An Investigation into the Aerodynamics of Trailing Edge Flap and Flap-Tab Airfoils Using CFD and Analytical Methods

The paper describes the development of analytical and CFD based methods to study the aerodynamics of a trailing edge flap and flap-tab concept for incompressible/compressible flows. Both steady and unsteady aerodynamic modeling of a flap-tab airfoil is considered. The theoretical analysis is based primarily on inviscid thin airfoil theory and provides a first order estimate for routine design airloads estimates. However, the analytical approach involves several simplifying assumptions (inviscid, irrotational, small perturbation, etc.) which limits it from capturing the finer details of the flow phenomena. In contrast, the CFD analysis better captures these effects (albeit at a higher computational cost) and is used in the present study to obtain a deeper understanding of the underlying flow physics in the non-linear regime. CFD predictions also help to identify the limitations and range of applicability of the analytical method. Although the theory is presented for a flap-tab airfoil, the steady CFD analysis focuses only on flap deflections with no tab. The unsteady analysis (which includes both time and frequency domain solutions) is validated for pure flap oscillations as well as for combined flap and tab oscillations. The results indicate that at subcritical Mach numbers, there is good agreement between the steady aerodynamic predictions using CFD and the analytical models even for high flap deflections. The unsteady aerodynamic theories are also observed to provide excellent estimates of the airloads for high flap deflection amplitudes. Overall, the study provides valuable tools for improved understanding of the steady and unsteady aerodynamics of flap-tab airfoils.