Turbulent Mixing of Coaxial Jets With Particular Reference to the Near-Exit Region

Measurements, obtained with hot wire anemometry, are reported in a co-axiol jet flow where the inner and outer initial maximum velocities were the same. The hot-wire signal was processed with a modified, linearized procedure which is described. The downstream results show that the coaxial jet develops more rapidly than a single jet but that, for example, the Reynolds shear stress has not attained a self-preserving condition at a distance of 30 external diameters. Particular attention was paid to the region of the wake of the pipe wall and two dominant frequencies were observed, corresponding to two orthogonal velocity components. The high frequencies of these fluctuations indicate that they must be regarded as turbulent fluctuations and, as might be expected, lead to regions of almost constant Prandtl and Prandtl-Kolmogorov length scales.