Microcapteurs de hautes fréquences pour des mesures en aéroacoustique

L aéroacoustique est une filière de l'acoustique qui étudie la génération de bruit par un mouvement fluidique turbulent ou par les forces aérodynamiques qui interagissent avec les surfaces. Ce secteur en pleine croissance a attiré des intérêts récents en raison de l évolution de la transportation aérienne, terrestre et spatiale. Les microphones avec une bande passante de plusieurs centaines de kHz et une plage dynamique couvrant de 40Pa à 4 kPa sont nécessaires pour les mesures aéroacoustiques. Dans cette thèse, deux microphones MEMS de type piézorésistif à base de silicium polycristallin (poly-Si) latéralement cristallisé par l induction métallique (MILC) sont conçus et fabriqués en utilisant respectivement les techniques de microfabrication de surface et de volume. Ces microphones sont calibrés à l'aide d'une source d onde de choc (N-wave) générée par une étincelle électrique. Pour l'échantillon fabriqué par le micro-usinage de surface, la sensibilité statique mesurée est 0.4 V/V/Pa, la sensibilité dynamique est 0.033 V/V/Pa et la plage fréquentielle couvre à partir de 100 kHz avec une fréquence du premier mode de résonance à 400kHz. Pour l'échantillon fabriqué par le micro-usinage de volume, la sensibilité statique mesurée est 0.28 V/V/Pa, la sensibilité dynamique est 0.33 V/V/Pa et la plage fréquentielle couvre à partir de 6 kHz avec une fréquence du premier mode de résonance à 715kHz.Aero-acoustics, a branch of acoustics which studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces, is a growing area and has received fresh emphasis due to advances in air, ground and space transportation. Microphones with a bandwidth of several hundreds of kHz and a dynamic range covering 40Pa to 4kPa are needed for aero-acoustic measurements. In this thesis, two metal-induced-lateral-crystallized (MILC) polycrystalline silicon (poly-Si) based piezoresistive type MEMS microphones are designed and fabricated using surface micromachining and bulk micromachining techniques, respectively. These microphones are calibrated using an electrical spark generated shockwave (N-wave) source. For the surface micromachined sample, the measured static sensitivity is 0.4 V/V/Pa, dynamic sensitivity is 0.033 V/V/Pa and the frequency range starts from 100kHz with a first mode resonant frequency of 400kHz. For the bulk micromachined sample, the measured static sensitivity is 0.28 V/V/Pa, dynamic sensitivity is 0.33 V/V/Pa and the frequency range starts from 6kHz with a first mode resonant frequency of 715kHz.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

The 1992 NASA Langley Measurement Technology Conference: Measurement Technology for Aerospace Applications in High-Temperature Environments

An intensive 2-day conference to discuss the current status of measurement technology in the areas of temperature/heat flux, stress/strain, pressure, and flowfield diagnostics for high temperature aerospace applications was held at Langley Research Center, Hampton, Virginia, on April 22 and 23, 1993. Complete texts of the papers presented at the Conference are included in these proceedings

Identification of Aerodynamic Tonal Noise Sources of a Centrifugal Compressor of a Turbocharger for Large Stationary Engines

The aerodynamics of centrifugal compressors is a topical issue, as the vibrations and noise reduce the comfort of people who are in proximity to the compressor. The current trend in rotating machinery research is therefore not only concerned with performance parameters but also increasingly with the effect on humans. An analysis of aerodynamic noise based on external acoustic field measurements may be a way to assess the nature of aerodynamic excitation. In this research, the experimental measurements at 20 operating points covered the entire characteristic operating range of the selected centrifugal compressor. The dominant noise arising at blade-passing frequency (BPF) was identified at all the operational points, and the dominant effect of the buzz-saw noise was identified at the maximum rotor speed. The determination of the total sound pressure level L-P(A) showed a trend towards an increasingly higher rotor speed and compressor surge line. In the amplitude-frequency characteristics, the sound pressure was found to be dependent on the rotor speed for BPF. On the other hand, non-monotonicity was detected between the operational points at given speed lines, confirming the complexity of the aerodynamics of rotating machines. The metric chosen to identify prominent tones determined by the tonality of individual tones in the frequency spectrum showed a clear effect of integer multiples of the rotational frequency on the overall noise. Thus, the results presented here confirm the dominant influence of BPF in terms of the psychoacoustic impact on humans

