Turbulence Structure in the Leading-Edge Separation Zone of a Blunt Circular Cylinder

This paper describes experimentally the turbulence structure in the separation zone at the leading edge of a blunt circular cylinder aligned with a uniform main flow. The experiment was made in a wind tunnel at a Reynolds number of 200 000. Turbulent velocities were measured by split-film probes and surface-pressure fluctuations by semiconductor strain-gauged pressure transducers mounted inside the cylinder. Profiles of the time-mean and r. m. s. values of the fluctuating quantities and the Reynolds shearing stress in the separation zone are presented. Cross correlations and power spectra of the surface pressures yield the translation velocity of large-scale vortices and the frequency at which they are shed from the separation zone. The unsteady nature of the flow is demonstrated by the reverse-flow intermittency and by the frequency of switching of the local-flow direction. Moreover, the above properties are discussed in comparison with those of a leading-edge separation zone of a two-dimensional blunt plate.