Experimental investigation of transverse and vortex gust encounters at low reynolds numbers

This paper aims to study the lift response of transverse and vortex gust encounters. A sine-squared transverse gust was created in a water towing tank using a water jet, whereas a vortex gust was created in a water channel by clockwise half-rotation of an upstream gust generator plate. Forces and flowfields were acquired for both gust types. The effects of the gust ratio and vertical positioning of the gust generator plate were investigated for the transverse gust and the vortex gust encounters, respectively. For a flat plate at a 0 deg angle of attack, changing the gust ratio for the transverse gust was found to have a major effect on the peak lift and a minor effect on the recovery phase; whereas changing the vertical positioning of the gust generator plate for the vortex gust was found to cause relatively minor effects at almost every point in the lift response. Both gust encounters resulted in large transients in the lift force, and the unsteady forcing was found to depend on the circulation shed from the leading edge of the wing. The lift force experienced and the circulation shed showed a steeper increase for the transverse gust encounters despite the same gust ratio of one. Average velocity variations in time were obtained from the flowfield measurements along an upstream line for both gust types, and variations in the gust-induced angle of attack were computed. The Helmbold equation was then used to predict the lift coefficients based on the calculated gust-induced angle of attack. The trends in the measured and predicted lift coefficients were found to compare well with each other, but the values were found to agree well only when the gust-induced angle of attack was low.