Study of Energetics in Drag-Reduced Turbulent Channel Flows

Changes in integral power budgets and scale energy fluxes as induced by certain active flow control strategies for turbulent skin-friction drag reduction are studied by performing Direct Numerical Simulation of turbulent channels. The innovative feature of the present study is that the flow is driven at Constant total Power Input (CtPI), which is a necessary enabling choice in order to meaningfully compare a reference unmanipulated flow with a modified one from the energetic standpoint. Spanwise wall oscillation and opposition control are adopted as model strategies, because of their very different control input power requirements. The global power budget show that the increase of dissipation of mean kinetic energy is not always related to drag reduction, while the preliminary analysis of the scale energy fluxes through the generalized Kolmogorov equation shows that the space- and scale properties of the scale energy source and fluxes are significantly modified in the near-wall region, while remain unaltered elsewhere.