Development of dynamic pressure sensor for high temperature applications

Pressure measurement under high temperature environments is required in many engineering applications and it poses many practical problems. Pressure patterns are highly desirable for health monitoring for improved performance and accurate prediction of remaining life of systems used in various applications. Data acquisition in harsh environments has always been a major challenge to the available technology. Sensing becomes more intricate in case if it has to operate under extreme conditions of temperature. Propulsion system applications represent one such area that requires a sensor that is absolutely accurate and has utmost sensitivity coupled with the ability to withstand high temperature. The need for such sensors is driven by the dependence of the performance of propulsion system on pressure pattern encountered along the gas path. Associated with that, high resolution, small size, low time dependent drift and stable range of measurement will complete the performance of such Microsystems Sensors using the current technology are capable of reliable measurement for a limited time at an extremely high cost and are bulky thereby preventing online monitoring. Improvement in the durability of the sensors requires new technology and will definitely open new areas of research. A number of technologies have been lately investigated, these technologies targeting specific applications and they are limited by the maximum operating temperature. The objective of this research is to develop a dynamic pressure measurement system that would be capable of operating at high temperatures with the technology of the device based on Silicon Carbon Nitride (SiCN). The principle of operation is based on the drag effect. Silicon carbon-nitride (SiCN) is a material that has been little explored. The service temperature of SiCN is in the range of 1400°C. The structure is produced from a liquid polymer precursor that could be originally formed into any shape. The proposed micro sensor can measure dynamic pressure and detects flow which is very important to know as the flow continuity is critical in many applications. Furthermore pressure measurement can be used as a base for many aspects. For example the proposed micro sensor could be designed and packaged to be fitted in the gas turbine engine. The correlation of the acquired data from the sensors may provide valuable timely information on imminent instability in the gas flow, detect leakage, improve efficiency et

The Development of a Research Technique for Low Speed Aeroacoustics

The aerodynamic sound generated by wind turbines was identified as a growing concern within the industry. Prior to performing wind turbine aeroacoustic research, however, a technique suitable for studying low speed airfoils needed to be designed, serving as the primary research objective. A review of aeroacoustic theory and literature indicated that low speed flows are best studied using experimental methods, leading to the design of a near field pressure measurement technique. To facilitate the near field pressure measurements, a custom piezoelectric sensor was developed, exhibiting a pressure and frequency range of approximately 67 to 140[dB], and 100 to 10000[Hz], respectively. As a secondary research objective, a series of experiments were performed to validate the designed technique. The experiments were performed in a non-anechoic wind tunnel using a cylindrical test specimen. Using the near field pressure measurements, as well as a simple far field measurement, the sources of aerodynamic sound were effectively resolved. The Strouhal numbers corresponding to the contributing flow structures were generally within 1.5[%] of correlation based predictions. The near field pressures were consistently 10 to 15[dB] higher than the far field, quantifying the benefit of the near field technique. The method was also effective in detecting the decreasing coherence of the aeroacoustic sources with increasing Reynolds number. A minor deficiency was observed in which the ability to localize aeroacoustic sources was impeded, however, the cylinder experiments were particularly vulnerable to such a deficiency. Although the near field pressure measurements were shown to be effective in characterizing the aeroacoustic sources, a number of recommendations are presented to further improve the flexibility and measurement uncertainty of the experimental technique

