Unsteady forcing on a flat-plate wing in large transverse gusts

Abstract

The effects of large-amplitude transverse gusts on lift and drag of a flat-plate wing were studied experimentally. Forces were measured and particle imaging velocimetry recorded as the wing was towed through a transverse gust with peak velocity of equal order of magnitude to the steady towing velocity. These results were compared across variations in gust ratio and wing pitch angle. Several cases with similar peak quasi-steady conditions but dissimilar initial conditions were shown to have similar peak measured forces, indicating that those forces are not dominated by the initial conditions. The measured forces were compared to predictions by several existing models, each of which was designed for use in small-amplitude gust encounters. The peak forces during the gust were found to be close to the semi-empirical quasi-steady predictions, but the transient forces after the gust peak were not. A semi-empirical unsteady model is proposed as an adaptation of the existing models. This model incorporates the unsteady characteristics of gust recovery, but it under-predicts the magnitude of the forces caused by the gust encounter.