Read Books Online and Download eBooks, EPub, PDF, Mobi, Kindle, Text Full Free.
Numerical Simulations Of Sound Generation From Jet Flows Through Orifices And Lobed Mixers
Download Numerical Simulations Of Sound Generation From Jet Flows Through Orifices And Lobed Mixers full books in PDF, epub, and Kindle. Read online Numerical Simulations Of Sound Generation From Jet Flows Through Orifices And Lobed Mixers ebook anywhere anytime directly on your device. Fast Download speed and no annoying ads. We cannot guarantee that every ebooks is available!
Book Synopsis Numerical Simulations of Sound Generation from Jet Flows Through Orifices and Lobed Mixers by : Kaveh Habibi
Download or read book Numerical Simulations of Sound Generation from Jet Flows Through Orifices and Lobed Mixers written by Kaveh Habibi and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "The design of modern aircraft turbofan engines with low noise emissions requires a thorough understanding of noise generation and absorption phenomena in turbulent mixing jets as well as passive noise reduction devices, e.g. lobed mixers or acoustic liners. At the design stage, such understanding should be provided by reliable and accurate prediction tools to avoid prohibitively expensive experiments. Common acoustic prediction tools are either based on semi-empirical models limited to specific applications, or high-order computational fluid dynamics (CFD) codes, involving prohibitive costs for complex problems. The present study investigates the application and validation of a relatively novel approach in Computational Aeroacoustics (CAA) in which the unsteady near-field flow that contains important noise sources is simulated using a three-dimensional Lattice Boltzmann Method (LBM). The far-field sound pressure is predicted using the Ffwocs Williams-Hawkings (FW-H) surface integral method. The effects of turbulence modelling, Reynolds number, Mach number and non-isothermal boundary conditions were tested for canonical jet noise problems. A commercial code, PowerFLOW, based on the Lattice Boltzmann kernel was utilized for the simulations. In the first part of this study, turbulent jet simulations were performed for various configurations including a circular pipe, the SMC000 single-stream nozzle, and internal mixing nozzles with various types of forced mixers. Mean flow and turbulence statistics were obtained as well as sound pressure levels in the far-field. Predictions were compared with experimental data at similar operating conditions for verification. In most cases in which direct comparison were made with experimental data, 1/3 octave band spectral levels were found in good agreement with measured values up to Strouhal number (St) of ~3.0-4.0, also the overall sound pressure levels from simulation were mostly within ~1.0 dB range of measured sound levels. In all case studies, the actual nozzle including various mixer configurations was included in the computational domain in order to achieve realistic flow conditions. In some cases, inflow conditions needed to be imposed using forcing functions in order to mimic experimental conditions and induce enough perturbation for jet transition to turbulence. Both regular and high-order D3Q19 LBM schemes were tested in this study. The former method was restricted to a relatively low Mach numbers up to 0.5, where the latter can technically simulate the flow-field within the higher subsonic range through high-order terms in the discretized momentum equations. In another parallel study, the problem of sound absorption by turbulent jets was studied using a similar Lattice Boltzmann technique. The sound and turbulent flow inside a standing wave tube terminated by a circular orifice in presence of a mean flow was simulated. The computational domain comprised a standard virtual impedance tube apparatus in which sound waves were produced by periodic pressure imposed at one end. A turbulent jet was formed at the discharge of a circular orifice plate by the steady flow inside the tube. The acoustic impedance and sound absorption coefficient of the orifice plate were calculated from a wave decomposition of the sound field upstream of the orifice. Simulations were carried out for different excitation frequencies, amplitudes and orifice Mach numbers. Results and trends were in quantitative agreement with available analytical solution and experimental data. Altogether, the work documented here supports the accuracy and validity of the LBM for detailed flow simulations of complex turbulent jets. This method offers some advantages over Navier-Stokes based simulations for internal and external flows"--
Book Synopsis On the Turbulence-generated Sound and Control of Compressible Mixing Layers by : Randall R. Kleinman
Download or read book On the Turbulence-generated Sound and Control of Compressible Mixing Layers written by Randall R. Kleinman and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A mixing layer is a common model used to study the noise generation and mixing characteristics of the near-nozzle region of jets. This work presents three separate but related studies that investigate sound generation and active control for noise mitigation and mixing enhancement of such mixing layers. High-fidelity direct numerical simulations of temporal and spatial mixing layers are used for this in two and three dimensions. The first study investigates the role of turbulence scales in generating the radiated far-field sound from temporally-developing, Mach 0.9 mixing layers. To do this, four mixing layers were simulated, starting from the same initial conditions but with Reynolds numbers that varied by a factor of twelve. Above a momentum thickness Reynolds number of 300, all the mixing layers radiate over 85 percent of the acoustic energy of the