Kun Zhao, 'Investigating of dual-jet air curtains for a landing gear noise reduction technology', [thesis], Trinity College Dublin, Ireland. Department of Mechanical and Manufacturing Engineering,pp.
Advancements in Jet Turbulence and Noise Modeling: Although large-scale numerical simulations are now able to simultaneously compute turbulent jets and their radiated sound, lost-cost, physically-motivated models are needed to guide noise-reduction efforts.
A particularly promising modeling approach centers around certain large-scale coherent structures, called wavepackets, that are observed in jets and their radiated sound.
The typical approach to modeling wavepackets is to approximate them as linear modal solutions of the Euler or Navier-Stokes equations linearized about the long-time mean of the turbulent flow field.
The near-field wavepackets obtained from these models show compelling agreement with those educed from experimental and simulation data for both subsonic and supersonic jets, but the acoustic radiation is severely under-predicted in the subsonic case.
This thesis contributes to two aspects of these models. First, two new solution methods are developed that can be used to efficiently compute wavepackets and their acoustic radiation, reducing the computational cost of the model by more than an order of magnitude.
The new techniques are spatial integration methods and constitute a well-posed, convergent alternative to the frequently used parabolized stability equations. Using concepts related to well-posed boundary conditions, the methods are formulated for general hyperbolic equations and thus have potential applications in many fields of physics and engineering.
Second, the nonlinear and stochastic forcing of wavepackets is investigated with the goal of identifying and characterizing the missing dynamics responsible for the under-prediction of acoustic radiation by linear wavepacket models for subsonic jets.
Specifically, we use ensembles of large-eddy-simulation flow and force data along with two data decomposition techniques to educe the actual nonlinear forcing experienced by wavepackets in a Mach 0.
Modes with high energy are extracted using proper orthogonal decomposition, while high gain modes are identified using a novel technique called empirical resolvent-mode decomposition. In contrast to the flow and acoustic fields, the forcing field is characterized by a lack of energetic coherent structures.
Furthermore, the structures that do exist are largely uncorrelated with the acoustic field. Instead, the forces that most efficiently excite an acoustic response appear to take the form of random turbulent fluctuations, implying that direct feedback from nonlinear interactions amongst wavepackets is not an essential noise source mechanism.
This suggests that the essential ingredients of sound generation in high Reynolds number jets are contained within the linearized Navier-Stokes operator rather than in the nonlinear forcing terms, a conclusion that has important implications for jet noise modeling.STUDY OF HIGH-SPEED TURBULENT JET NOISE USING DECOMPOSITION METHODS A DISSERTATION SUBMITTED TO THE DEPARTMENT OF MECHANICAL ENGINEERING AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY thesis.
This work is supported by The Boeing Company; Dr. K. Viswanathan is the. The main contribution of this thesis is the link between the fluid mechanics and the acoustics in the compressible starting jet.
We study the noise generation mechanisms in a turbulent and. JET NOISE MODELS FOR FORCED MIXER NOISE PREDICTIONS A Thesis Submitted to the Faculty of Purdue University by Loren A.
Garrison In Partial Fulﬁllment of the Requirements for the Degree of Masters of Science in Aeronautics and Astronautics December ii. THE IMPACT OF BILATERAL GAIN REDUCTION ON LOCALIZATION AND SPEECH PERCEPTION IN SPATIALLY-SEPARATED NOISE by Hua Ou An Abstract Of a thesis submitted in partial fulfillment of the requirements for the Doctor of.
In Chapter 2 of this thesis, an existing backscattered grain noise theory based on the single scattering assumption and the "Born" approximation is extended, leading to a formal theory predicting the spatial correlation of the backscattered grain noise. The role of flow acoustic interaction in jet noise studies Szewczyk, Victor Meirion () The role of flow acoustic interaction in jet noise studies.
University of Southampton, Institute of Sound and Vibration Research, Doctoral Thesis, pp.
Aircraft Noise Characteristics and Metrics A PARTNER Project 24 Report Shashikant Ramdas More PARTNER-COE July This work was conducted under PARTNER Projects 1, 2, and The Pennsylvania State University The Graduate School NUMERICAL SIMULATION OF JET NOISE A Thesis in Aerospace Engineering by Umesh Paliath c Umesh Paliath. Publications and Projects. One of the key noisy components in an aircraft is the jet engine, although there are many sources of noise. Building and designing a jet engine costs millions of pounds and furthermore to prove the engine is safe they have to be tested to destruction.
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