Some Aspects of the Aeroacoustics of High-Speed Jets PDF Download
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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722784638
Category :
Languages : en
Pages : 50
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Book Description
Some of the background to contemporary jet aeroacoustics is addressed. Then scaling laws for noise generation by low-Mach-number airflows and by turbulence convected at 'not so low' Mach number is reviewed. These laws take into account the influence of Doppler effects associated with the convection of aeroacoustic sources. Next, a uniformly valid Doppler-effect approximation exhibits the transition, with increasing Mach number of convection, from compact-source radiation at low Mach numbers to a statistical assemblage of conical shock waves radiated by eddies convected at supersonic speed. In jets, for example, supersonic eddy convection is typically found for jet exit speeds exceeding twice the atmospheric speed of sound. The Lecture continues by describing a new dynamical theory of the nonlinear propagation of such statistically random assemblages of conical shock waves. It is shown, both by a general theoretical analysis and by an illustrative computational study, how their propagation is dominated by a characteristic 'bunching' process. That process associated with a tendency for shock waves that have already formed unions with other shock waves to acquire an increased proneness to form further unions - acts so as to enhance the high-frequency part of the spectrum of noise emission from jets at these high exit speeds. Lighthill, James Unspecified Center NAS1-19480; RTOP 50-90-52-01...
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722784638
Category :
Languages : en
Pages : 50
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Book Description
Some of the background to contemporary jet aeroacoustics is addressed. Then scaling laws for noise generation by low-Mach-number airflows and by turbulence convected at 'not so low' Mach number is reviewed. These laws take into account the influence of Doppler effects associated with the convection of aeroacoustic sources. Next, a uniformly valid Doppler-effect approximation exhibits the transition, with increasing Mach number of convection, from compact-source radiation at low Mach numbers to a statistical assemblage of conical shock waves radiated by eddies convected at supersonic speed. In jets, for example, supersonic eddy convection is typically found for jet exit speeds exceeding twice the atmospheric speed of sound. The Lecture continues by describing a new dynamical theory of the nonlinear propagation of such statistically random assemblages of conical shock waves. It is shown, both by a general theoretical analysis and by an illustrative computational study, how their propagation is dominated by a characteristic 'bunching' process. That process associated with a tendency for shock waves that have already formed unions with other shock waves to acquire an increased proneness to form further unions - acts so as to enhance the high-frequency part of the spectrum of noise emission from jets at these high exit speeds. Lighthill, James Unspecified Center NAS1-19480; RTOP 50-90-52-01...
Author: Institute for Computer Applications in Science and Engineering
Publisher:
ISBN:
Category :
Languages : en
Pages : 50
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Book Description
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722052225
Category :
Languages : en
Pages : 38
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Book Description
Aeroacoustic noise generation in a supersonic round jet is studied to understand in particular the effect of turbulence structure on the noise without numerically compromising the turbulence itself. This means that direct numerical simulations (DNS's) are needed. In order to use DNS at high enough Reynolds numbers to get sufficient turbulence structure we have decided to solve the temporal jet problem, using periodicity in the direction of the jet axis. Physically this means that turbulent structures in the jet are repeated in successive downstream cells instead of being gradually modified downstream into a jet plume. Therefore in order to answer some questions about the turbulence we will partially compromise the overall structure of the jet. The first section of chapter 1 describes some work on the linear stability of a supersonic round jet and the implications of this for the jet noise problem. In the second section we present preliminary work done using a TVD numerical scheme on a CM5. This work is only two-dimensional (plane) but shows very interesting results, including weak shock waves. However this is a nonviscous computation and the method resolves the shocks by adding extra numerical dissipation where the gradients are large. One wonders whether the extra dissipation would influence small turbulent structures like small intense vortices. The second chapter is an extensive discussion of preliminary numerical work using the spectral method to solve the compressible Navier-Stokes equations to study turbulent jet flows. The method uses Fourier expansions in the azimuthal and streamwise direction and a 1-D B-spline basis representation in the radial direction. The B-spline basis is locally supported and this ensures block diagonal matrix equations which are solved in O(N) steps. A very accurate highly resolved DNS of a turbulent jet flow is expected. Rao, Ram Mohan and Lundgren, Thomas S. Ames Research Center NCC2-5017; DAAL03-89-C-0038...
Author: Fung K Y
Publisher: World Scientific
ISBN: 9814551570
Category :
Languages : en
Pages : 384
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Book Description
The aim of the symposium was to gather fellow researchers, colleagues and friends of Professor William R Sears, a member of the National Academy of Science and the Academy of Engineering, on the occasion of his 80th birthday. Professor Sears is a leader in Aerospace Science and Aerodynamics research and the symposium was held in honour of his work in these areas.The symposium focussed on four areas in aeronautical science in which Professor Sears has made major contributions. These are wing design, unsteady aerodynamics and separation, aeroacoustics and self-correcting wind tunnels.
