Open Rotor Aeroacoustic Modelling
Envia, Edmane
2012-01-01
Owing to their inherent fuel efficiency, there is renewed interest in developing open rotor propulsion systems that are both efficient and quiet. The major contributor to the overall noise of an open rotor system is the propulsor noise, which is produced as a result of the interaction of the airstream with the counter-rotating blades. As such, robust aeroacoustic prediction methods are an essential ingredient in any approach to designing low-noise open rotor systems. To that end, an effort has been underway at NASA to assess current open rotor noise prediction tools and develop new capabilities. Under this effort, high-fidelity aerodynamic simulations of a benchmark open rotor blade set were carried out and used to make noise predictions via existing NASA open rotor noise prediction codes. The results have been compared with the aerodynamic and acoustic data that were acquired for this benchmark open rotor blade set. The emphasis of this paper is on providing a summary of recent results from a NASA Glenn effort to validate an in-house open noise prediction code called LINPROP which is based on a high-blade-count asymptotic approximation to the Ffowcs-Williams Hawkings Equation. The results suggest that while predicting the absolute levels may be difficult, the noise trends are reasonably well predicted by this approach.
Open Rotor Aeroacoustic Modeling
Envia, Edmane
2012-01-01
Owing to their inherent fuel efficiency, there is renewed interest in developing open rotor propulsion systems that are both efficient and quiet. The major contributor to the overall noise of an open rotor system is the propulsor noise, which is produced as a result of the interaction of the airstream with the counter-rotating blades. As such, robust aeroacoustic prediction methods are an essential ingredient in any approach to designing low-noise open rotor systems. To that end, an effort has been underway at NASA to assess current open rotor noise prediction tools and develop new capabilities. Under this effort, high-fidelity aerodynamic simulations of a benchmark open rotor blade set were carried out and used to make noise predictions via existing NASA open rotor noise prediction codes. The results have been compared with the aerodynamic and acoustic data that were acquired for this benchmark open rotor blade set. The emphasis of this paper is on providing a summary of recent results from a NASA Glenn effort to validate an in-house open noise prediction code called LINPROP which is based on a high-blade-count asymptotic approximation to the Ffowcs-Williams Hawkings Equation. The results suggest that while predicting the absolute levels may be difficult, the noise trends are reasonably well predicted by this approach.
KSC VAB Aeroacoustic Hazard Assessment
Oliveira, Justin M.; Yedo, Sabrina; Campbell, Michael D.; Atkinson, Joseph P.
2010-01-01
NASA Kennedy Space Center (KSC) carried out an analysis of the effects of aeroacoustics produced by stationary solid rocket motors in processing areas at KSC. In the current paper, attention is directed toward the acoustic effects of a motor burning within the Vehicle Assembly Building (VAB). The analysis was carried out with support from ASRC Aerospace who modeled transmission effects into surrounding facilities. Calculations were done using semi-analytical models for both aeroacoustics and transmission. From the results it was concluded that acoustic hazards in proximity to the source of ignition and plume can be severe; acoustic hazards in the far-field are significantly lower.
Aeroacoustic Prediction and Noise Reduction
Delfs, Jan Werner
2011-01-01
An overview is given about aeroacoustic prediction and noise reduction technology from the field of aircraft noise. The simulation philosophy of the prediction methods is related to real world application, i.e. high Reynolds number flows, typical for aircraft. Noise reduction concepts are studied in two ways i) through a silent by design approach and b) by add-on treatments for existing aircraft components. Challenges are identified for future research.
Numerical techniques for computational aeroacoustics
Djambazov, Georgi Stefanov
1998-01-01
The problem of aerodynamic noise is considered following the Computational Aeroacoustics approach which is based on direct numerical simulation of the sound field. In the region of sound generation, the unsteady airflow is computed separately from the sound using Computational Fluid Dynamics (CFD) codes. Overlapping this region and extending further away is the acoustic domain where the linearised Euler equations governing the sound propagation in moving medium are solved numerically. Aft...
Computational Aeroacoustic Analysis System Development
Hadid, A.; Lin, W.; Ascoli, E.; Barson, S.; Sindir, M.
2001-01-01
Many industrial and commercial products operate in a dynamic flow environment and the aerodynamically generated noise has become a very important factor in the design of these products. In light of the importance in characterizing this dynamic environment, Rocketdyne has initiated a multiyear effort to develop an advanced general-purpose Computational Aeroacoustic Analysis System (CAAS) to address these issues. This system will provide a high fidelity predictive capability for aeroacoustic design and analysis. The numerical platform is able to provide high temporal and spatial accuracy that is required for aeroacoustic calculations through the development of a high order spectral element numerical algorithm. The analysis system is integrated with well-established CAE tools, such as a graphical user interface (GUI) through PATRAN, to provide cost-effective access to all of the necessary tools. These include preprocessing (geometry import, grid generation and boundary condition specification), code set up (problem specification, user parameter definition, etc.), and postprocessing. The purpose of the present paper is to assess the feasibility of such a system and to demonstrate the efficiency and accuracy of the numerical algorithm through numerical examples. Computations of vortex shedding noise were carried out in the context of a two-dimensional low Mach number turbulent flow past a square cylinder. The computational aeroacoustic approach that is used in CAAS relies on coupling a base flow solver to the acoustic solver throughout a computational cycle. The unsteady fluid motion, which is responsible for both the generation and propagation of acoustic waves, is calculated using a high order flow solver. The results of the flow field are then passed to the acoustic solver through an interpolator to map the field values into the acoustic grid. The acoustic field, which is governed by the linearized Euler equations, is then calculated using the flow results computed
Validating LES for Jet Aeroacoustics
Bridges, James
2011-01-01
Engineers charged with making jet aircraft quieter have long dreamed of being able to see exactly how turbulent eddies produce sound and this dream is now coming true with the advent of large eddy simulation (LES). Two obvious challenges remain: validating the LES codes at the resolution required to see the fluid-acoustic coupling, and the interpretation of the massive datasets that result in having dreams come true. This paper primarily addresses the former, the use of advanced experimental techniques such as particle image velocimetry (PIV) and Raman and Rayleigh scattering, to validate the computer codes and procedures used to create LES solutions. It also addresses the latter problem in discussing what are relevant measures critical for aeroacoustics that should be used in validating LES codes. These new diagnostic techniques deliver measurements and flow statistics of increasing sophistication and capability, but what of their accuracy? And what are the measures to be used in validation? This paper argues that the issue of accuracy be addressed by cross-facility and cross-disciplinary examination of modern datasets along with increased reporting of internal quality checks in PIV analysis. Further, it is argued that the appropriate validation metrics for aeroacoustic applications are increasingly complicated statistics that have been shown in aeroacoustic theory to be critical to flow-generated sound.
Computational Aerodynamics and Aeroacoustics for Wind Turbines
DEFF Research Database (Denmark)
Shen, Wen Zhong
To analyse the aerodynamic performance of wind turbine rotors, the main tool in use today is the 1D-Blade Element Momentum (BEM) technique combined with 2D airfoil data. Because of its simplicity, the BEM technique is employed by industry when designing new wind turbine blades. However, in order...... to obtain more detailed information of the flow structures and to determine more accurately loads and power yield of wind turbines or cluster of wind turbines, it is required to resort to more sophisticated techniques, such as Computational Fluid Dynamics (CFD). As computer resources keep on improving year...... and aero-acoustics of wind turbines. The papers are written in the period from 1997 to 2008 and numbered according to the list in page v. The work consists of two parts: an aerodynamic part based on Computational Fluid Dynamics and an aero-acoustic part based on Computational Aero Acoustics for wind...
Theoretical Aeroacoustics: Compiled Mathematical Derivations of Fereidoun 'Feri' Farassat
Miller, Steven A. E.
2016-01-01
Dr. Fereidoun 'Feri' Farassat was a theoretical aero-acoustician at the National Aeronautics and Space Administration (NASA) Langley Research Center. This book contains technical derivations, notes, and classes that Dr. Farassat produced during his professional career. The layout of the book has been carefully crafted so that foundational ideas through advanced theories, which altered the technical discipline of aeroacoustics, build upon one another. The book can be used to understand the theories of acoustics and learn one contemporary aeroacoustic prediction approach made popular by Dr. Farassat. Most importantly, this book gives the general reader insight into how one of NASA's best aeroacoustics theoreticians thought, constructed, and solved problems throughout his career.
Computational Aeroacoustics Using the Generalized Lattice Boltzmann Equation Project
National Aeronautics and Space Administration — The overall objective of the proposed project is to develop a generalized lattice Boltzmann (GLB) approach as a potential computational aeroacoustics (CAA) tool for...
Computational aerodynamics and aeroacoustics for wind turbines
Energy Technology Data Exchange (ETDEWEB)
Shen, W.Z.
2009-10-15
The present thesis consists of 19 selected papers dealing with the development and use of CFD methods for studying the aerodynamics and aero-acoustics of wind turbines. The papers are written in the period from 1997 to 2008 and numbered according to the list in page v. The work consists of two parts: an aerodynamic part based on Computational Fluid Dynamics and an aero-acoustic part based on Computational Aero Acoustics for wind turbines. The main objective of the research was to develop new computational tools and techniques for analysing flows about wind turbines. A few papers deal with applications of Blade Element Momentum (BEM) theory to wind turbines. In most cases the incompressible Navier-Stokes equations in primitive variables (velocity-pressure formulation) are employed as the basic governing equations. However, since fluid mechanical problems essentially are governed by vortex dynamics, it is sometimes advantageous to use the concept of vorticity (defined as the curl of velocity). In vorticity form the Navier-Stokes equations may be formulated in different ways, using a vorticity-stream function formulation, a vorticity-velocity formulation or a vorticity-potential-stream function formulation. In [1] - [3] two different vorticity formulations were developed for 2D and 3D wind turbine flows. In [4] and [5] numerical techniques for avoiding pressure oscillations were developed when solving the velocity-pressure coupling system in the in-house EllipSys2D/3D code. In [6] - [8] different actuator disc techniques combined with CFD are presented. This includes actuator disc, actuator line and actuator surface techniques, which were developed to simulate flows past one or more wind turbines. In [9] and [10] a tip loss correction method that improves the conventional models was developed for use in combination with BEM or actuator/Navier-Stokes computations. A simple and efficient technique for determining the angle of attack for flow past a wind turbine rotor
Aeroacoustic Computations for Turbulent Airfoil Flows
DEFF Research Database (Denmark)
Shen, Wen Zhong; Zhu, Wei Jun; Sørensen, Jens Nørkær
2009-01-01
The How-acoustic splitting technique for aeroacoustic computations is extended to simulate the propagation of acoustic waves generated by three-dimensional turbulent flows. In the flow part, a subgrid-scale turbulence model (the mixed model) is employed for large-eddy simulations. The obtained...... instantaneous How solution is employed as input for the acoustic part. At low Mach numbers, the differences in scales and propagation speed between the flow and the acoustic field are quite large, and hence different meshes and time steps can be used for the two parts. The model is applied to compute flows past...... characteristics for angles of attack up to stall. For the acoustic solutions, predicted noise spectra are validated quantitatively against experimental data. A parametrical study of the noise pattern for flows at angles of attack between 4 and 12 deg shows that the noise level is small for angles of attack below...
On the aeroacoustic properties of a beveled plate
Directory of Open Access Journals (Sweden)
van der Velden W.C.P.
2015-01-01
Full Text Available The flow around a beveled flat plate model with an asymmetric 25 degrees trailing edge with three rounding radii is analyzed using a Navier-Stokes based open source software package OpenFOAM in order to predict the aeroacoustic properties of the models. A Large Eddy Simulation with a dynamic Smagorinsky and implicit model are used as closure model for the flow solver, and are compared regarding their aeroacoustic performance. Velocity coherence and pressure correlation is determined in spanwise direction. The acoustic far field spectrum is obtained by solving Curle’s analogy in frequency domain as a post-processing step.
Aeroacoustic and Performance Simulations of a Test Scale Open Rotor
Claus, Russell W.
2013-01-01
This paper explores a comparison between experimental data and numerical simulations of the historical baseline F31/A31 open rotor geometry. The experimental data were obtained at the NASA Glenn Research Center s Aeroacoustic facility and include performance and noise information for a variety of flow speeds (matching take-off and cruise). The numerical simulations provide both performance and aeroacoustic results using the NUMECA s Fine-Turbo analysis code. A non-linear harmonic method is used to capture the rotor/rotor interaction.
Detection of aeroacoustic sound sources on aircraft and wind turbines
Oerlemans, Stefan
2009-01-01
This thesis deals with the detection of aeroacoustic sound sources on aircraft and wind turbines using phased microphone arrays. First, the reliability of the array technique is assessed using airframe noise measurements in open and closed wind tunnels. It is demonstrated that quantitative acoustic
An acoustic spacetime and the Lorentz transformation in aeroacoustics
Gregory, Alastair Logan; Agarwal, Anurag; Lasenby, Joan
2014-01-01
This paper introduces acoustic space-time and Geometric Algebra as a new theoretical framework for modelling aeroacoustic phenomena. This new framework is applied to sound propagation in uniform flows. The problem is modelled by means of transformations that turn the convected wave equation into an ordinary wave equation, in either time-space coordinates or frequency-wavenumber coordinates. The transformations are shown to combine a Galilean transformation with a Lorentz transformation and geometrical and physical interpretations are provided. The Lorentzian frame is the natural frame for describing acoustic waves in uniform flow. A key feature of this frame is that it combines space and time in a way that is best described using a hyperbolic geometry. The power of this new theoretical framework is illustrated by providing simple derivations for two classical aeroacoustic problems: the free-field Greens function for the convected wave equation and the Doppler shift for a stationary observer and a source in un...
Towards aeroacoustic sound generation by flow through porous media.
Hasert, Manuel; Bernsdorf, Joerg; Roller, Sabine
2011-06-28
In this work, we present single-step aeroacoustic calculations using the Lattice Boltzmann method (LBM). Our application case consists of the prediction of an acoustic field radiating from the outlet of a porous media silencer. It has been proved that the LBM is able to simulate acoustic wave generation and propagation. Our particular aim is to validate the LBM for aeroacoustics in porous media. As a validation case, we consider a spinning vortex pair emitting sound waves as the vortices rotate around a common centre. Non-reflective boundary conditions based on characteristics have been adopted from Navier-Stokes methods and are validated using the time evolution of a Gaussian pulse. We show preliminary results of the flow through the porous medium.
Open Rotor Computational Aeroacoustic Analysis with an Immersed Boundary Method
Brehm, Christoph; Barad, Michael F.; Kiris, Cetin C.
2016-01-01
Reliable noise prediction capabilities are essential to enable novel fuel efficient open rotor designs that can meet the community and cabin noise standards. Toward this end, immersed boundary methods have reached a level of maturity where more and more complex flow problems can be tackled with this approach. This paper demonstrates that our higher-order immersed boundary method provides the ability for aeroacoustic analysis of wake-dominated flow fields generated by a contra-rotating open rotor. This is the first of a kind aeroacoustic simulation of an open rotor propulsion system employing an immersed boundary method. In addition to discussing the methodologies of how to apply the immersed boundary method to this moving boundary problem, we will provide a detailed validation of the aeroacoustic analysis approach employing the Launch Ascent and Vehicle Aerodynamics (LAVA) solver. Two free-stream Mach numbers with M=0.2 and M=0.78 are considered in this analysis that are based on the nominally take-off and cruise flow conditions. The simulation data is compared to available experimental data and other computational results employing more conventional CFD methods. Spectral analysis is used to determine the dominant wave propagation pattern in the acoustic near-field.
Open Rotor Aeroacoustic Installation Effects for Conventional and Unconventional Airframes
Czech, Michael J.; Thomas, Russell H.
2013-01-01
As extensive experimental campaign was performed to study the aeroacoustic installation effects of an open rotor with respect to both a conventional tube and wing type airframe and an unconventional hybrid wing body airframe. The open rotor rig had two counter rotating rows of blades each with eight blades of a design originally flight tested in the 1980s. The aeroacoustic installation effects measured in an aeroacoustic wind tunnel included those from flow effects due to inflow distortion or wake interaction and acoustic propagation effects such as shielding and reflection. The objective of the test campaign was to quantify the installation effects for a wide range of parameters and configurations derived from the two airframe types. For the conventional airframe, the open rotor was positioned in increments in front of and then over the main wing and then in positions representative of tail mounted aircraft with a conventional tail, a T-tail and a U-tail. The interaction of the wake of the open rotor as well as acoustic scattering results in an increase of about 10 dB when the rotor is positioned in front of the main wing. When positioned over the main wing a substantial amount of noise reduction is obtained and this is also observed for tail-mounted installations with a large U-tail. For the hybrid wing body airframe, the open rotor was positioned over the airframe along the centerline as well as off-center representing a twin engine location. A primary result was the documentation of the noise reduction from shielding as a function of the location of the open rotor upstream of the trailing edge of the hybrid wing body. The effects from vertical surfaces and elevon deflection were also measured. Acoustic lining was specially designed and inserted flush with the elevon and airframe surface, the result was an additional reduction in open rotor noise propagating to the far field microphones. Even with the older blade design used, the experiment provided
Three-dimensional CFD simulation and aeroacoustics analysis of wind turbines
Khalili, Fardin
Wind turbines release aerodynamic noise that is one of the most barriers in wind energy development and public acceptance. Aeroacoustics is the noise generated by the interaction of blades, specifically the tip and trailing edge, with inflow turbulence structures and subsequent boundary layer separation and vortex shedding in the wake region. The objective of this study is to analyze the effects of different aerodynamic conditions on the performance and the aeroacoustic issue of wind turbines. Aerodynamic and aeroacoustic operation of a wind turbine is analyzed using a three-dimensional CFD and aeroacoustics model and using a commercial CFD Software, STAR-CCM+. Blades are modeled based on NREL S825 airfoil shape due to its high maximum lift and low profile drag. Wind turbine aerodynamic performance as well as broadband aeroacoustic noise with a focus on the trailing end, tip, inflow turbulence and boundary layer separation is investigated over a range of operating conditions.
NASA's Aeroacoustic Tools and Methods for Analysis of Aircraft Noise
Rizzi, Stephen A.; Lopes, Leonard V.; Burley, Casey L.
2015-01-01
Aircraft community noise is a significant concern due to continued growth in air traffic, increasingly stringent environmental goals, and operational limitations imposed by airport authorities. The ability to quantify aircraft noise at the source and ultimately at observers is required to develop low noise aircraft designs and flight procedures. Predicting noise at the source, accounting for scattering and propagation through the atmosphere to the observer, and assessing the perception and impact on a community requires physics-based aeroacoustics tools. Along with the analyses for aero-performance, weights and fuel burn, these tools can provide the acoustic component for aircraft MDAO (Multidisciplinary Design Analysis and Optimization). Over the last decade significant progress has been made in advancing the aeroacoustic tools such that acoustic analyses can now be performed during the design process. One major and enabling advance has been the development of the system noise framework known as Aircraft NOise Prediction Program2 (ANOPP2). ANOPP2 is NASA's aeroacoustic toolset and is designed to facilitate the combination of acoustic approaches of varying fidelity for the analysis of noise from conventional and unconventional aircraft. The toolset includes a framework that integrates noise prediction and propagation methods into a unified system for use within general aircraft analysis software. This includes acoustic analyses, signal processing and interfaces that allow for the assessment of perception of noise on a community. ANOPP2's capability to incorporate medium fidelity shielding predictions and wind tunnel experiments into a design environment is presented. An assessment of noise from a conventional and Hybrid Wing Body (HWB) aircraft using medium fidelity scattering methods combined with noise measurements from a model-scale HWB recently placed in NASA's 14x22 wind tunnel are presented. The results are in the form of community noise metrics and
Benchmark Problems Used to Assess Computational Aeroacoustics Codes
Dahl, Milo D.; Envia, Edmane
2005-01-01
The field of computational aeroacoustics (CAA) encompasses numerical techniques for calculating all aspects of sound generation and propagation in air directly from fundamental governing equations. Aeroacoustic problems typically involve flow-generated noise, with and without the presence of a solid surface, and the propagation of the sound to a receiver far away from the noise source. It is a challenge to obtain accurate numerical solutions to these problems. The NASA Glenn Research Center has been at the forefront in developing and promoting the development of CAA techniques and methodologies for computing the noise generated by aircraft propulsion systems. To assess the technological advancement of CAA, Glenn, in cooperation with the Ohio Aerospace Institute and the AeroAcoustics Research Consortium, organized and hosted the Fourth CAA Workshop on Benchmark Problems. Participants from industry and academia from both the United States and abroad joined to present and discuss solutions to benchmark problems. These demonstrated technical progress ranging from the basic challenges to accurate CAA calculations to the solution of CAA problems of increasing complexity and difficulty. The results are documented in the proceedings of the workshop. Problems were solved in five categories. In three of the five categories, exact solutions were available for comparison with CAA results. A fourth category of problems representing sound generation from either a single airfoil or a blade row interacting with a gust (i.e., problems relevant to fan noise) had approximate analytical or completely numerical solutions. The fifth category of problems involved sound generation in a viscous flow. In this case, the CAA results were compared with experimental data.
Aero-acoustic noise of wind turbines. Noise prediction models
Energy Technology Data Exchange (ETDEWEB)
Maribo Pedersen, B. [ed.
1997-12-31
Semi-empirical and CAA (Computational AeroAcoustics) noise prediction techniques are the subject of this expert meeting. The meeting presents and discusses models and methods. The meeting may provide answers to the following questions: What Noise sources are the most important? How are the sources best modeled? What needs to be done to do better predictions? Does it boil down to correct prediction of the unsteady aerodynamics around the rotor? Or is the difficult part to convert the aerodynamics into acoustics? (LN)
Exhaust System Experiments at NASA's AeroAcoustic Propulsion Lab
Bridges, James
2011-01-01
This presentation gives an overview of the planned testing in the AeroAcoustic Propulsion Lab (AAPL) in the coming 15 months. It was stressed in the presentation that these are plans that are subject to change due to changes in funding and/or programmatic direction. The first chart shows a simplified schedule of test entries with funding sponsor and dates for each. In subsequent charts are pages devoted to the Objectives and Issues with each test entry, along with a graphic intended to represent the test activity. The chart for each test entry also indicates sponsorship of the activity, and a contact person.!
Aeroacoustic response of coaxial wall-mounted Helmholtz resonators in a low-speed wind tunnel.
Slaton, William V; Nishikawa, Asami
2015-01-01
The aeroacoustic response of coaxial wall-mounted Helmholtz resonators with different neck geometries in a low-speed wind tunnel has been investigated. Experimental test results of this system reveal a strong aeroacoustic response over a Strouhal number range of 0.25 to 0.1 for both increasing and decreasing the flow rate in the wind tunnel. Aeroacoustic response in the low-amplitude range O(10(-3)) < Vac/Vflow < O(10(-1)) has been successfully modeled by describing-function analysis. This analysis, coupled with a turbulent flow velocity distribution model, gives reasonable values for the location in the flow of the undulating stream velocity that drives vortex shedding at the resonator mouth. Having an estimate for the stream velocity that drives the flow-excited resonance is crucial when employing the describing-function analysis to predict aeroacoustic response of resonators. PMID:25618056
Powering a Commercial Datalogger by Energy Harvesting from Generated Aeroacoustic Noise
International Nuclear Information System (INIS)
This paper reports the experimental demonstration of a wireless sensor node only powered by an aeroacoustic energy harvesting device, meant to be installed on an aircraft outside skin. New results related to the physical characterization of the energy conversion process are presented. Optimized interface electronics has been designed, which allows demonstrating aeroacoustic power generation by supplying a commercial wireless datalogger in conditions representative of an actual flight
Vanelderen, Bart; De Roeck, Wim; Vandeun, Dieter; Mattheys, Yannick; Sas, Paul; Desmet, Wim
2010-01-01
For the aeroacoustic design of mufflers, commonly installed in HVAC ducts, automotive exhaust systems or other confined flow applications, both the convective noise propagation and the aerodynamic noise generation mechanisms should be taken into account. An experimental procedure, based on an active two-port formulation, allows a straightforward characterization of both phenomena and gives further insight in the aeroacoustic performance of acoustic filters. This paper describes the developmen...
Aeroacoustics research in Europe: The CEAS-ASC report on 2014 highlights
Detandt, Yves
2015-11-01
The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. Each year the committee highlights some of the research and development projects in Europe. This paper is the 2014 issue of this collection of Aeroacoustic Highlights, compiled from informations submitted to the CEAS-ASC. The contributions are classified in different topics; the first categories being related to specific aeroacoustic challenges (airframe noise, fan and jet noise, helicopter noise, aircraft interior noise) and two last sections are respectively devoted to recent improvements and emerging techniques and to general advances in aeroacoustics. For each section, the present paper focus on accomplished projects, providing the state of the art in each research category in 2014. A number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are summarised in this paper, as well as highlights funded by national programmes or by industry.
Aeroacoustic environment of an advanced STOVL aircraft in hover
Wlezien, Richard W.; Ferraro, Peter J.
1990-01-01
The near-field aeroacoustic environment of a 6.02 pct scale advanced short takeoff and vertical landing aircraft is investigated in proximity to a simulated ground plane. The screech and impingement-tone characteristics of twin supersonic round and rectangular plumes are shown to be highly dependent on nozzle geometry and height above the ground plane. Shadowgraph and laser-sheet flow visualization are used to clarify the flowfield mechanisms responsible for time-dependent loads due to screech, impingement tones, and unsteady impingement of the upwash on the fuselage undersurface. Detailed dynamic pressure measurements from an array of transducers on the fuselage confirms that fountain impingement is responsible for the greatest unsteady loading.
Application of a new finite difference algorithm for computational aeroacoustics
Goodrich, John W.
1995-01-01
Acoustic problems have become extremely important in recent years because of research efforts such as the High Speed Civil Transport program. Computational aeroacoustics (CAA) requires a faithful representation of wave propagation over long distances, and needs algorithms that are accurate and boundary conditions that are unobtrusive. This paper applies a new finite difference method and boundary algorithm to the Linearized Euler Equations (LEE). The results demonstrate the ability of a new fourth order propagation algorithm to accurately simulate the genuinely multidimensional wave dynamics of acoustic propagation in two space dimensions with the LEE. The results also show the ability of a new outflow boundary condition and fourth order algorithm to pass the evolving solution from the computational domain with no perceptible degradation of the solution remaining within the domain.
Multi-model Simulation for Optimal Control of Aeroacoustics.
Energy Technology Data Exchange (ETDEWEB)
Collis, Samuel Scott; Chen, Guoquan
2005-05-01
Flow-generated noise, especially rotorcraft noise has been a serious concern for bothcommercial and military applications. A particular important noise source for rotor-craft is Blade-Vortex-Interaction (BVI)noise, a high amplitude, impulsive sound thatoften dominates other rotorcraft noise sources. Usually BVI noise is caused by theunsteady flow changes around various rotor blades due to interactions with vorticespreviously shed by the blades. A promising approach for reducing the BVI noise isto use on-blade controls, such as suction/blowing, micro-flaps/jets, and smart struc-tures. Because the design and implementation of such experiments to evaluate suchsystems are very expensive, efficient computational tools coupled with optimal con-trol systems are required to explore the relevant physics and evaluate the feasibilityof using various micro-fluidic devices before committing to hardware.In this thesis the research is to formulate and implement efficient computationaltools for the development and study of optimal control and design strategies for com-plex flow and acoustic systems with emphasis on rotorcraft applications, especiallyBVI noise control problem. The main purpose of aeroacoustic computations is todetermine the sound intensity and directivity far away from the noise source. How-ever, the computational cost of using a high-fidelity flow-physics model across thefull domain is usually prohibitive and itmight also be less accurate because of thenumerical diffusion and other problems. Taking advantage of the multi-physics andmulti-scale structure of this aeroacoustic problem, we develop a multi-model, multi-domain (near-field/far-field) method based on a discontinuous Galerkin discretiza-tion. In this approach the coupling of multi-domains and multi-models is achievedby weakly enforcing continuity of normal fluxes across a coupling surface. For ourinterested aeroacoustics control problem, the adjoint equations that determine thesensitivity of the cost
Fluid Dynamics Prize Otto Laporte Lecture:Turbulence and Aeroacoustics
Comte-Bellot, Genevieve
2014-11-01
Some significant advances obtained over the years for two closely related fields, Turbulence and Aeroacoustics, are presented. Particular focus is placed on experimental results and on physical mechanisms. For example, for a 2D channel flow, skewness factors of velocity fluctuations are discussed. The study of isotropic turbulence generated by grids in the «Velvet wind tunnel» of Stanley Corrsin, constitutes a masterpiece. Of particular note are the Eulerian memory times, analysed for all wavenumbers. Concerning hot-wire anemometry, the potential of the new constant voltage technique is presented. Some results obtained with Particule Image Velocimetry are also reported. Two flow control examples are illustrated: lift generation for a circular cylinder, and noise reduction for a high speed jet. Finally, the propagation of acoustic waves through turbulence is considered. Experimental data are here completed by numerical simulations showing the possible occurrence of caustics.
Aero-Acoustic Moldeling using Large Eddy Simulation
DEFF Research Database (Denmark)
Shen, Wen Zhong; Sørensen, Jens Nørkær
2008-01-01
The flow-acoustic splitting technique for aero-acoustic computations is extended to simulate the propagation of acoustic waves generated by three-dimensional turbulent flows. In the flow part, a sub-grid-scale turbulence model (the mixed model) is employed for Large-Eddy Simulations. The obtained...... instantaneous flow solution is employed as input for the acoustic part. At low Mach numbers the differences in scales and propagation speed between the flow and the acoustic field are quite large, hence different meshes and time-steps can be utilized for the two parts. The model is applied to compute flows past...... characteristics for angles of attack up to stall. For the acoustic solutions, predicted noise spectra are validated quantitatively against the experimental data of Brook et al. A parametrical study of the noise pattern for flows at angles of attack between 4 deg and 12 deg shows that the noise level is small...
Benchmark Solutions for Computational Aeroacoustics (CAA) Code Validation
Scott, James R.
2004-01-01
NASA has conducted a series of Computational Aeroacoustics (CAA) Workshops on Benchmark Problems to develop a set of realistic CAA problems that can be used for code validation. In the Third (1999) and Fourth (2003) Workshops, the single airfoil gust response problem, with real geometry effects, was included as one of the benchmark problems. Respondents were asked to calculate the airfoil RMS pressure and far-field acoustic intensity for different airfoil geometries and a wide range of gust frequencies. This paper presents the validated that have been obtained to the benchmark problem, and in addition, compares them with classical flat plate results. It is seen that airfoil geometry has a strong effect on the airfoil unsteady pressure, and a significant effect on the far-field acoustic intensity. Those parts of the benchmark problem that have not yet been adequately solved are identified and presented as a challenge to the CAA research community.
Aero-acoustics of Drag Generating Swirling Exhaust Flows
Shah, P. N.; Mobed, D.; Spakovszky, Z. S.; Brooks, T. F.; Humphreys, W. M. Jr.
2007-01-01
Aircraft on approach in high-drag and high-lift configuration create unsteady flow structures which inherently generate noise. For devices such as flaps, spoilers and the undercarriage there is a strong correlation between overall noise and drag such that, in the quest for quieter aircraft, one challenge is to generate drag at low noise levels. This paper presents a rigorous aero-acoustic assessment of a novel drag concept. The idea is that a swirling exhaust flow can yield a steady, and thus relatively quiet, streamwise vortex which is supported by a radial pressure gradient responsible for pressure drag. Flows with swirl are naturally limited by instabilities such as vortex breakdown. The paper presents a first aero-acoustic assessment of ram pressure driven swirling exhaust flows and their associated instabilities. The technical approach combines an in-depth aerodynamic analysis, plausibility arguments to qualitatively describe the nature of acoustic sources, and detailed, quantitative acoustic measurements using a medium aperture directional microphone array in combination with a previously established Deconvolution Approach for Mapping of Acoustic Sources (DAMAS). A model scale engine nacelle with stationary swirl vanes was designed and tested in the NASA Langley Quiet Flow Facility at a full-scale approach Mach number of 0.17. The analysis shows that the acoustic signature is comprised of quadrupole-type turbulent mixing noise of the swirling core flow and scattering noise from vane boundary layers and turbulent eddies of the burst vortex structure near sharp edges. The exposed edges are the nacelle and pylon trailing edge and the centerbody supporting the vanes. For the highest stable swirl angle setting a nacelle area based drag coefficient of 0.8 was achieved with a full-scale Overall Sound Pressure Level (OASPL) of about 40dBA at the ICAO approach certification point.
Aeroacoustic Evaluation of Flap and Landing Gear Noise Reduction Concepts
Khorrami, Mehdi R.; Humphreys, William M., Jr.; Lockard, David P.; Ravetta, Patricio A.
2014-01-01
Aeroacoustic measurements for a semi-span, 18% scale, high-fidelity Gulfstream aircraft model are presented. The model was used as a test bed to conduct detailed studies of flap and main landing gear noise sources and to determine the effectiveness of numerous noise mitigation concepts. Using a traversing microphone array in the flyover direction, an extensive set of acoustic data was obtained in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the information was acquired with the model in a landing configuration with the flap deflected 39 deg and the main landing gear alternately installed and removed. Data were obtained at Mach numbers of 0.16, 0.20, and 0.24 over directivity angles between 56 deg and 116 deg, with 90 deg representing the overhead direction. Measured acoustic spectra showed that several of the tested flap noise reduction concepts decrease the sound pressure levels by 2 - 4 dB over the entire frequency range at all directivity angles. Slightly lower levels of noise reduction from the main landing gear were obtained through the simultaneous application of various gear devices. Measured aerodynamic forces indicated that the tested gear/flap noise abatement technologies have a negligible impact on the aerodynamic performance of the aircraft model.
Aerodynamic and Aeroacoustic Wind Tunnel Testing of the Orion Spacecraft
Ross, James C.
2011-01-01
The Orion aerodynamic testing team has completed more than 40 tests as part of developing the aerodynamic and loads databases for the vehicle. These databases are key to achieving good mechanical design for the vehicle and to ensure controllable flight during all potential atmospheric phases of a mission, including launch aborts. A wide variety of wind tunnels have been used by the team to document not only the aerodynamics but the aeroacoustic environment that the Orion might experience both during nominal ascents and launch aborts. During potential abort scenarios the effects of the various rocket motor plumes on the vehicle must be accurately understood. The Abort Motor (AM) is a high-thrust, short duration motor that rapidly separates Orion from its launch vehicle. The Attitude Control Motor (ACM), located in the nose of the Orion Launch Abort Vehicle, is used for control during a potential abort. The 8 plumes from the ACM interact in a nonlinear manner with the four AM plumes which required a carefully controlled test to define the interactions and their effect on the control authority provided by the ACM. Techniques for measuring dynamic stability and for simulating rocket plume aerodynamics and acoustics were improved or developed in the course of building the aerodynamic and loads databases for Orion.
NASA Hybrid Wing Aircraft Aeroacoustic Test Documentation Report
Heath, Stephanie L.; Brooks, Thomas F.; Hutcheson, Florence V.; Doty, Michael J.; Bahr, Christopher J.; Hoad, Danny; Becker, Lawrence; Humphreys, William M.; Burley, Casey L.; Stead, Dan; Pope, Dennis S.; Spalt, Taylor B.; Kuchta, Dennis H.; Plassman, Gerald E.; Moen, Jaye A.
2016-01-01
This report summarizes results of the Hybrid Wing Body (HWB) N2A-EXTE model aeroacoustic test. The N2A-EXTE model was tested in the NASA Langley 14- by 22-Foot Subsonic Tunnel (14x22 Tunnel) from September 12, 2012 until January 28, 2013 and was designated as test T598. This document contains the following main sections: Section 1 - Introduction, Section 2 - Main Personnel, Section 3 - Test Equipment, Section 4 - Data Acquisition Systems, Section 5 - Instrumentation and Calibration, Section 6 - Test Matrix, Section 7 - Data Processing, and Section 8 - Summary. Due to the amount of material to be documented, this HWB test documentation report does not cover analysis of acquired data, which is to be presented separately by the principal investigators. Also, no attempt was made to include preliminary risk reduction tests (such as Broadband Engine Noise Simulator and Compact Jet Engine Simulator characterization tests, shielding measurement technique studies, and speaker calibration method studies), which were performed in support of this HWB test. Separate reports containing these preliminary tests are referenced where applicable.
Unstructured CFD and Noise Prediction Methods for Propulsion Airframe Aeroacoustics
Pao, S. Paul; Abdol-Hamid, Khaled S.; Campbell, Richard L.; Hunter, Craig A.; Massey, Steven J.; Elmiligui, Alaa A.
2006-01-01
Using unstructured mesh CFD methods for Propulsion Airframe Aeroacoustics (PAA) analysis has the distinct advantage of precise and fast computational mesh generation for complex propulsion and airframe integration arrangements that include engine inlet, exhaust nozzles, pylon, wing, flaps, and flap deployment mechanical parts. However, accurate solution values of shear layer velocity, temperature and turbulence are extremely important for evaluating the usually small noise differentials of potential applications to commercial transport aircraft propulsion integration. This paper describes a set of calibration computations for an isolated separate flow bypass ratio five engine nozzle model and the same nozzle system with a pylon. These configurations have measured data along with prior CFD solutions and noise predictions using a proven structured mesh method, which can be used for comparison to the unstructured mesh solutions obtained in this investigation. This numerical investigation utilized the TetrUSS system that includes a Navier-Stokes solver, the associated unstructured mesh generation tools, post-processing utilities, plus some recently added enhancements to the system. New features necessary for this study include the addition of two equation turbulence models to the USM3D code, an h-refinement utility to enhance mesh density in the shear mixing region, and a flow adaptive mesh redistribution method. In addition, a computational procedure was developed to optimize both solution accuracy and mesh economy. Noise predictions were completed using an unstructured mesh version of the JeT3D code.
Application of aeroacoustic models to design of wind turbine rotors
Energy Technology Data Exchange (ETDEWEB)
Fuglsang, P.; Madsen, H.A. [Risoe National Lab., Wind Energy and Atmospheric Physics Dept., Roskilde (Denmark)
1997-12-31
A design method is presented for wind turbine rotors. The design process is split into overall design of the rotor and detailed design of the blade tip. A numerical optimization tool is used together with a semi-empirical noise prediction code for overall rotor design. The noise prediction code is validated with measurements and good agreement is obtained both on the total noise emission and on the sensitivity to wind speed, tip pitch angle and tip speed. A design study for minimum noise emission for a 300 kW rotor shows that the total sound power level can be reduced by 3 dB(A) without loss in energy production and the energy production can be increased by 2% without increase in the total noise. Detailed CFD calculations are subsequently done to resolve the blade tip flow. The characteristics of the general flow and the tip vortex are found, and the relevant parameters for the aeroacoustic models are derived for a sharp rectangular tip. (au) 16 refs.
Aeroacoustics research in Europe: The CEAS-ASC report on 2003 highlights
Schröder, W.
2004-11-01
This is a report on some highlights of aeroacoustics research in Europe in 2003, compiled from information provided to the Aeroacoustics Specialists Committee of the Confederation of European Aerospace Societies (CEAS). The CEAS currently comprises the national Aerospace Societies of France (Association Aéronautique et Astronautique de France), Germany (Deutsche Gesellschaft für Luft- und Raumfahrt), Italy (Associazione Italiana di Aeronautica e Astronautica), The Netherlands (Nederlandse Vereniging voor Luchtvaarttechniek), Spain (Asociación de Ingenieros Aeronáuticos de España), Sweden (Flygtekniska Föreningen), Switzerland (Schweizerische Vereinigung für Flugwissenschaften) and the UK (The Royal Aeronautical Society).
Menthe, R. W.; Mccolgan, C. J.; Ladden, R. M.
1991-01-01
The Unified AeroAcoustic Program (UAAP) code calculates the airloads on a single rotation prop-fan, or propeller, and couples these airloads with an acoustic radiation theory, to provide estimates of near-field or far-field noise levels. The steady airloads can also be used to calculate the nonuniform velocity components in the propeller wake. The airloads are calculated using a three dimensional compressible panel method which considers the effects of thin, cambered, multiple blades which may be highly swept. These airloads may be either steady or unsteady. The acoustic model uses the blade thickness distribution and the steady or unsteady aerodynamic loads to calculate the acoustic radiation. The users manual for the UAAP code is divided into five sections: general code description; input description; output description; system description; and error codes. The user must have access to IMSL10 libraries (MATH and SFUN) for numerous calls made for Bessel functions and matrix inversion. For plotted output users must modify the dummy calls to plotting routines included in the code to system-specific calls appropriate to the user's installation.
Aeroacoustic characterization of scaled canonical nose landing gear configurations
Zawodny, Nikolas S.
Aircraft noise is a critical issue in the commercial airline industry. Airframe noise is a subcomponent of aircraft noise and is generally dominant over jet engine noise during approach conditions, which can lead to high community impact. Landing gears have been identified as major components of airframe noise during landing configurations for commercial aircraft. They are perhaps the least understood contributors to airframe noise due to complex flow patterns associated with intricate gear component geometries. Nose landing gear in particular have received much attention in recent years, exhibiting acoustic signatures on the order of the main landing gear assembly of an aircraft, while simultaneously being more amenable to scaled wind tunnel testing. In order to characterize the acoustic signature of a complex geometry such as a nose landing gear, it is important to isolate, study, and understand the acoustic contributions of individual component geometries. The purpose of this dissertation is to develop a correlation between the complex flow field nature and far-field acoustic signature of a nose landing gear sub-system. The model under investigation is a 1/2-scale shock-strut cylinder coupled with an adjustable torque link apparatus. This geometry was chosen due to its fundamental importance and implementation across a wide span of commercial aircraft. The fluid dynamic (surface pressure and stereoscopic particle image velocimety) and aeroacoustic (far-field microphone and phased array) experiments were performed in the University of Florida Aeroacoustic Flow Facility. The experimental data compare favorably with the results of a numerical simulation using PowerFLOW, a lattice-Boltzmann solver developed by the Exa Corporation. The far-field acoustic results of this dissertation have shown non-uniform scaling behavior as a function of frequency for the different model configurations tested. For frequencies that appropriately satisfied the condition of acoustic
Drage, P.; Wiesler, B.; Beek, P.J.G. van; Lier, L.J. van; Parchen, R.R.; Tibaut, P.
2007-01-01
Noise radiation from aircraft during the takeoff and landing has become a major issue for inhabitants living in the vicinity of airports and thus for regulation authorities and aircraft developers. However the numerical simulation of aeroacoustic noise, especially for complex geometries like a landi
Fourth Computational Aeroacoustics (CAA) Workshop on Benchmark Problems
Dahl, Milo D. (Editor)
2004-01-01
This publication contains the proceedings of the Fourth Computational Aeroacoustics (CAA) Workshop on Benchmark Problems. In this workshop, as in previous workshops, the problems were devised to gauge the technological advancement of computational techniques to calculate all aspects of sound generation and propagation in air directly from the fundamental governing equations. A variety of benchmark problems have been previously solved ranging from simple geometries with idealized acoustic conditions to test the accuracy and effectiveness of computational algorithms and numerical boundary conditions; to sound radiation from a duct; to gust interaction with a cascade of airfoils; to the sound generated by a separating, turbulent viscous flow. By solving these and similar problems, workshop participants have shown the technical progress from the basic challenges to accurate CAA calculations to the solution of CAA problems of increasing complexity and difficulty. The fourth CAA workshop emphasized the application of CAA methods to the solution of realistic problems. The workshop was held at the Ohio Aerospace Institute in Cleveland, Ohio, on October 20 to 22, 2003. At that time, workshop participants presented their solutions to problems in one or more of five categories. Their solutions are presented in this proceedings along with the comparisons of their solutions to the benchmark solutions or experimental data. The five categories for the benchmark problems were as follows: Category 1:Basic Methods. The numerical computation of sound is affected by, among other issues, the choice of grid used and by the boundary conditions. Category 2:Complex Geometry. The ability to compute the sound in the presence of complex geometric surfaces is important in practical applications of CAA. Category 3:Sound Generation by Interacting With a Gust. The practical application of CAA for computing noise generated by turbomachinery involves the modeling of the noise source mechanism as a
Theoretical and Numerical Modeling of Acoustic Metamaterials for Aeroacoustic Applications
Directory of Open Access Journals (Sweden)
Umberto Iemma
2016-05-01
Full Text Available The advent, during the first decade of the 21st century, of the concept of acoustic metamaterial has disclosed an incredible potential of development for breakthrough technologies. Unfortunately, the extension of the same concepts to aeroacoustics has turned out to be not a trivial task, because of the different structure of the governing equations, characterized by the presence of the background aerodynamic convection. Some of the approaches recently introduced to circumvent the problem are biased by a fundamental assumption that makes the actual realization of devices extremely unlikely: the metamaterial should guarantee an adapted background aerodynamic convection in order to modify suitably the acoustic field and obtain the desired effect, thus implying the porosity of the cloaking device. In the present paper, we propose an interpretation of the metamaterial design that removes this unlikely assumption, focusing on the identification of an aerodynamically-impermeable metamaterial capable of reproducing the surface impedance profile required to achieve the desired scattering abatement. The attention is focused on a moving obstacle impinged by an acoustic perturbation induced by a co-moving source. The problem is written in a frame of reference rigidly connected to the moving object to couple the convective wave equation in the hosting medium with the inertially-anisotropic wave operator within the cloak. The problem is recast in an integral form and numerically solved through a boundary-field element method. The matching of the local wave vector is used to derive a convective design of the metamaterial applicable to the specific problem analyzed. Preliminary numerical results obtained under the simplifying assumption of a uniform aerodynamic flow reveal a considerable enhancement of the masking capability of the convected design. The numerical method developed shows a remarkable computational efficiency, completing a simulation of the entire
Morino, Luigi
2015-01-01
A novel formulation for the analysis of viscous incompressible and compressible aerodynamics/aeroacoustics fields is presented. The paper is primarily of a theoretical nature, and presents the transition path from aerodynamics towards aeroacoustics. The basis of the paper is a variant of the so-called natural velocity decomposition, as v = ▿φ + w, where w is obtained from its own governing equation and not from the vorticity. With the novel decomposition, the governing equation for w and the generalized Bernoulli theorem for viscous fields assume a very elegant form. Another improvement pertains to the so-called material covariant components of w: For inviscid incompressible flows, they remain constant in time; minor modifications occur when we deal with viscous flows. In addition, interesting simplifications of the formulation are presented for almost-potential flows, namely for flows that are irrotational everywhere except for thin vortex layers, such as boundary layers and wakes. It is shown that, if th...
Predicting vibratory stresses from aero-acoustic loads
Shaw, Matthew D.
