Interpretation of large-scale structures observed in a turbulent plane Couette flow

Large-flow structures, not observed in turbulent Poiseuille flow, are found in direct numerical simulations of turbulent Couette flow. Because these structures are persistent in space and time, an interpretation is presented which approximates them by a secondary flow. The asymmetry of the velocity profile is favorable to the formation of flow modules that fill the whole channel. These modules can take the form of weak rotational inviscid roll cells. They affect the turbulence in such a way that they receive energy from the turbulence, contrary to the usual notion to an energy cascade from large-scale turbulence to small-scale turbulence. (C) 1997 by Elsevier Science Inc.