Design and Optimization of an Airfoil with Active Continuous Trailing-Edge Flap

This paper presents the design and optimization of an airfoil with active continuous trailing-edge flap (CTEF) investigated as a potential rotorcraft active control device. Several structural cross-section models are developed: high-fidelity NASTRAN and UM/VABS models and a reduced order analysis model. The validation of the reduced order model is established by comparing its predictions of CTEF deformations with those of NASTRAN and UM/VABS analyses, which both show good agreement. The 2D aerodynamic characteristics of the CTEF airfoil are evaluated using XFOIL and CFD analyses: FUN3D and OVERTURNS. XFOIL, coupled with the reduced order structure model, is adopted for optimization study. The accuracy of XFOIL in predicting the aerodynamic pressure of the CTEF airfoil is verified using CFD simulations, which shows sufficient fidelity. The predicted variations of aerodynamic coefficients with CTEF angle are compared among the aerodynamic analyses. The optimization process is developed and applied to two bimorph bender configurations: an MFC solid bender and an MFC stack bender. The solid bender is used to confirm the functioning of the optimization procedure and to use its optimal layout as a reference to the stack design, the primary design object. A linear tapered shape is found to be the optimum for a MFC solid bender, which generates average 63% more CTEF angles than those of an optimal rectangular bender. Optimized MFC stack bender is shown to resemble the shape of the solid bender. A four-ply bimorph is considered the best choice among the stack layouts because of its large output of CTEF angle and relatively less plies required. CTEF angle produced by the four-ply optimal layout ranges from 7:6° to 5:3° with speeds from 0 to 200 m/s at angle of attack of 6°. The reduction in CTEF angle with angle of attack is less steep than that with speed, ranging from 6:5° to 5:8° with angle of attack from 0 to 8° at speed of 166 m/s. An average 14% increase in CTEF angles is achieved through optimization for the four-ply bimorph.