UNSTEADY flow conditions experienced in wing–gust encoun-ters have been the focus of many experimental and computational studies [1–6]. Wing–gust encounters have been simulated experimentally in prior works through variations of wing kinematics [7, 8]. More recently, wing–gust-encounter investigations have relied on simulating the gust encounter by generating a gust flow in the test section of a wind tunnel or water tank [9–12]. Biler et al.[9] and Perrotta and Jones [10] developed and characterized a gust generator that produced a sine-squared transverse velocity profile. Even though the average velocity of the gust was well characterized, instantaneous flow from the gust meandered and was unreliable. The large uncertainty in the gust flow made it difficult to study pitch maneuvers that relied on a repeatable instantaneous flowfield. In addition, vorticity was spread throughout the gust and it had no distinct shear layers, which eliminated the possibility of studying the impact of shear layer width on the aerodynamics of wing–gust encounters. Elsewhere, Corkery et al.[11] developed a transverse top-hat gust with very low flow uncertainties by thoroughly conditioning the flow before the outlet, as well as adding a suction inlet opposite to the outlet. A gust profile between these two distributions is a trapezoidal gust profile, where the shear layer at the edges of the gust diffuses without becoming completely smooth, as in the sine-squared case. Studying this variation may help bridge the gap between the flow responses in the two aforementioned gusts.

In the current Technical Note, we present the design of a novel gust generator that produces a trapezoidal gust profile to bridge the gap between a sine-squared and a top-hat gust. Furthermore, we compare force and flow measurements between wing–gust encounters carried out in the sine-squared gust and the trapezoidal gust. The comparison highlights key differences in the gust flow as well as the wing’s response to the gust encounter between the two cases. We finally note the flow attachment aft of the leading-edge vortex during a gust encounter and discuss its implication on the lift force experienced by the wing.