Sonic fatigue has been a concern of jet aircraft engineers for many years. As engines become more powerful, structures become more lightly damped and complex, and materials become lighter, stiffer, and more complicated, the need to understand and predict structural response to aeroacoustic loads becomes more important. Despite decades of research, vibration in panels caused by random pressure loads, such as those found in a supersonic jet, is still difficult to predict. The work in this research improves on current prediction methods in several ways, in particular for the structural response due to wall pressures induced by supersonic turbulent flows. First, solutions are calculated using time-domain input pressure loads that include shock cells and their interaction with turbulent flow. The solutions include both mean (static) and oscillatory components. Second, the time series of stresses are required for many fatigue assessment counting algorithms. To do this, a method is developed to compute time-dependent solutions in the frequency domain. The method is first applied to a single-degree-of-freedom system. The equations of motion are derived and solved in both the frequency domain and the time domain. The pressure input is a random (broadband) signal representative of jet flow. The method is then applied to a simply-supported beam vibrating in flexure using a line of pressure inputs computed with computational fluid dynamics (CFD). A modal summation approach is used to compute structural response. The coupling between the pressure field and the structure, through the joint acceptance, is reviewed and discussed for its application to more complicated structures. Results from the new method and from a direct time domain method are compared for method verification. Because the match is good and the new frequency domain method is faster computationally, it is chosen for use in a more complicated structure. The vibration of a two-dimensional panel loaded by jet
Advanced Model for Extreme Lift and Improved Aeroacoustics (AMELIA)
Lichtwardt, Jonathan; Paciano, Eric; Jameson, Tina; Fong, Robert; Marshall, David
2012-01-01
tunnel model design would be completed, manufactured, and calibrated. During the fifth year the large scale wind tunnel test was conducted. This technical memo will describe all phases of the Advanced Model for Extreme Lift and Improved Aeroacoustics (AMELIA) project and provide a brief summary of the background and modeling efforts involved in the NRA. The conceptual designs considered for this project and the decision process for the selected configuration adapted for a wind tunnel model will be briefly discussed. The internal configuration of AMELIA, and the internal measurements chosen in order to satisfy the requirements of obtaining a database of experimental data to be used for future computational model validations. The external experimental techniques that were employed during the test, along with the large-scale wind tunnel test facility are covered in great detail. Experimental measurements in the database include forces and moments, and surface pressure distributions, local skin friction measurements, boundary and shear layer velocity profiles, far-field acoustic data and noise signatures from turbofan propulsion simulators. Results and discussion of the circulation control performance, over-the-wing mounted engines, and the combined performance are also discussed in great detail.
An Experimental Investigation of the Aeroacoustics of a Two-Dimensional Bifurcated Supersonic Inlet
LI, S.-M.; HANUSKA, C. A.; NG, W. F.
2001-11-01
An experiment was conducted on a two-dimensional bifurcated, supersonic inlet to investigate the aeroacoustics at take-off and landing conditions. A 104·1 mm (4·1 in) diameter turbofan simulator was coupled to the inlet to generate the noise typical of a turbofan engine. Aerodynamic and acoustic data were obtained in an anechoic chamber under ground-static conditions (i.e., no forward flight effect). Results showed that varying the distance between the trailing edge of the bifurcated ramp of the inlet and the fan face had negligible effect on the total noise level. Thus, one can have a large freedom to design the bifurcated ramp mechanically and aerodynamically, with minimum impact on the aeroacoustics. However, the effect of inlet guide vanes' (IGV) axial spacing to the fan face has a first order effect on the aeroacoustics for the bifurcated 2-D inlet. As much as 5 dB reduction in the overall sound pressure level and as much as 15 dB reduction in the blade passing frequency tone were observed when the IGV was moved from 0·8 chord of rotor blade upstream of the fan face to 2·0 chord of the blade upstream. The wake profile similarity of the IGV was also found in the flow environment of the 2-D bifurcated inlet, i.e., the IGV wakes followed the usual Gauss' function.
Aeroacoustic Study of a Model-Scale Landing Gear in a Semi-Anechoic Wind Tunnel
Remillieux, Marcel Christophe
2007-01-01
An aeroacoustic study was conducted on a 26%-scale Boeing 777 main landing gear in the Virginia Tech (VT) Anechoic Stability Wind Tunnel. The VT Anechoic Stability Wind Tunnel allowed noise measurements to be carried out using both a 63-elements microphone phased array and a linear array of 15 microphones. The noise sources were identified from the flyover view under various flow speeds and the phased array positioned in both the near and far-field. The directivity pattern of the landing ge...
Nakiboglu, G.; Manders, H.B.M.; Hirschberg, A.
2012-01-01
Aeroacoustic power generation due to a self-sustained oscillation by an axisymmetric compact cavity exposed to a low-Mach-number grazing flow is studied both experimentally and numerically. The feedback effect is produced by the velocity fluctuations resulting from a coupling with acoustic standing
Aeroacoustic Testing of Wind Turbine Airfoils: February 20, 2004 - February 19, 2008
Energy Technology Data Exchange (ETDEWEB)
Devenport, W.; Burdisso, R. A.; Camargo, H.; Crede, E.; Remillieux, M.; Rasnick, M.; Van Seeters, P.
2010-05-01
The U.S. Department of Energy (DOE), working through its National Renewable Energy Laboratory (NREL), is engaged in a comprehensive research effort to improve the understanding of wind turbine aeroacoustics. The motivation for this effort is the desire to exploit the large expanse of low wind speed sites that tend to be close to U.S. load centers. Quiet wind turbines are an inducement to widespread deployment, so the goal of NREL's aeroacoustic research is to develop tools that the U.S. wind industry can use in developing and deploying highly efficient, quiet wind turbines at low wind speed sites. NREL's National Wind Technology Center (NWTC) is implementing a multifaceted approach that includes wind tunnel tests, field tests, and theoretical analyses in direct support of low wind speed turbine development by its industry partners. NWTC researchers are working hand in hand with engineers in industry to ensure that research findings are available to support ongoing design decisions.
Overview of the Space Launch System Ascent Aeroacoustic Environment Test Program
Herron, Andrew J.; Crosby, William A.; Reed, Darren K.
2016-01-01
Characterization of accurate flight vehicle unsteady aerodynamics is critical for component and secondary structure vibroacoustic design. The Aerosciences Branch at the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center has conducted a test at the NASA Ames Research Center (ARC) Unitary Plan Wind Tunnels (UPWT) to determine such ascent aeroacoustic environments for the Space Launch System (SLS). Surface static pressure measurements were also collected to aid in determination of local environments for venting, CFD substantiation, and calibration of the flush air data system located on the launch abort system. Additionally, this test supported a NASA Engineering and Safety Center study of alternate booster nose caps. Testing occurred during two test campaigns: August - September 2013 and December 2013 - January 2014. Four primary model configurations were tested for ascent aeroacoustic environment definition. The SLS Block 1 vehicle was represented by a 2.5% full stack model and a 4% truncated model. Preliminary Block 1B payload and manned configurations were also tested, using 2.5% full stack and 4% truncated models respectively. This test utilized the 11 x 11 foot transonic and 9 x 7 foot supersonic tunnel sections at the ARC UPWT to collect data from Mach 0.7 through 2.5 at various total angles of attack. SLS Block 1 design environments were developed primarily using these data. SLS Block 1B preliminary environments have also been prepared using these data. This paper discusses the test and analysis methodology utilized, with a focus on the unsteady data collection and processing.
Working With the Wave Equation in Aeroacoustics: The Pleasures of Generalized Functions
Farassat, F.; Brentner, Kenneth S.; Dunn, mark H.
2007-01-01
The theme of this paper is the applications of generalized function (GF) theory to the wave equation in aeroacoustics. We start with a tutorial on GFs with particular emphasis on viewing functions as continuous linear functionals. We next define operations on GFs. The operation of interest to us in this paper is generalized differentiation. We give many applications of generalized differentiation, particularly for the wave equation. We discuss the use of GFs in finding Green s function and some subtleties that only GF theory can clarify without ambiguities. We show how the knowledge of the Green s function of an operator L in a given domain D can allow us to solve a whole range of problems with operator L for domains situated within D by the imbedding method. We will show how we can use the imbedding method to find the Kirchhoff formulas for stationary and moving surfaces with ease and elegance without the use of the four-dimensional Green s theorem, which is commonly done. Other subjects covered are why the derivatives in conservation laws should be viewed as generalized derivatives and what are the consequences of doing this. In particular we show how we can imbed a problem in a larger domain for the identical differential equation for which the Green s function is known. The primary purpose of this paper is to convince the readers that GF theory is absolutely essential in aeroacoustics because of its powerful operational properties. Furthermore, learning the subject and using it can be fun.
Experimental aeroacoustic study of a landing gear in the unsteady flow induced by a propeller
Chekiri, Rafik
An aeroacoustic study of a two-strut, two-wheel, nacelle-mounted landing gear was conducted to investigate the effects of an upstream propeller on the radiated noise. The development of a 1:10.8 scale model based on a Bombardier Q400 aircraft, consisting of a propeller, motor, nacelle, and landing gear assembly is discussed. Comparisons are made between cases with and without an actuated upstream propeller. Far-field microphone measurements out of the airstream are presented to characterize the acoustic effects of each model component. The main strut and wheels of the model were equipped with surface-mounted microphones to measure unsteady pressures. It is shown that the noise signature of the landing gear cannot be observed over the tunnel background noise in the far-field. Unsteady surface pressures on the main strut show dominant peaks related to vortex shedding from the drag strut for both steady and unsteady upstream conditions.
Aero-Acoustics of Modern Transonic Fans—Fan Noise Reduction from Its Sources
Institute of Scientific and Technical Information of China (English)
L. Xu; J.D. Denton
2003-01-01
The noise of aerodynamics nature from modern transonic fan is examined from its sources with the perspective of noise reduction through aero-acoustics design using advanced Computational Fluid Dynamics (CFD) tools.In particular the problems associated with the forward propagating noise in the front is addressed. It is identified that the shock wave spillage from the leading edge near the fan tip is the main source of the tone noise. Two different approaches have been studied to reduce the forward arc tone noise and two state-of-art transonic fans are designed using the strategies developed. The following rig tests show that while the fans exhibit other noise problems,the primary goals of noise reduction have been achieved through both fans and the novel noise reduction concept vindicated.
Aeromechanics and Aeroacoustics Predictions of the Boeing-SMART Rotor Using Coupled-CFD/CSD Analyses
Bain, Jeremy; Sim, Ben W.; Sankar, Lakshmi; Brentner, Ken
2010-01-01
This paper will highlight helicopter aeromechanics and aeroacoustics prediction capabilities developed by Georgia Institute of Technology, the Pennsylvania State University, and Northern Arizona University under the Helicopter Quieting Program (HQP) sponsored by the Tactical Technology Office of the Defense Advanced Research Projects Agency (DARPA). First initiated in 2004, the goal of the HQP was to develop high fidelity, state-of-the-art computational tools for designing advanced helicopter rotors with reduced acoustic perceptibility and enhanced performance. A critical step towards achieving this objective is the development of rotorcraft prediction codes capable of assessing a wide range of helicopter configurations and operations for future rotorcraft designs. This includes novel next-generation rotor systems that incorporate innovative passive and/or active elements to meet future challenging military performance and survivability goals.
Direct aeroacoustic simulation of acoustic feedback phenomena on a side-view mirror
Frank, Hannes M.; Munz, Claus-Dieter
2016-06-01
The flow around a side-view mirror and its noise generation are investigated using large eddy simulation and direct acoustic simulation. To this end, we use the high order discontinuous Galerkin spectral element method on non-conforming curved elements. Tonal noise is observed, which originates at the trailing edge downstream of laminar separation, coinciding with experimental results. In order to determine the nature of the tonal noise generation mechanism, we perform a linear stability analysis and employ a global perturbation approach in combination with dynamic mode decomposition. The perturbation analysis based on the whole flow field demonstrates the existence of a global instability involving convective disturbance growth, acoustic scattering at the trailing edge and acoustic receptivity at a rounded edge slightly upstream of separation. The results clearly show the tonal noise to be caused by the so-called acoustic feedback loop known from airfoil aeroacoustics. This phenomenon has been simulated here for the first time for a complex geometry.
Enhanced focal-resolution of dipole sources using aeroacoustic time-reversal in a wind tunnel
Mimani, A.; Moreau, D. J.; Prime, Z.; Doolan, C. J.
2016-05-01
This paper presents the first application of the Point-Time-Reversal-Sponge-Layer (PTRSL) damping technique to enhance the focal-resolution of experimental flow-induced dipole sources obtained using the Time-Reversal (TR) source localization method. Experiments were conducted in an Anechoic Wind Tunnel for the case of a full-span cylinder located in a low Mach number cross-flow. The far-field acoustic pressure sampled using two line arrays of microphones located above and below the cylinder exhibited a dominant Aeolian tone. The aeroacoustic TR simulations were implemented using the time-reversed signals whereby the source map revealed the lift-dipole nature at the Aeolian tone frequency. A PTRSL (centred at the predicted dipole location) was shown to reduce the size of dipole focal spots to 7/20th of a wavelength as compared to one wavelength without its use, thereby dramatically enhancing the focal-resolution of the TR technique.
Automated Development of Accurate Algorithms and Efficient Codes for Computational Aeroacoustics
Goodrich, John W.; Dyson, Rodger W.
1999-01-01
The simulation of sound generation and propagation in three space dimensions with realistic aircraft components is a very large time dependent computation with fine details. Simulations in open domains with embedded objects require accurate and robust algorithms for propagation, for artificial inflow and outflow boundaries, and for the definition of geometrically complex objects. The development, implementation, and validation of methods for solving these demanding problems is being done to support the NASA pillar goals for reducing aircraft noise levels. Our goal is to provide algorithms which are sufficiently accurate and efficient to produce usable results rapidly enough to allow design engineers to study the effects on sound levels of design changes in propulsion systems, and in the integration of propulsion systems with airframes. There is a lack of design tools for these purposes at this time. Our technical approach to this problem combines the development of new, algorithms with the use of Mathematica and Unix utilities to automate the algorithm development, code implementation, and validation. We use explicit methods to ensure effective implementation by domain decomposition for SPMD parallel computing. There are several orders of magnitude difference in the computational efficiencies of the algorithms which we have considered. We currently have new artificial inflow and outflow boundary conditions that are stable, accurate, and unobtrusive, with implementations that match the accuracy and efficiency of the propagation methods. The artificial numerical boundary treatments have been proven to have solutions which converge to the full open domain problems, so that the error from the boundary treatments can be driven as low as is required. The purpose of this paper is to briefly present a method for developing highly accurate algorithms for computational aeroacoustics, the use of computer automation in this process, and a brief survey of the algorithms that
Lee, Moohyung; Bolton, J. Stuart; Mongeau, Luc
2003-08-01
The purpose of this study was to develop methods for visualizing the sound radiation from aeroacoustic sources in order to identify their source strength distribution, radiation patterns, and to quantify the performance of noise control solutions. Here, cylindrical Near-field Acoustical Holography was used for that purpose. In a practical holographic measurement of sources comprising either partially correlated or uncorrelated subsources, it is necessary to use a number of reference microphones so that the sound field on the hologram surface can be decomposed into mutually incoherent partial fields before holographic projection. In this article, procedures are described for determining the number of reference microphones required when visualizing partially correlated aeroacoustic sources; performing source nonstationarity compensation; and applying regularization. The procedures have been demonstrated by application to a ducted fan. Holographic tests were performed to visualize the sound radiation from that source in its original form. The system was then altered to investigate the effect of two modifications on the fan's sound radiation pattern: first, leaks were created in the fan and duct assembly, and second, sound absorbing material was used to line the downstream duct section. Results in all three cases are shown at the blade passing frequency and for a broadband noise component. In the absence of leakage, both components were found to exhibit a dipole-like radiation pattern. Leakage was found to have a strong influence on the directivity of the blade passing tone. The increase of the flow resistance caused by adding the acoustical lining resulted in a nearly symmetric reduction of sound radiation.
Redonnet, S.
2014-01-01
International audience This article focuses on advanced noise prediction methodologies, in regard to aircraft noise mitigation. More precisely, the so-called aeroacoustic hybrid methodology is first recalled here, before illustrating its potentialities through several examples of application to realistic aircraft noise problems. Among other things, this paper highlights how Onera has contributed to the development of reliable computational methodologies over the last decade, which can now ...
de Gennaro, Michele
2010-01-01
Turbomachinery aerodynamic and aeroacoustic modelling is recognized to be one of the main areas of interest in the frame of industrial engineering, due to the large number of applications concerning the rotating fluid machines. Numerical modelling is today widely integrated in the design and development process of industrial components, as well as Computational Fluid Dynamics (CFD) is a tool well integrated into the industrial development and production life-cycles. This has been made because...
Gikadi, Jannis; Föller, Stephan; Sattelmayer, Thomas
2014-12-01
A powerful model to predict aeroacoustic interactions in the linear regime is the perturbed compressible linearized Navier-Stokes equations. Thus far, the frequently employed derivation suggests that the effect of turbulence and its associated Reynolds stresses is neglected and a quasi-laminar model is employed. In this paper, dynamic perturbation equations are derived incorporating the effect of turbulence and its interaction with perturbation quantities. This is done by employing a triple decomposition of the instantaneous variables. The procedure results in a closure problem for the Reynolds stresses for which a linear eddy-viscosity model is proposed. The resulting perturbation equations are applied to a grazing flow in a T-joint for which strong shear layer instabilities at certain frequencies are experimentally observed. Passive scattering properties of the grazing flow are validated against the experiments performed by Karlsson and Åbom and perturbation equations being quasi-laminar. We find that prediction models must include the effect of Reynolds stresses to capture the aeroacoustic interaction effects correctly. Neglecting its effect naturally results in the over prediction of vortex growth at the frequencies of shear layer instability and therewith in an over prediction of aeroacoustic interactions.
Aeroacoustic Simulation for NASA CC3 Centrifugal Compressor Operating at off Design Condition
Directory of Open Access Journals (Sweden)
Alqaradawi Mohamed
2016-01-01
Full Text Available This paper covers the characterization of the acoustic noise and the unsteady flow field of a high speed centrifugal compressor NASA CC3. In order to accurately predict the noise, all analyses are carried out through the use of Large Eddy Simulation and Ffowcs Williams–Hawkings model for noise prediction. The relative effect of hub cavity on flow characteristics and sound levels is investigated, for a compressor stage with a total pressure ratio equal to 4, working from surge to near choke condition. In comparison with the experimental results from literature, the predicted compressor performance and flow field are predicted well. The hub cavity flow effect on the compressor aeroacoustic generated noise is shown in the paper. The unsteady static pressure and sound pressure levels are compared not only at different location but also for design and off design operating points. The internal flow results inside the hub cavity are presented at surge, design and near choke points. The conclusion is that the cavity effect of the centrifugal compressor cannot be ignored in the numerical prediction of aerodynamic generated noise. The impeller back plate of the rotor experiences a strong pressure fluctuation, which is maxima at the impeller outer radius for all operating point, but higher pressure values at the surge point.
International Nuclear Information System (INIS)
Based on vortex theory, we experimentally and directly predict sound sources distributing in the flow field and determine the sound pressure level as a result of the spatial integration of sound sources. In employing this direct evaluation method for the aeroacoustic sound, the problem is that a large integration area is required to minimize errors caused by the sudden truncation of the integration area; we overcome it by adopting and applying a modified formula that neglects the quadrupole sound under the condition that the dipole sound is dominant at a low Mach number. Through the flow field measurement using a time-resolved particle image velocimetry (TR-PIV) technique, we will clearly demonstrate the feasibility of our method and the distribution of dipole sound sources in the vicinity of a body even if a comparatively small integration area must be taken. In this basic study, a circular cylinder with a diameter of 6.0 mm is used; the spatially integrated sound pressure is compared with the actual sound pressure which is measured with a microphone. Further, the sound sources evaluated using only the flow field are determined, which give us detailed information about the amplitude and phase of the sound source structure. This direct evaluation method for the dipole sound is applicable to a more complex body
Aeroacoustic Flow Phenomena Accurately Captured by New Computational Fluid Dynamics Method
Blech, Richard A.
2002-01-01
One of the challenges in the computational fluid dynamics area is the accurate calculation of aeroacoustic phenomena, especially in the presence of shock waves. One such phenomenon is "transonic resonance," where an unsteady shock wave at the throat of a convergent-divergent nozzle results in the emission of acoustic tones. The space-time Conservation-Element and Solution-Element (CE/SE) method developed at the NASA Glenn Research Center can faithfully capture the shock waves, their unsteady motion, and the generated acoustic tones. The CE/SE method is a revolutionary new approach to the numerical modeling of physical phenomena where features with steep gradients (e.g., shock waves, phase transition, etc.) must coexist with those having weaker variations. The CE/SE method does not require the complex interpolation procedures (that allow for the possibility of a shock between grid cells) used by many other methods to transfer information between grid cells. These interpolation procedures can add too much numerical dissipation to the solution process. Thus, while shocks are resolved, weaker waves, such as acoustic waves, are washed out.
Cartesian Mesh Linearized Euler Equations Solver for Aeroacoustic Problems around Full Aircraft
Directory of Open Access Journals (Sweden)
Yuma Fukushima
2015-01-01
Full Text Available The linearized Euler equations (LEEs solver for aeroacoustic problems has been developed on block-structured Cartesian mesh to address complex geometry. Taking advantage of the benefits of Cartesian mesh, we employ high-order schemes for spatial derivatives and for time integration. On the other hand, the difficulty of accommodating curved wall boundaries is addressed by the immersed boundary method. The resulting LEEs solver is robust to complex geometry and numerically efficient in a parallel environment. The accuracy and effectiveness of the present solver are validated by one-dimensional and three-dimensional test cases. Acoustic scattering around a sphere and noise propagation from the JT15D nacelle are computed. The results show good agreement with analytical, computational, and experimental results. Finally, noise propagation around fuselage-wing-nacelle configurations is computed as a practical example. The results show that the sound pressure level below the over-the-wing nacelle (OWN configuration is much lower than that of the conventional DLR-F6 aircraft configuration due to the shielding effect of the OWN configuration.
An experimental and theoretical study of the aeroacoustics of external-Coanda gas flares
Parsons, Caroline
Experimental and theoretical means have been used to investigate the fluid dynamics and aeroacoustics of both stepped and unstepped external Coanda flares. Flow visualization techniques have been used to observe the one-eight scale model flare flow fields whilst simultaneously carrying out various sound measurements in the hope of being able to relate observed flow features to specific types of aerodynamic noise. Particular attention has been paid to the stepped model flare in the present work, for comparison with previous work on the unstepped model flare. Test have been carried out on two full-scale flares of different sizes which confirm that the previously assumed inverse-length scaling law does indeed hold in the case of flare noise frequency. Comparisons can therefore be made between the results of model and full-size flare tests, and these indicate that although the full-size flare also emits discrete tones, the nature of these tones are very different from those emitted by the model flares. Several possible reasons for the differences in the two sets of results are discussed. A theoretical study of the high-frequency turbulent mixing noise associated with a model Indair flare jet has been carried out. Because of the complicated nature of such a curved radial wall-jet, the theory has first been developed for a plane two-dimensional wall-jet.
Greffrath, Fabian; Prieler, Robert; Telle, Rainer
2014-11-01
A new method for the experimental estimation of radiant heat emittance at high temperatures has been developed which involves aero-acoustic levitation of samples, laser heating and contactless temperature measurement. Radiant heat emittance values are determined from the time dependent development of the sample temperature which requires analysis of both the radiant and convective heat transfer towards the surroundings by means of fluid dynamics calculations. First results for the emittance of a corundum sample obtained with this method are presented in this article and found in good agreement with literature values.
Three-Dimensional Application of DAMAS Methodology for Aeroacoustic Noise Source Definition
Brooks, Thomas F.; Humphreys, William M., Jr.
2005-01-01
At the 2004 AIAA/CEAS Aeroacoustic Conference, a breakthrough in acoustic microphone array technology was reported by the authors. A Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) was developed which decouples the array design and processing influence from the noise being measured, using a simple and robust algorithm. For several prior airframe noise studies, it was shown to permit an unambiguous and accurate determination of acoustic source position and strength. As a follow-on effort, this paper examines the technique for three-dimensional (3D) applications. First, the beamforming ability for arrays, of different size and design, to focus longitudinally and laterally is examined for a range of source positions and frequency. Advantage is found for larger array designs with higher density microphone distributions towards the center. After defining a 3D grid generalized with respect to the array s beamforming characteristics, DAMAS is employed in simulated and experimental noise test cases. It is found that spatial resolution is much less sharp in the longitudinal direction in front of the array compared to side-to-side lateral resolution. 3D DAMAS becomes useful for sufficiently large arrays at sufficiently high frequency. But, such can be a challenge to computational capabilities, with regard to the required expanse and number of grid points. Also, larger arrays can strain basic physical modeling assumptions that DAMAS and all traditional array methodologies use. An important experimental result is that turbulent shear layers can negatively impact attainable beamforming resolution. Still, the usefulness of 3D DAMAS is demonstrated by the measurement of landing gear noise source distributions in a difficult hard-wall wind tunnel environment.
Design and aero-acoustic analysis of a counter-rotating wind turbine
Agrawal, Vineesh V.
Wind turbines have become an integral part of the energy business because they are one of the most economical and reliable sources of renewable energy. Conventional wind turbines are capable of capturing less than half of the energy present in the wind. Hence, to make the wind turbines more efficient, it is important to increase their performance. A horizontal axis wind turbine with multiple rotors is one concept that can achieve a higher power conversion rate. Also, a concern for wind energy is the noise generated by wind turbines. Hence, an investigation into the acoustic behavior of a multi-rotor horizontal axis wind turbine is required. In response to the need of a wind turbine design with higher power coefficient, a unique design of a counter-rotating horizontal axis wind turbine (CR-HAWT) is proposed. The Blade Element Momentum (BEM) theory is used to aerodynamically design the blades of the two rotors. Modifications are made to the BEM theory to accommodate the interaction of the two rotors. The tower effect on the noise generation of the downwind rotor is investigated. Predictions are made for the total noise generated by the wind turbine at its design operating conditions. A total power coefficient of 65.2% is predicted for the proposed CR-HAWT design. A low tip speed ratio is chosen to minimize the noise generation. The aeroacoustic analysis of the CR-HAWT shows that the noise generated at its design operating conditions is within an acceptable range. Thus, the CR-HAWT is predicted to be a quiet wind turbine with a high power coefficient, making it highly desirable for small wind turbine applications.
Sovardi, Carlo; Jaensch, Stefan; Polifke, Wolfgang
2016-09-01
A numerical method to concurrently characterize both aeroacoustic scattering and noise sources at a duct singularity is presented. This approach combines Large Eddy Simulation (LES) with techniques of System Identification (SI): In a first step, a highly resolved LES with external broadband acoustic excitation is carried out. Subsequently, time series data extracted from the LES are post-processed by means of SI to model both acoustic propagation and noise generation. The present work studies the aero-acoustic characteristics of an orifice placed in a duct at low flow Mach numbers with the "LES-SI" method. Parametric SI based on the Box-Jenkins mathematical structure is employed, with a prediction error approach that utilizes correlation analysis of the output residuals to avoid overfitting. Uncertainties of model parameters due to the finite length of times series are quantified in terms of confidence intervals. Numerical results for acoustic scattering matrices and power spectral densities of broad-band noise are validated against experimental measurements over a wide range of frequencies below the cut-off frequency of the duct.
Hybrid Wing Body Aircraft System Noise Assessment with Propulsion Airframe Aeroacoustic Experiments
Thomas, Russell H.; Burley, Casey L.; Olson, Erik D.
2010-01-01
A system noise assessment of a hybrid wing body configuration was performed using NASA s best available aircraft models, engine model, and system noise assessment method. A propulsion airframe aeroacoustic effects experimental database for key noise sources and interaction effects was used to provide data directly in the noise assessment where prediction methods are inadequate. NASA engine and aircraft system models were created to define the hybrid wing body aircraft concept as a twin engine aircraft with a 7500 nautical mile mission. The engines were modeled as existing technology high bypass ratio turbofans. The baseline hybrid wing body aircraft was assessed at 22 dB cumulative below the FAA Stage 4 certification level. To determine the potential for noise reduction with relatively near term technologies, seven other configurations were assessed beginning with moving the engines two fan nozzle diameters upstream of the trailing edge and then adding technologies for reduction of the highest noise sources. Aft radiated noise was expected to be the most challenging to reduce and, therefore, the experimental database focused on jet nozzle and pylon configurations that could reduce jet noise through a combination of source reduction and shielding effectiveness. The best configuration for reduction of jet noise used state-of-the-art technology chevrons with a pylon above the engine in the crown position. This configuration resulted in jet source noise reduction, favorable azimuthal directivity, and noise source relocation upstream where it is more effectively shielded by the limited airframe surface, and additional fan noise attenuation from acoustic liner on the crown pylon internal surfaces. Vertical and elevon surfaces were also assessed to add shielding area. The elevon deflection above the trailing edge showed some small additional noise reduction whereas vertical surfaces resulted in a slight noise increase. With the effects of the configurations from the
Three-dimensional vortex analysis and aeroacoustic source characterization of jet core breakdown
Violato, Daniele; Scarano, Fulvio
2013-01-01
The three-dimensional behavior of jet core breakdown is investigated with experiments conducted on a free water jet at Re = 5000 by time-resolved tomographic particle image velocimetry (TR-TOMO PIV). The investigated domain encompasses the range between 0 and 10 jet diameters. The characteristic pulsatile motion of vortex ring shedding and pairing culminates with the growth of four primary in-plane and out-of-plane azimuthal waves and leads to the formation of streamwise vortices. Vortex ring humps are tilted and ejected along the axial direction as they are subjected to higher axial velocities. By the end of the potential core, this process causes the breakdown of the vortex ring regime and the onset of streamwise filaments oriented at 30°-45° to the jet axis and "C" shaped peripheral structures. The latter re-organize further downstream in filaments oriented along the azimuthal direction at the jet periphery. Instead, in the vicinity of the jet axis the filaments do not exhibit any preferential direction resembling the isotropic turbulent regime. Following Powell's aeroacoustic analogy, the instantaneous spatial distribution of the acoustic source term is mapped by the second time derivative of the Lamb vector, revealing the highest activity during vortex ring breakdown. A three-dimensional modal analysis of velocity, vorticity, Lamb vector, and Lamb vector second time derivative fields is conducted by proper orthogonal decomposition (POD) within the first 10 modes. The decomposed velocity fluctuations describe a helical organization in the region of the jet core-breakdown and, further downstream, jet axis flapping and precession motions. By the end of the potential core, vorticity modes show that vortex rings are dominated by travelling waves of radial and axial vorticity with a characteristic 40°-45° inclination to the jet axis. The Lamb vector and the Lamb vector second time derivative modes exhibit similar patterns for the azimuthal component, whereas the
Propulsion Airframe Aeroacoustic Integration Effects for a Hybrid Wing Body Aircraft Configuration
Czech, Michael J.; Thomas, Russell H; Elkoby, Ronen
2012-01-01
An extensive experimental investigation was performed to study the propulsion airframe aeroacoustic effects of a high bypass ratio engine for a hybrid wing body aircraft configuration where the engine is installed above the wing. The objective was to provide an understanding of the jet noise shielding effectiveness as a function of engine gas condition and location as well as nozzle configuration. A 4.7% scale nozzle of a bypass ratio seven engine was run at characteristic cycle points under static and forward flight conditions. The effect of the pylon and its orientation on jet noise was also studied as a function of bypass ratio and cycle condition. The addition of a pylon yielded significant spectral changes lowering jet noise by up to 4 dB at high polar angles and increasing it by 2 to 3 dB at forward angles. In order to assess jet noise shielding, a planform representation of the airframe model, also at 4.7% scale was traversed such that the jet nozzle was positioned from downstream of to several diameters upstream of the airframe model trailing edge. Installations at two fan diameters upstream of the wing trailing edge provided only limited shielding in the forward arc at high frequencies for both the axisymmetric and a conventional round nozzle with pylon. This was consistent with phased array measurements suggesting that the high frequency sources are predominantly located near the nozzle exit and, consequently, are amenable to shielding. The mid to low frequency sources were observed further downstream and shielding was insignificant. Chevrons were designed and used to impact the distribution of sources with the more aggressive design showing a significant upstream migration of the sources in the mid frequency range. Furthermore, the chevrons reduced the low frequency source levels and the typical high frequency increase due to the application of chevron nozzles was successfully shielded. The pylon was further modified with a technology that injects air
Herron, A. J.; Reed, D. K.; Nance, D. K.
2015-01-01
Characterization of launch vehicle unsteady aerodynamics is a field best studied through experimentation, which is often carried out in the form of large scale wind tunnel testing. Measurement of the fluctuating pressures induced by the boundary layer noise is customarily made with miniature pressure transducers installed into a model of the vehicle of interest. Literature shows that noise level increases between two to five decibels (dB referenced to 20 micropascal) can be induced when the transducer surface is not mounted perfectly flush with the model outer surface. To reduce this artificially induced noise, special transducer holders have been used for aeroacoustic wind tunnel testing by NASA. This holder is a sleeve into which the transducer fits, with a cap that allows it to be mounted in a recessed hole in the model. A single hole in the holder allows the transport of the tunnel medium so the transducer can discriminate the fluctuating pressure due to the turbulent boundary layer noise. The holder is first dry fitted into the model and any difference in height between the holder and the model surface can be sanded flush. The holder is then removed from the model, the transducer glued inside the holder, and the holder replaced in the model, secured also with glue, thus eliminating the problem of noise level increases due to lack of flushness. In order to work with this holder design, special transducers have been ordered with their standard screen removed and the diaphragm moved as close to the top of the casing as possible to minimize any cavity volume. Although this greatly reduces induced noise due to the transducers being out of flush, the holders can also induce a cavity resonance that is usually at a very high frequency. This noise is termed transducer mount induced noise (XMIN). The peak of the mode can vary with the cavity depth, boundary layer noise that can excite the mode, tunnel flow medium, and the build of the transducers. Because the boundary
Bruggeman, J. C.; Hirschberg, A.; van Dongen, M. E. H.; Wijnands, A. P. J.; Gorter, J.
1991-11-01
A theoretical model is proposed for the aero-acoustic sources responsible for low-frequency self-sustained pulsations in pipes with closed side branches. The theory successfully explains the acoustic and hydrodynamic conditions for resonance in experiments with a single side branch. It also predicts the order of magnitude of the pulsation amplitude and the effect of losses due to friction and radiation. A high pulsation level, with acoustic velocities of the order of magnitude of the main flow, is observed in a double side branch set-up when the edges at the junctions are rounded. When in the double side branch set-up the rounded upstream edge of the second T-joint is replaced by a sharp edge, the pulsation amplitude is reduced by a factor of five. This effect, which can be explained with the theory of vortex sound, leads us to the design of spoilers. Various "spoilers" have been tested in scale model and full scale experiments. Some of these reduce the pulsation level by 40 dB.
DEFF Research Database (Denmark)
Bertagnolio, Franck; Aagaard Madsen, Helge; Fischer, Andreas;
2016-01-01
rotor noise model is presented. It includes the main sources of aeroacoustic noise from wind turbines: turbulent inflow, trailing edge and stall noise. The noise measured by one microphone located directly downstream of the wind turbine is compared to the model predictions at the microphone location....... A good qualitative agreement is found. When wind speed increases, the rotor noise model shows that at high frequencies the stall noise becomes dominant. It also shows that turbulent inflow noise is dominant at low frequencies for all wind speeds and that trailing edge noise is dominant at low wind speeds...
高速面铣刀气动噪声及其频谱分析%Spectra Analysis of Face Milling Cutter Aeroacoustic Noise
Institute of Scientific and Technical Information of China (English)
刘战强; 吉春辉; 刘鲁宁; 艾兴
2011-01-01
The noise produced by high speed face milling is detrimental to the machine operators.The major source of aeroacoustic noise is primarily dipole in nature.A noise prediction model based on Ffowcs Williams-Hawkings equation is used to predict aeroacoustic noise in face milling cutters.Numerical simulation of air flow in the milling cutter system is performed by using CFD method.The predicted sound pressure level based on mathematical model is 4.0 dB lower than measurement results at 9 000 rpm.And the error is about 7％.The chip flute region and insert rake face are found to be important factors in determining aeroacoustic noise in rotating face milling cutter.The directivity of aeroacoustic noise is verified in the axial direction.The broadband noise spreads over a broad range of frequencies and contributes significantly to overall noise, but the discrete noise at the rotational frequency is significantly higher.It can provide theory for low noise design and prediction of high speed face milling cutter.%高速面铣削过程中的噪声严重影响工作人员的健康,偶极子声源是气动噪声的主要声源,基于Ffowcs Williams-Hawkings(FW-H)方程建立高速面铣刀气动噪声预测模型,采用计算流体动力学(Computational fluid dynamics,CFD)的方法对气体流动特性进行数值模拟,进行高速面铣刀空转噪声测试试验,噪声预测声压级比噪声测试声压级低4.0 dB左右.研究结果表明容屑槽区域和刀片前刀面是影响高速面铣刀气动噪声的主要因素,高速面铣刀气动噪声在轴向具有明显指向性.结合频谱分析发现紊流噪声分布在较广的频率段,决定了气动噪声的大小,但旋转频率上离散噪声的强度往往很大.高速面铣刀气动噪声预测模型可为低噪声高速面铣刀设计和合理应用提供理论依据.
常规闭口风洞相阵列气动声学试验%Aeroacoustic phased array measurements in closed-section wind tunnel
Institute of Scientific and Technical Information of China (English)
赵磊; 赵小见; 李潜
2012-01-01
传统气动声学研究观点认为,精确的声学测量要求风洞背景噪声和洞壁反射足够低,传声器测量结果有足够高的信噪比,这是大多数风洞无法达到的要求.近些年,基于声纳和雷达技术发展起来的麦克风相阵列技术可以通过增加阵列的传声器数目从而大幅提高声学测量的信噪比,具有噪声源研究和定位能力,并被成功地应用于非声学固壁风洞噪声源测量和噪声物理机制研究.作者基于相阵列波束生成频域算法研制出常规闭口风洞相阵列系统及相关技术,在FD-09风洞尝试进行了相阵列校准试验和某民机噪声测量试验.结果表明:相阵列技术能够准确捕捉到真实的校准声源,并从技术上验证了相阵列系统在常规闭口风洞测量气动噪声是有效的.%As conventional viewpoint, aeroacoustic measurements require low background noise and minimal reflections for accurate results. So proper design of wind tunnel components and test apparatus are critical to successful aeroacoustic measurements. Over the past several years, microphone phased arrays have been developed based on sonar and radar technology. One of the biggest advantages is that the signal to noise ratio (SNR) is increased with the number of sensors in the array. This technology can be used to measure and identify the noise sources. It has been used in non-acoustic, hardwall wind tunnels, as a research tool to gain insight into noise and into the physical mechanisms causing the noise. Based on the frequency domain approach of beamforming algorithm, microphone phased array system has been developed by the author for aeroacoustic measurements in low speed closed-section wind tunnel. Array calibration and aeroacoustic measurements for a commercial aircraft were performed in FD-09 wind tunnel. The results indicated that array can identify the calibration resource accurately, and the availability of aeroacousitc measurement was validated by array
增升装置气动噪声研究现状与发展趋势%Current Status and Future Trend for Aero-acoustics Research on High-lift Devices
Institute of Scientific and Technical Information of China (English)
邓一菊; 段卓毅; 侯银珠
2012-01-01
在对绿色航空发展要求、噪声适航标准、机体噪声概念介绍的基础上，对增升装置气动噪声进行了详细论述，包括数值分析技术、试验研究、飞行试验、降噪设计等的研究现状；阐述了增升装置气动噪声研究的重要性，提出重视机理研究和数值分析方法验证工作的观点，指出增升装置气动与噪声一体化设计的发展趋势。%Based on the green aviation requirements, FAR noise standards, air frame noise sources, the state of the art of aero-acoustics techniques including CFD, wind tunnel test, flight test and noise reduction are discussed in details. The importance of aero-acoustics research on high-lift devices is described, the viewpoint of paying regard to mechanism research and verifying by digital analysis method is presented and the future trend of high- lift devices aero-acoustics, i.e. the aero acoustics and high-lift devices integrated design, is clearly pointed out.
Gliebe, P; Mani, R.; Shin, H.; Mitchell, B.; Ashford, G.; Salamah, S.; Connell, S.; Huff, Dennis (Technical Monitor)
2000-01-01
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-noise correlation model was developed from engine acoustic test results. This work provided several insights on potential approaches to reducing aircraft engine noise. Code development is described in this report, and those insights are discussed.
Aeroacoustics of Musical Instruments
Fabre, B.; Gilbert, J.; Hirschberg, A.; Pelorson, X.
2012-01-01
We are interested in the quality of sound produced by musical instruments and their playability. In wind instruments, a hydrodynamic source of sound is coupled to an acoustic resonator. Linear acoustics can predict the pitch of an instrument. This can significantly reduce the trial-and-error process
Institute of Scientific and Technical Information of China (English)
卓文涛; 季锃钏; 陈二云; 戴韧; 黄逸
2012-01-01
Taking both the aerodynamic and aeroacoustic performance as the objectives of optimization, a multi-objective optimization method was proposed for low-speed airfoils by using Bezier curves to describe the airfoil geometry, applying the analysis method of iterative potential flow and boundary layer （IBL） flow to calculate the flow field, using the Brooks-Pope-Marcolini airfoil self-noise semi-empirical model to predict the aerodynamic noise and adopting Powell method to obtain the optimized airfoil. The multi-objective optimization method has been verified with a NACA0012 prototype airfoil in different weight assignment schemes. Results show that compared with the prototype airfoil, the optimized one has a higher liftdrag ratio, lower acoustic level and better aerodynamic and aeroacoustic performance under design condi- tions.%将风力机翼型气动性能与气动噪声同时作为翼型优化目标,建立了低速翼型的多目标优化设计方法,包括利用Bezier曲线对翼型几何结构进行参数化建模,使用位势流动与边界层迭代（IBL）的流动分析方法计算翼型流场,采用Brooks-Pope-Marcolini翼型自噪声半经验模型预测气动噪声,利用Powell优化方法求得优化翼型.以naca0012翼型为例,对多种目标权重分配方案的优化目标进行设计和计算.结果表明：与原始翼型相比,在设计工况下,优化翼型的升阻比提高,噪声降低,可以获得更好的气动性能和声学性能.
内埋武器舱关键气动及声学问题研究%Investigation on key aerodynamic and aeroacoustic problems of internal weapons bay
Institute of Scientific and Technical Information of China (English)
吴继飞; 罗新福; 徐来武; 范召林
2016-01-01
An experimental investigation was conducted in a high speed wind tunnel to ex-plore key aerodynamic and aeroacoustic problems of internal weapons bay.Steady pressure meas-urement,fluctuation pressure measurement and grid measurement were applied to obtain detailed characteristics of static pressure,fluctuating pressure and internal weapon aerodynamic in this experiment.Results indicated that flow types of internal weapons bay can be defined by the static pressure distributions on its floor.Aeroacoustic environment for open cavity flow is much worse than closed cavity flow,and the maximum sound pressure level can reach up to more than 170dB. Several tones of different modes can be found in the internal weapons bay sound pressure spectra. Internal weapon may occur large positive pitching moment during separating from the bay,and positive pitching moment is harmful to safe separation between fighter plane and weapons.Re-sults also indicated that mass-injection at the fore-edge of internal weapons bay can reduce static pressure gradient,suppress the intensity of noise and improve internal weapon’s aerodynamic separation characteristics.%以风洞试验为手段，在高速风洞中对内埋武器舱关键气动问题进行了深入研究。利用静态压力测量、脉动压力测量、网格测力等测试手段，获取了典型弹舱流场静压分布特性、气动声学特性以及武器分离特性。研究结果表明：舱内静压分布变化明显，可以此定义弹舱流场类型；开式弹舱流场气动声学环境恶劣，总声压级强度可达170dB 以上，且频谱曲线上存在多个明显的能量尖峰；武器从舱内分离过程中可能产生较大的抬头力矩，影响机/弹安全分离；在弹舱前缘施以流动控制能降低舱内静压梯度、抑制气动噪声，且有利于改善武器分离特性。
Carpenter, P. W.; Smith, C.
1997-12-01
The paper describes two studies of the effects of flow control devices on the aerodynamics and aeroacoustics of a high-speed Coanda flow that is formed when a supersonic jet issues from a radial nozzle and adheres to a tulip-shaped body of revolution. Shadowgraphy and other flow-visualization techniques are used to reveal the various features of the complex flow fields. The acoustic characteristics are obtained from far- and near-field measurements with an array of microphones in an anechoic chamber. First the effects of incorporating a step between the annular exit slot and the Coanda surface are investigated. The step is incorporated to ensure that the breakaway pressure is raised to a level well above the maximum operating pressure. It substantially increases the complexity of the flow field and acoustic characteristics. In particular, it promotes the generation of two groups of discrete tones. A theoretical model based on a self-generated feedback loop is proposed to explain how these tones are generated. The second study investigates the effects of replacing the annular exit slot with a saw-toothed one with the aim of eliminating the discrete tones and thereby substantially reducing the level of noise generated.
Spectral variance of aeroacoustic data
Rao, K. V.; Preisser, J. S.
1981-01-01
An asymptotic technique for estimating the variance of power spectra is applied to aircraft flyover noise data. The results are compared with directly estimated variances and they are in reasonable agreement. The basic time series need not be Gaussian for asymptotic theory to apply. The asymptotic variance formulae can be useful tools both in the design and analysis phase of experiments of this type.
Energy Technology Data Exchange (ETDEWEB)
Gustafson, D.E.; Hofmeister, W.H.; Bayuzick, R.J.; Nagashio, K.; Kuribayashi, K
2003-01-20
This paper presents the results of rapid solidification experiments performed on the copper oxide superconductors Y{sub x}Nd{sub 1-x}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} (0{<=}x{<=}0.9). Spherical rare earth (RE) 123 specimens were levitated in O{sub 2} using aero-acoustic levitation (AAL), melted with a laser, undercooled, and solidified. The peritectic transformation temperature for the reaction RE{sub 2}BaCuO{sub 5}+liquid{yields}REBa{sub 2}Cu{sub 3}O{sub 7-{delta}} corresponding to the maximum recalescence temperature during solidification was determined. RE123 was formed directly from the melt for Y-Nd binary alloy compositions with Nd concentration greater than 20% (Y concentration less than 80%). A minimum in the peritectic transformation temperature for the Nd/Y123 system corresponding to a composition Y{sub 0.3}Nd{sub 0.7}123 was determined at 66 deg. C below the peritectic of pure Nd123.
