An experimental investigation of the near-field flow development in coaxial jets

Abstract

The near-field region of a coaxial jet having inner to outer diameter ratio di / do = 0.39 is investigated experimentally for four ratios of annular to central jet velocities of η=0.18, 0.48, 0.8, and 1.11. Measurements were acquired nonintrusively using molecular tagging velocimetry at downstream distances up to six inner jet diameters. High spatial-resolution profiles of mean axial velocity, axial turbulent intensity, skewness, kurtosis, radial gradients of mean velocity, and velocity gradient fluctuations are presented and discussed. In the near-exit region of the inner mixing layer, evidence suggests the existence of two trains of vortices shed from the inner jet wall for velocity ratios..