An analysis of nonlinear transfer of energy during transition

Abstract: This paper explores the energy transfer mechanisms that play a key role during transition in channel flow. This is achieved through a decomposition of the flow field into a laminar base flow and fluctuations. We study the turbulent kinetic energy (TKE) budget in Fourier space, paying attention to the modes that contribute to the largest increase in TKE (via production) and the modes that contribute the most to the nonlinear transport of energy. A unique feature of this work is our examination of the mode-to-mode nonlinear transfer of energy. We centre the analysis on a handful of key modes to analyze the mode-to-mode interactions and individual contributions to the formation of the mean flow. A direct numerical simulation (DNS) is performed in a channel at Re = 115 for a K-Type transition scenario. Results show that streamwise-constant modes are the primary contributors of energy to the mean mode during transition. A handful of oblique modes are also shown to support the formation of the mean. Keywords: Energy transfer, turbulent transition, channel flow