apparently asymptotically high-Reynolds-number value we are able to compute. Wavenumber spectra of turbulence energy and pressure show the expected Reynolds number dependence: the two highest Reynolds number simulations show evidence of an inertial range and Kolmogorov scaling at the highest wavenumbers. Far-field pressure spectra all decay much more rapidly with wavenumber than the corresponding near-field spectra and show significantly less sensitivity to Reynolds number. Low wavenumbers account for nearly all of the radiated acoustic energy. Implications of these results for jet noise large-eddy simulations are discussed. The second study uses direct numerical simulations of Mach 1.3 mixing layers to characterize the physical mechanisms of flow actuation by localized arc-filament plasma actuators. A validated numerical model of the actuator is devised and placed, as in corresponding experiments, in a cavity in the nozzle near its exit. A rapid Joule heating caused by the plasma is thought to be the root mechanism of flow actuation based upon experimental observation. Simulations show that in the confined space of the cavity, the actuator creates a rapid flow expansion, which transfers fluid mass upward and outward creating a synthetic-jet-like perturbation to the boundary layer. The actuation promotes vortex creation much closer to the nozzle than the baseline flow without actuation, increases the layer growth rate, and organizes the large flow structures. Placing the actuator in a cavity of half the original width increases the velocities responsible for the jet-like boundary layer perturbation and downstream mixing layer growth rate. An actuator model designed to produce the same pressure response without the rapid heating provides similar control authority. The final study implements an automatic optimization procedure based on the adjoint of the perturbed and linearized flow equations. An algorithm is formulated to provide optimized control actuation for noise reduction and mixing enhancement objectives. The method is demonstrated to be successful on several model problems in two and three dimensions, in cases both with an explicitly represented "splitter" plate and cases where an appropriate inflow condition is imposed in its place. Cost functionals for noise reduction and mixing enhancement based on cross-stream velocity and pressure are formulated. Two-dimensional mixing layers with near-wall control are presented with velocity- and pressure-based spreading enhancement cost functionals. Both controls are able to maximize their respective cost functionals by over 50% and increase mixing layer thickness by 10-15% over the optimization time horizon. A three-dimensional, turbulent (spatially-developing) mixing layer is simulated and optimized with a noise reduction cost functional. The control successfully reduces the noise on a target plane below the mixing layer by 28% after 4 line search iterations of the optimization scheme.
Book Synopsis Numerical Simulation of Noise Propagation in Jet Engine Ducts by : Kenneth J. Baumeister
Download or read book Numerical Simulation of Noise Propagation in Jet Engine Ducts written by Kenneth J. Baumeister and published by . This book was released on 1973 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: A finite difference formulation is presented which is useful in the study of acoustically treated inlet and exhaust ducts used in turbofan engines. The difference formulation can readily handle acoustic flow field complications, such as axial variations in wall impedance and cross-sectional area, that would occur in a sonic inlet. In formulating the difference solutions, the continuous acoustic field is lumped into a series of grid points spread uniformly throughout the field. At each point, the pressure is separated into its real and imaginary terms. Example solutions are presented for sound propagation in a one-dimensional straight hard-wall duct and in a two-dimensional straight soft-wall duct without steady flow.
Book Synopsis Sound Generation Using Data from Direct Numerical Simulations of Mixing Layers by : E. J. Avital
Download or read book Sound Generation Using Data from Direct Numerical Simulations of Mixing Layers written by E. J. Avital and published by . This book was released on 1996 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Direct Numerical Simulation of Aerodynamic Noise by :
Download or read book Direct Numerical Simulation of Aerodynamic Noise written by and published by . This book was released on 1989 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt: Direct Numerical Simulation of Aerodynamic Noise is a part of an overall research program in compressible turbulence including the study of the physics of compressible turbulence, shock-turbulence interactions, reacting flows with heat release, and aerodynamic sound generation in shear flows. The objective of the work in aerodynamic sound generation is to use direct numerical simulations as a tool to study the noise generation processes directly, specifically answer the following questions: 1. Can one relate particular flow regions and events to the far-field noise? 2. What regions are the dominant contributors to the far-field noise? 3. What is the role played by pairing process in noise generation? 4. How important are the small scales to the noise generation? 5. What processes control the far-field directivity pattern? To answer these questions in shear flows, first study the acoustics of simple building block flows. The discussion below presents recent results obtained for one of the building block flows, the scattering of sound by a vortex. A short discussion of numerical accuracy is also given. Finally, results are presented for aerodynamic sound generation from a 2-d temporal mixing-layer. (jhd).
