Uncertainty assessment of coupled Digital Image Correlation and Particle Image Velocimetry for fluid-structure interaction wind tunnel experiments

The development of advanced composite structures for maritime and aerospace applications requires the ability to quantify their actual performance under known fluid loads. One example is the need to investigate the differences in fluid-structure response of passive adaptive composite structures. A wind tunnel based method is used to quantify the structural behaviour, and fluid response, of a flexible aerofoil under fluid loading. The technique measures the deflection of the structure, with high speed stereoscopic Digital Image Correlation (DIC). The tip vortex position is measured using high resolution stereoscopic Particle Image Velocimetry (PIV). The accuracy of the two full-field optical measurement systems is quantified and the effect of optical interactions is assessed. A flexible NACA0015 rectangular plan-form aerofoil of 0.9 m span and aspect ratio of two is subjected to aerodynamic loading within a closed circuit wind tunnel. The wind speed was varied from 10 to 25 m/s within a 3.5 m x 2.4 m working section. The structural response is measured simultaneously with the fluid flow field around the tip vortex. The tip vortex core, which moved by ≈62 mm at the highest wind speed, is directly compared to the deformation of the structure, which deflected by ≈58 mm. A maximum foil twist of ≈0.6° was observed. The DIC accuracy is evaluated in static and transient conditions for translational and rotational movement. The DIC maximum error for translations, greater than or equal to 0.5 mm, is less than 3% and less than 0.6% in dynamic motions. The DIC total error for rotations is less than 5% in static motions and 1% in dynamic rotations. The PIV uncertainty is quantified a posteriori providing the errors due to the correlation algorithm and the experimental setup. The mean in-plane velocity component uncertainties in the vortex region varied between 1.2% and 3.5% depending on flow speed (≈0.1 px). The mean out-of-plane velocity uncertainty around the vortex varies between 2% and 3.3% depending on flow speed.