Single- and Two-Point LDA Measurements in the Turbulent Near Wake of a Circular Cylinder

Abstract

This chapter reviews results of single and two-point Laser-Doppler anemometry (LDA) measurements in the turbulent near wake of a circular cylinder. Turbulence characteristics are determined in the near wake of a circular cylinder at Rd = 6700 and 7200 by means of LDA measurements. Conditional averaging is employed to separate the contributions from large-scale organized motions associated with the passage of vortices shed from the cylinder and two-point measurements provided information on the spatial coherency of the fine-scale turbulence during the early stages. Between five and ten diameters downstream of the cylinder, the contribution from coherent motions to the total stresses shows a significant drop associated with the diminishing strength of the shed vortices. The corresponding contribution from random turbulence highlights less of a variation but the conditionally averaged distributions tend to become more homogeneous and isotropic. This trend is reflected in the measurement of the Taylor length microscales. The chapter aims at improving understanding of the relation between large-scale coherent structures and fine-scale turbulence in vortex shedding flows and expands the availability of data to other properties, such as length microscales and dissipation.