The development of major commercial airports promotes the air transport industry and generates positive economic benefits to the airport and to its host economy. However, external costs are associated with these benefits. Any increase in aircraft movement causes negative environmental impacts, especially noise pollution. Governments have reduced aircraft noise levels at their sources, or introduced aircraft noise management strategies (ANMS); however the problems have never been satisfactorily resolved. This research aims at developing a better understanding of the impacts of aircraft noise on community health and well-being by exploring two core research questions: (1) ???Is health related quality of life worse in communities chronically exposed to aircraft noise than in communities not exposed????; and (2) ???Does long-term aircraft noise exposure associate with adult high blood pressure level via noise stress as a mediating factor????. The Sydney (Kingsford Smith) Airport has been selected as a case study. The health survey instruments have been developed and piloted, and then translated from English into Greek and Arabic. A postal self-administrative health survey (with follow-up letters) has been implemented in the areas surrounding Sydney Airport (called ???aircraft noise exposure group???) and in the matched control group. The total sample size was 1,500 with 47% response rate. This thesis has developed a ???new??? noise index (named Noise Gap Index, NGI) to describe and assess aircraft noise in such a way that is easily understood by the layperson. Factorial analysis of covariance revealed that ???Health related quality of life, in term of physical functioning, general health, vitality, and mental health, of community chronically exposed to high aircraft noise level were worse than the matched control area???. Binary logistic regression analysis found that ???Subjects (aged 15 ??? 87) who have been chronically exposed to high aircraft noise level have the odds of 2.61 of having chronic noise stress. In addition person who have chronic noise stress have the odds of 2.74 of having hypertension compared with those without chronic noise stress???. Finally, the robust hypotheses of effects of aircraft noise on community health and well-being for future experimental study were proposed.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In Brazil, research to quantify annoyance caused by aircraft noise on people living close to airports and air bases is still incipient. Due to the augmented risk of accidents associated to armed aircraft operations but also due to noise emissions by military aircraft air bases, in general, should be located far away from populated areas. Nevertheless, urban development often approximates habited areas to airbases, causing several problems. The actual work aimed to investigate the opinions of a community, composed by civilians and military personnel, that resides close to the Santa Maria airbase (BASM) regarding various aspects, such as aircraft noise and satisfaction with other aspects, such as interference of aircraft noise in daily life, general effects of aircraft noise and individuals attitudes against exposure to aircraft noise. Besides the presence of the BASM and the actual operations on that airbase an expected expansion of the passenger terminal, which is expected to cause an increase in the number of civil aircraft operations and consequently an increase of noise emission, was relevant for the development of this research. The methodology adopted was of qualitative and quantitative nature. By means of observation of the daily life and the use of semistructured interviews the researcher seeked the approximation to the phenomenon of discomfort caused by aircraft noise in the vicinity of Santa Maria Air Base. The qualitative data obtained were analysed using the Grounded Theory, resulting in a conceptual model that shows the relationship between aircraft noise, context of the neighborhood and satisfaction with other aspects than aircraft noise. Based on the results from the qualitative data analysis a structured questionnaire was developed. The questionnaire was applied to 400 individuals in order to measure those aspects that were identified as important during the qualitative approximation the phenomenon of discomfort caused by aircraft noise in the vicinity of Santa Maria Air Base. The results were analysed using univariate and multivariate statistics (Principal Axis Factoring). Factor scores for the effects factor and the annoyance the aircraft operations factor were computed and compared between civilians and military personnel showing both groups are similarly affected by the aircraft operations the comparison of the individual scores of civilians and military personnel on the annoyance the aircraft operations factor showed that the civilians feel more incomfortable than the military personnel / No Brasil, as pesquisas para quantificar o incômodo ocasionado pelo ruído aeronáutico sobre as populações próximas aos aeroportos e bases aéreas são incipientes. Devido ao risco de acidentes associados a operações de aeronaves com armamentos e às emissões de ruído