Turbulence structure in the intermediate wake of a rotating flat plate. (Large-scale vortices)

Abstract

The structure of large-scale vortices behind a thin flat plate being rotated in a uniform stream around its axis with a constant angular velocity is described experimentally by a flow-visualization technique and a phase-averaging technique. The time-mean velocity, turbulent energies and Reynolds shear stresses are also obtained. These measurements are made with 712 plate widths downstream of the centre of the plate; this region was termed as the intermediate wake. Using the phase of rotation of the plate as a reference signal, phase-averaging is made with a minimal dispersion because the large-scale vortices in the intermediate wake were well locked to the rotation. Results are presented for a Reynolds number of 1.25 × 104 and for spin parameters of S=0.28±0.003 and 0.51±0.004. The structure and motion of the large-scale vortices are demonstrated in terms of the vorticity contours in a space-time (or space-phase) domain. a wide region of the negative turbulent-energy production is found in the wake.