Effect of the Separation Wall in the Mixing Properties of Coaxial Jets

The velocity and mixing field of two coaxial jet configurations has been experimentally characterized by means of hotand cold-wire anemometry to investigate the effect of the initial conditions on the flow development, and to determine the leading processes in the “mixing transition” of the two streams. Amongst the possible operating conditions, four configurations with different inner and outer jet bulk velocity pairs (Ui, Uo) have been spatially characterized in terms of velocity and mixing field covering a region where 0.5 ≤ ru = Uo/Ui ≤ 3 with two different separation wall geometries, namely a sharp and a thick separating wall. For high velocity ratios the difference between the two geometries appears small and inside the experimental accuracy. On the other hand, for nearly unitary velocity ratio and with the thick wall configuration, the presence of a strong wake instability increases the interpenetration between the two streams enhancing the mixing process.