Structural and aerodynamic response of an aeroelastic NACA0012 wing subject to variations in the integral length scale of free stream turbulence

The effect of variations in the integral length scale of incoming Free Stream Turbulence (FST) on an aeroelastic NACA0012 wing at a chord-based Reynolds number of 200,000 is investigated. An active grid is employed to generate a range of integral scales from 0.5c to 1c, where c is the chord length, at a turbulence intensity of 15%. Force, moment, Digital Image Correlation (DIC) and planar Particle Image Velocimetry (PIV) measurements are utilised to understand the effect of integral length scale variations.

With the introduction of FST, the peak time-averaged lift increases by over 30% and the onset of stall is delayed by 5 degrees. From analysis of the spectral content of the forces in conjunction with the DIC measurements, an excitation in the structural bending mode is found for integral length scales of 1c. As the integral length scale of the incoming FST reduces to 0.5c the magnitude of the spectral content shifts to a higher frequency. A proper orthogonal decomposition is applied to the PIV measurements to determine spatial modes. Using these spatial modes, alongside concurrent force measurements, linear stochastic estimation is applied to determine the nature of the flow field at integral length scales of 0.5c and 1c. It is found that the higher frequency observed is an aerodynamic vortex shedding mode excited by the incoming FST at an integral scale of 0.5c. Corroborated by the DIC measurements, the lower frequency mode is a structural bending mode excited by the incoming FST at an integral length scale of 1c.