PIV measurements in co-flowing jets subjected to axial forcing. Vorticity and strain field structure

摘要

A study of the evolving shear layer in the near field of Re_D=7000, co-flowing water jets is presented. The inner jet is subjected to a strong axial forcing and to a small, controlled azimuthal perturbation. This flow configuration is characterised by a strong lateral expansion of the inner jet in the near field, controlled by the forcing parameters. Instantaneous, whole-field, 2D velocity measurements were obtained, using the Digital Particle Image Velocimetry (DPIV) technique. The two-component velocity measurements allows for the computation of fields of azimuthal vorticity and strain in a plane. These parameters control the inviscid dynamics of the structures of azimuthal vorticity that dominates the near field evolution of the flow. The combined information of these flow parameters provides a deep insight in the flow nature and evolution.