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Simulation of N-Wave and Shaped Supersonic Signature Turbulent Variations.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Simulation of N-Wave and Shaped Supersonic Signature Turbulent Variations./
作者:	Stout, Trevor A.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	419 p.
附註:	Source: Dissertations Abstracts International, Volume: 80-10, Section: B.
Contained By:	Dissertations Abstracts International80-10B.
標題:	Aerospace engineering. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13871925
ISBN:	9781392040300

Simulation of N-Wave and Shaped Supersonic Signature Turbulent Variations.
Stout, Trevor A.

Simulation of N-Wave and Shaped Supersonic Signature Turbulent Variations. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 419 p.

Source: Dissertations Abstracts International, Volume: 80-10, Section: B.

Thesis (Ph.D.)--The Pennsylvania State University, 2018.

One of the design paradigms for the next generation of civil supersonic aircraft targets a reduction in sonic boom amplitude and impulsivity, creating a "shaped" signature at the ground which is likely more acceptable to the public. The unshaped, conventional "N-wave" sonic boom is well known to distort due to atmospheric turbulence or wind and temperature fluctuations, randomly increasing or decreasing the loudness perceived by listeners. However, the effect of turbulence on the shaped signature is not well understood. No acoustic databases from powered, fully-shaped aircraft yet exist because these prototypes are currently in development. Thus, the present work uses a numerical model based on an augmented nonlinear KZK propagation equation and simulated shaped signatures to analyze the turbulence effects. The KZK equation accounts for absorption, nonlinearity, advection due to turbulence and resultant diffraction, as well as other propagation effects. A novel implementation of a fully time-domain solution is put forth along with a method for generating turbulent fields throughout the planetary boundary layer according to an approximate atmospheric turbulence model. As is typically done in the literature, the solution to the KZK equation in two dimensions is predominantly used in the present work, though a computationally-intensive 3D algorithm is applied to a limited case. As part of the recently-completed Sonic Booms in Atmospheric Turbulence (SonicBAT) project, supersonic flyover measurement campaigns were conducted to produce the first database of its kind with acoustic data of N-waves from powered, piloted aircraft and concurrent atmospheric turbulence and weather data. One objective of the measurements was to provide suitable inputs for the present numerical model so that the simulated output statistics could be compared with the measured. This comparison shows reasonable agreement between the model and the measurement for most cases across a wide range of atmospheric and turbulence parameters, suggesting that the KZK and atmospheric turbulence model is suitable for predicting full-scale sonic boom loudness variations. Using the validated algorithm, turbulence effects on N-waves are analyzed in many hypothetical atmospheres and the turbulized outputs are used to create finite impulse response (FIR) filters which quickly approximate turbulent distortions of signature waveforms. Propagation through turbulence is shown to increase the standard deviation of the Perceived Level (PL) loudness metric up to a maximum value depending on the turbulence strength. The mean effect of turbulence is a reduction of the mean PL which becomes more significant with further propagation through turbulence and higher turbulence strength. In similar simulations, the effects of turbulence on both the N-wave and shaped signature are compared, revealing that the boom shaping tends to reduce PL standard deviations. Thus, the shaped signature has a more consistent PL value after propagation through turbulence than the N-wave, which may be of benefit to efforts in assessing noise impact and setting certification standards. In an investigation involving successive simulations in the linear and nonlinear regime, the loudness variation reduction is largely explained by the resistance of the shaped signature to nonlinear effects, while nonlinearity amplifies the N-wave scattering at high frequencies. Regressions on simulated N-wave and shaped signature PL statistics are performed which offer a quick reference for estimating loudness variations with knowledge of some atmospheric parameters. Finally, the prevailing use of 2D simulations in the literature and the present work is qualified by comparison to comparable 3D simulations, finding that inclusion of the third dimension somewhat augments the turbulence effects and increases the predicted probability of high-amplitude N-wave booms. Monte Carlo sampling of the 3D results further suggests that the total span of a linear microphone array is more important than the number of microphones when attempting to accurately sample the PL standard deviation or precisely sample the PL mean with a single array measurement.

ISBN: 9781392040300Subjects--Topical Terms:

1002622
Aerospace engineering.

Simulation of N-Wave and Shaped Supersonic Signature Turbulent Variations.
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500 $a Source: Dissertations Abstracts International, Volume: 80-10, Section: B.
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520 $a One of the design paradigms for the next generation of civil supersonic aircraft targets a reduction in sonic boom amplitude and impulsivity, creating a "shaped" signature at the ground which is likely more acceptable to the public. The unshaped, conventional "N-wave" sonic boom is well known to distort due to atmospheric turbulence or wind and temperature fluctuations, randomly increasing or decreasing the loudness perceived by listeners. However, the effect of turbulence on the shaped signature is not well understood. No acoustic databases from powered, fully-shaped aircraft yet exist because these prototypes are currently in development. Thus, the present work uses a numerical model based on an augmented nonlinear KZK propagation equation and simulated shaped signatures to analyze the turbulence effects. The KZK equation accounts for absorption, nonlinearity, advection due to turbulence and resultant diffraction, as well as other propagation effects. A novel implementation of a fully time-domain solution is put forth along with a method for generating turbulent fields throughout the planetary boundary layer according to an approximate atmospheric turbulence model. As is typically done in the literature, the solution to the KZK equation in two dimensions is predominantly used in the present work, though a computationally-intensive 3D algorithm is applied to a limited case. As part of the recently-completed Sonic Booms in Atmospheric Turbulence (SonicBAT) project, supersonic flyover measurement campaigns were conducted to produce the first database of its kind with acoustic data of N-waves from powered, piloted aircraft and concurrent atmospheric turbulence and weather data. One objective of the measurements was to provide suitable inputs for the present numerical model so that the simulated output statistics could be compared with the measured. This comparison shows reasonable agreement between the model and the measurement for most cases across a wide range of atmospheric and turbulence parameters, suggesting that the KZK and atmospheric turbulence model is suitable for predicting full-scale sonic boom loudness variations. Using the validated algorithm, turbulence effects on N-waves are analyzed in many hypothetical atmospheres and the turbulized outputs are used to create finite impulse response (FIR) filters which quickly approximate turbulent distortions of signature waveforms. Propagation through turbulence is shown to increase the standard deviation of the Perceived Level (PL) loudness metric up to a maximum value depending on the turbulence strength. The mean effect of turbulence is a reduction of the mean PL which becomes more significant with further propagation through turbulence and higher turbulence strength. In similar simulations, the effects of turbulence on both the N-wave and shaped signature are compared, revealing that the boom shaping tends to reduce PL standard deviations. Thus, the shaped signature has a more consistent PL value after propagation through turbulence than the N-wave, which may be of benefit to efforts in assessing noise impact and setting certification standards. In an investigation involving successive simulations in the linear and nonlinear regime, the loudness variation reduction is largely explained by the resistance of the shaped signature to nonlinear effects, while nonlinearity amplifies the N-wave scattering at high frequencies. Regressions on simulated N-wave and shaped signature PL statistics are performed which offer a quick reference for estimating loudness variations with knowledge of some atmospheric parameters. Finally, the prevailing use of 2D simulations in the literature and the present work is qualified by comparison to comparable 3D simulations, finding that inclusion of the third dimension somewhat augments the turbulence effects and increases the predicted probability of high-amplitude N-wave booms. Monte Carlo sampling of the 3D results further suggests that the total span of a linear microphone array is more important than the number of microphones when attempting to accurately sample the PL standard deviation or precisely sample the PL mean with a single array measurement.
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856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13871925