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UNIVERSITY OF CINCINNATI Date:___________________August 12, 2008 I, _________________________________________________________,Christopher A. Harris hereby submit this work as part of the requirements for the degree of: Master of Science in: Aerospace Engineering It is entitled: Acoustics and Fluid Dynamics Studies of High Speed Jet Noise Reduction Devices This work and its defense approved by: Chair: _______________________________Dr. Ephraim J. Gutmark _______________________________Dr. Paul D. Orkwis _______________________________Dr. Steven Martens _______________________________Dr. John P. Wojno _______________________________ Acoustics and Fluid Dynamics Studies of High Speed Jet Noise Reduction Devices A thesis submitted to the Graduate School Of the University of Cincinnati In partial fulfillment of the Requirements for the degree of Master of Science In the Department of Aerospace Engineering and Engineering Mechanics Of the College of Engineering 2009 By Christopher A. Harris B.S., Boston University, 2002 Committee Chair: Dr. Ephraim J. Gutmark Abstract Jet noise reduction was investigated on a scale model turbofan exhaust simulator rig at a Reynold’s Number O(106) through mean and time-resolved flow and aeroacoustic measurements. Various stream-wise vorticity production devices, including conventional and modified chevron nozzles and CVG’s (Coupled Vortex Generators), were installed to increase turbulent shear layer mixing and ultimately reduce far-field radiated noise. Simplified flow simulations using a steady RANS k- epsilon turbulence model aid to elucidate the initial vortex development for several geometries. CVG’s were installed in axisymmetric arrangements on both the core and fan streams of the exhaust simulator, and in the various boundary layers. Measurements of the nozzle boundary layer characteristics were performed using a total pressure probe on the baseline hardware to determine appropriate mean spatial scales, and to evaluate the boundary layer momentum thickness influence on noise for a coaxial, turbulent jet. LDV of two velocity components determined the turbulence properties in the jet at various locations in the initial mixing region and past the potential core. Acoustic far-field measurements showed that high levels of peak noise reduction were possible with added high-frequency energy. One purpose was to offer an explanation of this ‘self’ noise component and mixing mechanisms, in comparison with delta tabs which also incur high-frequency noise. With properly scaled geometry design, and installation configurations, the CVG’s can achieve SPL peak noise reductions for essentially all directivity angles, with the addition of a high-frequency source that appears consistent with a self-noise induced dipole. 2 Acknowledgements I would like to thank those who supported this work, and the great amount of work that never will be represented throughout my time at UC, and the labs at GE. Dr. Ephraim Gutmark was particularly supportive, allowing freedom to investigate these issues as I saw fit, under his guidance. Also, he provided a world- class environment with which to pursue this research effort. Dr. John Wojno at GE Aviation was my technical research supervisor and lead to whom I owe many valuable open conversations about jet noise and acoustics, and from paying close attention I received a great deal in return. I appreciate his willingness to let me take as much of a role in the technology development process as I could handle. Dr. Steve Martens, now of GE GRC, I owe sincere thanks to for building a great collaboration with UC. Sharing his particularly insightful oversight of our methods and investigations, and offering the resources of many other experts in the GE acoustics group was invaluable in producing this data, and forming analyses. Dr. Richard Cedar, besides offering his own valuable experience and insight in engine technology development, brought the driving force to make these experiments as practical as possible while pursuing a basic level of fundamental understanding. I am glad to have been exposed to his perspective. To Russ Dimicco I owe a great deal for oversight of the facility and equipment, and his tenacious distaste for substandard anything. The quality of data, and the resources to get things done was by his doing. To my colleagues Olaf Rask, Dave Munday, and Seth Harrison, I owe many sets of data, completed only with your help. Olaf provided not only the initial mentorship that helped me advance my knowledge so quickly, but was a useful backboard for discussing ideas in fluids and acoustics. I owe a good amount of my success to Olaf. But thanks also to Boo and If Then Elsa for all their data collection and processing help, both exceptional