Aeroacoustic noise prediction in high speed trains due to attached and detached flow

This paper aims to set out the influence of the flow field around high speed trains in open field. To achieve this parametric analysis of the sound pressure inside the train was performed. Three vibroacoustic models of a characteristic train section are used to predict the noise inside the train in open field by using finite element method FEM, boundary element method (BEM) and statistical energy analysis (SEA) depending on the frequency range of analysis. The turbulent boundary layer excitation is implemented as the only airborne noise source, in order to focus on the study of the attached and detached flow in the surface of the train. The power spectral densities of the pressure fluctuation in the train surface proposed by [Cockburn and Roberson 1974, Rennison et al. 2009] are applied on the exterior surface of the structural subsystems in the vibroacoustic models. An increase in the sound pressure level up to10 dB can be appreciated due to the detachment of the flow around the train. These results highlight the importance to determine the detached regions prediction, making critical the airborne noise due to turbulent boundary layer

Trade-off aproaches for the vibroacoustic analysis of trains

Passengers’ comfort in terms of acoustic noise levels is a key design driver for train design. The problem is especially relevant for high speed trains, where the aerodynamic induced noise is dominant, but it is also important for medium speed trains where the mechanical sources of noise may have more influence. The numerical interior noise prediction inside the train is a very comp lex problem, involving many different parameters: complex geometries and materials, different noise sources, com- plex interactions among those sources, broad range of frequencies where the phenomenon is important, etc. In this paper, the main findings of this work developed at IDR/UPM (Instituto de Microgravedad “Ignacio Da Riva”, Universidad Politécnica de Madrid) are presented, concentrat ing on the different modelling methodologies used for the different frequency ranges of interest, from FEM-BEM models, hybrid FEM-SEA to pure SEA models. The advantages and disadvantages of the different approaches are summarized. Different modelling techniques have also been evaluated and compared, taking into account the various and specific geometrical configurations typical in this type of structures, and the material properties used in the models. The critical configuration of the train inside a tunnel is studied in order to evaluate the external loads due to noise sources of the train. In this work, a SEA-model composed by periodic characteristic sections of a high spee d train is analysed inside a tunnel

Aeroacoustic noise prediction in high speed trains due to attached and detached flow

This paper aims to set out the influence of the flow field around high speed trains in open field. To achieve this parametric analysis of the sound pressure inside the train was performed. Three vibroacoustic models of a characteristic train section are used to predict the noise inside the train in open field by using finite element method FEM, boundary element method (BEM) and statistical energy analysis (SEA) depending on the frequency range of analysis. The turbulent boundary layer excitation is implemented as the only airborne noise source, in order to focus on the study of the attached and detached flow in the surface of the train. The power spectral densities of the pressure fluctuation in the train surface proposed by [Cockburn and Roberson 1974, Rennison et al. 2009] are applied on the exterior surface of the structural subsystems in the vibroacoustic models. An increase in the sound pressure level up to10 dB can be appreciated due to the detachment of the flow around the train. These results highlight the importance to determine the detached regions prediction, making critical the airborne noise due to turbulent boundary layer

