Dynamics of spatially developing turbulent/turbulent interfaces in the absence of mean shear

Spatially evolving turbulent/turbulent interfaces (TTIs) in the absence of mean shear are studied using direct numerical simulation (DNS). To this end, a novel approach was developed, allowing for six different TTIs to be created with a Taylor-based Reynolds number in the range of $146 \lesssim {Re}_{\lambda }\lesssim 296$ . The analysis of classical statistics of turbulence intensity, fluctuating vorticity and integral length scale clearly indicates that one of the two distinct turbulent regions bounding the interface tends to dominate the other one. The half-width thickness is found to be dependent on the turbulent properties of each layer, ultimately suggesting that the large-scale quantities dictate the spreading of each turbulent region. Small scale quantities, e.g. the enstrophy, exhibit an universal conditional mean profile when normalised by the local Kolmogorov (velocity and time) scales of motion. In contrast, the large-scale properties of the flow do not modify the enstrophy statistics. Additionally, when taking the difference of fluctuating vorticity levels on each layer ad extremum , profiles typical of turbulent/non-turbulent interfaces (TNTIs) are observed. The budget terms of enstrophy and rate-of-strain magnitude support these findings.