1,720,972 research outputs found
Streaks in near-wall turbulent flow and generalisation of the optimal perturbations theory
No full textGeneralised optimal perturbation theory for predicting the streak spacing in turbulent flow
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Regeneration mechanism of streaks in near-wall quasi-2D turbulence
No full textA direct numerical simulation of quasi-2D (that is with flow variables independent of streamwise direction) decaying and forced turbulent flow in a channel was performed in order to seek out the sustenance mechanism of near-wall turbulence by uncovering the mechanism of streak formation. We found the existence of streaks in quasi-2D turbulent flows, thereby demonstrating that feedback from longitudinal flow is not necessary for streak formation. Passive scalars having different mean profiles were introduced in forced quasi-2D turbulent flows in order to compare the streak spacing of the scalars deduced from two-point correlations of DNS results with those obtained from optimal perturbation and Reynolds normal stress anisotropy instability mechanisms. It has been found that although for all the passive scalars the vortex structure is the same, there is a marked variation in streak spacing of the scalars implying that the preferential streak spacing is not necessarily linked to the preferential vortex spacing
Streaks and vortices in near-wall turbulence
No full textThis paper presents evidence that organization of wall-normal motions plays almost no role in the creation of streaks. This evidence consists of the theory of streak generation not requiring the existence of organized vortices, extensive quantitative comparisons between the theory and direct numerical simulations, including examples of large variation in average spacing of the streaks of different scalars simultaneously present in the flow, and an example of the scalar streaks in an artificially created purely random flow
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