulting from the present work are summed up and some recommendations for future work are given.
O transporte de partículas do solo pelo vento é de enorme relevância numa ampla gama de eventos, desde os relacionados com a agricultura (por exemplo, o transporte de sementes) até a formação e modificação da paisagem. Um exemplo clássico são as dunas de areia, que se podem formar, mover ou erodir totalmente devido a processos eólicos. Por outro lado, o transporte de partículas pode provocar sérios danos no sector dos transportes, comunicações e graves problemas ambientais, como a degradação da qualidade do ar devido à dispersão de poluentes provenientes de pilhas de armazenamento. A exposição ao vento pode levar ao movimento das partículas através de vários mecanismos, tais como, suspensão, arrastamento, saltação e bombardeamento das partículas em saltação. Consequentemente, a superfície livre irá mudar ao longo do tempo devido aos fenómenos de arrastamento e deposição. O objetivo principal deste estudo é investigar as características do fluxo de ar sobre e ao redor de pilhas tridimensionais (3D) complexas de material granular quando sujeitas à erosão do vento e avaliar a sua influência no comportamento da superfície livre, bem como na taxa de emissão. Uma revisão bibliográfica foi feita sobre os principais temas de interesse para o presente trabalho, desde o básico, como material granular e mecanismos de transporte eólicos, até às grandezas chave envolvidas nos fenómenos de erosão do vento. Estudos realizados para calcular a emissão de poeira de pilhas de armazenamento são apresentados e revistos juntamente com a metodologia, amplamente aplicada, da Agência de Proteção Ambiental dos Estados Unidos (United States Environmental Protection Agency - USEPA). Esta metodologia estima as emissões de partículas a partir de pilhas de armazenamento apenas durante eventos de erosão específicos, tais como rajadas, quando as emissões na realidade ocorrem em muitas outras ocasiões. O presente trabalho oferece a possibilidade de realizar a determinação de emissões de pilhas de armazenamento ao longo do tempo; esta abordagem torna viável seguir a evolução dependente do tempo da superfície livre, aumentando assim a precisão das previsões. Portanto, estudos relacionados com a evolução da superfície livre são também revistos. O presente trabalho tem uma componente experimental significativa, e a tese descreve em considerável detalhe a montagem experimental e os procedimentos, incluindo o túnel de vento, material granular, as configurações de pilhas testadas e os testes executadas – em particular, testes de erosão e de medição da tensão de atrito (com sondas Irwin). Adicionalmente, o uso da Dinâmica de Fluidos Computacional (em inglês: Computational Fluid Dynamics — CFD) desempenha um papel importante no presente estudo, assim sendo, para completar, conceitos chave relacionados a CFD estão incluídos nesta tese, juntamente com uma breve pesquisa de estudos que empregam a metodologia CFD para avaliar a erosão eólica. Os presentes estudos CFD foram realizados usando um software CFD de código aberto - OpenFOAM (OF). A motivação para a seleção do OF, como ferramenta CFD, está relacionada com a sua ampla aceitação na comunidade científica; e além disso, a sua aplicação na previsão e estudo da erosão eólica é uma contribuição original para este campo de pesquisa. A descrição completa do modelo numérico e da sua implementação são dadas juntamente com a metodologia utilizada na validação do modelo. Foram estudadas duas configurações de pilha diferentes - uma pilha triangular bidimensional (2D) e uma pilha tridimensional (3D) oblonga. A crescente complexidade geométrica das pilhas permitiu ganhar experiência de forma gradual com os procedimentos e metodologias envolvidos no estudo. Os estudos experimentais e numéricos para estes casos, bem como os seus resultados, são analisados e discutidos No que diz respeito às pilhas oblongas, os resultados numéricos são correlacionados com a deformação de superfície livre das pilhas e comparados com outro estudo disponível na literatura, no qual foram realizados testes de visualização de filmes de óleo e utilizada uma ferramenta CFD diferente. Considerando que a validação do modelo é parcialmente realizada através da comparação dados experimentais; especial atenção foi dada à sua precisão. Para as pilhas triangulares, a comparação é feita, principalmente, com resultados da tensão de atrito da parede medidos através das sondas Irwin, as quais foram construídas e calibradas para este trabalho. O estudo efetuado com estas sondas foi extenso e contribuiu de forma inovadora e significativa para esta área de pesquisa, o que justifica uma Parte B integrada, mas autónoma desta tese. Devido à versatilidade da montagem experimental construída para auxiliar a calibração das sondas Irwin, um estudo mais aprofundado foi também realizado sobre escoamentos em condutas retangulares com seção transversal constante e variável. Finalmente, as principais conclusões que resultam do presente trabalho são resumidas e sugerem-se algumas recomendações para o trabalho futuro.

