DOCSLIB.ORG

Computational Aeroacoustics: Progress on Nonlinear Problems of Soundgeneration Tim Coloniusa,Ã, Sanjiva K

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Computational Aeroacoustics: Progress on Nonlinear Problems of Soundgeneration Tim Coloniusa,Ã, Sanjiva K ARTICLE IN PRESS Progress in Aerospace Sciences 40 (2004) 345–416 Computational aeroacoustics: progress on nonlinear problems of soundgeneration Tim Coloniusa,Ã, Sanjiva K. Leleb aDepartment of Mechanical Engineering, California Institute of Technology, Mail Code 104-44 Pasadena, CA 91125, USA bDepartment of Aeronautics and Astronautics and Department of Mechanical Engineering, Stanford University, Stanford, CA 94305-4035, USA Abstract Computational approaches are being developed to study a range of problems in aeroacoustics. These aeroacoustic problems may be classifiedbasedon the physical processes responsible for the soundradiation,andrange from linear problems of radiation, refraction, and scattering in known base flows or by solid bodies, to sound generation by turbulence. In this article, we focus mainly on the challenges andsuccesses associatedwith numerically simulating soundgeneration by turbulent flows. We discuss a hierarchy of computational approaches that range from semi-empirical schemes that estimate the noise sources using mean-flow and turbulence statistics, to high-fidelity unsteady flow simulations that resolve the sound generation process by direct application of the fundamental conservation principles. We stress that high-fidelity methods such as Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) have their merits in helping to unravel the flow physics and the mechanisms of sound generation. They also provide rich databases for modeling activities that will ultimately be needed to improve existing predictive capabilities. Spatial and temporal discretization schemes that are well-suited for aeroacoustic calculations are analyzed, including the effects of artificial dispersion and dissipation on uniform and nonuniform grids. We stress the importance of the resolving power of the discretization as well as computational efficiency of the overall scheme. Boundary conditions to treat the flow of disturbances in and out of the computational domain, as well as methods to mimic anechoic domain extension are discussed. Test cases on some benchmark problems are included to provide a realistic assessment of several boundary condition treatments. Finally, highlights of recent progress are given using selected model problems. These include subsonic cavity noise and jet noise. In the end, the current challenges in aeroacoustic modeling and in simulation algorithms are revisited with a look towardthe future developments. r 2004 Elsevier Ltd. All rights reserved. ÃCorresponding author. Tel.: +1 626 395 4021; fax: +1 626 568 2719. E-mail address: [email protected] (T. Colonius). 0376-0421/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.paerosci.2004.09.001 ARTICLE IN PRESS 346 T. Colonius, S.K. Lele / Progress in Aerospace Sciences 40 (2004) 345–416 Nomenclature Roman characters t eddy turnover time tij viscous stress tensor A amplitude function y momentum thickness a finite-difference coefficients, Section 4.1 y phase function, Section 4.1 a speedof sound C airfoil chord Subscripts c wave speed cg group velocity 1 free-stream or far-fieldvalue cp phase speed c centerline Cp; Cs; CT LES model coefficients j jet value at nozzle lip D (jet) diameter p peak E three-dimensional energy spectrum t turbulent El total energy density f frequency Superscripts and constructs h gridspacing K modified wavenumber hð Þi ensemble or time averaged k wavenumber ðÞ LES filtered L turbulence integral scale ðÞb LES test-filteredor Fourier transformed M Mach number ðÞ~ windowed 0 mi subgridmass flux vector fluctuating quantity or derivative n order of accuracy p pressure Abbreviations qi heat flux vector rij subgridmomentum flux tensor BC boundary condition Re Reynolds number CAA computational aeroacoustics Sij symmetric strain rate tensor CFD computational fluiddynamics St Strouhal number CFL Courant–Friedrichs–Levy T temperature DNS direct numerical simulation T ij Lighthill stress tensor DRP dispersion-relation-preserving U velocity (usually reference value) ENO essentially non-oscillatory u velocity FCT flux-correctedtransport Uc convective velocity FD finite difference w window function Ff–H Ffowcs Williams–Hawkings q vector of dependent variables IC initial condition qsi subgridenergy flux vector LDD low dissipation and dispersion LEE LinearizedEuler equations Greek characters LES large eddy simulation LM linear multi-step a finite-difference coefficients, Section 4.1 NPSE nonlinear ParabolizedStability equations a shear layer