de aeronaves em bases aéreas militares, em geral, estas deveriam estar localizadas longe de áreas povoadas. No entanto, com o desenvolvimento urbano, muitas vezes as áreas habitadas se aproximam das bases aéreas causando vários problemas. Este trabalho teve como objetivo investigar as opiniões de uma população composta por indivíduos civis e militares que residem próximos da Base Aérea de Santa Maria (BASM), em relação a diversos aspectos, tais como, a interferência do ruído das aeronaves na vida diária , os efeitos gerais do ruído das aeronaves e as atitudes dos indivíduos perante a exposição ao ruído dos aviões. Além da presença da BASM, as atuais operações da base aérea e a expansão do terminal de passageiros, que deverá causar aumento do número de operações de aeronaves civis e consequentemente um aumento da emissão de ruído, foram relevantes para o desenvolvimento desta pesquisa. A metodologia adotada foi de natureza qualitativa e quantitativa. Por meio da observação da vida diária e o uso de entrevistas semiestruturadas a pesquisadora buscou a aproximação com o fenômeno do incômodo causado pelo ruído das aeronaves nas proximidades da Base Aérea de Santa Maria. Os dados qualitativos obtidos foram analisados utilizando a Grounded Theory, resultando em um modelo conceitual que mostra a relação entre o ruído das aeronaves, o contexto do bairro e a satisfação com outros aspectos do ruído das aeronaves. Com base nos resultados da análise qualitativa dos dados foi desenvolvido um questionário estruturado. O questionário foi aplicado a 400 indivíduos, com a finalidade de medir os aspectos que foram identificados como importantes durante a aproximação qualitativa e o fenômeno do incômodo causado pelo ruído das aeronaves nas proximidades da Base Aérea de Santa Maria. Os resultados foram analisados utilizando estatística univariada e multivariada (Principal Axis Factoring). Os escores fatoriais para o fator efeitos e o fator incômodo provocado pelas operações aeronáuticas foram calculados e comparados entre civis e militares mostrando que ambos os grupos são igualmente afetados pelas operações das aeronaves e a comparação das pontuações individuais de civis e militares no fator incômodo mostrou que os civis se sentem mais incomodados que os indivíduos militares.

Este trabalho apresenta uma avaliação do ruído aeronáutico nas proximidades do Aeroporto Internacional Salgado Filho, no município de Porto Alegre, RS, através de um estudo em escolas localizadas dentro das zonas do Plano Específico de Zoneamento de Ruído – PEZR. Segundo a Organização Mundial da Saúde, as crianças são consideradas o grupo mais vulnerável aos efeitos do ruído e, atualmente, os prejuízos na vida escolar possuem evidências científicas comprovadas. No entanto, as atividades escolares dentro das zonas de ruído mais críticas no entorno dos aeroportos, que não são permitidas segundo legislações nacionais e municipais, ocorrem em ambientes com características construtivas inadequadas aos níveis de exposição. A avaliação da percepção e do incômodo do ruído aeronáutico nas escolas localizadas dentro dos limites do PEZR do Aeroporto Internacional Salgado Filho, fundamentou-se em critérios quantitativos e qualitativos, com medições acústicas, aplicação de questionários, realização de entrevistas e observações de comportamento e de ocupação dos ambientes nas Escolas. Os resultados indicam um grande incômodo manifestado por alunos e professores que convivem em ambientes ruidosos, além de encontrar relações com a interferência em possíveis problemas vocais e auditivos, em função da necessidade da elevação no volume da voz. Outro aspecto levantado foi o comprometimento do desempenho escolar, que é afetado diretamente pela falta de critérios de conforto acústico no projeto das edificações. / This paper aims at evaluating aircraft noise in the vicinity of Salgado Filho International Airport, with research done in two schools inside Zona I of Plano Específico de Zoneamento de Ruído - PEZR. According to the World Health Organization, children are considered the most vulnerable group regarding the effects of noise. In addition, scientific evidence has proved that school life is harmed. However, school activities inside the most critical noise zones around airports, which are not allowed according to national and municipal legislation, take place in environments with constructive building features unsuitable to the exposure levels. This study aims at evaluating the perception and inconvenience of aircraft noise in schools within Zona I of PZER of Salgado Filho International Airport, based on quantitative and qualitative criteria, with acoustics measurement, surveys, interviews, and observation of behavior and use of school environment. The primary results show a lot of annoyance reported by students and teachers who live in noisy environments. Such results may also indicate possible vocal and auditory problems as a consequence of the need to raise one's voice. Another aspect which has been pointed out was problems in school performance because of the frequent interruption in the communication between teacher and students whenever planes flew over the place.

