Non-equilibrium turbulent phenomena in transitional flat plate boundary-layer flows

Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state. By analyzing a direct numerical simulation (DNS) database of a transitional boundary-layer flow, we show that the transition region and the non-equilibrium turbulence region, which are located in different streamwise zones, present different non-equilibrium scalings. Moreover, in the wall-normal direction, the viscous sublayer, log layer, and outer layer show different non-equilibrium phenomena which differ from those in grid-generated turbulence and transitional channel flows. These findings are expected to shed light on the modelling of various types of non-equilibrium turbulent flows.