spreading rate OASPL overall soundpressure level aj apparent velocity, Section 4.1 PML perfectly matchedlayer D LES filter width, or difference PSE ParabolizedStability equations d shock thickness RANS Reynolds-averaged Navier–Stokes d% displacement thickness RK Runge–Kutta do vorticity thickness SAT simultaneous approximation term turbulence dissipation SBP summation-by-parts Z Kolmogorov scale SGS sub-gridstress g ratio of specific heats SPL soundpressure level l1 Taylor microscale TKE turbulent kinetic energy m viscosity TVD total variation diminishing r density URANS unsteady Reynolds-averaged Navier–Stokes s damping coefficient WENO weightedessentially non-oscillatory ARTICLE IN PRESS T. Colonius, S.K. Lele / Progress in Aerospace Sciences 40 (2004) 345–416 347 Contents 1. Introduction . 348 2. Classification of aeroacoustic problems . 349 2.1. Linear problems of propagation andgeneralizedscattering . 349 2.2. Nonlinear problems of flow acoustics or aeroacoustics . 349 2.3. Illustrative examples . 350 2.3.1. Airfoil/hydrofoil trailing-edge noise at low speed . 350 2.3.2. High speedjet noise . 352 3. A hierarchy of CAA simulations . 353 3.1. Direct computation of sound. 353 3.1.1. DNS or LES with compressible Navier–Stokes . 354 3.1.2. Extension of DNS or LES near-fields. 355 3.2. Hybrid methods for noise prediction . 355 3.2.1. DNS/LES with acoustic analogy . 355 3.2.2. Vortex methods with acoustic analogy . 357 3.2.3. Incompressible/acoustic split . 357 3.2.4. LinearizedEuler with source terms . 357 3.3. Large eddy simulation . 358 3.3.1. LES equations andsubgridmodeling. 358 3.3.2. Numerical issues particular to LES . 359 3.3.3. Refinedsubgridmodels. 360 3.3.4. Acoustic implications of SGS models. 360 4. Computational issues . 362 4.1. Spatial discretization . 362 4.1.1. Wave propagation characteristics of finite-difference schemes. 364 4.1.2. Dispersion anddissipation . 366 4.1.3. Spurious waves, artificial viscosity, andfiltering . 367 4.1.4. Boundary closures . 369 4.1.5. Computational efficiency . 369 4.1.6. Viscous and second-derivative terms . 371 4.1.7. Gridstretching andgeneralizedcurvilinear coordinates. 372 4.2. Temporal discretization . 375 4.3. Boundary conditions . 377 4.3.1. LinearizedBC . 378 4.3.2. Nonlinear BC: Thompson’s approach . 382 4.3.3. Nonlinear BC: Buffer zone techniques . 384 4.3.4. Solid wall boundary conditions . 388 4.4. Shocks . 388 5. Recent progress in nonlinear CAA . 389 5.1. CAA studies related to vortex dynamics and interaction of vortices with shock waves . 389 5.2. CAA studies related to jet noise . 392 5.2.1. Representation of jet turbulence andjet mixing noise . 392 5.2.2. Jet screech andshock-associatednoise . 393 5.2.3. Computation of jet noise using DNS andLES . 394 5.2.4. Model problems related to jet noise . 395 5.3. Model problems of cavity noise . 401 5.3.1. Computational efforts . 402 5.3.2. Summary. 404 6. Closure . 404 ARTICLE IN PRESS 348 T. Colonius, S.K. Lele / Progress in Aerospace Sciences 40 (2004) 345–416 Acknowledgements . 406 References . 406 1. Introduction to make some pragmatic simplification. The first step is a classification of the problem according to the The aerodynamic noise of airplanes at take-off and in dominant mechanism of sound generation. Such a the landing configuration continues to be a critical classification is presentedin Section 2. The next step is factor in the future development of aviation. Commu- a careful synthesis of a computational problem nity noise concerns at busy airports constrain the design that incorporates the requireddetailsof the sound of new airplanes, subsonic or supersonic, andof generation process. In a general flow it is not possible rotorcraft. The current operational fleet is also subject to unambiguously separate the ‘flow’ from the ‘sound’. to new increasingly stringent noise regulations. Aviation However, when the flow Mach number is small it is technology with dramatically lower community noise advantageous to separate the task of predicting footprint, for example one that limits the noise footprint the unsteady vortical motion, i.e. flow prediction, to the airport perimeter, is envisionedin NASA’s from that of noise prediction. To help gain a pers- ambitious long term plan for the next 20 years. Such pective on this issue two specific model problems long term targets andspecific near-term noise reduction of trailing-edge noise and jet-noise are presented in goals are driving active research in aeroacoustics. As Section 2.3. an example, jet noise has traditionally been reduced Predicting the noise radiation associated with un- by increasing the bypass ratio of turbofan engines. steady flows is the central theme of aeroacoustics. A However, this trendcannot be continuedindefinitely variety of.
