Measurements of mean velocity, the three normal stresses and Reynolds shear stress are reported in the developing region of coaxial jet flows. The measurements were obtained with three velocity ratios, i.e., values of the ratio of maximum initial pipe velocity to maximum initial annulus velocity of 0, 0.23, and 0.62 and at downstream distances up to 17 outer diameters. The results show that coaxial jets tend to reach a self-preserving state much more rapidly than axisymmetric single jets; that the mean velocity, normal stresses, and Reynolds shear stress attain this state at a similar downstream location; and that, for the particular geometry investigated, a velocity ratio of around 0.15 corresponds to the slowest rate of development. Relationships between mean velocity gradient, Reynolds shear stress, and turbulent kinetic energy are examined to assess their ability to characterize the present flow: the results indicate the need to take account of the normal stresses in any proposed mathematical model.

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