DEVELOPMENT OF A MUFFLER INSERTION LOSS FLOW RIG

Mufflers and silencers are commonly used to attenuate noise sources such as internal combustion engines and HVAC systems. Typically, these environments contain mean flow that can affect the acoustic properties of the muffler components and may produce flow generated noise. To characterize the muffler performance, common metrics such as insertion and transmission loss and noise reduction are used in industry. Though transmission loss without flow is often measured and is a relatively simple bench top experiment and useful for model validation purposes, mean flow can significantly affect the muffler performance. There are a few existing and commercial transmission loss rigs that incorporate flow into the measurement procedure. These rigs are useful for model verification including flow but do not predict how the muffler will perform in the system since the source, termination, and pipe lengths significantly impact performance. In this research, the development of an insertion loss test rig is detailed. This testing strategy has the advantage of being simpler, quantifying the self-generated noise due to flow, and taking into account the effect of tailpipe length and a realistic termination. However, the test does not include the actual source and is not as useful for model validation. An electric blower produces the flow and a silencer quiets the flow. Loudspeakers are positioned just downstream of the flow silencer and they are used as the sound source. The low frequency source is a subwoofer installed in a cylindrical enclosure that includes a conical transition from speaker to pipe. Special care is taken to reduce any flow generated noise. Qualification of the system is detailed by comparing the measured transmission loss, noise reduction, and insertion loss to one-dimensional plane wave models. The results demonstrate that the developed rig should be useful as a muffler evaluation tool after a prototype has been constructed. The rig can also be used for transmission loss and noise reduction determination which will prove beneficial for laboratory testing

A practical approach to the exhaust silencing of a pneumatic rock drill

One-third octave spectrum analyses of the exhaust noise produced by a medium sized pneumatic rock drill were obtained during free recriprocation to determine the most troublesome bands of noise. Noise reduction techniques were then used to design exhaust mufflers which would reduce the level of the exhaust noise to an acceptable level with a minimum increase in back pressure. The prototype mufflers evaluated included an expansion chamber, a resonator, and various modified expansion chambers. One of the modified expansion chambers tested provided very good attenuation reducing the exhaust noise from 113 dBA to 87 dBA at the operator\u27s ear position. It caused only a slight increase in the back pressure and no detrimental effect on drill performance. The resonator muffler did not provide acceptable attenuation of the exhaust noise. Muffler development progressed under the assumption that icing would not be a problem. However, the icing characteristics of the final prototype muffler were studied and a possible method to prevent icing is suggested --Abstract, page ii

The design and construction of an apparatus for the plane wave analysis of mufflers

In the following report, a method for evaluating the attenuation characteristics of a general muffler as well as the design, construction and use of the associated apparatus are described. The method combines accepted plane wave theory and experimental techniques into a relatively straightforward approach to the analysis of acoustic filters. Equations are developed to cover the frequency range between 300 and 4000 cycles per second. Deviations from these equations extend the use of the equipment to low frequencies without the need for unduly long and cumbersome apparatus. This method, which may be called the standing wave method, utilizes a standing wave tube with a sliding microphone pickup to determine the reflection characteristics of a given termination. then, the reflection characteristics so determined are used with data collected in a transmission tube apparatus to determine the transmission characteristics of the termination. The experimental analysis of a variable length expansion chamber is compared to its theoretically determined characteristics to demonstrate the usefulness of the equipment. An auto muffler, which is not amenable to theoretical analysis, is then analyzed experimentally over the frequency range of interest. The analysis is discussed and compared to the noise spectrum measured at the end of the tailpipe for the same type of muffler mounted on an automobile. Certain errors which are inherent in the experimental equipment or procedure are pointed out and their effect on the data is estimated whenever possible. Recommendations for the improvement of the apparatus are made --Abstract, page viii-ix

A Combined FEM-CFD Methodology to Study and Optimize Acoustic Properties of Marine Exhaust Lines