Single-axis Ultrasonic Anemometer in Rotational Motion

Los anemómetros ultrasónicos son instrumentos modernos para la medida exacta de la velocidad del viento que se han utilizado extensamente en aplicaciones meteorológicas e industria de la energía eólica. A pesar de su extendida aplicación es cada vez mayor, ya se han prestado poca atención a los anemómetros ultrasónicos giratorios de eje único que pueden medir con precisión tanto la velocidad del viento como su dirección en un aparato único y robusto. Recientemente, se emplean en plataformas móviles tales como es el caso de los aerogeneradores. Esto requiere un proceso de calibración exacto y correcto para corregir las señales de salida del anemómetro durante la rotación. En esta tesis, se han realizado varias series de pruebas en túnel de viento para estudiar sus mediciones de velocidad en condiciones oscilatorias utilizando un anemómetro ultrasónico modificado de un eje giro. Este estudio se ha llevado a cabo realizando medidas estáticas a diferentes ángulos de trayectoria de señal de los transductores con la dirección del viento, y con medidas dinámicas en las que el anemómetro está girando a diferentes velocidades de rotación. La velocidad medida por el anemómetro ultrasónico en los ensayos estáticos se calibra con datos de tubo pitot y la interpolación de los coeficientes de calibración obtenidos se utiliza para corregir la velocidad ultrasónica medida en ensayos dinámicos. Se observa que las mediciones de velocidad del viento con el anemómetro ultrasónico tras la calibración se ajustan adecuadamente a las velocidades de referencia en pruebas dinámicas. De acuerdo con los resultados, las mediciones de velocidad con el anemómetro ultrasónico en pruebas estáticas y dinámicas se ven afectadas por las distorsiones de la cabeza de los transductores y el desplazamiento en la trayectoria del pulso acústico debido al movimiento rotacional no afecta las mediciones del anemómetro en los casos dinámicos. Además, se obtiene un ángulo de fase en función de la orientación de la trayectoria de señal del anemómetro a partir de los ensayos estáticos que se debe al efecto de sombra del transductor y se utiliza para construir un modelo de calibración para corregir la velocidad del viento medida por anemómetro ultrasónico tanto estática como dinámicas. Se observa que, en las pruebas dinámicas, el retardo o retraso entre el anemómetro ultrasónico y el sensor de posición angular junto con el efecto Doppler, imparten un desplazamiento de fase en las señales medidas por el anemómetro, que se debe añadir a los datos de posición para corregir el desalineamiento de guiñada. Los datos experimentales se utilizaron para construir un modelo teórico, basado en el Método de Superficie de Respuesta, para corregir el cambio de fase para varias velocidades del viento y velocidades de rotación del anemómetro. Este modelo ha demostrado corregir con éxito la velocidad indicada por el anemómetro giratorio para el cambio de fase debido a la rotación, y puede usarse fácilmente en el proceso de calibración para tales anemómetros. Por otro lado, los datos experimentales han servido para validar un modelo teórico, basado en el Método de Superficie de Respuesta, y predecir la velocidad de salida del anemómetro para diferentes velocidades de viento y rotación como variables independientes. El modelo obtenido tiene una estructura simple y es fácil de usar, con una buena precisión para predecir los datos experimentales incluso en las zonas sombreadas del transductor. El modelo teórico propuesto puede usarse en la calibración de dichos anemómetros en condiciones de rotación y funciona para la condición estacionaria estableciendo que la velocidad angular en el modelo sea cero. El mismo modelo con diferentes coeficientes constantes aún se mantiene para cualquier otro anemómetro ultrasónico. ----------ABSTRACT---------- Ultrasonic anemometers are the modern instruments for accurate wind speed measurements that have been widely used in meteorological applications and wind energy industry. Despite their widespread and ever increasing applications, little attentions have already been paid to the spinning single-axis ultrasonic anemometers which can accurately measure both the wind speed and its direction in a single and robust apparatus. Recently, they are employed in dynamic spinning conditions on mobile platforms such as spinner anemometry on wind turbines. This necessitates an exact and proper calibration process to correct the anemometer output signals during the rotation. In this thesis, series of wind-tunnel tests have been performed on a modified single-axis ultrasonic anemometer to study its velocity measurements in oscillatory conditions. This has been carried out with static measures at various stationary angles of transducers signal path with wind direction, and with dynamic measures in which the anemometer is rotating with various rotational speeds. The velocity measured by ultrasonic anemometer in static tests is calibrated with pitot-tube data, and the interpolation of obtained calibration coefficients is used to correct the ultrasonic velocity measured in dynamic tests. It is observed that the calibrated ultrasonic wind speed measurements in dynamic tests are in a good agreement with the reference velocities. According to the results, the ultrasonic velocity measurements in both static and dynamic tests are affected by transducers head distortions, and the shifting in acoustic pulse trajectory due to the rotational motion does not affect the anemometer outputs in dynamic cases. Besides, a phase angle as a function of the orientation of anemometer’s signal path is obtained from the static tests which is due to transducer shadow effect and it is used to construct a calibration model for correcting the wind speed measured by ultrasonic anemometer in both static and dynamic conditions. It is observed that in the spinning tests, the time lag or delay between ultrasonic anemometer and angular position sensor along with Doppler Effect, impart a phase shift in the signals measured by the anemometer, which should be added into the position data for correcting the yaw misalignment. The experimental data were used to construct a theoretical model, based on Response Surface Method, to correct the phase shift for various wind speeds and anemometer rotational velocities. This model has been shown to successfully correct the velocity indicated by the spinning anemometer for the phase shift due to the rotation, and can easily be used in the calibration process for such anemometers. Additionally, the experimental data were used to construct a theoretical model, based on Response Surface Method, to predict the anemometer output velocity for various wind and rotational speeds as the independent variables. The obtained model has a simple structure and is easy to use, with a good accuracy to predict the experimental data even in the shadow zones of the transducer. The proposed theoretical model can be used in the calibration of such anemometers in rotational conditions and works for the stationary condition by setting the angular velocity in the model to be zero. The same model with different constant coefficients still holds for any other ultrasonic anemometers