Investigación de fenómenos de galope en cuerpos de diversa sección transversal

Los fenómenos aeroelásticos son relativamente frecuentes en las construcciones civiles modernas como edificios de oficinas, terminales de aeropuertos o fábricas. En este tipo de arquitectura aparecen con frecuencia estructuras flexibles sometidas a la acción del viento, como por ejemplo persianas formadas por láminas con distintos perfiles. Uno de estos perfiles es el perfil en Z, formado por un elemento central y dos alas laterales. Las inestabilidades de tipo galope se determinan en la práctica utilizando el criterio Glauert-Den Hartog. Este criterio precisa de la predicción exacta de la dependencia de los coeficientes aerodinámicos del ángulo de ataque. En esta tesis se presenta un estudio sistemático, tanto por métodos experimentales como numéricos de una familia completa de perfiles en Z que permite determinar sus regiones de inestabilidad frente al galope. Los análisis numéricos han sido validados con ensayos estáticos realizados en túnel de viento. Para la parte numérica se ha utilizado el código DLR TAU, que es un código de amplia utilización en la industria aeronáutica europea. En esta tesis se enfoca sobre todo a la predicción del galope en este tipo de perfiles en Z. Los resultados se presentan en forma de mapas de estabilidad. A lo largo del trabajo se realizan también comparaciones entre resultados numéricos y experimentales para varios niveles de detalle de las mallas empleadas y diversos modelos de turbulencia. ABSTRACT Aeroelastic effects are relatively common in the design of modern civil constructions such as office blocks, airport terminal buildings, and factories. Typical flexible structures exposed to the action of wind are shading devices, normally slats or louvers. A typical cross-section for such elements is a Z-shaped profile,made out of a central web and two-sidewings. Galloping instabilities are often determined in practice using the Glauert-DenHartog criterion.This criterion relies on accurate predictions of the dependence of the aerodynamic force coefficients with the angle of attack. The results of a parametric analysis based on both experimental and numerical analysis and performed on different Z-shaped louvers to determine translational galloping instability regions are presented in this thesis. These numerical analysis results have been validated with a parametric analysis of Z-shaped profiles based on static wind tunnel tests. In order to perform this validation, the DLR TAU Code, which is a standard code within the European aeronautical industry, has been used. This study highlights the focus on the numerical prediction of the effect of galloping, which is shown in a visible way, through stability maps. Comparisons between numerical and experimental data are presented with respect to various meshes and turbulence models.

Analysis of air flow past and through the 2415-3S airfoil for an unmanned aerial vehicle with internal propulsion system

This paper deals with the prediction of velocity fields on the 2415-3S airfoil which will be used for an unmanned aerial vehicle with internal propulsion system and in this way analyze the air flow through an internal duct of the airfoil using computational fluid dynamics. The main objective is to evaluate the effect of the internal air flow past the airfoil and how this affects the aerodynamic performance by means of lift and drag forces. For this purpose, three different designs of the internal duct were studied; starting from the base 2415-3S airfoil developed in previous investigation, basing on the hypothesis of decreasing the flow separation produced when the propulsive airflow merges the external flow, and in this way obtaining the best configuration. For that purpose, an exhaustive study of the mesh sensitivity was performed. It was used a non-structured mesh since the computational domain is three-dimensional and complex. The selected mesh contains approximately 12.5 million elements. Both the computational domain and the numerical solution were made with commercial CAD and CFD software, respectively. Air, incompressible and steady was analyzed. The boundary conditions are in concordance with experimental setup in the AF 6109 wind tunnel. The k-e model is utilized to describe the turbulent flow process as followed in references. Results allowed obtaining velocity contours as well as lift and drag coefficients and also the location of separation and reattachment regions in some cases for zero degrees of angle of attack on the internal and external surfaces of the airfoil. Finally, the selection of the configuration with the best aerodynamic performance was made, selecting the option without curved baffles.

