Influence of initial conditions on the evolution towards similarity of passive scalar in turbulent round jets

The effect of initial conditions on the scalar mixing in two jets issuing from two different nozzles is studied. The flows are slightly heated and temperature is considered as a passive scalar. The large jet, designed to approach a top hat type profile, develops faster towards equilibrium than the small jet. The difference in initial conditions impacts the evolution laws of kinetic energy and temperature dissipation. The consequence is more visible on Taylor micro-scale than Corrsin micro-scale. The dissipative Kolmogorov length scales are not affected by the difference in the initial conditions. Turbulent Reynolds number for the small jet is slower to reach a plateau along the jet axis than the large jet; the equilibrium asymptotic value for the two jets is ∼Rj1/2 in agreement with the literature. For the small jet, the scalar turbulent Pecklet number reached its constant value before turbulent Reynolds number Rλq  (Pe̲q∼0.6.Rj1/2and∼0.6Rλq).

► Kinetic energy dissipation similarity is reached earlier for the large.
► Temperature dissipation reached equilibrium earlier for the large jet.
► Kolmogorov dissipation scales increase linearly with the same slope for both jets.
► Rλq   is slower to reach a constant value for the small jet ∼Rj1/2.
► Peq(Peq∼0.6Rj1/2 and ∼0.6 Rλq.