Behaviour of accelerating entropy spots

Combustion noise has become a major research interest within the aerospace community. Stricter pollutant emission regulations have forced the introduction of lean premixed pre-vaporised combustors, which produce less NOx but burn more unsteadily, generating more noise and creating the potential for combustion instabilities. Pressure fluctuations in combustion chambers are traditionally classified as direct and indirect noise. The former arises directly from the heat release rate perturbations in the flame. The latter is generated indirectly from the acceleration of regions of non-uniform temperature, density and composition (entropy and composition spots) through narrow passages such as nozzles or turbine guide vanes. Entropy-generated sound waves are both transmitted downstream of the acceleration point, contributing to the overall noise emission, and reflected upstream, where they may couple with the acoustics of the system, potentially triggering instabilities. Presently, the processes causing the generation of indirect noise and the triggering mechanisms for secondary instabilities are still not completely understood and need further investigation. The aim of this thesis is to shed light on the behaviour of accelerating entropy spots, providing analytical and experimental tools to identify and isolate travelling entropy spots and the sound generated from their acceleration. The physical mechanisms of entropy-to-sound conversion are investigated using a model non-reacting flow system (the Entropy Generator Rig, EGR), designed to mimic the behaviour of a combustor in a controlled environment. The contribution of indirect noise can be easily identified and isolated in the acquired pressure traces, allowing the first direct comparison between experimental data and a newly developed analytical model for the entropy-to-sound conversion in non-isentropic systems. An important challenge that has limited the understanding of indirect noise is the lack of experimental techniques capable to detect and characterise the production and decay of entropic perturbations in combustion chambers. Laser-Induced Grating Spectroscopy (LIGS) is a promising optical technique for the diagnostics in the gas phase, which measures the local speed of sound, temperature and composition. LIGS has been previously applied as a low frequency (10 Hz) diagnostic technique in flows containing a seeded or natural absorbing molecule. In the present work, two advances are demonstrated. Firstly, LIGS is applied in a pressurised reacting flow environment using the fundamental Nd:YAG laser wavelength, taking advantage of the absorption line of the water in the flame products. Secondly, high repetition rate lasers (1-100 kHz) are used to obtain signals at high frequency in non-reacting and reacting flows, enabling time resolved measurements. This work opens up a new avenue to capture the evolution of unsteady scalars involved in the convection of entropy spots and turbulence.Qualcomm EPSRC Zonta International KAUST visiting programm

Fluid dynamic aspects of jet noise generation

Jet engine noise generation and noise propagation was investigated by studying supersonic nozzle flow of various nozzle configurations in an experimental test facility. The experimental facility was constructed to provide a coaxial axisymmetric jet flow of unheated air. In the test setup, an inner primary flow exhausted from a 7 in. exit diameter convergent--divergent nozzle at Mach 2, while a secondary flow had a 10 in. outside diameter and was sonic at the exit. The large dimensions of the jets permitted probes to be placed inside the jet core without significantly disturbing the flow. Static pressure fluctuations were measured for the flows. The nozzles were designed for shock free (balanced) flow at Mach 2. Data processing techniques and experimental procedures were developed in order to study induced disturbances at the edge of the supersonic flows, and the propagation of those disturbances throughout the flows. Equipment used (specifications are given) to record acoustic levels (far field noise) is described. Results and conclusions are presented and discussed. Diagrams of the jet flow fields are included along with photographs of the test stand

Solvent Evaporation-Assisted Three-Dimensional Printing of Piezoelectric Sensors from Polyvinylidene Fluoride and its Nanocomposites

