Effect Of Sound On Boundary Layer Stability
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| Author | : National Aeronautics and Space Administration (NASA) |
| Publisher | : Createspace Independent Publishing Platform |
| Total Pages | : 104 |
| Release | : 2018-07-17 |
| Genre | : |
| ISBN | : 9781723038815 |
Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-traveling sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2 lambda(sub TS)/pi of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations, and the Stokes wave subtracted) show the generation of 3-D T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modeling are observed. Saric, William S. and Spencer, Shelly Anne Unspecified Center ASYMPTOTIC SERIES; BOUNDARY LAYER STABILITY; BOUNDARY LAYERS; LEADING EDGES; MATHEMATICAL MODELS; NEAR FIELDS; SOUND WAVES; SURFACE ROUGHNESS; WIND TUNNEL TESTS; NORMAL DENSITY FUNCTIONS; PREDICTION ANALYSIS TECHNIQUES; VIBRATION...
| Author | : |
| Publisher | : |
| Total Pages | : |
| Release | : 1998 |
| Genre | : |
| ISBN | : |
| Author | : Paul Jonathan Shapiro |
| Publisher | : |
| Total Pages | : 89 |
| Release | : 1977 |
| Genre | : Laminar flow |
| ISBN | : |
This paper presents the results of an experimental investigation into the effects of pure-tone acoustic excitation on Tollmien-Schlichting waves in a subsonic Blasius boundary layer. Longitudinal growth rates were measured for naturally-existing waves in a low-noise, low-turbulence wind tunnel, and for waves excited by an externally imposed sound field. The results were compared to numerical results from the standard Orr-Sommerfeld equation. The excited Tollmien-Schlichting waves matched the theory well in most respects, and it was concluded that the acoustic excitation merely generated a larger initial wave amplitude, ahead of Branch I of the neutral stability curve. For excitation levels larger than the residual tunnel disturbances, this initial amplitude was constant and equal to the disturbance velocity of the sound wave. The naturally-existing waves showed growth rates smaller than theory predicted. This leads to the conclusion that natural waves are not initially two-dimensional.
| Author | : Francis J. Jackson |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 1962 |
| Genre | : Aeroacoustics |
| ISBN | : |
Investigations were performed utilizing a localized surface source of acoustic energy to generate disturbances in a laminar boundary layer flow to uncover the influcence of induced surface vibrations on the stability of a shear flow boundary layer. Explorations were carried out over a frequency range of from 50 to 10,000 cps, using input sound pressure levels of up to 145 db re 0. 0002 dynes/sq cm. Results are presented which indicate the effect of sonic parameters (frequency, amplitude) on both the mean and fluctuating components of the boundary layer flow. Induced boundary layer oscillations are discussed, where appropriate, in terms of the stability theory of Tollmien and Schlichting. Studies of distortion of boundary layer oscillations are described and the role of such distortion in producing transition is discussed. Nonlinear secondary flows (streaming) generated by the localized source are also treated. Exploration of the influence of sonic excitation on premature transition produced both by increasing the free stream turbulence level and by use of a tripping wire is described.
| Author | : William K. Blake |
| Publisher | : Academic Press |
| Total Pages | : 696 |
| Release | : 2017-08-14 |
| Genre | : Science |
| ISBN | : 0128122900 |
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 | : Frederick W. Boltz |
| Publisher | : |
| Total Pages | : 84 |
| Release | : 1960 |
| Genre | : |
| ISBN | : |
| Author | : Francis J. Jackson |
| Publisher | : |
| Total Pages | : 56 |
| Release | : 1962 |
| Genre | : Acoustics |
| ISBN | : |
Investigations were performed utilizing a localized surface source of acoustic energy to generate disturbances in a laminar boundary layer flow to uncover the influence of induced surface vibrations on the stability of a shear flow boundary layer. Explorations were carried out over a frequency range of from 50 to 10,000 cps, using input sound pressure levels of up to 145 db re 0. 0002 dynes/sq cm. Results are presented which indicate the effect of sonic parameters (frequency, amplitude) on both the mean and fluctuating components of the boundary layer flow. Induced boundary layer oscillations are discussed, where appropriate, in terms of the stability theory of Tollmien and Schlichting. Studies of distortion of boundary layer oscillations are described and the role of such distortion in producing transition is discussed. Nonlinear secondary flows (streaming) generated by the localized source are also treated. Exploration of the influence of sonic excitation on premature transition produced both by increasing the free stream turbulence level and by use of a tripping wire is described.
| Author | : Anthony L. Laganelli |
| Publisher | : |
| Total Pages | : 184 |
| Release | : 1984 |
| Genre | : Ballistic missiles |
| ISBN | : |
An experimental program was conducted at the AEDC von Karman facility, Tunnels A and B, in which acoustic pressure fluctuation data were acquired on a 7 degree half-cone-angle model featuring a control surface. The objective was to define the aeroacoustic environment applicable to re-entry vibration response analysis for both ballistic and maneuvering vehicles. Wind tunnel measurements were obtained at Mach 4 and 8 for several values of freestream Reynolds number and model angle of attack. Stationary zones of laminar, transitional, and turbulent flow over the model were achieved. Acoustic data were reduced to rms fluctuating pressure, and power and cross-power spectral densities. Results were normalized using local boundary layer parameters for comparison with previous high speed measurements. The present study re-examined the aeroacoustic environment prediction capability relative to compressible flow conditions. Moreover, boundary layer characteristic lengths and velocities were reviewed in order to develop normalization procedures required for development of appropriate aeroacoustic scaling laws. It was determined that fluctuating pressure characteristics described by incompressible theory as well as empirical correlations could be modified to a compressible state through a transformation function. In this manner, compressible data were transformed to the incompressible plane where direct use of more tractable prediction techniques are available for engineering design analyses.
| Author | : Thomas Ira Hutchinson |
| Publisher | : |
| Total Pages | : 66 |
| Release | : 1963 |
| Genre | : |
| ISBN | : |
| Author | : |
| Publisher | : |
| Total Pages | : 702 |
| Release | : 1995 |
| Genre | : Aeronautics |
| ISBN | : |