Author: Harvey H. Hubbard
Publisher:
ISBN:
Category : Aerodynamic noise
Languages : en
Pages : 620
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Book Description
Author: John M. Seiner
Publisher:
ISBN:
Category :
Languages : en
Pages : 40
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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781721634903
Category :
Languages : en
Pages : 30
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Book Description
We have succeeded in measuring a substantial portion of the two-point space-time velocity correlation in hot, high speed turbulent jets. This measurement, crucial in aeroacoustic theory and the prediction of jet noise, has been sought for a long time, but has not been made due to the limitations of anemometry. Particle Image Velocimetry has reached a stage of maturity where sufficient measurement density in both time and space allow the computation of space-time correlations. This paper documents these measurements along with lower-order statistics to document the adherence of the jet rig and instrumentation to conventional measures of the turbulence of jets. These measures have been made for a simple round convergent nozzle at acoustic Mach numbers of 0.5, 0.9, both cold and at a static temperature ratio of 2.7, allowing some estimation of the changes in turbulence that take place with changes in jet temperature. Since the dataset described in this paper is very extensive, attention will be focused on validation of the rig and of the measurement systems, and on some of the interesting observations made from studying the statistics, especially as they relate to jet noise. Of note is the effort to study the acoustically relevant part of the space-time correlation by addressing that part of the turbulence kinetic energy that has sonic phase speed. Bridges, James and Wernet, Mark Glenn Research Center NASA/TM-2004-212508, AIAA Paper 2003-3130, E-14068
Author: A. Krothapalli
Publisher: Springer Science & Business Media
ISBN: 146124840X
Category : Science
Languages : en
Pages : 511
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Book Description
The Joint Institute for Aeronautics and Acoustics at Stanford University was established in October 1973 to provide an academic environment for long-term cooperative research between Stanford and NASA Ames Research Center. Since its establishment, the Institute has conducted theoretical and experimental work in the areas of aerodynamics, acoustics, fluid mechanics, flight dynamics, guidance and control, and human factors. This research has involved Stanford faculty, research associates, graduate students, and many distinguished visitors in collaborative efforts with the research staff of NASA Ames Research Center. The occasion of the Institute's tenth anniversary was used to reflect back on where that research has brought us, and to consider where our endeavors should be directed next. Thus, an International Symposium was held to review recent advances in the fields relevant to the activities of the Institute and to discuss the areas of research to be undertaken in the future. This anniversary was also chosen as an opportunity to honor one of the Institute's founders and its director, Professor Krishnamurty Karamcheti. It has been his crea tive inspiration that has provided the ideal research environment at the Joint Institute.
Author: Ganesh Raman
Publisher:
ISBN: 9780906522943
Category :
Languages : en
Pages : 579
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Book Description
Jet Aeroacoustics is a growing area, a function of the significant projected growth in global air transportation. With the era of widespread supersonic flight and the proliferation of general aviation aircraft on future horizons, the noise generated by the high speed flow from aircraft engine exhaust is of great concern for communities near airports, for passengers in the aircraft's cabin, and for the structural integrity of the airframe. In addition, there are a number of industrial situations that desire lower noise from high pressure gas jets. Examples from industry include the noise from v.
Author: Darren Slotnick
Publisher:
ISBN:
Category :
Languages : en
Pages :
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The noise produced by supersonic, military jets is a significant health hazard for Naval personnel and an annoyance to communities located in close proximity to a military base. It is more important than ever to learn how nozzle designs and different flow conditions affect the noise produced by these supersonic jets. This thesis presents the acoustic data produced by subsonic and supersonic jets exiting from an aspect ratio 4 rectangular nozzle. Experiments were conducted at various azimuthal angles, followed by the generation of power spectral density plots and overall sound pressure level plots. These plots showed that the rectangular nozzle is in the quiet plane when orientated at 0° azimuthal angle, with the narrow side of the nozzle facing the microphones. Experimental results also indicate that noise from the nozzle increases as the simulated temperature of the jet increases and as the azimuthal angle of the nozzle increases to from 0° to 90°. Comparing results to other experimental campaigns show that the rectangular nozzle is comparable, but slightly louder than a more conventional faceted circular nozzle. Moving forward, this data will be used help generate models that can predict the flow and noise levels of various jet engine exhaust nozzle designs. It is critical to document important methods used throughout an experimentation process so that experiments can be repeated and results replicated at a later date. This thesis will present the process and results of an effort to create a comprehensive Laboratory Procedure Manual that can be used in the High Speed Jet Aeroacoustics Facility at the Pennsylvania State University. The lab manual created contains detailed instructions and descriptions for general lab processes, as well as two major facility configurations, including those conducted with an exhaust jet exiting from a nozzle with an aft deck.
