Numerical simulations are performed to study the effect of freestream turbulence on small-amplitude limit-cycle oscillations of an airfoil at transitionalReynolds numbers.Aone-degree-of-freedomaeroelastic modelwas coupledwith the National Research Council Canada in-house computational-fluid-dynamics code INSflow to perform unsteady Reynolds-averaged Navier-Stokes simulations for flows around a rigid NACA 0012 airfoil in free-to-rotate conditions. Without coupling a transitionmodel, unsteadyReynolds-averagedNavier-Stokes computations basedonthe commonly used shear-stress-transport turbulencemodel could not capture the limit-cycle oscillations. Thiswas expected because it had been previously shown that the limit-cycle oscillations were fed by negative aerodynamic damping due to laminar boundary-layer separation. A correlation-based transition model was then implemented in the code and applied to investigate the turbulence effects. The computed results confirmed qualitatively the experimental observations of the turbulence effects on the limit-cycle oscillations by varying the values of the turbulence intensity and length scale. It was observed that the limit-cycle oscillationsweremore sensitive to the turbulence intensity than to the latter. In general, the freestream turbulence suppressed the limit-cycle oscillations. The pitch amplitude became smaller when the freestream turbulence intensity was increased, which was qualitatively in good agreement with experimental results. The limit-cycle oscillations could not be sustainedwhen the input freestreamturbulence level reached around 1.25%.An examination of the unsteady flowfield revealed that the freestream turbulence affected the location of the separation points and suppressed the laminar-turbulent transition process.
Journal of Aircraft52, no. 4 (10 September 2014): 1214–1225.