Drag Optimization Study of Variable Camber Continuous Trailing Edge Flap (VCCTEF) Using OVERFLOW

This paper reports the results of a computational study that was conducted to explore the effect of various Variable Camber Continuous Trailing Edge Flap (VCCTEF) configurations on the lift and drag of a NASA Generic Transport Model (GTM) wing section at a span-wise location called the break station that marks a sharp change in the wing trailing edge slope. The OVERFLOW solver with the the one-equation SpalartAllmaras (SA) turbulence model and the two-equation (k − ω) Shear Stress Transport (SST) turbulence model was first applied to a NACA0021 airfoil case and the results were compared with experimental data of Harris and ARC2D results. The comparison showed good agreement between earlier results and the SA model. Therefore, SA model was used for all the simulations in this study. Design cruise condition at 36,000 feet at free stream Mach number of 0.797 and Reynolds number of 30.734x10 was simulated for an angle of attack (AoA) sweep from -3 deg. to 10 deg. Five VCCTEF configurations with varying camber in the flap region were considered along with an unmodified (no flap deflection) airfoil as the baseline case. Comparison of lift and drag corresponding to these configurations with baseline configuration (retracted flaps) showed a definite trend in the results. Although the baseline configuration produced the lowest lift at a given AoA among the set under investigation, it produces stall after about 5 deg AoA, whereas with the VCCTEF settings, stall occurs earlier between 3 and 4 deg AoA. The lift enhancement was significant with the extended flaps, but it was accompanied with a drag penalty, as expected. But, the lift versus drag L/D results showed that at the design cruise lift coefficient of 0.51, the L/D characteristics improved from the baseline to four of the five VCCTEF configurations. Among these four configurations, the configuration which reflects a parabolic-like camber is more optimal than the other three configurations in terms of improved L/D and well-behaved Cp distribution. The lift prediction is compared against theoretical lift prediction from potential flow theory. Excellent agreement between computed and theoretical incremental lift is shown.