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Transition Delay by Oblique Roughness Elements in a Blasius Boundary-Layer Flow

Lemarechal, Jonathan (2017) Transition Delay by Oblique Roughness Elements in a Blasius Boundary-Layer Flow. Doktoranden Seminar des Instituts für Aerodynamik, 19. Dez. 2017, Stuttgart, Deutschland.

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Abstract

A passive device to delay the laminar-turbulent transition in a Blasius boundary-layer flow is tested at low Reynolds numbers in the laminar water channel. The passive device consists of oblique surface roughness elements lined up perpendicular to the flow. Each element has the shape of a cuboid, is oriented 45° to the direction of the oncoming flow, and generates a non-symmetric vortex system. These vortices generate high and low speed streaks inside of the boundary layer through the lift-up effect. The streaks alter the two-dimensional (2D) boundary layer into a three-dimensional (3D) one. For correctly placed and sized roughness elements the 2D Tollmien-Schlichting wave is altered into a 3D less amplified wave and the transition occurs further downstream. The flow is investigated by means of surface visualizations with the Temperature-Sensitive Paint (TSP) method and velocity measurements with hot-film anemometry. With the TSP method the laminar-turbulent transition was measured with high spatial and temporal resolution. The changes of transition location and changes of transition mechanism are weil captured.

Item URL in elib:https://elib.dlr.de/118680/
Document Type:Conference or Workshop Item (Speech)
Title:Transition Delay by Oblique Roughness Elements in a Blasius Boundary-Layer Flow
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Lemarechal, JonathanJonathan.Lemarechal (at) dlr.deUNSPECIFIED
Date:2017
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:laminar-turbulent transition, Blasius boundary layer, k-type transition, passive transition delay, streaks, temperature-sensitive paint, TSP, hot-film anemometry, laminar water channel, Laminarwasserkanal, low Reynolds number experiment
Event Title:Doktoranden Seminar des Instituts für Aerodynamik
Event Location:Stuttgart, Deutschland
Event Type:Other
Event Dates:19. Dez. 2017
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:fixed-wing aircraft
DLR - Research area:Aeronautics
DLR - Program:L AR - Aircraft Research
DLR - Research theme (Project):L - Simulation and Validation
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Experimental Methods, GO
Deposited By: Bachmann, Barbara
Deposited On:02 Feb 2018 14:38
Last Modified:02 Feb 2018 14:38

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