Load more

Recommended publications
  • Numerical Buckling Analysis of Hybrid Honeycomb Cores for Advanced Helmholtz Resonator Liners
    Article Numerical Buckling Analysis of Hybrid Honeycomb Cores for Advanced Helmholtz Resonator Liners Moritz Neubauer , Martin Dannemann * , Michael Kucher , Niklas Bleil, Tino Wollmann and Niels Modler Institute of Lightweight Engineering and Polymer Technology (ILK), Technische Universität Dresden, Holbeinstraße 3, 01307 Dresden, Germany; [email protected] (M.N.); [email protected] (M.K.); [email protected] (N.B.); [email protected] (T.W.); [email protected] (N.M.) * Correspondence: [email protected]; Tel.: +49-351-463-38134 Abstract: In order to realize novel acoustic liners, honeycomb core structures specially adapted to these applications are required. For this purpose, various design concepts were developed to create a hybrid cell core by combining flexible wall areas based on thermoplastic elastomer films and rigid honeycomb areas made of fiber-reinforced thermoplastics. Within the scope of the presented study, a numerical approach was introduced to analyze the global compressive failure of the hybrid composite core structure, considering local buckling and composite failure according to Puck and Cuntze. Therefore, different geometrical configurations of fiber-reinforced tapes were compared with respect to their deformation as well as their resulting failure behavior by means of a finite element analysis. The resulting compression strength obtained by a linear buckling analysis agrees largely with calculated strengths of the more elaborate application of the failure criteria according to Puck and Cuntze, which were implemented in the framework of a nonlinear buckling analysis. Citation: Neubauer, M.; The findings of this study serve as a starting point for the realization of the manufacturing concept, Dannemann, M.; Kucher, M.; Bleil, N.; for the design of experimental tests of hybrid composite honeycomb core structures, and for further Wollmann, T.; Modler, N.
    [Show full text]
  • Development of a Fully-Coupled Harmonic Balance Method and A
    Development of a Fully-Coupled Harmonic Balance Method and a Refined Energy Method for the Computation of Flutter-Induced Limit Cycle Oscillations of Bladed Disks with Nonlinear Friction Contacts Christian Bertholdb, Johann Grossa, Christian Freyb, Malte Kracka aInstitute of Aircraft Propulsion Systems, University of Stuttgart, Pfaffenwaldring 6, 70569 Stuttgart, Germany [email protected], [email protected] bInstitute of Propulsion Technology, German Aerospace Center, Linder Höhe, 51147 Cologne, Germany [email protected], [email protected] Abstract Flutter stability is a dominant design constraint of modern gas and steam turbines. To further increase the feasible design space, flutter-tolerant designs are currently explored, which may undergo Limit Cycle Oscillations (LCOs) of acceptable, yet not vanishing, level. Bounded self-excited oscillations are a priori a nonlinear phenomenon, and can thus only be explained by nonlinear interactions such as dry stick-slip friction in mechanical joints. The currently available simulation methods for blade flutter account for nonlinear interactions, at most, in only one domain, the structure or the fluid, and assume the behavior in the other domain as linear. In this work, we develop a fully-coupled nonlinear frequency domain method which is capable of resolving nonlinear flow and structural effects. We demonstrate the computational performance of this method for a state-of-the-art aeroelastic model of a shrouded turbine blade row. Besides simulating limit cycles, we predict, for the first time, the phenomenon of nonlinear instability, i.e. , a situation where the equilibrium point is locally stable, but for sufficiently strong perturbation (caused e.g.
