Coherent Structures of the Turbulent Mixing Layer at High Reynolds Numbers. 1st Report. Instantaneous Structures and Phase-Averaged Flow Features of the Large-Scale Motion.

Abstract

In the present paper, coherent structures of the turbulent mixing layer are investigated by means of a hot-wire rake technique. Reynolds number based on the vorticity thickness is 34 000. The u and v velocity components of the mixing layer were measured by the rake of 12X wires crossing the layer. Time-averaged turbulent statistics show the self-similar features of the turbulent mixing layer. The large-scale motions are found in the quasi-instantaneous structures viewed in a reference frame of the convective velocity. To study the large-scale structures in detail, a diagnostic that classifies the rollers and braids is employed. The diagnostic reveals that the instantaneous large-scale structure consists of roller dominance regions and/or strain dominance regions. Furthermore, phase-averaged turbulent statistics of the large-scale motion show that Reynolds stresses of high intensity are generated by the large-scale motion of strain dominance properties.