Este trabalho apresenta uma avaliação do ruído aeronáutico nas proximidades do Aeroporto Internacional Salgado Filho, no município de Porto Alegre, RS, através de um estudo em escolas localizadas dentro das zonas do Plano Específico de Zoneamento de Ruído – PEZR. Segundo a Organização Mundial da Saúde, as crianças são consideradas o grupo mais vulnerável aos efeitos do ruído e, atualmente, os prejuízos na vida escolar possuem evidências científicas comprovadas. No entanto, as atividades escolares dentro das zonas de ruído mais críticas no entorno dos aeroportos, que não são permitidas segundo legislações nacionais e municipais, ocorrem em ambientes com características construtivas inadequadas aos níveis de exposição. A avaliação da percepção e do incômodo do ruído aeronáutico nas escolas localizadas dentro dos limites do PEZR do Aeroporto Internacional Salgado Filho, fundamentou-se em critérios quantitativos e qualitativos, com medições acústicas, aplicação de questionários, realização de entrevistas e observações de comportamento e de ocupação dos ambientes nas Escolas. Os resultados indicam um grande incômodo manifestado por alunos e professores que convivem em ambientes ruidosos, além de encontrar relações com a interferência em possíveis problemas vocais e auditivos, em função da necessidade da elevação no volume da voz. Outro aspecto levantado foi o comprometimento do desempenho escolar, que é afetado diretamente pela falta de critérios de conforto acústico no projeto das edificações. / This paper aims at evaluating aircraft noise in the vicinity of Salgado Filho International Airport, with research done in two schools inside Zona I of Plano Específico de Zoneamento de Ruído - PEZR. According to the World Health Organization, children are considered the most vulnerable group regarding the effects of noise. In addition, scientific evidence has proved that school life is harmed. However, school activities inside the most critical noise zones around airports, which are not allowed according to national and municipal legislation, take place in environments with constructive building features unsuitable to the exposure levels. This study aims at evaluating the perception and inconvenience of aircraft noise in schools within Zona I of PZER of Salgado Filho International Airport, based on quantitative and qualitative criteria, with acoustics measurement, surveys, interviews, and observation of behavior and use of school environment. The primary results show a lot of annoyance reported by students and teachers who live in noisy environments. Such results may also indicate possible vocal and auditory problems as a consequence of the need to raise one's voice. Another aspect which has been pointed out was problems in school performance because of the frequent interruption in the communication between teacher and students whenever planes flew over the place.

