Feasibility Study of Slotted, Natural-Laminar-Flow Airfoils for High-Lift Applications

A computational fluid dynamics approach to evaluate the feasibility of a slotted, natural-laminar-flow airfoil designed for transonic applications, to perform as a high-lift system was developed. Reynolds-Averaged Navier-Stokes equations with a laminar-turbulent transition model for subsonic flow at representative flight conditions were used for this analysis. Baseline high-lift simulations were performed to understand the stall characteristics of the slotted, natural-laminar-flow airfoil. Maximum aerodynamic efficiency was observed with a constant slot-width. In addition, the effectiveness of the aft-element as a high-lift device was explored. Results indicate that a micro-flap is a viable option as a lift effector. These are most effective when combined with a Fowler-like motion. However, the maximum lift coefficient was limited, in part, by an early leading-edge stall largely due to the small nose radius required for supporting laminar flow. As a result, a drooped leading edge was added to the S207, the latest evolution of slotted, natural-laminar-flow airfoil technology. Morphing technology was also applied to mitigate abrupt wing-stall characteristics and further increase maximum lift. The use of morphing technology was observed to produce superior high-lift performance over hinged leading edge flap motions. However, off-body separation and narrow stall region in lift curves were observed for the S207's high-lift system due to the aft-element position. The aft-element position was based on a previous study for the S204, a placeholder airfoil. Hence, an S207 aft-element optimized for high-lift was identified as the natural next step. A low-fidelity, slot-width sensitivity study was performed with the S207's aft element in the form of a 9-point study. The focus of this study was to identify sensitivities of the slotted, natural-laminar-flow high-lift system to aft-element position variability. Three positioning boundaries were selected in reference to the stowed aft element and the gap between elements. Results show that the S207's flap schedule should be dependent on the flap deflection angle and exit slot-width gap. Finally, a delayed-detached-eddy simulation was performed to improve confidence in the developed methodology. Strong agreement between RANS and DDES results was observed. These findings contribute novel knowledge to the state-of-the-art understanding of the revolutionary slotted, natural-laminar-flow airfoil technology.