Institute of Scientific and Technical Information of China (English)
董帆; 陈启明; 于跃平
2013-01-01
To speed up the noise prediction of aeroacoustic sources,the retarded-time equation for a subsonic uniformly rotating point source was transformed into a simple and efficient one.A more accurate initial value estimation method based on the piecewise parabolic approximation of the trigonometric function was presented.Moreover,the Newton's method and the Halley's method were applied to solve the reformed retarded-time equation iteratively.The results show that the present initial value estimation method will reduce the computational time by 20％,and the Halley's method behaves better than the Newton's method in computation efficiency and convergence characteristics.%为提高气动噪声时域数值算法的计算速度,针对亚音速匀速圆周运动的点声源,将延迟时间方程的求解问题转化为求抛物线与余弦曲线的交点,转化后的方程形式简洁并且数值计算效率更高.使用分段二次函数对延迟时间方程中的余弦函数进行替换,得到一种新的高精度迭代初值计算方法,并分别采用Newton迭代和Halley迭代算法求解延迟时间方程.研究表明:相对于通常的固定初值给定法,所提出的分段二次近似迭代初值计算方法可以减少约20％的计算时间,且Halley迭代算法具有较好的计算效率和收敛特性.
Institute of Scientific and Technical Information of China (English)
苟湘; 夏冰; 连晶红; 尹业彬
2016-01-01
热交换器是供热系统乃至动力系统中常见的重要设备之一，其中汽水混合加热器是一种直接将蒸汽与水混合以加热水的热交换装置。利用宽频噪声源模型对喷管式汽水混合加热器进行气动噪声数值模拟，获得了加热器的声场分布。在相同工况下实验测量了加热器表面噪声声压级，模拟值与实验值相比，误差为4.6%，说明宽频噪声源模型在模拟混合加热器表面噪声声压级方面有较好的精度，对喷管式汽水混合加热器的降噪改进设计具有重要的参考价值。%Heat exchanger is one of the common and important equipment of heating systems and power systems.Steam-water mixing heater is a kind of heat transfer equipment,which heats water by directly mixing water and steam.The broadband noise source model was applied to numerically simulate the aeroacoustics of j et pipe steam-water mixing heater in this paper and accoustic field distribution was obtained.The surface accoustic pressure level of the heater was also measured experimentally under the same conditions.The error of the numerical predictions compared to the measurments is within 4.6%.It reveals that broadband noise source model has the better accuracy in respect of simulating the surface sound pressure level of mixing heater,which has an important reference value for improving the design of noise reduction of the j et pipe steam-water mixing heater.
Institute of Scientific and Technical Information of China (English)
刘翠伟; 李玉星; 王武昌; 谢祝祝
2014-01-01
为区分输气管道泄漏音波与阀门噪声，为输气管道音波法泄漏检测提供理论依据及数据库、控制阀门噪声提供解决办法，从音波产生机理角度采用CFD软件耦合专业声学软件方法对输气管道气体流经阀门产生的气动噪声进行研究，建立气动噪声模型，探究气动噪声产生机理及传播、衰减规律。在CFD（Computational Fluid Dynamics）软件中采用大涡湍流模型对气体流经阀门时的瞬态流场求解分析，获得流场分布如脉动压力、脉动速度数据；将CFD计算所得数据导入专业声学软件进行联合仿真，生成气动噪声源项，包括偶极子声源及四极子声源，建立气动噪声产生传播模型，求解输气管道气体流经阀门的气动噪声。%In order to distinguish leakage noise and valve noise,a theoretical basis and a database for leak detection and location based on acoustic method were provided and the method to control valve noise was introduced.The aero-noise induced by gas flow through valves in gas pipelines was studied from the view point of sound generation mechanism and an aero-noise model was built from which the rules governing the aero-noise generation,transmission and attenuation were concluded.The transient flow field with fluctuating pressure and fluctuating velocity was obtained with the help of large eddy simulation model by using computational fluid dynamics software when gas flows through valves in gas-pipelines.Then the data were imported into acoustic BEM software SYSNOISE to carry through numerical analysis,to generate noise source terms,including the dipole source and quadrupole source,to build the aero-noise model and finally to solve the aero-acoustics problems.
Aeroacoustic Analysis of a Simplified Landing Gear
Lockard, David P.; Khorrami, Mehdi, R.; Li, Fei
2004-01-01
A hybrid approach is used to investigate the noise generated by a simplified landing gear without small scale parts such as hydraulic lines and fasteners. The Ffowcs Williams and Hawkings equation is used to predict the noise at far-field observer locations from flow data provided by an unsteady computational fluid dynamics calculation. A simulation with 13 million grid points has been completed, and comparisons are made between calculations with different turbulence models. Results indicate that the turbulence model has a profound effect on the levels and character of the unsteadiness. Flow data on solid surfaces and a set of permeable surfaces surrounding the gear have been collected. Noise predictions using the porous surfaces appear to be contaminated by errors caused by large wake fluctuations passing through the surfaces. However, comparisons between predictions using the solid surfaces with the near-field CFD solution are in good agreement giving confidence in the far-field results.
Computational aeroacoustic study of a landing gear
Khanal, B.; Knowles, K.; Saddington, Alistair J.; Obayashi, S
2009-01-01
Computational study of a single wheel landing gear con guration was completed to understand the noise source and it's nature. The ow eld visualisation showed the present of large structural shedding in the wake side of the the landing gear wheel. These large structures were responsible for the low frequency noise. Spectral peaks at frequencies lower than 200 Hz were found to exist from the analysis of the frequency content of the pressure signals at far eld. These low freque...
Aeroacoustics of advanced STOVL aircraft plumes
Ahuja, K. K.; Spencer, D. A.
1988-01-01
This paper summarizes a basic and well-controlled experimental study involving flow visualization and noise measurements to define the acoustic and flow fields of single plumes impinging on a simulated ground plane. The flow visualization was made by strobing a laser light source at the discrete frequencies generated by the impingement of the jets and measured by a nearfield microphone. This enabled visualization of instability waves generated by the interaction between the plumes and the sound generated during impingement, and also by dynamic coupling between the two plumes. These data were acquired as a function of distance between the ground and the nozzle exit. Nearfield acoustic data were acquired simultaneously. Data for nozzle diameters of 0.265 in. and 0.4 in. are described. For selected nozzles, effects of exit boundary layer characteristics and nozzle protrusion through a simulated aircraft body are also presented.
Aeroacoustic computation of low Mach number flow
Energy Technology Data Exchange (ETDEWEB)
Dahl, K.S.
1996-12-01
This thesis explores the possibilities of applying a recently developed numerical technique to predict aerodynamically generated sound from wind turbines. The technique is a perturbation technique that has the advantage that the underlying flow field and the sound field are computed separately. Solution of the incompressible, time dependent flow field yields a hydrodynamic density correction to the incompressible constant density. The sound field is calculated from a set of equations governing the inviscid perturbations about the corrected flow field. Here, the emphasis is placed on the computation of the sound field. The nonlinear partial differential equations governing the sound field are solved numerically using an explicit MacCormack scheme. Two types of non-reflecting boundary conditions are applied; one based on the asymptotic solution of the governing equations and the other based on a characteristic analysis of the governing equations. The former condition is easy to use and it performs slightly better than the characteristic based condition. The technique is applied to the problems of the sound generation of a pulsating sphere, which is a monopole; a co-rotating vortex pair, which is a quadrupole, and the viscous flow over a circular cylinder, which is a dipole. The governing equations are written and solved for spherical, Cartesian, and cylindrical coordinates, respectively, thus, representing three common orthogonal coordinate systems. Numerical results agree very well with the analytical solutions for the problems of the pulsating sphere and the co-rotating vortex pair. Numerical results for the viscous flow over a cylinder are presented and evaluated qualitatively. The technique has potential for applications to airfoil flows as they are on a wind turbine blade, as well as for other low Mach number flows. (au) 2 tabs., 33 ills., 48 refs.
The Aeroacoustics of Turbulent Coanda Wall Jets
Lubert, Caroline; Fox, Jason
2007-11-01
Turbulent Coanda wall jets have become increasingly widely used in a variety of industrial applications in recent years, due to the substantial flow deflection that they afford. A related characteristic is the enhanced turbulence levels and entrainment they offer, compared with conventional jet flows. This characteristic is, however, generally accompanied by a significant increase in the noise levels associated with devices employing this effect. As a consequence, the potential offered by Coanda devices is yet to be fully realized. This problem provides the impetus for the research detailed in this poster. To date, some work has been done on developing a mathematical model of the Turbulent Mixing Noise emitted by such a device, assuming that the surface adjoining the turbulent flow was essentially 2-D. This poster extends this fundamental model, through a combination of mathematical modeling and acoustical and optical experiments. The effect of a variety of parameters, including nozzle configuration and jet exit velocity will be discussed, and ways of reducing or attenuating the noise generated by such flow, whilst still maintaining the crucial flow characteristics, will be presented.
Aero-Acoustic Computations of Wind Turbines
DEFF Research Database (Denmark)
Zhu, Wei Jun
2008-01-01
both for laminar and turbulent flows. Results have shown that sound generation is due to the unsteadiness of the flow field and the spectrum of sound has a strong relation with fluctuating forces on the solid body. Flow and acoustic simulation were also carried out for a wind turbine where general...
Aerodynamic and aeroacoustic for wind turbine
Energy Technology Data Exchange (ETDEWEB)
Mohamed, Maizi [Centre de Développement des Energies Renouvelables (cder). Alger (Algeria); Rabah, Dizene [Université des Sciences et de Technologie Haouari Boumdienne (USTHB). Alger (Algeria)
2015-03-10
This paper describes a hybrid approach forpredicting noise radiated from the rotating Wind Turbine (HAWT) blades, where the sources are extracted from an unsteady Reynolds-Averaged-Navier Stocks (URANS) simulation, ANSYS CFX 11.0, was used to calculate The near-field flow parameters around the blade surface that are necessary for FW-H codes. Comparisons with NREL Phase II experimental results are presented with respect to the pressure distributions for validating a capacity of the solver to calculate the near-field flow on and around the wind turbine blades, The results show that numerical data have a good agreement with experimental. The acoustic pressure, presented as a sum of thickness and loading noise components, is analyzed by means of a discrete fast Fourier transformation for the presentation of the time acoustic time histories in the frequency domain. The results convincingly show that dipole source noise is the dominant noise source for this wind turbine.
Aero-acoustic Computations of Wind Turbines
DEFF Research Database (Denmark)
Shen, Wen Zhong; Michelsen, Jess; Sørensen, Jens Nørkær
2002-01-01
A numerical algorithm for acoustic noise generation is extended to 3D flows. The approach involves two parts comprising a viscous incompressible flow part and an inviscid acoustic part. In order to simulate noise generated from a wind turbine, the incompressible and acoustic equations are written...
Aero-Acoustic Propulsion Lab (AAPL)
Federal Laboratory Consortium — This facility is an acoustically treated geodesic dome. The 130-ft-diameter dome is 65-ft high and acts as a noise barrier, protecting adjacent Glenn buildings and...
Aeroacoustic computation of low mach number flow
Energy Technology Data Exchange (ETDEWEB)
Skriver Dahl, K. [Risoe National Laboratory, Roskilde (Denmark)
1997-12-31
The possibilities of applying a recently developed numerical technique to predict aerodynamically generated sound from wind turbines is explored. The technique is a perturbation technique that has the advantage that the underlying flow field and the sound field are computed separately. Solution of the incompressible, time dependent flow field yields a hydrodynamic density correction to the incompressible constant density. The sound field is calculated from a set of equations governing the inviscid perturbations about the corrected flow field. Here, the emphasis is placed on the computation of the sound field. The nonlinear partial differential equations governing the sound fields are solved numerically using an explicit MacCormack scheme. Two types of non-reflecting boundary conditions are applied; one based on the asymptotic solution of the governing equations and the other based on a characteristic analysis of the governing equations. The former condition is easy to use and it performs slightly better than the charcteristic based condition. The technique is applied to the problems of the sound generation of a co-rotating vortex pair, which is a quadrupole, and the viscous flow over a circular cylinder, which is a dipole. Numerical results agree very well with the analytical solution for the problem of the co-rotating vortex pair. Numerical results for the viscous flow over a cylinder are presented and evaluated qualitatively. (au)
Institute of Scientific and Technical Information of China (English)
吉春辉; 刘战强
2011-01-01
高速面铣刀气动噪声由离散噪声与对总噪声影响较大的宽带噪声组成.针对高速面铣刀流场和声场的非定常特点,采用计算流体动力学(computational fluid dynamics,CFD)方法对面铣刀周围气流特性进行数值模拟,分析铣刀容屑槽区域的速度分布.计算线性欧拉方程(linear eulerequation,LEE)中的声源项确定铣刀表面声源位置及强度.通过应用基于Lighthill声学类比的Ffowcs Williams-Hawkings(FW-H)积分变换方程计算获得远场噪声.针对铣刀表面不同声源产生的气动噪声频谱进行分析,发现铣刀容屑槽及刀片前刀面是高速面铣刀气动噪声的主要声源.等距及不等距铣刀噪声频谱分析表明不等齿距布置可改变频谱声能分布,降低离散噪声的基频峰值,进而可降低铣刀气动总噪声.%The aeroacoustic noise generated in high speed face milling cutter consists of discrete noise and broadband noise contributing significantly to overall noise. A numerical simulation on air flow using computational fluid dynamics (CFD) method is developed through considering features of airflow and acoustic fields outside high speed face milling cutters. The airflow velocity distributions in the gullet region on milling cutter are analyzed. The locations and intensity of the sound source are obtained by computing the sound source item with the linear Euler equation. The sound pressure level is predicted using Ffowcs Williams- Hawkings (FW-H) formula based on the Lighthill's equation. The noise spectra of different sources on cutter surface show that the cutter gullet and the insert rake faces are the dominant noise sources. The comparisons of noise spectra generated in milling cutters with equally spaced inserts and cutters with unequally spaced inserts show that the use of unequally spaced inserts can alter the distribution of sound power and decrease the discrete noise peak value at the fundamental frequency, thus the overall noise
Physics Based Tool for Rotorcraft Computational Aeroacoustics Project
National Aeronautics and Space Administration — Reduction of noise is critical to the public acceptance and mission suitability of rotorcraft. Accurate prediction of rotorcraft noise is directly related to the...
Physics-based aeroacoustic modelling of bluff-bodies
Peers, Edward
2009-01-01
In this work physics-based modelling of bluff-body noise was performed with application to landing gear noise production. The landing gear is a primary contributor to airframe noise during approach. Noise is primarily generated from the unsteady pressures resulting from the turbulent flow around various components. The research was initiated in response to the need for an improved understanding of landing gear noise prediction tools. A computational approach was adopted so that the noise ...
Aeroacoustic control of landing gear noise using perforated fairings
Boorsma, Koen
2008-01-01
A study was performed to investigate and optimize the application of perforated fairings for landing gear noise control. The sparse knowledge about this new subject has necessitated a more fundamental study involving a basic fairing-strut configuration, followed by wind tunnel tests on a simplified landing gear configuration incorporating perforated fairings. For the basic configuration, various exchangeable perforated half-cylindrical shells shrouding a circular cylinder we...
Computational Aeroacoustics Using the Generalized Lattice Boltzmann Equation Project
National Aeronautics and Space Administration — The research proposed targets airframe noise (AFN) prediction and reduction. AFN originates from complex interactions of turbulent flow with airframe components...
An Aero-Acoustic Tool for Terminal Area Operations Project
National Aeronautics and Space Administration — In this highly interconnected world, transportation systems must feature increased flexibility and shorter door-to-door trip times to be successful. Shorter...
New formulation of Hardin-Pope equations for aeroacoustics
DEFF Research Database (Denmark)
Ekaterinaris, J.A.
1999-01-01
Dynamics, Vol. 6, No. 5-6, 1994, pp. 334-340). This method requires detailed information about the unsteady aerodynamic flowfield, which usually is obtained from a computational fluid dynamics solution. A new, conservative formulation of the equations governing acoustic disturbances is presented....... The conservative form of the governing equations is obtained after application of a transformation of variables that produces a set of inhomogeneous equations similar to the conservation-law form of the compressible Euler equations. The source term of these equations depends only on the derivatives...... of the hydrodynamic variables. Explicit time marching is performed. A high-order accurate, upwind-biased numerical scheme is used for numerical solution of the conservative equations. The convective fluxes are evaluated using upwind-biased formulas and flux-vector splitting. Solutions are obtained for the acoustic...
The Low Frequency Aeroacoustics of Buried Nozzle Systems
Taylor, M. V.; Crighton, D. G.; Cargill, A. M.
1993-05-01
A simplified model of a "buried nozzle" aeroengine system is considered. The primary flow issues into a co-annular flow within a mixing chamber, and then the co-annular flow issues into the ambient medium from a secondary nozzle. Within the mixing chamber only fine scale mixing takes place, and shear layers within the mixing chamber and downstream of the secondary nozzle are assumed to sustain large scale instability waves. Excitation of this system is provided by low frequency plane waves, incident from upstream on the primary nozzle (and emanating from combustion processes in the hot core of an aeroengine). The response of this system, in the acoustic far field and in the mixing chamber, is obtained analytically from the asymptotic solution, at low frequency, of model sub-problems the solutions of which determine the wave reflection and transmission processes at the primary and secondary nozzles. In these sub-problems the shear layers are represented by vortex sheets and the nozzle walls by semi-infinite circular ducts, with Kutta conditions imposed on the unsteady flow at the primary and secondary nozzle lips. Analytical descriptions are given of the various wave modes (quasi-plane acoustic waves, and instability waves localized on the primary and secondary shear layers), of the acoustic field strength and directivity (essentially monopole, dipole and quadrupole fields), and of the conditions under which near-resonant response may occur, with large amplitudes of the perturbations in the mixing chamber and in the acoustic field.
High-speed PIV analysis of trailing edge aeroacoustics
Pröbsting, S.; Serpieri, J.; Scarano, F.
2013-01-01
Tonal noise generated by airfoils observed at low to moderate Reynolds numbers is related to laminar boundary layer instabilities, which has lead to the term laminar boundary layer instability noise. The particular features of the acoustic spectrum have been discussed and a number of theories have b
Prediction of the Aero-Acoustic Performance of Open Rotors
VanZante, Dale; Envia, Edmane
2014-01-01
The rising cost of jet fuel has renewed interest in contrarotating open rotor propulsion systems. Contemporary design methods offer the potential to maintain the inherently high aerodynamic efficiency of open rotors while greatly reducing their noise output, something that was not feasible in the 1980's designs. The primary source mechanisms of open rotor noise generation are thought to be the front rotor wake and tip vortex interacting with the aft rotor. In this paper, advanced measurement techniques and high-fidelity prediction tools are used to gain insight into the relative importance of the contributions to the open rotor noise signature of the front rotor wake and rotor tip vortex. The measurements include three-dimensional particle image velocimetry of the intra-rotor flowfield and the acoustic field of a model-scale open rotor. The predictions provide the unsteady flowfield and the associated acoustic field. The results suggest that while the front rotor tip vortex can have a significant influence on the blade passing tone noise produced by the aft rotor, the front rotor wake plays the decisive role in the generation of the interaction noise produced as a result of the unsteady aerodynamic interaction of the two rotors. At operating conditions typical of takeoff and landing operations, the interaction noise level is easily on par with that generated by the individual rotors, and in some cases is even higher. This suggests that a comprehensive approach to reducing open rotor noise should include techniques for mitigating the wake of the front rotor as well as eliminating the interaction of the front rotor tip vortex with the aft rotor blade tip.
Research status on aero-acoustic noise from wind turbine blades
International Nuclear Information System (INIS)
This paper describes the noise mechanisms and categories of modern large wind turbine and main noise sources. Then the latest progresses in wind turbine noise researches are described from three aspects: noise prediction model, detection of noise sources by microphone array technique and methods for noise reduction. Although the turbine is restricted to horizontal axis wind turbines, the noise prediction model and reduction methods also can be applied to other turbines when the noise mechanisms are similar. Microphone array technique can be applied to locate any kind of noise sources
Computational Aero-Acoustic Using High-order Finite-Difference Schemes
DEFF Research Database (Denmark)
Zhu, Wei Jun; Shen, Wen Zhong; Sørensen, Jens Nørkær
2007-01-01
In this paper, a high-order technique to accurately predict flow-generated noise is introduced. The technique consists of solving the viscous incompressible flow equations and inviscid acoustic equations using a incompressible/compressible splitting technique. The incompressible flow equations are...... discretizations of the acoustic equations. The classical fourth-order Runge-Kutta time scheme is applied to the acoustic equations for time discretization....
National Aeronautics and Space Administration — Intelligent Light, the makers of the FIELDVIEW CFD post-processing software, in response to NASA SBIR Phase 1 solicitation, proposes an effort that addresses A2.10...
National Aeronautics and Space Administration — Intelligent Light, the makers of the FIELDVIEW CFD post-processing software, in response to NASA SBIR Phase 2 solicitation, proposes an effort that addresses A2.10...
Identification of Landing Gear Aeroacoustic Noise Sources with the Synthetic Array Technique Project
National Aeronautics and Space Administration — In this program, Innovative Technology Applications Company (ITAC), LLC and collaborators propose to advance "synthetic phased array" technology to improve...
Application of FUN3D Solver for Aeroacoustics Simulation of a Nose Landing Gear Configuration
Vatsa, Veer N.; Lockard, David P.; Khorrami, Mehdi R.
2011-01-01
Numerical simulations have been performed for a nose landing gear configuration corresponding to the experimental tests conducted in the Basic Aerodynamic Research Tunnel at NASA Langley Research Center. A widely used unstructured grid code, FUN3D, is examined for solving the unsteady flow field associated with this configuration. A series of successively finer unstructured grids has been generated to assess the effect of grid refinement. Solutions have been obtained on purely tetrahedral grids as well as mixed element grids using hybrid RANS/LES turbulence models. The agreement of FUN3D solutions with experimental data on the same size mesh is better on mixed element grids compared to pure tetrahedral grids, and in general improves with grid refinement.
Aeroacoustic Simulations of a Nose Landing Gear Using FUN3D on Pointwise Unstructured Grids
Vatsa, Veer N.; Khorrami, Mehdi R.; Rhoads, John; Lockard, David P.
2015-01-01
Numerical simulations have been performed for a partially-dressed, cavity-closed (PDCC) nose landing gear configuration that was tested in the University of Florida's open-jet acoustic facility known as the UFAFF. The unstructured-grid flow solver FUN3D is used to compute the unsteady flow field for this configuration. Mixed-element grids generated using the Pointwise(TradeMark) grid generation software are used for these simulations. Particular care is taken to ensure quality cells and proper resolution in critical areas of interest in an effort to minimize errors introduced by numerical artifacts. A hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) turbulence model is used for these simulations. Solutions are also presented for a wall function model coupled to the standard turbulence model. Time-averaged and instantaneous solutions obtained on these Pointwise grids are compared with the measured data and previous numerical solutions. The resulting CFD solutions are used as input to a Ffowcs Williams-Hawkings noise propagation code to compute the farfield noise levels in the flyover and sideline directions. The computed noise levels compare well with previous CFD solutions and experimental data.
Aeroacoustic Simulation of Nose Landing Gear on Adaptive Unstructured Grids With FUN3D
Vatsa, Veer N.; Khorrami, Mehdi R.; Park, Michael A.; Lockhard, David P.
2013-01-01
Numerical simulations have been performed for a partially-dressed, cavity-closed nose landing gear configuration that was tested in NASA Langley s closed-wall Basic Aerodynamic Research Tunnel (BART) and in the University of Florida's open-jet acoustic facility known as the UFAFF. The unstructured-grid flow solver FUN3D, developed at NASA Langley Research center, is used to compute the unsteady flow field for this configuration. Starting with a coarse grid, a series of successively finer grids were generated using the adaptive gridding methodology available in the FUN3D code. A hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) turbulence model is used for these computations. Time-averaged and instantaneous solutions obtained on these grids are compared with the measured data. In general, the correlation with the experimental data improves with grid refinement. A similar trend is observed for sound pressure levels obtained by using these CFD solutions as input to a FfowcsWilliams-Hawkings noise propagation code to compute the farfield noise levels. In general, the numerical solutions obtained on adapted grids compare well with the hand-tuned enriched fine grid solutions and experimental data. In addition, the grid adaption strategy discussed here simplifies the grid generation process, and results in improved computational efficiency of CFD simulations.
Aeroacoustic Simulation of a Nose Landing Gear in an Open Jet Facility Using FUN3D
Vatsa, Veer N.; Lockhard, David P.; Khorrami, Mehdi R.; Carlson, Jan-Renee
2012-01-01
Numerical simulations have been performed for a partially-dressed, cavity-closed nose landing gear configuration that was tested in NASA Langley s closed-wall Basic Aerodynamic Research Tunnel (BART) and in the University of Florida s open-jet acoustic facility known as UFAFF. The unstructured-grid flow solver, FUN3D, developed at NASA Langley Research center is used to compute the unsteady flow field for this configuration. A hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) turbulence model is used for these computations. Time-averaged and instantaneous solutions compare favorably with the measured data. Unsteady flowfield data obtained from the FUN3D code are used as input to a Ffowcs Williams-Hawkings noise propagation code to compute the sound pressure levels at microphones placed in the farfield. Significant improvement in predicted noise levels is obtained when the flowfield data from the open jet UFAFF simulations is used as compared to the case using flowfield data from the closed-wall BART configuration.
Directory of Open Access Journals (Sweden)
Luís M. B. C. Campos
2015-02-01
Full Text Available Air traffic is growing at a steady rate of 3% to 5% per year in most regions of the world, implying a doubling every 15–25 years. This requires major advances in aircraft noise reduction at airports, just not to increase the noise exposure due to the larger number of aircraft movements. In fact it can be expected, as a consequence of increased opposition to noise by near airport residents, that the overall noise exposure will have to be reduced, by bans, curfews, fines, and other means and limitations, unless significantly quieter aircraft operations are achieved. The ultimate solution is aircraft operations inaudible outside the airport perimeter, or noise levels below road traffic and other existing local noise sources. These substantial noise reductions cannot come at the expense of a degradation of cruise efficiency, that would affect not just economics and travel time, but would increase fuel consumption and emission of pollutants on a global scale. The paper reviews the: (i current knowledge of the aircraft noise sources; (ii the sound propagation in the atmosphere and ground effects that determine the noise annoyance of near-airport residents; (iii the noise mitigation measures that can be applied to current and future aircraft; (iv the prospects of evolutionary and novel aircraft designs towards quieter aircraft in the near term and eventually to operations inaudible outside the airport perimeter. The 20 figures and 1 diagram with their legends provide a visual summary of the review.
Luís M. B. C. Campos
2015-01-01
Air traffic is growing at a steady rate of 3% to 5% per year in most regions of the world, implying a doubling every 15–25 years. This requires major advances in aircraft noise reduction at airports, just not to increase the noise exposure due to the larger number of aircraft movements. In fact it can be expected, as a consequence of increased opposition to noise by near airport residents, that the overall noise exposure will have to be reduced, by bans, curfews, fines, and other means and li...
Specific features of a stopped pipe blown by a turbulent jet: Aeroacoustics of the panpipes.
Auvray, Roman; Fabre, Benoît; Meneses, Felipe; de la Cuadra, Patricio; Lagrée, Pierre-Yves
2016-06-01
Flute-like instruments with a stopped pipe were widely used in ancient cultures and continue to be used in many musical expressions throughout the globe. They offer great flexibility in the input control parameters, allowing for large excursions in the flux and in the geometrical configuration for the lips of the instrumentalist. For instance, the transverse offset of the jet axis relative to the labium can be shifted beyond the operational limits found in open-open pipes, and the total jet flux can be increased up to values that produce highly turbulent jets while remaining on the first oscillating regime. Some of the fundamental aspects of the acoustics and hydrodynamics of this kind of instrument are studied, like the instability of the jet wave and the static aerodynamic balance in the resonator. A replica of an Andean siku has been created to observe, through the Schlieren flow visualization, the behavior of both excitation and resonator of the instrument. PMID:27369145
Towards a generic non-reflective characteristic boundary condition for aeroacoustic simulations
Fattah, Ryu; Gill, James; Zhang, Xin
2016-01-01
A blended zonal characteristic boundary condition is proposed following a quantita- tive investigation of the performance of several non-reflective boundary conditions. Two test cases are considered that investigate the effects of acoustic and vortical plane waves impinging on the domain outflow region. A third test case investigates the effects of broad- band turbulent flow impinging on a non-reflective outflow boundary condition. From these studies, two non-reflective boundar...
DEFF Research Database (Denmark)
Fischer, Andreas
2011-01-01
blades makes a transition from laminar to turbulent. In the turbulent boundary layer eddies are created which are a potential noise sources. They are ineffective as noise source on the airfoil surface or in free flow, but when convecting past the trailing edge of the airfoil their efficiency is much......The present work aims at the characterization of aerodynamic noise from wind turbines. There is a consensus among scientists that the dominant aerodynamic noise mechanism is turbulent boundary trailing edge noise. In almost all operational conditions the boundary layer flow over the wind turbine...... increased and audible sound is radiated. We performed measurements of the boundary layer velocity fluctuations and the fluctuating surface pressure field in two different wind tunnels and on three different airfoils. The first wind tunnel is the one of LM Wind Power A/S following the classic concept...
Turner, Travis L. (Inventor); Kidd, Reggie T. (Inventor); Lockard, David P (Inventor); Khorrami, Mehdi R. (Inventor); Streett, Craig L. (Inventor); Weber, Douglas Leo (Inventor)
2016-01-01
A slat cove filler is utilized to reduce airframe noise resulting from deployment of a leading edge slat of an aircraft wing. The slat cove filler is preferably made of a super elastic shape memory alloy, and the slat cove filler shifts between stowed and deployed shapes as the slat is deployed. The slat cove filler may be configured such that a separate powered actuator is not required to change the shape of the slat cove filler from its deployed shape to its stowed shape and vice-versa. The outer contour of the slat cove filler preferably follows a profile designed to maintain accelerating flow in the gap between the slat cove filler and wing leading edge to provide for noise reduction.
3D flow organization and dynamics in subsonic jets: Aeroacoustic source analysis by tomographic PIV
Violato, D.V.
2013-01-01
To meet the increasingly stringent noise regulation, aircraft manufacturers are searching for solutions to jet noise. This, which constitutes a significant amount of the total noise emitted by civil aircrafts, is generated by the mixing processes between the exhaust flow leaving the engine and the a
Three-dimensional vortex analysis and aeroacoustic source characterization of jet core breakdown
Violato, D.; Scarano, F.
2013-01-01
The three-dimensional behavior of jet core breakdown is investigated with experiments conducted on a free water jet at Re = 5000 by time-resolved tomographic particle image velocimetry (TR-TOMO PIV). The investigated domain encompasses the range between 0 and 10 jet diameters. The characteristic pul
Aero-acoustic Measurement and Monitoring of Dynamic Pressure Fields Project
National Aeronautics and Space Administration — This innovative and practical measurement and monitoring system optimally defines dynamic pressure fields, including sound fields. It is based on passive acoustic...
A Comparison of Computational Aeroacoustic Prediction Methods for Transonic Rotor Noise
Brentner, Kenneth S.; Lyrintzis, Anastasios; Koutsavdis, Evangelos K.
1996-01-01
This paper compares two methods for predicting transonic rotor noise for helicopters in hover and forward flight. Both methods rely on a computational fluid dynamics (CFD) solution as input to predict the acoustic near and far fields. For this work, the same full-potential rotor code has been used to compute the CFD solution for both acoustic methods. The first method employs the acoustic analogy as embodied in the Ffowcs Williams-Hawkings (FW-H) equation, including the quadrupole term. The second method uses a rotating Kirchhoff formulation. Computed results from both methods are compared with one other and with experimental data for both hover and advancing rotor cases. The results are quite good for all cases tested. The sensitivity of both methods to CFD grid resolution and to the choice of the integration surface/volume is investigated. The computational requirements of both methods are comparable; in both cases these requirements are much less than the requirements for the CFD solution.
Practical computational aeroacoustics for compact surfaces in low mach number flows
DEFF Research Database (Denmark)
Pradera-Mallabiabarrena, Ainara; Keith, Graeme; Jacobsen, Finn;
2011-01-01
Sound generation has been widely studied using numerical hybrid methods. The aim of this paper is to introduce a flexible procedure where the acoustic source data may be synthesized and stored from commercially available Computational Fluid Dynamics (CFD) codes and later used to predict radiated ...
Aero-Acoustic Optimization of the Fans and Cooling Circuit on Sncf's X 72500 Railcar
CLEON, L.-M.; WILLAIME, A.
2000-03-01
This paper presents the results of studies concerning the fans on SNCF's X 72500 railcar with a view to reducing the level of ambient noise. The paper first describes the operation of an axial fan and then the main sources of noise generated by this type of fan. The interactions between acoustic emissions and mass output are then described to illustrate the advantages of an acoustic and pneumatic predictive device. Finally, a new design of axial wheel on the SNCF railcar is described which has reduced the acoustic emission by 10 db whilst still improving the initial ventilation performance.
Aeroacoustics of Flight Vehicles: Theory and Practice. Volume 2: Noise Control
Hubbard, Harvey H. (Editor)
1991-01-01
Flight vehicles and the underlying concepts of noise generation, noise propagation, noise prediction, and noise control are studied. This volume includes those chapters that relate to flight vehicle noise control and operations: human response to aircraft noise; atmospheric propagation; theoretical models for duct acoustic propagation and radiation; design and performance of duct acoustic treatment; jet noise suppression; interior noise; flyover noise measurement and prediction; and quiet aircraft design and operational characteristics.
Computational Aero-Acoustic Using High-order Finite-Difference Schemes
Zhu, Wei Jun; Shen, Wen Zhong; Sørensen, Jens Nørkær
2007-01-01
In this paper, a high-order technique to accurately predict flow-generated noise is introduced. The technique consists of solving the viscous incompressible flow equations and inviscid acoustic equations using a incompressible/compressible splitting technique. The incompressible flow equations are solved using the in-house flow solver EllipSys2D/3D which is a second-order finite volume code. The acoustic solution is found by solving the acoustic equations using high-order finite difference sc...
DEFF Research Database (Denmark)
Pradera-Mallabiabarrena, Ainara; Jacobsen, Finn; Svendsen, Christian;
2013-01-01
The purpose of this paper is to demonstrate that a recently published methodology for predicting flow generated noise by compact surfaces under free-field conditions [1] can be extended to a different and more complex configuration of industrial interest. In the previous paper, the methodology wa...
Tonon, D.; Moers, E.M.T.; Golliard, J.; Hirschberg, A.
2012-01-01
Acoustical dampers are used in order to avoid the noise propagation. Well known examples are the aero-engine liners, the IC-engine exhaust muffers, and the liners in combustion chambers. These devices comprise wall perforations, responsible for their sound absorbing features. Understanding the effec
DEFF Research Database (Denmark)
Si, Haiqing; Shen, Wen Zhong; Zhu, Wei Jun
2013-01-01
Acoustic propagation in the presence of a non-uniform mean flow is studied numerically by using two different acoustic propagating models, which solve linearized Euler equations (LEE) and acoustic perturbation equations (APE). As noise induced by turbulent flows often propagates from near field t...
In Search of the Physics: The Interplay of Experiment and Computation in Slat Aeroacoustics
Khorrami, Mehdi R.; Choudhari, Meelan; Singer, Bart A.; Lockard, David P.; Streett, Craig L.
2003-01-01
The synergistic use of experiments and numerical simulations can uncover the underlying physics of airframe noise sources. We focus on the high-lift noise component associated with a leading-edge slat; flap side-edge noise is discussed in a companion paper by Streett et al. (2003). The present paper provides an overview of how slat noise was split into subcomponents and analyzed with carefully planned complementary experimental and numerical tests. We consider both tonal and broadband aspects of slat noise. The predicted far-field noise spectra are shown to be in good qualitative (and, to lesser extent, good quantitative agreement) with acoustic array measurements. Although some questions remain unanswered, the success of current airframe noise studies provides ample promise that remaining technical issues can be successfully addressed in the near future.
Aeroacoustic Calculations of Wind Turbine Noise with the Actuator Line/ Navier-Stokes Technique
DEFF Research Database (Denmark)
Debertshäuser, Harald; Shen, Wen Zhong; Zhu, Wei Jun
2016-01-01
Noise regulations in many countries are becoming extremely strict and wind turbine noise is thus becoming a barrier for further development of onshore wind turbines. Low noise wind turbine airfoil and blade design is an important technique for noise reduction. However, the ow situation of a wind ...
National Aeronautics and Space Administration — ATA Engineering, Inc. proposes an STTR program to develop innovative tools and methods that will significantly improve the accuracy of random vibration response...
Implicit Higher Order Temporal Differencing for Aeroacoustic and CFD Applications Project
National Aeronautics and Space Administration — This proposal presents a stand-alone implicit high order temporal differencing solver concept that will interface with research and commercial numerical analysis...
Benchmark Data for Evaluation of Aeroacoustic Propagation Codes With Grazing Flow
Jones, Michael G.; Watson, Willie R.; Parrott, Tony L.
2005-01-01
Increased understanding of the effects of acoustic treatment on the propagation of sound through commercial aircraft engine nacelles is a requirement for more efficient liner design. To this end, one of NASA s goals is to further the development of duct propagation and impedance reduction codes. A number of these codes have been developed over the last three decades. These codes are typically divided into two categories: (1) codes that use the measured complex acoustic pressure field to reduce the acoustic impedance of treatment that is positioned along the wall of the duct, and (2) codes that use the acoustic impedance of the treatment as input and compute the sound field throughout the duct. Clearly, the value of these codes is dependent upon the quality of the data used for their validation. Over the past two decades, data acquired in the NASA Langley Research Center Grazing Incidence Tube have been used by a number of researchers for comparison with their propagation codes. Many of these comparisons have been based upon Grazing Incidence Tube tests that were conducted to study specific liner technology components, and were incomplete for general propagation code validation. Thus, the objective of the current investigation is to provide a quality data set that can be used as a benchmark for evaluation of duct propagation and impedance reduction codes. In order to achieve this objective, two parallel efforts have been undertaken. The first of these is the development of an enhanced impedance eduction code that uses data acquired in the Grazing Incidence Tube. This enhancement is intended to place the benchmark data on as firm a foundation as possible. The second key effort is the acquisition of a comprehensive set of data selected to allow propagation code evaluations over a range of test conditions.
Numerical Simulation of the Oscillations in a Mixer: An Internal Aeroacoustic Feedback System
Jorgenson, Philip C. E.; Loh, Ching Y.
2004-01-01
The space-time conservation element and solution element method is employed to numerically study the acoustic feedback system in a high temperature, high speed wind tunnel mixer. The computation captures the self-sustained feedback loop between reflecting Mach waves and the shear layer. This feedback loop results in violent instabilities that are suspected of causing damage to some tunnel components. The computed frequency is in good agreement with the available experimental data. The physical phenomena are explained based on the numerical results.
Large-Eddy Simulation of the Aerodynamic and Aeroacoustic Performance of a Ventilation Fan
Directory of Open Access Journals (Sweden)
Stefano Bianchi
2013-01-01
Full Text Available There are controversial requirements involved in developing numerical methodologies in order to compute the flow in industrial fans. The full resolution of turbulence spectrum in such high-Reynolds number flow configurations entails unreasonably expensive computational costs. The authors applied the study to a large unidirectional axial flow fan unit for tunnel ventilation to operate in the forward direction under ambient conditions. This delivered cooling air to the tunnel under routine operation, or hot gases at 400∘C under emergency conditions in the event of a tunnel fire. The simulations were carried out using the open source code OpenFOAM, within which they implemented a very large eddy simulation (VLES based on one-equation SGS model to solve a transport equation for the modelled (subgrid turbulent kinetic energy. This subgrid turbulence model improvement is a remedial strategy in VLES of high-Reynolds number industrial flows which are able to tackle the turbulence spectrum’s well-known insufficient resolution. The VLES of the industrial fan permits detecting the unsteady topology of the rotor flow. This paper explores the evolution of secondary flow phenomena and speculates on its influence on the actual load capability when operating at peak-pressure condition. Predicted noise emissions, in terms of sound pressure level spectra, are also compared with experimental results and found to agree within the uncertainty of the measurements.
A Hybrid approach for aeroacoustic analysis of the engine exhaust system
Sathyanarayana, Y; Munjal, ML
2000-01-01
This paper presents a new hybrid approach for prediction of noise radiation from engine exhaust systems. It couples the time domain analysis of the engine and the frequency domain analysis of the muffler, and has the advantages of both. In this approach, cylinder/cavity is analyzed in the time domain to calculate the exhaust mass flux history at the exhaust valve by means of the method of characteristics, avoiding the tedious procedure of interpolation at every mesh point and solving a number...
Aero-acoustic simulation of a subsonic hot jet; Simulation aeroacoustique d'un jet chaud subsonique
Energy Technology Data Exchange (ETDEWEB)
Biancherin, A.; Rahier, G.; Prieur, J.; Vuillot, F.; Lupoglazoff, N.
2002-07-01
This paper presents a numerical simulation of subsonic a hot jet (M 0,7) and its acoustic analysis. The MSD code of the ONERA is used to resolve the Navier-Stokes equations. A detailed study, parametric and theoretical is realized to analyze the influence of the formulation, the position, the part and the nature of the control surface on the acoustic calculation results. The acoustic predictions in far field are compared to measures realized by the ONERA in the anechoic CEPRA 19 wind tunnel. (A.L.B.)
International Nuclear Information System (INIS)
Operating wind turbines generate tonal and broadband noises affecting the living environment adversely; especially small wind turbines located in the vicinity of human living places. Therefore, it is important to determine the level of noise pollution of such type of wind turbine installation. The current study carries out numerical prediction for aerodynamic noise radiated from an H-Darrieus Vertical Axis Wind Turbine. Incompressible LES (Large Eddy Simulation) is conducted to obtain the instantaneous turbulent flow field. The noise predictions are performed by the Ffowcs Williams and Hawkings (FW–H) acoustic analogy formulation. Simulations are performed for five different tip-speed ratios. First, the mean torque coefficient is compared with the experimental data, and good agreement is observed. Then, the research focuses on the broadband noises of the turbulent boundary layers and the tonal noises due to blade passing frequency. The contribution of the thickness, loading and quadrupole noises are investigated, separately. The results indicate a direct relation between the strength of the radiated noise and the rotational speed. Furthermore, the effect of receiver distance on the OASPL (Overall Sound Pressure Level) is investigated. It is concluded that the OASPL varies with a logarithmic trend with the receiver distance as it was expected. - Highlights: • Large Eddy Simulation has been used to predict the turbulent flow field. • The Ffowcs Williams and Hawkings method was employed to predict radiated noise. • There is a direct relation between the radiated noise and the tip speed ratio. • The quadrupole noises have negligible effect on the tonal noises
Directory of Open Access Journals (Sweden)
Renzo Arina
2016-02-01
Full Text Available The propagation of small perturbations in complex geometries can involve hydrodynamic-acoustic interactions, coupling acoustic waves and vortical modes. A propagation model, based on the linearized Navier–Stokes equations, is proposed. It includes the mechanism responsible for the generation of vorticity associated with the hydrodynamic modes. The linearized Navier–Stokes equations are discretized in space using a discontinuous Galerkin formulation for unstructured grids. Explicit time integration and non-reflecting boundary conditions are described. The linearized Navier–Stokes (LNS model is applied to two test cases. The first one is the time-harmonic source line in an incompressible inviscid two-dimensional mean shear flow in an infinite domain. It is shown that the proposed model is able to capture the trailing vorticity field developing behind the mass source and to represent the redistribution of the vorticity. The second test case deals with the analysis of the acoustic propagation of an incoming perturbation inside a circular duct with a sudden area expansion in the presence of a mean flow and the evaluation of its scattering matrix. The computed coefficients of the scattering matrix are compared to experimental data for three different Mach numbers of the mean flow, M0 = 0.08, 0.19 and 0.29. The good agreement with the experimental data shows that the proposed method is suitable for characterizing the acoustic behavior of this kind of network.
Moore, P.D.
2009-01-01
Jet noise is an extensively studied phenomenon since the deployment of the first civil jet aircraft more than 50 years ago. Jet noise makes up a considerable portion of the total noise of jet aircraft, and the expansion of the numbers of airplanes and airports has only been possible by keeping the
Analysis-Driven Design Optimization of a SMA-Based Slat-Cove Filler for Aeroacoustic Noise Reduction
Scholten, William; Hartl, Darren; Turner, Travis
2013-01-01
Airframe noise is a significant component of environmental noise in the vicinity of airports. The noise associated with the leading-edge slat of typical transport aircraft is a prominent source of airframe noise. Previous work suggests that a slat-cove filler (SCF) may be an effective noise treatment. Hence, development and optimization of a practical slat-cove-filler structure is a priority. The objectives of this work are to optimize the design of a functioning SCF which incorporates superelastic shape memory alloy (SMA) materials as flexures that permit the deformations involved in the configuration change. The goal of the optimization is to minimize the actuation force needed to retract the slat-SCF assembly while satisfying constraints on the maximum SMA stress and on the SCF deflection under static aerodynamic pressure loads, while also satisfying the condition that the SCF self-deploy during slat extension. A finite element analysis model based on a physical bench-top model is created in Abaqus such that automated iterative analysis of the design could be performed. In order to achieve an optimized design, several design variables associated with the current SCF configuration are considered, such as the thicknesses of SMA flexures and the dimensions of various components, SMA and conventional. Designs of experiment (DOE) are performed to investigate structural response to an aerodynamic pressure load and to slat retraction and deployment. DOE results are then used to inform the optimization process, which determines a design minimizing actuator forces while satisfying the required constraints.
Taddeucci, J.; Sesterhenn, J.; Scarlato, P.; Stampka, K.; Del Bello, E.; Pena Fernandez, J. J.; Gaudin, D.
2014-05-01
High-speed imaging of explosive eruptions at Stromboli (Italy), Fuego (Guatemala), and Yasur (Vanuatu) volcanoes allowed visualization of pressure waves from seconds-long explosions. From the explosion jets, waves radiate with variable geometry, timing, and apparent direction and velocity. Both the explosion jets and their wave fields are replicated well by numerical simulations of supersonic jets impulsively released from a pressurized vessel. The scaled acoustic signal from one explosion at Stromboli displays a frequency pattern with an excellent match to those from the simulated jets. We conclude that both the observed waves and the audible sound from the explosions are jet noise, i.e., the typical acoustic field radiating from high-velocity jets. Volcanic jet noise was previously quantified only in the infrasonic emissions from large, sub-Plinian to Plinian eruptions. Our combined approach allows us to define the spatial and temporal evolution of audible jet noise from supersonic jets in small-scale volcanic eruptions.