Este trabalho apresenta uma avaliação do ruído aeronáutico nas proximidades do Aeroporto Internacional Salgado Filho, no município de Porto Alegre, RS, através de um estudo em escolas localizadas dentro das zonas do Plano Específico de Zoneamento de Ruído – PEZR. Segundo a Organização Mundial da Saúde, as crianças são consideradas o grupo mais vulnerável aos efeitos do ruído e, atualmente, os prejuízos na vida escolar possuem evidências científicas comprovadas. No entanto, as atividades escolares dentro das zonas de ruído mais críticas no entorno dos aeroportos, que não são permitidas segundo legislações nacionais e municipais, ocorrem em ambientes com características construtivas inadequadas aos níveis de exposição. A avaliação da percepção e do incômodo do ruído aeronáutico nas escolas localizadas dentro dos limites do PEZR do Aeroporto Internacional Salgado Filho, fundamentou-se em critérios quantitativos e qualitativos, com medições acústicas, aplicação de questionários, realização de entrevistas e observações de comportamento e de ocupação dos ambientes nas Escolas. Os resultados indicam um grande incômodo manifestado por alunos e professores que convivem em ambientes ruidosos, além de encontrar relações com a interferência em possíveis problemas vocais e auditivos, em função da necessidade da elevação no volume da voz. Outro aspecto levantado foi o comprometimento do desempenho escolar, que é afetado diretamente pela falta de critérios de conforto acústico no projeto das edificações. / This paper aims at evaluating aircraft noise in the vicinity of Salgado Filho International Airport, with research done in two schools inside Zona I of Plano Específico de Zoneamento de Ruído - PEZR. According to the World Health Organization, children are considered the most vulnerable group regarding the effects of noise. In addition, scientific evidence has proved that school life is harmed. However, school activities inside the most critical noise zones around airports, which are not allowed according to national and municipal legislation, take place in environments with constructive building features unsuitable to the exposure levels. This study aims at evaluating the perception and inconvenience of aircraft noise in schools within Zona I of PZER of Salgado Filho International Airport, based on quantitative and qualitative criteria, with acoustics measurement, surveys, interviews, and observation of behavior and use of school environment. The primary results show a lot of annoyance reported by students and teachers who live in noisy environments. Such results may also indicate possible vocal and auditory problems as a consequence of the need to raise one's voice. Another aspect which has been pointed out was problems in school performance because of the frequent interruption in the communication between teacher and students whenever planes flew over the place.

Com o aumento do tráfego aéreo no aeroporto de Ribeirão Preto - SP e o conhecimento de várias reclamações sobre o incômodo sonoro junto ao Ministério Público é apresentada uma análise, através de simulação computacional, de como ficou as curvas de ruído deste aeródromo. O objetivo deste estudo foi verificar como a população, que está no seu entorno, é afetada pela operação das aeronaves e qual o percentual a ser encontrado após a simulação realizada com o programa INM (Integrated Noise Model). A simulação indicou que o aumento das operações no Aeroporto Leite Lopes SBRP não ocasionou um impacto maior na população afetada dentro da área definida pela curva de 65 dB(A), ficando este valor dentro de parâmetros aceitáveis pelas normas adotadas. A velocidade e a direção dos ventos locais contribuem para o aumento do impacto ambiental, sugerindo a necessidade de alterar as rotas das aeronaves conforme ocorrerem estas mudanças meteorológicas. O estudo indicou a necessidade de alteração das rotas de pouso e decolagem. Orientar os pilotos através dos controladores de voo que pousos e decolagens sejam efetuados pela cabeceira da pista 36 (trinta e seis), prolongando o eixo de decolagem em mais 2 milhas náuticas ou 2 km. Para mitigar o efeito do impacto produzido pelas operações das aeronaves no aeroporto, se faz necessário a realização de novos estudos para que possamos orientar o planejamento urbano do entorno utilizando novas rotas de voos com novos levantamentos de campo e simulações. / With increasing air traffic at the airport of Ribeirão Preto - SP and the knowledge of numerous complaints about noise nuisance with the Public Ministry, it is presented an analysis through computer simulation of how would be the noise curves of this airfield. The objective of this study was to determine how the population, which is in its surroundings, is affected by the operation of aircraft and what percentage to be found after the simulation performed with the program INM (Integrated Noise Model).The simulation indicated that the increase in operations in Leite Lopes Airport - SBRP did not cause increases in the affected population within the area defined by the curve 65 dB(A), with this value within acceptable parameters by the standards adopted. The speed and direction of local winds contribute to the increased environmental impact, suggesting the need to change the routes of aircraft as these weather changes occur. The study indicated the need for change in takeoff and landing routes. Guide the pilots through the flight controllers that takeoffs and landings are made by the end of the runway 36 (thirty six), extending the shaft off at over 2 nautical miles or 2 km. To mitigate the effect of the impact produced by aircraft operations at the airport, it is necessary to carry out further research so we can guide the planning of urban environment using new flight routes with new field surveys and simulations.