    [Show full text]
  • Application of the Bernoulli Enthalpy Concept to the Study of Vortex ‘Noise and Jet Impingement Noise
    NASA Contractor Report 2987 Application of the Bernoulli Enthalpy Concept to the Study of Vortex ‘Noise and Jet Impingement Noise John E. Yates CONTRACT NASJ-14503 APRIL 1978 - I TECH LIBRARY KAFB, NM NASA Contractor Report 2987 Application of the Bernoulli Enthalpy Concept to the Study of Vortex Noise and Jet Impingement Noise John E. Yates Aeromuticd Research Associates of Pritlceton, Ix. Primeton, New Jersey Prepared for Langley Research Center under Contract NASI-14503 National Aeronautics and Space Administration Scientific and Technical Information Office 1978 -- - TABLE OF CONTENTS SUMMARY 1 I. INTRODUCTION 2 Nomenclature 3 II. ACOUSTIC THEORY OF HOMENTROPIC FLOWS A. Assumptions and Basic Equations B. A Kinematic Definition of Sound L4 C. Acoustic Theory 11 D. Energy Theorem 14 E. The Kinetic Origin of Sound - The Liepmann Analogy 15 F. How is Sound Processed by a Fluid Flow? 18 G. How Does Sound Affect a Fluid Flow? 20 H. Comparison with Other Theories 20 III. INTERACTION OF SOUND WITH STEADY VORTEX FLOWS A. Plane Wave Scattering by a Vortex with Core Structure 24 B. Acoustic Interaction with Discrete Weakly Interacting Vortices C. Line Source Interaction with a ‘,ine Vortex D. Scattering of Engine Noise by an Aircraft Vortex Wake IV. PRODUCTION OF SOUND BY VORTEX FLOWS A. The Corotating Vortex Pair 48 B. Jet Impingement Noise C. A Suggested Problem 2: V. EXCITATION OF A FLUID FLOW BY SOUND A. Discussion of Experimental Results B. The Liepmann Analogy Revisited 2 C. Excitation of the Corotating Vortex Pair 62 D. Qualitative Comparison with Experiment 69 VI. CONCLUSIONS 76 REFERENCES iii John E.
    [Show full text]
  • Aeroacoustics of Space Vehicles
    National Aeronautics and Space Administration Aeroacoustics of Space Vehicles Jayanta Panda NASA Ames Research Center Moffett Field, CA Presentation for Applied Modeling & Simulation (AMS) Seminar Series Building N258, Auditorium (Room 127), NASA Ames Research Center Moffett Field, CA April 8, 2014 1 Jay Panda (NASA ARC) 4/7/2014 National Aeronautics and Space Administration Introduction ● Definition Aeroacoustics ●Aeroacoustics for Airplanes Mostly for community noise reduction very few vibro-acoustics concerns (such as failures of nozzle cowlings) ● Aeroacoustics for space vehicles Mostly for vibro-acoustic concern Intense vibrational environment for payload, electronics and navigational equipment and a large number of subsystems Community noise - little concern until recent time Environment inside ISS– separate issue ____Jay Panda (NASA ARC) 4/8/2014 2 National Aeronautics and Space Administration Introduction 185 Inside flame trench Typical levels (dB) of surface pressure 180 Shock-plume interaction fluctuations on launch vehicles Pad/low altitude abort Transonic Oscillating shock High altitude abort ? 170 AbortAcoustics Base of Vehicle Protuberances, Separated flow regions 160 20dB = X10 40dB = X100 60dB =X1000 Ascent AcousticsAscent 150 Launch AcousticsLaunch Smooth parts of vehicle 140 Tip of Vehicle Level inside cargo compt, payload fairing 130 Threshold of ear pain 120 dB Max Level inside Crew cabin 115 Loud Rock Concert ____Jay Panda (NASA ARC) 4/7/2014 3 National Aeronautics and Space Administration Introduction The end
    [Show full text]
  • Aerodynamic Analysis of the Undertray of Formula 1