Numerical analysis of air flow past the 2415-3S airfoil for an unmanned aerial vehicle with internal propulsion system

This paper deals with the prediction of pressure and velocity fields on the 2415-3S airfoil which will be used for and unmanned aerial vehicle with internal propulsion system and in this way analyze the air flow through an internal duct of the airfoil using computational fluid dynamics. The main objective is to evaluate the effect of the internal air flow past the airfoil and how this affects the aerodynamic performance by means of lift and drag forces. For this purpose, three different designs of the internal duct were studied; starting from the base 2415-3S airfoil developed in previous investigation, basing on the hypothesis of decreasing the flow separation produced when the propulsive airflow merges the external flow, and in this way obtaining the best configuration. For that purpose, an exhaustive study of the mesh sensitivity was performed. It was used a non-structured mesh since the computational domain is tridimensional and complex. The selected mesh contains approximately 12.5 million elements. Both the computational domain and the numerical solution were made with commercial CAD and CFD software respectively. Air, incompressible and steady was analyzed. The boundary conditions are in concordance with experimental setup in the AF 6109 wind tunnel. The k-ε model is utilized to describe the turbulent flow process as followed in references. Results allowed obtaining pressure and velocity contours as well as lift and drag coefficients and also the location of separation and reattachment regions in some cases for zero degrees of angle of attack on the internal and external surfaces of the airfoil. Finally, the selection of the configuration with the best aerodynamic performance was made, selecting the option without curved baffles.

Vortex-induced vibrations on bridges : the interaction mechanism in complex sections and a new proposed semi-empirical model

El presente trabajo de investigación se ocupa del estudio de las vibraciones verticales inducidas por vórtices (VIV) en aquellos puentes que, por sus características geométricas y propiedades dinámicas, muestran cierta sensibilidad este tipo de fenómeno aeroelástico. El objeto principal es el análisis del mecanismo de interacción viento-estructura sobre secciones no fuseladas de geometría simple, con objeto de realizar una adecuada caracterización del problema y poder abordar posteriormente el análisis de otras secciones de geometría más compleja, representativas de los principales elementos estructurales de los puentes, como arcos, tableros, torres y pilas. Este aspecto es fundamental durante la fase de diseño del puente, donde deberán tenerse en cuenta también una serie de detalles que pueden influir significativamente su sensibilidad ante problemas aerodinámicos, como la morfología y dimensiones principales de la sección transversal del tablero, la disposición de barreras de seguridad y barreras cortaviento, o las riostras que unen diferentes elementos estructurales. La configuración de dos elementos en tándem o la construcción de un puente en las inmediaciones de otro existente son otros aspectos a considerar respecto a la sensibilidad frente a efectos aeroelásticos. El estudio se ha llevado a cabo principalmente mediante la implementación de simulaciones numéricas que reproducen la interacción entre la corriente de aire y secciones representativas de modelos estructurales, a partir de un código CFD basado en el método de las partículas de vórtices (VPM), siguiendo por tanto un esquema Lagrangiano. Los resultados han sido validados con datos experimentales existentes, valores procedentes de ensayos en túnel de viento y registros reales a partir de diferentes casos de estudio: Alconétar (2006), Niterói (1980), Trans- Tokyo Bay (1995) y Volgogrado (2010). Finalmente, se propone un modelo semi-empírico para la estimación del rango de velocidades críticas y amplitudes de oscilación basado en la utilización de las derivadas de flameo de Scanlan, y la densidad espectral de las fuerzas aerodinámicas en el dominio de la frecuencia. The present research work concerns the study of vertical vortex-induced vibrations (VIV) in bridges which show certain sensitivity to this type of aeroelastic phenomenon. It focuses on the analysis of the wind-structure interaction mechanism on bluff sections, with the objective of making a good characterisation of the problem and subsequently addressing the analysis of sections with a complex geometry, which are representative of the bridge structural elements, such as arches, decks, towers and piers. This issue is of relative importance during the bridge design phase, since minor details of the aforementioned elements can significantly influence its sensitivity to aerodynamic problems. The shape and main dimensions of the deck cross section, the addition of safety barriers and windshields, the presence of braces to enhance the structure mechanical properties, the utilisation of cross sections in tandem arrangement, or the erection of a new bridge in the vicinity of another existing one are some of the aspects to be considered regarding the sensitivity to the aeroelastic effects. The study has been carried out mainly through the implementation of numerical simulations that reproduces the interaction between the airflow and the representative cross section of a structural bridge model, by the use of a CFD code based on the vortex particle method (VPM), thus following a Lagrangian scheme. The results have been validated with existing experimental data, values from wind tunnel tests and full scale observations from the different case studies: Alconétar (2006), Niterói (1980), Trans-Tokyo Bay (1995) and Volgograd (2010). Finally, a new semi-empirical model is proposed for the estimation of the critical wind velocity ranges and oscillation amplitudes based on the use of the Scanlan’s flutter derivatives and the power spectral density of aerodynamic force time history in the frequency domain.

