J. Turbul. 15 (2014), pp. 555-568

Statistics of the turbulent / non-turbulent interface in a spatially developing mixing layer

A Attili, J C Cristancho. and F Bisetti. "Statistics of the turbulent / non-turbulent interface in a spatially developing mixing layer". J. Turbul. 15 (2014), pp. 555-568.​​

A Attili, J C Cristancho, F Bisetti
turbulent/non-turbulent interface, turbulent mixing layer, scalar mixing, scalar dissipation rate
​The thin interface separating the inner turbulent region from the outer irrotational fluid is analyzed in a direct numerical simulation of a spatially developing turbulent mixing layer. A vorticity threshold is defined to detect the interface separating the turbulent from the non-turbulent regions of the flow, and to calculate statistics conditioned on the distance from this interface. The conditional statistics for velocity are in remarkable agreement with the results for other types of free shear flow available in the literature, such as turbulent jets and wakes. In addition, an analysis of the passive scalar field in the vicinity of the interface is presented. It is shown that the scalar has a jump at the interface, even stronger than that observed for velocity. The strong jump for the scalar has been observed before in the case of high Schmidt number. In the present study, such a strong jump is observed for a scalar with Sc ≈ 1. Conditional statistics of kinetic energy and scalar dissipation are presented. While the kinetic energy dissipation has its maximum far from the interface, the scalar dissipation is characterized by a strong peak very close to the interface. Finally, it is shown that the geometric features of the contorted interfaces correlate with relatively large-scale structures that can be visualized by low-pressure isosurfaces.