The committee was asked to identify sources of potentially damaging noise in the military setting and to review and assess available evidence on hearing loss incurred by members of the armed services as a result of noise exposure during military service since World War II. Concern about noise exposure and hearing loss among military personnel has been evident throughout this period e. Examples of the kinds of data collected through these efforts are provided.
Processus d'atomisation des nappes liquides turbulentes: Through an injector, the liquid is delivered into the combustion chamber and breaks down into droplets. The finer the drops, the quicker their evaporation and the more proper their mixing with air.
A proficient combustion could hence be expected, with low pollutant emissions. Atomization quality is primarily affected by the injector design and the operating conditions which shape the internal flow structure, the turbulence level, the velocity profile at the nozzle outlet, the cavitation and so forth.
All these features are determinants of the breakup of the external liquid flow. Another key parameter to optimize the atomization process is the fuel physical properties. One can think of, among others, the dynamic surface tension controlled by the diffusion of the surfactants on the liquid-gas interface or the extensional viscosity which makes a liquid to become more resistant to the stretching, thereby affecting the breakup.
Effects of the injector design, the operating conditions and the liquid properties on the atomization are inter-dependent. Analyses of experimental data help us to understand the involved mechanisms and their interactions.
On the one hand, this is useful for the numerical developments which should be carried out depending upon the configuration. On the other hand, quantitative criterion could be established to validate the simulation results. Following the above research methodology, we aim to study the disintegration of planar turbulent liquid sheets produced by a triple-disk injector.
Experimental measurements provide the sheet images, used as input for a multi-scale analysis. We investigate, thanks to the latter, the behaviours of the liquid sheet, the ligaments appearing on its edges and the resulting droplets. Moreover, two immersed boundary methods are developed, aiming to simultaneously solve the nozzle flow and the breakup process.
Experiments show that acoustic velocity can lead to severe atomization. Two different breakup modes are pointed out and described which depend on the nozzle diameter. It is also reported that jet trajectory can deviate under specific acoustic conditions.
Two theoretical models are proposed. The first one consists in a modal analysis of the vibrations of a jet when it flows into a transverse stationary acoustic field ; it shows the underlying physical phenomenon which is responsible for one of the breakup mode experimentally observed.
The second model calls out for acoustic radiation pressure to explain deviation of jets. While longitudinal modes have been observed in many previous studies at low frequencies, the present work also focusses on high-frequency transverse modes. First, a premixed flame stabilized on a V-fame holder is investigated where experimental results obtained by Volvo are used to validate the simulations.
For different operating conditions, longitudinal and transverse modes are observed in Large Eddy Simulations LES and show good agreement with the experimental data in terms of pressure frequency and flow dynamics.
Transverse combustion instabilities are analyzed and key elements which drive instabilities are identied. These observations are used to reformulate the classic Flame Transfer Function FTF in order to predict the stability of transverse modes by use of an Helmholtz solver.
These instabilities are known to have detrimental effects leading, in some cases, to the destruction of the propulsion system. To avoid the appearance of such instabilities it is important to gain an understanding of the processes driving such dynamical phenomena.
One has to consider the complex coupling between injection, combustion and the acoustic resonances of the system. The present work contributes to this objective by developing three items. The first deals with numerical simulations of non-reactive and reactive jets submitted to different modulation conditions to understand the interaction between jets, flames and their environment.The Pennsylvania State University The Graduate School NUMERICAL SIMULATION OF JET NOISE A Thesis in Aerospace Engineering by Umesh Paliath c Umesh Paliath.
Study of jet exhaust noise sources and their mitigation through lobed mixers and chevrons A thesis submitted to: Graduate School The of the University of Cincinnati.
Some aspects of RANS based jet noise prediction Azarpeyvand, Mahdi () Some aspects of RANS based jet noise prediction. University of Southampton, Institute of Institute of Sound and Vibration Research, Doctoral Thesis, pp. Record type: Thesis (Doctoral) PDF Ppdf - .
Essay on Noise Pollution: Sources, Effects and Control! Noise may not seem as harmful as the contamination of air or water, but it IS a pollution problem that affects human health and can contribute to a general deterioration of environmental quality.
FAA Response: DNL has been widely accepted as the best available method to describe aircraft noise exposure and is the noise descriptor required by the FAA for use in aircraft noise exposure analyses and noise compatibility planning.
The Pennsylvania State University The Graduate School A NEW ALGORITHM FOR NONLINEAR PROPAGATION OF BROADBAND JET NOISE A Thesis in Aerospace Engineering.