Download or read book Towards Computational Aeroacoustics Prediction of Realistic Turbofan Broadband Noise Using Synthetic Turbulence Modeling written by Adrian Sescu and published by . This book was released on 2011 with total page 271 pages. Available in PDF, EPUB and Kindle. Book excerpt: The prediction of broadband noise radiating from realistic turbulent flows interacting with complex geometries, using nonlinear time-domain algorithms, is still in infancy. The main obstacle is related to the computational efficiency--both in terms of processing time and storage capacity--but equally important is the accuracy of imposing realistic turbulence superposed on deterministic vortical gusts at the inflow boundary, or the initiation of the solution with a realistic turbulent flow. The main objective of this thesis is to derive a divergence-free synthetic turbulence model, and to impose turbulent wakes at the inflow boundary, for the prediction of broadband noise radiating from the interaction between rotor wakes and stator vanes in a realistic bypass turbofan engine. The tool is an advanced Computational Aeroacoustics code, NASA Broadband Aeroacoustic Stator Simulation (BASS) code, which employs state-of-the-art spatial and temporal schemes, and accurate boundary conditions. A number of synthetic turbulence models have been implemented in BASS code, including a new divergence free model based on the assumption that turbulence can be considered as a superposition of random eddies satisfying certain conditions. The divergence free condition is satisfied by using a streamfunction which is a scalar in two dimensions and a vector in three dimensions, and the momentum equations linearized about the mean flow. The synthetic turbulence model uses the statistics from the experimental turbulent data taken from NASA Source Diagnostic Test rig. The thesis also includes the derivation and analysis of the multidimensional finite difference schemes designed to improve the isotropy of waves propagating in multidimensions. The dispersion properties of the schemes in multidimensions are analyzed using Fourier analysis, and the isotropy error is found to be very low. The stability of the multidimensional schemes in combination with either linear multistep time marching methods and Runge-Kutta schemes are extensively analyzed. Various test cases in two or three dimensions show that the multidimensional schemes have low isotropy error, and perform more efficiently when compared to corresponding conventional schemes. The thesis begins with a thorough introduction on turbofan broadband noise prediction techniques, including a comprehensive literature review on turbofan noise and synthetic turbulence modeling. In chapter 2, an overview of Computational Aeroacoustics is included, with a description of actual fields of research, and available tools and techniques. Here, the derivation and analysis of multidimensional finite difference schemes in terms of isotropy error and stability are also included. In chapter 3, the nonlinear time-domain analysis tool, BASS code, is described, and the description and derivation of the new synthetic turbulence model are included. Chapter 4 is reserved to various results from different tests cases, and chapter 5 to comments, conclusions and remarks on future directions related to the research in this thesis.

Download or read book Aeroacoustic Prediction Codes written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-27 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes work performed on Contract NAS3-27720AoI 13 as part of the NASA Advanced Subsonic Transport (AST) Noise Reduction Technology effort. Computer codes were developed to provide quantitative prediction, design, and analysis capability for several aircraft engine noise sources. The objective was to provide improved, physics-based tools for exploration of noise-reduction concepts and understanding of experimental results. Methods and codes focused on fan broadband and 'buzz saw' noise and on low-emissions combustor noise and compliment work done by other contractors under the NASA AST program to develop methods and codes for fan harmonic tone noise and jet noise. The methods and codes developed and reported herein employ a wide range of approaches, from the strictly empirical to the completely computational, with some being semiempirical analytical, and/or analytical/computational. Emphasis was on capturing the essential physics while still considering method or code utility as a practical design and analysis tool for everyday engineering use. Codes and prediction models were developed for: (1) an improved empirical correlation model for fan rotor exit flow mean and turbulence properties, for use in predicting broadband noise generated by rotor exit flow turbulence interaction with downstream stator vanes: (2) fan broadband noise models for rotor and stator/turbulence interaction sources including 3D effects, noncompact-source effects. directivity modeling, and extensions to the rotor supersonic tip-speed regime; (3) fan multiple-pure-tone in-duct sound pressure prediction methodology based on computational fluid dynamics (CFD) analysis; and (4) low-emissions combustor prediction methodology and computer code based on CFD and actuator disk theory. In addition. the relative importance of dipole and quadrupole source mechanisms was studied using direct CFD source computation for a simple cascadeigust interaction problem, and an empirical combustor-nois...

