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Numerical studies on receptivity and control of a three-dimensional boundary layer
KTH, School of Engineering Sciences (SCI), Mechanics.
2012 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Numeriska studier av receptivitet och kontroll av tredimensionella gränsskikt (Swedish)
Abstract [en]

Receptivity in three-dimensional boundary layer ow to localized roughness elements over a at plate is studied by means of direct numerical simulations (DNS). The surface roughness is modeled by applying nonhomogeneous boundary conditions along the wall as well as considering as a surface deformation by inserting the bump shape into the numerical mesh. Under the assumption of the small amplitudes of the roughness, although dierent disturbances amplitudes are observed in the vicinity of the bump for the meshed and modeled case, the boundary layer response downstream of the roughness is independent if the way of the bump implementation. Dierent roughness heights are considered in order to compare the boundary layer response of two approaches. Also, the boundary layer is excited by random distributed surface roughness and the receptivity results are studied. Moreover, a simple model for natural roughness excites steady multi wavenumber crossow instabilities. A localised surface roughness i.e. control roughness is applied to stabilise the latter. The control mode which is subcritical with respect to transition aects the most steady unstable mode. Suppression of the most dangerous mode is observed through nonlinear interactions with the control mode.

Place, publisher, year, edition, pages
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Engineering and Technology
URN: urn:nbn:se:kth:diva-87117OAI: diva2:501400
Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2012-02-14Bibliographically approved

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