Fluid-structure and pedestrian-structure interaction phenomena are extremely important for non-conventional bridges. The results presented in this volume concern: simplified formulas for flutter assessment; innovative structural solutions to increase the aeroelastic stability of long-span bridges; numerical simulations of the flow around a benchmark rectangular cylinder; examples of designs of large structures assisted by wind-tunnel tests; analytical, computational and experimental investigation of the synchronisation mechanisms between pedestrians and footbridge structures. The present book is addressed to a wide audience including professionals, doctoral students and researchers, aiming to increase their know-how in the field of wind engineering, bluff-body aerodynamics and bridge dynamics.

The present study addresses two aspects of the horseshoe vortex, namely its significance in the secondary flow in a turbine blade passage and the possibility of reducing its strength by an active flow mechanism, i.e the transverse injection of coolant air through a slot in a cylinder-endwall junction. The study reports on the results of two experiments in low speed wind tunnels, which employed a calibrated five-hole Pitot tube to measure the velocity vectors and the resulting secondary flowfields. The first aspect was studied in a 90° square cross section bend duct. The two horseshoe vortex legs were simulated by two half-Delta wing vortex generators. The results showed that the horseshoe vortices influence two regions of the secondary flowfield, i.e one near the passage entrance, where the pressure side leg forces a three dimensional separation of the endwall boundary layer, and the other is in the exit plane, where the coupling of the horseshoe with the passage vortex redistributes the flow with total pressure losses, without affecting the total loss, and increases the secondary kinetic energy by about 20%. For the second aspect, a rectangular bluff body, with a cylindrical leading edge, was positioned over the tunnel endwall and the transverse air injection was implemented through a thin slot, covering the 180° arc in the leading edge-endwall junction. The results showed that, for an average injection velocity equal to 35% that of the mainstream, the size and strength of the horseshoe vortex leg were reduced by nearly 60%. On the other hand, for stronger injection rates the vortex size and strength were increased.

The continuous development of wind turbine technology gradually leads to larger, more flexible blades with increasing aspect ratios and high tip speeds, while in everyday operation or extreme cases the blades experience stalled flow conditions. These aforementioned facts create the need for further study and physical understanding of stall induced vibrations – stall flutter. In this context an aeroelastic setup was constructed at the NTUA subsonic wind tunnel with a rigid rectangular wing (500 mm × 1400 mm) of a NACA 64-418 airfoil supported by a spring system that enables pitching and plunging motions. The elastic axis of the wing is located 35% of the chord far from the leading edge while its center of mass at 46%. Increasing the free stream velocity (up to Re = 670 000) under various initial static angles of attack, the wing was set at fluid induced oscillations (pitching and plunging). The response of the wing under these conditions was recorded employing two accelerometers and two wire sensors for both the rotational and linear wing displacements. At the same time, in the middle of the wing span thirty (30) fast responsive pressure transducers measured the pressure distribution along the chord, while strain gauges attached to the wing rotating shaft measured the applied unsteady aerodynamic loading. Based on the above simultaneously measured quantities various aspects of the aeroelastic instability of the examined wing were revealed.

Abstract A spring-supported test for a rectangular cross section with the side ratio of B/D = 1.18 (B: along-wind length, D: cross-wind length) was conducted to simulate the phenomenon in a closed circuit wind tunnel at Kyushu Institute of Technology. A new finding was that vibrations were confirmed in the neighborhoods of reduced wind speeds Vr = V/fD = 2 and Vr = 8 (V: wind speed (m/s), f: natural frequency (Hz)). Because the reduced wind speed in motion-induced vortex vibration is calculated as Vr = 1.67 × B/D = 1.67 × 1.18 = 2.0, vibrations around Vr = 2 were considered to be motion-induced vortex vibration. On the other hand, vibrations around Vr = 8 were considered to be Kármán vortex-induced vibrations, because Vr = 1/St = 8.1. St has a Strouhal number of 0.124 measured by wind tunnel test using a rectangular cross section of B/D = 1.18. In this paper, the authors focused on the wind tunnel model configuration. Rectangular column flanges in steel structures have not usually been taken into account when manufacturing wind tunnel test models. Wind tunnel tests were carried out in order to clarify the effects of rectangular column flanges in steel structures on motion-induced vortex vibration. Spring-supported tests, smoke flow visualizations and measurements of Strouhal number and unsteady aerodynamic lift were performed with or without flanges changing angle of attack. Models were forced-oscillating in smoke flow visualizations and unsteady aerodynamic lift measurements. All wind tunnel tests were conducted in a smooth flow. As a result, it was found that it could be very important to model rectangular column flanges in steel structures for wind tunnel tests, especially bracing members of long-spanned truss bridges from a wind engineering point of view.

