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The surface area of turbulent/non-turbulent interfaces (TNTIs) iscontinuously produced and destroyed via stretching and curvature/propagationeffects. Here, the mechanisms responsible for TNTI area growth and destructionare investigated in a turbulent flow with and without stable stratificationthrough the time evolution equation of the TNTI area. We show that both termshave broad distributions and may locally contribute to either production ordestruction. On average, however, the area growth is driven by stretching,which is approximately balanced by destruction by the curvature/propagationterm. To investigate the contribution of different length scales to theseprocesses, we apply spatial filtering to the data. In doing so, we find thatthe averages of the stretching and the curvature/propagation terms balance outacross spatial scales of TNTI wrinkles and this scale-by-scale balance isconsistent with an observed scale invariance of the nearby coherent vortices.Through a conditional analysis, we demonstrate that the TNTI area production(destruction) localizes at the front (lee) edge of the vortical structures inthe interface proximity. Finally, we show that while basic mechanisms remainthe same, increasing stratification reduces the rates at which TNTI surfacearea is produced as well as destroyed. We provide evidence that this reductionis largely connected to a change in the multiscale geometry of the interface,which tends to flatten in the wall-normal direction at all active length scalesof the TNTI.

Connecting the time evolution of the turbulence interface to coherent structures