Effect of Full-Span Gurney Flap Height on Wing Wake Vortex Alleviation

Abstract

T HE hazard posed by wake vortices trailing behind heavy airplanes to following aircraft has beenwell known, and the area has been researched to considerable depth since the introduction of the first jumbo jets in the early 1970s. The reader is referred to [1] for an outstanding review of the subject area. The present author has been active in this area since the early 1990s. Gurney flap is an aerodynamic concept that dates back to the 1970s. It represents a long and narrow plate placed at a wing’s trailing edge on its pressure side and perpendicular to it. It was first proposed and utilized quite successfully byDanGurney as a means to increase the downforce on his racing cars. The concept has received some attention in the aerospace community; see, for example, [2–12], with rather limited implementation in actual airplanewing design. For a rather extensive review ofGurneyflap-related research the reader is referred to [13]. It will be stated here only that the flap regularly increases both the wing’s lift and drag and decreases its aerodynamic efficiency. The major effect of this modification is an increased circulation at the wing trailing edge. Since early 2004 the author has been studying the potential use of Gurney flaps for wake vortex alleviation. First, a Gurney flap having a height equal to 6% of the wing chord was studied. Several flow visualization techniqueswere used to qualitatively compare the nearfield wake flows behind a baseline wing vs a Gurney flap equipped wing [13]. A new quantitative description of the vortex strength, a roll-up tightness factor (RTF) was proposed and used. It was found that the flap indeed affected the near-field wing wake to a significant degree [14]. Next, an additional Gurney flap, one having a height equal to 1.5% of the wing chord, i.e., 0:015c, was investigated [15]. The results followed the trends presented in [13,14] quite well. To further expand the investigation matrix, an intermediate-height Gurney flap, one with a height equal to 0:04c, has been examined recently. Once again, both the effects on the aerodynamic characteristics of the configurations and their respective vortex strengths have been recorded and analyzed. A discussion of these results is presented in the next sections.