Computational Analysis of Pitch Stability for a Slotted Airfoil in Ground Effect

Ground effect is a phenomenon which occurs when flow is displaced around a moving body in close proximity to the ground. This displacement is caused by compressed air that becomes trapped during motion between the body and the ground. The added upward thrust caused by ground effect can be used to generate and augment lift on a small aircraft. AirRay is a small single person, recreational downhill glider that operates within this ground effect. When launched from the top of a hill, it can glide to the base using ground effect for lift.;One of the amplified effects of operating close to the ground is a shifting center-of-pressure. This effect, exacerbated by the changing ground roughness and varying passenger size, can create an unstable pitch contributing to the complexity of the vehicle\u27s control. To minimize the control requirements necessitates the stabilization and restriction in the movement of the center-of-pressure.;To restrict the movement of the center-of-pressure, patent pending slots will be used to modify the airfoil surfaces. Through computational analysis, the effects of slots and their placement on the aerodynamic characteristics will be determined as well as the optimal conditions for pitch stability. Computational fluid dynamics (CFD) will be used to compare the effects of placing a slot on a two dimensional Wortmann FX63-137 airfoil in ground effect. The Wortmann FX63-137 is a low speed airfoil with a high coefficient of lift that is commonly used on sail planes and is ideally suited for AirRay. The geometric shape of the slot will vary according to the angle of the slot with respect to the chord line and the position of the slot along the chord line. In addition, the analysis will include five different angles of attack: -3º, 0º, 5º, 10º, and 15º in order to determine the effects on the aerodynamic characteristics.;In order to perform the computational analysis, 2-D models of the airfoil with the different types of slots will be created in Gambit. These were uploaded to Fluent and tested in a turbulence simulation which is representative of the environment for which AirRay is being designed. From these results, the optimal modifications for controlling the center-of-pressure and therefore the pitch were determined. The x-20, d-40, w-2 slot configuration was able to control the travel of the center-of-pressure 14% more effectively than the baseline airfoil