Roger, Michel; Schram, Christophe; Moreau, Stéphane
2014-01-01
A linear analytical model is developed for the chopping of a cylindrical vortex by a flat-plate airfoil, with or without a span-end effect. The major interest is the contribution of the tip-vortex produced by an upstream rotating blade in the rotor-rotor interaction noise mechanism of counter-rotating open rotors. Therefore the interaction is primarily addressed in an annular strip of limited spanwise extent bounding the impinged blade segment, and the unwrapped strip is described in Cartesian coordinates. The study also addresses the interaction of a propeller wake with a downstream wing or empennage. Cylindrical vortices are considered, for which the velocity field is expanded in two-dimensional gusts in the reference frame of the airfoil. For each gust the response of the airfoil is derived, first ignoring the effect of the span end, assimilating the airfoil to a rigid flat plate, with or without sweep. The corresponding unsteady lift acts as a distribution of acoustic dipoles, and the radiated sound is obtained from a radiation integral over the actual extent of the airfoil. In the case of tip-vortex interaction noise in CRORs the acoustic signature is determined for vortex trajectories passing beyond, exactly at and below the tip radius of the impinged blade segment, in a reference frame attached to the segment. In a second step the same problem is readdressed accounting for the effect of span end on the aerodynamic response of a blade tip. This is achieved through a composite two-directional Schwarzschild's technique. The modifications of the distributed unsteady lift and of the radiated sound are discussed. The chained source and radiation models provide physical insight into the mechanism of vortex chopping by a blade tip in free field. They allow assessing the acoustic benefit of clipping the rear rotor in a counter-rotating open-rotor architecture.
Aeroacoustic study of landing gear by detached eddy simulation%基于分离涡模拟的起落架气动噪声研究
Institute of Scientific and Technical Information of China (English)
胡宁; 郝璇; 苏诚; 张卫民; 马汉东
2015-01-01
用基于 SA 湍流模式的非定常 RANS、分离涡模拟（DES）和延迟分离涡模拟（DDES）分别对四轮基本起落架模型进行了数值模拟，并根据所得的非定常流场计算了表面声压级分布和声压谱。三种方法所用的时间成本大致相同，URANS 略低于其它两种，而 DDES 由于在附着流动区更好地保持 RANS 特性，故时间成本略低于 DES。计算显示，非定常 RANS 在附着流动区能够得到合理的结果，但不能准确刻画分离流动的流动形态。DES 和DDES 都能较好地刻画起落架绕流的定常和非定常特性，DDES 的结果略好于 DES。因为起落架流动属于大分离流动，所以 DES 也能够得到相对正确的结果。研究结果验证了分离涡模拟在起落架大分离非定常流动预测与噪声预测中的可行性，对减小起落架噪声的方法研究具有一定的意义。%A four-wheel rudimentary landing gear is studied numerically by unsteady RANS (URANS),detached eddy simulation (DES)and delayed detached eddy simulation (DDES) based on the Spalart-Allmaras turbulence model.The surface sound pressure level and sound pressure spectra are calculated using the obtained unsteady flow field.The 3 methods cost ap-proximately the same time,with URANS slightly lower than the other two.DDES uses slightly less time than DES since it retains RANS mode in attached flow region.The investigation shows that URANS can give reasonable results in the attached flow region but cannot describe correctly the flow pattern in the detached flow.Both DES and DDES can describe the steady and unsteady properties in the flow around rudimentary landing gear.DDES is slightly superior over DES,and DES can also give reasonable results since the flow around the landing gear is a massive separated flow.The results prove the feasibility of DES type methods in massive separated unsteady flow field and aerodynamic noise prediction for landing gear,and can be used in the study of landing gear noise reduction.
Magliozzi, B.; Hanson, D. B.
1991-01-01
An analysis of tone noise propagation through a boundary layer and fuselage scattering effects was derived. This analysis is a three dimensional and the complete wave field is solved by matching analytical expressions for the incident and scattered waves in the outer flow to a numerical solution in the boundary layer flow. The outer wave field is constructed analytically from an incident wave appropriate to the source and a scattered wave in the standard Hankel function form. For the incident wave, an existing function - domain propeller noise radiation theory is used. In the boundary layer region, the wave equation is solved by numerical methods. The theoretical analysis is embodied in a computer program which allows the calculation of correction factors for the fuselage scattering and boundary layer refraction effects. The effects are dependent on boundary layer profile, flight speed, and frequency. Corrections can be derived for any point on the fuselage, including those on the opposite side from the source. The theory was verified using limited cases and by comparing calculations with available measurements from JetStar tests of model prop-fans. For the JetStar model scale, the boundary layer refraction effects produce moderate fuselage pressure reinforcements aft of and near the plane of rotation and significant attenuation forward of the plane of rotation at high flight speeds. At lower flight speeds, the calculated boundary layer effects result in moderate amplification over the fuselage area of interest. Apparent amplification forward of the plane of rotation is a result of effective changes in the source directivity due to boundary layer refraction effects. Full scale effects are calculated to be moderate, providing fuselage pressure amplification of about 5 dB at the peak noise location. Evaluation using available noise measurements was made under high-speed, high-altitude flight conditions. Comparisons of calculations made of free field noise, using a current frequency-domain propeller noise prediction method, and fuselage effects using this new procedure show good agreement with fuselage measurements over a wide range of flight speeds and frequencies. Correction factors for the JetStar measurements made on the fuselage are provided in an Appendix.
Koschatzky, V.
2011-01-01
This thesis deals with the problem of noise. Sound is a constant presence in our lives. Most of the times it is something wanted and it serves a purpose, such as communication through speech or entertainment by listening to music. On the other hand, quite often sound is an annoying and unwanted by-p
Aeroacoustic scattering via the fast scattering method%变截面风扇管道快速声散射计算
Institute of Scientific and Technical Information of China (English)
王同庆; 张莉爽; 杨兵; 杨明绥
2011-01-01
针对航空发动机消声短舱声学设计的需要,发展了一种结合快速声散射和直接边界元计算发动机远场声散射的方法,用于计算包含了壁面声阻抗影响的复杂截面管道声散射问题.应用该方法针对某风扇实验台进行了管道消声的数值模拟,得到了远场声散射结果,进行了声衬声阻抗影响的计算,并通过与文献结果的对比表明该方法具有工程应用价值.%The fast scattering method was developed in this paper, which could be used for predicting the acoustic propagation problems in the varying cross-section ducts with the acoustic liners. The method can handle the complex section relatively easily by using the direct boundary element method. The noise reduction of a real fan with the duct liners was predicted. The influence of the liner impedance and the sound scattering from the moving body was investigated by comparing the results with those given in the literature. The results illustrate that the present method can be used for the design of the duct liner in the engineerlng.
Turner, Travis L.; Kidd, Reggie T.; Hartl, Darren J.; Scholten, William D.
2013-01-01
Airframe noise is a significant part of the overall noise produced by typical, transport-class aircraft during the approach and landing phases of flight. Leading-edge slat noise is a prominent source of airframe noise. The concept of a slat-cove filler was proposed in previous work as an effective means of mitigating slat noise. Bench-top models were deployed at 75% scale to study the feasibility of producing a functioning slat-cove filler. Initial results from several concepts led to a more-focused effort investigating a deformable structure based upon pseudoelastic SMA materials. The structure stows in the cavity between the slat and main wing during cruise and deploys simultaneously with the slat to guide the aerodynamic flow suitably for low noise. A qualitative parametric study of SMA-enabled, slat-cove filler designs was performed on the bench-top. Computational models were developed and analyses were performed to assess the displacement response under representative aerodynamic load. The bench-top and computational results provide significant insight into design trades and an optimal design.
Institute of Scientific and Technical Information of China (English)
许远; 龙双丽; 薛彩军; 聂宏
2012-01-01
起落架噪声是飞机着陆阶段噪声的主要组成部分。以某型飞机前起落架为研究对象，通过分离涡模拟方法对其支柱及扭力臂结构件简化模型的周围流场进行非定常计算，利用Fw—H方程积分法对各部件表面产生的声场进行求解，分析缓冲支柱及扭力臂结构件气动噪声的产生机制、声源特性。对该飞机起落架支柱及扭力臂结构件进行声学风洞试验，通过麦克风对噪声的测量获得结构件噪声频谱特性。仿真及试验结果均表明：支柱及扭力臂结构件气动噪声包含支柱和扭力臂引起的钝体扰流噪声和两者相对位置引起的干扰噪声，支柱噪声对总噪声的贡献大于扭力臂噪声，噪声辐射特性具有偶极子声源的辐射特性。%Aircrafts' noise produced by landing gears is the main noise in the landing stage. Simulation analysis using Detached Eddy Simulation is performed to simulate the flow field around the simplified structure including the strut and torque link of an aircraft's nose landing gear. The acoustic field radiated from different model parts and total model are calculated via FW-H equation. The noise mechanism and acoustic characteristics of the noise from the structure are analyzed. Wind tunnel test is performed to measure the noise spectra of the structure by microphones. The simulation and experiment results show that the noise of the assembly of strut and torque link include bluff body and interaction noise. Noise from the strut has greater contribution to total noise than that from the torque link. The whole model noise radiation direetivity is similar to the dipole characteristics.
National Aeronautics and Space Administration — An aeroacoustic computational code based upon a numerical solution of the full Navier-Stokes equations will be developed to provide a deep understanding of the...
Phased array technique for low signal-to-noise ratio wind tunnels Project
National Aeronautics and Space Administration — Closed wind tunnel beamforming for aeroacoustics has become more and more prevalent in recent years. Still, there are major drawbacks as current microphone arrays...
Flow induced pulsations in pipe systems
Bruggeman, Jan Cornelis
1987-12-01
The aeroacoustic behavior of a low Mach number, high Reynolds number flow through a pipe with closed side branches was investigated. Sound is generated by coherent structures of concentrated vorticity formed periodically in the separated flow in the T-shaped junctions of side branches and the main pipe. The case of moderate pulsation amplitudes was investigated. It appears that the vortical flow in a T-joint is an aeroacoustic source of constant strength when acoustic energy losses due to radiation and friction are small but not negligible. When acoustic energy losses due to radiation and friction are negligible, the nonlinear character of vortex damping is the amplitude limiting mechanism. It is stressed that aeroacoustic sources should not be neglected in studies of the response of a piping lay-out with flow to, e.g., the pulsating output of a compressor.
Compressive sensing beamforming based on covariance for acoustic imaging with noisy measurements.
Zhong, Siyang; Wei, Qingkai; Huang, Xun
2013-11-01
Compressive sensing, a newly emerging method from information technology, is applied to array beamforming and associated acoustic applications. A compressive sensing beamforming method (CSB-II) is developed based on sampling covariance matrix, assuming spatially sparse and incoherent signals, and then examined using both simulations and aeroacoustic measurements. The simulation results clearly show that the proposed CSB-II method is robust to sensing noise. In addition, aeroacoustic tests of a landing gear model demonstrate the good performance in terms of resolution and sidelobe rejection.
Overview of the Testing of a Small-Scale Proprotor
Young, Larry A.; Yamauchi, Gloria K.; Booth, Earl R., Jr.; Botha, Gavin; Dawson, Seth
1999-01-01
This paper presents an overview of results from the wind tunnel test of a 1/4-scale V-22 proprotor in the Duits-Nederlandse Windtunnel (DNW) in The Netherlands. The small-scale proprotor was tested on the isolated rotor configuration of the Tilt Rotor Aeroacoustic Model (TRAM). The test was conducted by a joint team from NASA Ames, NASA Langley, U.S. Army Aeroflightdynamics Directorate, and The Boeing Company. The objective of the test was to acquire a benchmark database for validating aeroacoustic analyses. Representative examples of airloads, acoustics, structural loads, and performance data are provided and discussed.
Young, L. A.; Lillie, D.; McCluer, M.; Yamauchi, G. K.; Derby, M. R.
2001-01-01
A recent experimental investigation into tiltrotor aerodynamics and acoustics has resulted in the acquisition of a set of data related to tiltrotor airframe aerodynamics and rotor and wing interactional aerodynamics. This work was conducted in the National Full-scale Aerodynamics Complex's (NFAC) 40-by-80 Foot Wind Tunnel, at NASA Ames Research Center, on the Full-Span Tilt Rotor Aeroacoustic Model (TRAM). The full-span TRAM wind tunnel test stand is nominally based on a quarter-scale representation of the V-22 aircraft. The data acquired will enable the refinement of analytical tools for the prediction of tiltrotor aeromechanics and aeroacoustics.
Experimental investigation of the source locations for whistling short corrugated pipes
Golliard, J.; Tonon, D.; Belfroid, S.P.C.
2010-01-01
The goal of this study is to investigate the issue of the aeroacoustic source location within corrugated pipes. A configuration with a short pipe and well defined boundary conditions has been chosen, in order to have a precise knowledge of the distribution of the acoustic velocity and pressure withi
Numerical Studies on a Rotor with Distributed Suction for Noise Reduction
Lutz, Thorsten; Arnold, Benjamin; Wolf, Alexander; Krämer, Ewald
2014-06-01
Minimizing the flow-induced noise is an important issue in the design of modern onshore wind turbines. There is a number of proven passive means to reduce the aeroacoustic noise, such as the implementation of serrations, porous trailing edges or the aeroacoustic airfoil design. The noise emission can be further reduced by active flow control techniques. In the present study the impact of distributed boundary layer suction on the noise emission of an airfoil and a complete rotor is investigated. Aerodynamic and aeroacoustic wind tunnel tests were performed for the NACA 64-418 airfoil and supplemented by numerical calculations. The aeroacoustic analyses have been conducted by means of the institute's Rnoise prediction scheme. The 2D studies have shown that noise reductions of 5 dB can be achieved by suction at moderate mass flow rates. To study the impact of three-dimensional effects numerical investigations have been conducted on the example of the generic NREL 5MW rotor with suction applied in the outer part of the blade. The predictions for the complete rotor provided smaller benefits compared to those for the isolated airfoil, mainly because the examined suction configurations were not optimized with respect to the extent of the suction patch and suction distribution.
Airfoil noise computation use high-order schemes
DEFF Research Database (Denmark)
Zhu, Wei Jun; Shen, Wen Zhong; Sørensen, Jens Nørkær
2007-01-01
High-order finite difference schemes with at least 4th-order spatial accuracy are used to simulate aerodynamically generated noise. The aeroacoustic solver with 4th-order up to 8th-order accuracy is implemented into the in-house flow solver, EllipSys2D/3D. Dispersion-Relation-Preserving (DRP...
Design of low noise wind turbine blades using Betz and Joukowski concepts
DEFF Research Database (Denmark)
Shen, Wen Zhong; Hrgovan, Iva; Okulov, Valery;
2014-01-01
This paper presents the aerodynamic design of low noise wind turbine blades using Betz and Joukowski concepts. The aerodynamic model is based on Blade Element Momentum theory whereas the aeroacoustic prediction model is based on the BPM model. The investigation is started with a 3MW baseline/refe...
The effects of viscosity on sound radiation near solid surfaces
DEFF Research Database (Denmark)
Morfey, C.L.; Sorokin, Sergey; Gabard, G.
2012-01-01
Although the acoustic analogy developed by Lighthill, Curle, and Ffowcs Williams and Hawkings for sound generation by unsteady flow past solid surfaces is formally exact, it has become accepted practice in aeroacoustics to use an approximate version in which viscous quadrupoles are neglected. Her...
Wind Tunnel Measurements at Virginia Tech
DEFF Research Database (Denmark)
Fischer, Andreas; Bertagnolio, Franck
2012-01-01
In this section, the wind tunnel configuration used for aerodynamic and aeroacoustic measurement is described. Then, the validation of the method for evaluating far-field noise from surface microphones as described in Section 5 is presented. Finally, the design concept proposed in Section 6...
Wind Tunnel Measurements at Virginia Tech
Fischer, Andreas; Bertagnolio, Franck
2012-01-01
In this section, the wind tunnel configuration used for aerodynamic and aeroacoustic measurement is described. Then, the validation of the method for evaluating far-field noise from surface microphones as described in Section 5 is presented. Finally, the design concept proposed in Section 6 is verified.
On the use of Particle Image Velocimetry to predict trailing edge noise
Tuinstra, M.; Probsting, S.; Scarano, F.
2013-01-01
The feasibility of aeroacoustic noise predictions based on Particle Image Velocimetry (PIV) measurements is studied. For this purpose, experiments are conducted on a sharp trailing edge (TE) flow developed along a flat plate at free stream velocity of 15m/s. The acoustic emissions were characterized
Unsteady computational fluid dynamics in aeronautics
Tucker, P G
2014-01-01
The field of Large Eddy Simulation (LES) and hybrids is a vibrant research area. This book runs through all the potential unsteady modelling fidelity ranges, from low-order to LES. The latter is probably the highest fidelity for practical aerospace systems modelling. Cutting edge new frontiers are defined. One example of a pressing environmental concern is noise. For the accurate prediction of this, unsteady modelling is needed. Hence computational aeroacoustics is explored. It is also emerging that there is a critical need for coupled simulations. Hence, this area is also considered and the tensions of utilizing such simulations with the already expensive LES. This work has relevance to the general field of CFD and LES and to a wide variety of non-aerospace aerodynamic systems (e.g. cars, submarines, ships, electronics, buildings). Topics treated include unsteady flow techniques; LES and hybrids; general numerical methods; computational aeroacoustics; computational aeroelasticity; coupled simulations and...
Simulation of the noise transmission through automotive door seals
Hazir, Andreas
2016-01-01
Andreas Hazir is investigating the door seal contribution to the interior noise level of production vehicles. These investigations contain experimental contribution analyses of real production vehicles and of academic test cases as well as the development of a simulation methodology for noise transmission through sealing systems and side windows. The simulations are realized by coupling transient computational aeroacoustics of the exterior flow to nonlinear finite element simulations of the structural transmission. By introducing a linear transmission model, the setup and computational costs of the seal noise transmission are significantly reduced, resulting in the feasibility of numerical contribution analyses of real production vehicles. Contents Contribution Analyses of Production Vehicles Acoustic Excitation versus Aeroacoustic Excitation Development of a Simulation Methodology Sensitivity Analysis of Noise Transmission Simulations Target Groups Researchers and students in the field of automotive engineer...
Modeling of wind turbine noise sources and propagation in the atmosphere
Tian, Yuan
2016-01-01
The purpose of this work is to model wind turbine noise sources and propagation in the atmosphere in order to better understand the characteristics of wind turbine noise at long range and to help wind turbine manufacturers and wind farm developers meet the noise regulations. By coupling physically-based aeroacoustic source and propagation models, we are able to predict wind turbine noise spectra, directivity and amplitude modulation in various atmospheric conditions. Amiet's analytical model ...
Younsi, Mohand
2007-01-01
Forward centrifugal fans are widely used in several applications. These fans are characterized by highly detached complex flows and a weak aerodynamic efficiency. This thesis concerns the numerical prediction and the implementation of an experimental analysis of the unsteady flow and the aeroacoustic behavior of forward centrifugal fans. This work consists of numerical simulation of the internal unsteady flow in these fans. The numerical simulations based on the URANS approach have been carri...
The Reduction of Ducted Fan Engine Noise Via a Boundary Integral Equation Method
Tweed, John
2000-01-01
Engineering studies for reducing ducted fan engine noise were conducted using the noise prediction code TBIEM3D. To conduct parametric noise reduction calculations, it was necessary to advance certain theoretical and computational aspects of the boundary integral equation method (BIEM) described in and implemented in TBIEM3D. Also, enhancements and upgrades to TBIEM3D were made for facilitating the code's use in this research and by the aeroacoustics engineering community.
New Fan Engine Noise-Reduction Concept Using Trailing Edge Blowing of Fan Blades Demonstrated
Heidelberg, Laurence J.
2002-01-01
A major source of noise in commercial turbofan engines is the interaction of the fan blade wakes with the fan exit vanes (stators). These wakes can be greatly reduced by filling them with air blown out of the blade trailing edge. Extensive testing of this concept has demonstrated significant noise reductions. These tests were conducted on a low-speed, 4- ft-diameter fan using hollow blades at NASA Glenn Research Center's Aeroacoustic Propulsion Laboratory (AAPL).
Analytical reconstruction of isotropic turbulence spectra based on the Gaussian transform
Wohlbrandt, Attila; Hu, Nan; Guerin, Sebastien; Ewert, Roland
2015-01-01
The Random Particle Mesh (RPM) method used to simulate turbulence-induced broadband noise in several aeroacoustic applications is extended to realise isotropic turbulence spectra. With this method turbulent fluctuations are synthesised by filtering white noise with a Gaussian filter kernel that in turn gives a Gaussian spectrum. The Gaussian function is smooth and its derivatives and integrals are again Gaussian functions. The Gaussian filter is efficient and finds wide-spread applications in...
ONERA. 1997 scientific and technical activities; ONERA. Activites scientifiques et techniques 1997
Energy Technology Data Exchange (ETDEWEB)
Vuillot, F.; Lupoglazoff, N.; Dupays, J.; Basset, Th.; Daniel, E. [Universite de Provence, 13 - Marseille (France); Devincre, B.; Veyssiere, P.; Kubin, L.; Saada, G. [ONERA, CNRS,LEM (France); Hertl, M.; Dorval, N.; Jolly, J. [ONERA-CNRS, Laboratoire Plasmas Reactifs en Interactions avec les Materiaux (France); Thierry, G.; Guillen, Ph.; Prieur, J.; Lewy, S.; Nastasi, V.; Lerat, A.; Sides, J.; Gely, D.; Chanetz, B.; Pot, T.; Jacquin, L.; Geffroy, P.; Merienne, M.C.; Mebarki, Y.; Reijasse, P.; Corbel, B.; Reijasse, P.; Murer, Y.; Millan, P.; Pauzin, S.; Reulet, P.; Coustols, E.; Sauvage, Ph.; Bissieres, D.; Estivalezes, J.L.; Lavergne, G.; Casalis, G.; Troff, B.; Thivet, F.; Moschetta, J.M.; Deniau, H.; Grondin, G.; Grenon, R.; Bettschart, N.; Gardarein, P.; Moens, F.; Costes, M.; Gaveriaux, R.; Flodrops, J.P.; Paquet, J.B.; Leplat, M.; Sgarzi, O.; Zamuner, B.; Moreau, P.; Collin, G.; Magre, P.; Duterque, J.; Hommel, J.; Masson, C.; Forconi, H.; Fradin, C.; Roehle, I.; Hervat, P.; Soucail, M.; Octor, H.; Marty, M.; Dorvaux, J.M.; Lavigne, O.; Mevrel, R.; Poulain, M.; Lapasset, G.; Morel, A.; Naka, S.; Sanchez, C.; Thomas, M.; Krapez, J.C.; Lepoutre, F.; Balageas, D.; Chaboche, J.L.; Jung, O.; Deletombe, E.; Malherbe, B.; Ousset, Y.; Sudre, O.; Parlier, M.; Guichet, B.; Bretheau, T.; Kruch, S.; Vassel, A.; Boust, F.; Flavin, E.; Petot, D.; Rapin, M.; Morvan, A.; Lebihan, D.; Petitjean, B.; Leconte, P.; Grisval, J.P.; Sauvignet, C.; Johan, Z.; Loiseau, A.; Lesturgie, M.; Martineau, P.; Titin-Schnaider, C.; Vieillard, G.; Dreuillet, P.; Castelli, J.C.; Lacour, D.; Ferriere, X.; Bonnet, P.; Gobin, V.; Alliot, J.C.; Grisch, F.; Labrune, L.; Larigaldie, S.; Ory, M.; Lalande, P.; Bondiou-Clegerie, A.; Kayser, P.; Deyrac, F.; Le Traon, O.; Besson, C.; Serrot, G.; Bodilis, M.; Duffaut, J.; Conan, J.M.; Mugnier, L.; Michau, V.; Fusco, T.; Madec, P.Y.; Rousset, G.; Simoneau, P.; Barillot, Ph.; Dolfi, A.; Robineau, J.; Mugnier, L.; Cassaing, F.; Rousset, G.; and others
1997-12-31
The ONERA is the first French research office in the aerospace domain. This annual report summarizes the main research studies carried out by the different ONERA departments in 1997 in the domains of fluid mechanics and energetics (numerical simulation, aero-acoustics, aerodynamics, propellants, propulsion systems), materials and structures (metals and processes, solid mechanics, material testing, composite materials and systems, structure dynamics, microstructures), physics (space environment, electromagnetism and radars, physical measurements, optics), data processing and systems, and technical means. (J.S.)
INDUSTRIAL CFD SIMULATION OF AERODYNAMIC NOISE
Caridi, Domenico
2008-01-01
Real challenges to suppress undesirable fluid-excited acoustics are posed by a wide variety of engineering disciplines. Noise regulations, passenger comfort and component stability are motivators which are continuing to stimulate substantial efforts towards the understanding of aeroacoustic phenomena, and not least to quantify the usability (practicability and value) of traditional and advanced prediction methods. The latter is the primary focus of this thesis, particularly as applied to the ...
Accurate Finite Difference Algorithms
Goodrich, John W.
1996-01-01
Two families of finite difference algorithms for computational aeroacoustics are presented and compared. All of the algorithms are single step explicit methods, they have the same order of accuracy in both space and time, with examples up to eleventh order, and they have multidimensional extensions. One of the algorithm families has spectral like high resolution. Propagation with high order and high resolution algorithms can produce accurate results after O(10(exp 6)) periods of propagation with eight grid points per wavelength.
Optimization Design and Experimental Study of Low-Pressure Axial Fan with Forward-Skewed Blades
Li Yang; Ouyang Hua; Du Zhao-Hui
2007-01-01
This paper presents an experimental study of the optimization of blade skew in low pressure axial fan. Using back propagation (BP) neural network and genetic algorithm (GA), the optimization was performed for a radial blade. An optimized blade is obtained through blade forward skew. Measurement of the two blades was carried out in aerodynamic and aeroacoustic performance. Compared to the radial blade, the optimized blade demonstrated improvements in efficiency, total pres...
Leveraging Windows Workflow Foundation for Scientific Workflows in Wind Tunnel Applications
Paventhan, A.; Takeda, Kenji; Cox, Simon J.; Nicole, Denis A.
2006-01-01
Scientific and engineering experiments often produce large volumes of data that must be processed and visualised in near-realtime. An example of this, described in this paper, is microphone array processing of data from wind tunnels for aeroacoustic measurements. The overall turnaround time from data acquisition and movement, to data processing and visualization is often inhibited by factors such as manual data movement, system interoperability issues, manual resource discovery for job schedu...
On the use of Particle Image Velocimetry to predict trailing edge noise
Tuinstra, M.; Probsting, S.; Scarano, F.
2013-01-01
The feasibility of aeroacoustic noise predictions based on Particle Image Velocimetry (PIV) measurements is studied. For this purpose, experiments are conducted on a sharp trailing edge (TE) flow developed along a flat plate at free stream velocity of 15m/s. The acoustic emissions were characterized in the NLR Small Anechoic Wind Tunnel (KAT) by means of microphone measurements. The result is used for benchmarking the PIV based noise predictions. PIV measurements were carried in a low-speed w...
The development of technologies and devices for protection from noise generated by power equipment
Mikhailov, V. E.; Khomenok, L. A.; Yablonik, L. R.
2010-01-01
The main lines of currently conducted research and development activities on suppressing noise produced by power-generating equipment are presented. Matters related to preventing the occurrence of aeroacoustic self-excited vibrations, optimizing dissipative noise silencers, using structural methods for damping acoustic vibrations, suppressing low-frequency noise, and analyzing the effectiveness of soundproof coatings are considered. The process diagrams and parameters of devices for suppressing noise generated during discharge into the atmosphere of high-pressure gaseous media are discussed.
On the role of glottis-interior sources in the production of voiced sound
Howe, M. S.; McGowan, R. S.
2012-01-01
The voice source is dominated by aeroacoustic sources downstream of the glottis. In this paper an investigation is made of the contribution to voiced speech of secondary sources within the glottis. The acoustic waveform is ultimately determined by the volume velocity of air at the glottis, which is controlled by vocal fold vibration, pressure forcing from the lungs, and unsteady backreactions from the sound and from the supraglottal air jet. The theory of aerodynamic sound is applied to study...
Optimisation multidisciplinaire de pales d'hélice d'avion
Marinus, Benoît
2011-01-01
Open rotors are known to have significant advantages in terms of propulsive efficiency. These advantages translate directly in reduced fuel burn so that they nowadays benefit from a surge of interest. At the same time, recent advances in numerical simulations make the application of multidisciplinary optimization for the demanding design of transonic propeller blades, an affordable option. Therefore, an optimization method in which the performance objectives of aerodynamics, aeroacoustics and...
International Nuclear Information System (INIS)
The variational Riemann problem (VRP) is defined as the first variation of the solution to Riemann's initial-value problem, also known as the problem of breakup of an arbitrary discontinuity in a gas, when the initial data undergo small variations. We show that the solution to the VRP can be analytically obtained, provided that the solution to the baseline Riemann problem is known. This solution describes the interaction of two abutting parcels of small disturbances against the background of a given base flow and therefore can be efficiently implemented in numerical methods for aeroacoustics. When the spatial distribution of disturbances and base flow parameters are given at a time moment at mesh points of a computational grid, one can exactly determine the disturbance evolution for a short lapse of time by solving the VRP at mesh interfaces. This can then be applied to update disturbance values to a new time moment by using the standard finite-volume scheme. In other words, the VRP can be used in computational aeroacoustics in the similar way to the Riemann problem used in Godunov-type methods for computational fluid dynamics. The present paper elaborates on this idea and adopts the solution to the VRP as a building block for a finite-volume Godunov-type method for aeroacoustics
USAGE OF PRESSURE OSCILLATIONS OF FLUCTUATING GAS FLOW FOR HANDLING OF 40X HARDENED STEEL SAMPLES
Directory of Open Access Journals (Sweden)
E. E. Il'ina
2016-07-01
Full Text Available Subject of Research. The paper deals with experience in the use of advanced technology of aeroacoustic treatment of materials for impact toughness improvement of the 40X type constructional steel samples. The method is based on the influence of pulsating air stream with oscillating shock-wave structures on the sample. As a result, the so-called Maxwell's waves are generated in the sample, that can lead to a beneficial transformation in the micro- and substructure and also in the phase structure of hardened steels. Obtained changes may be enough to improve impact toughness and decrease the residual stresses that arise in the course of previous treatments. Distortion of components decreases in this case, and failure probability becomes lower at the further treatment and operation. The advantage of technology is elimination of the additional heat treatment, for example, of the relaxation annealing that serves to reduce the residual stresses. This can be useful, particularly, for the preservation of high hardness and wear resistance, obtained by hardening and low-temperature tempering (about 200 ° C, as the relaxation annealing has typically a higher temperature and will result in their reduction. The toughness increase of the samples is assumed as an indicator of the positive impact of the considered treatment. Main Results. We have defined characteristics and modes of experimental acoustic transducer implementing the aeroacoustic processing. Experiments have been carried out on the impact assessment of aeroacoustic effects on the toughness of widely used 40X type steel. The obtained results enable to suggest that the application of aeroacoustic treatment for samples hardened by heat treatment leads to the toughness increasing of the investigated material. In this case an increased value of hardness obtained after heat treatment is maintained. Practical Relevance. The results supplement previously obtained experimental data for aeroacoustic
A Comparative Study of a 1/4-Scale Gulfstream G550 Aircraft Nose Gear Model
Khorrami, Mehdi R.; Neuhart, Dan H.; Zawodny, Nikolas S.; Liu, Fei; Yardibi, Tarik; Cattafesta, Louis; Van de Ven, Thomas
2009-01-01
A series of fluid dynamic and aeroacoustic wind tunnel experiments are performed at the University of Florida Aeroacoustic Flow Facility and the NASA-Langley Basic Aerodynamic Research Tunnel Facility on a high-fidelity -scale model of Gulfstream G550 aircraft nose gear. The primary objectives of this study are to obtain a comprehensive aeroacoustic dataset for a nose landing gear and to provide a clearer understanding of landing gear contributions to overall airframe noise of commercial aircraft during landing configurations. Data measurement and analysis consist of mean and fluctuating model surface pressure, noise source localization maps using a large-aperture microphone directional array, and the determination of far field noise level spectra using a linear array of free field microphones. A total of 24 test runs are performed, consisting of four model assembly configurations, each of which is subjected to three test section speeds, in two different test section orientations. The different model assembly configurations vary in complexity from a fully-dressed to a partially-dressed geometry. The two model orientations provide flyover and sideline views from the perspective of a phased acoustic array for noise source localization via beamforming. Results show that the torque arm section of the model exhibits the highest rms pressures for all model configurations, which is also evidenced in the sideline view noise source maps for the partially-dressed model geometries. Analysis of acoustic spectra data from the linear array microphones shows a slight decrease in sound pressure levels at mid to high frequencies for the partially-dressed cavity open model configuration. In addition, far field sound pressure level spectra scale approximately with the 6th power of velocity and do not exhibit traditional Strouhal number scaling behavior.
Landing gear noise prediction using high-order finite difference schemes
Liu, W.; Kim, J. W.; Zhang, X; Angland, D.; BASTIEN, C
2012-01-01
Aerodynamic noise from a generic two-wheel landing-gear model is predicted by a CFD/FW-H hybrid approach. The unsteady flow-field is computed using a compressible Navier–Stokes solver based on high-order finite difference schemes and a fully structured grid. The calculated time history of the surface pressure data is used in an FW-H solver to predict the far-field noise levels. Both aerodynamic and aeroacoustic results are compared to wind tunnel measurements and are found to be in good agree...
Determination of HART I Blade Structural Properties by Laboratory Testing
Jung, Sung N.; Lau, Benton H.
2012-01-01
The structural properties of higher harmonic Aeroacoustic Rotor Test (HART I) blades were measured using the original set of blades tested in the German-dutch wind tunnel (DNW) in 1994. the measurements include bending and torsion stiffness, geometric offsets, and mass and inertia properties of the blade. the measured properties were compared to the estimated values obtained initially from the blade manufacturer. The previously estimated blade properties showed consistently higher stiffness, up to 30 percent for the flap bending in the blade inboard root section.
Wind energy department: Scientific and technical progress 1999 - 2000
Energy Technology Data Exchange (ETDEWEB)
Skrumsager, B.; Larsen, G. [eds.
2001-01-01
The activities of the Wind Energy Department fall within boundary layer meteorology, atmospheric turbulence, aerodynamics, aero-acoustics, structural dynamics, machine and construction technology and design of power systems and power system controls. The objective is to develop methods for design; test and siting of wind turbines; prediction of wind loads and wind resources as well as methods to determine the dispersion, transformation and effect of air pollution. The present report describes the organisation of the department and presents selected scientific highlights and results from the two-year period 1999-2000. (au)
The effect of acoustic forcing on an airfoil tonal noise mechanism.
Schumacher, Karn L; Doolan, Con J; Kelso, Richard M
2014-08-01
The response of the boundary layer over an airfoil with cavity to external acoustic forcing, across a sweep of frequencies, was measured. The boundary layer downstream of the cavity trailing edge was found to respond strongly and selectively at the natural airfoil tonal frequencies. This is considered to be due to enhanced feedback. However, the shear layer upstream of the cavity trailing edge did not respond at these frequencies. These findings confirm that an aeroacoustic feedback loop exists between the airfoil trailing edge and a location near the cavity trailing edge.
"Ladder" structure in tonal noise generated by laminar flow around an airfoil.
Chong, Tze Pei; Joseph, Phillip
2012-06-01
The presence of a "ladder" structure in the airfoil tonal noise was discovered in the 1970s, but its mechanism hitherto remains a subject of continual investigation in the research community. Based on the measured noise results and some numerical analysis presented in this letter, the variations of four types of airfoil tonal noise frequencies with the flow velocity were analyzed individually. The ladder structure is proposed to be caused by the acoustic/hydrodynamic frequency lag between the scattering of the boundary layer instability noise and the discrete noise produced by an aeroacoustic feedback loop.
Wind energy department: Scientific and technical progress 1999 - 2000
International Nuclear Information System (INIS)
The activities of the Wind Energy Department fall within boundary layer meteorology, atmospheric turbulence, aerodynamics, aero-acoustics, structural dynamics, machine and construction technology and design of power systems and power system controls. The objective is to develop methods for design; test and siting of wind turbines; prediction of wind loads and wind resources as well as methods to determine the dispersion, transformation and effect of air pollution. The present report describes the organisation of the department and presents selected scientific highlights and results from the two-year period 1999-2000. (au)
Analysis and modeling of infrasound from a four-stage rocket launch.
Blom, Philip; Marcillo, Omar; Arrowsmith, Stephen
2016-06-01
Infrasound from a four-stage sounding rocket was recorded by several arrays within 100 km of the launch pad. Propagation modeling methods have been applied to the known trajectory to predict infrasonic signals at the ground in order to identify what information might be obtained from such observations. There is good agreement between modeled and observed back azimuths, and predicted arrival times for motor ignition signals match those observed. The signal due to the high-altitude stage ignition is found to be low amplitude, despite predictions of weak attenuation. This lack of signal is possibly due to inefficient aeroacoustic coupling in the rarefied upper atmosphere. PMID:27369137
Analysis and modeling of infrasound from a four-stage rocket launch.
Blom, Philip; Marcillo, Omar; Arrowsmith, Stephen
2016-06-01
Infrasound from a four-stage sounding rocket was recorded by several arrays within 100 km of the launch pad. Propagation modeling methods have been applied to the known trajectory to predict infrasonic signals at the ground in order to identify what information might be obtained from such observations. There is good agreement between modeled and observed back azimuths, and predicted arrival times for motor ignition signals match those observed. The signal due to the high-altitude stage ignition is found to be low amplitude, despite predictions of weak attenuation. This lack of signal is possibly due to inefficient aeroacoustic coupling in the rarefied upper atmosphere.
A 3-D discontinuous Galerkin Method for jet engine buzz-saw noise propagation
International Nuclear Information System (INIS)
This paper presents a 3-D methodology for solving jet engine aero-acoustics problems in the presence of strong shocks and rarefactions. For example, turbofan engines suffer from Multiple Pure Tone noise, also called Buzz-saw noise, generated by the fan when the blade rotational tip speed is supersonic. These waves are composed of a series of shocks and rarefactions produced by a coalescence of shocks due to non-uniformities in the blade spacing and in the blade stagger angles, arising from manufacturing tolerances
AERODYNAMIC SOUND OF A BODY IN ARBITRARY, DEFORMABLE MOTION, WITH APPLICATION TO PHONATION
Howe, M. S.; McGowan, R. S.
2013-01-01
The method of tailored Green’s functions advocated by Doak (Proceedings of the Royal Society A254 (1960) 129 – 145.) for the solution of aeroacoustic problems is used to analyse the contribution of the mucosal wave to self-sustained modulation of air flow through the glottis during the production of voiced speech. The amplitude and phase of the aerodynamic surface force that maintains vocal fold vibration are governed by flow separation from the region of minimum cross-sectional area of the g...
Seung Heo; Cheolung Cheong; Taehoon Kim
2015-01-01
In this study, efficient numerical method is proposed for predicting tonal and broadband noises of a centrifugal fan unit. The proposed method is based on Hybrid Computational Aero-Acoustic (H-CAA) techniques combined with Unsteady Fast Random Particle Mesh (U-FRPM) method. The U-FRPM method is developed by extending the FRPM method proposed by Ewert et al. and is utilized to synthesize turbulence flow field from unsteady RANS solutions. The H-CAA technique combined with U-FRPM method is appl...
Several rotor noise sources and treatments
Energy Technology Data Exchange (ETDEWEB)
Tangler, J. [National Renewable Energy Laboratory, Golden, CO (United States)
1997-12-31
Noise has been a design consideration in the development of advanced blades and turbines at the National Renewable Energy Laboratory. During atmospheric testing associated with these efforts various types of aeroacoustic noise have been encountered. This presentation discusses several of these noise sources and treatments used to mitigate or eliminate the noise. Tonal noise resulting from tip-vortex/trailing-edge interaction and laminar separation bubbles was found to be easily eliminated. Impulsive noise resulting from blade/vortex interaction for rotors that furl and that due to tower shadow can be mitigated by various means. (au)
Hempert, F.; Hoffmann, M.; Iben, U.; Munz, C.-D.
2016-06-01
In the present investigation, we demonstrate the capabilities of the discontinuous Galerkin spectral element method for high order accuracy computation of gas dynamics. The internal flow field of a natural gas injector for bivalent combustion engines is investigated under its operating conditions. The simulations of the flow field and the aeroacoustic noise emissions were in a good agreement with the experimental data. We tested several shock-capturing techniques for the discontinuous Galerkin scheme. Based on the validated framework, we analyzed the development of the supersonic jets during different opening procedures of a compressed natural gas injector. The results suggest that a more gradual injector opening decreases the noise emission.
Fares, Ehab; Duda, Benjamin; Khorrami, Mehdi R.
2016-01-01
Unsteady flow computations are presented for a Gulfstream aircraft model in landing configuration, i.e., flap deflected 39deg and main landing gear deployed. The simulations employ the lattice Boltzmann solver PowerFLOW(Trademark) to simultaneously capture the flow physics and acoustics in the near field. Sound propagation to the far field is obtained using a Ffowcs Williams and Hawkings acoustic analogy approach. Two geometry representations of the same aircraft are analyzed: an 18% scale, high-fidelity, semi-span model at wind tunnel Reynolds number and a full-scale, full-span model at half-flight Reynolds number. Previously published and newly generated model-scale results are presented; all full-scale data are disclosed here for the first time. Reynolds number and geometrical fidelity effects are carefully examined to discern aerodynamic and aeroacoustic trends with a special focus on the scaling of surface pressure fluctuations and farfield noise. An additional study of the effects of geometrical detail on farfield noise is also documented. The present investigation reveals that, overall, the model-scale and full-scale aeroacoustic results compare rather well. Nevertheless, the study also highlights that finer geometrical details that are typically not captured at model scales can have a non-negligible contribution to the farfield noise signature.
Survey of CFD studies on automotive buffeting
International Nuclear Information System (INIS)
In the current automobile market buffeting is one of the customer frequent complaints on luxury cars and SUVs. Buffeting is a low frequency but high level wind noise and makes people inside the vehicle uncomfortable if it lasts for a long period of time. The physical mechanism of buffeting is a complicated phenomenon of aeroacoustic resonance. The aeroacoustic characteristics of buffeting depend on vehicle features and operating conditions. In this paper, a survey of CFD studies on the automotive buffeting is presented. Firstly, several buffeting related concepts, such as Helmholtz resonator, flow over a cavity, shear layer instability and vortex shedding, are reviewed and relevant references are listed. Then, a historic survey of the buffeting investigation is made with emphasis on computational studies. As an example, the buffeting studies at DaimlerChrysler are selected to demonstrate the procedure of CFD simulation for automotive buffeting. The procedure is then validated by the correlation with wind tunnel testing. After that the validated procedure is applied to find solutions for buffeting reduction. Finally, some comments on buffeting studies are addressed. (author)
Pressure-Velocity Correlations in the Cove of a Leading Edge Slat
Wilkins, Stephen; Richard, Patrick; Hall, Joseph
2015-11-01
One of the major sources of aircraft airframe noise is related to the deployment of high-lift devices, such as leading-edge slats, particularly when the aircraft is preparing to land. As the engines are throttled back, the noise produced by the airframe itself is of great concern, as the aircraft is low enough for the noise to impact civilian populations. In order to reduce the aeroacoustic noise sources associated with these high lift devices for the next generation of aircraft an experimental investigation of the correlation between multi-point surface-mounted fluctuating pressures measured via flush-mounted microphones and the simultaneously measured two-component velocity field measured via Particle Image Velocimetry (PIV) is studied. The development of the resulting shear-layer within the slat cove is studied for Re =80,000, based on the wing chord. For low Mach number flows in air, the major acoustic source is a dipole acoustic source tied to fluctuating surface pressures on solid boundaries, such as the underside of the slat itself. Regions of high correlations between the pressure and velocity field near the surface will likely indicate a strong acoustic dipole source. In order to study the underlying physical mechanisms and understand their role in the development of aeroacoustic noise, Proper Orthogonal Decomposition (POD) by the method of snapshots is employed on the velocity field. The correlation between low-order reconstructions and the surface-pressure measurements are also studied.
Improvement of airfoil trailing edge bluntness noise model
Directory of Open Access Journals (Sweden)
Wei Jun Zhu
2016-02-01
Full Text Available In this article, airfoil trailing edge bluntness noise is investigated using both computational aero-acoustic and semi-empirical approach. For engineering purposes, one of the most commonly used prediction tools for trailing edge noise are based on semi-empirical approaches, for example, the Brooks, Pope, and Marcolini airfoil noise prediction model developed by Brooks, Pope, and Marcolini (NASA Reference Publication 1218, 1989. It was found in previous study that the Brooks, Pope, and Marcolini model tends to over-predict noise at high frequencies. Furthermore, it was observed that this was caused by a lack in the model to predict accurately noise from blunt trailing edges. For more physical understanding of bluntness noise generation, in this study, we also use an advanced in-house developed high-order computational aero-acoustic technique to investigate the details associated with trailing edge bluntness noise. The results from the numerical model form the basis for an improved Brooks, Pope, and Marcolini trailing edge bluntness noise model.
Toward Establishing a Realistic Benchmark for Airframe Noise Research: Issues and Challenges
Khorrami, Mehdi R.
2010-01-01
The availability of realistic benchmark configurations is essential to enable the validation of current Computational Aeroacoustic (CAA) methodologies and to further the development of new ideas and concepts that will foster the technologies of the next generation of CAA tools. The selection of a real-world configuration, the subsequent design and fabrication of an appropriate model for testing, and the acquisition of the necessarily comprehensive aeroacoustic data base are critical steps that demand great care and attention. In this paper, a brief account of the nose landing-gear configuration, being proposed jointly by NASA and the Gulfstream Aerospace Company as an airframe noise benchmark, is provided. The underlying thought processes and the resulting building block steps that were taken during the development of this benchmark case are given. Resolution of critical, yet conflicting issues is discussed - the desire to maintain geometric fidelity versus model modifications required to accommodate instrumentation; balancing model scale size versus Reynolds number effects; and time, cost, and facility availability versus important parameters like surface finish and installation effects. The decisions taken during the experimental phase of a study can significantly affect the ability of a CAA calculation to reproduce the prevalent flow conditions and associated measurements. For the nose landing gear, the most critical of such issues are highlighted and the compromises made to resolve them are discussed. The results of these compromises will be summarized by examining the positive attributes and shortcomings of this particular benchmark case.
