Journal ArticleDOI
A study of hairpin vortices in a laminar boundary layer. Part 1. Hairpin vortices generated by a hemisphere protuberance
M. S. Acarlar,C. R. Smith +1 more
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In this article, the hairpin vortices generated by the interaction of a hemisphere protuberancee within a developing laminar boundary layer were examined and the shedding characteristics of the hemispheres were determined using hot-film-anemometry techniques.Abstract:
It has been suggested that hairpin vortices may play a key role in developing and sustaining the turbulence process in the near-wall region of turbulent boundary layers. To examine this suggestion, a study was done of the hairpin vortices generated by the interaction of a hemisphere protuberancee within a developing laminar boundary layer. Under the proper conditions, hairpin vortices are shed extremely periodically, which allows detailed examination of their behaviour. Shedding characteristics of the hemispheres were determined using hot-film-anemometry techniques. The flow patterns created by the presence of the hairpin vortices have been documented using flow visualization and hot-film-anemometry techniques, and cross-compared with the patterns observed in the near-wall of a fully turbulent boundary layer. In general, it has been observed that many of the visual patterns observed in the near-wall region of a turbulent boundary layer can also be observed in the wake of the hairpin-shedding hemisphere, which appears supportive of the importance of hairpin vortices in the near-wall turbulence production process. Furthermore, velocity measurements indicate the presence of strong inflexional profiles just downstream of the hairpin-vortex generation region which evolve into fuller profiles with downstream distance, eventually developing a remarkable similarity to a turbulent-boundary-layer velocity profile.read more
Citations
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Vortex organization in the outer region of the turbulent boundary layer
TL;DR: In this paper, the structure of energy-containing turbulence in the outer region of a zero-pressure-gradient boundary layer has been studied using particle image velocimetry (PIV) to measure the instantaneous velocity fields in a streamwise-wall-normal plane.
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On a self-sustaining process in shear flows
TL;DR: In this article, a self-sustaining process for wall-bounded shear flows is investigated, which consists of streamwise rolls that redistribute the mean shear to create streaks that wiggle to maintain the rolls.
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Control of an axisymmetric jet using vortex generators
TL;DR: In this article, the effect of vortex generators at the nozzle exit on the evolution of a jet was investigated, and the results of an experimental investigation on the effect on the vortex generators were reported.
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Applications of Holography in Fluid Mechanics and Particle Dynamics
Joseph Katz,Jian Sheng +1 more
TL;DR: In this article, a review summarizes recent advances in volumetric particle detection and 3D flow velocimetry involving holography and discusses the debilitating depth-of-focus problem, along with methods that have been implemented to circumvent it.
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Self-similar vortex clusters in the turbulent logarithmic region
TL;DR: In this article, the authors analyzed the organization of vortex clusters above the buffer layer of turbulent channels using direct numerical simulations at friction Reynolds numbers up to Re τ = 1900, where Re τ is the Reynolds number of vortex heads.
References
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The three-dimensional nature of boundary-layer instability
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New aspects of turbulent boundary-layer structure
TL;DR: For the zero-pressure-gradient turbulent boundary layer over the Reynolds-number range 500 2000, say, the layer appears to consist very largely of elongated hairpin vortices or vortex pairs, originating in the wall region and extending through a large part of the boundary layer thickness or beyond it; they are for the most part inclined to the wall at a characteristic angle in the region of 40-50°.
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A visual investigation of the wall region in turbulent flow
E. R. Corino,Robert S. Brodkey +1 more
TL;DR: In this paper, the authors investigate for turbulent flow the fluid motions very near a solid boundary, and to create a physical picture which relates these motions to turbulence generation and transport processes.
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On the mechanism of wall turbulence
A. E. Perry,Min S Chong +1 more
TL;DR: In this article, a model for wall turbulence was proposed based on the horse-shoe, hairpin or "A" vortex, which gave a connection between the mean-velocity distribution, the broad-band turbulence-intensity distributions and the turbulence spectra.