kth_logo.gif

Artikel

A mechanism for bypass transition from localized disturbances.

Författare: Henningson, D.S.H., Lundbladh, A., Johansson, A.V.J.
Dokumenttyp: Artikel
Tillstånd: Publicerad
Tidskrift: J. Fluid Mech.
Volym: 250   169-207
År: 1993

Abstract

The linear, nonlinear and breakdown stages in the transition of localized disturbances in plane Poiseuille flow is studied by direct numerical simulations and analysis of the linearized Navier-Stokes equations. Three-dimensionality plays a key role and allows for algebraic growth of the normal vorticity through the linear lift-up mechanism. This growth primarily generates elongated structures in the streamwise direction since it is largest at low streamwise wavenumbers. For finite-amplitude disturbances such structures will be generated essentially independent of the details of the initial disturbance, since the preferred nonlinear interactions transfer energy to low streamwise wavenumbers. The nonlinear interactions also give a decrease in the span-wise scales. For the stronger initial disturbances the streamwise vorticity associated with the slightly inclined streaks was found to roll up into distinct streamwise vortices in the vicinity of which breakdown occurred.