Actively controlled trailing-edge flaps (ACFs) have been extensively studied for vibration and noise control in rotorcraft using various approximate aerodynamic models. In this study, two-dimensional unsteady airloads due to oscillating flap motion obtained from computational fluid dynamics (CFD) are compared with approximate unsteady loads. The approximate loads are obtained from the Rational Function Approximation (RFA) model, which is a state-space, time-domain model that accounts for unsteadiness, compressibility and time-varying freestream effect, developed for use with comprehensive rotorcraft simulation codes. Unsteady compressible Reynolds-averaged Navier-Stokes computations are based on an overset mesh that accounts for oscillatory flap motion. The comparison is conducted over a wide range of unsteady flow conditions representing combinations of parameters such as airfoil angle of attack, flap deflection amplitudes, reduced frequencies, and freestream Mach numbers. The comparison between the RFA model and CFD based calculations indicates the limitations of the approximate theory, particularly at transonic Mach numbers and high angles of attack where nonlinear effects dominate. Nevertheless, the RFA model yields a good approximation for the unsteady effects of the trailing-edge flap under conditions representative of rotorcraft aerodynamic environment. The drag predicted by the CFD solver is also compared with a simple drag correction developed for flap deflection. The comparison indicates that drag prediction due to flap motion needs to be computed using refined tools so as to predict performance penalty associated with active flap deflections.
Comparison of approximate time domain aerodynamics for flapped airfoils with CFD based results with applications
Vergleich von approximierenden aerodynamischen Zeitbereichsverfahren zur Berechnung von Strömungsprofilen mit Klappen mit CFD-Ergebnissen
2008
17 Seiten, 32 Quellen
Conference paper
English
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