Estudio y validación experimental del efecto de aire interno en un perfil aerodinámico hueco

La presente investigación se llevó a cabo en la Universidad Politécnica de Madrid (España) conjuntamente con la Universidad Nacional Experimental del Táchira (Venezuela). El estudio consistió en diseñar una cavidad interna dentro del perfil aerodinámico 2415-3s, el cual fue desarrollado en la Universidad Técnica Checa (Praga, República Checa). Se realizó un estudio computacional, mediante la técnica del CFD, de diferentes modelos de cavidades internas en este perfil, para seleccionar el diseño más adecuado, fabricando un prototipo en 3D; logrando de esta manera validar la simulación computacional con los datos experimentales obtenidos con los ensayos en el túnel de viento AF6109 de la Universidad Nacional Experimental del Táchira. También se aplicaron técnicas de visualización en el túnel de viento, como líneas de corriente de humo y películas de aceite sobre el perfil aerodinámico. Dicho procedimiento permitió corroborar la validación de la simulación computacional. El perfil aerodinámico seleccionado se denominó 2415-3s-TC, cuya característica principal consiste en tres canales independientes entre sí, alojados dentro de la cavidad interna, permitiendo que el flujo de aire forzado a través de la cavidad, cambiara de dirección, para desembocar lo más tangencialmente, así como, lo más perpendicularmente posible al escalón del perfil aerodinámico 2415-3s. Esta configuración de diseñó permitió elevar el coeficiente de sustentación para ángulos de ataque mayores a 8º, así como para ángulos cercanos al ángulo crítico. ABSTRACT This research was conducted at the Polytechnic University of Madrid (Spain) together with the National Experimental University of Táchira (Venezuela). The study was to design an internal cavity within the airfoil 2415-3s, which was developed in the Czech Technical University (Prague, Czech Republic). A computational study was performed using CFD technique, different models of internal cavities in the profile to select the most appropriate design, manufacturing a prototype 3D; thus achieving validate the computer simulation with experimental data obtained from the tests in the wind tunnel AF6109 of the National Experimental University of Táchira. Visualization techniques were also applied in the wind tunnel, as streamlines smoke and oil films on the airfoil. This procedure corroborated validation of computational simulation. The airfoil selected denominated 2415-3s-TC, whose main characteristic consists of three independent channels each other, housed within the inner cavity, allowing the forced air flow through the cavity, change direction, to lead as more tangentially and, as perpendicular as possible to the step 2415-3s aerofoil. This configuration designed allowed increasing the lift coefficient for higher angles of attack to 8º, and for angles near the critical angle.

Optimization of energy extraction in transverse galloping

A numerical method to analyse the stability of transverse galloping based on experimental measurements, as an alternative method to polynomial fitting of the transverse force coefficient Cz, is proposed in this paper. The Glauert–Den Hartog criterion is used to determine the region of angles of attack (pitch angles) prone to present galloping. An analytic solution (based on a polynomial curve of Cz) is used to validate the method and to evaluate the discretization errors. Several bodies (of biconvex, D-shape and rhomboidal cross sections) have been tested in a wind tunnel and the stability of the galloping region has been analysed with the new method. An algorithm to determine the pitch angle of the body that allows the maximum value of the kinetic energy of the flow to be extracted is presented.

Model of the aerodynamic behavior of a pararotor

Asimple semi-empirical model for the aerodynamic behavior of a low-aspect ratio pararotor in autorotation at low Reynolds numbers is presented. The paper is split into three sections: Sec. II deals with the theoretical model derivation, Sec. III deals with the wind-tunnel measurements needed for tuning the theoretical model, and Sec. IV deals with the tuning between the theoretical model and the experimental data. The study is focused on the effect of both the blade pitch angle and the blade roughness and also on the stream velocity, on the rotation velocity, and on the drag of a model. Flow pattern visualizations have also been performed. The value of the free aerodynamic parameters of the semi-empirical model that produces the best fit with the experimental results agrees with the expected ones for the blades at the test conditions. Finally, the model is able to describe the behavior of a pararotor in autorotation that rotates fixed to a shaft, validated for a range of blade pitch angles. The movement of the device is found to be governed by a reduced set of dimensionless parameters.