High-speed cinematography of gas-metal atomization
Energy Technology Data Exchange (ETDEWEB)
Ting, Jason [ALCOA Specialty Metals Division, 100 Technical Drive, Alcoa Center, PA 15069 (United States)]. E-mail: jason.ting@alcoa.com; Connor, Jeffery [Material Science Engineering Department, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Ridder, Stephen [Metallurgical Processing Group, NIST, 100 Bureau Dr. Stop 8556, Gaithersburg, MD 20899 (United States)
2005-01-15
A high-speed cinematographic footage of a 304L stainless steel gas atomization, recorded at the National Institute of Standard and Technology (NIST), was analyzed using a discrete Fourier transform (DFT) algorithm. The analysis showed the gas atomization process possesses two prominent frequency ranges of melt oscillation (pulsation). A low-frequency oscillation in the melt flow occurring between 5.41 and 123 Hz, with a dominant frequency at 9.93 Hz, was seen in the recirculation zone adjacent to the melt orifice. A high-frequency melt oscillation range was observed above 123 Hz, and was more prominent one melt-tip-diameter downstream in the melt atomization image than upstream near the melt tip. This high-frequency range may reflect the melt atomization frequency used to produce finely atomized powder. This range also included a prominent high frequency at 1273 Hz, which dominated in the image further away downstream from the melt tip. This discrete high-frequency oscillation is most probably caused by the aeroacoustic ''screech'' phenomenon, intrasound (<20 kHz), a result of the atomizing gas jets undergoing flow resonance. It is hypothesized that this discrete intrinsic aeroacoustic tone may enhance melt breakup in the atomization process with evidence of this fact in the melt images.
A method for obtaining a statistically stationary turbulent free shear flow
Timson, Stephen F.; Lele, S. K.; Moser, R. D.
1994-01-01
The long-term goal of the current research is the study of Large-Eddy Simulation (LES) as a tool for aeroacoustics. New algorithms and developments in computer hardware are making possible a new generation of tools for aeroacoustic predictions, which rely on the physics of the flow rather than empirical knowledge. LES, in conjunction with an acoustic analogy, holds the promise of predicting the statistics of noise radiated to the far-field of a turbulent flow. LES's predictive ability will be tested through extensive comparison of acoustic predictions based on a Direct Numerical Simulation (DNS) and LES of the same flow, as well as a priori testing of DNS results. The method presented here is aimed at allowing simulation of a turbulent flow field that is both simple and amenable to acoustic predictions. A free shear flow is homogeneous in both the streamwise and spanwise directions and which is statistically stationary will be simulated using equations based on the Navier-Stokes equations with a small number of added terms. Studying a free shear flow eliminates the need to consider flow-surface interactions as an acoustic source. The homogeneous directions and the flow's statistically stationary nature greatly simplify the application of an acoustic analogy.
Prediction of Hydrodynamic Noise of Open Cavity Flow
Institute of Scientific and Technical Information of China (English)
GENG Donghan; WANG Yu
2009-01-01
In this paper, the hydrodynamically generated noise by the flow over an open cavity is studied. First, aeroacoustic theories and computational aeroacoustic(CAA)methodologies are reviewed in light of hydrodynamic acoustics, based on which, a hybrid method is presented. In the coupling procedure, the unsteady cavity flow field is computed using large-eddy simulation(LES), while the radiated sound is calculated by the Ffowcs Williams-Hawkings(FW-H)acoustic analogy with acoustic source terms extracted from the time-dependent solutions of the unsteady flow. The hybrid LES-FW-H acoustic analogy method is tested with an open cavity flow at Mach number of 0.006 and Reynolds number of 105. Following the reflection theorem of Powell, the contributions from different source terms are quantified, and the terms involving wall-pressure fluctuations are found to account for most of the radiated intensity. The radiation field is investigated in the frequency domain. For the longitudinal direction, the sound propagates with a dominant radiation downstream the cavity in the near-field and a flatter directivity in the far-field, while for the spanwise direction, the acoustic waves have a similar propagation along +z and-z directions, with no visible directivity.
Improvement of airfoil trailing edge bluntness noise model
DEFF Research Database (Denmark)
Zhu, Wei Jun; Shen, Wen Zhong; Sørensen, Jens Nørkær;
2016-01-01
, Pope, and Marcolini airfoil noise prediction model developed by Brooks, Pope, and Marcolini (NASA Reference Publication 1218, 1989). It was found in previous study that the Brooks, Pope, and Marcolini model tends to over-predict noise at high frequencies. Furthermore, it was observed...... that this was caused by a lack in the model to predict accurately noise from blunt trailing edges. For more physical understanding of bluntness noise generation, in this study, we also use an advanced in-house developed high-order computational aero-acoustic technique to investigate the details associated...... with trailing edge bluntness noise. The results from the numerical model form the basis for an improved Brooks, Pope, and Marcolini trailing edge bluntness noise model....
Single velocity-component modeling of leading edge turbulence interaction noise.
Gill, J; Zhang, X; Joseph, P
2015-06-01
A computational aeroacoustics approach is used to predict leading edge turbulence interaction noise for real airfoils. One-component (transverse), two-component (transverse and streamwise), and three-component (transverse, streamwise, and spanwise) synthesized turbulence disturbances are modeled instead of harmonic transverse gusts, to which previous computational studies of leading edge noise have often been confined. The effects of the inclusion of streamwise and spanwise disturbances on the noise are assessed. It is shown that accurate noise predictions can be made by modeling only transverse disturbances which reduces the computational expense of simulations. The accuracy of using only transverse disturbances is assessed for symmetric and cambered airfoils, and also for airfoils at non-zero angle of attack.
The design of modern gas turbine design : beyond CFD
Energy Technology Data Exchange (ETDEWEB)
Kenny, D.P. [Pratt and Whitney Canada, Longueuil, PQ (Canada)
1998-09-01
The progress that has been made in recent years of applying computational fluid dynamics (CFD) to the design of advanced turbine engines was discussed. Pratt and Whitney has successfully transitioned the design of the company`s advanced turbine engines from a five-year design cycle based on a succession of design-test-redesign cycles to a three-year design cycle based on an analytical design methodology. The development of 3-D viscous CFD and computational structural mechanics (CSM) codes as primary design tools and a multi-disciplinary approach to applications have been major factors in achieving this success. The company also made significant progress in the development of a fully implicit unsteady stage scheme, with marked impact on performance and durability. Improvements also have been made in the life of the hot end components and in aero-acoustics. 9 figs.
Heller, Gerd; Kreplin, Hans-Peter; Nitsche, Wolfgang; Peltzer, Inken
2013-01-01
This volume contains the contributions to the 17th Symposium of STAB (German Aerospace Aerodynamics Association). STAB includes German scientists and engineers from universities, research establishments and industry doing research and project work in numerical and experimental fluid mechanics and aerodynamics, mainly for aerospace but also for other applications. Many of the contributions collected in this book present results from national and European Community sponsored projects. This volume gives a broad overview of the ongoing work in this field in Germany and spans a wide range of topics: airplane aerodynamics, multidisciplinary optimization and new configurations, hypersonic flows and aerothermodynamics, flow control (drag reduction and laminar flow control), rotorcraft aerodynamics, aeroelasticity and structural dynamics, numerical simulation, experimental simulation and test techniques, aeroacoustics as well as the new fields of biomedical flows, convective flows, aerodynamics and acoustics of high-s...
Numerical method to compute acoustic scattering effect of a moving source.
Song, Hao; Yi, Mingxu; Huang, Jun; Pan, Yalin; Liu, Dawei
2016-01-01
In this paper, the aerodynamic characteristic of a ducted tail rotor in hover has been numerically studied using CFD method. An analytical time domain formulation based on Ffowcs Williams-Hawkings (FW-H) equation is derived for the prediction of the acoustic velocity field and used as Neumann boundary condition on a rigid scattering surface. In order to predict the aerodynamic noise, a hybrid method combing computational aeroacoustics with an acoustic thin-body boundary element method has been proposed. The aerodynamic results and the calculated sound pressure levels (SPLs) are compared with the known method for validation. Simulation results show that the duct can change the value of SPLs and the sound directivity. Compared with the isolate tail rotor, the SPLs of the ducted tail rotor are smaller at certain azimuth. PMID:27610323
Institute of Scientific and Technical Information of China (English)
LI Yang; LIU Jie; OUYANG Hua; DU Zhao-Hui
2008-01-01
This article presents the flow mechanism analysis and experimental study of a forward-skewed impeller and a radial impeller in low pressure axial fan. The forward-skewed blade was obtained by the optimization design of the radial blade and CFD technique. Measurement of the two blades was carried out in aerodynamic and aeroacoustic performance. Compared to the radial blade, the forward-skewed blade has demonstrated the improvements in efficiency, total pressure ratio, Stable Operating Range (SOR) and less aerodynamic noise. Detailed flow measurement and computation were performed for outlet flow field for investigating the responsible flow mechanisms. The results show the forward-skewed blade can cause a spanwise redistribution of flow toward the blade mid-span and reduce tip loading. This results in reduced significantly total pressure loss near hub and shroud endwall region, despite the slight increase of total pressure loss at mid-span.
Modellingthe Turbulent Mixing Noise Associated with Coanda Jets
Smith, Caroline
2004-11-01
Turbulent Mixing Noise (TMN) is a primary high-frequency noise source in aeronautical and aerospace applications that utilize the Coanda effect, due to the enhanced turbulence levels and entrainment that devices employing this effect generally offer when compared with conventional jet flows. A theory, previously developed to predict the TMN emitted by unit volume of jet-type shear-layer turbulence close to a rigid plane, is extended to predict the aeroacoustic characteristics of a three-dimensional turbulent flow over a particular Coanda surface. The ability to accurately predict this significant source of high frequency acoustic radiation will allow investigation of modifications to basic Coanda devices, so that the benefits of such devices can be fully exploited, without this unfortunate side effect.
Accoustic aerials measure the sound. Akustische Antennen vermessen den Schall
Energy Technology Data Exchange (ETDEWEB)
Michel, U. (Deutsche Forschungsanstalt fuer Luft- und Raumfahrt e.V. (DLR), Berlin (Germany). Abt. fuer Turbulenzforschung)
1999-02-01
In the frame of the co-operation with the French Air Travel Research Centre ONERA an aerial with a total of 161 microphones has been applied in September 1998 for measurements at flying heights above 100 metres. The plane microphone array of the DLR for an analysis of high frequencies was combined with the crucial array of ONERA for lower frequencies. The measurements provide information on the noise source and on already existing low-noise solutions. In order to abate efficiently the noise emission of identified sources additional investigations at models and original parts must be carried out in aero-acoustic wind channels. Investigations were realised upon co-ordination with the DLR Institute for Design Aerodynamics. (orig.)
Viscous effects on the acoustics and stability of a shear layer over a non-rigid wall
Khamis, Doran
2016-01-01
The effect of viscosity and thermal conduction on the acoustics in a shear layer above an impedance wall is investigated numerically and asymptotically by solving the linearised compressible Navier-Stokes equations (LNSE). Viscothermal effects are found to be as important as shear, and therefore including only shear by solving the linearised Euler equations (LEE) is questionable. In particular, the damping rate of upstream propagating waves is found to be underpredicted by the LEE, and dramatically so in certain instances. The effects of viscosity on stability are also found to be important. Short wavelength disturbances are stabilised by viscosity, greatly altering the characteristic wavelength and maximum growth rate of instability. For the parameters considered here (chosen to be typical of aeroacoustic situations), the Reynolds number below which the flow stabilizes ranges from $10^5$ to $10^7$. By assuming a thin but nonzero-thickness boundary layer, asymptotic analysis leads to a system of boundary laye...
Yates, J. E.
1979-01-01
The basic theory of aeroacoustics of homentropic fluid media is applied to the problems of sound scattering, production, and stimulated emission. A general theory of scattering from low speed three-dimensional vortex flows is presented. Specific results are given for the horseshoe vortex and vortex ring. The noise of an elementary corotating vortex pair in various flows is calculated. It is shown that a potential flow and shear flow can substantially increase the basic pair noise. Small reverse shears can annihilate vortex pairs and eliminate the pair noise mechanism. The pair results are used to explain qualitatively the operation of noise suppression devices. The stimulated emission of a single vortex pair and four and six vortex arrays is demonstrated. The results for six vortices illustrate how external pure tones can amplify the broadband noise of a jet in agreement with recent experimental evidence.
Gen 2.0 Mixer/Ejector Nozzle Test at LSAF June 1995 to July 1996
Arney, L. D.; Sandquist, D. L.; Forsyth, D. W.; Lidstone, G. L.; Long-Davis, Mary Jo (Technical Monitor)
2005-01-01
Testing of the HSCT Generation 2.0 nozzle model hardware was conducted at the Boeing Low Speed Aeroacoustic Facility, LSAF. Concurrent measurements of noise and thrust were made at critical takeoff design conditions for a variety of mixer/ejector model hardware. Design variables such as suppressor area ratio, mixer area ratio, liner type and thickness, ejector length, lobe penetration, and mixer chute shape were tested. Parallel testing was conducted at G.E.'s Cell 41 acoustic free jet facility to augment the LSAF test. The results from the Gen 2.0 testing are being used to help shape the current nozzle baseline configuration and guide the efforts in the upcoming Generation 2.5 and 3.0 nozzle tests. The Gen 2.0 results have been included in the total airplane system studies conducted at MDC and Boeing to provide updated noise and thrust performance estimates.
Kaltenbacher, Manfred
2015-01-01
Like the previous editions also the third edition of this book combines the detailed physical modeling of mechatronic systems and their precise numerical simulation using the Finite Element (FE) method. Thereby, the basic chapter concerning the Finite Element (FE) method is enhanced, provides now also a description of higher order finite elements (both for nodal and edge finite elements) and a detailed discussion of non-conforming mesh techniques. The author enhances and improves many discussions on principles and methods. In particular, more emphasis is put on the description of single fields by adding the flow field. Corresponding to these field, the book is augmented with the new chapter about coupled flow-structural mechanical systems. Thereby, the discussion of computational aeroacoustics is extended towards perturbation approaches, which allows a decomposition of flow and acoustic quantities within the flow region. Last but not least, applications are updated and restructured so that the book meets mode...
The Aerodynamics of Heavy Vehicles III : Trucks, Buses and Trains
Orellano, Alexander
2016-01-01
This volume contains papers presented at the International conference “The Aerodynamics of Heavy Vehicles III: Trucks, Buses and Trains” held in Potsdam, Germany, September 12-17, 2010 by Engineering Conferences International (ECI). Leading scientists and engineers from industry, universities and research laboratories, including truck and high-speed train manufacturers and operators were brought together to discuss computer simulation and experimental techniques to be applied for the design of more efficient trucks, buses and high-speed trains in the future. This conference was the third in the series after Monterey-Pacific Groove in 2002 and Lake Tahoe in 2007. The presentations address different aspects of train aerodynamics (cross wind effects, underbody flow, tunnel aerodynamics and aeroacoustics, experimental techniques), truck aerodynamics (drag reduction, flow control, experimental and computational techniques) as well as computational fluid dynamics and bluff body, wake and jet flows.
Some improvements to the model of discrete sound field nearby multi-propeller aircraft
Institute of Scientific and Technical Information of China (English)
王同庆; 李晓东; 周盛
1995-01-01
Improvements to the mathematical-physical model of discrete sound field of multi-propeller aircraft have been made by using aeroacoustic analogy method, which considers the effects of fuselage boundary as well as the interference process of the multiple propeller sound field. The calculated results illustrate the effects of fuselage on the propeller sound field, the ’beating noise’ phenomenon and the principle of noise control of synchrophaser system. The model for boundaries with arbitrary shapes can also be used to calculate the effects of rigid boundaries in other harmonic sound fields. Results for sound scattering of a rigid sphere in a planar harmonic wave calculated by using this model are satisfactorily coincident with those by the analytical method.
A First Look at the DGEN380 Engine Acoustic Data from a Core-Noise Perspective
Hultgren, Lennart S.
2015-01-01
This work is a first look at acoustic data acquired in the NASA Glenn Research Center Aero-Acoustic Propulsion Laboratory using the Price Induction DGEN380 small turbofan engine, with particular emphasis on broadband combustor (core) noise. Combustor noise is detected by using a two-signal source separation technique employing one engine-internal sensor and one semi-far-field microphone. Combustor noise is an important core-noise component and is likely to become a more prominent contributor to overall airport community noise due to turbofan design trends, expected aircraft configuration changes, and advances in fan-noise-mitigation techniques. This work was carried out under the NASA Fundamental Aeronautics Program, Fixed Wing Project, Quiet Performance Subproject
Saiyed, Naseem H.
2000-01-01
Typical installed separate-flow exhaust nozzle system. The jet noise from modern turbofan engines is a major contributor to the overall noise from commercial aircraft. Many of these engines use separate nozzles for exhausting core and fan streams. As a part of NASA s Advanced Subsonic Technology (AST) program, the NASA Glenn Research Center at Lewis Field led an experimental investigation using model-scale nozzles in Glenn s Aero-Acoustic Propulsion Laboratory. The goal of the investigation was to develop technology for reducing the jet noise by 3 EPNdB. Teams of engineers from Glenn, the NASA Langley Research Center, Pratt & Whitney, United Technologies Research Corporation, the Boeing Company, GE Aircraft Engines, Allison Engine Company, and Aero Systems Engineering contributed to the planning and implementation of the test.
Buono, Armand C.
The numerical method presented in this study attempts to predict the mean, non-uniform flow field upstream of a propeller partially immersed in a thick turbulent boundary layer with an actuator disk using CFD based on RANS in ANSYS FLUENT. Three different configurations, involving an infinitely thin actuator disk in the freestream (Configuration 1), an actuator disk near a wall with a turbulent boundary layer (Configuration 2), and an actuator disk with a hub near a wall with a turbulent boundary layer (Configuration 3), were analyzed for a variety of advance ratios ranging from J = 0.48 to J =1.44. CFD results are shown to be in agreement with previous works and validated with experimental data of reverse flow occurring within the boundary layer above the flat plate upstream of a rotor in the Virginia Tech's Stability Wind Tunnel facility. Results from Configuration 3 will be used in future aero-acoustic computations.
Masini, Christopher P.; Mann, J. Adin
2005-09-01
System Engineering processes were applied to create a Cooling Fan System Noise Analysis Tool for a back-hoe loader machine. The Cooling Fan System Noise Analysis Tool combined elements of aeroacoustic theory, Fan Law, sound power measurements and particle image velocimetry into a single computer analysis tool. The cooling fan system consisted of a cooling fan, multiple radiators in front of the cooling fan, a shroud, a mock engine behind the cooling fan, and a simulated engine compartment. A vortex flow structure was measured in front of the cooling fan. The cooling fan system sound power spectrum was measured. The radiated sound power spectrum for the vortex interaction with the fan blades was calculated. Measured and predicted cooling fan system sound power results were compared. The overall structure and approach will be presented along with an overview of the theory and initial results.
Response Analysis Of Payload Fairing Due To Acoustic Excitation
Directory of Open Access Journals (Sweden)
Annu Cherian
2015-08-01
Full Text Available Abstract During flight missions launch vehicles are subjected to a severe dynamic pressure loading aero-acoustic and structure-borne excitations of various circumstances which can endanger the survivability of the payload and the vehicles electronic equipment and consequently the success of the mission. The purpose of the fairing is to protect the satellite from damage during launch until deployment in space. Both the structural and acoustic loads are significant during the first few minutes of a launch and have the potential to damage the payload. This paper describes the analysis of mechanical structure and the inner acoustic cavity of the payload fairing subjected to acoustic field. The vibro-acoustic behaviour of the fairing is analyzed using Statistical Energy Analysis SEA Model. The software VA One is used for the statistical energy analysis of launch vehicle payload fairing due to acoustic excitation.
Analytic subject index to 2012
Institute of Scientific and Technical Information of China (English)
2012-01-01
43.05. History; 43.10. General; 43.15. Standards; 43.20. General linear acoustics; 43.25. Nonlinear acoustics; 43.28. Aeroacoustics and atmospheric sound; 43.30. Underwater sound; 43.35. Ultrasonics, quantum acoustics, and physical effects of sound; 43.38. Transduction, acoustical devices for the gen- eration and reproduction of sound; 43.40. Structural acoustics and vibration; 43.50. Noise： its effects and control; 43.55. Architectura] acoustics; 43.58. Acoustical measurements and instrumentation; 43.60. Acoustic signal processing; 43.64. Physiological acoustics; 43.66. Psychological acoustics; 43.70. Speech production; 43.71. Speech perception; 43.72. Speech processing and communication systems; 43.75. Music and musical instruments; 43.80. Bioacoustics; 43.90. Other tooics in acou.~tic.~.
Analytic subject index to 2011
Institute of Scientific and Technical Information of China (English)
2011-01-01
43.05. History; 43.10. General; 43.15. Standards; 43.20. General linear acoustics; 43.25. Nonlinear acoustics; 43.28. Aeroacoustics and atmospheric sound; 43.30. Underwater sound; 43.35. Ultrasonics, quantum acoustics, and physical effects of sound; 43.38. Transduction, acoustical devices for the generation and reproduction of sound; 43.40. Structural acoustics and vibration; 43.50. Noise： its effects and control; 43.55. Architectural acoustics; 43.58. Acoustical measurements and instrumentation; 43.60. Acoustic signal processing; 43.64. Physiological acoustics; 43.66. Psychological acoustics; 43.70. Speech production; 43.71. Speech perception; 43.72. Speech processing and communication systems; 43.75. Music and musical instruments; 43.80. Bioacoustics; 43.90. Other topics in acoustics.
Institute of Scientific and Technical Information of China (English)
Shigeru MATSUO; Kenbu TERAMOTO; Ashraful ALAM; Toshiaki SETOGUCHI; Heuy Dong KIM; Shen YU
2007-01-01
The unsteady phenomena in the transonic flow around airfoils are observed in the flow field of fan, compressor blades and butterfly valves, and this often causes serious problems such as the aeroacoustic noise, the vibration. In the transonic or supersonic flow where vapour is contained in the main flow, the rapid expansion of the flow may give rise to a non-equilibrium condensation. However, the effect of non-equilibrium condensation on the transonic internal flows around the airfoil has not yet been clarified satisfactorily. In the present study, the effect of non-equilibrium condensation of moist air on the self-excited shock wave oscillation on a circular arc blade was investigated numerically. The results showed that in the case with non-equilibrium condensation, frequencies of the flow oscillation became smaller than those without the non-equilibrium condensation.
Gust Acoustic Response of a Swept Rectilinear Cascade Using The Space-Time CE/SE Method
Wang, X. Y.; Himansu, A.; Jorgenson, P. C.; Chang, S. C.
2001-01-01
The benchmark problem 3 in Category 3 of the third Computational Aero-Acoustics (CAA) Workshop sponsored by NASA Glenn Research Center is solved using the space-time conservation element and solution element (CE/SE) method. This problem concerns the unsteady response of a rectilinear swept cascade to an incident gust. The acoustic field generated by the interaction of the gust with swept at plates in the cascade is computed by solving the 3D nonlinear Euler equations using the space-time CE/SE method. A parallel version of the 3D CE/SE Euler solver is employed to obtain numerical solutions for several sweep angles. Numerical solutions are presented and compared with the analytical solutions.
Gust Acoustics Computation with a Space-Time CE/SE Parallel 3D Solver
Wang, X. Y.; Himansu, A.; Chang, S. C.; Jorgenson, P. C. E.; Reddy, D. R. (Technical Monitor)
2002-01-01
The benchmark Problem 2 in Category 3 of the Third Computational Aero-Acoustics (CAA) Workshop is solved using the space-time conservation element and solution element (CE/SE) method. This problem concerns the unsteady response of an isolated finite-span swept flat-plate airfoil bounded by two parallel walls to an incident gust. The acoustic field generated by the interaction of the gust with the flat-plate airfoil is computed by solving the 3D (three-dimensional) Euler equations in the time domain using a parallel version of a 3D CE/SE solver. The effect of the gust orientation on the far-field directivity is studied. Numerical solutions are presented and compared with analytical solutions, showing a reasonable agreement.
Ivanco, Thomas G.; Sekula, Martin K.; Piatak, David J.; Simmons, Scott A.; Babel, Walter C.; Collins, Jesse G.; Ramey, James M.; Heald, Dean M.
2016-01-01
A data acquisition system upgrade project, known as AB-DAS, is underway at the NASA Langley Transonic Dynamics Tunnel. AB-DAS will soon serve as the primary data system and will substantially increase the scan-rate capabilities and analog channel count while maintaining other unique aeroelastic and dynamic test capabilities required of the facility. AB-DAS is configurable, adaptable, and enables buffet and aeroacoustic tests by synchronously scanning all analog channels and recording the high scan-rate time history values for each data quantity. AB-DAS is currently available for use as a stand-alone data system with limited capabilities while development continues. This paper describes AB-DAS, the design methodology, and the current features and capabilities. It also outlines the future work and projected capabilities following completion of the data system upgrade project.
Towards Identifying Contribution of Wake Turbulence to Inflow Noise from Wind Turbines
Directory of Open Access Journals (Sweden)
Agrawal Bharat Raj
2015-01-01
Full Text Available Downstream turbines in a wind farm often operate under the influence of wakes from upstream turbines. Aerodynamic losses and aeromechanical issues (stochastic loads associated with such wake-turbine interactions have been investigated before. However, the role such interactions play in the generation of aerodynamic noise has not been evaluated. This paper presents a two-step approach for predicting noise due to wake-turbine interaction. The first step involves an aerodynamic analysis of a wind farm using large eddy simulations. Time accurate data and turbulence statistics in the turbine wakes are obtained from this simulation just ahead of the downstream wind turbines. The second step uses the turbulence information with aeroacoustic models to predict radiated noise in the far field. Simulation results of two simplified model problems corresponding to these two steps are presented in this paper.
AERODYNAMIC SOUND OF A BODY IN ARBITRARY, DEFORMABLE MOTION, WITH APPLICATION TO PHONATION.
Howe, M S; McGowan, R S
2013-08-19
The method of tailored Green's functions advocated by Doak (Proceedings of the Royal Society A254 (1960) 129 - 145.) for the solution of aeroacoustic problems is used to analyse the contribution of the mucosal wave to self-sustained modulation of air flow through the glottis during the production of voiced speech. The amplitude and phase of the aerodynamic surface force that maintains vocal fold vibration are governed by flow separation from the region of minimum cross-sectional area of the glottis, which moves back and forth along its effective length accompanying the mucosal wave peak. The correct phasing is achieved by asymmetric motion of this peak during the opening and closing phases of the glottis. Limit cycle calculations using experimental data of Berry et al. (Journal of the Acoustical Society of America 110 (2001) 2539 - 2547.) obtained using an excised canine hemilarynx indicate that the mechanism is robust enough to sustain oscillations over a wide range of voicing conditions. PMID:24031098
Heller, Gerd; Krämer, Ewald; Kreplin, Hans-Peter; Nitsche, Wolfgang; Rist, Ulrich
2014-01-01
This book presents contributions to the 18th biannual symposium of the German Aerospace Aerodynamics Association (STAB). The individual chapters reflect ongoing research conducted by the STAB members in the field of numerical and experimental fluid mechanics and aerodynamics, mainly for (but not limited to) aerospace applications, and cover both nationally and EC-funded projects. By addressing a number of essential research subjects, together with their related physical and mathematics fundamentals, the book provides readers with a comprehensive overview of the current research work in the field, as well as its main challenges and new directions. Current work on e.g. high aspect-ratio and low aspect-ratio wings, bluff bodies, laminar flow control and transition, active flow control, hypersonic flows, aeroelasticity, aeroacoustics and biofluid mechanics is exhaustively discussed here. .
Optimization Design and Experimental Study of Low-Pressure Axial Fan with Forward-Skewed Blades
Directory of Open Access Journals (Sweden)
Li Yang
2007-01-01
Full Text Available This paper presents an experimental study of the optimization of blade skew in low pressure axial fan. Using back propagation (BP neural network and genetic algorithm (GA, the optimization was performed for a radial blade. An optimized blade is obtained through blade forward skew. Measurement of the two blades was carried out in aerodynamic and aeroacoustic performance. Compared to the radial blade, the optimized blade demonstrated improvements in efficiency, total pressure ratio, stable operating range, and aerodynamic noise. Detailed flow measurement was performed in outlet flow field for investigating the responsible flow mechanisms. The optimized blade can cause a spanwise redistribution of flow toward the blade midspan and reduce tip loading. This results in reduced significantly total pressure loss near hub and shroud endwall region, despite the slight increase of total pressure loss at midspan. In addition, the measured spectrums show that the broadband noise of the impeller is dominant.
System design and integration of the large-scale advanced prop-fan
Huth, B. P.
1986-01-01
In recent years, considerable attention has been directed toward improving aircraft fuel consumption. Studies have shown that blades with thin airfoils and aerodynamic sweep extend the inherent efficiency advantage that turboprop propulsion systems have demonstrated to the higher speed to today's aircraft. Hamilton Standard has designed a 9-foot diameter single-rotation Prop-Fan. It will test the hardware on a static test stand, in low speed and high speed wind tunnels and on a research aircraft. The major objective of this testing is to establish the structural integrity of large scale Prop-Fans of advanced construction, in addition to the evaluation of aerodynamic performance and the aeroacoustic design. The coordination efforts performed to ensure smooth operation and assembly of the Prop-Fan are summarized. A summary of the loads used to size the system components, the methodology used to establish material allowables and a review of the key analytical results are given.
5th Symposium on Hybrid RANS-LES Methods
Haase, Werner; Peng, Shia-Hui; Schwamborn, Dieter
2015-01-01
This book gathers the proceedings of the Fifth Symposium on Hybrid RANS-LES Methods, which was held on March 19-21 in College Station, Texas, USA. The different chapters, written by leading experts, reports on the most recent developments in flow physics modelling, and gives a special emphasis to industrially relevant applications of hybrid RANS-LES methods and other turbulence-resolving modelling approaches. The book addresses academic researchers, graduate students, industrial engineers, as well as industrial R&D managers and consultants dealing with turbulence modelling, simulation and measurement, and with multidisciplinary applications of computational fluid dynamics (CFD), such as flow control, aero-acoustics, aero-elasticity and CFD-based multidisciplinary optimization. It discusses in particular advanced hybrid RANS-LES methods. Further topics include wall-modelled Large Eddy Simulation (WMLES) methods, embedded LES, and a comparison of the LES methods with both hybrid RANS-LES and URANS methods. ...
Integrating CFD, CAA, and Experiments Towards Benchmark Datasets for Airframe Noise Problems
Choudhari, Meelan M.; Yamamoto, Kazuomi
2012-01-01
Airframe noise corresponds to the acoustic radiation due to turbulent flow in the vicinity of airframe components such as high-lift devices and landing gears. The combination of geometric complexity, high Reynolds number turbulence, multiple regions of separation, and a strong coupling with adjacent physical components makes the problem of airframe noise highly challenging. Since 2010, the American Institute of Aeronautics and Astronautics has organized an ongoing series of workshops devoted to Benchmark Problems for Airframe Noise Computations (BANC). The BANC workshops are aimed at enabling a systematic progress in the understanding and high-fidelity predictions of airframe noise via collaborative investigations that integrate state of the art computational fluid dynamics, computational aeroacoustics, and in depth, holistic, and multifacility measurements targeting a selected set of canonical yet realistic configurations. This paper provides a brief summary of the BANC effort, including its technical objectives, strategy, and selective outcomes thus far.
Numerical Simulation of a Negative Impulsive Wave
Institute of Scientific and Technical Information of China (English)
ToshiakiSETOGUCHI; ShenYU; 等
1996-01-01
A compression wave discharged from an open end of a tube causes positive impulsive noise,Active noise cancellation which is the cancelling of the noise by the addition of an inverse wave is a useful technique for reducing impulsive noise,The main objective of this study is to present the design for a negative impulsive wave generator utilizing unsteady mass influx.In this paper,in order to clarify the relationship between the unsteady mass influx and the negative impulsive wave,numerical and aeroacoustic analyses have been carried out using an unsteady expansion wave discharged from an open end of a shock tube.As a result,the effect of an unsteady expansion wave on a negative impulsive wave was charified.
Proposed military handbook for dynamic data acquisition and analysis - An invitation to review
Himelblau, Harry; Wise, James H.; Piersol, Allan G.; Grundvig, Max R.
1990-01-01
A draft Military Handbook prepared under the sponsorship of the USAF Space Division is presently being distributed throughout the U.S. for review by the aerospace community. This comprehensive document provides recommended guidelines for the acquisition and analysis of structural dynamics and aeroacoustic data, and is intended to reduce the errors and variability commonly found in flight, ground and laboratory dynamic test measurements. In addition to the usual variety of measurement problems encountered in the definition of dynamic loads, the development of design and test criteria, and the analysis of failures, special emphasis is given to certain state-of-the-art topics, such as pyroshock data acquisition and nonstationary random data analysis.
Rotating Blade Flow Instability as a Source of Noise in Axial Turbomachines
Kameier, F.; Neise, W.
1997-06-01
An experimental study is presented to investigate the aeroacoustic generation mechanism of the tip clearance noise in axial turbomachines. In addition to the increased broadband levels reported in the literature when the tip clearance is enlarged, significant level increases were observed within narrow frequency bands below the blade passing frequency. Measurements of the pressure fluctuations at the casing wall just upstream of the entrance plane of the impeller and on the rotating blades reveal that the tip clearance noise is associated with a rotating blade flow instability at the blade tip which in turn is only present under reversed flow conditions in the tip clearance gap. The rotating instability is interpreted as a rotating source or vortex mechanism which moves relative to the blade row at a fraction of the impeller shaft speed, similar to the cell(s) of rotating stall. A model for the generation of the narrow-band tip clearance noise is presented.
Deconvolution for the localization of sound sources using a circular microphone array
DEFF Research Database (Denmark)
Tiana Roig, Elisabet; Jacobsen, Finn
2013-01-01
During the last decade, the aeroacoustic community has examined various methods based on deconvolution to improve the visualization of acoustic fields scanned with planar sparse arrays of microphones. These methods assume that the beamforming map in an observation plane can be approximated...... by a convolution of the distribution of the actual sources and the beamformer's point-spread function, defined as the beamformer's response to a point source. By deconvolving the resulting map, the resolution is improved, and the side-lobes effect is reduced or even eliminated compared to conventional beamforming....... Even though these methods were originally designed for planar sparse arrays, in the present study, they are adapted to uniform circular arrays for mapping the sound over 360°. This geometry has the advantage that the beamforming output is practically independent of the focusing direction, meaning...
Numerical simulation of tonal fan noise of computers and air conditioning systems
Aksenov, A. A.; Gavrilyuk, V. N.; Timushev, S. F.
2016-07-01
Current approaches to fan noise simulation are mainly based on the Lighthill equation and socalled aeroacoustic analogy, which are also based on the transformed Lighthill equation, such as the wellknown FW-H equation or the Kirchhoff theorem. A disadvantage of such methods leading to significant modeling errors is associated with incorrect solution of the decomposition problem, i.e., separation of acoustic and vortex (pseudosound) modes in the area of the oscillation source. In this paper, we propose a method for tonal noise simulation based on the mesh solution of the Helmholtz equation for the Fourier transform of pressure perturbation with boundary conditions in the form of the complex impedance. A noise source is placed on the surface surrounding each fan rotor. The acoustic fan power is determined by the acoustic-vortex method, which ensures more accurate decomposition and determination of the pressure pulsation amplitudes in the near field of the fan.
Institute of Scientific and Technical Information of China (English)
F.Hempert; M.Hoffmann; U.Iben; C.-D.Munz
2016-01-01
In the present investigation,we demonstrate the capabilities of the discontinuous Galerkin spectral element method for high order accuracy computation of gas dynamics.The internal flow field of a natural gas injector for bivalent combustion engines is investigated under its operating conditions.The simulations of the flow field and the aeroacoustic noise emissions were in a good agreement with the experimental data.We tested several shockcapturing techniques for the discontinuous Galerkin scheme.Based on the validated framework,we analyzed the development of the supersonic jets during different opening procedures of a compressed natural gas injector.The results suggest that a more gradual injector opening decreases the noise emission.
Institute of Scientific and Technical Information of China (English)
Lei Shi; Chengchun Zhang; Jing Wang; Luquan Ren
2012-01-01
Flow control can effectively reduce the aerodynamic noise radiated from a circular cylinder.As one of the flow control methods,a bionic method,inspired by the serrations at the leading edge of owls' wing,was proposed in this paper.The effects of bionic serrated structures arranged on the upper and lower sides of a cylinder on the aerodynamic and aeroacoustic performance of the cylinder were numerically investigated.At a free stream speed of 24.5 m·s-1,corresponding to Reynolds number of 1.58 × 104,the simulation results indicate that the bionic serrated structures can decrease the frequency of the vortex shedding and control the fluctuating aerodynamic force acting on the cylinder,thus reduce the aerodynamic noise.A qualitative-view of the vorticity in the wake of the cylinder suggest that the serrated structures reduce aerodynamic sound by suppressing the unsteady motion of vortices.
Aerodynamic flow control of a high lift system with dual synthetic jet arrays
Alstrom, Robert Bruce
Implementing flow control systems will mitigate the vibration and aeroacoustic issues associated with weapons bays; enhance the performance of the latest generation aircraft by reducing their fuel consumption and improving their high angle-of-attack handling qualities; facilitate steep climb out profiles for military transport aircraft. Experimental research is performed on a NACA 0015 airfoil with a simple flap at angle of attack of 16o in both clean and high lift configurations. The results of the active control phase of the project will be discussed. Three different experiments were conducted; they are Amplitude Modulated Dual Location Open Loop Control, Adaptive Control with Amplitude Modulation using Direct Sensor Feedback and Adaptive Control with Amplitude Modulation using Extremum Seeking Control. All the closed loop experiments are dual location. The analysis presented uses the spatial variation of the root mean square pressure fluctuations, power spectral density estimates, Fast Fourier Transforms (FFTs), and time frequency analysis which consists of the application of the Morlet and Mexican Hat wavelets. Additionally, during the course of high speed testing in the wind tunnel, some aeroacoustic phenomena were uncovered; those results will also be presented. A cross section of the results shows that the shape of the RMS pressure distributions is sensitive to forcing frequency. The application of broadband excitation in the case adaptive control causes the flow to select a frequency to lock in to. Additionally, open loop control results in global synchronization via switching between two stable states and closed loop control inhibits the switching phenomena, but rather synchronizes the flow about multiple stable shedding frequencies.
Rotorcraft Aeromechanics Branch Home Page on the World Wide Web
Peterson, Randall L.; Warmbrodt, William (Technical Monitor)
1996-01-01
The tilt rotor aircraft holds great promise for improving air travel in the future. It's benefits include vertical take off and landing combined with airspeeds comparable to propeller driven aircraft. However, the noise from a tilt rotor during approach to a landing is potentially a significant barrier to widespread acceptance of these aircraft. This approach noise is primarily caused by Blade Vortex Interactions (BVI), which are created when the blade passes near or through the vortex trailed by preceding blades. The XV- 15 Aeroacoustic test will measure the noise from a tilt rotor during descent conditions and demonstrate several possible techniques to reduce the noise. The XV- 15 Aeroacoustic test at NASA Ames Research Center will measure acoustics and performance for a full-scale XV-15 rotor. A single XV-15 rotor will be mounted on the Ames Rotor Test Apparatus (RTA) in the 80- by 120-Foot Wind Tunnel. The test will be conducted in helicopter mode with forward flight speeds up to 100 knots and tip path plane angles up to +/- 15 degrees. These operating conditions correspond to a wide range of tilt rotor descent and transition to forward flight cases. Rotor performance measurements will be made with the RTA rotor balance, while acoustic measurements will be made using an acoustic traverse and four fixed microphones. The acoustic traverse will provide limited directionality measurements on the advancing side of the rotor, where BVI noise is expected to be the highest. Baseline acoustics and performance measurements for the three-bladed rotor will be obtained over the entire test envelope. Acoustic measurements will also be obtained for correlation with the XV-15 aircraft Inflight Rotor Aeroacoustic Program (IRAP) recently conducted by Ames. Several techniques will be studied in an attempt to reduce the highest measured BVI noise conditions. The first of these techniques will use sub-wings mounted on the blade tips. These subwings are expected to alter the size
An experimental study of airfoil instability tonal noise with trailing edge serrations
Chong, Tze Pei; Joseph, Phillip F.
2013-11-01
This paper presents an experimental study of the effect of trailing edge serrations on airfoil instability noise. Detailed aeroacoustic measurements are presented of the noise radiated by an NACA-0012 airfoil with trailing edge serrations in a low to moderate speed flow under acoustical free field conditions. The existence of a separated boundary layer near the trailing edge of the airfoil at an angle of attack of 4.2 degree has been experimentally identified by a surface mounted hot-film arrays technique. Hot-wire results have shown that the saw-tooth surface can trigger a bypass transition and prevent the boundary layer from becoming separated. Without the separated boundary layer to act as an amplifier for the incoming Tollmien-Schlichting waves, the intensity and spectral characteristic of the radiated tonal noise can be affected depending upon the serration geometry. Particle Imaging Velocimetry (PIV) measurements of the airfoil wakes for a straight and serrated trailing edge are also reported in this paper. These measurements show that localized normal-component velocity fluctuations that are present in a small region of the wake from the laminar airfoil become weakened once serrations are introduced. Owing to the above unique characteristics of the serrated trailing edges, we are able to further investigate the mechanisms of airfoil instability tonal noise with special emphasis on the assessment of the wake and non-wake based aeroacoustic feedback models. It has been shown that the instability tonal noise generated at an angle of attack below approximately one degree could involve several complex mechanisms. On the other hand, the non-wake based aeroacoustic feedback mechanism alone is sufficient to predict all discrete tone frequencies accurately when the airfoil is at a moderate angle of attack. Larger Δf, which is defined as (fn+1-fn). In other words, a larger margin of velocity increase is required in order to "shift" the fn and fn+1 across fs
F15B-Quiet Spike Aeroservoelastic Flight Test Data Analysis
Brenner, Martin J.
2007-01-01
Airframe structural morphing technologies designed to mitigate sonic boom strength are being developed by Gulfstream Aerospace Corporation (GAC). Among these technologies is a concept in which an aircraft's frontend would be extended prior to supersonic acceleration. This morphing would effectively lengthen the vehicle, reducing peak sonic boom amplitude, but is also expected to partition the otherwise strong bow shock into a series of reduced-strength, non-coalescing shocklets. This combination of boom shaping techniques is predicted to transform the classic, high-impulse N-wave pattern typically generated by an aircraft traveling at supersonic speed into a signature more closely resembling a sinusoidal wave with a greatly reduced perceived loudness. 'QuietSpike' is GAC's nomenclature for its recently patented front-end vehicle morphing arrangement. The ability of Quiet Spike to effectively shape a vehicle's far- field sonic boom signature is highly dependent on the area distribution characteristics of the aircraft. The full aeroacoustic benefits of front-end morphing at farfield are only possible when the QuietSpike article and vehicle configuration are designed in consideration of each other. Adding QuietSpike technology to the airframe of an existing, non-boom-optimized supersonic vehicle is unlikely to result in an improved far-field signature due to the generally over-powering influence of wing- and inlet-generated shocks. Therefore, it is generally recognized within NASA and the industry that a clean-sheet vehicle design is required to demonstrate the theoretically predicted far-field aeroacoustic benefits of QuietSpike type morphing and other boom- mitigating concepts. NASA's Aeronautics Research Mission Directorate (ARMD) Supersonics Division has placed increased priority on near-term development and flight-testing of such a vehicle. To help achieve this objective, static and dynamic aerostructural proof-of-concept testing was considered a prudent step
Computation of Gust-Cascade Interaction Using the CE/SE Method
Wang, X.-Y.; Himansu, A.; Chang, S.-C.; Jorgenson, P. C. E.
2004-01-01
The problem 2 in Category 3 of the 4th Computational Aeroacoustic(CAA) Workshop is solved using the space-time conservation element and solution element (CE/SE) method. This problem models rotor-stator interaction in a 2D cascade. It involves complex geometries and flow physics including vortex shedding and acoustic radiation. The parallel version of the 2D nonlinear Euler solver is used with an unstructured triangular mesh to solve this problem. The Giles approach is incorporated with the CE/SE method to handle non-equal pitches of the rotor and stator. Validation on the Giles approach is performed using Problem 3.1 in the 2nd CAA Workshop. The space-time CE/SE method is a finite volume method with second-order accuracy in both space and time. The flux conservation is enforced in both space and time instead of space only. It has low numerical dissipation and dispersion errors. It uses simple non-reflecting boundary conditions and is compatible with unstructured meshes. It is simple, flexible, and generate reasonably accurate solutions. The CE/SE method has been successfully applied to solve numerous practical problems, especially aeroacoustic problems. Some preliminary numerical results of the benchmark problem 3.2 of the 4th CAA Workshop are shown. The steady-state pressure contour is plotted. The mean pressure distribution on the blade surface is compared with Turbo solution showing a good agreement. The sound pressure level versus the rotor harmonic n at the six designated positions on the blade surface, three locations at inlet plane, and three locations at the outlet plane are plotted. It can be seen that the acoustic response exists only at the excitation frequencies (n = 1,2,3). On the blade surface, the acoustic wave at n = 1 is dominant, while at the inlet and outlet planes, the sound pressure level at n = 2 becomes the largest, which is similar to the results presented. The distribution of sound pressure level at different spatial modes along the z
Indirect combustion noise of auxiliary power units
Tam, Christopher K. W.; Parrish, Sarah A.; Xu, Jun; Schuster, Bill
2013-08-01
Recent advances in noise suppression technology have significantly reduced jet and fan noise from commercial jet engines. This leads many investigators in the aeroacoustics community to suggest that core noise could well be the next aircraft noise barrier. Core noise consists of turbine noise and combustion noise. There is direct combustion noise generated by the combustion processes, and there is indirect combustion noise generated by the passage of combustion hot spots, or entropy waves, through constrictions in an engine. The present work focuses on indirect combustion noise. Indirect combustion noise has now been found in laboratory experiments. The primary objective of this work is to investigate whether indirect combustion noise is also generated in jet and other engines. In a jet engine, there are numerous noise sources. This makes the identification of indirect combustion noise a formidable task. Here, our effort concentrates exclusively on auxiliary power units (APUs). This choice is motivated by the fact that APUs are relatively simple engines with only a few noise sources. It is, therefore, expected that the chance of success is higher. Accordingly, a theoretical model study of the generation of indirect combustion noise in an Auxiliary Power Unit (APU) is carried out. The cross-sectional areas of an APU from the combustor to the turbine exit are scaled off to form an equivalent nozzle. A principal function of a turbine in an APU is to extract mechanical energy from the flow stream through the exertion of a resistive force. Therefore, the turbine is modeled by adding a negative body force to the momentum equation. This model is used to predict the ranges of frequencies over which there is a high probability for indirect combustion noise generation. Experimental spectra of internal pressure fluctuations and far-field noise of an RE220 APU are examined to identify anomalous peaks. These peaks are possible indirection combustion noise. In the case of the
Institute of Scientific and Technical Information of China (English)
余雷; 宋文萍
2013-01-01
采用非线性计算气动声学方法和基于雷诺平均NS方程的计算流体力学方法对常规尖后缘风力机翼型及其修型后的钝后缘翼型的气动噪声进行了计算.首先,对两种方法得到的翼型气动性能及翼型绕流流动进行了对比,结果表明非线性方法提供的湍流相关信息比基于雷诺平均NS方程的计算方法更加详细.然后,将声学计算结果与相关声学实验进行了对比,非线性方法对两种翼型气动噪声的预测结果与实验结果吻合良好,而基于雷诺平均NS的计算方法则明显低估了尖后缘风力机翼型的气动噪声.最后,对两种翼型不同的噪声产生机理进行了分析,并讨论了两种计算方法不同的数值模拟能力.%The aerodynamic noise of a conventional sharp trailing edge wind turbine airfoil and its flatback version has been predicted using a non-linear computational aeroacoustics method and a traditional Reynold averaged Navier-Stokes (RANS) computational fluid dynamics method in this paper. The flow structure obtained from the two methods is observed and compared, indicating that the non-linear method can provide much more detailed turbulence informations than the traditional RANS method. Compared with the aeroacoustics experimental data, results from the non-linear method show good agreement for both airfoils, while the other method gives an obvious underestimate for the sharp trailing edge airfoil. Finally, different noise generation mechanisms of the two airfoils are analyzed and different simulation capabilities of the two methods are discussed.
