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:
GET BOOK

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.

The Response of a Laminar Boundary Layer to Sound and Wall Vibration

The Response of a Laminar Boundary Layer to Sound and Wall Vibration
Author: Charles Joseph Gedney
Publisher:
Total Pages: 344
Release: 1983
Genre:
ISBN:
GET BOOK

An experimental analysis of the interaction of sound and plate vibration with a laminar boundary layer is presented. The two excitations generate disturbances at the leading edge of the plate which develop into Tollmien-Schlichting (TS) waves in the quasi-parallel region of the boundary layer. It is demonstrated that the TS wave and the sound wave coexist independently in this region, as predicted by the linear theory. A TS wave generated by a vibrating ribbon is shown to superimpose linearly with the sound-generated TS wave. Plate vibration is used to successfully cancel a sound-excited TS wave.

Effect of Localized Acoustic Excitation on the Stability of a Laminar Boundary Layer

Effect of Localized Acoustic Excitation on the Stability of a Laminar Boundary Layer
Author: Francis J. Jackson
Publisher:
Total Pages: 0
Release: 1962
Genre: Aeroacoustics
ISBN:
GET BOOK

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.

Experimental Studies on the Interaction of Strong Sound Fields with Free Convection Boundary Layers

Experimental Studies on the Interaction of Strong Sound Fields with Free Convection Boundary Layers
Author: E. E. Soehngen
Publisher:
Total Pages: 84
Release: 1960
Genre: Heat
ISBN:
GET BOOK

Experiments have been conducted on the interaction of strong sound fields with freq convection boundary layers on horizontal heated cylinders of 0.750-inch diameter. The interaction effects were observed through the measurements of total heat transfer from the cylinders to air under the influence of different types of sound environments. Three different types of sound fields were employed for the experiments: (1) standing plane waves generated by loud-speakers in an anechoic chamber; (2) Traveling plane wave fields generated by a mechanical siren in an anechoic duct; (3) Constant pressure or diffuse sound fields generated by a mechanical siren in a reverberant chamber. In all cases the generated sound was monochromatic ...

Effect of Localized Acoustic Excitation on the Stability of a Laminar Boundary Layer

Effect of Localized Acoustic Excitation on the Stability of a Laminar Boundary Layer
Author: Francis J. Jackson
Publisher:
Total Pages: 56
Release: 1962
Genre: Acoustics
ISBN:
GET BOOK

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.