On sonic anemometer measurement theory

In this paper a model for the measuring process of sonic anemometers (ultrasound pulse based) is presented. The differential equations that describe the travel of ultrasound pulses are solved in the general case of non-steady, non-uniform atmospheric flow field. The concepts of instantaneous line-average and travelling pulse-referenced average are established and employed to explain and calculate the differences between the measured turbulent speed (travelling pulse-referenced average) and the line-averaged one. The limit k1l=1 established by Kaimal in 1968, as the maximum value which permits the neglect of the influence of the sonic measuring process on the measurement of turbulent components is reviewed here. Three particular measurement cases are analysed: A non-steady, uniform flow speed field, a steady, non-uniform flow speed field and finally an atmospheric flow speed field. In the first case, for a harmonic time-dependent flow field, Mach number, M (flow speed to sound speed ratio) and time delay between pulses have revealed themselves to be important parameters in the behaviour of sonic anemometers, within the range of operation. The second case demonstrates how the spatial non-uniformity of the flow speed field leads to an influence of the finite transit time of the pulses (M≠0) even in the absence of non-steady behaviour of the wind speed. In the last case, a model of the influence of the sonic anemometer processes on the measurement of wind speed spectral characteristics is presented. The new solution is compared to the line-averaging models existing in the literature. Mach number and time delay significantly distort the measurement in the normal operational range. Classical line averaging solutions are recovered when Mach number and time delay between pulses go to zero in the new proposed model. The results obtained from the mathematical model have been applied to the calculation of errors in different configurations of practical interest, such as an anemometer located on a meteorological mast and the transfer function of a sensor in an atmospheric wind. The expressions obtained can be also applied to determine the quality requirements of the flow in a wind tunnel used for ultrasonic anemometer calibrations.

La aplicación de stop-motion en arquitectura: materia y luz

Se inicia un análisis de los procesos de trabajo de stop-motion porque ayudan a comprender las diferentes escalas en arquitectura donde las maquetas se convierten en futuros prototipos de infraestructuras de edificios o de paisaje. Stop motion es una técnica de animación fotograma a fotograma de objetos estáticos mediante la manipulación de figuras de plastilina en entornos fijos con cambios de luz, color y sonido. Igual que dicha técnica reúne lo mejor del rodaje tradicional -story board, escenografía, fotografía, personajes, iluminación- la animación de maquetas de interiores sintetiza micro-procesos de mayor repercusión -habitaciones con cambios de humedad, de temperatura, de ventilación y de iluminación- incorporando efectos especiales que son procesados digitalmente en post-producción. Se construyen varios prototipos de habitación con parámetros fijos como el tamaño y la posición de la cámara y otros variables como los materiales, los personajes y la iluminación. Representan un mundo en miniatura que intenta aportar un acercamiento sensorial y atmosférico analizando la magia y la fantasía que Junichirô Tanizaki describe en la penumbra de las construcciones tradicionales japonesas y estudiando las imperfecciones de los escenarios que Tim Burton manipula en su películas de animación con una textura que las tecnologías digitales no pueden igualar. El objetivo es utilizar una escala micro para realizar unos modelos interiores donde las condiciones atmosféricas están controladas y reducidas, y tomar datos que se podrían aplicar a un proceso de modelado a escala intermedia para testar prototipos de edificios como el túnel de viento; o, finalmente, a una escala macro con maquetas de un sector de la costa o de un río donde los fenómenos meteorológicos son los protagonistas para simular inundaciones y diseñar futuras medidas de prevención y seguridad.

Experimental studies of the aerodynamics of ground effect machines.

"Task 9R99-01-005-02, contract DA44-177-TC-776."

Low airspeed differential pressure integrating system /

Mode of access: Internet.

