Effect of density variation on the dynamic characteristic of coaxial swirling jet flows

We experimentally investigated the effect of density variation on the dynamic behavior of coaxial co-rotating swirling jets, focusing on how the difference of density between the inner and outer jets affect the flow at a high swirl number. When the density of the inner jet is higher than that of the outer jet (ρ/ρ_o ≈ 1.64. Here, ρ_i and ρ_o is the density of the inner and outer jet respectively.), both large-scale vortical structure and stagnating flow is induced by the hydrodynamic shear layer instability become easier to form when compared to that obtained for the case of iso-density jet (ρ/ρ_o = 1). The velocity field at the inner swirl number, S_i = 0.6 is obtained using the Particle Image Velocimetry (PIV) analysis. The velocity field shows the absence of velocity vectors pointing towards the jet core downstream of the CO₂ jets stagnation point. In contrast, when the density of the inner jet is lower than that of the outer jet (ρ/ρ_o ≈ 0.15), the inner jet does not form a stagnating point even at a high inner swirl number (S_i = 0.6), and does not significantly change in response to swirl of inner jet.