The effect of external intermittency on the scaling and self-similarity of structure functions in turbulent shear flows
Résumé
The edge of a free turbulent shear flow is characterized by a turbulent/non-turbulent interface (TNTI) which is a distinct and highly contorted layer that separates turbulent from irrotational flow regions. Transfers of mass, momentum and scalar quantities, such as species or heat, occur over the thickness of this layer, which renders its physical understanding crucial for a variety of engineering and environmental applications. Moreover, strong fluctuations are created in the vicinity of the TNTI and are transported by the mechanism of entrainment into the turbulent core of the flow. These fluctuations are known as external intermittency. In this study, we investigate the impact of external intermittency on velocity and scalar structure functions of different orders. It is shown that external intermittency breaks the self-similarity of structure functions and invalidates the classical scaling relations proposed by Kolmogorov. By conditioning structure functions on an intermittency parameter, we show that self-similarity of these structure functions can be recovered. The analysis is based on highly resolved direct numerical simulations of turbulent jet flows and mixing layers.