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Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Boundary layer transition is an important contributor to sensor flow-induced self noise. The pressure fluctuations caused by this spatially bounded and intermittent, phenomenon encompass a very wide range of spatial wave numbers and temporal frequencies. Here, we analyze the wavevector-frequency spectrum of the wall pressure fluctuations due to subsonic boundary-layer transition as it occurs on a flat plate under zero pressure gradient conditions. Based on previous measurements of the statistic of the boundary-layer intermittence it is found that transition induces higher low-streamwise wave number wall pressure level than does a fully-developed turbulent boundary layer (TBL) that might superficially exist at the same location and at the same Reynolds number. The transition zone spanwise wavenunmber pressure components are virtually unchanged from the TBL ease. The results suggest that transition may be more effective than the TBL in forcing structural excitation at low Mach numbers and it may have a more intense radiated noise contribution on a per unit area basis. This may help explain increases in measured sensor self noise when the sensors are placed near the transition zone.
Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Boundary layer transition is an important contributor to sensor flow-induced self noise. The pressure fluctuations caused by this spatially bounded and intermittent, phenomenon encompass a very wide range of spatial wave numbers and temporal frequencies. Here, we analyze the wavevector-frequency spectrum of the wall pressure fluctuations due to subsonic boundary-layer transition as it occurs on a flat plate under zero pressure gradient conditions. Based on previous measurements of the statistic of the boundary-layer intermittence it is found that transition induces higher low-streamwise wave number wall pressure level than does a fully-developed turbulent boundary layer (TBL) that might superficially exist at the same location and at the same Reynolds number. The transition zone spanwise wavenunmber pressure components are virtually unchanged from the TBL ease. The results suggest that transition may be more effective than the TBL in forcing structural excitation at low Mach numbers and it may have a more intense radiated noise contribution on a per unit area basis. This may help explain increases in measured sensor self noise when the sensors are placed near the transition zone.
Author: Mark Jay Moeller Publisher: ISBN: Category : Languages : en Pages : 87
Book Description
The low wavenumber components of the turbulent boundary layer wavenumber frequency spectrum of wall pressure fluctuations were measured with two flush-mounted rectangular plates having approximately clamped boundary conditions. The plates were designed to provide low wavenumber measurements at higher frequencies and wavenumbers than previous plate experiments in order to provide data comparable with measurements made by Farabee and Geib (7) with an array of flush-mounted microphones. The low wavenumber measurements were made in the M.I.T. low noise low turbulence subsonic wind tunnel under zero and adverse pressure gradient conditions. When nondimensionalized on outer boundary layer variables the adverse pressure gradient data do not exhibit increased levels from those of the zero pressure gradient data. The zero pressure gradient data are in good agreement with the levels reported by Farabeen and Geib (7) for the same nondimensional frequency and wavenumber range. (Author).
Author: J. E Cole (III.) Publisher: ISBN: Category : Languages : en Pages : 45
Book Description
The objective of this study is to examine the sensitivity of the low wavenumber portion of the wall pressure field under a turbulent boundary layer to both flow and wall conditions. The analytical procedure makes use of a method for calculating the broadband correlation function of the wall pressure field in which the specific flow characteristics enter through profiles of the mean velocity shear and turbulence intensity across the boundary layer. The basic assumption used to extend the results of this procedure to narrowband frequency characteristics is that there is a range of large spatial separations in which Strouhal scaling is not important. Several specific boundary layers are considered including flows on smooth and rough walls and in zero, favorable, and adverse pressure gradients. Results are presented for the point pressure, the spatial correlation function, and the low wavenumber spectral level. Keywords: GHR(General Hydromechanics Research) program; Wall pressure fluctuations; Low Wavenumber.
Author: M. A. Josserand Publisher: ISBN: Category : Languages : en Pages : 184
Book Description
The laminar to turbulent transition zone continues to be of interest from the flow noise point of view. A theoretical model was developed to predict the radiated component (wavenumber less than or equal to the sonic wavenumber) of the pressure fluctuations that occur in this zone. It is also recognized that wavenumbers greater than the sonic wavenumber are also important because pressure fluctuations at these higher wavenumbers may couple with structural vibrations. Keywords: flow noise; turbulence, pressure fluctuations; boundary layer; transition; theoretical; experimental; spectrum.
Author: Howard H. Schloemer Publisher: ISBN: Category : Boundary layer noise Languages : en Pages : 89
Book Description
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).
Author: William K. Blake Publisher: Academic Press ISBN: 0128122900 Category : Science Languages : en Pages : 696
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
Author: Thomas S. Mautner Publisher: ISBN: Category : Languages : en Pages : 9
Book Description
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.
Author: Charles Joseph Gedney Publisher: ISBN: Category : Boundary layer noise Languages : en Pages : 114
Book Description
Detailed measurements of wall pressure fluctuations have been made in the intermittent region of a flat plate boundary layer. Digital sampling and processing were used. The properties of these pressure fluctuations were found to be similar to the previous measurements made in the fully turbulent region. The measurements were repeated with a single two dimensional surface roughness on the plate. The only changes in the results were a decrease in the transition Reynolds number from 2.0 to 1.2 million per foot and an increase in the decay rate of the longitudinal cross-spectral density magnitude by a factor of about 1.5. Emmons' analytical model of the burst rate in the transition region was found to be inaccurate. His model treats the sources of the turbulent spots as independent random events with prescribed probability density functions. Both a delta function and a constant were used as the source density functions and in each case the burst rate was about two times higher than the present measurements. (Author).
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Author: Mark Jay Moeller
Author: J. E Cole (III.)
Author: D. R. Blackman
Author: M. A. Josserand
Author: Eric Manoha
Author: Howard H. Schloemer
Author: William K. Blake
Author: Thomas S. Mautner
Author: Charles Joseph Gedney