Effect of Sound on Boundary Layer Stability

Effect of Sound on Boundary Layer Stability
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...

The Influence of Sound Upon Laminar Boundary Layer Instability

The Influence of Sound Upon Laminar Boundary Layer Instability
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.

Mechanism of Noise Generation in the Turbulent Boundary Layer

Mechanism of Noise Generation in the Turbulent Boundary Layer
Author: John Laufer
Publisher:
Total Pages: 100
Release: 1964
Genre: Boundary layer noise
ISBN:

The first chapter briefly states the problem and gives its historical development; the second reviews some basic notions of classical acoustics with special emphasis on the sound field produced by elementary sound sources, while the third one contains the generalized wave equation governing the pressure field radiated by nonuniform nonstationary flow. Subsequent chapters describe the methods proposed by the various authors for finding a solution to the radiation problem. The experimental approach is discussed. (Author).