    Treball de Fi de Grau Grau en Enginyeria en Tecnologies Industrials Aerodynamic analysis of the undertray of Formula 1 MEMORY Autor: Alberto Gómez Blázquez Director: Enric Trillas Gay Convocatòria: Juny 2016 Escola Tècnica Superior d’Enginyeria Industrial de Barcelona Aerodynamic analysis of the undertray of Formula 1 INDEX SUMMARY ................................................................................................................................... 2 GLOSSARY .................................................................................................................................... 3 1. INTRODUCTION .................................................................................................................... 4 1.1 PROJECT ORIGIN ................................................................................................................................ 4 1.2 PROJECT OBJECTIVES .......................................................................................................................... 4 1.3 SCOPE OF THE PROJECT ....................................................................................................................... 5 2. PREVIOUS HISTORY .............................................................................................................. 6 2.1 SINGLE-SEATER COMPONENTS OF FORMULA 1 ........................................................................................ 6 2.1.1 Front wing [3] .......................................................................................................................
    [Show full text]
  • An Introduction to Aeroacoustics
    An introduction to aeroacoustics A. Hirschberg∗ and S.W. Rienstra∗∗ Eindhoven University of Technology, ∗Dept. of App. Physics and ∗∗Dept. of Mathematics and Comp. Science, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. Email: [email protected] and [email protected] 18 Jul 2004 20:23 18 Jul 2004 1 version: 18-07-2004 1 Introduction Due to the nonlinearity of the governing equations it is very difficult to predict the sound production of fluid flows. This sound production occurs typically at high speed flows, for which nonlinear inertial terms in the equation of motion are much larger than the viscous terms (high Reynolds numbers). As sound production represents only a very minute fraction of the energy in the flow the direct prediction of sound generation is very difficult. This is particularly dramatic in free space and at low subsonic speeds. The fact that the sound field is in some sense a small perturbation of the flow, can, however, be used to obtain approximate solutions. Aero-acoustics provides such approximations and at the same time a definition of the acoustical field as an extrapolation of an ideal reference flow. The difference between the actual flow and the reference flow is identified as a source of sound. This idea was introduced by Lighthill [68, 69] who called this an analogy. A second key idea of Lighthill [69] is the use of integral equations as a formal solution. The sound field is obtained as a convolution of the Green’s function and the sound source. The Green’s function is the linear response of the reference flow, used to define the acoustical field, to an impulsive point source.
    [Show full text]
  • Linearized Navier-Stokes Solver for In-Duct Aeroacoustics
    Linearized Navier-Stokes solver for in-duct aeroacoustics GUNILLA EFRAIMSSON Department of Aeronautical and Vehicle Engineering KTH, Stockholm, Sweden [email protected] Axel Kierkegaard, Wei Na, Mats Åbom, Ciarán O’Reilly, Susann Boij, Hans Bodén Outline • Tango-aspects • Linearized Navier-Stokes equations solver • Two tecases - Area expansion - Thick orifice • Conclusions and future work Tango setting Q˙ 0 Unsteady heat release Generation of sound waves Perturbation flow & flame Pressure Oscillation p0 Study the coupling sound , flow and heat release using linearized Navier-Stokes equations Generation and Propagation of Sound • Generation Fans, rotor-stator interaction, constrictions, jets, combustion - Acoustic analogies, direct methods - Transient phenomena è transient simulations (LES,, DES, uRANS) or scaling laws • Propagation Free air, pipes, influence of flow, influence of solid surfaces (shielding), coupling of sound and flow (whistling, damping of sound), duct terminations - Linear equations in time or frequency domain: Helmholtz equation, wave equation, linearized Euler equations etc Propagation of sound in ducts with constrictions Straight cylindrical duct with orifice plate Turbulent meanflow Incoming waves are partly reflected and partly transmitted Reflections from downstream obstacles (or boundary conditions) Zone I Zone III Zone IV Zone II x 0 1 = x2 = 0 Propagation of sound in ducts with constrictions Straight cylindrical duct with orifice plate Turbulent meanflow Incoming waves are partly reflected and partly transmitted Reflections
