Transonic Wind-Tunnel Testing of a Slotted, Natural-Laminar-Flow Wing at Full-Scale Conditions

A semi-span wing based on the slotted, natural-laminar-flow (SNLF) airfoil concept was experimentally tested in the NASA Ames Unitary Plan Wind Tunnel 11-ft transonic test section to validate the viability of SNLF for commercial transport applications. The model is based on the S207, SNLF airfoil, which was designed using requirements derived from a transonic, truss-braced wing (TTBW) aircraft. The wind-tunnel model itself is a constant-chord, constant-sweep to emphasize the airfoil aerodynamics. Three rows of pressure orifices are present, and distributed between the fore and aft elements. Total force and moment measurements were collected using a floor balance. Transition locations were measured using IR thermography, facilitated by the model being coated with a low-emissivity black paint finished to a roughness below 20 microinches. The capabilities of the wind tunnel allowed for testing at Reynolds and Mach numbers exceeding those expected for the reference TTBW aircraft, which is notable for ground testing. It was found that the model achieved extensive runs of laminar flow around its design point, validating the concept at flight-relevant conditions. Low-speed testing with the aft element deflected like a Fowler flap showed significant increases in maximum lift compared to the cruise configuration. Altogether, the data confirm the viability of SNLF for commercial transport applications.