Lo sviluppo di sistemi di abbattimento compatti in grado di ridurre sia NOx che SOx è di forte interesse, per la difficoltà di combinare su una nave sia sistemi di riduzione catalitica selettiva che tecnologie di scrubber. Quindi, la ricerca sviluppata in questa tesi nasce dalla necessità di integrazione del sistema lungo la linea di scarico per risparmiare spazio e dalla necessità di disporre di un modello numerico adeguato per simulare le proprietà acustiche dei sistemi di depurazione dei gas di scarico per la loro ottimizzazione. L'obiettivo di questa tesi è sviluppare una metodologia numerica efficiente dal punto di vista computazionale che utilizzi una combinazione di simulazioni CFD e FEM, per consentire lo studio e l'ottimizzazione delle proprietà acustiche dei componenti della linea di scarico, rispettando i limiti imposti sia ai parametri geometrici che alle caratteristiche del flusso dalle reazioni chimiche necessarie per soddisfare le normative NOx e SOx. Sono stati eseguiti alcuni studi preliminari per ottimizzare l’onere computazionale delle simulazioni numeriche. Inoltre, sono state eseguite misurazioni sperimentali, sia su un set-up semplificato (tubo di impedenza) sia su un mockup di una linea di scarico di un Genset marino, al fine di valutare i risultati numerici. Le simulazioni CFD e FEM validate sono poi utilizzate per l'approccio combinato che, in primo luogo, calcola il campo di flusso (velocità e temperatura) con una simulazione CFD in regime stazionario e, poi, importa questo campo nel modello acustico FEM tramite il mesh mapping per valutare la trnsmission loss della geometria studiata in presenza di flusso. L'approccio combinato è stato quindi utilizzato per valutare e modellare le proprietà acustiche sia del catalizzatore di ossidazione diesel che dello scrubber costruiti per il Genset. La loro transmission loss raggiunge valori fino a 60 dB, permettendo di eliminare il silenziatore tradizionale, riducendo così l'ingombro della linea di scarico.The development of compact abatement systems capable of reducing both NOx and SOx is of strong interest, due to the difficulty of combining both selective catalytic reduction systems and scrubber technologies on a ship. So, the research developed in this thesis comes from the need for system integration along the exhaust line to save space and the need to have a proper numerical model to simulate the acoustic properties of exhaust gas cleaning systems for their optimization. The objective of this thesis is to develop a computationally-efficient numerical methodology employing a combination of both CFD and FEM simulations, to allow the investigation and optimization of acoustic properties of exhaust line components, while respecting the limits imposed on both geometrical parameters and flow characteristics by the chemical reactions needed to satisfy NOx and SOx regulations. Some preliminary studies are performed to optimize computational effort of numerical simulations. Moreover, experimental measurements are performed on both a simplified set-up (impedance tube) and a mockup of a marine Genset exhaust line in order to assess the numerical results. The assessed CFD and FEM simulations are used for the combined approach that, firstly, calculates the flow field (velocity and temperature) with a steady-state CFD simulation and, then, imports this field into the acoustic FEM model through mesh mapping to evaluate the transmission loss of the studied geometry in presence of flow. The combined approach is then used on real systems, to assess and model the acoustics properties of both diesel oxidation catalyst and scrubber constructed for a Genset mockup. Their transmission loss reach values up to 60 dB, which allows elimination of the traditional silencer, thus reducing the overall dimensions

Development of a Method to Model an Enclosed, Coaxial Carbon Nanotube Speaker with Experimental Validation

Carbon nanotube (CNT) speakers operate on heat as compared to conventional loudspeakers that operate on vibration. CNT speakers are extremely lightweight, stretchable, flexible, and have high operating temperatures. Due to these advantages, CNT speakers are being considered as a viable replacement option for conventional loudspeakers. One such application is automotive exhaust noise control. The goal of this research is to design an enclosed, coaxial CNT speaker and to develop a modeling method to model this speaker using COMSOL Multiphysics. As part of this research, an enclosed, coaxial CNT speaker was designed and manufactured for automotive exhaust noise control. The first prototype was a proof of concept that the design is feasible, and the speaker works. Two additional prototypes have been developed to improve the manufacturing feasibility and performance. The first task undertaken during the modeling method development has been to create COMSOL models that simulated the CNT film temperature oscillation and the corresponding SPL. The simulation results have been compared with a MATLAB model for a planar CNT speaker. In addition, the SPL generated by the coaxial speaker has been compared with the simulated SPL generated by the CNT speaker. In addition, the performance of the coaxial speaker has been simulated in the presence of flow. Generally, a good correlation has been observed between the experimental SPL and simulated SPL. The models can be improved with the future development of improved material properties

High Reynolds Number Hybrid Laminar Flow Control (HLFC) Flight Experiment

This document describes the design of the leading edge suction system for flight demonstration of hybrid laminar flow control on the Boeing 757 airplane. The exterior pressures on the wing surface and the required suction quantity and distribution were determined in previous work. A system consisting of porous skin, sub-surface spanwise passages ("flutes"), pressure regulating screens and valves, collection fittings, ducts and a turbocompressor was defined to provide the required suction flow. Provisions were also made for flexible control of suction distribution and quantity for HLFC research purposes. Analysis methods for determining pressure drops and flow for transpiration heating for thermal anti-icing are defined. The control scheme used to observe and modulate suction distribution in flight is described

A nonlinear Quasi-3D approach for the modeling of mufflers with perforated elements and sound-absorbing material

Increasing demands on the capabilities of engine thermo-�uid dynamic simulation and the ability to accurately predict both performance and acoustics have led to the development of several approaches, ranging from fully 3D to simpli�ed 1D models. e quasi-3D approach is proposed as a compromise between the time-demanding 3D CFD analysis and the fast 1D approach; it allows to model the acoustics of intake and exhaust system components, used in internal combustion engines, resorting to a 3D network of 0D cells. Due to its 3D nature, the model predicts high-order modes, improving the accuracy at high frequencies with respect to conventional plane-wave approaches. e conservation equations of mass and energy are solved at cell centers, whereas the momentum equation is applied to cell connections including speci�c source term to account for the of sound-absorbing materials and perforated elements. e quasi-3D approach has been validated by comparing the predicted transmission loss to measured data for a number of standard con�gurations typical of internal combustion engine exhaust systems: a reverse-�ow chamber and series chambers with perforates and resistive material

