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Non-Localized Acoustic Receptivity of Laminar Boundary Layers

Wiegel, M. and Wlezien, R.W. (1994) Non-Localized Acoustic Receptivity of Laminar Boundary Layers. Second International Conference on Experiment Fluid Mechanics 2.7.-8.7.94, Turin, Italien.

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Abstract

Hot-wire measurements are used to investigate acoustic receptivity of laminar boundary layers at surfaces with non-localized low-amplitude (40 um) waviness. Particular attention to measurement techniques is required in order to minimize facility-dependent flow and acoustic field anomalies. Balanced arrays of acoustic sources upstream and downstream of the test section effectively minimize the standing modes which contaminated previous experiments, thereby producing a purely-traveling acoustic mode in the test section. Tollmien-Schlichting (T-S) mode shapes due to wavy-wall receptivity are shown to be in excellent agreement with theory. By incrasing the number of wall wavelenghts, it is shown that only a small region in the vicinity of lower branch effectively contributes to receptivity. Furthermore it is shown that receptivity at distributed waviness is five times greater than that at localized surface inhomogenities. The effect of mismatching the neutral instability wavelength with the fixed wall wavelength is investigated by changing the freestream velocity at a constant forcing frequency. Strong receptivity occurs only over a narrow band where the waveiness and the T-S wavelength are matched. The findings from the present experiment follow trentd predicted by theory and match well with absolute values from direct simulation.

Document Type:Conference or Workshop Item (Paper)
Additional Information: LIDO-Berichtsjahr=1994, pages=10,
Title:Non-Localized Acoustic Receptivity of Laminar Boundary Layers
Authors:
AuthorsInstitution or Email of Authors
Wiegel, M.UNSPECIFIED
Wlezien, R.W.UNSPECIFIED
Date:1994
Status:Published
Keywords:Acoustic Receptivity, Non-Localized Receptivity, Wavy-wall, Blasius Flow
Event Title:Second International Conference on Experiment Fluid Mechanics 2.7.-8.7.94, Turin, Italien
HGF - Research field:UNSPECIFIED
HGF - Program:Aeronautics
HGF - Program Themes:other
DLR - Research area:UNSPECIFIED
DLR - Program:L TG - Querschnittstechnologien
DLR - Research theme (Project):UNSPECIFIED
Location: Köln-Porz , Braunschweig , Göttingen
Institutes and Institutions:Institute of Aerodynamics and Flow Technology > Institut für Strömungsmechanik > Institut für Experimentelle Strömungsmechanik
Deposited By: elib DLR-Beauftragter
Deposited On:03 Apr 2006
Last Modified:27 Apr 2009 10:08

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