The influence of the spatial frequency content of discrete roughness distributions on the development of the crossflow instability

Evelien van Bokhorst, Marco Placidi, Chris Atkin

Research output: Chapter in Book/Report/Conference proceedingConference contribution

3 Citations (Scopus)


An experimental investigation on the influence of the spatial frequency content of roughness distributions on the development of crossflow instabilities has been carried out. From previous research it is known that micro roughness elements can have a large influence on the crossflow development. When the spanwise spacing is chosen such that it is the most unstable wavelength (following linear stability analysis), stationary crossflow waves are amplified. While in earlier studies the focus was on the height or spanwise spacing of roughness elements, in the present study it is chosen to vary the shape of the elements. Through the modification of the shape the forcing at the critical wavelength is increased, while the forcing at the harmonics of the critical wavelength is damped. Experiments were carried in the low turbulence wind tunnel at City University London (Tu=0.006%) on a swept flat plate in combination with displacement bodies to create a sufficiently strong favourable pressure gradient. Hot wire measurements across the plate tracked the development of stationary and travelling crossflow waves. Initially, stronger crossflow waves were found for the elements with stronger forcing, while further downstream the effect of forcing diminished. Spatial frequency spectra showed that the stronger forcing at the critical wavelength (via the roughness shape) dominates the response of the flow while low forcing at the harmonics has no notable effect. Additionally, high resolution streamwise hot wire scans showed that the onset of secondary instability is not significantly influenced by the spatial frequency content of the roughness distribution.

Original languageEnglish
Title of host publication8th AIAA Flow Control Conference
PublisherAmerican Institute of Aeronautics and Astronautics Inc. (AIAA)
ISBN (Print)9781624104329
Publication statusPublished - 10 Jun 2016
Event8th AIAA Flow Control Conference, 2016 - Washington, United States
Duration: 13 Jun 201617 Jun 2016

Publication series

Name8th AIAA Flow Control Conference


Conference8th AIAA Flow Control Conference, 2016
Country/TerritoryUnited States

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