Entrainment at turbulent/non-turbulent interface of wall-bounded turbulent flow

Abstract

Direct numerical simulation (DNS) of turbulent channel, pipe flow, and turbulent boundary layer with zero pressure gradient (ZPG) and adverse pressure gradient (APG) are investigated to scrutinize the interfaces of wall-bounded turbulent flow. Similarity between internal interfaces of channel and pipe flow, and interface of boundary layer is observed by using turbulent statistics near the interfaces. First, we identify the organization between large-scale motions near the interface and geometry of the interface using DNS data of turbulent channel flow. The large-scale motions also have an influence on the distribution of vortical structure near the interface. Second, these large-scale motions are the wall-attached structures of u, and the wall-attached structures affect the transport phenomena at the interface from the DNS data of turbulent pipe flow. Finally, APG turbulent boundary layer shows that the presence of APG develop the complexity of the interface geometry and vortical structure near the interface. It is observed that the influence of the development on the structural change of the interface and the viscous contribution of the entrainment velocity enhance the entrainment phenomenon at the interface.