Effect Of Transverse Gust Velocity Profiles

A large variety of gusts that develop in the atmospheric boundary layer affect aerial vehicles. This study, performed in water tow tanks, compares the response of a flat plate wing to transverse vertical gusts with a top-hat and a sine-squared velocity profile at Reynolds numbers of 20,000-30,000. Experiments are performed for a wide range of gust ratios (0.5-1.5) and angles of attack (0-20 deg). Force measurements for a sine-squared gust show a smoother increase in lift and a lower peak compared with a top-hat gust for the same gust ratio. Linear models are found to work reasonably well predicting the force response for the sine-squared gust, whereas the top-hat gust exhibits significant nonlinear effects at the largest gust ratios. This nonlinear behavior is linked to high levels of circulation shed from the wing edges and the development of nonplanar wakes. Nevertheless, the gust momentum inflow on the wing is directly linked to many characteristics of the lift response, independently of gust velocity profile. In addition, the lift response for the two gusts is found to increase with angle of attack until the wing inclination is large enough to produce a separated wake before gust entry.