Learning, odour preference and flower foraging in moths

Floral volatiles play a major role in plant-insect communication. We examined the influence of two volatiles, phenylacetaldehyde and a-pinene, on the innate and learnt foraging behaviour of the moth Helicoverpa armigera. In dual-choice wind tunnel tests, adult moths flew upwind towards both volatiles, with a preference for phenylacetaldehyde. When exposure to either of these volatiles was paired with a feeding stimulus (sucrose), all moths preferred the learnt odour in the preference test. This change in preference was not seen when moths were exposed to the odour without a feeding stimulus. The learnt preference for the odour was reduced when moths were left unfed for 24 h before the preference test. We tested whether moths could discriminate between flowers that differed in a single volatile component. Moths were trained to feed on flowers that were odour-enhanced using either phenylacetaldehyde or a-pinene. Choice tests were then carried out in an outdoor flight cage, using flowers enhanced with either volatile. Moths showed a significant preference for the flower type on which they were trained. Moths that were conditioned on flowers that were not odour-enhanced showed no preference for either of the odour-enhanced flower types. The results imply that moths may be discriminating among odour profiles of individual flowers from the same species. We discuss this behaviour within the context of nectar foraging in moths and odour signalling by flowering plants.

Rotary atomizer drop size distribution database

Wind tunnel measurements of drop Size distributions from Micronair A U4000 and A U5000 rotary atomizers were collected to develop a database for model use. The measurements varied tank mix, flow rate, air speed, and blade angle conditions, which were correlated by multiple regressions (average R-2 = 0.995 for A U4000 and 0.988 for AU5000). This database replaces an outdated set of rotary atomizer data measured in the 1980s by the USDA Forest Service and fills in a gap in data measured in the 1990s by the Spray Drift Task Force. Since current USDA Forest Service spray projects rely on rotary atomizers, the creation of the database (and its multiple regression interpolation) satisfies a need seen for ten years.

Evaluation of performance reference compounds in polyethylene-based passive air samplers

Polyethylene-based passive air samplers (PSDs) were loaded with performance reference compounds (PRCs) and deployed in a wind tunnel to examine the effects of wind speed on sampler performance. PRCs could be loaded reproducibly into PSDs, with coefficients of variation only exceeding 20% for the more volatile compounds. When PSDs were exposed to low (0.5-1.5 m s(-1)) and high (3.5-4.5 m s(-1)) wind speeds, PRC loss rate constants generally increased with increasing wind speed and decreased with increasing sampler/air partition coefficients. PSD-based air concentrations calculated using PRC loss rate constants and sampler/air partition coefficients and air concentrations measured using active samplers compared closely. PRCs can be used to account for the effect of differences in wind speeds on sampler performance and measure air concentrations with reasonable accuracy. (c) 2006 Elsevier Ltd. All rights reserved.

The drying of small drops of particulate slurries

The literature on the evaporation of drops of pure liquids, drops containing solids and droplet sprays has been critically reviewed. An experimental study was undertaken on the drying of suspended drops of pure water and aqueous sodium sulphate decahydrate with concentrations varying from 5 to 54. 1 wt. %. Individual drops were suspended from a glass filament balance in a 26 mm I.D. vertical wind tunnel, designed and constructed to supply hot de-humidified air, to simulate conditions encountered in commercial spray driers. A novel thin film thermocouple was developed to facilitate the simultaneous measurement of drop weight and core temperature. The heat conduction through the thermocouple was reduced because of its unique design; using essentially a single 50μ diameter nickel wire. For pure water drops, the Nusselt number was found to be a function of the Reynolds, Prandtl and Transfer numbers for a temperature range between 19 to 79°C.                  Nu = 2 + 0.19 (1/B)0.24 Re0.5 Pr0.33 Two distinct periods were observed during the drying of aqueous sodium sulphate decahydrate. The first period was characterised by the evaporation from a free liquid surface, whilst drying in the second period was controlled by the crust resistance. Fracturing of the crust occurred randomly but was more frequent at higher concentrations and temperatures. A model was proposed for the drying of slurry drops, based on a receding evaporation interface. The model was solved numerically for the variation of core temperature, drop weight and crust thickness as a function of time. Experimental results were in excellent agreement with the model predictions although at higher temperatures modifications to the model had to be made to accommodate the unusual behaviour of sodium sulphate slurries, i.e. the formation of hydrates.