RÉSUMÉ Les matériaux piézoélectriques sont connus pour générer des charges électriques lors de leur déformation. Leur capacité à transformer linéairement l'énergie mécanique en énergie électrique, et vice versa, est utilisée dans la détection, l'actionnement, la récupération et le stockage d'énergie. Ces appareils trouvent des applications dans les domaines de l'aérospatiale, de la biomédecine, des systèmes micro-électromécaniques, de la robotique et des sports, pour n'en nommer que quelques-uns. On retrouve la propriété de piézoélectricité dans certaines céramiques, roches, monocristaux et quelques polymères. Le poly(fluorure de vinylidène) (PVDF) est un polymère piézoélectrique qui présente un coefficient piézoélectrique très élevé par rapport aux céramiques, ce qui laisse présager des applications de détection et de récupération d'énergie. La facilité de fabrication, la flexibilité et la biocompatibilité du PVDF sont autant de qualité qui en font un très bon candidat pour ces applications. Les dispositifs actuels à base de PVDF commercial sont disponibles en films plats ou en fibres unidimensionnelles (1D). L'impression tridimensionnelle (3D) du PVDF peut amener à des sensibilités, souplesses et capacités de fabrication accrues des capteurs embarqués en cas d'impression multi-matériaux. Le PVDF est un polymère semi-cristallin possédant cinq polymorphes, dont la phase β polaire qui présente les meilleures propriétés piézoélectriques. Malheureusement, le PVDF, provenant de la fusion ou de la dissolution, cristallise en une phase α non polaire thermodynamiquement stable. Diverses transformations physiques telles que le recuit, l'addition de charge, l'étirement ou le polissage sont effectuées pour transformer la phase α en phase β. En raison de la cristallisation inhérente du PVDF dans la phase α, il y a eu très peu de tentatives de fabrication de structures 3D à partir du PVDF. L'électrofilage en champ proche et la Déposition de Filament Fondu ont permis de fabriquer certaines structures 3D couche par couche avec du PVDF, soit avec l'application de hautes tensions électriques, soit avec la fusion à haute température du polymère. Et les deux nécessitent un traitement de polarisation pour conférer la piézoélectricité aux structures imprimés. Pour fabriquer des capteurs incorporés ou conformes, sur des substrats donnés, il est essentiel de ne pas avoir d'effets négatifs sur les matériaux adjacents à cause de la polarisation pendant le processus d'impression. Ainsi, dans ce travail, nous avons développé un procédé d'impression 3D qui crée des structures PVDF principalement en phase β, à température ambiante et sans application de tension de polarisation.----------ABSTRACT Piezoelectric materials are known to generate electric charges upon deformation. Their ability to linearly transform mechanical energy into electrical energy and vice versa, is utilized in sensing, actuation, transducing, energy harvesting and storage. These devices find applications in aerospace, biomedicine, micro electromechanical systems, robotics and sports, to name a few. Piezoelectricity is found in some ceramics, rocks, single crystals and a few polymers. Polyvinylidene fluoride (PVDF) is a piezoelectric polymer that exhibits a very high piezoelectric stress coefficient as compared to the ceramics, making it the forerunner for sensing and energy harvesting applications. PVDF’s formability, flexibility and biocompatibility, further reinforce its candidature. Present commercial PVDF-based devices come in flat films or one-dimensional (1D) fibers. Three-dimensional (3D) printing of PVDF leads to higher sensitivity, better compliance, and ability to print embedded sensors in case of multi-material printing. PVDF is a semi-crystalline polymer possessing five polymorphs, of which the polar β-phase exhibits highest piezoelectric properties. Unfortunately, PVDF from melt or solution crystallizes into a thermodynamically stable non-polar α-phase. Various physical transformations like annealing, filler addition, stretching or poling are carried out to transform the α-phase into β-phase. Due to the inherent crystallization of PVDF into α-phase, there have been very few attempts in fabricating 3D structures from PVDF. Near-field electrospinning and fused deposition modelling have demonstrated some layer-by-layer 3D structures with PVDF, either with application of high electric voltages or high temperature melting of the polymer, respectively. Also, both these techniques require a poling treatment to impart the desired piezoelectricity to the printed features. To fabricate embedded or conformal sensors on given substrates, it is essential to not have any adverse effects on the adjacent or substrate materials due to poling during the printing process. Thus, in this work, we develop a 3D printing process, that creates PVDF structures that inherently crystallize in the piezoelectric oriented β-phase at room temperature without any applied voltages. Solvent-evaporation assisted 3D printing is employed to print 3D piezoelectric structures of PVDF based solutions. In this process, the polymer solution is filled into a syringe which is inserted into a pneumatic dispenser. The pneumatic dispenser is mounted on a robotic arm that is controlled via a computer program

Experimental evaluation of vehicle cabin noise from suspension induced vibrations using transfer path and psychoacoustic analysis techniques

Given the automotive industry\u27s awareness of the importance of the perception of NVH emissions, there is an increased focus on the psychoacoustics, or sound quality, of vehicle cabin noise. The present work aims to qualitatively evaluate and compare automobile cabin noise by measuring the road-induced noise and vibration of a driven and motored vehicle. Evaluation of transmission paths and psychoacoustic analysis of the cabin acoustics are primary objectives. A psychoacoustic analysis using the acoustic pressure measurements taken inside the vehicle cabin was performed using both subjective and objective approaches. Testing also included vibration measurements from several structural positions to evaluate vibroacoustic excitations. Using this noise and vibration data, it was possible to evaluate the transfer path of the excitation energy into the vehicle cabin. Further, an attempt to establish a correlation between the noise and vibration measurements and the psychoacoustic observations was also proven possible with some inherent limitations