A vorticity stretching diagnostic for turbulent and transitional flows
2012 (English)In: Theoretical and Computational Fluid Dynamics, ISSN 0935-4964, E-ISSN 1432-2250, Vol. 26, no 6, 485-499 p.Article in journal (Refereed) Published
Vorticity stretching in wall-bounded turbulent and transitional flows has been investigated by means of a new diagnostic measure, denoted by , designed to pick up regions with large amounts of vorticity stretching. It is based on the maximum vorticity stretching component in every spatial point, thus yielding athree-dimensional scalar field. The measure was applied in four different flows with increasing complexity: (a) the near-wall cycle in an asymptotic suction boundary layer (ASBL), (b) K-type transition in a plane channelflow, (c) fully turbulent channel flow at Reτ = 180 and (d) a complex turbulent three-dimensional separated flow. Instantaneous data show that the coherent structures associated with intense vorticity stretching in all four cases have the shape of flat ‘pancake’ structures in the vicinity of high-speed streaks, here denoted ‘h-type’events. The other event found is of ‘l-type’, present on top of an unstable low-speed streak. These events (l-type) are further thought to be associated with the exponential growth of streamwise vorticity in the turbulent near-wall cycle. It was found that the largest occurrence of vorticity stretching in the fully turbulent wall-bounded flows is present at a wall-normal distance of y + = 6.5, i.e. in the transition between the viscous sublayer and buffer layer. The associated structures have a streamwise length of ∼200–300 wall units. In K-type transition, the -measure accurately locates the regions of interest, in particular the formation of high-speed streaks nearthe wall (h-type) and the appearance of the hairpin vortex (l-type). In the turbulent separated flow, the structures containing large amounts of vorticity stretching increase in size and magnitude in the shear layer upstreamof the separation bubble but vanish in the backflow region itself. Overall, the measure proved to be useful inshowing growing instabilities before they develop into structures, highlighting the mechanisms creating high shear region on a wall and showing turbulence creation associated with instantaneous separations.
Place, publisher, year, edition, pages
2012. Vol. 26, no 6, 485-499 p.
Laminar-turbulent transition, vorticity stretching, turbulent flows
Engineering and Technology
Research subject SRA - E-Science (SeRC)
IdentifiersURN: urn:nbn:se:kth:diva-50287DOI: 10.1007/s00162-011-0245-7ISI: 000310538000001ScopusID: 2-s2.0-84869080518OAI: oai:DiVA.org:kth-50287DiVA: diva2:461516
FunderSwedish Research CouncilSwedish e‐Science Research Center
QC 201211132011-12-042011-12-042012-12-03Bibliographically approved