Scientific and Technical Aerospace Reports


Book Description

Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.







Comparison of the Wall Pressure Fluctuations in Artificially Generated Turbulent Spots, Natural Transition and Turbulent Boundary Layers


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Experiments have been conducted to measure the wall pressure fluctuations associated with artificially generated turbulent spots in a laminar boundary layer. The results show that both the rms wall pressure and the wall pressure spectra of turbulent spots are influenced by the local mean flow pressure gradient. The zero and favorable pressure gradient wall pressure data are in agreement with turbulent boundary layer results. However, the current spot data shows that, in the presence of an adverse pressure gradient, the spot's rms wall pressure is approximately 1.5-2.5 times larger than that found for the zero and favorable pressure gradient cases. These results are in general agreement with the adverse pressure gradient data of Huang and Hannan (1975). Additionally, the nearly constant magnitude of the spot's adverse pressure gradient wall pressure spectrum indicates a nearly even distributions of energy with frequency. Keywords: Turbulent boundary layer, Laminar boundary layer, Wall pressure fluctuations.







Effects of Pressure Gradients on Turbulent Boundary-layer Wall-pressure Fluctuations


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The low-turbulence subsonic wind tunnel was significantly modified so that turbulent boundary-layer pressure fluctuation measurements could be made with adequate signal-to-noise ratio over a wide frequency range. Measurements were made in a mild adverse and a mild favorable pressure gradient with natural transition occurring in the boundary layer. To make certain that the facility was operating correctly and to establish a basis for comparison, the zero-pressure gradient case was investigated. For this case, the spectral density, magnitude of the normalized longitudinal and lateral cross-spectral density functions, and convection velocity as a function of longitudinal separation and frequency were in excellent agreement with other experimenters. When comparison is made to the zero-pressure gradient in the same non-dimensionalized frequency band and at similar non-dimensionalized longitudinal spacings, the convection velocity ratio is higher in the favorable and lower in the adverse pressure gradients, primarily due to the change in shape of the mean velocity profile. The effect of an adverse pressure gradient on the non-dimensionalized spectral density is to increase the low-frequency content without influencing the high-frequency portion appreciably, when compared to the zero-pressure gradient case. (Author).







Technical Abstract Bulletin


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Mechanics of Flow-Induced Sound and Vibration, Volume 2


Book Description

Mechanics of Flow-Induced Sound and Vibration, Volume 2: Complex Flow-Structure Interactions, Second Edition, enables readers to fully understand flow-induced vibration and sound, unifying the disciplines of fluid dynamics, structural dynamics, vibration, acoustics, and statistics in order to classify and examine each of the leading sources of vibration and sound induced by various types of fluid motion. Starting from classical theories of aeroacoustics and hydroacoustics, a formalism of integral solutions valid for sources near boundaries is developed and then broadened to address different source types, including hydrodynamically induced cavitation and bubble noise, turbulent wall-pressure fluctuations, pipe and duct systems, lifting surface flow noise and vibration, and noise from rotating machinery. Each chapter is illustrated with comparisons of leading formulas and measured data. Combined with its companion book, Mechanics of Flow-Induced Sound and Vibration, Volume 1: General Concepts and Elementary Sources, the book covers everything an engineer needs to understand flow-induced sound and vibration. This book will be a vital source of information for postgraduate students, engineers and researchers with an interest in aerospace, ships and submarines, offshore structures, construction, and ventilation. Presents every important topic in flow-induced sound and vibration Covers all aspects of the topics addressed, from fundamental theory, to the analytical formulas used in practice Provides the building blocks of computer modeling for flow-induced sound and vibration