Experimental gas-fired pulse-combustion studies

Experimental studies conducted at Argonne National Laboratory on a gas-fired, water-cooled, Helmholtz-type pulse combustion burner are discussed. In addition to the experimental work, information is presented on the evolution of pulse combustion, the types of pulse combustion burners and their applications, and the types of fuels used. Also included is a survey of other pertinent studies of gas-fired pulse combustion. The burner used in the Argonne research effort was equipped with adjustable air and gas flapper valves and was operated stably over a heat-input range of 30,000 to 200,000 Btu/h. The burner's overall heat transfer in the pulsating mode was 22 to 31% higher than when the unit was operated in the steady mode. Important phenomena discussed include (1) effects on performance produced by inserting a corebustor to change tailpipe diameter, (2) effects observed following addition of an air-inlet decoupling chamber to the unit, and (3) occurrence of carbon monoxide in the exhaust gas

Parallel object-oriented algorithms for simulation of multiphysics : application to thermal systems

The present and the future expectation in parallel computing pose a new generational change in simulation and computing. Modern High Performance Computing (HPC) facilities have high computational power in terms of operations per second -today peta-FLOPS (10e15 FLOPS) and growing toward the exascale (10e18 FLOPS) which is expected in few years-. This opens the way for using simulation tools in a wide range of new engineering and scientific applications. For example, CFD&HT codes will be effectively used in the design phase of industrial devices, obtaining valuable information with reasonable time expenses. However, the use of the emerging computer architectures is subjected to enhancements and innovation in software design patterns. So far, powerful codes for individually studying heat and mass transfer phenomena at multiple levels of modeling are available. However, there is no way to combine them for resolving complex coupled problems. In the current context, this PhD thesis presents the development of parallel methodologies, and its implementation as an object-oriented software platform, for the simulation of multiphysics systems. By means of this new software platform, called NEST, the distinct codes can now be integrated into single simulation tools for specific applications of social and industrial interest. This is done in an intuitive and simple way so that the researchers do not have to bother either on the coexistence of several codes at the same time neither on how they interact to each other. The coupling of the involved components is controlled from a low level code layer, which is transparent to the users. This contributes with appealing benefits on software projects management first and on the flexibility and features of the simulations, later. In sum, the presented approaches pose a new paradigm in the production of physics simulation programs. Although the thesis pursues general purpose applications, special emphasis is placed on the simulation of thermal systems, in particular on buildings energy assessment and on hermetic reciprocating compressors.Las expectativas puestas en el uso de la computación en paralelo plantean un cambio generacional en simulación y computación. Las más modernas instalaciones computacionales de alto nivel -High Performance Computing (HPC)- alcanzan ya la capacidad de realizar gran cantidad de operaciones por segundo -hoy del orden de peta-FLOPS (1e15 FLOPS) y dirigiéndose hacia exaFlops (1e18 FLOPS)-. Esto abre la posibilidad de usar la simulación por ordenador en un amplio espectro de nuevas aplicaciones en ciencia e ingeniería. Por ejemplo, los códigos de CFD&HT van a poder usarse de una forma más efectiva en la fase de diseño de dispositivos industriales ya que se obtendrán resultados muy valiosos en tiempos de ejecución razonables. Por el momento, hay muchos códigos disponibles para el estudio individual de fenómenos de transferencia de calor i de masa con distintos niveles de modelización. Sin embargo, estos códigos no se pueden combinar entre sí para abordar problemas más complejos, en los cuales varios fenómenos físicos interactúan simultáneamente. Bajo este contexto, en esta tesis doctoral se presenta el desarrollo de una metodología de estrategia paralela, y su implementación en una plataforma informática, para la simulación de sistemas multi-físicos. De éste modo, ahora los distintos códigos pueden ser integrados para la creación de nuevas herramientas de simulación destinadas a aplicaciones específicas de interés tanto social como industrial. Esto se hace de una manera intuitiva y simple de manera que los investigadores no tienen que preocuparse ni por la coexistencia de varios códigos simultáneamente ni en cómo hacer que interactúen entre ellos. El acoplamiento entre los diferentes componentes involucrados en una simulación se realiza mediante un código más básico con el cual el usuario solamente interacciona a través de una interfase. Esto aporta interesantes beneficios tanto en la gestión de los proyectos de programario como en la flexibilidad y las características de las simulaciones. En resumen, la estrategia que se propone plantea un nuevo paradigma en la producción de programas de simulación de fenómenos físicos. Aunque la tesis persigue aplicaciones de propósito general se ha puesto especial atención en la simulación de sistemas térmicos, en particular en la evaluación energética de edificios y en compresores herméticos alternativos.Postprint (published version