Experimental and numerical investigations of wing flap motion aerodynamics

Abstract

The tailing wake vortices produced behind wing of an aircraft play an important role on wing performance due to its induced velocity. In addition, a condition in which wing is located in the wake region of preceding wing causes more complicated problems. In fixed wing, the trailing vortices from heavy aircraft can pose a hazard to the following aircraft. In helicopters, noise and vibration problems caused by interactions between the trailing vortices from rotor blades and following blades have been a challenging topic. The active trailing-edge flap can be a possible alternative to resolve the blade-vortex interaction (BVI) problem and to achieve the reduced wake vortex age. In this study, aerodynamic and wake characteristics of wing with moving flap were investigated through experiment and numerical simulations. The numerical simulations using vortex lattice method (VLM) including wake vortices produced between wing and flap juncture were performed and validated by comparing with the experimental data. A new gap modeling method to model the wing-flap juncture is developed, which can simulate the unsteady aerodynamic flap motions by considering the shed vortex components detached from the trailing edge. The aerodynamic characteristics of flap-deflected wings were validated through comparisons with the experimental data from NASA technical note. The wake behaviors of four-vortex system on triangular-flapped wing were simulated and compared with the reference experiment, and the limits of the developed wing-flap gap model were investigated. For the unsteady flap motions, a wing model, which has SMA-actuated two flaps symmetrically located at the middle of the span, was designed, fabricated, and tested its control performance. Subsequently, aerodynamic characteristics depending on phase difference of the two flaps were measured through the wind tunnel experiments. The lift coefficients depending on the flap motions from the simulations were validated through the experimental data, and the corresponding wake configurations can be obtained. In addition, the simulations with and without the gap model, and the simulations using quasi-unsteady and unsteady gap models were performed and compared. Further studies on various flap angles and frequencies using the developed gap model are expected to be able to predict the aerodynamic characteristics and simulate the wake behaviors in an aircraft wing and rotor blades with active flap. Moreover, it is expected that many improvements in wake-induced problems can be achieved by utilizing the proposed gap model in designing the active-flapped wing.