Book Synopsis Numerical Simulations of Sound from a Confined Pulsating Axisymmetric Jet by : W. Zhao
Download or read book Numerical Simulations of Sound from a Confined Pulsating Axisymmetric Jet written by W. Zhao and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Numerical Study of Jet Noise Generated by Turbofan Engine Nozzles Equipped with Internal Forced Lobed Mixers Using the Lattice Boltzmann Method by : Hao Gong
Download or read book Numerical Study of Jet Noise Generated by Turbofan Engine Nozzles Equipped with Internal Forced Lobed Mixers Using the Lattice Boltzmann Method written by Hao Gong and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Lobed mixers were found to decrease the sound pressure level at mid frequencies, and to significantly decrease noise emissions at low frequencies. The introduction of scalloping did not provide the same low-frequency noise reduction advantage as unscalloped mixers, but yielded noise reduction benefits at low frequencies compared to the baseline case. Deep scalloping tended to trade off low-frequency noise suppression for a noise decrease at high frequencies. The SPL directivity indicated the angle of maximum emissions changed with scalloping depth. The results were found to be in qualitative agreement with published experimental data." --
Book Synopsis International Aerospace Abstracts by :
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1996 with total page 944 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Sound Generation by Turbulent Wall Jet Flow Over a Trailing Edge by : Richard E. Hayden
Download or read book Sound Generation by Turbulent Wall Jet Flow Over a Trailing Edge written by Richard E. Hayden and published by . This book was released on 1969 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Large Eddy Simulation of Sound Generation by Turbulent Reacting and Nonreacting Shear Flows by : Alireza Najafi-Yazdi
Download or read book Large Eddy Simulation of Sound Generation by Turbulent Reacting and Nonreacting Shear Flows written by Alireza Najafi-Yazdi and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of the present study was to investigate the mechanisms of sound generation by subsonic jets. Large eddy simulations were performed along with bandpass filtering of the flow and sound in order to gain further insight into the pole of coherent structures in subsonic jet noise generation. A sixth-order compact scheme was used for spatial discretization of the fully compressible Navier-Stokes equations. Time integration was performed through the use of the standard fourth-order, explicit Runge-Kutta scheme. An implicit low dispersion, low dissipation Runge-Kutta (ILDDRK) method was developed and implemented for simulations involving sources of stiffness such as flows near solid boundaries, or combustion. A surface integral acoustic analogy formulation, called Formulation 1C, was developed for farfield sound pressure calculations. Formulation 1C was derived based on the convective wave equation in order to take into account the presence of a mean flow...
Download or read book Applied mechanics reviews written by and published by . This book was released on 1948 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Study of Jet Exhaust Noise Sources and Their Mitigation Through Lobed Mixers and Chevrons by : Danielle Grage
Download or read book Study of Jet Exhaust Noise Sources and Their Mitigation Through Lobed Mixers and Chevrons written by Danielle Grage and published by . This book was released on 2011 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: As regulations to reduce noise pollution become more stringent, understanding the noise sources within jet exhaust and how they can be mitigated is important as jet noise is one of the dominant contributors to the overall acoustic signature of an engine. The objective of this study is to understand the effects two exhaust mixing devises, lobed mixers and chevrons. To this end, three basic configurations were studied: a confluent mixer and nozzle (Confluent), a buried lobed mixer with a circular nozzle (MixerA), and a buried lobed mixer with a chevron nozzle (Chevron+MixerB). The hardware was tested at GE Aviation's Cell-41 - Anechoic free jet facility. Acoustic data was acquired, as well as flowfield data using Particle Image Velocimetry (PIV). RANS-based (Reynolds Averaged Navier-Stokes) Computational Fluid Dynamics (CFD) analyses were also conducted to complement the test data. Three operating conditions were considered, defined by their shear level, which is a function of the average mixed velocity of the core flow: low shear (80%), nominal shear (100%), and high shear (112%). The results from the PIV and CFD were used for mutual validation and very good correlation was observed for the MixerA configuration with good correlation overall. The acoustic results were consistent with the flowfield analysis, as well as previous studies, and showed that the presence of mixing devices can provide a low frequency acoustic benefit with some modest increase in high frequency noise, due to increasing mixing near the nozzle and reduced turbulence downstream. An additional high frequency noise source was also identified for MixerA at the high shear condition, which was not present for other configurations. This source showed similar features to the High Mach Lift (HML) previously reported by Tester et al and Garrison et al in 2005. It is thought to be the result of shear layer interaction with a normal shock, resulting from localized pockets of supersonic flow that form near the nozzle exit plane. This source was absent for the Chevron+MixerB configuration and more work must be done to better understand the phenomenon.
