Download or read book Computation of Exhaust Mixing Noise Using Large eddy Simulation Turbulence Modeling and Lighthill s Acoustic Analogy written by David Brian Schein and published by . This book was released on 2003 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Computation of the Sound Generated by Isotropic Turbulence written by Institute for Computer Applications in Science and Engineering and published by . This book was released on 1993 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Journal of the Acoustical Society of America written by Acoustical Society of America and published by . This book was released on 2007 with total page 1452 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Computation of Sound Generated by Viscous Flow Over a Circular Cylinder written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-08-16 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Lighthill acoustic analogy approach combined with Reynolds-averaged Navier Stokes is used to predict the sound generated by unsteady viscous flow past a circular cylinder assuming a correlation length of 10 cylinder diameters. The two-dimensional unsteady flow field is computed using two Navier-Stokes codes at a low Mach number over a range of Reynolds numbers from 100 to 5 million. Both laminar flow as well as turbulent flow with a variety of eddy viscosity turbulence models are employed. Mean drag and Strouhal number are examined, and trends similar to experiments are observed. Computing the noise within the Reynolds number regime where transition to turbulence occurs near the separation point is problematic: laminar flow exhibits chaotic behavior and turbulent flow exhibits strong dependence on the turbulence model employed. Comparisons of far-field noise with experiment at a Reynolds number of 90,000, therefore, vary significantly, depending on the turbulence model. At a high Reynolds number outside this regime, three different turbulence models yield self-consistent results. Cox, Jared S. and Rumsey, Christopher L. and Brentner, Kenneth S. and Younis, Bassam A. Langley Research Center NASA-TM-110339, NAS 1.15:110339 RTOP 533-31-21-04...

Download or read book Computational Aero Acoustic Studies of an Exhaust Diffuser written by C. Jayatunga and published by . This book was released on 2003 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present paper describes work underway to develop a computational approach that can adequately simulate both the aerodynamic and acoustic behavior of a typical exhaust diffuser/volute combination, such as are commonly used in industrial gas turbines for power generation use. An experimental rig was constructed to obtain a detailed understanding of the flow and acoustic properties of the system, and to provide guidance for computational modelling. Two different approaches are described for analysis of this system. The first uses CFD predictions carried out with a time-averaged RANS-based approach and a statistical turbulence model. Examples of the flow-field from this approach are presented. The second approach uses Large Eddy Simulation CFD, on a simplified geometry chosen on the basis of the experimental evidence, to provide information on the unsteady flow behavior. This information is analyzed and used to specify parameters for an acoustic analogy model. The acoustic model is also a simplified representation of the dominant noise source constructed from an experimentally derived viewpoint. The model is based on a ring of dipoles simulating the fluctuating pressure field associated with the unsteady vortex shedding/growth/merging process in the shear layer emerging from the diffuser exit. Spectral analysis of the unsteady velocity field provided by the LES calculation is used to determine amplitude, frequency dependence and phase relationships in the acoustic model. The basis of the model is described and sample outputs from both LES and acoustic model components are used to illustrate its performance.

Download or read book Computation of the Sound Generated by Isotropic Turbulence written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-30 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: The acoustic radiation from isotropic turbulence is computed numerically. A hybrid direct numerical simulation approach which combines direct numerical simulation (DNS) of the turbulent flow with the Lighthill acoustic analogy is utilized. It is demonstrated that the hybrid DNS method is a feasible approach to the computation of sound generated by turbulent flows. The acoustic efficiency in the simulation of isotropic turbulence appears to be substantially less than that in subsonic jet experiments. The dominant frequency of the computed acoustic pressure is found to be somewhat larger than the dominant frequency of the energy-containing scales of motion. The acoustic power in the simulations is proportional to epsilon (M(sub t))(exp 5) where epsilon is the turbulent dissipation rate and M(sub t) is the turbulent Mach number. This is in agreement with the analytical result of Proudman (1952), but the constant of proportionality is smaller than the analytical result. Two different methods of computing the acoustic power from the DNS data bases yielded consistent results. Sarkar, S. and Hussaini, M. Y. Langley Research Center NAS1-19480; RTOP 505-90-52-01...

Download or read book Noise Sources in Turbulent Shear Flows Fundamentals and Applications written by Roberto Camussi and published by Springer Science & Business Media. This book was released on 2013-02-11 with total page 453 pages. Available in PDF, EPUB and Kindle. Book excerpt: The articles in this volume present the state-of-the-art in noise prediction, modeling and measurement. The articles are partially based on class notes provided during the course `Noise sources in turbulent shear flows', given at CISM on April 2011. The first part contains general concepts of aero acoustics, including vortex sound theory and acoustic analogies, in the second part particular emphasis is put into arguments of interest for engineers and relevant for aircraft design: jet noise, airfoil broadband noise, boundary layer noise (including interior noise and its control) and the concept of noise sources, their theoretical modeling and identification in turbulent lows. All these arguments are treated extensively with the inclusion of many practical examples and references to engineering applications.

