An Alternative Symmetry for Large-Scale Structures in Channel Flow

摘要

Applying bifurcation analysis in conjunction with direct numerical simulation, two distinct nontrivial equilibrium states in plane Poiseuille flow are obtained. The two states are distinguished by the symmetries imposed. One of these states is of the same form as the exact coherent structure obtained previously by Waleffe. The other state has a pair of counter-rotating streamwise vortices that can develop across the channel midplane, and may provide an exact expression for largescale structures observed in fully turbulent flow. A truncated dynamical model describing these states predicts that streaky components induced by large-scale circulations spanning the whole of the channel width may survive even in the limit of infinite Reynolds number.