Hairpins et al. in Turbulent Boundary Layers

• Main Authors: Schlatter, Philipp, Ilak, Milos, Chevalier, Mattias, Brethouwer, Geert, Johansson, Arne V, Henningson, Dan S
• Format: Journal Article
• Language: English
• Published: 18.10.2011
• Subjects: Physics - Fluid Dynamics
• DOI: 10.48550/arxiv.1110.3975

A new set of three-dimensional visualisations of a large-scale direct numerical simulations (DNS) of a turbulent boundary layer is presented. The Reynolds number ranges from $Re_\theta=180$ to 4300, based on the momentum-loss thickness $\theta$ and the free-stream velocity $U_\infty$. The focus of the present fluid dynamics video is on analysing the coherent vortical structures in the boundary layer: It is clearly shown that the initial phases are dominated by coherent so-called hairpin vortices which are characteristic remainders of the laminar-turbulent transition at lower Reynolds numbers. At higher $Re$ (say $Re_\theta>2000$), these structures are no longer seen as being dominant; the coherence is clearly lost, both in the near-wall region as well as in the outer layer of the boundary layer. Note, however, that large-scale streaks in the streamwise velocity, which have their peak energy at about half the boundary-layer thickness, are unambiguously observed. In addition to visualisation with classical three-dimensional isosurfaces, the video is also rendered using stereoscopic views using red-cyan anaglyphs.