Download or read book Les Numerical Analysis of the Aerodynamic Noise Prediction in Dns And written by Alexander Lozovskiy and published by LAP Lambert Academic Publishing. This book was released on 2011-01 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents the rigorous numerical analysis of the aerodynamic noise generation via Lighthill acoustic analogy, which is a non-homogeneous wave equation describing the sound waves. Over more than five decades, the Lighthill analogy was extensively used as one of the major tools in engineering applications in acoustics. However, the first mathematical research of the Finite Element approximation for it is introduced here. Specifically, the focus is on both Direct Numerical and Large Eddy Simulations. The semidiscrete and fully discrete Finite Element methods in DNS are presented. Also, three independent ways of computing the sound power in the semidiscrete case in DNS are introduced. All of these methods are based on the Finite Element scheme. The methods are compared from the point of view of computational cost, accuracy and simplicity. Finally, the concept of Large Eddy Simulation is introduced for aeroacoustic research via Lighthill analogy. Two subgrid scale models are presented for the filtered acoustic analogy. The semidiscrete Finite Elemet Method is analyzed for both. The computational experiments are presented.

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 A Coupled Large Eddy Simulation synthetic Turbulence Method for Predicting Jet Noise written by Joshua Daniel Blake and published by . This book was released on 2020 with total page 203 pages. Available in PDF, EPUB and Kindle. Book excerpt: The noise generated by jet engines represents a significant environmental concern that still needs to be addressed. Accurate and efficient numerical predictions are a key step towards reducing jet noise. The current standard in high-fidelity prediction of jet noise is large eddy simulation (LES), which resolves the large turbulent scales responsible for the low and medium frequency noise and models the smallest turbulent scales that correspond to the high frequency noise. While LES requires significant computational resources to produce an accurate solution, it fails to resolve the noise in the high frequency range, which cannot be simply ignored. To circumvent this, in this dissertation the Coupled LES-Synthetic Turbulent method (CLST) was developed to model the missing frequencies that relate to un-resolved sub-grid scale fluctuations in the flow. The CLST method combines the resolved, large-scale turbulent fluctuations from very large eddy simulations (VLES) with modeled, small-scale fluctuations from a synthetic turbulence model. The noise field is predicted using a formulation of the linearized Euler equations (LEE), where the acoustic waves are generated by source terms from the combined fluctuations of the VLES and the synthetic fields. This research investigates both a Fourier mode-based stochastic turbulence model and a synthetic eddy-based turbulence model in the CLST framework. The Fourier mode-based method is computationally less expensive than the synthetic eddy method but does not account for sweeping. Sweeping and straining of the synthetic fluctuations by large flow scales from VLES are accounted for in the synthetic eddy method. The two models are tested on a Mach 0.9 jet at a moderately-high Reynolds number and at a low Reynolds number. The CLST method is an efficient and viable alternative to high resolution LES or DNS because it can resolve the high frequency range in the acoustic noise spectrum at a reasonable expense.

Download or read book NASA Technical Memorandum written by and published by . This book was released on 1994 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Trailing Edge Noise Prediction Using Large Eddy Simulation and Acoustic Analogy written by Eric Manoha and published by . This book was released on 1998 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dissertation Abstracts International written by and published by . This book was released on 2003 with total page 674 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Development of Computational Aeroacoustics Code for Jet Noise and Flow Prediction written by National Aeronautics and Space Adm Nasa and published by . This book was released on 2018-09-27 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate prediction of jet fan and exhaust plume flow and noise generation and propagation is very important in developing advanced aircraft engines that will pass current and future noise regulations. In jet fan flows as well as exhaust plumes, two major sources of noise are present: large-scale, coherent instabilities and small-scale turbulent eddies. In previous work for the NASA Glenn Research Center, three strategies have been explored in an effort to computationally predict the noise radiation from supersonic jet exhaust plumes. In order from the least expensive computationally to the most expensive computationally, these are: 1) Linearized Euler equations (LEE). 2) Very Large Eddy Simulations (VLES). 3) Large Eddy Simulations (LES). The first method solves the linearized Euler equations (LEE). These equations are obtained by linearizing about a given mean flow and the neglecting viscous effects. In this way, the noise from large-scale instabilities can be found for a given mean flow. The linearized Euler equations are computationally inexpensive, and have produced good noise results for supersonic jets where the large-scale instability noise dominates, as well as for the tone noise from a jet engine blade row. However, these linear equations do not predict the absolute magnitude of the noise; instead, only the relative magnitude is predicted. Also, the predicted disturbances do not modify the mean flow, removing a physical mechanism by which the amplitude of the disturbance may be controlled. Recent research for isolated airfoils' indicates that this may not affect the solution greatly at low frequencies. The second method addresses some of the concerns raised by the LEE method. In this approach, called Very Large Eddy Simulation (VLES), the unsteady Reynolds averaged Navier-Stokes equations are solved directly using a high-accuracy computational aeroacoustics numerical scheme. With the addition of a two-equation turbulence model and the use of a relatively c...

Download or read book Computation of Rotor Noise Generation in Turbulent Flow Using Large eddy Simulation written by Junye Wang and published by . This book was released on 2017 with total page 107 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Aeroacoustics of Flight Vehicles written by Harvey H. Hubbard and published by . This book was released on 1991 with total page 620 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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.