Experimental and computational studies of several representative IACC appendage geometries were carried out to establish baseline data and verify computational models and methods. Wind tunnel tests of an unheeled, unswept, constant section, rectangular planform keel mounted on a ground plane included force and moment measurements, and wake surveys at various angles of attack. Test configurations (all at constant draft) included the addition of ballast bulbs and winglets. Correlations of computational results with experimental wind tunnel data were made. A502/PAN AIR potential flow induced drag predictions proved to be in good agreement with the wind tunnel data. Comparisons are also presented between A598 (A502 + boundary layer), wind tunnel results and empirical predictions. Again good agreement was shown for cases within the limitations of the boundary layer method.

Most granular flows at environmental conditions are unsteady and exhibit a complex physical behavior. Dune formation and migration in the desert are controlled not only by the flow of saltating particles over the sand bed, but also by turbulent atmospheric airflow. In fact, sediments are transported by the atmospheric airflow within a thin layer only a few centimeters above the sandy surface. These jumping particles reach a maximum sediment mass flux level at a certain delay time (known as the “saturation time”) after the initial movement by sliding and rolling begins. Unlike sediment transport in water where the particles are lifted by the turbulent suspension, the saltating particles are kept alive in the layer mainly due to particle-particle and particle-bed collisions. In order to model this Aeolian transport of sand, Jenkins and Pasini [1] proposed a two-fluid model (one-dimensional and steady state) using Granular Kinetic Theory (GKT) to describe the solid-phase stress. The present work extends the original idea of Jenkins and Pasini [1] by using a more robust model of GKT for the kinetic/collisional contributions to the solid-phase stress tensor, together with a friction model activated for sustained contacts between particles. In addition, a standard k-ε turbulence model for the air and a drag model for the interaction between the phases are employed. A rectangular 2D geometry was chosen with a logarithmic profile for the inlet air velocity, along with an initial amount of sand at rest in the lower part of the simulation domain, resembling the particle saltating flow commonly seen in the vertical middle plane within saltation wind tunnels. This model is validated with experimental data from Liu and Dong [2] and the results given by Pasini and Jenkins [1]. A good estimation for the particle erosion and mass flux in the saltation layer is predicted, even though the profiles of mass flux and concentration within the transport layer are very thin and lower.

A wind tunnel study was carried out to examine the low speed instability of rectangular cross sections, which could occur at a lower wind speed range than that of Karman vortex-induced oscillation, if the Scruton number Sc = 2mδ/(ρD2), in which m = the mass of the system per length; δ = the system damping measured in still air; ρ = air density; D = is a reference length, is very small. The low speed instability was found by the full-scale measurements at bracing members having a rectangular cross section of the long-spanned truss bridge in Japan. The Scruton number of the bracing members was estimated to be approximately 2–3, therefore the low speed instability was thought to occur. However, the occurrence depended on the wind conditions. Unfortunately there are few past researches on the low speed instability on a rectangular cross section of B/D of less than 2, which is the ratio of the width B and height D. In this study, the free oscillation experiment and unsteady aerodynamic lift measurement were conducted in order to clarify the effects of an angle of attack, a yaw angle, cross section shapes and the turbulence intensity on the low speed instability.

Abstract The low-speed rectangular exit wind tunnel with sectioned contraction is widely used. The secondary flow vortices are found at contraction exit, which would lead to the non-uniform boundary layer and influence the aerodynamic experiment accuracy. In this paper, experimental and numerical approaches are adopted so as to clarify reasons for the formation of the secondary crossflow occurring at contraction exit and take measures to control it. The conclusions can be gotten as: the secondary crossflow is formed and developed in the second (rectangular-to-rectangular) contraction, and the first (circular-to-rectangular) contraction promote the secondary flow vortices to migrate to the middle of flow field to a certain extent; the formation of the secondary crossflow is related to the static pressure gradient in the contraction. Based on the mechanism analysis results, several methods aimed to control the secondary crossflow are proposed and verified, the results can be concluded as: in terms of the rectangular-to-rectangular contraction that contracts along one direction, it is difficult to effectively control the secondary crossflow just by optimizing contraction curves and contraction ratios, while adopting the boundary layer suction can significantly improve the boundary layer uniformity; if the rectangular-to-rectangular contraction contracts in two directions, such secondary crossflow can be well controlled.