High Bypass Ratio Jet Noise Reduction and Installation Effects Including Shielding Effectiveness
Thomas, Russell H.; Czech, Michael J.; Doty, Michael J.
2013-01-01
An experimental investigation was performed to study the propulsion airframe aeroacoustic installation effects of a separate flow jet nozzle with a Hybrid Wing Body aircraft configuration where the engine is installed above the wing. Prior understanding of the jet noise shielding effectiveness was extended to a bypass ratio ten application as a function of nozzle configuration, chevron type, axial spacing, and installation effects from additional airframe components. Chevron types included fan chevrons that are uniform circumferentially around the fan nozzle and T-fan type chevrons that are asymmetrical circumferentially. In isolated testing without a pylon, uniform chevrons compared to T-fan chevrons showed slightly more low frequency reduction offset by more high frequency increase. Phased array localization shows that at this bypass ratio chevrons still move peak jet noise source locations upstream but not to nearly the extent, as a function of frequency, as for lower bypass ratio jets. For baseline nozzles without chevrons, the basic pylon effect has been greatly reduced compared to that seen for lower bypass ratio jets. Compared to Tfan chevrons without a pylon, the combination with a standard pylon results in more high frequency noise increase and an overall higher noise level. Shielded by an airframe surface 2.17 fan diameters from nozzle to airframe trailing edge, the T-fan chevron nozzle can produce reductions in jet noise of as much as 8 dB at high frequencies and upstream angles. Noise reduction from shielding decreases with decreasing frequency and with increasing angle from the jet inlet. Beyond an angle of 130 degrees there is almost no noise reduction from shielding. Increasing chevron immersion more than what is already an aggressive design is not advantageous for noise reduction. The addition of airframe control surfaces, including vertical stabilizers and elevon deflection, showed only a small overall impact. Based on the test results, the best
Landing-gear noise prediction using high-order finite difference schemes
Liu, Wen; Wook Kim, Jae; Zhang, Xin; Angland, David; Caruelle, Bastien
2013-07-01
Aerodynamic noise from a generic two-wheel landing-gear model is predicted by a CFD/FW-H hybrid approach. The unsteady flow-field is computed using a compressible Navier-Stokes solver based on high-order finite difference schemes and a fully structured grid. The calculated time history of the surface pressure data is used in an FW-H solver to predict the far-field noise levels. Both aerodynamic and aeroacoustic results are compared to wind tunnel measurements and are found to be in good agreement. The far-field noise was found to vary with the 6th power of the free-stream velocity. Individual contributions from three components, i.e. wheels, axle and strut of the landing-gear model are also investigated to identify the relative contribution to the total noise by each component. It is found that the wheels are the dominant noise source in general. Strong vortex shedding from the axle is the second major contributor to landing-gear noise. This work is part of Airbus LAnding Gear nOise database for CAA validatiON (LAGOON) program with the general purpose of evaluating current CFD/CAA and experimental techniques for airframe noise prediction.
Landing Gear Aerodynamic Noise Prediction Using Building-Cube Method
Directory of Open Access Journals (Sweden)
Daisuke Sasaki
2012-01-01
Full Text Available Landing gear noise prediction method is developed using Building-Cube Method (BCM. The BCM is a multiblock-structured Cartesian mesh flow solver, which aims to enable practical large-scale computation. The computational domain is composed of assemblage of various sizes of building blocks where small blocks are used to capture flow features in detail. Because of Cartesian-based mesh, easy and fast mesh generation for complicated geometries is achieved. The airframe noise is predicted through the coupling of incompressible Navier-Stokes flow solver and the aeroacoustic analogy-based Curle’s equation. In this paper, Curle’s equation in noncompact form is introduced to predict the acoustic sound from an object in flow. This approach is applied to JAXA Landing gear Evaluation Geometry model to investigate the influence of the detail components to flows and aerodynamic noises. The position of torque link and the wheel cap geometry are changed to discuss the influence. The present method showed good agreement with the preceding experimental result and proved that difference of the complicated components to far field noise was estimated. The result also shows that the torque link position highly affects the flow acceleration at the axle region between two wheels, which causes the change in SPL at observation point.
Increased Fidelity in Prediction Methods For Landing Gear Noise
Lopes, Leonard V.; Brentner, Kenneth S.; Morris, Philip J.; Lockhard, David P.
2006-01-01
An aeroacoustic prediction scheme has been developed for landing gear noise. The method is designed to handle the complex landing gear geometry of current and future aircraft. The gear is represented by a collection of subassemblies and simple components that are modeled using acoustic elements. These acoustic elements are generic, but generate noise representative of the physical components on a landing gear. The method sums the noise radiation from each component of the undercarriage in isolation accounting for interference with adjacent components through an estimate of the local upstream and downstream flows and turbulence intensities. The acoustic calculations are made in the code LGMAP, which computes the sound pressure levels at various observer locations. The method can calculate the noise from the undercarriage in isolation or installed on an aircraft for both main and nose landing gear. Comparisons with wind tunnel and flight data are used to initially calibrate the method, then it may be used to predict the noise of any landing gear. In this paper, noise predictions are compared with wind tunnel data for model landing gears of various scales and levels of fidelity, as well as with flight data on fullscale undercarriages. The present agreement between the calculations and measurements suggests the method has promise for future application in the prediction of airframe noise.
The Numerical Simulation of Infrasound Generated by Convective Storms
Schecter, D.; Nicholls, M. E.
2009-12-01
Recent observations and theoretical considerations suggest that a developing tornado has a detectable signature in the infrasound of a severe weather system [A.J. Bedard Jr., Mon. Weather Rev., 133, 241 (2005)]. In order to reliably distinguish the vortex signal from extraneous noise, it is essential to advance current understanding of the various mechanisms that produce infrasound in atmospheric convection. Without detailed observations of the acoustic sources within a storm, numerical modeling may be the best method of investigation. Here, we consider the feasibility of using a special version of the Regional Atmospheric Modeling System (RAMS) that is customized to simulate aeroacoustics. Comparison to analytical results demonstrates that the customized model adequately generates the infrasound of tornado-like vortices, and of basic diabatic cloud processes. Sensitivity to the microphysics parameterization is briefly addressed. Provisional simulations suggest that a moderate-to-strong tornado can adiabatically generate infrasound of much greater intensity than the infrasound of a generic hail-producing thunderstorm, in the 0.1-3 Hz frequency range [D.A. Schecter et al., J. Atmos. Sci., 65, 685 (2008)]. More detailed numerical studies are underway to verify this conclusion, and to further understand the production of infrasound in a broad spectrum of convective systems, ranging from non-precipitating cumuli to tornadic thunderstorms.
Counter Rotating Fans—An Aircraft Propulsion for the Future?
Institute of Scientific and Technical Information of China (English)
Peter Schimming
2003-01-01
In the mid seventies a new propulsor for aircraft was designed and investigated-the so-called PROPFAN.With regard to the total pressure increase, it ranges between a conventional propeller and a turbofan with very high bypass ratio.This new propulsion system promised a reduction in fuel consumption of 15 to 25% compared to engines at that time. A lot of propfans (Hamilton Standard, USA) with different numbers of blades and blade shapes have been designed and tested in wind tunnels in order to find an optimum in efficiency, Fig. 1. Parallel to this development GE, USA, made a design of a counter rotating unducted propfan, the so-called UDF, Fig.2. A prototype engine was manufactured and investigated on an in-flight test bed mounted at the MD82 and the B727. Since that time there has not been any further development of propfans (except AN 70 with NK 90—engine, Ukraine, which is more or less a propeller design) due to relatively low fuel prices and technical obstacles. Only technical programs in different countries are still going on in order to prepare a data base for designing counter rotating fans in terms of aeroacoustics, aerodynamics and aeroelasticities.In DLR, Germany, a lot of experimental and numerical work has been undertaken to understand the physical behaviour of the unsteady flow in a counter rotating fan.
Assessment of NASA's Aircraft Noise Prediction Capability
Dahl, Milo D. (Editor)
2012-01-01
A goal of NASA s Fundamental Aeronautics Program is the improvement of aircraft noise prediction. This document provides an assessment, conducted from 2006 to 2009, on the current state of the art for aircraft noise prediction by carefully analyzing the results from prediction tools and from the experimental databases to determine errors and uncertainties and compare results to validate the predictions. The error analysis is included for both the predictions and the experimental data and helps identify where improvements are required. This study is restricted to prediction methods and databases developed or sponsored by NASA, although in many cases they represent the current state of the art for industry. The present document begins with an introduction giving a general background for and a discussion on the process of this assessment followed by eight chapters covering topics at both the system and the component levels. The topic areas, each with multiple contributors, are aircraft system noise, engine system noise, airframe noise, fan noise, liner physics, duct acoustics, jet noise, and propulsion airframe aeroacoustics.
Aircraft noise and its nearfield propagation computations
Zhang, Xin
2012-08-01
Noise generated by civil transport aircraft during take-off and approach-to-land phases of operation is an environmental problem. The aircraft noise problem is firstly reviewed in this article. The review is followed by a description and assessment of a number of sound propagation methods suitable for applications with a background mean flow field pertinent to aircraft noise. Of the three main areas of the noise problem, i.e. generation, propagation, and radiation, propagation provides a vital link between near-field noise generation and far-field radiation. Its accurate assessment ensures the overall validity of a prediction model. Of the various classes of propagation equations, linearised Euler equations are often casted in either time domain or frequency domain. The equations are often solved numerically by computational aeroacoustics techniques, bur are subject to the onset of Kelvin-Helmholtz (K-H) instability modes which may ruin the solutions. Other forms of linearised equations, e.g. acoustic perturbation equations have been proposed, with differing degrees of success.
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
[篇名 ] 40kW pitch & flap type wind turbine generator system, [ 篇名 ] A design and performance prediction of shrouded wind turbine with brimmed-diffuser, [ 篇名 ] A framework for dynamic and aeroelastic analysis of horizontal axis wind turbines, [篇名] A frequency domain approach to wind turbines for flicker analysis, [ 篇名 ] A hybrid power system with using alternative energy facilities in isolated island, [ 篇名 ] A neuro-fuzzy model for the control operation of a wind-diesel-battery hybrid power system, [ 篇名 ] A new maximum power point tracking control scheme for wind generation, [篇名] A new power stabilization control system based on making use of mechanical inertia of a variable-speed w ind-turbine for stand-alone wind-diesel applications, [篇名 ] A study of a wind farm power system, [ 篇名 ] A STUDY OF STRAIGHT WING VERTICAL AXIS WIND TURBINE GENERATION SYSTEMS (A PEFORMANCE CALCULATION ABOUT STRAIGHT WING VERTICAL AXIS WIND TURBINE), [篇名] Acoustic Emission Monitoring of Field Tests of an Operating Wind Turbine, [ 篇名 ] Acoustic emission monitoring of small wind turbine blades, [ 篇名 ] Aero-acoustic computations of wind turbines, [ 篇名 ] Aerodynamic Loads on a Horizontal Axis Wind Turbine Rotor Exerted by Turbulent Inflow.
Airframe Noise from a Hybrid Wing Body Aircraft Configuration
Hutcheson, Florence V.; Spalt, Taylor B.; Brooks, Thomas F.; Plassman, Gerald E.
2016-01-01
A high fidelity aeroacoustic test was conducted in the NASA Langley 14- by 22-Foot Subsonic Tunnel to establish a detailed database of component noise for a 5.8% scale HWB aircraft configuration. The model has a modular design, which includes a drooped and a stowed wing leading edge, deflectable elevons, twin verticals, and a landing gear system with geometrically scaled wheel-wells. The model is mounted inverted in the test section and noise measurements are acquired at different streamwise stations from an overhead microphone phased array and from overhead and sideline microphones. Noise source distribution maps and component noise spectra are presented for airframe configurations representing two different approach flight conditions. Array measurements performed along the aircraft flyover line show the main landing gear to be the dominant contributor to the total airframe noise, followed by the nose gear, the inboard side-edges of the LE droop, the wing tip/LE droop outboard side-edges, and the side-edges of deployed elevons. Velocity dependence and flyover directivity are presented for the main noise components. Decorrelation effects from turbulence scattering on spectral levels measured with the microphone phased array are discussed. Finally, noise directivity maps obtained from the overhead and sideline microphone measurements for the landing gear system are provided for a broad range of observer locations.
Auralization of NASA N+2 Aircraft Concepts from System Noise Predictions
Rizzi, Stephen A.; Burley, Casey L.; Thomas, Russel H.
2016-01-01
Auralization of aircraft flyover noise provides an auditory experience that complements integrated metrics obtained from system noise predictions. Recent efforts have focused on auralization methods development, specifically the process by which source noise information obtained from semi-empirical models, computational aeroacoustic analyses, and wind tunnel and flight test data, are used for simulated flyover noise at a receiver on the ground. The primary focus of this work, however, is to develop full vehicle auralizations in order to explore the distinguishing features of NASA's N+2 aircraft vis-à-vis current fleet reference vehicles for single-aisle and large twin-aisle classes. Some features can be seen in metric time histories associated with aircraft noise certification, e.g., tone-corrected perceived noise level used in the calculation of effective perceived noise level. Other features can be observed in sound quality metrics, e.g., loudness, sharpness, roughness, fluctuation strength and tone-to-noise ratio. A psychoacoustic annoyance model is employed to establish the relationship between sound quality metrics and noise certification metrics. Finally, the auralizations will serve as the basis for a separate psychoacoustic study aimed at assessing how well aircraft noise certification metrics predict human annoyance for these advanced vehicle concepts.
Computational study of a contoured plug-nozzle as a supersonic jet noise suppressor
Khavaran, A.; Das, A. P.; Das, I.S.
1996-01-01
The report summarizes a computational jet noise study of an ideal contoured plug-nozzle (CPN). The gasdynamics of the jet flows have been predicted using the CFD code, NPARC with k-epsilon turbulence model; these data are then used as inputs to perform the noise computations based on the modified version of General Electric MGB code. The study covers a range of operating pressure ratio, 2.0 less than xi less than 5.0 (shockless flow at design pressure ratio, xi(d) = 3.62). The agreement of the computational aeroacoustics results with the available experimental data may be considered to be favorable. The computational results indicate consistent noise reduction effectiveness of the CPN at all operating pressure ratios. At the design pressure ratio (shockless), the codes predict overall sound pressure levels within +3.O dB of the experimental data. But at the off-design pressure ratios (flaws with shocks), the agreement is rather mixed. The theory overpredicts the OASPL's at all pressure ratios except at lower angles to the jet axis in overexpanded mode (xi less than xi(d)), the deviations being within 4.5 dB. The mechanism of shock formations in the CPN jet flows is noted to be basically different from those in the convergent-divergent nozzle jet flows.
Vortex Noise Reductions from a Flexible Fiber Model of Owl Down
Jaworski, Justin; Peake, Nigel
2013-11-01
Many species of owl rely on specialized plumage to reduce their self-noise levels and enable hunting in acoustic stealth. In contrast to the leading-edge comb and compliant trailing-edge fringe attributes of owls, the aeroacoustic impact of the fluffy down material on the upper wing surface remains largely speculative as a means to eliminate aerodynamic noise across a broad range of frequencies. The down is presently idealized as a collection of independent and rigid fibers, which emerge perpendicularly from a rigid plane and are allowed to rotate under elastic restraint. Noise generation from an isolated fiber is effected by its interaction with a point vortex, whose motion is induced by the presence of the rigid half-plane and the elastically-restrained fiber. Numerical evaluations of the vortex path and acoustic signature furnish a comparison with known analytical results for stationary fibers, and results from this primitive model seek to address how aerodynamic noise could be mitigated by flexible fibers.
Discharge of a shock Wave from an Open End of a Tube
Institute of Scientific and Technical Information of China (English)
HideoKashimura; HiroyasuNakayama; 等
2000-01-01
When a pressure wave propagates along a constant area straight tube and reaches at the open end,an impulsive wave is emitted outwared from the tube exit toward the surrounding area and causes an impulsive noise like a sonic oom.In order to clarify the magnitude of an impulsive wave obtainde by the discharge of a weak shock wave from an open end of a tube in relation to the noise problem and the industrial devices,the experimental and numerical investigations have been carried out for various strength of a shock wave.A simple open end shock tuby with the flange at the tube exit was used and the numerical calculation using the TVD scheme was performed.The effective equations which concerns with the magnitude of an impulsive wave generated by the emission of a shock wave have been obtained from the procedure of the open end correction based on the aeroacoustic theory and the numerical results.The influence of open end correction length and the diameter of a flange on the magnitude of an impulsive wave has been discussed.
Effects of increasing tip velocity on wind turbine rotor design.
Energy Technology Data Exchange (ETDEWEB)
Resor, Brian Ray; Maniaci, David Charles; Berg, Jonathan Charles; Richards, Phillip William
2014-05-01
A reduction in cost of energy from wind is anticipated when maximum allowable tip velocity is allowed to increase. Rotor torque decreases as tip velocity increases and rotor size and power rating are held constant. Reduction in rotor torque yields a lighter weight gearbox, a decrease in the turbine cost, and an increase in the capacity for the turbine to deliver cost competitive electricity. The high speed rotor incurs costs attributable to rotor aero-acoustics and system loads. The increased loads of high speed rotors drive the sizing and cost of other components in the system. Rotor, drivetrain, and tower designs at 80 m/s maximum tip velocity and 100 m/s maximum tip velocity are created to quantify these effects. Component costs, annualized energy production, and cost of energy are computed for each design to quantify the change in overall cost of energy resulting from the increase in turbine tip velocity. High fidelity physics based models rather than cost and scaling models are used to perform the work. Results provide a quantitative assessment of anticipated costs and benefits for high speed rotors. Finally, important lessons regarding full system optimization of wind turbines are documented.
Institute of Scientific and Technical Information of China (English)
李小艳; 李晓东
2012-01-01
The main objective is to validate the feasibility and accuracy of a multi-freedom time domain impedance boundary condition for broadband sound propagation problems.The NASA(National Aeronautics and Space Administration) grazing incidence tube experiment data was selected for numerical validation.The linearized Euler equation was solved by a high order computational aeroacoustics approach.The obtained numerical results are in good agreement with both the experimental data and results from single frequency simulation.It is demonstrated that the multi-freedom broadband impedance boundary condition is viable and accurate for the description of broadband sound propagation over impedance surfaces.%旨在验证一种多自由度时域阻抗边界条件在宽频声传播问题中的适用性与精度,选用NASA（美国国家航空航天局）流管实验数据进行数值校核；采用高精度计算气动声学方法数值求解线化欧拉方程,计算结果与实验数据及单频结果均吻合很好，表明了该多自由度时域阻抗边界条件具备精确处理宽频声传播问题的能力。
HART-II Acoustic Predictions using a Coupled CFD/CSD Method
Boyd, D. Douglas, Jr.
2009-01-01
This paper documents results to date from the Rotorcraft Acoustic Characterization and Mitigation activity under the NASA Subsonic Rotary Wing Project. The primary goal of this activity is to develop a NASA rotorcraft impulsive noise prediction capability which uses first principles fluid dynamics and structural dynamics. During this effort, elastic blade motion and co-processing capabilities have been included in a recent version of the computational fluid dynamics code (CFD). The CFD code is loosely coupled to computational structural dynamics (CSD) code using new interface codes. The CFD/CSD coupled solution is then used to compute impulsive noise on a plane under the rotor using the Ffowcs Williams-Hawkings solver. This code system is then applied to a range of cases from the Higher Harmonic Aeroacoustic Rotor Test II (HART-II) experiment. For all cases presented, the full experimental configuration (i.e., rotor and wind tunnel sting mount) are used in the coupled CFD/CSD solutions. Results show good correlation between measured and predicted loading and loading time derivative at the only measured radial station. A contributing factor for a typically seen loading mean-value offset between measured data and predictions data is examined. Impulsive noise predictions on the measured microphone plane under the rotor compare favorably with measured mid-frequency noise for all cases. Flow visualization of the BL and MN cases shows that vortex structures generated in the prediction method are consist with measurements. Future application of the prediction method is discussed.
Computing Axisymmetric Jet Screech Tones using Unstructured Grids
Jorgenson, Philip C. E.; Loh, Ching Y.
2003-01-01
The purpose of this paper is to show that computations with an aeroacoustic feedback loop, the jet screech noise, can be obtained using truly unstructured grid technology. Numerical results are presented for a nozzle with two different lip thicknesses which will be referred to in this paper as a thin and a thick lip nozzle respectively. The space-time conservation element and solution element (CE/SE) method is used to solve the conservation laws of the compressible axisymmetric Navier-Stokes equations. The equations are time marched to predict the unsteady flow and the near-field screech tone noise issuing from an underexpanded circular jet. The CE/SE method uses an unstructured grid based data structure. The unstructured grids for these calculations are generated based on the method of Delaunay triangulation. Comparisons of numerical results with available experimental data are shown for flows corresponding to several different jet Mach numbers. Generally good agreement is obtained in terms of flow physics, screech tone frequency, and sound pressure level.
Assessment of Soft Vane and Metal Foam Engine Noise Reduction Concepts
Jones, Michael G.; Parrott, Tony L.; Sutliff, Daniel L.; Hughes, Chris
2009-01-01
Two innovative fan-noise reduction concepts developed by NASA are presented - soft vanes and over-the-rotor metal foam liners. Design methodologies are described for each concept. Soft vanes are outlet guide vanes with internal, resonant chambers that communicate with the exterior aeroacoustic environment via a porous surface. They provide acoustic absorption via viscous losses generated by interaction of unsteady flows with the internal solid structure. Over-the-rotor metal foam liners installed at or near the fan rotor axial plane provide rotor noise absorption. Both concepts also provide pressure-release surfaces that potentially inhibit noise generation. Several configurations for both concepts are evaluated with a normal incidence tube, and the results are used to guide designs for implementation in two NASA fan rigs. For soft vanes, approximately 1 to 2 dB of broadband inlet and aft-radiated fan noise reduction is achieved. For over-the-rotor metal foam liners, up to 3 dB of fan noise reduction is measured in the low-speed fan rig, but minimal reduction is measured in the high-speed fan rig. These metal foam liner results are compared with a static engine test, in which inlet sound power level reductions up to 5 dB were measured. Brief plans for further development are also provided.
Jiang, Weili; Zheng, Xudong; Xue, Qian
2015-11-01
Human voice quality is directly determined by the interplay of dynamic behavior of glottal flow, vibratory characteristics of VFs and acoustic characteristics of upper airway. These multiphysics constituents are tightly coupled together and precisely coordinate to produce understandable sound. Despite many years' research effort, the direct relationships among the detailed flow features, VF vibration and aeroacoustics still remains elusive. This study utilizes a first-principle based, flow-structure-acoustics interaction computational modeling approach to study the process of voice production inside an entire human airway. In the current approach, a sharp interface immersed boundary method based incompressible flow solver is utilized to model the glottal flow; A finite element based solid mechanics solver is utilized to model the vocal vibration; A high-order immersed boundary method based acoustics solver is utilized to directly compute sound. These three solvers are fully coupled to mimic the complex flow-structure-acoustic interaction during voice production. The geometry of airway is reconstructed based on the in-vivo MRI measurement reported by Story et al. (1995) and a three-layer continuum based vocal fold model is taken from Titze and Talkin (1979). Results from these simulations will be presented and further analyzed to get new insight into the complex flow-structure-acoustic interaction during voice production. This study is expected to improve the understanding of fundamental physical mechanism of voice production and to help to build direct cause-effect relationship between biomechanics and voice sound.
Deri, E.; Ouvrard, H.; Braza, M.; Hunt, J.; Hoarau, Y.; Cazin, S.; Cid, E.; Harran, G.
2011-12-01
The present study aims at a physical analysis of the coherent and chaotic vortex dynamics in the near wake around a flat plate at incidence, to provide new elements in respect of the flow physics turbulence modelling for high-Reynolds number flows around bodies. This constitutes nowadays a challenge in the aeronautics design. A special attention is paid to capture the thin shear layer interfaces downstream of the separation, responsible for aeroacoustics phenomena related to noise reduction and directly linked to an accurate prediction of the aerodynamic forces. The experimental investigation is carried out by means of tomographic PIV. The interaction of the most energetic coherent structures with the random turbulence is discussed. Furthermore, the POD analysis allowed evaluation of 3D phase averaged dynamics as well as the influence of higher modes associated with the finer-scale turbulence. The numerical study by means of the Organised Eddy Simulation, OES approach ensured a reduced turbulence diffusion that allowed development of the von Karman instability and of capturing of the thin shear-layer interfaces, by using appropriate criteria based on vorticity and dissipation rate of kinetic energy. A comparison between the experiments and the simulations concerning the coherent vortex pattern is carried out.
Numerical Simulation of the Generation of Axisymmetric Mode Jet Screech Tones
Shen, Hao; Tam, Christopher K. W.
1998-01-01
An imperfectly expanded supersonic jet, invariably, radiates both broadband noise and discrete frequency sound called screech tones. Screech tones are known to be generated by a feedback loop driven by the large scale instability waves of the jet flow. Inside the jet plume is a quasi-periodic shock cell structure. The interaction of the instability waves and the shock cell structure, as the former propagates through the latter, is responsible for the generation of the tones. Presently, there are formulas that can predict the tone frequency fairly accurately. However, there is no known way to predict the screech tone intensity. In this work, the screech phenomenon of an axisymmetric jet at low supersonic Mach number is reproduced by numerical simulation. The computed mean velocity profiles and the shock cell pressure distribution of the jet are found to be in good agreement with experimental measurements. The same is true with the simulated screech frequency. Calculated screech tone intensity and directivity at selected jet Mach number are reported in this paper. The present results demonstrate that numerical simulation using computational aeroacoustics methods offers not only a reliable way to determine the screech tone intensity and directivity but also an opportunity to study the physics and detailed mechanisms of the phenomenon by an entirely new approach.
Suh, Jungsoo; Frankel, Steven H
2007-06-01
Large eddy simulation (LES)-based computational aeroacoustics techniques were applied to a static model of the human glottis, idealized here as a planar channel with an orifice, to study flow-acoustic interactions related to speech. Rigid models of both converging and diverging glottal passages, each featuring a 20 deg included angle and a minimal glottal diameter of 0.04 cm, with an imposed transglottal pressure of 15 cm H2O, were studied. The Favre-filtered compressible Navier-Stokes equations were integrated for this low-Mach-number flow using an additive semi-implicit Runge-Kutta method and a high-order compact finite-difference scheme with characteristic-based nonreflecting boundary conditions and a multiblock approach. Flow asymmetries related to the Coanda effect and transition to turbulence, as well as the far-field sound, were captured. Acoustic-analogy-based far-field sound predictions were compared with direct simulations and showed that dipole sources, arising from unsteady flow forces exerted on the glottal walls, are primarily responsible for the tonal sound observed in the divergent glottis case. PMID:17552723
Directory of Open Access Journals (Sweden)
Tatiana Petrova
2016-08-01
Full Text Available An extremely interesting problem in aero-hydrodynamics is the sound radiation of a single vortical structure. Currently, this type of problem is mainly considered for an incompressible medium. In this paper a method was developed to take into account the viscosity and thermal conductivity of gas. The acoustic radiation frequency of a cylindrical vortex on a flat wall in viscous heat-conducting gas (air has been investigated. The problem is solved on the basis of the Navier–Stokes equations using the small initial vorticity approach. The power expansion of unknown functions in a series with a small parameter (vorticity is used. It is shown that there are high-frequency oscillations modulated by a low-frequency signal. The value of the high frequency remains constant for a long period of time. Thus the high frequency can be considered a natural frequency of the vortex radiation. The value of the natural frequency depends only on the initial radius of the cylindrical vortex, and does not depend on the intensity of the initial vorticity. As expected from physical considerations, the natural frequency decreases exponentially as the initial radius of the cylinder increases. Furthermore, the natural frequency differs from that of the oscillations inside the initial cylinder and in the outer domain. The results of the paper may be of interest for aeroacoustics and tornado modeling.
The integrated motion measurement simulation for SOFIA
Kaswekar, Prashant; Greiner, Benjamin; Wagner, Jörg
2014-07-01
The Stratospheric Observatory for Infrared Astronomy SOFIA consists of a B747-SP aircraft, which carries aloft a 2.7-meter reflecting telescope. The image stability goal for SOFIA is 0:2 arc-seconds rms. The performance of the telescope structure is affected by elastic vibrations induced by aeroacoustic and suspension disturbances. Active compensation of such disturbances requires a fast way of estimating the structural motion. Integrated navigation systems are examples of such estimation systems. However they employ a rigid body assumption. A possible extension of these systems to an elastic structure is shown by different authors for one dimensional beam structures taking into account the eigenmodes of the structural system. The rigid body motion as well as the flexible modes of the telescope assembly, however, are coupled among the three axes. Extending a special mathematical approach to three dimensional structures, the aspect of a modal observer based on integrated motion measurement is simulated for SOFIA. It is in general a fusion of different measurement methods by using their benefits and blinding out their disadvantages. There are no mass and stillness properties needed directly in this approach. However, the knowledge of modal properties of the structure is necessary for the implementation of this method. A finite-element model is chosen as a basis to extract the modal properties of the structure.
Physics of Acoustic Radiation from Jet Engine Inlets
Tam, Christopher K. W.; Parrish, Sarah A.; Envia, Edmane; Chien, Eugene W.
2012-01-01
Numerical simulations of acoustic radiation from a jet engine inlet are performed using advanced computational aeroacoustics (CAA) algorithms and high-quality numerical boundary treatments. As a model of modern commercial jet engine inlets, the inlet geometry of the NASA Source Diagnostic Test (SDT) is used. Fan noise consists of tones and broadband sound. This investigation considers the radiation of tones associated with upstream propagating duct modes. The primary objective is to identify the dominant physical processes that determine the directivity of the radiated sound. Two such processes have been identified. They are acoustic diffraction and refraction. Diffraction is the natural tendency for an acoustic wave to follow a curved solid surface as it propagates. Refraction is the turning of the direction of propagation of sound waves by mean flow gradients. Parametric studies on the changes in the directivity of radiated sound due to variations in forward flight Mach number and duct mode frequency, azimuthal mode number, and radial mode number are carried out. It is found there is a significant difference in directivity for the radiation of the same duct mode from an engine inlet when operating in static condition and in forward flight. It will be shown that the large change in directivity is the result of the combined effects of diffraction and refraction.
Flow-excited acoustic resonances of coaxial side-branches in an annular duct
Arthurs, D.; Ziada, S.
2009-01-01
This paper investigates the aeroacoustic response of an annular duct with closed coaxial side-branches, and examines the effect of several passive countermeasures on the resonance intensity. The investigated geometry is inspired by the design of the Roll-Posts in the Rolls-Royce LiftSystem® engine, which is currently being developed for the Lockheed Martin Joint Strike Fighter (JSF®) aircraft. The effects of design parameters, such as diameter ratio, branch length ratio and thickness of the annular flow on the frequency and resonance intensity of the first acoustic mode are studied experimentally. Numerical simulations of the acoustic mode shapes and frequencies are also performed. The annular flow has been found to excite several acoustic modes, the strongest in all cases being the first acoustic mode, which consists of a quarter wavelength along the length of each branch. The ratios of the branch length and diameter, with respect to the main duct diameter, have been found to have strong effects on the frequency of the acoustic modes.
Optimization of the poro-serrated trailing edges for airfoil broadband noise reduction.
Chong, Tze Pei; Dubois, Elisa
2016-08-01
This paper reports an aeroacoustic investigation of a NACA0012 airfoil with a number of poro-serrated trailing edge devices that contain porous materials of various air flow resistances at the gaps between adjacent members of the serrated-sawtooth trailing edge. The main objective of this work is to determine whether multiple-mechanisms on the broadband noise reduction can co-exist on a poro-serrated trailing edge. When the sawtooth gaps are filled with porous material of low-flow resistivity, the vortex shedding tone at low-frequency could not be completely suppressed at high-velocity, but a reasonably good broadband noise reduction can be achieved at high-frequency. When the sawtooth gaps are filled with porous material of very high-flow resistivity, no vortex shedding tone is present, but the serration effect on the broadband noise reduction becomes less effective. An optimal choice of the flow resistivity for a poro-serrated configuration has been identified, where it can surpass the conventional serrated trailing edge of the same geometry by achieving a further 1.5 dB reduction in the broadband noise while completely suppressing the vortex shedding tone. A weakened turbulent boundary layer noise scattering at the poro-serrated trailing edge is reflected by the lower-turbulence intensity at the near wake centreline across the whole spanwise wavelength of the sawtooth.
On the lift increments with the occurrence of airfoil tones at low Reynodls numbers
Ikeda, Tomoaki; Fujimoto, Daisuke; Inasawa, Ayumu; Asai, Masahito
2015-11-01
The aeroacoustic effects on the aerodynamics of an NACA 0006 airfoil are investigated experimentally at relatively low Reynolds numbers, Re = 30 , 000 - 70 , 000 . By employing two wind-testing airfoil models at different chord lengths, L = 40 and 100 [mm], the aerodynamic dependence on Mach number is examined at a given Reynolds number. In a particular range of Reynolds number, tonal peaks of trailing-edge noise are obtained from a shorter-chord airfoil, while no apparent tones are observed with longer chord length at a lower Mach number. Surprisingly, the occurrence of a tonal noise leads to a greater lift slope in the present wind-tunnel experiment, evaluated via a PIV approach. The lift curves obtained experimentally at higher Mach numbers agree well with two-dimensional numerical simulations, performed at M = 0 . 2 . At the Mach number, the numerical results clearly indicate the occurrence of an acoustic feedback loop with discrete tones, within a range of angle of attack. A few three dimensional numerical results are also presented. In the simulation at Re = 50 , 000 , the suppression of tonal noise corresponds to the development of a turbulent wedge in the suction-side boundary layer at the angle of attack 4 . 0 [deg.], which agrees with the experiment. This work was supported by Grant-in-Aid for Scientific Research from Japan Society for the Promotion of Science (Grant No. 25420139).
Results From a Parametric Acoustic Liner Experiment Using P and W GEN1 HSR Mixer/Ejector Model
Boyd, Kathleen C.; Wolter, John D.
2004-01-01
This report documents the results of an acoustic liner test performed using a Gen 1 HSR mixer/ejector model installed on the Jet Exit Rig in the Nozzle Acoustic Test Rig in the Aeroacoustic Propulsion Laboratory or NASA Glenn Research Center. Acoustic liner effectiveness and single-component thrust performance results are discussed. Results from 26 different types of single-degree-of-freedom and bulk material liners are compared with each other and against a hardwall baseline. Design parameters involving all aspects of the facesheet, the backing cavity, and the type of bulk material were varied in order to study the effects of these design features on the acoustic impedance, acoustic effectiveness and on nozzle thrust performance. Overall, the bulk absorber liners are more effective at reducing the jet noise than the single-degree-of-freedom liners. Many of the design parameters had little effect on acoustic effectiveness, such as facesheeet hole diameter and honeycomb cell size. A relatively large variation in the impedance of the bulk absorber in a bulk liner is required to have a significant impact on the noise reduction. The thrust results exhibit a number of consistent trends, supporting the validity of this new addition to the facility. In general, the thrust results indicate that thrust performance benefits from increased facesheet thickness and decreased facesheet porosity.
A study on the multi-freedom broadband impedance model for time-domain simulations
Institute of Scientific and Technical Information of China (English)
LI Xiaodong; LI Xiaoyan
2012-01-01
The purpose of this paper is to construct a general broadband impedance model, which is suited for predicting acoustic propagation problems in time domain. A multi-freedom broadband impedance model for sound propagation over impedance surfaces is proposed and the corresponding time domain impedance boundary condition is presented. Basing on the extended Helmholtz resonator, the multi-freedom impedance model is constructed through combing with a sum of rational functions in the form of general complex-conjugate pole-residue pairs and it is proved that the impedance model is well posed. The impedance boundary condition can be implemented into a computational aeroacoustics solver by a rectlrsive convolution technique, which results in a fast and computationally efficient algorithm. The two dimensional and three dimensional benchmark problems are selected to validate the accuracy of the proposed impedance model and time domain simulations. The numerical results are in good agreement with the reference solutions. It is demonstrated that the proposed impedance model can be used to describe the broadband characteristics of acoustic liners, and the corresponding time domain impedance boundary condition is viable and accurate for the prediction of sound propagation over broadband impedance surfaces.
Janardan, B. A.; Hoff, G. E.; Barter, J. W.; Martens, S.; Gliebe, P. R.; Mengle, V.; Dalton, W. N.; Saiyed, Naseem (Technical Monitor)
2000-01-01
This report describes the work performed by General Electric Aircraft Engines (GEAE) and Allison Engine Company (AEC) on NASA Contract NAS3-27720 AoI 14.3. The objective of this contract was to generate quality jet noise acoustic data for separate-flow nozzle models and to design and verify new jet-noise-reduction concepts over a range of simulated engine cycles and flight conditions. Five baseline axisymmetric separate-flow nozzle models having bypass ratios of five and eight with internal and external plugs and 11 different mixing-enhancer model nozzles (including chevrons, vortex-generator doublets, and a tongue mixer) were designed and tested in model scale. Using available core and fan nozzle hardware in various combinations, 28 GEAE/AEC separate-flow nozzle/mixing-enhancer configurations were acoustically evaluated in the NASA Glenn Research Center Aeroacoustic and Propulsion Laboratory. This report describes model nozzle features, facility and data acquisition/reduction procedures, the test matrix, and measured acoustic data analyses. A number of tested core and fan mixing enhancer devices and combinations of devices gave significant jet noise reduction relative to separate-flow baseline nozzles. Inward-flip and alternating-flip core chevrons combined with a straight-chevron fan nozzle exceeded the NASA stretch goal of 3 EPNdB jet noise reduction at typical sideline certification conditions.
Aero-Propulsion Technology (APT) Task V Low Noise ADP Engine Definition Study
Holcombe, V.
2003-01-01
A study was conducted to identify and evaluate noise reduction technologies for advanced ducted prop propulsion systems that would allow increased capacity operation and result in an economically competitive commercial transport. The study investigated the aero/acoustic/structural advancements in fan and nacelle technology required to match or exceed the fuel burned and economic benefits of a constrained diameter large Advanced Ducted Propeller (ADP) compared to an unconstrained ADP propulsion system with a noise goal of 5 to 10 EPNDB reduction relative to FAR 36 Stage 3 at each of the three measuring stations namely, takeoff (cutback), approach and sideline. A second generation ADP was selected to operate within the maximum nacelle diameter constrain of 160 deg to allow installation under the wing. The impact of fan and nacelle technologies of the second generation ADP on fuel burn and direct operating costs for a typical 3000 nm mission was evaluated through use of a large, twin engine commercial airplane simulation model. The major emphasis of this study focused on fan blade aero/acoustic and structural technology evaluations and advanced nacelle designs. Results of this study have identified the testing required to verify the interactive performance of these components, along with noise characteristics, by wind tunnel testing utilizing and advanced interaction rig.
A levitation instrument for containerless study of molten materials
Nordine, Paul C.; Merkley, Dennis; Sickel, Jeffrey; Finkelman, Steve; Telle, Rainer; Kaiser, Arno; Prieler, Robert
2012-12-01
A new aero-acoustic levitation instrument (AAL) has been installed at the Institute for Mineral Engineering at RWTH University in Aachen, Germany. The AAL employs acoustically stabilized gas jet levitation with laser-beam heating and melting to create a contact-free containerless environment for high temperature materials research. Contamination-free study of liquids is possible at temperatures in excess of 3000 °C and of undercooled liquids at temperatures far below the melting point. Digital control technology advances the art of containerless experiments to obtain long-term levitation stability, allowing new experiments in extreme temperature materials research and to study operation of the levitation instrument itself. Experiments with liquid Al2O3 at temperatures more than 3200 °C, 1200 °C above the melting point, and with liquid Y3Al5O12 far below the melting point are reported. Fast pyrometry and video recording instruments yield crystallization rates in undercooled liquid Al2O3 as a function of temperature. Levitation of dense liquid HfO2 at temperatures above 2900 °C is demonstrated. Capabilities are described for resonant frequency matching in the three-axis acoustic positioning system, acoustic control of sample spin, and position control of standing wave nodes to stabilize levitation under changing experimental conditions. Further development and application of the levitation technology is discussed based on the results of experiments and modeling of instrument operations.
Aircraft noise and its nearfield propagation computations
Institute of Scientific and Technical Information of China (English)
Xin Zhang
2012-01-01
Noise generated by civil transport aircraft during take-off and approach-to-land phases of operation is an environmental problem.The aircraft noise problem is firstly reviewed in this article.The review is followed by a description and assessment of a number of sound propagation methods suitable for applications with a background mean flow field pertinent to aircraft noise.Of the three main areas of the noise problem,i.e.generation,propagation,and radiation,propagation provides a vital link between near-field noise generation and far-field radiation.Its accurate assessment ensures the overall validity of a prediction model.Of the various classes of propagation equations,linearised Euler equations are often casted in either time domain or frequency domain.The equations are often solved numerically by computational aeroacoustics techniques,bur are subject to the onset of Kelvin-Helmholtz (K-H) instability modes which may ruin the solutions. Other forms of linearised equations,e.g.acoustic perturbation equations have been proposed,with differing degrees of success.
A numerical study of nonlinear infrasound propagation in a windy atmosphere.
Sabatini, R; Marsden, O; Bailly, C; Bogey, C
2016-07-01
Direct numerical simulations of the two-dimensional unsteady compressible Navier-Stokes equations are performed to study the acoustic field generated by an infrasonic source in a realistic atmosphere. Some of the main phenomena affecting the propagation of infrasonic waves at large distances from the source are investigated. The effects of thermal and wind-related refraction on the signals recorded at ground level are highlighted, with particular emphasis on the phase shift induced by the presence of caustics in the acoustic field. Nonlinear waveform steepening associated with harmonic generation, and period lengthening, both of which are typical of large source amplitudes, are illustrated, and the importance of thermoviscous absorption in the upper atmosphere is clearly demonstrated. The role of diffraction in the shadow zone, around caustics and at stratospheric altitudes is also pointed out. The Navier-Stokes equations are solved using high-order finite-differences and a Runge-Kutta time integration method both originally developed for aeroacoustic applications, along with an adaptive shock-capturing algorithm which allows high-intensity acoustic fields to be examined. An improvement to the shock detection procedure is also proposed in order to meet the specificities of nonlinear propagation at long range. The modeling as well as the numerical results are reported in detail and discussed. PMID:27475186
Development of Optophone with No Diaphragm and Application to Sound Measurement in Jet Flow
Directory of Open Access Journals (Sweden)
Yoshito Sonoda
2012-01-01
Full Text Available The optophone with no diaphragm, which can detect sound waves without disturbing flow of air and sound field, is presented as a novel sound measurement technique and the present status of development is reviewed in this paper. The method is principally based on the Fourier optics and the sound signal is obtained by detecting ultrasmall diffraction light generated from phase modulation by sounds. The principle and theory, which have been originally developed as a plasma diagnostic technique to measure electron density fluctuations in the nuclear fusion research, are briefly introduced. Based on the theoretical analysis, property and merits as a wave-optical sound detection are presented, and the fundamental experiments and results obtained so far are reviewed. It is shown that sounds from about 100 Hz to 100 kHz can be simultaneously detected by a visible laser beam, and the method is very useful to sound measurement in aeroacoustics. Finally, present main problems of the optophone for practical uses in sound and/or noise measurements and the image of technology expected in the future are shortly shown.
Horne, William C.
2011-01-01
Measurements of background noise were recently obtained with a 24-element phased microphone array in the test section of the Arnold Engineering Development Center 80- by120-Foot Wind Tunnel at speeds of 50 to 100 knots (27.5 to 51.4 m/s). The array was mounted in an aerodynamic fairing positioned with array center 1.2m from the floor and 16 m from the tunnel centerline, The array plate was mounted flush with the fairing surface as well as recessed in. (1.27 cm) behind a porous Kevlar screen. Wind-off speaker measurements were also acquired every 15 on a 10 m semicircular arc to assess directional resolution of the array with various processing algorithms, and to estimate minimum detectable source strengths for future wind tunnel aeroacoustic studies. The dominant background noise of the facility is from the six drive fans downstream of the test section and first set of turning vanes. Directional array response and processing methods such as background-noise cross-spectral-matrix subtraction suggest that sources 10-15 dB weaker than the background can be detected.
Modifications to the 4x7 meter tunnel for acoustic research: Engineering feasibility study
1986-01-01
The NASA-Langley Research Center 4 x 7 Meter Low Speed Wind Tunnel is currently being used for low speed aerodynamics, V/STOL aerodynamics and, to a limited extent, rotorcraft noise research. The deficiencies of this wind tunnel for both aerodynamics and aeroacoustics research have been recognized for some time. Modifications to the wind tunnel are being made to improve the test section flow quality and to update the model cart systems. A further modification of the 4 x 7 Meter Wind Tunnel to permit rotorcraft model acoustics research has been proposed. As a precursor to the design of the proposed modifications, NASA is conducted both in-house and contracted studies to define the acoustic environment within the wind tunnel and to provide recommendations or the reduction of the wind tunnel background noise to a level acceptable to acoustics researchers. One of these studies by an acoustics consultant, has produced the primary reference documents that define the wind tunnel noise sources and outline recommended solutions.
Latorre Iglesias, E.; Thompson, D. J.; Smith, M. G.
