Separation Control by Self-Activated Movable Flaps

Abstract

Separation control is an important issue in the physiology of birdflight. Here, the adaption of the separation control mechanism by bird feathers to the requirements of engineering applications is described in detail. Self-activated movable flaps similar to artificial bird feathers represent a high-lift system for increasing the maximum lift of airfoils. Their effect on the unsteady flow around a two-dimensional airfoil configuration is investigated by a joint numerical and experimental study. First, attention is paid to the automatic opening and closing mechanism of the flap. Following this, its beneficial effect on lift is investigated for varying incidences and flap configurations. In-depth analysis of experimental and numerical results provides a detailed description of the important phenomena and the effect of self-adjusting flaps on the flow around the airfoil. In the second part of this paper, a contribution is made to verification of the applicability of unsteady Reynolds-averaged approaches using statistical turbulence models for unsteady flows with particular attention to turbulent time scales with comparison to the results of a hybrid simulation based on unsteady Reynolds-averaged Navier-Stokes equations and large-eddy simulation. Finally, flight experiments are described using an aircraft with movable flaps fitted on its laminar wing.