Coherent Structures in Excited Spatially Evolving Round Jets

Direct and Large-eddy simulations (DNS/LES) were used to analyze the vortex dynamics and statistical behavior of bifurcating jets. The Reynolds numbers analyzed go from Re D 1.5 × 103 to Re D 5.0 × 104. The jet bifurcation was achieved by means of an active jet control superimposed to a spatially evolving round jet. Three types of forcing were analyzed, which reproduce the forcing methods used in experimental bifurcating jets [8], although using a much lower amplitude forcing, more realistic in terms of potential industrial applications. The study analyses coherent structures resulting from each of the forcing types and explains their impact in the statistical behavior of the bifurcating jets. Special emphasis is made in the influence of increasing Reynolds number in the spatial evolution of each excited jet. Finally, this work addressed also the dynamics of the near field coherent structures in a coaxial by means of DNS. The Reynolds number was Re D1 = 3000. The interaction between the inner and outer shear layers and its consequences for the transition process was analyzed in detail. In particular t is postulated that the inner streamwise vortex pairs are stretched by the central backflow region.