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 Computational Aeroacoustic Prediction of Airfoil Self noise at Static Angles of Attack written by Alison Zilstra and published by . This book was released on 2019 with total page 79 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aeroacoustic noise from wind turbines is often an obstacle in the implementation of wind farms. Reduction of this noise is key to allowing the expansion of the wind energy sector which is crucial for decreasing the dependence on fossil fuel energy sources. The use of a fully analytical computational model for aeroacoustic noise will allow for acoustics to be incorporated into the design stage of new wind turbine technologies. This thesis investigates the use of a predictive model for the noise from two dimensional (2D) blade segments using computational fluid dynamics (CFD). The simulation uses Reynolds Averaged Navier-Stokes (RANS) to initialize the simulation, and then a combination of Large Eddy Simulation (LES) and the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy to predict the flow and acoustics, respectively. The SD 7037 and NACA 0012 airfoils were simulated and compared against experimental flow and acoustics data. The SD 7037 airfoil was tested using incompressible and compressible LES simulation for a Reynolds number of Re=4.25x104. The results show good prediction of both the flow and acoustics, and the source of the tonal noise generated by the airfoil at 0° angle of attack (AOA) was determined to be a result of 2D boundary layer behaviour, and also the transition from 2D to 3D behaviour. The 1° AOA results did not predict the tonal noise found in experiments, but it was determined that inaccuracies in some of the simulations caused the boundary layer behaviour to falsely change to that of the experimental 2° or 3° AOA. The NACA 0012 airfoil was tested using incompressible LES for a high Re case of Re=1.5x106. The flow simulation for this case was good, however the acoustic prediction was at a higher sound pressure level (SPL) than the experimental data. The second case of this simulation predicted tonal noise when experiments predicted broadband noise only. The simulation of this false tonal noise was attributed to instabilities in the simulation. The differences between the SD 7037 1° results, where instabilities caused no tones to be simulated, and the NACA 0012 results for the second case, where instabilities caused false tones to be predicted, shows that care must be taken in the setup of the simulation. Recommendations for future work are to perform a grid independence study and sensitivity analysis to determine the cause of these false predictions. That being said, overall, the predictive abilities of the computational aeroacoustic model result in good prediction of the airfoil self-noise for static AOAs.

Download or read book Development of Computational Aeroacoustics Code for Jet Noise and Flow Prediction written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-20 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 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"--

Download or read book Large Eddy Simulation for Acoustics written by Claus Wagner and published by Cambridge University Press. This book was released on 2007-01-15 with total page 389 pages. Available in PDF, EPUB and Kindle. Book excerpt: Noise around airports, trains, and industries attracts environmental concern and regulation. Large-eddy simulation (LES) is used for noise-reduced design and acoustical research. This 2007 book, by 30 experts, presents the theoretical background of acoustics and LES, and details about numerical methods, e.g. discretization schemes, boundary conditions, and coupling aspects.

Download or read book Fan Broadband Interaction Noise Prediction Using a Synthetic Turbulence Method written by Carolin Anja Kissner and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Fundamentals of High Lift for Future Civil Aircraft written by Rolf Radespiel and published by Springer Nature. This book was released on 2020-10-17 with total page 634 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reports on the latest numerical and experimental findings in the field of high-lift technologies. It covers interdisciplinary research subjects relating to scientific computing, aerodynamics, aeroacoustics, material sciences, aircraft structures, and flight mechanics. The respective chapters are based on papers presented at the Final Symposium of the Collaborative Research Center (CRC) 880, which was held on December 17-18, 2019 in Braunschweig, Germany. The conference and the research presented here were partly supported by the CRC 880 on “Fundamentals of High Lift for Future Civil Aircraft,” funded by the DFG (German Research Foundation). The papers offer timely insights into high-lift technologies for short take-off and landing aircraft, with a special focus on aeroacoustics, efficient high-lift, flight dynamics, and aircraft design.

Download or read book Computational Aeroacoustics written by Jay C. Hardin and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 525 pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational aeroacoustics is rapidly emerging as an essential element in the study of aerodynamic sound. As with all emerging technologies, it is paramount that we assess the various opportuni ties and establish achievable goals for this new technology. Essential to this process is the identification and prioritization of fundamental aeroacoustics problems which are amenable to direct numerical siIn ulation. Questions, ranging from the role numerical methods play in the classical theoretical approaches to aeroacoustics, to the correct specification of well-posed numerical problems, need to be answered. These issues provided the impetus for the Workshop on Computa tional Aeroacoustics sponsored by ICASE and the Acoustics Division of NASA LaRC on April 6-9, 1992. The participants of the Work shop were leading aeroacousticians, computational fluid dynamicists and applied mathematicians. The Workshop started with the open ing remarks by M. Y. Hussaini and the welcome address by Kristin Hessenius who introduced the keynote speaker, Sir James Lighthill. The keynote address set the stage for the Workshop. It was both an authoritative and up-to-date discussion of the state-of-the-art in aeroacoustics. The presentations at the Workshop were divided into five sessions - i) Classical Theoretical Approaches (William Zorumski, Chairman), ii) Mathematical Aspects of Acoustics (Rodolfo Rosales, Chairman), iii) Validation Methodology (Allan Pierce, Chairman), iv) Direct Numerical Simulation (Michael Myers, Chairman), and v) Unsteady Compressible Flow Computa tional Methods (Douglas Dwoyer, Chairman).

