Effect of Surface Roughness Geometry on Boundary-Layer Transition and Far-Field Noise

Q. Ye, F. Avallone, D. Ragni, Meelan Choudhari, D. Casalino

Research output: Contribution to journalArticleScientificpeer-review

6 Downloads (Pure)


Surface roughness elements are often used to force laminar to turbulent transition in aerodynamic and aeroacoustic wind-tunnel experiments. The statistical features and spectral content of the pressure fluctuations in the resulting turbulent boundary layer at the trailing edge can affect far-field noise. To elucidate this dependence, boundary-layer transition induced by randomly distributed roughness elements and a zigzag strip of the same height over a NACA 0012 airfoil is investigated experimentally. The effects of roughness geometry on the near-field flow topology, transition location, and far-field noise are addressed in the common experimental setting for the first time. For a fixed roughness height, distributed roughness elements are less effective in forcing transition than the zigzag strip at low freestream velocity (u∞<20  m/s). As u∞ increases, the transition front for the distributed roughness elements moves closer to the roughness location, reaching the same or even further upstream locations compared to the transition onset in the presence of the zigzag strip. The far-field noise depends on the transition location. For u∞≤20  m/s, a higher noise level is measured for the distributed roughness elements with respect to the zigzag strip. In contrast, for u∞>20  m/s, the earlier onset of transition with the distributed surface roughness leads to a lower noise level than that with the zigzag strip. The data confirm that an adequate characterization of the boundary-layer transition is necessary when measuring the far-field noise during wind-tunnel experiments.
Original languageEnglish
Pages (from-to)2396-2408
Number of pages13
JournalAIAA Journal: devoted to aerospace research and development
Issue number7
Publication statusPublished - 2021

Bibliographical note

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care
Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.


Dive into the research topics of 'Effect of Surface Roughness Geometry on Boundary-Layer Transition and Far-Field Noise'. Together they form a unique fingerprint.

Cite this