Effect of Step Depth and Angle on the Aerodynamics of a Sliding Morphing Skin

Abstract

The past two decades have witnessed a growing interest among aerospace researchers and designers in aircraft morphing technology. A single aircraft with morphing wings can perform near optimum at different flight regimes by changing the geometry of its wings. With the advancements achieved in this field, a need for a reliable morphing skin is emerging. The demanding task of designing a morphing skin has to compromise between flexibility to ensure low actuation requirements, and high stiffness to carry all the aerodynamic loads. One of the viable designs that fulfills the mechanical requirements is the segmented sliding skin. In such a design, discrete panels overlap to cover the surface of the wing and slide against each other during the morphing motion. From the aerodynamic perspective, the sliding panels introduce backward-facing steps on airfoil surface. In the process of determining the optimum panels’ thickness, this paper presents a comprehensive numerical study on the effect of the step depth and angle on the aerodynamics of an airfoil with a backward-facing step employed on its lower surface. Results showed a significant improvement in the lifting capabilities of the stepped airfoil, and this improvement is directly proportional to the step depth. On the other hand, the separated flow at the step edge induced a low pressure recirculation zone that created a suction force directly proportional to the effective area of the backward-facing step. This resulted in a drag coefficient value that is directly proportional to the step depth. The aerodynamic efficiency of the stepped airfoil was degraded in terms of the lift-to-drag ratio, however decreasing the step depth largely mitigated these adverse effects. Studying different step angles showed that the step can be tilted over a wide range of angles with a negligible effect on the aerodynamics of the stepped airfoil.