The objective of this research is to examine how to design low-noise transport aircraft using Multidisciplinary Design Optimization (MDO). The subject is approached by designing for low-noise both implicitly and explicitly. The explicit design approach involves optimizing an aircraft while explicitly constraining the noise level. An MDO framework capable of optimizing both a cantilever wing and a Strut-Braced-Wing (SBW) aircraft was developed. The framework employs aircraft analysis codes previously developed at the Multidisciplinary Design and Analysis (MAD) Center at Virginia Tech (VT). These codes have been improved here to provide more detailed and realistic analysis. The Aircraft Noise Prediction Program (ANOPP) is used for airframe noise analysis. The objective is to use the MDO framework to design aircraft for low-airframe-noise at the approach conditions and quantify the change in weight and performance with respect to a traditionally designed aircraft. The results show that reducing airframe noise by reducing approach speed alone, will not provide significant noise reduction without a large performance and weight penalty. Therefore, more dramatic changes to the aircraft design are needed to achieve a significant airframe noise reduction. Another study showed that the trailing-edge (TE) flap can be eliminated, as well as all the noise associated with that device, without incurring a significant weight and performance penalty. To achieve approximately 10 EPNdB TE flap noise reduction the flap area was reduced by 82% while the wing reference area was increased by 12.4% and the angle of attack increased from 7.6 degrees to 12.1 degrees to meet the required lift at approach. The wing span increased by approximately 2.2%. Since the flap area is being minimized, the wing weight suffers only about a 2,000 lb penalty. The increase in wing span provides a reduction in induced drag to balance the increased parasite drag due to a lower wing aspect ratio. As a result, the aircraft has been designed to have minimal TE flaps without any significant performance penalty. If noise due to the leading-edge (LE) slats and landing gear are reduced, which is currently being pursued, the elimination of the flap will be very significant as the clean wing noise will be the next 'noise barrier'. Lastly, a comparison showed that SBW aircraft can be designed to be 10% lighter and require 15% less fuel than cantilever wing aircraft. Furthermore, an airframe noise analysis showed that SBW aircraft with short fuselage-mounted landing gear could have similar or potentially a lower airframe noise level than comparable cantilever wing aircraft. The implicit design approach involves selecting a configuration that supports a low-noise operation, and optimizing for performance. A Blended-Wing-Body (BWB) transport aircraft has the potential for significant reduction in environmental emissions and noise compared to a conventional transport aircraft. A BWB with distributed propulsion was selected as the configuration for the implicit low-noise design in this research. An MDO framework previously developed at the MAD Center at Virginia Tech has been refined to give more accurate and realistic aircraft designs. To study the effects of distributed propulsion, two different BWB configurations were optimized. A conventional propulsion BWB with four pylon mounted engines and two versions of a distributed propulsion BWB with eight boundary layer ingestion inlet engines. A 'conservative' distributed propulsion BWB design with a 20% duct weight factor and a 95% duct efficiency, and an 'optimistic' distributed propulsion BWB design with a 10% duct weight factor and a 97% duct efficiency were studied. The results show that 65% of the possible savings due to 'filling in' the wake are required for the 'optimistic' distributed propulsion BWB design to have comparable $TOGW$ as the conventional propulsion BWB, and 100% savings are required for the 'conservative' design. Therefore, considering weight alone, this may not be an attractive concept. Although a significant weight penalty is associated with the distributed propulsion system presented in this study, other characteristics need to be considered when evaluating the overall effects. Potential benefits of distributed propulsion are, for example, reduced propulsion system noise, improved safety due to engine redundancy, a less critical engine-out condition, gust load/flutter alleviation, and increased affordability due to smaller, easily-interchangeable engines. / Ph. D.

