Small-scale mixing at the turbulent/non-turbulent interface in turbulent jets

The numerical simulation of the turbulent mixing between the turbulent core flow region and the non‐turbulent irrotational ambient region requires a reliable modelling of the mass and momentum transfer in the intermittent zone. The dominant role of the small‐scale whirling motion in the turbulent entrainment process particularly challenges the subgrid‐scale (SGS) modelling in Large‐Eddy Simulation (LES). The present work carried out a Direct Numerical Simulation (DNS) of a round jet to analyze the scalar mixing conditions near the turbulent/non‐turbulent interface. The obtained statistical results widely confirm existing experimental and analytical findings made in previous studies on the momentum transfer. An a priori test of the DNS data reveals the limits of the standard Smagorinsky‐type SGS‐model for the eddy diffusivity in the description of the subgrid‐scale mixing near the interface. The extension to a dynamic SGS‐model using non‐constant, flow dependent model coefficients does not lead to a substantial improvement. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)