Computational fluid dynamics and doublet-lattice calculation of unsteady control surface aerodynamics

Accurate prediction of control surface aerodynamics has been a challenge si nce the dawn of aviation. Whereas this has been an important problem for ma ny years, recent increases in the use of control surfaces for active contro l (load alleviation and flutter suppression) have increased the importance of accurate steady and unsteady control surface aerodynamics. Because of th e strong influence of viscosity on the pressures on a trailing-edge control surface, the aerodynamic theories based on the linear potential equation h ave had only marginal success in predicting control surface aerodynamics, a nd in practice, large corrections (based on wind-tunnel data) are often req uired for acceptable accuracy. Recent advances in computing technology and unsteady aerodynamic codes based on the Navier-Stokes equation are allowing more accurate analyses to be performed. Unsteady aerodynamic calculations due to control surface oscillations are made using a linear potential code (N5K) and a Navier-Stokes code (CFL3D.AE-BA version 4.1). The Navier-Stokes calculations are performed in the time domain using an exponential pulse t echnique and are transformed to the frequency domain using Fourier transfor m. For low reduced-frequency cases, the Navier-Stokes calculations are comp ared to the doublet-lattice method and to experiment, and the advantages of the nonlinear analysis are clearly demonstrated. Correlation between Navie r-Stokes and doublet-lattice results is then studied for higher reduced fre quencies.