Linear stability of channel entrance flow

Biau, Damien

doi:10.1016/j.euromechflu.2007.11.004

Cited by 5 publications

(1 citation statement)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has for consequence to stabilize the flow with respect to the so-called Tollmien-Schlichting mode. Up to now, linear theories fail to ascribe subcritical transition observed in the plane channel flow to stability properties of the streamwise velocity profiles in the channel entry flow, as shown by Biau [2]. However, these theoretical studies focus on the region downstream the entry zone where the evolution of the flow has a universal character (see Asai and Floryan [3]) and therefore are not directly connected to the flow behaviour near the inlet.…”

Section: Introductionmentioning

confidence: 99%

Space–time dynamics of optimal wavepackets for streaks in a channel entrance flow

et al. 2018

View full text Add to dashboard Cite

The laminar–turbulent transition of a plane channel entrance flow is revisited using global linear optimization analyses and direct numerical simulations. The investigated case corresponds to uniform upstream velocity conditions and a moderate value of Reynolds number so that the two-dimensional developing flow is linearly stable under the parallel flow assumption. However, the boundary layers in the entry zone are capable of supporting the development of streaks, which may experience secondary instability and evolve to turbulence. In this study, global optimal linear perturbations are computed and studied in the nonlinear regime for different values of streak amplitude and optimization time. These optimal perturbations take the form of wavepackets having either varicose or sinuous symmetry. It is shown that, for short optimization times, varicose wavepackets grow through a combination of Orr and lift-up effects, whereas for longer target times, both sinuous and varicose wavepackets exhibit an instability mechanism driven by the presence of inflection points in the streaky flow. In addition, while the optimal varicose modes obtained for short optimization times are localized near the inlet, where the base flow is strongly three-dimensional, when the target time is increased, the sinuous and varicose optimal modes are displaced farther downstream, in the nearly parallel streaky flow. Finally, the optimal wavepackets are found to lead to turbulence for sufficiently high initial amplitudes. It is noticed that the resulting turbulent flows have the same wall-shear stress, whether the wavepackets have been obtained for short or for long time optimization.

show abstract

Section: Introductionmentioning

confidence: 99%