The first bypass turbofan engines came into operation in the early 1970s. The need for reductions in the fuel consumption affected aircraft noise positively through reductions in the jet noise. Over the past decades, the bypass ratio of turbofan engines has continuously increased and, as a result, aircraft engine noise has decreased to a level comparable to the noise originated from the turbulent flow around the airframe for take-off and landing conditions. Although aircraft have become quieter, the number of individuals affected by the aviation growth is likely to increase. Airframe noise has been currently identified as the ultimate aircraft noise barrier and many efforts devoted to its reductions have focused specifically on landing gears and high-lift devices, which are the most relevant noise contributors. Some devices have been designed to reduce flap noise, however, not all of them have been successfully tested in a detailed large-scale flap model due to their difficult implementation in real flap side-edges. This research investigates the relationship between the parameters of a large-scale flap model at 1.50×106 Reynolds number and the physics responsible for flap side-edge noise generation, one of the most dominant sources of the airframe noise. Experimental tests were conducted in a wind-tunnel and flow-field measurements were taken by a multi-hole pitot probe and an aerodynamic balance and complemented by phased microphone array techniques towards a deeper understanding of flap side-edge noise sources and their correlations to unsteady vorticity fluctuations. Conventional beamforming and CLEAN-SC and DAMAS deconvolution methodologies provided far-field acoustic spectra estimations and noise source mapping. The model used for the tests consists of an unswept isolated flap element with representative tip details present in conventional medium-range transport aircraft. The instrumentation includes 106 steady pressure taps distributed chord-wise and span-wise and a sand trip tape to transition the laminar boundary layer. Different side-edge devices were assessed towards airframe noise reductions. A perforated side-edge treatment was also applied to the flap side-edge. Results of aerodynamic and aeroacoustic tests conducted in the LAE-1 closed circuit wind tunnel with a closed test section at the São Carlos School of Engineering - University of São Paulo (EESC-USP) at up to 40 m/s flow speeds provided specific information on the aeroacoustic and aerodynamic characterization of the dominant acoustic source mechanisms of the flap model. / Os primeiros motores turbofan com razão de desvio entraram em operação no início dos anos 70. A necessidade de reduções no consumo de combustível afetou positivamente o ruído das aeronaves através de reduções no ruído do jato. Nas últimas décadas, a razão de desvio de motores turbofan aumentou continuamente e, como resultado, o ruído do motor da aeronave diminuiu para um nível comparável ao ruído originado do fluxo turbulento ao redor do airframe para as condições de decolagem e pouso. Embora as aeronaves tenham-se tornado mais silenciosas, é provável que o número de indivíduos afetados pelo crescimento da aviação aumente. Atualmente, o ruído de airframe tem sido identificado como a barreira máxima de ruído para aeronaves e muitos esforços dedicados à sua redução se concentraram especificamente no trem de pouso e dispositivos de alta sustentação, que são os contribuidores de ruído mais relevantes. Alguns dispositivos foram projetados para reduzir o ruído do flap, no entanto, nem todos deles foram testados com sucesso em um modelo detalhado de flap de grande escala, devido a sua difícil implementação nas bordas laterais do flap real. Esta pesquisa investiga a relação entre os parâmetros de um modelo de flap de grande escala com número de Reynolds de 1.50 × 106 e a física responsável pela geração de ruído na borda lateral do flap, uma das fontes mais dominantes do ruido de airframe. Testes experimentais foram realizados em um túnel de vento e as medidas do escoamento foram tomadas por uma sonda pitot de múltiplos furos e uma balança aerodinâmica e complementadas por técnicas de antenas de microfones para um entendimento mais profundo das fontes de ruído da ponta do flap e suas correlações com flutuações instáveis de vorticidade. O beamforming convencional e as metodologias de deconvolução CLEAN-SC e DAMAS forneceram estimativas de espectros acústicos de campo distante e mapeamento de fontes de ruído. O modelo usado para os testes consiste em um elemento de flap isolado, sem enflechamento, com detalhes de ponta representativos presentes em aeronaves convencionais de transporte de médio alcance. A instrumentação inclui 106 tomadas de pressão estacionárias distribuídas na corda e na envergadura e um trip de fita de areia para fazer a transição da camada limite laminar. Diferentes dispositivos de borda lateral foram avaliados em relação às reduções de ruído de airframe. Um tratamento perfurado de borda lateral também foi aplicado à borda lateral do flap. Os resultados dos testes aerodinâmicos e aeroacústicos realizados no túnel de vento de circuito fechado LAE-1, com seção de provas fechada na Escola de Engenharia de São Carlos - Universidade de São Paulo (EESC-USP) com velocidade de fluxo de até 40 m/s forneceram informações específicas sobre a caracterização aeroacústica e aerodinâmica dos mecanismos dominantes de fonte acústica do modelo de flap.