Book Synopsis Ground and Flight Evaluation of a Small-Scale Inflatable-Winged Aircraft by :
Download or read book Ground and Flight Evaluation of a Small-Scale Inflatable-Winged Aircraft written by and published by . This book was released on 2002 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: A small-scale, instrumented research aircraft was flown to investigate the flight characteristics of inflatable wings. Ground tests measured the static structural characteristics of the wing at different inflation pressures, and these results compared favorably with analytical predictions. A research-quality instrumentation system was assembled, largely from commercial off-the-shelf components, and installed in the aircraft. Initial flight operations were conducted with a conventional rigid wing having the same dimensions as the inflatable wing. Subsequent flights were conducted with the inflatable wing. Research maneuvers were executed to identify the trim, aerodynamic performance, and longitudinal stability and control characteristics of the vehicle in its different wing configurations. For the angle-of-attack range spanned in this flight program.
Book Synopsis Fundamentals of Rocket Propulsion by : DP Mishra
Download or read book Fundamentals of Rocket Propulsion written by DP Mishra and published by CRC Press. This book was released on 2017-07-20 with total page 364 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book follows a unified approach to present the basic principles of rocket propulsion in concise and lucid form. This textbook comprises of ten chapters ranging from brief introduction and elements of rocket propulsion, aerothermodynamics to solid, liquid and hybrid propellant rocket engines with chapter on electrical propulsion. Worked out examples are also provided at the end of chapter for understanding uncertainty analysis. This book is designed and developed as an introductory text on the fundamental aspects of rocket propulsion for both undergraduate and graduate students. It is also aimed towards practicing engineers in the field of space engineering. This comprehensive guide also provides adequate problems for audience to understand intricate aspects of rocket propulsion enabling them to design and develop rocket engines for peaceful purposes.
Book Synopsis Aeroacoustic Measurements by : Thomas J. Mueller
Download or read book Aeroacoustic Measurements written by Thomas J. Mueller and published by Springer Science & Business Media. This book was released on 2013-11-27 with total page 327 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book describes recent developments in aeroacoustic measurements in wind tunnels and the interpretation of the resulting data. The reader will find the latest measurement techniques described along with examples of the results.
Download or read book Blindsight written by Peter Watts and published by Macmillan. This book was released on 2006-10-03 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hugo and Shirley Jackson award-winning Peter Watts stands on the cutting edge of hard SF with his acclaimed novel, Blindsight Two months since the stars fell... Two months of silence, while a world held its breath. Now some half-derelict space probe, sparking fitfully past Neptune's orbit, hears a whisper from the edge of the solar system: a faint signal sweeping the cosmos like a lighthouse beam. Whatever's out there isn't talking to us. It's talking to some distant star, perhaps. Or perhaps to something closer, something en route. So who do you send to force introductions with unknown and unknowable alien intellect that doesn't wish to be met? You send a linguist with multiple personalities, her brain surgically partitioned into separate, sentient processing cores. You send a biologist so radically interfaced with machinery that he sees x-rays and tastes ultrasound. You send a pacifist warrior in the faint hope she won't be needed. You send a monster to command them all, an extinct hominid predator once called vampire, recalled from the grave with the voodoo of recombinant genetics and the blood of sociopaths. And you send a synthesist—an informational topologist with half his mind gone—as an interface between here and there. Pray they can be trusted with the fate of a world. They may be more alien than the thing they've been sent to find. At the Publisher's request, this title is being sold without Digital Rights Management Software (DRM) applied.
Book Synopsis Turbulent Jets and Plumes by : Joseph Hun-wei Lee
Download or read book Turbulent Jets and Plumes written by Joseph Hun-wei Lee and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 391 pages. Available in PDF, EPUB and Kindle. Book excerpt: Jets and plumes are shear flows produced by momentum and buoyancy forces. Examples include smokestack emissions, fires and volcano eruptions, deep sea vents, thermals, sewage discharges, thermal effluents from power stations, and ocean dumping of sludge. Knowledge of turbulent mixing by jets and plumes is important for environmental control, impact and risk assessment. Turbulent Jets and Plumes introduces the fundamental concepts and develops a Lagrangian approach to model these shear flows. This theme persists throughout the text, starting from simple cases and building towards the practically important case of a turbulent buoyant jet in a density-stratified crossflow. Basic ideas are illustrated by ample use of flow visualization using the laser-induced fluorescence technique. The text includes many illustrative worked examples, comparisons of model predictions with laboratory and field data, and classroom tested problems. An interactive PC-based virtual-reality modelling software (VISJET) is also provided. Engineering and science students, researchers and practitioners may use the book both as an introduction to the subject and as a reference in hydraulics and environmental fluid mechanics.