Download or read book Trailing Edge Noise Prediction Using the Non Linear Disturbance Equations written by Abhishek Jain and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: AIRFOIL self-noise consists of five major sources. One of these identified sources is turbulent boundary layer -- trailing edge (TBL-TE) noise, which is an important source of rotor and wind turbine broadband noise, and the focus of this thesis. Trailing edge noise is the result of unsteady flow interacting with the trailing edge of an airfoil or other sharp edged flow surface. The presence of the sharp trailing edge scatters the sound generated by the turbulent eddies very efficiently, especially for sources in the immediate vicinity of the edge. There is a need for accurate and computationally efficient methods to calculate the turbulent boundary layer trailing-edge (TBL-TE) noise that are not reliant on empirical data. The majority of the current semi-empirical techniques are based on measurements from symmetric NACA airfoil sections (i.e. NACA 0012). These techniques are generally not coupled with CFD solvers to obtain turbulent boundary layer data that provides pertinent parameters used in the acoustic calculations. Some methods exist that incorporate CFD solutions like Large Eddy simulations (LES) into their noise prediction algorithms. But these are prohibitively expensive and impractical for routine use. The method described in this paper is a first principles approach that aims to predict the TBL-TE noise using computational aeroacoustic (CAA) techniques without resorting to empiricism.The prediction of trailing edge noise requires an accurate calculation of the boundary layer fluctuations in the vicinity of the trailing edge. Scales in the computational domain ranging from the small turbulent boundary layer scales to those of the long-range noise propagation need to be resolved. These data can be obtained using simulation techniques like Direct Numerical Simulation (DNS) or Large Eddy Simulation (LES). However such simulations for complete helicopters or wind turbine rotors are impractical given today's computational resources. Also, DNS becomes unrealistic for the propagation of the acoustic signal to distant observers. The method described here overcomes these limitations by using a hybrid CAA approach coupled with a flow solver based on the non-linear disturbance equations (NLDE). The overall problem is separated into component problems with the NLDE equations applied over a relatively small noise generating region i.e. approximately the last 10% of the chord or less. This makes the solution more computationally efficient than LES for the full airfoil or rotor and enables the use of the most computationally efficient methods in the required regions. The proposed method is advantageous to helicopter and wind turbine manufacturers as it provides a tool for the prediction of rotor broadband noise at the design stage. This can also be used as a tool to reduce noise through the analysis of appropriate noise reduction devices.

Download or read book Turbulent Wake Interaction LES and Aeroacoustic Predictions written by Christopher C. Yu and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: As increased scrutiny and regulation is placed on the environmental impact of air transportation, tools and methods which enable design of lower footprint next generation aircraft become critical. One of the major environmental obstacles to air travel is noise impact on communities during departure and arrival. Jet noise, dominant during take off, has been studied extensively and as the field has matured, attention has turned to airframe noise - a significant fraction of the total noise signature during approach to landing. As a result, the development of accurate prediction tools for noise generated by complex airframe systems is necessary. Since direct simulation of aerodynamic noise, particularly when realistic geometries and Reynolds numbers are considered, is prohibitively expensive, hybrid methods have become the de-facto standard. In such methods, the near flow field is computed by a given Computational Fluid Dynamics (CFD) simulation while the far-field noise is predicted by a separate acoustic analogy. In this dissertation, we first demonstrate the advantages and challenges of Large Eddy Simulation for the prediction of the near flow field using a simple tandem cylinder geometry. This configuration has been identified by the computational aeroacoustic (CAA) community as a benchmark problem, representative of airframe components such as landing gear struts and hydraulic lines. Since realistic engineering problems typically occur in high Reynolds number flow regimes, forced transition trips are often employed in experiments which are used as benchmarks for simulation results. This was the case in the tandem cylinder problem, and it was found that a naively applied numerical transition trip resulted in significant extraneous noise generation. In the second part of this work, we develop an improved numerical trip which reduces the acoustic impact on the far field. The bulk of this work concentrates on the prediction of noise generated by a model airfoil-cylinder interaction problem. The objective of this portion is twofold: first, common industry practice in the noise prediction of complicated geometries is to exclude the effect of volume noise source terms ("quadrupole sources") due to the prohibitive cost of including them. This is based on the commonly held assumption that their effect is minimal compared to that of surface fluctuation source terms ("dipole sources") in low Mach number conditions. The goal here is to determine if this is still a valid assumption when turbulent flow interaction between two or more bodies is present. Additionally, if volume sources are necessary for accurate prediction, our goal is to examine when they may be important to include (based on Mach number and variation in geometry) and what the volume sources physically represent. The second objective is to compare the results of three separate acoustic prediction methods to explore possible generation of erroneous numerical noise when using common porous-surface Ffowcs Williams & Hawkings (FWH) integration predictions.

