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Receptivity to free-stream vorticity of flow past a flat plate with elliptic leading edge
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-4346-4732
Department of Mechanical Engineering, University of Ottawa,.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-7864-3071
2010 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 653, 245-271 p.Article in journal (Refereed) Published
Abstract [en]

Receptivity of the two-dimensional boundary layer on a flat plate with elliptic leading edge is studied by numerical simulation. Vortical perturbations in the oncoming free stream are considered, impinging on two leading edges with different aspect ratio to identify the effect of bluntness. The relevance of the three vorticity components of natural free-stream turbulence is illuminated by considering axial, vertical and spanwise vorticity separately at different angular frequencies. The boundary layer is most receptive to zero-frequency axial vorticity, triggering a streaky pattern of alternating positive and negative streamwise disturbance velocity. This is in line with earlier numerical studies on non-modal growth of elongated structures in the Blasius boundary layer. We find that the effect of leading-edge bluntness is insignificant for axial free-stream vortices alone. On the other hand, vertical free-stream vorticity is also able to excite non-modal instability in particular at zero and low frequencies. This mechanism relies on the generation of streamwise vorticity through stretching and tilting of the vertical vortex columns at the leading edge and is significantly stronger when the leading edge is blunt. It can thus be concluded that the non-modal boundary-layer response to a free-stream turbulence field with three-dimensional vorticity is enhanced in the presence of a blunt leading edge. At high frequencies of the disturbances the boundary layer becomes receptive to spanwise free-stream vorticity, triggering Tollmien-Schlichting (T-S) modes and receptivity increases with leading-edge bluntness. The receptivity coefficients to free-stream vortices are found to be about 15% of those to sound waves reported in the literature. For the boundary layers and free-stream perturbations considered, the amplitude of the T-S waves remains small compared with the low-frequency streak amplitudes.

Place, publisher, year, edition, pages
2010. Vol. 653, 245-271 p.
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-25447DOI: 10.1017/S0022112010000376ISI: 000279322000008ScopusID: 2-s2.0-77953609890OAI: diva2:358500
Uppdaterad till Artikel 2010 QC 20101022Available from: 2010-10-22 Created: 2010-10-22 Last updated: 2010-12-17Bibliographically approved
In thesis
1. Receptivity of Boundary Layers under Pressure Gradient
Open this publication in new window or tab >>Receptivity of Boundary Layers under Pressure Gradient
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Boundary-layer flow over bodies such as aircraft wings or turbine blades is characterized by a pressure gradient due to the curved surface of the body. The boundary layer may experience modal and non-modal instability, and the type of dominant instability depends on whether the body is swept with respect to the oncoming flow or not. The growth of these disturbances causes transition of the boundary-layer flow to turbulence. Provided that they are convective in nature, the instabilities will only arise and persist if the boundary layer is continuously exposed to a perturbation environment. This may for example consist of turbulent fluctuations or sound waves in the free stream or of non-uniformities on the surface of the body. In engineering, it is of relevance to understand how susceptive to such perturbations the boundary layer is, and this issue is subject of receptivity analysis.


In this thesis, receptivity of simplified prototypes for flow past a wing is studied. In particular, the three-dimensional swept-plate boundary layer and the boundary layer forming on a flat plate with elliptic leading edge are considered. The response of the boundary layer to vortical free-stream disturbances and surface roughness is analyzed, receptivity mechanisms are identified and their efficiency is quantified.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vi, 23 p.
Trita-MEK, ISSN 0348-467X ; 2008:08
Leading-edge effects
urn:nbn:se:kth:diva-9379 (URN)978-91-7415-155-8 (ISBN)
2008-10-29, K1, Teknikringen 56, KTH Campus Valhallavägen, Stockholm, 10:15 (English)
76218 VR Receptivity
QC 20101022Available from: 2008-10-30 Created: 2008-10-27 Last updated: 2012-02-23Bibliographically approved

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