Large-Scale and Small-Scale Turbulence Structure in the Intermediate Wake of a Two-Dimensional Normal Plate

Abstract

Turbulence structure in the intermediate wake of a normal flat plate was studied experimentally by a conditional-sampling technique. The measurements were made at a section 8.0 heights downstream of the front face of the plate. Velocity fluctuations were decomposed into those produced by large-scale structures and those associated with small-scale structures : the former fluctuations were again decomposed into the phase-averaged fundamental component and the deviation form it (large-scale deviation). Velocity vector fields, contours of streamlines, vorticity of the fundamental component, together with contours of intensity and correlation of the large-scale deviation velocity, were presented and discussed. Contours of intensity, correlation and turbulence intermittency of the small-scale fluctuations were also presented in and around the large-scale structures. Large Reynolds shear stress associated with the large-scale deviation velocity was suggested to be the result of a stretching of vortex filaments in the saddle-point flow region.