Investigation of Vortex Structure Behavior Induced by Different Drag Reduction Devices in the Near Field

Abstract

The paper deals with a proposal of possible solutions for wingtip vortex analysis, induced in the near field and performed by visual inspection using smoke screen and laser sheet setup in a subsonic wind tunnel. Wingtip vortices emerge as a result of unevenly distributed lift along the wing when pressure differences above and below the wing are interacting at the wingtips, contributing to generation of induced drag, which significantly affects the aerodynamical efficiency and important factors such as fuel consumption, maximum operational range, maximum achievable speeds, grater endurance etc. The aim of the research is to appropriately design procedures to perform a visual analysis and evaluation of wingtip vortices’ behavior, to establish suitable evaluative parameters, allowing to reliably define the number of vortices, location and area of its individual cores as well as providing the overall size of vortex structures, induced by investigated wingtips and winglets. The visual analysis of six configurations consisting of one net airfoil and five drag reduction devices, commonly used on civil aircraft, was performed in rectangular test section of a subsonic wind tunnel with dimensions of 350 mm × 350 mm. The authors used NACA 4415 airfoil at a flow speed of Re = 17 × 104, with configurations at the angles of attack α = 3°, 9° and 16°, to simulate cruise and non-cruise flight phases. The research proved the use of five proposed evaluative parameters for visual evaluation of vortex structures’ behavior, when using only the visually based setup. The authors also pointed out the limitations and shortcomings of proposed methodology. The results showed that proposed method could not directly provide numerical evaluation of drag component induced by drag reduction devices, but it is an effective tool for identifying the key-characteristics of the vortex at individual angles of attack, i.e., the number of vortices, location of individual areas of interest (cores), their numbers, areas, and dimensions.