    [Show full text]
  • Aerodynamics and Aeroacoustics of a Vertical Axis Wind Turbine
    15th EAWE PhD Seminar on Wind Energy 29-31 October 2019 Ecole Centrale de Nantes, France Aerodynamics and aeroacoustics of a Vertical Axis Wind Turbine L Brandettia, F Avallonea, C J Simao Ferreiraa, D Casalinoa a AWEP Dept., Faculty of Aerospace Engineering, Delft University of Technology, Delft, the Netherlands E-mail: [email protected] Keywords: Vertical Axis Wind Turbine, Aeroacoustics, Aerodynamics. According to the orientation of the axis of rotation, wind turbines are classified in: Horizontal Axis Wind Turbines (HAWTs) and Vertical Axis Wind Turbines (VAWTs). Next to the most conventional and economically feasible HAWTs, VAWTs have advantages: the intrinsic omnidirectionality of VAWTs does not require the design of yaw motors; the location of the generator on the ground leads to easier access and, consequently, lower maintenance cost [1]; they are visually more appealing and suitable for the installation into urban environments. In order to be located in an urban environment, noise regulations must be respected. For operating wind turbines, it is possible to distinguish between mechanical and aerodynamic noise sources. The first one is caused by the dynamic response of the moving mechanical components while the latter is produced by the interaction of the airflow with the blades [2]. Nowadays, the major focus is on aerodynamic noise, proving that mechanical noise has been already optimized [3]. Aerodynamic noise can be divided in: turbulent-impingement (T-I) noise and airfoil-self noise. T-I noise occurs when the incoming turbulence interacts with the blade leading edge [4][5]. In literature, there is no agreement on how to model it.
    [Show full text]
  • Fundamentals of Fan Aeroacoustics Overview of Lecture
    Fundamentals of Fan Aeroacoustics Overview of Lecture • Noise Sources and Generation Mechanisms – Sources of Noise for Typical Fans – Fluid-Structure Interaction as a Noise Generation Mechanism – Coupling to the Duct: Propagating Modes and Cut-off Phenomena • Modeling of Fan Noise The Acoustic Analogy Computational Methods:Aeroacoustics and UnsteadyAerodynamics The Linear Cascade Model Effects of Geometry and Blade Loading on Acoustic Radiation • Recent Developments in Fan Modeling – Tonal and Broadband Noise – Nonuniform Mean Flow Effects:swirl – Three-Dimensional Effects – High Frequency Effects • Conclusions Dominant Noise Sources for Turbofan Engines High Bypass Ratio Fan Flyover Noise Maximum Perceived Noise Level Approach Takeoff Typical Turbomachinery Sound Power Spectra Subsonic Tip Speed Supersonic Tip Speed Turbomachinery Noise Generation Process Rotor-Stator Interaction Fluid-Structure Interaction as a Noise Generation Mechanism • The interaction of nonuniform flows with structural components such as blades and guide vanes produce fluctuating aerodynamic forces on the blades and radiates sound in the farfield. • Noise Sources: Flow Nonuniformities: Inlet Turbulence, Boundary Layers, Tip and Hub Vortices,Wakes etc. • Mechanism: Interaction with Rotating Components (rotor noise), Scattering by Sharp Edges (trailing edge noise), Impingement of Unsteady Nonuniformities on Guide Vanes (rotor/stator interaction). • Propagation in the Duct: Sound Must Propagate in a Duct: therefore only high frequency acoustic modes will propagate.
