Transition to Turbulence in Wall-Bounded Shear Flows

Albeit great advancement, transition to turbulence continues to be an intriguing subject, challenging many researchers worldwide. The current research covers several aspects of transition – The evolution of coherent structures, such as counter-rotating vortex pairs and hairpins, observed in various transitional as well as turbulent flows is studied using a novel analytical-based numerical method for the evolution of localized disturbances in homogenous shear base-flows. A minimal element model capable of following the evolution of packets of hairpins is developed and compared successfully with experiments. Finally, an analytical model for transition via secondary instability of counter-rotating vortices in channel flow is presented. The model utilizes separation of scales between the slowly evolving base-flow and the rapidly evolving secondary disturbance to capture most transition stages using the multiple time scales method and its predictions are verified by comparison with direct numerical simulations.