2016-01-01
Vortex shedding from cylinders has been extensively studied due to its occurrence in many engineering fields. Many experimental studies reported in the literature focus on the aerodynamics of the vortex shedding process but the literature about the radiated noise is more scarce. The aim of the work presented here is to extend the available noise data. Aero-acoustic wind tunnel tests were carried out using cylinders with different cross-sections: circular, square, rectangular and elliptical. Flow speeds between 20 and 50 m/s were used, corresponding to Reynolds numbers in the range from 1.6×104 to 1.2×105. The dependence of the noise on the yaw angle, flow speed, cross-sectional shape, angle of attack and radiation angle (directivity) is assessed. The results obtained are compared, where possible, with those found in the literature for similar cases. It is intended that the results can be used for the validation and calibration of numerical and empirical aerodynamic noise prediction models.
Formation of Y(x)Nd(1-x) Ba2Cu3O(7-delta) (0 = or Levitation
Gustafson, D. E.; Hofmeister, W. H.; Bayuzick, R. J.
2001-01-01
Melt processing of RE123 superconductors has gained importance in recent years. While the first high temperature superconductors (HTSCs) were made using traditional ceramic press and sinter technology, recent fabrication efforts have employed alternate processing techniques including laser ablation and ion beam assisted deposition for thin film fabrication of tapes and wires and melt growth for bulk materials. To optimize these techniques and identify other potential processing strategies, phase relation studies on HTSCs have been conducted on a wide variety of superconducting compounds using numerous processing strategies. This data has enhanced the understanding of these complex systems and allowed more accurate modeling of phase interactions. All of this research has proved useful in identifying processing capabilities for HTSCs but has failed to achieve a breakthrough for wide spread application of these materials. This study examines the role of full to partial substitution of Nd in the Y123 structure under rapid solidification conditions. Aero-acoustic levitation (AAL) was used to levitate and undercool RE123 in pure oxygen binary alloys with RE = Nd an Y along a range of compositions corresponding to Y(x)Nd(1-x) Ba2Cu3O(7-delta) (0 = or < x < or = 0.7) which were melted by a CO2 laser. Higher Y content spheres could not be melted in the AAL and were excluded from this report. Solidification structures were examined using scanning electron microscopy, electron dispersive spectroscopy, and powder x-ray diffraction to characterize microstructures and identify phases.
Evaluation of Rotor Structural and Aerodynamic Loads using Measured Blade Properties
Jung, Sung N.; You, Young-Hyun; Lau, Benton H.; Johnson, Wayne; Lim, Joon W.
2012-01-01
The structural properties of Higher harmonic Aeroacoustic Rotor Test (HART I) blades have been measured using the original set of blades tested in the wind tunnel in 1994. A comprehensive rotor dynamics analysis is performed to address the effect of the measured blade properties on airloads, blade motions, and structural loads of the rotor. The measurements include bending and torsion stiffness, geometric offsets, and mass and inertia properties of the blade. The measured properties are correlated against the estimated values obtained initially by the manufacturer of the blades. The previously estimated blade properties showed consistently higher stiffnesses, up to 30% for the flap bending in the blade inboard root section. The measured offset between the center of gravity and the elastic axis is larger by about 5% chord length, as compared with the estimated value. The comprehensive rotor dynamics analysis was carried out using the measured blade property set for HART I rotor with and without HHC (Higher Harmonic Control) pitch inputs. A significant improvement on blade motions and structural loads is obtained with the measured blade properties.
Aero and vibroacoustics of automotive turbochargers
Energy Technology Data Exchange (ETDEWEB)
Nguyen-Schaefer, Hung [Bosch Mahle Turbo Systems GmbH, Stuttgart (Germany)
2013-02-01
First book about the aeroacoustics of automotive turbochargers. Author of the book ''Rotordynamics of Automotive Turbochargers'', Springer, 2012. Written by an R and D expert in the turbocharger industry. Aero and Vibroacoustics of Automotive Turbochargers is a topic involving aspects from the working fields of thermodynamics of turbomachinery, aerodynamics, rotordynamics, and noise propagation computation. In this broadly interdisciplinary subject, thermodynamics of turbomachinery is used to design the turbocharger and to determine its operating conditions. Aerodynamics is needed to study the compressor flow dynamics and flow instabilities of rotating stall and surge, which can produce growling and whining-type noises. Rotordynamics is necessary to study rotor unbalance and self-excited oil-whirl instabilities, which lead to whistling and constant tone-type noises in rotating floating oil-film type bearings. For the special case of turbochargers using ball bearings, some high-order harmonic and wear noises also manifest in the rotor operating range. Lastly, noise propagation computation, based on Lighthill's analogy, is required to investigate airborne noises produced by turbochargers in passenger vehicles. The content of this book is intended for advanced undergraduates, graduates in mechanical engineering, research scientists and practicing engineers who want to better understand the interactions between these working fields and the resulting impact on the interesting topic of Aero and Vibroacoustics of Automotive Turbochargers.
Optimal Design and Acoustic Assessment of Low-Vibration Rotor Blades
Directory of Open Access Journals (Sweden)
G. Bernardini
2016-01-01
Full Text Available An optimal procedure for the design of rotor blade that generates low vibratory hub loads in nonaxial flow conditions is presented and applied to a helicopter rotor in forward flight, a condition where vibrations and noise become severe. Blade shape and structural properties are the design parameters to be identified within a binary genetic optimization algorithm under aeroelastic stability constraint. The process exploits an aeroelastic solver that is based on a nonlinear, beam-like model, suited for the analysis of arbitrary curved-elastic-axis blades, with the introduction of a surrogate wake inflow model for the analysis of sectional aerodynamic loads. Numerical results are presented to demonstrate the capability of the proposed approach to identify low vibratory hub loads rotor blades as well as to assess the robustness of solution at off-design operating conditions. Further, the aeroacoustic assessment of the rotor configurations determined is carried out in order to examine the impact of low-vibration blade design on the emitted noise field.
Acoustic detection, tracking, and characterization of three tornadoes.
Frazier, William Garth; Talmadge, Carrick; Park, Joseph; Waxler, Roger; Assink, Jelle
2014-04-01
Acoustic data recorded at 1000 samples per second by two sensor arrays located at ranges of 1-113 km from three tornadoes that occurred on 24 May 2011 in Oklahoma are analyzed. Accurate bearings to the tornadoes have been obtained using beamforming methods applied to the data at infrasonic frequencies. Beamforming was not viable at audio frequencies, but the data demonstrate the ability to detect significant changes in the shape of the estimated power spectral density in the band encompassing 10 Hz to approximately 100 Hz at distances of practical value from the sensors. This suggests that arrays of more closely spaced sensors might provide better bearing accuracy at practically useful distances from a tornado. Additionally, a mathematical model, based on established relationships of aeroacoustic turbulence, is demonstrated to provide good agreement to the estimated power spectra produced by the tornadoes at different times and distances from the sensors. The results of this analysis indicate that, qualitatively, an inverse relationship appears to exist between the frequency of an observed peak of the power spectral density and the reported tornado intensity. PMID:25234974
Aerodynamically generated noise by lightning arrester
Directory of Open Access Journals (Sweden)
Váchová J.
2007-10-01
Full Text Available This paper presents the general solution of aerodynamically generated noise by lightning arrester. Governing equations are presented in form of Lighthill acoustic analogy, as embodied in the Ffowcs Williams-Hawkings (FW-H equation. This equation is based on conservation laws of fluid mechanics rather than on the wave equation. Thus, the FW-H equation is valid even if the integration surface is in nonlinear region. That’s why the FWH method is superior in aeroacoustics. The FW-H method is implemented in program Fluent and the numerical solution is acquired by Fluent code.The general solution of acoustic signal generated by lightning arrester is shown and the results in form of acoustic pressure and frequency spectrum are presented. The verification of accuracy was made by evaluation of Strouhal number. A comparison of Strouhal number for circumfluence of a cylinder and the lightning arrester was done, because the experimental data for cylinder case are known and these solids are supposed to be respectively in shape relation.
Supersonics/Airport Noise Plan: An Evolutionary Roadmap
Bridges, James
2011-01-01
This presentation discusses the Plan for the Airport Noise Tech Challenge Area of the Supersonics Project. It is given in the context of strategic planning exercises being done in other Projects to show the strategic aspects of the Airport Noise plan rather than detailed task lists. The essence of this strategic view is the decomposition of the research plan by Concept and by Tools. Tools (computational, experimental) is the description of the plan that resources (such as researchers) most readily identify with, while Concepts (here noise reduction technologies or aircraft configurations) is the aspects that project management and outside reviewers most appreciate as deliverables and milestones. By carefully cross-linking these so that Concepts are addressed sequentially (roughly one after another) by researchers developing/applying their Tools simultaneously (in parallel with one another), the researchers can deliver milestones at a reasonable pace while doing the longer-term development that most Tools in the aeroacoustics science require. An example of this simultaneous application of tools was given for the Concept of High Aspect Ratio Nozzles. The presentation concluded with a few ideas on how this strategic view could be applied to the Subsonic Fixed Wing Project's Quiet Aircraft Tech Challenge Area as it works through its current roadmapping exercise.
Prospects for Nonlinear Laser Diagnostics in the Jet Noise Laboratory
Herring, Gregory C.; Hart, Roger C.; Fletcher, mark T.; Balla, R. Jeffrey; Henderson, Brenda S.
2007-01-01
Two experiments were conducted to test whether optical methods, which rely on laser beam coherence, would be viable for off-body flow measurement in high-density, compressible-flow wind tunnels. These tests measured the effects of large, unsteady density gradients on laser diagnostics like laser-induced thermal acoustics (LITA). The first test was performed in the Low Speed Aeroacoustics Wind Tunnel (LSAWT) of NASA Langley Research Center's Jet Noise Laboratory (JNL). This flow facility consists of a dual-stream jet engine simulator (with electric heat and propane burners) exhausting into a simulated flight stream, reaching Mach numbers up to 0.32. A laser beam transited the LSAWT flow field and was imaged with a high-speed gated camera to measure beam steering and transverse mode distortion. A second, independent test was performed on a smaller laboratory jet (Mach number < 1.2 and mass flow rate < 0.1 kg/sec). In this test, time-averaged LITA velocimetry and thermometry were performed at the jet exit plane, where the effect of unsteady density gradients is observed on the LITA signal. Both experiments show that LITA (and other diagnostics relying on beam overlap or coherence) faces significant hurdles in the high-density, compressible, and turbulent flow environments similar to those of the JNL.
Direct Numerical Simulation of Automobile Cavity Tones
Kurbatskii, Konstantin; Tam, Christopher K. W.
2000-01-01
The Navier Stokes equation is solved computationally by the Dispersion-Relation-Preserving (DRP) scheme for the flow and acoustic fields associated with a laminar boundary layer flow over an automobile door cavity. In this work, the flow Reynolds number is restricted to R(sub delta*) < 3400; the range of Reynolds number for which laminar flow may be maintained. This investigation focuses on two aspects of the problem, namely, the effect of boundary layer thickness on the cavity tone frequency and intensity and the effect of the size of the computation domain on the accuracy of the numerical simulation. It is found that the tone frequency decreases with an increase in boundary layer thickness. When the boundary layer is thicker than a certain critical value, depending on the flow speed, no tone is emitted by the cavity. Computationally, solutions of aeroacoustics problems are known to be sensitive to the size of the computation domain. Numerical experiments indicate that the use of a small domain could result in normal mode type acoustic oscillations in the entire computation domain leading to an increase in tone frequency and intensity. When the computation domain is expanded so that the boundaries are at least one wavelength away from the noise source, the computed tone frequency and intensity are found to be computation domain size independent.
Loh, Ching Y.; Jorgenson, Philip C. E.
2007-01-01
A time-accurate, upwind, finite volume method for computing compressible flows on unstructured grids is presented. The method is second order accurate in space and time and yields high resolution in the presence of discontinuities. For efficiency, the Roe approximate Riemann solver with an entropy correction is employed. In the basic Euler/Navier-Stokes scheme, many concepts of high order upwind schemes are adopted: the surface flux integrals are carefully treated, a Cauchy-Kowalewski time-stepping scheme is used in the time-marching stage, and a multidimensional limiter is applied in the reconstruction stage. However even with these up-to-date improvements, the basic upwind scheme is still plagued by the so-called "pathological behaviors," e.g., the carbuncle phenomenon, the expansion shock, etc. A solution to these limitations is presented which uses a very simple dissipation model while still preserving second order accuracy. This scheme is referred to as the enhanced time-accurate upwind (ETAU) scheme in this paper. The unstructured grid capability renders flexibility for use in complex geometry; and the present ETAU Euler/Navier-Stokes scheme is capable of handling a broad spectrum of flow regimes from high supersonic to subsonic at very low Mach number, appropriate for both CFD (computational fluid dynamics) and CAA (computational aeroacoustics). Numerous examples are included to demonstrate the robustness of the methods.
APS presents prizes in fluid dynamics and plasma physics
International Nuclear Information System (INIS)
This article reviews the presentation of the American Physical Society awards in fluid dynamics and plasma physics. The recipient of the plasma physics James Clerk Maxwell Prize was John M. Green for contributions to the theory of magnetohydrodynamics equilibria and ideal and resistive instabilities, for discovering the inverse scattering transform leading to soliton solutions of many nonlinear partial differential equations and for inventing the residue method of determining the transition to global chaos. The excellence in Plasma Physics Research Award was presented to Nathaniel A. Fisch for theoretical investigations of noninductive current generation in toroidally confined plasma. Wim Pieter Leemans received the Simon Ramo Award for experimental and simulational contributions to laser-plasma physics. William R. Sears was given the 1992 Fuid Dynamics Prize for contributions to the study of steady and unsteady aerodynamics, aeroacoustics, magnetoaerodynamics,and wind tunnel design. William C. Reynolds received the Otto Laporte Award for experimental, theoretical, and computational work in turbulence modeling and control and leadership in direct numerical simulation and large eddy simulation
Current R and D needs in wind energy technology
International Nuclear Information System (INIS)
The meeting, hosted by NOVEM, the Netherlands Agency for Energy and the Environment, was attended by 22 people. The purpose of the meeting was to get an impression of how far the efforts spent until now on worldwide research and development have brought the general understanding of, and possibly solutions to, the various problems within wind energy technology - thereby providing some guidance as to where to go from now. In 1994 it was estimated that more than 100 million U.S. dollars was spent on R, D and D by those OECD countries which have a wind energy program, and that since 1974 at least 1000 mil. U.S. dollars must have been spent. The necessity of continued basic research within certain areas was recognized, and it was emphasized that the size of the research teams should always be greater than 'the critical mass'. There seemed to be consensus among all participants that the areas for continued research were the following: aerodynamics, aeroelasticity and load calculations, aeroacoustics (verification of fatigue calculation procedures for 3D stress distribution, establishing a data base of material properties), lightning protection measures, offshore installations (combined wind/wave loading, dynamics of support structures, wind and turbulence over the open sea), power conversion and wind turbine - grid interaction. (EG)
Institute of Scientific and Technical Information of China (English)
Min LIU; Keqi WU
2008-01-01
Based on the immersed boundary method (IBM) and the finite volume optimized pre-factored compact (FVOPC) scheme, a numerical simulation of noise propagation inside and outside the casing of a cross flow fan is estab-lished. The unsteady linearized Euler equations are solved to directly simulate the aero-acoustic field. In order to validate the FVOPC scheme, a simulation case: one dimensional linear wave propagation problem is carried out using FVOPC scheme, DRP scheme and HOC scheme. The result of FVOPC is in good agreement with the ana-lytic solution and it is better than the results of DRP and HOC schemes, the FVOPC is less dispersion and dissi-pation than DRP and HOC schemes. Then, numerical simulation of noise propagation problems is performed. The noise field of 36 compact rotating noise sources is obtained with the rotating velocity of 1000r/min. The PML absorbing boundary condition is applied to the sound far field boundary condition for depressing the numerical reflection. Wall boundary condition is applied to the casing. The results show that there are reflections on the casing wall and sound wave interference in the field. The FVOPC with the IBM is suitable for noise propagation problems under the complex geometries for depressing the dispersion and dissipation, and also keeping the high order precision.
Kim, Jae Wook
2013-05-01
This paper proposes a novel systematic approach for the parallelization of pentadiagonal compact finite-difference schemes and filters based on domain decomposition. The proposed approach allows a pentadiagonal banded matrix system to be split into quasi-disjoint subsystems by using a linear-algebraic transformation technique. As a result the inversion of pentadiagonal matrices can be implemented within each subdomain in an independent manner subject to a conventional halo-exchange process. The proposed matrix transformation leads to new subdomain boundary (SB) compact schemes and filters that require three halo terms to exchange with neighboring subdomains. The internode communication overhead in the present approach is equivalent to that of standard explicit schemes and filters based on seven-point discretization stencils. The new SB compact schemes and filters demand additional arithmetic operations compared to the original serial ones. However, it is shown that the additional cost becomes sufficiently low by choosing optimal sizes of their discretization stencils. Compared to earlier published results, the proposed SB compact schemes and filters successfully reduce parallelization artifacts arising from subdomain boundaries to a level sufficiently negligible for sophisticated aeroacoustic simulations without degrading parallel efficiency. The overall performance and parallel efficiency of the proposed approach are demonstrated by stringent benchmark tests.
Flight Performance Feasibility Studies for the Max Launch Abort System
Tarabini, Paul V.; Gilbert, Michael G.; Beaty, James R.
2013-01-01
In 2007, the NASA Engineering and Safety Center (NESC) initiated the Max Launch Abort System Project to explore crew escape system concepts designed to be fully encapsulated within an aerodynamic fairing and smoothly integrated onto a launch vehicle. One objective of this design was to develop a more compact launch escape vehicle that eliminated the need for an escape tower, as was used in the Mercury and Apollo escape systems and what is planned for the Orion Multi-Purpose Crew Vehicle (MPCV). The benefits for the launch vehicle of eliminating a tower from the escape vehicle design include lower structural weights, reduced bending moments during atmospheric flight, and a decrease in induced aero-acoustic loads. This paper discusses the development of encapsulated, towerless launch escape vehicle concepts, especially as it pertains to the flight performance and systems analysis trade studies conducted to establish mission feasibility and assess system-level performance. Two different towerless escape vehicle designs are discussed in depth: one with allpropulsive control using liquid attitude control thrusters, and a second employing deployable aft swept grid fins to provide passive stability during coast. Simulation results are presented for a range of nominal and off-nominal escape conditions.
Progress Towards an LES Wall Model Including Unresolved Roughness
Craft, Kyle; Redman, Andrew; Aikens, Kurt
2015-11-01
Wall models used in large eddy simulations (LES) are often based on theories for hydraulically smooth walls. While this is reasonable for many applications, there are also many where the impact of surface roughness is important. A previously developed wall model has been used primarily for jet engine aeroacoustics. However, jet simulations have not accurately captured thick initial shear layers found in some experimental data. This may partly be due to nozzle wall roughness used in the experiments to promote turbulent boundary layers. As a result, the wall model is extended to include the effects of unresolved wall roughness through appropriate alterations to the log-law. The methodology is tested for incompressible flat plate boundary layers with different surface roughness. Correct trends are noted for the impact of surface roughness on the velocity profile. However, velocity deficit profiles and the Reynolds stresses do not collapse as well as expected. Possible reasons for the discrepancies as well as future work will be presented. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. Computational resources on TACC Stampede were provided under XSEDE allocation ENG150001.
Isolated Open Rotor Noise Prediction Assessment Using the F31A31 Historical Blade Set
Nark, Douglas M.; Jones, William T.; Boyd, D. Douglas, Jr.; Zawodny, Nikolas S.
2016-01-01
In an effort to mitigate next-generation fuel efficiency and environmental impact concerns for aviation, open rotor propulsion systems have received renewed interest. However, maintaining the high propulsive efficiency while simultaneously meeting noise goals has been one of the challenges in making open rotor propulsion a viable option. Improvements in prediction tools and design methodologies have opened the design space for next generation open rotor designs that satisfy these challenging objectives. As such, validation of aerodynamic and acoustic prediction tools has been an important aspect of open rotor research efforts. This paper describes validation efforts of a combined computational fluid dynamics and Ffowcs Williams and Hawkings equation methodology for open rotor aeroacoustic modeling. Performance and acoustic predictions were made for a benchmark open rotor blade set and compared with measurements over a range of rotor speeds and observer angles. Overall, the results indicate that the computational approach is acceptable for assessing low-noise open rotor designs. Additionally, this approach may be used to provide realistic incident source fields for acoustic shielding/scattering studies on various aircraft configurations.
APS presents prizes in fluid dynamics and plasma physics
Energy Technology Data Exchange (ETDEWEB)
1992-12-01
This article reviews the presentation of the American Physical Society awards in fluid dynamics and plasma physics. The recipient of the plasma physics James Clerk Maxwell Prize was John M. Green for contributions to the theory of magnetohydrodynamics equilibria and ideal and resistive instabilities, for discovering the inverse scattering transform leading to soliton solutions of many nonlinear partial differential equations and for inventing the residue method of determining the transition to global chaos. The excellence in Plasma Physics Research Award was presented to Nathaniel A. Fisch for theoretical investigations of noninductive current generation in toroidally confined plasma. Wim Pieter Leemans received the Simon Ramo Award for experimental and simulational contributions to laser-plasma physics. William R. Sears was given the 1992 Fuid Dynamics Prize for contributions to the study of steady and unsteady aerodynamics, aeroacoustics, magnetoaerodynamics,and wind tunnel design. William C. Reynolds received the Otto Laporte Award for experimental, theoretical, and computational work in turbulence modeling and control and leadership in direct numerical simulation and large eddy simulation.
Soderman, Paul T.; Olson, Larry (Technical Monitor)
1995-01-01
The NFAC 40- by 80- Foot Wind Tunnel at Ames is being refurbished with a new, deep acoustic lining in the test section which will make the facility nearly anechoic over a large frequency range. The modification history, key elements, and schedule will be discussed. Design features and expected performance gains will be described. Background noise reductions will be summarized. Improvements in aeroacoustic research techniques have been developed and used recently at NFAC on several wind tunnel tests of High Speed Research models. Research on quiet inflow microphones and struts will be described. The Acoustic Survey Apparatus in the 40x80 will be illustrated. A special intensity probe was tested for source localization. Multi-channel, high speed digital data acquisition is now used for acoustics. And most important, phased microphone arrays have been developed and tested which have proven to be very powerful for source identification and increased signal-to-noise ratio. Use of these tools for the HEAT model will be illustrated. In addition, an acoustically absorbent symmetry plane was built to satisfy the HEAT semispan aerodynamic and acoustic requirements. Acoustic performance of that symmetry plane will be shown.
vanderWall, Berend G.; Lim, Joon W.; Smith, Marilyn J.; Jung, Sung N.; Bailly, Joelle; Baeder, James D.; Boyd, D. Douglas, Jr.
2013-01-01
Significant advancements in computational fluid dynamics (CFD) and their coupling with computational structural dynamics (CSD, or comprehensive codes) for rotorcraft applications have been achieved recently. Despite this, CSD codes with their engineering level of modeling the rotor blade dynamics, the unsteady sectional aerodynamics and the vortical wake are still the workhorse for the majority of applications. This is especially true when a large number of parameter variations is to be performed and their impact on performance, structural loads, vibration and noise is to be judged in an approximate yet reliable and as accurate as possible manner. In this article, the capabilities of such codes are evaluated using the HART II International Workshop database, focusing on a typical descent operating condition which includes strong blade-vortex interactions. A companion article addresses the CFD/CSD coupled approach. Three cases are of interest: the baseline case and two cases with 3/rev higher harmonic blade root pitch control (HHC) with different control phases employed. One setting is for minimum blade-vortex interaction noise radiation and the other one for minimum vibration generation. The challenge is to correctly predict the wake physics-especially for the cases with HHC-and all the dynamics, aerodynamics, modifications of the wake structure and the aero-acoustics coming with it. It is observed that the comprehensive codes used today have a surprisingly good predictive capability when they appropriately account for all of the physics involved. The minimum requirements to obtain these results are outlined.
Serration Design Methodology for Wind Turbine Noise Reduction
Mathew, J.; Singh, A.; Madsen, J.; Arce León, C.
2016-09-01
Trailing edge serrations are today an established method to reduce the aeroacoustic noise from wind turbine blades. In this paper, a brief introduction to the aerodynamic and acoustic design procedure used at LM Wind Power is given. Early field tests on serrations, retrofitted to the turbine blades, gave preliminary indication of their noise reduction potential. However, a multitude of challenges stand in the way of any proof of concept and a viable commercial product. LM undertook a methodical test and validation procedure to understand the impact of design parameters on serration performance, and quantify the uncertainties associated with the proposed designs. Aerodynamic and acoustic validation tests were carried out in number of wind tunnel facilities. Models were written to predict the aerodynamic, acoustic and structural performance of the serrations. LM serration designs have evolved over the period of time to address constraints imposed by aero performance, structural reliability, manufacturing and installation. The latest LM serration offering was tested in the field on three different wind turbines. A consistent noise reduction in excess of 1.5 dB was achieved in the field for all three turbines.
Baumeister, Kenneth J.; Baumeister, Joseph F.
1994-01-01
An analytical procedure is presented, called the modal element method, that combines numerical grid based algorithms with eigenfunction expansions developed by separation of variables. A modal element method is presented for solving potential flow in a channel with two-dimensional cylindrical like obstacles. The infinite computational region is divided into three subdomains; the bounded finite element domain, which is characterized by the cylindrical obstacle and the surrounding unbounded uniform channel entrance and exit domains. The velocity potential is represented approximately in the grid based domain by a finite element solution and is represented analytically by an eigenfunction expansion in the uniform semi-infinite entrance and exit domains. The calculated flow fields are in excellent agreement with exact analytical solutions. By eliminating the grid surrounding the obstacle, the modal element method reduces the numerical grid size, employs a more precise far field boundary condition, as well as giving theoretical insight to the interaction of the obstacle with the mean flow. Although the analysis focuses on a specific geometry, the formulation is general and can be applied to a variety of problems as seen by a comparison to companion theories in aeroacoustics and electromagnetics.
An unsteady aerodynamic formulation for efficient rotor tonal noise prediction
Gennaretti, M.; Testa, C.; Bernardini, G.
2013-12-01
An aerodynamic/aeroacoustic solution methodology for predction of tonal noise emitted by helicopter rotors and propellers is presented. It is particularly suited for configurations dominated by localized, high-frequency inflow velocity fields as those generated by blade-vortex interactions. The unsteady pressure distributions are determined by the sectional, frequency-domain Küssner-Schwarz formulation, with downwash including the wake inflow velocity predicted by a three-dimensional, unsteady, panel-method formulation suited for the analysis of rotors operating in complex aerodynamic environments. The radiated noise is predicted through solution of the Ffowcs Williams-Hawkings equation. The proposed approach yields a computationally efficient solution procedure that may be particularly useful in preliminary design/multidisciplinary optimization applications. It is validated through comparisons with solutions that apply the airloads directly evaluated by the time-marching, panel-method formulation. The results are provided in terms of blade loads, noise signatures and sound pressure level contours. An estimation of the computational efficiency of the proposed solution process is also presented.
Directory of Open Access Journals (Sweden)
Nicolas Lippitz
2016-08-01
Full Text Available As a reaction to the increasing noise pollution, caused by the expansion of airports close to residential areas, porous trailing edges are investigated to reduce the aeroacoustic noise produced by flow around the airframe. Besides mechanical and acoustical investigations of porous materials, the fouling behavior of promising materials is an important aspect to estimate the performance in long-term use. For this study, two sintered fiber felts were selected for a long-term fouling experiment where the development of the flow resistivity and accumulation of dirt was observed. Based on 3D structural characterizations obtained from X-ray tomography of the initial materials, acoustic models (Biot and Johnson–Champoux–Allard in the frame of the transfer matrix method were applied to the sintered fiber felts. Flow resistivity measurements and the measurements of the absorption coefficient in an impedance tube are the basis for a fouling model for sintered fiber felts. The contribution will conclude with recommendations concerning the modeling of pollution processes of porous materials.
Screening of Potential Landing Gear Noise Control Devices at Virginia Tech For QTD II Flight Test
Ravetta, Patricio A.; Burdisso, Ricardo A.; Ng, Wing F.; Khorrami, Mehdi R.; Stoker, Robert W.
2007-01-01
In support of the QTD II (Quiet Technology Demonstrator) program, aeroacoustic measurements of a 26%-scale, Boeing 777 main landing gear model were conducted in the Virginia Tech Stability Tunnel. The objective of these measurements was to perform risk mitigation studies on noise control devices for a flight test performed at Glasgow, Montana in 2005. The noise control devices were designed to target the primary main gear noise sources as observed in several previous tests. To accomplish this task, devices to reduce noise were built using stereo lithography for landing gear components such as the brakes, the forward cable harness, the shock strut, the door/strut gap and the lower truck. The most promising device was down selected from test results. In subsequent stages, the initial design of the selected lower truck fairing was improved to account for all the implementation constraints encountered in the full-scale airplane. The redesigned truck fairing was then retested to assess the impact of the modifications on the noise reduction potential. From extensive acoustic measurements obtained using a 63-element microphone phased array, acoustic source maps and integrated spectra were generated in order to estimate the noise reduction achievable with each device.
Institute of Scientific and Technical Information of China (English)
赵小见; 赵磊; 陈农
2013-01-01
The CLEAN arithmetic based on Spatial Source Coherence is developed and then applied to the wind tunnel test in the paper. The mechanism for this method is introducing a clean beam to instead the main lobe of beam picture iteratively, and getting rid of side lobe for background noise of wind tunnel or microphones distribution in phase array. The data from test in wind tunnel is optimized with this method. The results show that it improves the resolving power of low frequency noise and increases the signal-to-noise of the aero-acoustics test greatly. In the paper, coefficient K for judging the performance of phase array is also introduced, which including the effect to the resolving power both for frequency and distance from array to sound source plane. To some point, it is helpful to improve the efficiency for the coefficient K inducted.%发展应用了基于相干声源假设的CLEAN优化算法,该算法通过反复引入洁净波束来代替波束图上主瓣,逐步去掉由于背景噪声或者阵列阵元分布特点引入的旁瓣.用该算法对风洞实验结果进行了优化,提高了低频噪声的分辨率和试验的信噪比.还首次提出衡量相阵列声源分辨率的综合指标系数K,它综合反映了不同分析频率、不同阵列与声源平面距离对声源分辨率的影响,在一定程度上可以提高阵列设计的效率.
Open Rotor Tone Shielding Methods for System Noise Assessments Using Multiple Databases
Bahr, Christopher J.; Thomas, Russell H.; Lopes, Leonard V.; Burley, Casey L.; Van Zante, Dale E.
2014-01-01
Advanced aircraft designs such as the hybrid wing body, in conjunction with open rotor engines, may allow for significant improvements in the environmental impact of aviation. System noise assessments allow for the prediction of the aircraft noise of such designs while they are still in the conceptual phase. Due to significant requirements of computational methods, these predictions still rely on experimental data to account for the interaction of the open rotor tones with the hybrid wing body airframe. Recently, multiple aircraft system noise assessments have been conducted for hybrid wing body designs with open rotor engines. These assessments utilized measured benchmark data from a Propulsion Airframe Aeroacoustic interaction effects test. The measured data demonstrated airframe shielding of open rotor tonal and broadband noise with legacy F7/A7 open rotor blades. Two methods are proposed for improving the use of these data on general open rotor designs in a system noise assessment. The first, direct difference, is a simple octave band subtraction which does not account for tone distribution within the rotor acoustic signal. The second, tone matching, is a higher-fidelity process incorporating additional physical aspects of the problem, where isolated rotor tones are matched by their directivity to determine tone-by-tone shielding. A case study is conducted with the two methods to assess how well each reproduces the measured data and identify the merits of each. Both methods perform similarly for system level results and successfully approach the experimental data for the case study. The tone matching method provides additional tools for assessing the quality of the match to the data set. Additionally, a potential path to improve the tone matching method is provided.
Offshore Renewable Energy R&D (Fact Sheet)
Energy Technology Data Exchange (ETDEWEB)
2011-10-01
This fact sheet describes the offshore renewable energy R&D efforts at NREL's NWTC. As the United States increases its efforts to tap the domestic energy sources needed to diversify its energy portfolio and secure its energy supply, more attention is being focused on the rich renewable resources located offshore. Offshore renewable energy sources include offshore wind, waves, tidal currents, ocean and river currents, and ocean thermal gradients. According to a report published by the National Renewable Energy Laboratory (NREL) in 2010,1 U.S. offshore wind resources have a gross potential generating capacity four times greater than the nation's present electric capacity, and the Electric Power Research Institute estimates that the nation's ocean energy resources could ultimately supply at least 10% of its electric supply. For more than 30 years, NREL has advanced the science of renewable energy while building the capabilities to guide rapid deployment of commercial applications. Since 1993, NREL's National Wind Technology Center (NWTC) has been the nation's premier wind energy research facility, specializing in the advancement of wind technologies that range in size from a kilowatt to several megawatts. For more than 8 years, the NWTC has been an international leader in the field of offshore floating wind system analysis. Today, researchers at the NWTC are taking their decades of experience and extensive capabilities and applying them to help industry develop cost-effective hydrokinetic systems that convert the kinetic energy in water to provide power for our nation's heavily populated coastal regions. The center's capabilities and experience cover a wide spectrum of wind and water energy engineering disciplines, including atmospheric and ocean fluid mechanics, aerodynamics; aeroacoustics, hydrodynamics, structural dynamics, control systems, electrical systems, and testing.
Space-Time Conservation Element and Solution Element Method Being Developed
Chang, Sin-Chung; Himansu, Ananda; Jorgenson, Philip C. E.; Loh, Ching-Yuen; Wang, Xiao-Yen; Yu, Sheng-Tao
1999-01-01
The engineering research and design requirements of today pose great computer-simulation challenges to engineers and scientists who are called on to analyze phenomena in continuum mechanics. The future will bring even more daunting challenges, when increasingly complex phenomena must be analyzed with increased accuracy. Traditionally used numerical simulation methods have evolved to their present state by repeated incremental extensions to broaden their scope. They are reaching the limits of their applicability and will need to be radically revised, at the very least, to meet future simulation challenges. At the NASA Lewis Research Center, researchers have been developing a new numerical framework for solving conservation laws in continuum mechanics, namely, the Space-Time Conservation Element and Solution Element Method, or the CE/SE method. This method has been built from fundamentals and is not a modification of any previously existing method. It has been designed with generality, simplicity, robustness, and accuracy as cornerstones. The CE/SE method has thus far been applied in the fields of computational fluid dynamics, computational aeroacoustics, and computational electromagnetics. Computer programs based on the CE/SE method have been developed for calculating flows in one, two, and three spatial dimensions. Results have been obtained for numerous problems and phenomena, including various shock-tube problems, ZND detonation waves, an implosion and explosion problem, shocks over a forward-facing step, a blast wave discharging from a nozzle, various acoustic waves, and shock/acoustic-wave interactions. The method can clearly resolve shock/acoustic-wave interactions, wherein the difference of the magnitude between the acoustic wave and shock could be up to six orders. In two-dimensional flows, the reflected shock is as crisp as the leading shock. CE/SE schemes are currently being used for advanced applications to jet and fan noise prediction and to chemically
NASA Tech Briefs, February 2007
2007-01-01
Topics covered include: Calibration Test Set for a Phase-Comparison Digital Tracker; Wireless Acoustic Measurement System; Spiral Orbit Tribometer; Arrays of Miniature Microphones for Aeroacoustic Testing; Predicting Rocket or Jet Noise in Real Time; Computational Workbench for Multibody Dynamics; High-Power, High-Efficiency Ka-Band Space Traveling-Wave Tube; Gratings and Random Reflectors for Near-Infrared PIN Diodes; Optically Transparent Split-Ring Antennas for 1 to 10 GHz; Ice-Penetrating Robot for Scientific Exploration; Power-Amplifier Module for 145 to 165 GHz; Aerial Videography From Locally Launched Rockets; SiC Multi-Chip Power Modules as Power-System Building Blocks; Automated Design of Restraint Layer of an Inflatable Vessel; TMS for Instantiating a Knowledge Base With Incomplete Data; Simulating Flights of Future Launch Vehicles and Spacecraft; Control Code for Bearingless Switched- Reluctance Motor; Machine Aided Indexing and the NASA Thesaurus; Arbitrating Control of Control and Display Units; Web-Based Software for Managing Research; Driver Code for Adaptive Optics; Ceramic Paste for Patching High-Temperature Insulation; Fabrication of Polyimide-Matrix/Carbon and Boron-Fiber Tape; Protective Skins for Aerogel Monoliths; Code Assesses Risks Posed by Meteoroids and Orbital Debris; Asymmetric Bulkheads for Cylindrical Pressure Vessels; Self-Regulating Water-Separator System for Fuel Cells; Self-Advancing Step-Tap Drills; Array of Bolometers for Submillimeter- Wavelength Operation; Delta-Doped CCDs as Detector Arrays in Mass Spectrometers; Arrays of Bundles of Carbon Nanotubes as Field Emitters; Staggering Inflation To Stabilize Attitude of a Solar Sail; and Bare Conductive Tether for Decelerating a Spacecraft.
A Comparison of the Noise Characteristics of a Conventional Slat and Krueger Flap
Bahr, Christopher J.; Hutcheson, Florence V.; Thomas, Russell H.; Housman, Jeffery A.
2016-01-01
An aeroacoustic test of two types of leading-edge high-lift devices has been conducted in the NASA Langley Quiet Flow Facility. The test compares a conventional slat with a notional equivalent-mission Krueger flap. The test matrix includes points that allow for direct comparison of the conventional and Krueger devices for equivalent-mission configurations, where the two high-lift devices satisfy the same lift requirements for a free air flight path at the same cruise airfoil angle of attack. Measurements are made for multiple Mach numbers and directivity angles. Results indicate that the Krueger flap shows similar agreement to the expected power law scaling of a conventional flap, both in terms of Strouhal number and fixed frequency (as a surrogate for Helmholtz number). Directivity patterns vary depending on the specific slat and Krueger orientations. Varying the slat gap while holding overlap constant has the same influence on both the conventional slat and Krueger flap acoustic signature. Closing the gap shows dramatic reduction in levels for both devices. Varying the Krueger overlap has a different effect on the data when compared to varying the slat overlap, but analysis is limited by acoustic sources that regularly present themselves in model-scale wind tunnel testing but are not present for full-scale vehicles. The Krueger cavity is found to have some influence on level and directivity, though not as much as the other considered parameter variations. Overall, while the spectra of the two devices are different in detail, their scaling behavior for varying parameters is extremely similar.
Crivellini, A.
2016-02-01
This paper deals with the numerical performance of a sponge layer as a non-reflective boundary condition. This technique is well known and widely adopted, but only recently have the reasons for a sponge failure been recognised, in analysis by Mani. For multidimensional problems, the ineffectiveness of the method is due to the self-reflections of the sponge occurring when it interacts with an oblique acoustic wave. Based on his theoretical investigations, Mani gives some useful guidelines for implementing effective sponge layers. However, in our opinion, some practical indications are still missing from the current literature. Here, an extensive numerical study of the performance of this technique is presented. Moreover, we analyse a reduced sponge implementation characterised by undamped partial differential equations for the velocity components. The main aim of this paper relies on the determination of the minimal width of the layer, as well as of the corresponding strength, required to obtain a reflection error of no more than a few per cent of that observed when solving the same problem on the same grid, but without employing the sponge layer term. For this purpose, a test case of computational aeroacoustics, the single airfoil gust response problem, has been addressed in several configurations. As a direct consequence of our investigation, we present a well documented and highly validated reference solution for the far-field acoustic intensity, a result that is not well established in the literature. Lastly, the proof of the accuracy of an algorithm for coupling sub-domains solved by the linear and non-liner Euler governing equations is given. This result is here exploited to adopt a linear-based sponge layer even in a non-linear computation.
A Model for Shear Layer Effects on Engine Noise Radiation
Nark, Douglas M.; Farassat, F.; Pope, D. Stuart; Vatsa, V.
2004-01-01
Prediction of aircraft engine noise is an important aspect of addressing the issues of community noise and cabin noise control. The development of physics based methodologies for performing such predictions has been a focus of Computational Aeroacoustics (CAA). A recent example of code development in this area is the ducted fan noise propagation and radiation code CDUCT-LaRC. Included within the code is a duct radiation model that is based on the solution of FfowcsWilliams-Hawkings (FW-H) equation with a penetrable data surface. Testing of this equation for many acoustic problems has shown it to provide generally better results than the Kirchhoff formula for moving surfaces. Currently, the data surface is taken to be the inlet or exhaust plane for inlet or aft-fan cases, respectively. While this provides reasonable results in many situations, these choices of data surface location lead to a few limitations. For example, the shear layer between the bypass ow and external stream can refract the sound waves radiated to the far field. Radiation results can be improved by including this effect, as well as the rejection of the sound in the bypass region from the solid surface external to the bypass duct surrounding the core ow. This work describes the implementation, and possible approximation, of a shear layer boundary condition within CDUCT-LaRC. An example application also illustrates the improvements that this extension offers for predicting noise radiation from complex inlet and bypass duct geometries, thereby providing a means to evaluate external treatments in the vicinity of the bypass duct exhaust plane.
Aerodynamic Performance of Scale-Model Turbofan Outlet Guide Vanes Designed for Low Noise
Hughes, Christopher E.
2001-01-01
The design of effective new technologies to reduce aircraft propulsion noise is dependent on an understanding of the noise sources and noise generation mechanisms in the modern turbofan engine. In order to more fully understand the physics of noise in a turbofan engine, a comprehensive aeroacoustic wind tunnel test programs was conducted called the 'Source Diagnostic Test.' The text was cooperative effort between NASA and General Electric Aircraft Engines, as part of the NASA Advanced Subsonic Technology Noise Reduction Program. A 1/5-scale model simulator representing the bypass stage of a current technology high bypass ratio turbofan engine was used in the test. The test article consisted of the bypass fan and outlet guide vanes in a flight-type nacelle. The fan used was a medium pressure ratio design with 22 individual, wide chord blades. Three outlet guide vane design configurations were investigated, representing a 54-vane radial Baseline configuration, a 26-vane radial, wide chord Low Count configuration and a 26-vane, wide chord Low Noise configuration with 30 deg of aft sweep. The test was conducted in the NASA Glenn Research Center 9 by 15-Foot Low Speed Wind Tunnel at velocities simulating the takeoff and approach phases of the aircraft flight envelope. The Source Diagnostic Test had several acoustic and aerodynamic technical objectives: (1) establish the performance of a scale model fan selected to represent the current technology turbofan product; (2) assess the performance of the fan stage with each of the three distinct outlet guide vane designs; (3) determine the effect of the outlet guide vane configuration on the fan baseline performance; and (4) conduct detailed flowfield diagnostic surveys, both acoustic and aerodynamic, to characterize and understand the noise generation mechanisms in a turbofan engine. This paper addresses the fan and stage aerodynamic performance results from the Source Diagnostic Test.
Viscous Flutter of a Finite Elastic Membrane in Poiseuille Flow
Huang, L.
2001-10-01
Flow-induced vibration in a collapsible tube is relevant to many biomedical applications including the human respiratory system. This paper presents a linear analysis of the coupling between Poiseuille flow and a tensioned membrane of finite length using an eigenvalue approach. The undisturbed state of the channel flow is perfectly parallel. To some extent, this configuration bridges the gap between two types of theoretical models: one for the travelling-wave flutter in an infinite, flexible channel, and the other for the self-induced oscillation of a collapsing section of a Starling-resistor tube. In our study, we focus on the parameter range where the wall-to-fluid mass ratio is high (100), and the Reynolds number based on the maximum flow velocity in the channel is moderately high (200). Eigenmodes representing both static divergence and flutter are found. Particular attention is paid to the energetics of flutter modes. It is shown that energy transfer from the flow to the membrane occurs as a result of unstable, downstream-travelling waves, while the upstream-travelling waves are stable and release most of the transferred energy back to the flow. Coupling between different in vacuo modes offers another view of the origin of energy transfer. In addition, an energy conservation analysis similar to the one used in aeroacoustics is carried out. It is shown that terms directly proportional to fluid viscosity contribute most to the production of fluctuation energy, leading to a special type of dynamic instability which resembles both Tollmien-Schlichting instability in the sense that the fluid viscosity destabilises, and traditional travelling wave flutter since the structural damping plays the role of stabilising. Effects of the membrane mass, length and structural damping are also studied. The characteristics of the membrane flutter are found to depend crucially on the upstream and downstream boundary conditions.
Active Flow Effectors for Noise and Separation Control
Turner, Travis L.
2011-01-01
New flow effector technology for separation control and enhanced mixing is based upon shape memory alloy hybrid composite (SMAHC) technology. The technology allows for variable shape control of aircraft structures through actively deformable surfaces. The flow effectors are made by embedding shape memory alloy actuator material in a composite structure. When thermally actuated, the flow effector def1ects into or out of the flow in a prescribed manner to enhance mixing or induce separation for a variety of applications, including aeroacoustic noise reduction, drag reduction, and f1ight control. The active flow effectors were developed for noise reduction as an alternative to fixed-configuration effectors, such as static chevrons, that cannot be optimized for airframe installation effects or variable operating conditions and cannot be retracted for off-design or fail-safe conditions. Benefits include: Increased vehicle control, overall efficiency, and reduced noise throughout all f1ight regimes, Reduced flow noise, Reduced drag, Simplicity of design and fabrication, Simplicity of control through direct current stimulation, autonomous re sponse to environmental heating, fast re sponse, and a high degree of geometric stability. The concept involves embedding prestrained SMA actuators on one side of the chevron neutral axis in order to generate a thermal moment and def1ect the structure out of plane when heated. The force developed in the host structure during def1ection and the aerodynamic load is used for returning the structure to the retracted position. The chevron design is highly scalable and versatile, and easily affords active and/or autonomous (environmental) control. The technology offers wide-ranging market applications, including aerospace, automotive, and any application that requires flow separation or noise control.
Thomas, Russell H.; Burley, Casey L.; Lopes, Leonard V.; Bahr, Christopher J.; Gern, Frank H.; VanZante, Dale E.
2014-01-01
An aircraft system noise assessment was conducted for a hybrid wing body freighter aircraft concept configured with three open rotor engines. The primary objective of the study was to determine the aircraft system level noise given the significant impact of installation effects including shielding the open rotor noise by the airframe. The aircraft was designed to carry a payload of 100,000 lbs on a 6,500 nautical mile mission. An experimental database was used to establish the propulsion airframe aeroacoustic installation effects including those from shielding by the airframe planform, interactions with the control surfaces, and additional noise reduction technologies. A second objective of the study applied the impacts of projected low noise airframe technology and a projection of advanced low noise rotors appropriate for the NASA N+2 2025 timeframe. With the projection of low noise rotors and installation effects, the aircraft system level was 26.0 EPNLdB below Stage 4 level with the engine installed at 1.0 rotor diameters upstream of the trailing edge. Moving the engine to 1.5 rotor diameters brought the system level noise to 30.8 EPNLdB below Stage 4. At these locations on the airframe, the integrated level of installation effects including shielding can be as much as 20 EPNLdB cumulative in addition to lower engine source noise from advanced low noise rotors. And finally, an additional set of technology effects were identified and the potential impact at the system level was estimated for noise only without assessing the impact on aircraft performance. If these additional effects were to be included it is estimated that the potential aircraft system noise could reach as low as 38.0 EPNLdB cumulative below Stage 4.
