High Reynolds number testing of a laminar airfoil under forced harmonic pitching oscillations at cryogenic conditions

Abstract

Steady and unsteady aerodynamic testing of a pitching 2D laminar airfoil model was conducted at high Reynolds numbers under cryogenic conditions. The influence of the unsteady laminar-turbulent boundary layer transition on the aeroelastic stability and flutter behavior was investigated to assess the risk of applying this technology to transport aircraft. In first tests the influence of free transition on a typical laminar CAST-10/2 airfoil on its aeroelastic stability could be derived. As the aim of the present test was to obtain unsteady aerodynamic data for an oscillating laminar airfoil in the high Reynolds number regime, a new hydraulic pitching mechanism was built that could be operated in an environment of low temperatures down to 100 K. Furthermore a new wind-tunnel model with NLF-0415 airfoil shape was built and equipped with unsteady pressure sensors, hot-film sensors and accelerometers. During the test systematic variations of the Mach number at constant Reynolds number and a variation of the Reynolds number at constant Mach number were performed. Steady lift and moment polars were recorded at Reynolds numbers of up to 14·106. As a first result, nonlinear behavior as already found for the CAST-10/2 airfoil in the transonic regime for low Reynolds numbers of 2·106, can also be found for the NLF-0415 airfoil for Reynolds numbers of up to 8·106.