undergraduate research assistants. i Table of Contents List of Figures iv List of Tables x Nomenclature xi Chapter 1 Introduction 1 1.1 Jet Noise Background 3 1.2 Motivation for Source Noise Reduction 6 1.2.1 Psychoacoustics and Aircraft Noise Effects 7 1.2.1.1 Psychoacoustics of Interest in Aircraft Noise 8 1.2.1.2 Health Effects (Non-Auditory) of Aircraft Noise 11 1.2.2 U.S. Commercial Aircraft Noise Regulations 12 1.3 Objectives 15 1.4 Thesis Outline 16 Chapter 2 Background 20 2.1 Qualitative Jet Description 21 2.1.1 Mean Subsonic Coaxial Velocity Field & Similarity 23 2.1.2 Supersonic Jet Structure 26 2.2 Aeroacoustic Theory 28 2.3 Jet Instabilities 34 2.3.1 Effects of Initial Condition on Mixing Layer and Acoustics 35 2.3.2 Influence of Jet Instability Modes on Flow and Acoustics 38 2.4 Mixing Nozzle Research 40 2.4.1 Tabbed and Chevron Mixing Nozzles 41 2.4.2 Near-Field Fluid Structures of Vortex Generators 48 Chapter 3 Experimental Facilities & Methods 52 3.1 GDPL Anechoic Aeroacoustic Test Facility 53 3.2 ATF High Bypass Model Rig & Hardware 54 3.2.1 Conventional Core and Fan Nozzles 56 3.2.2 Modified Conventional Core Nozzles 57 3.2.3 Vortex Generators on Core and Fan Nozzles 58 3.3 Acoustic and Fluid Measurement Systems 60 3.3.1 Acoustic Far-Field Microphone Array 60 3.3.2 Boundary Layer Total Pressure Pitot Measurements 62 3.3.3 Dual-Component Laser Doppler Velocimetry 63 3.3.3.1 Flow Tracker Particle Seeding 66 Chapter 4 Boundary Layer Flow and Noise Results 67 ii 4.1 Core Baseline and Chevron Nozzles Mean Initial Velocity Profiles - Clean and Tripped 68 4.2 Acoustic Far-Field Sensitivity to Boundary Layer Characteristics 74 Chapter 5 Initial Mixing Region Turbulence via LDV 80 5.1 Mean Results 81 5.2 Turbulence Statistics in Axial and Radial Velocities 86 5.3 Turbulence Velocity Spectra 92 Chapter 6 Acoustic Far-Field Noise Reduction Results 95 6.1 Baseline and Modified Chevron Root Geometry 96 6.2 Internal Chevron Core Nozzle Results 101 Chapter 7 Incompressible CFD Simulations 105 7.1 Computational Domain and Case Setup 106 7.2 Flowfield Scalar Results 109 7.3 Stream-wise Vortical Structures Development 115 Chapter 8 Conclusions 126 Bibliography 128 iii List of Figures FIGURE 1.1 – CONTOURS OF EQUAL PERCEIVED NOISINESS AT VARIOUS NOYS LEVELS [10] .................................................................................................................................... 9 FIGURE 1.2 - SYSTEM NOISE COMPONENT ESTIMATES, [] ................................................ 13 FIGURE 1.3 - THRUST NORMALIZED AIRCRAFT NOISE LEVEL HISTORY [11] ................. 14 FIGURE 2.1 - SHADOWGRAPH FLOWFIELD OF HEATED COAXIAL MODEL JET AT CRUISE CONDITIONS. [34] .......................................................................................................... 21 FIGURE 2.3 - SCHEMATIC OF SHOCK-CELL FLOW STRUCTURE DEVELOPMENT FOR SIMPLIFIED SINGLE AXISYMMETRIC JET WITHOUT CENTERBODY PLUG [44]....... 26 FIGURE 2.4 - SUPERSONIC MIXING LAYER DETAILED SHOCK TIP SCHEMATIC [34] ...... 27 FIGURE 2.5 - SCHLIEREN NANOSPARK IMAGING OF UNDEREXPANDED CONICAL NOZZLE CORE FLOW IN STATIC CONDITIONS AT THE UC AEROACOUSTIC TEST FACILITY [48] ................................................................................................................. 27 FIGURE 2.6 - SOURCE CONVECTION EFFECT ON DIRECTIONAL RADIATION OF JET NOISE, FOR VARIOUS JET MACH NUMBERS [52] ........................................................ 31 FIGURE 2.7 - EARLY "TABBED" MIXER NOZZLE OF WESTLEY & LILLEY, 1952 [72]........ 41 FIGURE 3.1 - A) SCHEMATIC OF AEROACOUSTIC TEST FACILITY FAR-FIELD MICROPHONE ARRAY, B) NOZZLE ACOUSTIC TEST RIG WITH CHEVRON NOZZLE INSTALLED DURING LDV BACKSCATTER MEASUREMENTS .................................... 53 FIGURE 3.2 - CUTAWAY VIEW & COMPONENTS OF HIGH BYPASS RATIO (8) NOZZLE ACOUSTIC TEST RIG...................................................................................................... 55 FIGURE 3.3 - CORE AND FAN STREAM CONVENTIONAL NOZZLES INCLUDED IN TESTING CONFIGURATIONS. A) BASELINE CONIC CORE NOZZLE, B) 8LP CORE NOZZLE, C) 8LP SIN CORE NOZZLE, D) 16HP FAN NOZZLE ....................................... 56 FIGURE 3.4 - MODIFIED 8HP CORE CHEVRON NOZZLE WITH SINUSOIDAL ROOT A) NOZZLE B) DIMENSIONS............................................................................................... 57 iv FIGURE 3.5 - CVG GEOMETRY DEFINITIONS AND MODEL RIG INSTALLATION. A) DELTA CVG (DVG), B) MUSHROOM CVG (MVG), C) CVG NOZZLE SECTION (NONE INSTALLED), D) SEAT FOR CVG’S ................................................................................ 58 FIGURE 3.6 - INTERNAL CHEVRON CORE NOZZLE. A) INTERNAL SURFACE, B) EXTERNAL SURFACE, B) COVERED ............................................................................. 59