Directory of Open Access Journals (Sweden)
Seung Heo
2015-09-01
Full Text Available In this study, efficient numerical method is proposed for predicting tonal and broadband noises of a centrifugal fan unit. The proposed method is based on Hybrid Computational Aero-Acoustic (H-CAA techniques combined with Unsteady Fast Random Particle Mesh (U-FRPM method. The U-FRPM method is developed by extending the FRPM method proposed by Ewert et al. and is utilized to synthesize turbulence flow field from unsteady RANS solutions. The H-CAA technique combined with U-FRPM method is applied to predict broadband as well as tonal noises of a centrifugal fan unit in a household refrigerator. Firstly, unsteady flow field driven by a rotating fan is computed by solving the RANS equations with Computational Fluid Dynamic (CFD techniques. Main source regions around the rotating fan are identified by examining the computed flow fields. Then, turbulence flow fields in the main source regions are synthesized by applying the U-FRPM method. The acoustic analogy is applied to model acoustic sources in the main source regions. Finally, the centrifugal fan noise is predicted by feeding the modeled acoustic sources into an acoustic solver based on the Boundary Element Method (BEM. The sound spectral levels predicted using the current numerical method show good agreements with the measured spectra at the Blade Pass Frequencies (BPFs as well as in the high frequency range. On the more, the present method enables quantitative assessment of relative contributions of identified source regions to the sound field by comparing predicted sound pressure spectrum due to modeled sources.
Heo, Seung; Cheong, Cheolung; Kim, Taehoon
2015-09-01
In this study, efficient numerical method is proposed for predicting tonal and broadband noises of a centrifugal fan unit. The proposed method is based on Hybrid Computational Aero-Acoustic (H-CAA) techniques combined with Unsteady Fast Random Particle Mesh (U-FRPM) method. The U-FRPM method is developed by extending the FRPM method proposed by Ewert et al. and is utilized to synthesize turbulence flow field from unsteady RANS solutions. The H-CAA technique combined with U-FRPM method is applied to predict broadband as well as tonal noises of a centrifugal fan unit in a household refrigerator. Firstly, unsteady flow field driven by a rotating fan is computed by solving the RANS equations with Computational Fluid Dynamic (CFD) techniques. Main source regions around the rotating fan are identified by examining the computed flow fields. Then, turbulence flow fields in the main source regions are synthesized by applying the U-FRPM method. The acoustic analogy is applied to model acoustic sources in the main source regions. Finally, the centrifugal fan noise is predicted by feeding the modeled acoustic sources into an acoustic solver based on the Boundary Element Method (BEM). The sound spectral levels predicted using the current numerical method show good agreements with the measured spectra at the Blade Pass Frequencies (BPFs) as well as in the high frequency range. On the more, the present method enables quantitative assessment of relative contributions of identified source regions to the sound field by comparing predicted sound pressure spectrum due to modeled sources.
Directory of Open Access Journals (Sweden)
M. Younsi
2007-01-01
Full Text Available The aim of this study is to evaluate the influence of design parameters on the unsteady flow in a forward-curved centrifugal fan and their impact on the aeroacoustic behavior. To do so, numerical and experimental studies have been carried out on four centrifugal impellers designed with various geometrical parameters. The same volute casing has been used to study these impellers. The effects on the unsteady flow behavior related to irregular blade spacing, blade count and radial distance between the impeller periphery and the volute tongue have been studied. The numerical simulations of the unsteady flow have been carried out using computational fluid dynamics (CFD tools based on the unsteady Reynolds averaged Navier Stokes (URANS approach. The study is focused on the unsteadiness induced by the aerodynamic interaction between the volute and the rotating impeller blades. In order to predict the acoustic pressure at far field, the unsteady flow variables provided by the CFD calculations have been used as inputs in the Ffowcs Williams-Hawkings equations (FW-H. The experimental part of this work concerns measurement of aerodynamic performance of the fans using a test bench built according to ISO 5801 (1997 standard. In addition to this, pressure microphones have been flush mounted on the volute tongue surface in order to measure the wall pressure fluctuations. The sound pressure level (SPL measurements have been carried out in an anechoic room in order to remove undesired noise reflections. Finally, the numerical results have been compared with the experimental measurements and a correlation between the wall pressure fluctuations and the far field noise signals has been found.
Numerical simulation of the generation mechanism of axisymmetric supersonic jet screech tones
Li, X. D.; Gao, J. H.
2005-08-01
In this paper an axisymmetric computational aeroacoustic procedure is developed to investigate the generation mechanism of axisymmetric supersonic jet screech tones. The axisymmetric Navier-Stokes equations and the two equations standard k-ɛ turbulence model modified by Turpin and Troyes ["Validation of a two-equation turbulence model for axisymmetric reacting and non-reaction flows," AIAA Paper No. 2000-3463 (2000)] are solved in the generalized curvilinear coordinate system. A generalized wall function is applied in the nozzle exit wall region. The dispersion-relation-preserving scheme is applied for space discretization. The 2N storage low-dissipation and low-dispersion Runge-Kutta scheme is employed for time integration. Much attention is paid to far-field boundary conditions and turbulence model. The underexpanded axisymmetric supersonic jet screech tones are simulated over the Mach number from 1.05 to 1.2. Numerical results are presented and compared with the experimental data by other researchers. The simulated wavelengths of A0, A1, A2, and B modes and part of simulated amplitudes agree very well with the measurement data by Ponton and Seiner ["The effects of nozzle exit lip thickness on plume resonance," J. Sound Vib. 154, 531 (1992)]. In particular, the phenomena of modes jumping have been captured correctly although the numerical procedure has to be improved to predict the amplitudes of supersonic jet screech tones more accurately. Furthermore, the phenomena of shock motions are analyzed. The predicted splitting and combination of shock cells are similar with the experimental observations of Panda ["Shock oscillation in underexpanded screeching jets," J. Fluid. Mech. 363, 173 (1998)]. Finally, the receptivity process is numerically studied and analyzed. It is shown that the receptivity zone is associated with the initial thin shear layer, and the incoming and reflected sound waves.
Proceedings of the XXII A.I.VE.LA. National Meeting
Primo Tomasini, Enrico
2015-11-01
A.I.VE.LA. - the Italian Association of Laser Velocimetry and non-invasive diagnostics - is a non-profit cultural association whose objective is to promote and support research in the field of non-contact or minimally invasive measurement techniques, particularly electromagnetic-based techniques and optical techniques. Through its Annual Meeting, AIVELA aims to create an active and stimulating forum where current research results and technical advances can be exchanged and the development of new systems for laboratory use, field testing and industrial application can be promoted. The techniques covered include Laser Doppler Anemometry - LDA, Phase Doppler Anemometry - PDA, Image Velocimetry - PIV, Flow visualization techniques, Spectroscopic measurement techniques (LIF, Raman, etc.), Laser Doppler Vibrometry - LDV, Speckle Pattern Interferometry - ESPI, Holographic techniques, Shearography, Digital Image Correlation - DIC, Moiré techniques, Structured light techniques, Infrared imaging, Photoelasticity, Image based measurement techniques, Ultrasonic sensing, Acoustic and Aeroacoustic measurements, etc. The first Annual Meeting was held back in October 1992 and since then there has been a large consensus among the research and scientific communities that the papers presented at the event are of a high scientific interest. The XXII AIVELA Annual Meeting was held at the Faculty of Engineering of University of Rome Tor Vergata on 15-16 December 2014 and was organised in collaboration with the International Master Courses in "Protection Against CBRNe Events". This volume contains a selection of the papers presented at the event. The detailed Programme of the Meeting can be found at: http://www.aivela.org/XXII_Convegno/index.html Trusting our Association and its initiatives will meet your interest, I wish to thank you in advance for your kind attention and hope to meet you soon at one of our events.
Yang, Jun; Yuan, Shouqi; Yuan, Jianping; Si, Qiaorui; Pei, Ji
2014-05-01
With the increasing noise pollution, low noise optimization of centrifugal pimps has become a hot topic. However, experimental study on this problem is unacceptable for industrial applications due to unsustainable cost. A hybrid method that couples computational fluid dynamics (CFD) with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects. Under Langthjem's assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps, the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software. The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency (BPF) noise, and the sound pressure level (SPL) reached peaks near the cutoff that corresponded with the pressure pulsation in this region. An experiment is performed to validate this prediction. Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model. The simulation results for the noise are analyzed and compared with the experimental results. The variation in the calculated noise with changes in the flow agreed well with the experimental results. When the flow rate was increased, the SPL first decreased and reached the minimum near the best efficient point (BEP); it then increased when the flow rate was further increased. The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps. The noise simulation method in current study has a good feasibility and suitability, which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.
Humphreys, William M., Jr.; Lockard, David P.; Khorrami, Mehdi R.; Culliton, William G.; McSwain, Robert G.; Ravetta, Patricio A.; Johns, Zachary
2016-01-01
A new aeroacoustic measurement capability has been developed consisting of a large channelcount, field-deployable microphone phased array suitable for airframe noise flyover measurements for a range of aircraft types and scales. The array incorporates up to 185 hardened, weather-resistant sensors suitable for outdoor use. A custom 4-mA current loop receiver circuit with temperature compensation was developed to power the sensors over extended cable lengths with minimal degradation of the signal to noise ratio and frequency response. Extensive laboratory calibrations and environmental testing of the sensors were conducted to verify the design's performance specifications. A compact data system combining sensor power, signal conditioning, and digitization was assembled for use with the array. Complementing the data system is a robust analysis system capable of near real-time presentation of beamformed and deconvolved contour plots and integrated spectra obtained from array data acquired during flyover passes. Additional instrumentation systems needed to process the array data were also assembled. These include a commercial weather station and a video monitoring / recording system. A detailed mock-up of the instrumentation suite (phased array, weather station, and data processor) was performed in the NASA Langley Acoustic Development Laboratory to vet the system performance. The first deployment of the system occurred at Finnegan Airfield at Fort A.P. Hill where the array was utilized to measure the vehicle noise from a number of sUAS (small Unmanned Aerial System) aircraft. A unique in-situ calibration method for the array microphones using a hovering aerial sound source was attempted for the first time during the deployment.
Henderson, Brenda S.; Doty, Mike
2012-01-01
Acoustic and flow-field experiments were conducted on exhaust concepts for the next generation supersonic, commercial aircraft. The concepts were developed by Lockheed Martin (LM), Rolls-Royce Liberty Works (RRLW), and General Electric Global Research (GEGR) as part of an N+2 (next generation forward) aircraft system study initiated by the Supersonics Project in NASA s Fundamental Aeronautics Program. The experiments were conducted in the Aero-Acoustic Propulsion Laboratory at the NASA Glenn Research Center. The exhaust concepts presented here utilized lobed-mixers and ejectors. A powered third-stream was implemented to improve ejector acoustic performance. One concept was found to produce stagnant flow within the ejector and the other produced discrete-frequency tones (due to flow separations within the model) that degraded the acoustic performance of the exhaust concept. NASA's Environmentally Responsible Aviation (ERA) Project has been investigating a Hybrid Wing Body (HWB) aircraft as a possible configuration for meeting N+2 system level goals for noise, emissions, and fuel burn. A recently completed NRA led by Boeing Research and Technology resulted in a full-scale aircraft design and wind tunnel model. This model will be tested acoustically in NASA Langley's 14-by 22-Foot Subsonic Tunnel and will include dual jet engine simulators and broadband engine noise simulators as part of the test campaign. The objectives of the test are to characterize the system level noise, quantify the effects of shielding, and generate a valuable database for prediction method development. Further details of the test and various component preparations are described.
Kadem, L.; Knapp, Y.; Pibarot, P.; Bertrand, E.; Garcia, D.; Durand, L. G.; Rieu, R.
2005-12-01
The effective orifice area (EOA) is the most commonly used parameter to assess the severity of aortic valve stenosis as well as the performance of valve substitutes. Particle image velocimetry (PIV) may be used for in vitro estimation of valve EOA. In the present study, we propose a new and simple method based on Howe’s developments of Lighthill’s aero-acoustic theory. This method is based on an acoustical source term (AST) to estimate the EOA from the transvalvular flow velocity measurements obtained by PIV. The EOAs measured by the AST method downstream of three sharp-edged orifices were in excellent agreement with the EOAs predicted from the potential flow theory used as the reference method in this study. Moreover, the AST method was more accurate than other conventional PIV methods based on streamlines, inflexion point or vorticity to predict the theoretical EOAs. The superiority of the AST method is likely due to the nonlinear form of the AST. There was also an excellent agreement between the EOAs measured by the AST method downstream of the three sharp-edged orifices as well as downstream of a bioprosthetic valve with those obtained by the conventional clinical method based on Doppler-echocardiographic measurements of transvalvular velocity. The results of this study suggest that this new simple PIV method provides an accurate estimation of the aortic valve flow EOA. This new method may thus be used as a reference method to estimate the EOA in experimental investigation of the performance of valve substitutes and to validate Doppler-echocardiographic measurements under various physiologic and pathologic flow conditions.
Core Noise - Increasing Importance
Hultgren, Lennart S.
2011-01-01
This presentation is a technical summary of and outlook for NASA-internal and NASA-sponsored external research on core (combustor and turbine) noise funded by the Fundamental Aeronautics Program Subsonic Fixed Wing (SFW) Project. Sections of the presentation cover: the SFW system-level noise metrics for the 2015, 2020, and 2025 timeframes; turbofan design trends and their aeroacoustic implications; the emerging importance of core noise and its relevance to the SFW Reduced-Perceived-Noise Technical Challenge; and the current research activities in the core-noise area, with additional details given about the development of a high-fidelity combustor-noise prediction capability as well as activities supporting the development of improved reduced-order, physics-based models for combustor-noise prediction. The need for benchmark data for validation of high-fidelity and modeling work and the value of a potential future diagnostic facility for testing of core-noise-reduction concepts are indicated. The NASA Fundamental Aeronautics Program has the principal objective of overcoming today's national challenges in air transportation. The SFW Reduced-Perceived-Noise Technical Challenge aims to develop concepts and technologies to dramatically reduce the perceived aircraft noise outside of airport boundaries. This reduction of aircraft noise is critical to enabling the anticipated large increase in future air traffic. Noise generated in the jet engine core, by sources such as the compressor, combustor, and turbine, can be a significant contribution to the overall noise signature at low-power conditions, typical of approach flight. At high engine power during takeoff, jet and fan noise have traditionally dominated over core noise. However, current design trends and expected technological advances in engine-cycle design as well as noise-reduction methods are likely to reduce non-core noise even at engine-power points higher than approach. In addition, future low-emission combustor
New trends in turbulence; Turbulence: nouveaux aspects
Energy Technology Data Exchange (ETDEWEB)
Lesieur, M. [Institut National Polytechnique, LEGI/INPG, Institut de Mecanique, UMR 101, 38 - Grenoble (France); Yaglom, A. [Institut of Atmospheric Physics, Russian Academy of Sciences, Moscow (Russian Federation)]|[MIT, Dept. of Aeronautics and Astronautics, Cambridge, MA (United States); David, F. [CEA Saclay, SPhT, 91 - Gif-sur-Yvette (France)
2001-07-01
According to a Russian scientist, the flow of fluids actually met both in nature and engineering practice are turbulent in the overwhelmingly majority of cases. This document that reviews all the progress made recently in the understanding of turbulence, is made up of 10 courses. Course 1 ''a century of turbulence'' deals with the linear and non-linear points of views. In course 2 ''measures of anisotropy and the universal properties of turbulence'' the author gives a very complete account of fully developed turbulence experimental data both in the laboratory and in the atmosphere. Course 3 ''large-eddy simulations of turbulence (LES)'', LES are powerful tools to simulate the coherent vortices formation and evolution in a deterministic way. In Course 4 ''statistical turbulence modelling for the computation of physically complex flows'' the author describes methods used for predicting statistical industrial flows, where the geometry is right now too complex to allow the use of LES. In course 5 ''computational aero-acoustics'' an informative review of computational aero-acoustics with many applications to aircraft noise, is made. In course 6 ''the topology of turbulence'' the author presents the basis of topological fluid dynamics and stresses the importance of helicity in neutral and in magnetohydrodynamics (MHD) flows. In course 7 ''burgulence'' the authors deal with finite-time singularities, but mostly on the basis of Burger equations in one or several dimensions with the formation of multiple shocks. In course 8 ''2-dimensional turbulence'' the author presents numerous examples of 2D turbulence in the laboratory (rotating or MHD flows, plasmas), in the ocean and in the planetary atmosphere. Course 9 ''analysing and computing turbulent flows using wavelets'' is a useful presentation of
Numerical analysis on noise of rotor with unconventional blade tips based on CFD/Kirchhoff method
Institute of Scientific and Technical Information of China (English)
Wang Bo; Zhao Qijun; Xu Guohua; Ye Liang; Wang Junyi
2013-01-01
A solver is developed aiming at efficiently predicting rotor noise in hover and forward flight.In this solver,the nonlinear near-field solutions are calculated by a hybrid approach which includes the Navier-Stokes and Euler equations based on a moving-embedded grid system and adaptive grid methodology.A combination of the third-order upwind scheme and flux-difference splitting scheme,instead of the second-order center-difference scheme which may cause larger wake dissipation,has been employed in the present computational fluid dynamics (CFD) method.The sound pressure data in the near field can be calculated directly by solving the Navier-Stokes equations,and the sound propagation can be predicted by the Kirchhoffmethod.A harmonic expansion approach is presented for rotor far-field noise prediction,which gives an analytical expression for the integral function in the Kirchhoff formula.As a result,the interpolation process is simplified and the efficiency and accuracy of the interpolation are improved.Then,the high-speed impulsive (HIS) noise of a helicopter rotor at different tip Mach numbers and on different observers is calculated and analyzed in hover and forward flight,which shows a highly directional characteristic of the rotor HIS noise with a maximum value in the rotor plane,and the HSI noise weakens rapidly with the increasing of the directivity angle.In order to investigate the effects of the rotor blade-tip shape on its aeroacoustic characteristics,four kinds of blade tips are designed and their noise characteristics have been simulated.At last,a new unconventional CLOR-Ⅱ blade tip has been designed,and the noise characteristics of the presented CLOR-Ⅱ model rotor have been simulated and measured compared to the reference rotors with a rectangular or swept-back platform blade tip.The results demonstrate that the unconventional CLOR-Ⅱblade tip can significantly reduce the HSI noise of a rotor.
Energy Technology Data Exchange (ETDEWEB)
Andersson, N.; Davidson, L. [Chalmers Univ. of Technology, Goeteborg (Sweden). Division of Thermo and Fluid Dynamics; Eriksson, L.E. [Chalmers Univ. of Technology, Goeteborg (Sweden). Division of Thermo and Fluid Dynamics; Volvo Aero Vorp., Trollhaettan (Sweden)
2005-06-01
Programme, G4RD-CT2000-00313, Laboratoire d'Etude Aerodynamiques, Poitiers; Jordan, P., Gervais, Y., Valiere, J.-C., Foulon, H., 2002. Results from acoustic field measurements. Project deliverable D3.6, JEAN-EU 5th Framework Programme, G4RD-CT2000-00313, Laboratoire d'Etude Aerodynamiques, Poitiers; Jordan, P., Gervais, Y., 2003. Modeling self and shear noise mechanisms in anisotropic turbulence. In: The 9th AIAA/CEAS Aeroacoustics Conference. No. 8743 in AIAA 2003. Hilton Head, SC]. (Author)
International Nuclear Information System (INIS)
-00313, Laboratoire d'Etude Aerodynamiques, Poitiers; Jordan, P., Gervais, Y., Valiere, J.-C., Foulon, H., 2002. Results from acoustic field measurements. Project deliverable D3.6, JEAN-EU 5th Framework Programme, G4RD-CT2000-00313, Laboratoire d'Etude Aerodynamiques, Poitiers; Jordan, P., Gervais, Y., 2003. Modeling self and shear noise mechanisms in anisotropic turbulence. In: The 9th AIAA/CEAS Aeroacoustics Conference. No. 8743 in AIAA 2003. Hilton Head, SC
压力系数分析法的低噪声鼻锥设计%Low-noise Nose-cone Design Using Pressure Coefficient Analysis Method
Institute of Scientific and Technical Information of China (English)
栾海霞; 陈宝; 李兴龙
2016-01-01
在航空声学风洞内进行气流内的噪声测量时，需要在传声器前端安装鼻锥，以降低流场波动对传声器振膜的干扰噪声。目前使用的鼻锥，当流速超过40 m/s时，自噪声大幅度提高，因而无法用于更高速度的流场测试。利用一种鼻锥低噪声设计的分析方法，分析鼻锥表面的压力系数分布规律，并提出一种降低鼻锥自噪声的改进形式，降低不稳定的静态压力的干扰。将鼻锥的透声孔设置在压力稳定区域，可减少流场内不稳定压力波动对被测声波信号的干扰，提高测试结果的准确性，满足更高速度的流场测试需求。%In airflow noise measurements in aero-acoustic wind tunnel, microphone must be jacketed with nose-cone to reduce the disturbance of the air-flow field fluctuation noise to the microphone. However, this method does not work when the flow velocity exceeds 40 m/s since the self-noise of the nose-cone increases dramatically. In this paper, the pressure distribution on the nose-cone surface was analyzed. On this basis, a modified nose-cone shape was proposed which can reduce the disturbance of the unstable static pressure so that the self-noise of the nose-cone can be diminished. By setting the sound-penetrating holes in the steady pressure region, the disturbance of the instable pressure fluctuation to the acoustic signal can be diminished. Therefore, the measurement accuracy is raised and can satisfy the requirements of higher speed wind tunnel tests.
Passive Acoustic Detection of Wind Turbine In-Flow Conditions for Active Control and Optimization
Energy Technology Data Exchange (ETDEWEB)
Murray, Nathan E.
2012-03-12
Wind is a significant source of energy; however, the human capability to produce electrical energy still has many hurdles to overcome. One of these is the unpredictability of the winds in the atmospheric boundary layer (ABL). The ABL is highly turbulent in both stable and unstable conditions (based on the vertical temperature profile) and the resulting fluctuations can have a dramatic impact on wind turbine operation. Any method by which these fluctuations could be observed, estimated, or predicted could provide a benefit to the wind energy industry as a whole. Based on the fundamental coupling of velocity fluctuations to pressure fluctuations in the nearly incompressible flow in the ABL, This work hypothesizes that a ground-based array of infrasonic pressure transducers could be employed to estimate the vertical wind profile over a height relevant for wind turbines. To analyze this hypothesis, experiments and field deployments were conducted. Wind tunnel experiments were performed for a thick turbulent boundary layer over a neutral or heated surface. Surface pressure and velocity probe measurements were acquired simultaneously. Two field deployments yielded surface pressure data from a 49 element array. The second deployment at the Reese Technology Center in Lubbock, TX, also included data from a smaller aperture, 96-element array and a 200-meter tall meteorological tower. Analysis of the data successfully demonstrated the ability to estimate the vertical velocity profile using coherence data from the pressure array. Also, dynamical systems analysis methods were successful in identifying and tracking a gust type event. In addition to the passive acoustic profiling method, this program also investigated a rapid response Doppler SODAR system, the optimization of wind turbine blades for enhanced power with reduced aeroacoustic noise production, and the implementation of a wireless health monitoring system for the wind turbine blades. Each of these other objectives
Airframe Noise Prediction by Acoustic Analogy: Revisited
Farassat, F.; Casper, Jay H.; Tinetti, A.; Dunn, M. H.
2006-01-01
The present work follows a recent survey of airframe noise prediction methodologies. In that survey, Lighthill s acoustic analogy was identified as the most prominent analytical basis for current approaches to airframe noise research. Within this approach, a problem is typically modeled with the Ffowcs Williams and Hawkings (FW-H) equation, for which a geometry-independent solution is obtained by means of the use of the free-space Green function (FSGF). Nonetheless, the aeroacoustic literature would suggest some interest in the use of tailored or exact Green s function (EGF) for aerodynamic noise problems involving solid boundaries, in particular, for trailing edge (TE) noise. A study of possible applications of EGF for prediction of broadband noise from turbulent flow over an airfoil surface and the TE is, therefore, the primary topic of the present work. Typically, the applications of EGF in the literature have been limited to TE noise prediction at low Mach numbers assuming that the normal derivative of the pressure vanishes on the airfoil surface. To extend the application of EGF to higher Mach numbers, the uniqueness of the solution of the wave equation when either the Dirichlet or the Neumann boundary condition (BC) is specified on a deformable surface in motion. The solution of Lighthill s equation with either the Dirichlet or the Neumann BC is given for such a surface using EGFs. These solutions involve both surface and volume integrals just like the solution of FW-H equation using FSGF. Insight drawn from this analysis is evoked to discuss the potential application of EGF to broadband noise prediction. It appears that the use of a EGF offers distinct advantages for predicting TE noise of an airfoil when the normal pressure gradient vanishes on the airfoil surface. It is argued that such an approach may also apply to an airfoil in motion. However, for the prediction of broadband noise not directly associated with a trailing edge, the use of EGF does not
Institute of Scientific and Technical Information of China (English)
李晓东; 李小艳
2011-01-01
The purpose of this paper is to construct a general broadband impedance model which is suited for predicting acoustic propagation problems in time domain. A multi-freedom broadband impedance model for sound propagation over impedance surfaces is proposed and the corresponding time domain impedance boundary condition is presented. Basing on the Extended Helmholtz resonator, the multi-freedom impedance model is constructed through combing with a sum of rational functions with general complex-conjugate pole-residue pairs and it is proved that the impedance model is well-posed. The impedance boundary condition can be implemented into a computational aeroacoustics solver by a recursive convolution technique which results in a fast and computationally efficient algorithm. The two dimensional and three dimensional benchmark problems are selected to validate the accuracy of the current impedance model and time domain simulations. The numerical results are in good agreement with the reference solutions. It is demonstrated that the proposed impedance model can be used to describe the broadband characteristics of acoustic liners. And the corresponding time domain impedance boundary condition is viable and accurate for the prediction of sound propagation over broadband impedance surfaces.%旨在建立通用且适定的宽频阻抗模型用于时域数值模拟计算.基于扩展的Helmholtz共振腔阻抗模型,通过引入共轭复数极点-残值对有理分式组合的方式,提出了一种新型多自由度宽频阻抗模型,并证明了该模型的适定性.频域内阻抗边界条件通过傅里叶反变换的方法转换为宽频时域阻抗边界条件,时域模拟采用递推算法快速实现.分别采用二维和三维标准问题对该宽频阻抗模型及相应的时域边界条件进行校核,数值解和参考解一致.研究结果表明所提出的多自由度阻抗模型能够描述声衬宽频特性,相应的宽频时域阻抗边界条件可以精确预测
High-Temperature Smart Structures for Engine Noise Reduction and Performance Enhancement
Quackenbush, Todd R.; McKillip, Robert M., Jr.
2011-01-01
. The overall conclusion of these design studies was that the cut chevron concept is a critical enabling step in bringing the variable geometry core chevron within reach. The presence of the cut may be aerodynamically undesirable in some respects, but it is present only when the chevron is not immersed in the core jet exhaust. When deployed, the gap closes as the chevron tip enters the high-speed, high-temperature core stream. Aeroacoustic testing and flow visualization support the contention that this cut is inconsequential to chevron performance.
A practical discrete-adjoint method for high-fidelity compressible turbulence simulations
Vishnampet, Ramanathan; Bodony, Daniel J.; Freund, Jonathan B.
2015-03-01
accuracy is limited by computing precision, and we demonstrate it on the aeroacoustic control of a mixing layer with a challengingly broad range of turbulence scales. For comparison, the error from a corresponding discretization of the continuous-adjoint equations is quantified to potentially explain its limited success in past efforts to control jet noise. The differences are illuminating: the continuous-adjoint is shown to suffer from exponential error growth in (reverse) time even for the best-resolved largest turbulence scales. Implications for jet noise reduction and turbulence control in general are discussed.
The sound of oscillating air jets: Physics, modeling and simulation in flute-like instruments
de La Cuadra, Patricio
Flute-like instruments share a common mechanism that consists of blowing across one open end of a resonator to produce an air jet that is directed towards a sharp edge. Analysis of its operation involves various research fields including fluid dynamics, aero-acoustics, and physics. An effort has been made in this study to extend this description from instruments with fixed geometry like recorders and organ pipes to flutes played by the lips. An analysis of the jet's response to a periodic excitation is the focus of this study, as are the parameters under the player's control in forming the jet. The jet is excited with a controlled excitation consisting of two loudspeakers in opposite phase. A Schlieren system is used to visualize the jet, and image detection algorithms are developed to extract quantitative information from the images. In order to study the behavior of jets observed in different flute-like instruments, several geometries of the excitation and jet shapes are studied. The obtained data is used to propose analytical models that correctly fit the observed measurements and can be used for simulations. The control exerted by the performer on the instrument is of crucial importance in the quality of the sound produced for a number of flute-like instruments. The case of the transverse flute is experimentally studied. An ensemble of control parameters are measured and visualized in order to describe some aspects of the subtle control attained by an experienced flautist. Contrasting data from a novice flautist are compared. As a result, typical values for several non-dimensional parameters that characterize the normal operation of the instrument have been measured, and data to feed simulations has been collected. The information obtained through experimentation is combined with research developed over the last decades to put together a time-domain simulation. The model proposed is one-dimensional and driven by a single physical input. All the variables in the
Application of Tomo-PIV in a large-scale supersonic jet flow facility
Wernet, Mark P.
2016-09-01
aeroacoustics research.
Time-Averaged Velocity, Temperature and Density Surveys of Supersonic Free Jets
Panda, Jayanta; Seasholtz, Richard G.; Elam, Kristie A.; Mielke, Amy F.
2005-01-01
A spectrally resolved molecular Rayleigh scattering technique was used to simultaneously measure axial component of velocity U, static temperature T, and density p in unheated free jets at Mach numbers M = 0.6,0.95, 1.4 and 1.8. The latter two conditions were achieved using contoured convergent-divergent nozzles. A narrow line-width continuous wave laser was passed through the jet plumes and molecular scattered light from a small region on the beam was collected and analyzed using a Fabry-Perot interferometer. The optical spectrum analysis air density at the probe volume was determined by monitoring the intensity variation of the scattered light using photo-multiplier tubes. The Fabry-Perot interferometer was operated in the imaging mode, whereby the fringe formed at the image plane was captured by a cooled CCD camera. Special attention was given to remove dust particles from the plume and to provide adequate vibration isolation to the optical components. The velocity profiles from various operating conditions were compared with that measured by a Pitot tube. An excellent comparison within 5m's demonstrated the maturity of the technique. Temperature was measured least accurately, within 10K, while density was measured within 1% uncertainty. The survey data consisted of centerline variations and radial profiles of time-averaged U, T and p. The static temperature and density values were used to determine static pressure variations inside the jet. The data provided a comparative study of jet growth rates with increasing Mach number. The current work is part of a data-base development project for Computational Fluid Dynamics and Aeroacoustics codes that endeavor to predict noise characteristics of high speed jets. A limited amount of far field noise spectra from the same jets are also presented. Finally, a direct experimental validation was obtained for the Crocco-Busemann equation which is commonly used to predict temperature and density profiles from known velocity
Compressible turbulent channel flow with impedance boundary conditions
Scalo, Carlo; Bodart, Julien; Lele, Sanjiva K.
2015-03-01
We have performed large-eddy simulations of isothermal-wall compressible turbulent channel flow with linear acoustic impedance boundary conditions (IBCs) for the wall-normal velocity component and no-slip conditions for the tangential velocity components. Three bulk Mach numbers, Mb = 0.05, 0.2, 0.5, with a fixed bulk Reynolds number, Reb = 6900, have been investigated. For each Mb, nine different combinations of IBC settings were tested, in addition to a reference case with impermeable walls, resulting in a total of 30 simulations. The adopted numerical coupling strategy allows for a spatially and temporally consistent imposition of physically realizable IBCs in a fully explicit compressible Navier-Stokes solver. The IBCs are formulated in the time domain according to Fung and Ju ["Time-domain impedance boundary conditions for computational acoustics and aeroacoustics," Int. J. Comput. Fluid Dyn. 18(6), 503-511 (2004)]. The impedance adopted is a three-parameter damped Helmholtz oscillator with resonant angular frequency, ωr, tuned to the characteristic time scale of the large energy-containing eddies. The tuning condition, which reads ωr = 2πMb (normalized with the speed of sound and channel half-width), reduces the IBCs' free parameters to two: the damping ratio, ζ, and the resistance, R, which have been varied independently with values, ζ = 0.5, 0.7, 0.9, and R = 0.01, 0.10, 1.00, for each Mb. The application of the tuned IBCs results in a drag increase up to 300% for Mb = 0.5 and R = 0.01. It is shown that for tuned IBCs, the resistance, R, acts as the inverse of the wall-permeability and that varying the damping ratio, ζ, has a secondary effect on the flow response. Typical buffer-layer turbulent structures are completely suppressed by the application of tuned IBCs. A new resonance buffer layer is established characterized by large spanwise-coherent Kelvin-Helmholtz rollers, with a well-defined streamwise wavelength λx, traveling downstream with
A practical discrete-adjoint method for high-fidelity compressible turbulence simulations
Energy Technology Data Exchange (ETDEWEB)
Vishnampet, Ramanathan [Department of Mechanical Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801 (United States); Bodony, Daniel J. [Department of Aerospace Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801 (United States); Freund, Jonathan B., E-mail: jbfreund@illinois.edu [Department of Mechanical Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801 (United States); Department of Aerospace Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801 (United States)
2015-03-15
its accuracy is limited by computing precision, and we demonstrate it on the aeroacoustic control of a mixing layer with a challengingly broad range of turbulence scales. For comparison, the error from a corresponding discretization of the continuous-adjoint equations is quantified to potentially explain its limited success in past efforts to control jet noise. The differences are illuminating: the continuous-adjoint is shown to suffer from exponential error growth in (reverse) time even for the best-resolved largest turbulence scales. Implications for jet noise reduction and turbulence control in general are discussed.
The DAN-AERO MW experiments. Final report
Energy Technology Data Exchange (ETDEWEB)
Aagaard Madsen, H.; Bak, C.; Schmidt Paulsen, U.; Gaunaa, M. (Risoe DTU, Roskilde (Denmark)); Fuglsang, P. (LM Glasfiber, Kolding (Denmark)); Romblad, J.; Olesen, N.A. (Vestas Wind Systems, Ringkoebing (Denmark)); Enevoldsen, P.; Laursen, J. (Siemens Wind Power, Ballerup (Denmark)); Jensen, Leo (DONG Energy, Fredericia (Denmark))
2010-09-15
This report describes the DAN-AERO MW experiments carried out within a collaborative, three years research project between Risoe DTU and the industrial partners LM Glasfiber, Siemens Wind Power, Vestas Wind Systems A/S and the utility company DONG Energy. The main objective of the project was to establish an experimental data base which can provide new insight into a number of fundamental aerodynamic and aero-acoustic issues, important for the design and operation of MW size turbines. The most important issue is the difference between airfoil characteristics measured under 2D, steady conditions in a wind tunnel and the unsteady 3D flow conditions on a rotor. The different transition characteristics might explain some of the differences between the 2D and 3D airfoil data and the experiments have been set up to provide data on this subject. The overall experimental approach has been to carry out a number of coordinated, innovative measurements on full scale MW size rotors as well as on airfoils for MW size turbines in wind tunnels. Shear and turbulence inflow characteristics were measured on a Siemens 3.6 MW turbine with a five hole pitot tube. Pressure and turbulent inflow characteristics were measured on a 2MW NM80 turbine with an 80 m rotor. One of the LM38.8 m blades on the rotor was replaced with a new LM38.8 m blade where instruments for surface pressure measurements at four radial sections were build into the blade during the blade production process. Additionally, the outmost section on the blade was further instrumented with around 50 microphones for high frequency surface pressure measurements. The surface pressure measurements have been correlated with inflow measurements from four five hole pitot tubes and two sensors for measuring the high frequency (50 Hz to10 kHz) contents of the inflow turbulence. In parallel, 2D wind tunnel measurements on common airfoils for wind turbine applications have been conducted in three different wind tunnels at Delft
PREFACE: The Science of Making Torque from Wind
Sørensen, Jens N.; Hansen, Martin O. L.; Hansen, Kurt S.
2007-06-01
conference to bring together scientists and engineers working in the fields of aerodynamics, aeroelasticity, aeroacoustics, aeroelastic control, wind conditions and wind farms. The first conference entitled `The Science of making Torque from Wind' was organized by DUWIND and held at Delft University, 19-21 April 2004. Owing to the great success of this conference where more than 60 papers were presented, we decided to follow it with a similar conference at the Technical University of Denmark (DTU) in Lyngby. It is our hope that others will take up the idea and continue this series of conferences. An explicit objective of the conference is to meet the high standards applied in several other branches of science and technology. The EAWE has the responsibility for the scientific quality of the content. All papers presented at the conference have had an abstract review as well as a full paper review by at least two reviewers. Out of the approximately 120 submitted abstracts, 86 papers were finally approved to be presented at the conference. It is expected that many of the papers will subsequently be published in scientific journals. Toward that end, the editors of Wind Energy and Journal of Solar Energy Engineering have expressed their interest in letting the most promising papers be subjected to a second review, for the purpose of having them published as journal papers. The EWEA staff is thanked for organizing the PR on the conference and the EAWE board members for valuable help in the reviewing process and for delivering session chairmen. Staff members at the Department of Mechanical Engineering at DTU and Risø were responsible for the organization. Special thanks go to DTU for providing lecture and meeting rooms, and to LM Glasfiber, Vestas Wind Systems and Siemens Wind Power for financial support. Jens Nørkær Sørensen, Conference Chairman 21 June 2007
Numerical modeling of aerodynamics of airfoils of micro air vehicles in gusty environment
Gopalan, Harish
The superior flight characteristics exhibited by birds and insects can be taken as a prototype of the most perfect form of flying machine ever created. The design of Micro Air Vehicles (MAV) which tries mimic the flight of birds and insects has generated a great deal of interest as the MAVs can be utilized for a number of commercial and military operations which is usually not easily accessible by manned motion. The size and speed of operation of a MAV results in low Reynolds number flight, way below the flying conditions of a conventional aircraft. The insensitivity to wind shear and gust is one of the required factors to be considered in the design of airfoil for MAVs. The stability of flight under wind shear is successfully accomplished in the flight of birds and insects, through the flapping motion of their wings. Numerous studies which attempt to model the flapping motion of the birds and insects have neglected the effect of wind gust on the stability of the motion. Also sudden change in flight conditions makes it important to have the ability to have an instantaneous change of the lift force without disturbing the stability of the MAV. In the current study, two dimensional rigid airfoil, undergoing flapping motion is studied numerically using a compressible Navier-Stokes solver discretized using high-order finite difference schemes. The high-order schemes in space and in time are needed to keep the numerical solution economic in terms of computer resources and to prevent vortices from smearing. The numerical grid required for the computations are generated using an inverse panel method for the streamfunction and potential function. This grid generating algorithm allows the creation of single-block orthogonal H-grids with ease of clustering anywhere in the domain and the easy resolution of boundary layers. The developed numerical algorithm has been validated successfully against benchmark problems in computational aeroacoustics (CAA), and unsteady viscous
High-Flow Jet Exit Rig Designed and Fabricated
Buehrle, Robert J.; Trimarchi, Paul A.
2003-01-01
The High-Flow Jet Exit Rig at the NASA Glenn Research Center is designed to test single flow jet nozzles and to measure the appropriate thrust and noise levels. The rig has been designed for the maximum hot condition of 16 lbm/sec of combustion air at 1960 R (maximum) and to produce a maximum thrust of 2000 lb. It was designed for cold flow of 29.1 lbm/sec of air at 530 R. In addition, it can test dual-flow nozzles (nozzles with bypass flow in addition to core flow) with independent control of each flow. The High- Flow Jet Exit Rig was successfully fabricated in late 2001 and is being readied for checkout tests. The rig will be installed in Glenn's Aeroacoustic Propulsion Laboratory. The High-Flow Jet Exit Rig consists of the following major components: a single component force balance, the natural-gas-fueled J-79 combustor assembly, the plenum and manifold assembly, an acoustic/instrumentation/seeding (A/I/S) section, a table, and the research nozzles. The rig will be unique in that it is designed to operate uncooled. The structure survives the 1960 R test condition because it uses carefully selected high temperature alloy materials such as Hastelloy-X. The lower plenum assembly was designed to operate at pressures to 450 psig at 1960 R, in accordance with the ASME B31.3 piping code. The natural gas-fueled combustor fires directly into the lower manifold. The hot air is directed through eight 1-1/2-in. supply pipes that supply the upper plenum. The flow is conditioned in the upper plenum prior to flowing to the research nozzle. The 1-1/2-in. supply lines are arranged in a U-shaped design to provide for a flexible piping system. The combustor assembly checkout was successfully conducted in Glenn's Engine Component Research Laboratory in the spring of 2001. The combustor is a low-smoke version of the J79 combustor used to power the F4 Phantom military aircraft. The natural gas-fueled combustor demonstrated high-efficiency combustion over a wide range of operating
输气管道泄漏音波产生机理研究%Leak-acoustics generation mechanism for natural gas pipelines
Institute of Scientific and Technical Information of China (English)
刘翠伟; 李玉星; 王武昌; 付俊涛; 方丽萍
2013-01-01
In order to study the law and use of leak detection for gas pipelines based on acoustic method, a study was made for leak-acoustics generation mechanism of natural gas pipelines. Firstly, the aero-acoustics generation mechanism was studied in theory so that the wave equation of sources could be derived when gas pipelines were leaking. Secondly, the leak-acoustics generated by quadrupole sonic sources and dipole sonic sources were simulated to analyze the law of their characteristics. Thirdly, the leak-acoustics were acquired with tests under the same conditions as those for the simulation. The leak-acoustics simulated were compared with those obtained from tests to testify the simulation method. And then, the comparative analyses were accomplished between the leak-acoustics simulated and those acquired with tests under variable operating conditions. At last, the law and use of leak detection for gas pipelines based on acoustic method were concluded after analyzing the leak-acoustics generation mechanism and the working principle of dynamic pressure sensors. The results indicated that the quadrupoles and dipoles generated by turbulent fluctuations cause the leak-acoustics ; the main components of pressure perturbations acquired by dynamic pressure sensors are acoustic perturbations generated by sonic sources; both the simulation method and the experiment method can be used to study the leak-acoustics generation mechanism for natural gas pipelines.%为研究输气管道音波法泄漏检测技术基本原理及应用方法,对输气管道中泄漏音波产生机理进行研究,理论上确定输气管道气动噪声产生机理；将仿真模拟所得四极子声源和偶极子声源产生的泄漏音波进行分析并总结规律；将音波传感器测得泄漏音波与仿真模拟所得泄漏音波对比验证；分析多工况条件下仿真模拟与实验方法得到的泄漏音波；通过分析仿真模拟中泄漏音波产生机理和实验中所用音波传
Aeroelastic research programme EFP-2001[YAW;STALL]; Forskning i aeroelasticitet EFP-2001
Energy Technology Data Exchange (ETDEWEB)
Aagaard Madsen, H. (ed.)
2002-12-01
The project covers the one year period from mid 2001 to mid 2002 and is the last part of a 5 years research programme on aeroelasticity. The overall objectives of the project are to improve the load and design basis for wind turbines and to ensure in collaboration with industry a continu-ously running process on development of new designs and solution of actual problems. Specifi-cally the main objectives for the present period are the following: a) development of a design tool for analysis of dynamic stability b) investigations of blade tip aerodynamics and blade tip design on basis of 3D CFD computa-tions c) publication of an airfoil catalogue d) load reduction using new control strategies e) aeroacoustic modelling of noise propagation During the present project period the computer code HAWCModal has been finished. The code computes the modal characteristics for a turbine as function of rotational speed. It is based on the structural modelling in the aeroelastic code HAWC and uses the same input files. The computed eigen frequencies are shown in a Campbell diagram and the corresponding modal forms can be shown graphically for an operating turbine. Finally, the structural damping is also computed by the code. HAWCModal is the basis for the stability analysis tool HAWCStab which is now under devel-opment. With HAWCStab the aeroelastic stability of a turbine can be analysed. The complex aerodynamics at three different blade tip shapes have been analysed with the three-dimensional CFD code EllipSys3D. The tip vortex was visualised and the lift and drag coef-ficients in the tip region were analysed in order to study the influence of the tip geometry on the performance and aerodynamic damping. An airfoil catalogue containing computations on 28 different airfoils for wind turbine applica-tion in comparison with experimental data has been developed and is available via the internet. Besides the main themes of the project as mentioned above there have been research
Hughes, Christopher E.; Podboy, Gary, G.; Woodward, Richard P.; Jeracki, Robert, J.
2013-01-01
The design of effective new technologies to reduce aircraft propulsion noise is dependent on identifying and understanding the noise sources and noise generation mechanisms in the modern turbofan engine, as well as determining their contribution to the overall aircraft noise signature. Therefore, a comprehensive aeroacoustic wind tunnel test program was conducted called the Fan Broadband Source Diagnostic Test as part of the NASA Quiet Aircraft Technology program. The test was performed in the anechoic NASA Glenn 9- by 15-Foot Low Speed Wind Tunnel using a 1/5 scale model turbofan simulator which represented a current generation, medium pressure ratio, high bypass turbofan aircraft engine. The investigation focused on simulating in model scale only the bypass section of the turbofan engine. The test objectives were to: identify the noise sources within the model and determine their noise level; investigate several component design technologies by determining their impact on the aerodynamic and acoustic performance of the fan stage; and conduct detailed flow diagnostics within the fan flow field to characterize the physics of the noise generation mechanisms in a turbofan model. This report discusses results obtained for one aspect of the Source Diagnostic Test that investigated the effect of the bypass or fan nozzle exit area on the bypass stage aerodynamic performance, specifically the fan and outlet guide vanes or stators, as well as the farfield acoustic noise level. The aerodynamic performance, farfield acoustics, and Laser Doppler Velocimeter flow diagnostic results are presented for the fan and four different fixed-area bypass nozzle configurations. The nozzles simulated fixed engine operating lines and encompassed the fan stage operating envelope from near stall to cruise. One nozzle was selected as a baseline reference, representing the nozzle area which would achieve the design point operating conditions and fan stage performance. The total area change from