Receptivity, instability and breakdown of Görtler flow
2011 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 682, 362-396 p.Article in journal (Refereed) Published
Receptivity, disturbance growth and breakdown to turbulence in Gortler flow are studied by spatial direct numerical simulation (DNS). The boundary layer is exposed to free-stream vortical modes and localized wall roughness. We propose a normalization of the roughness-induced receptivity coefficient by the square root of the Gortler number. This scaling removes the dependence of the receptivity coefficient on wall curvature. It is found that vortical modes are more efficient at generating Gortler vortices than localized roughness. The boundary layer is most receptive to zero- and low-frequency free-stream vortices, exciting steady and slowly travelling Gortler modes. The associated receptivity mechanism is linear and involves the generation of boundary-layer streaks, which soon evolve into unstable Gortler vortices. This connection between transient and exponential amplification is absent on flat plates and promotes transition to turbulence on curved walls. We demonstrate that the Gortler boundary layer is also receptive to high-frequency free-stream vorticity, which triggers steady Gortler rolls via a nonlinear receptivity mechanism. In addition to the receptivity study, we have carried out DNS of boundary-layer transition due to broadband free-stream turbulence with different intensities and frequency spectra. It is found that nonlinear receptivity dominates over the linear mechanism unless the free-stream fluctuations are concentrated in the low-frequency range. In the latter case, transition is accelerated due to the presence of travelling Gortler modes.
Place, publisher, year, edition, pages
2011. Vol. 682, 362-396 p.
boundary layer receptivity, transition to turbulence
IdentifiersURN: urn:nbn:se:kth:diva-25488DOI: 10.1017/jfm.2011.229ISI: 000294775800016ScopusID: 2-s2.0-80052174354OAI: oai:DiVA.org:kth-25488DiVA: diva2:358788
FunderSwedish Research CouncilSwedish e‐Science Research Center
QC 20101025. Updated from submitted to published.2010-10-252010-10-252012-05-24Bibliographically approved