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Water Tunnel Studies of Dynamic Wing Flap Effects

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Technical Report

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Naval Postgraduate School Monterey United States

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The flow features developing over a two-element NACA 0012 airfoil, with the rear portion serving as a trailing edge flap, were investigated using dye flow visualization in the NPS water tunnel. The original motivation for the work arose from a need to identify any potential to enhance maneuverability of aircraft to enable smoother landing under adverse flight situations. The flap portion was maneuvered in two different unsteady motion histories by a drive mechanism a constant pitch rate motion and a sinusoidal oscillatory motion, at Reynolds numbers of 7,500 and 37,500. Comparisons were also drawn with steady flow features under similar conditions. In both unsteady cases, features of dynamic stall flow were observed. Unlike standard airfoil dynamic stall, the unsteady flow over a dynamic flap develops in the wake of the airfoil main element. This introduces many flow complexities such as reversed flows at low flap deflection angles of attack, dynamic stall developing from the wrap-around trailing edge flow that also interacts with main element boundary layer flow, unusual behavior for the main element, and flap clearance gap flow. However, since dynamic stall was observed at such flap deflections, it indicates that by differentially oscillating the flaps, it might be possible to develop differential lift on the two sides of a flight vehicle, which may provide better control authority than seen in steady flows. The results could be applied to unmanned air vehicles as well.

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