Download or read book Broadband Fan Noise Generated by Small Scale Turbulence written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes the development of prediction methods for broadband fan noise from aircraft engines. First, experimental evidence of the most important source mechanisms is reviewed. It is found that there are a number of competing source mechanism involved and that there is no single dominant source to which noise control procedures can be applied. Theoretical models are then developed for: (1) ducted rotors and stator vanes interacting with duct wall boundary layers, (2) ducted rotor self noise, and (3) stator vanes operating in the wakes of rotors. All the turbulence parameters required for these models are based on measured quantities. Finally the theoretical models are used to predict measured fan noise levels with some success. Glegg, Stewart A. L. Langley Research Center FAN BLADES; NOISE (SOUND); TURBULENCE; WAKES; NOISE REDUCTION; NOISE INTENSITY; AERODYNAMIC NOISE; MATHEMATICAL MODELS; WALLS; VANES; ROTOR AERODYNAMICS; PREDICTION ANALYSIS TECHNIQUES; DUCTS; BOUNDARY LAYERS; AIRCRAFT ENGINES...

Download or read book Time conservative Finite volume Method with Large eddy Simulation for Computational Aeroacoustics written by Orhan Aybay and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents a time-conservative finite-volume method based on a modern flow simulation technique developed by the author. Its applicability to technically relevant aeroacoustic applications is demonstrated. The time-conservative finite-volume method has unique features and advantages in comparison to traditional methods. The main objectives of this study are to develop an advanced, high-resolution, low dissipation second-order scheme and to simulate the near acoustic field with similar accuracy as higher-order (e.g., 4th-order, 6th-order, etc.) numerical schemes. Other aims are to use a large-eddy simulation (LES) technique to directly predict the near-field aerodynamic noise and to simulate the turbulent flow field with high-fidelity. A three-dimensional parallel LES solver is developed in order to investigate the near acoustic field. Several cases with wide ranges of flow regimes have been computed to validate and verify the accuracy of the method as well as to demonstrate its effectiveness. The time-conservative finite-volume method is efficient and yields high-resolution results with low dissipation similar to higher-order conventional schemes. The time-conservative finite-volume approach offers an accurate way to compute the most relevant frequencies and acoustic modes for aeroacoustic calculations. Its accuracy was checked by solving demonstrative test cases including the prediction of narrowband and broadband cavity acoustics as well as the screech tones and the broadband shock-associated noise of a planar supersonic jet. The second-order time-conservative finite-volume method can solve practically relevant aeroacoustic problems with high-fidelity which is an exception to the conventional second-order schemes commonly regarded as inadequate for computational aeroacoustic (CAA) applications.

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 Broadband Noise of Fans With Unsteady Coupling Theory to Account for Rotor and Stator Reflection Transmission Effects written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-09-23 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report examines the effects on broadband noise generation of unsteady coupling between a rotor and stator in the fan stage of a turbofan engine. Whereas previous acoustic analyses treated the blade rows as isolated cascades, the present work accounts for reflection and transmission effects at both blade rows by tracking the mode and frequency scattering of pressure and vortical waves. The fan stage is modeled in rectilinear geometry to take advantage of a previously existing unsteady cascade theory for 3D perturbation waves and thereby use a realistic 3D turbulence spectrum. In the analysis, it was found that the set of participating modes divides itself naturally into "independent mode subsets" that couple only among themselves and not to the other such subsets. This principle is the basis for the analysis and considerably reduces computational effort. It also provides a simple, accurate scheme for modal averaging for further efficiency. Computed results for a coupled fan stage are compared with calculations for isolated blade rows. It is found that coupling increases downstream noise by 2 to 4 dB. Upstream noise is lower for isolated cascades and is further reduced by including coupling effects. In comparison with test data, the increase in the upstream/downstream differential indicates that broadband noise from turbulent inflow at the stator dominates downstream noise but is not a significant contributor to upstream noise.Hanson, Donald B.Glenn Research CenterTURBOFAN ENGINES; ENGINE NOISE; ROTOR STATOR INTERACTIONS; NOISE MEASUREMENT; TURBULENT FLOW; SIGNAL ANALYZERS; ACOUSTIC COUPLING; SOUND TRANSMISSION; WAVE REFLECTION; BROADBAND