In the year 1983/84, the Commonwealth Government decided to redevelop a RAAF airstrip at Tindal into a northern air base in NT. It would replace RAAF Base Darwin that was situated close to the coast and susceptible to both cyclonic weather and any 'enemy' sneak raid attacks. Tindal is located about fifteen kilometres south from Katherine on the Stuart Highway. A social survey conducted in the second half of 1983 formed the basis for SIA predictions that appeared in the EIS. These encompassed social impacts that would occur during the construction phase and later throughout the operational phase. Included among the predicted impacts on local residents was aircraft noise from military aircraft flying overhead and this was confirmed by a social survey conducted in 1994. Other predictions included the integration of a RAAF population with its own set of values into a conservative Katherine community. The social survey of 1994 asks the same type of questions as asked in 1983, and the two sets of answers are compared over time. A subsequent longitudinal analysis follows the structural development of the Katherine population/community. A group of 1994 respondents was found to have resided in Katherine in 1983 and cohort by cohort their state of affairs discovered. As Katherine developed into a regional centre the views of respondents toward the RAAF became more accepting and residual social impacts from the redevelopment phase were difficult to find.

A systematic research on aeroacoustics conducted around the world for the last few decades has revealed various inherent characteristics of the jet noise radiation. However, a lot more needs to be done for the theoretical as well as experimental predictions of various jet noise features based on actual flow details. The work reported in the present thesis is an attempt in this direction. A critical study of existing literature on jet noise shows that none of the general wave equations lends itself easily for predictions of all the jet noise features. It is shown that while LighthilPs classical acoustic analogy approach, with some reasonable approximations, can be used to yield most of the information needed by the engineers, the convected wave equations of Phillips and Lilley are required to study the acoustic radiation in what has come to be known as "Refraction valley" or "Cone of relative silence". The characteristics of the sound field of underexpanded cold jet impingement flows were studied by measuring the noise emanating from two convergent nozzles of throat diameter 2.5 mm and 5 mm each and a convergent - divergent nozzle of exit diameter of 6.49 mm, when the jet impinges on a flat plate kept perpendicular to the direction of the jet. The measurements were conducted upstream of the nozzle over an extensive envelope of jet operating conditions such as chamber stagnation pressure, mass flow rate through the nozzle and diameter of the nozzle. The source strength at the jet boundary was obtained by measuring acoustic pressure amplitude close to the jet contour assuming it as locally cylindrical. Particular attention was focussed on backward projection of the sound field on to a cylindrical surface. This is the application of acoustic holography to study the sound radiation in the audio frequency region. With the help of FFT and software developed for this purpose, the theoretical predictions using data from several cylindrical surfaces were compared. A detailed analysis of noise radiation from a cold sonic and supersonic free jet was also carried out. The experimental work involved the measurement of noise field from a 2.5 mm, 5 mm convergent and a convergent - divergent nozzle of exit diameter of 6.49 mm and area ratio 1.687 for designed Mach number of two. The experimental setup consisted essentially of a pressure chamber made of mild steel, designed to withstand 50 bar pressure. This chamber is a cylinder with dia 0.421 m and length 0.85 m. The nozzles were made of mild steel. Compressed air approximately at room temperature is supplied to the nozzle via a control valve. The measuring and recording instruments consists of B & K Microphones, Preamplifiers, Conditioning amplifier and a Mediator, which measure a Sound Pressure Level at a point. The nozzles were operated at pressure ratio upto 25 bar. The noise signal was processed through 12 channel data acquisition system. Acoustic pressure and SPL were" calculated using theoretical relations and software developed. Using this software Fast Fourier Transformations of raw signal was obtained from 20 Hz to 20 kHz. Also constant SPL contour graphs were obtained. Source strength distribution at the jet boundary has been obtained by the principle of acoustic holography. Experimental values are closely matching with the results obtained by acoustic holography. The percentage error for acoustic pressure and SPL were less than 12%. The experimental results were used to obtain the source distribution in terms of gross jet parameters.