    [Show full text]
  • Surface Integral Methods in Computational Aeroacoustics
    Surface Integral Metho ds in Computational Aeroacoustics -From the CFD Near-Field to the Acoustic Far-Field y Anastasios S. Lyrintzis Scho ol of Aeronautics and Astronautics Purdue University W. Lafayette, IN 47907-2023 Abstract A review of recent advances in the use of integral metho ds in Computational AeroAcoustics CAA for the extension of near- eld CFD results to the acoustic far- eld is given. These integral formulations i.e. Kirchho 's metho d, p ermeable p orous surface Ffowcs-Williams Hawkings FW-H equation allow the radiating sound to b e evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the far- eld sound, instead of the volume integrals required by the traditional acoustic analogy metho d i.e. Lighthill, rigid b o dy FW-H equa- tion. A numerical CFD metho d is used for the evaluation of the ow- eld solution in the Presented at the CEAS Workshop \From CFD to CAA" Athens Greece, Nov. 2002. y Professor, e-mail: [email protected]. 1 near eld and thus on the control surface. Di usion and disp ersion errors asso ciated with wave propagation in the far- eld are avoided. The surface integrals and the rst derivatives needed can b e easily evaluated from the near- eld CFD data. Both metho ds can b e ex- tended in order to include refraction e ects outside the control surface. The metho ds have b een applied to helicopter noise, jet noise, prop eller noise, ducted fan noise, etc.
    [Show full text]
  • Interdependence of Friction, Wear, and Noise: a Review
    Friction 9(6): 1319–1345 (2021) ISSN 2223-7690 https://doi.org/10.1007/s40544-021-0500-x CN 10-1237/TH REVIEW ARTICLE Interdependence of friction, wear, and noise: A review Kevin LONTIN*, Muhammad KHAN Cranfield University, MK43 0AL, UK Received: 02 July 2020 / Revised: 02 November 2020 / Accepted: 29 January 2021 © The author(s) 2021. Abstract: Phenomena of friction, wear, and noise in mechanical contacts are particularly important in the field of tribomechanics but equally complex if one wants to represent their exact relationship with mathematical models. Efforts have been made to describe these phenomena with different approaches in past. These efforts have been compiled in different reviews but most of them treated friction, wear mechanics, and acoustic noise separately. However, an in-depth review that provides a critical analysis on their interdependencies is still missing. In this review paper, the interdependencies of friction, wear, and noise are analysed in the mechanical contacts at asperitical level. The origin of frictional noise, its dependencies on contact’s mechanical properties, and its performance under different wear conditions are critically reviewed. A discussion on the existing mathematical models of friction and wear is also provided in the last section that leads to uncover the gap in the existing literature. This review concludes that still a comprehensive analytical modelling approach is required to relate the interdependencies of friction, noise, and wear with mathematical expressions. Keywords: noise; acoustic emission; wear; friction 1 Introduction computations using only the dominant harmonic components as opposed to full harmonic components Wear processes present a severe challenge in industry.
    [Show full text]
  • Wind Energy Aerodynamics/Aeroacoustics
    National Wind Technology Center Wind Energy Aerodynamics/Aeroacoustics Overview Wind turbine aerodynamic research has grown from blade and rotor aerodynamics, and now includes wind plant and atmospheric inflow effects. The energy capture of wind farms is dependent on all aerodynamic interactions. Research is crucial to understanding how wind turbines function in large, multiple row wind farms. Such work is important because these conditions impact the cumulative fatigue damage of turbine structural components that ultimately effect the useful lifetime of wind turbines. This work also is essential for understanding and maximizing turbine and wind farm energy production. Both turbine lifetime and wind farm energy production are key determinants of the cost of wind generated electricity. Another consideration in wind energy is the sound wind turbines Schematic of wind farm interactions with atmospheric boundary layer, terrain, and vegetation. emit. Researching where the sound originates and what causes it will lead to design methods to reduce it. advances improve machine operability, life span, energy capture, Aerodynamics and power quality, all of which ultimately enable continued reductions to the cost of wind generated electricity. Understanding wind turbine blade aerodynamics can enhance the accuracy and reliability of aerodynamic force predictions in Wind tunnel experiments in the NASA Ames 80 ft x 120 ft wind engineering models used to design wind turbines. These tunnel allowed researchers to measure and understand turbine blade rotational augmentation and dynamic stall, which occur frequently during routine turbine operation. This research fostered a more complete understanding of rotationally augmented blade flows and dynamic stall, and thus facilitated more accurate predictions and improved turbine design.
    [Show full text]