Efficient laminar flow control

Research studies conducted over the years have demonstrated that wall suction is a highly effective laminar flow control (LFC) technique to delay laminar to turbulent transition. In this work, we investigated efficient LFC configurations. These are evaluated both in terms of the drag and power exerted by the flow and demanded by the LFC system. To derive the LFC power, the literature analyses on drag reduction for turbulent flows were adapted for the LFC applications hereby considered, leading to the identification of the relevant power-contributing terms. Two methods, originally developed to predict the transition location for uncontrolled flows, were employed to explore LFC configurations. These are specifically the so-called e N method, derived from the linear stability theory, and the γ − Re θ model. Only the γ − Re θ approach gave more robust results for LFC applications. As such, it was embedded in an iterative framework exploiting Bayesian optimization to find the most beneficial configurations, for uniform suction LFC, to control the archetypal, bidimensional, and incompressible flat plate flow. Overall, 700 configurations were explored. Efficient LFC configurations were found with the optimal configuration delivering 34% of total power saving. This study, establishing a robust and computationally affordable methodology, while developing the power budget breakdown, paves the way for efficient LFC for aeronautical flows, possibly considering nonuniform suction, pressure gradients, surface curvature, the third spatial direction as well as flows at different Reynolds and Mach numbers.