SYMMETRY PROPERTIES OF DEVELOPING 3-DIMENSIONAL LAMINAR DISTURBANCES IN PLANE POISEUILLE FLOW

The evolution of a finite-amplitude point-like laminar disturbance in plane Poiseuille flow is investigated using hot-wire anemometry. In co ntrast to earlier experiments, the initial disturbance was introduced simultaneously through both the upper and lower wall of the channel, r esulting in an antisymmetric disturbance in the normal velocity. Altho ugh the initial disturbance mainly generated symmetrical streamwise ve locity modes, the subsequent development of the perturbation showed a marked tendency for antisymmetry.