SUBSONIC UNSTEADY AERODYNAMICS CAUSED BY GUSTS USING THE INDICIAL METHOD

Indicial approximations are derived for the lift on an airfoil penetra ting a stationary sharp-edge gust in two-dimensional subsonic flow. Us ing an assumed exponential form, the approximations have been generali zed in terms of Mach number alone by means of an optimization algorith m where certain coefficients of the approximations are free parameters , The optimization is subject to prescribed constraints in terms of th e initial and asymptotic behavior of the gust response, and by requiri ng the response closely match the known exact solutions given by subso nic linear theory at earlier values of time. An alternative approximat ion is obtained by using results from a direct numerical simulation of the gust problem using computational fluid dynamics (CFD), For an air foil-vortex interaction problem, comparisons were made with experiment al data and CFD results. Finally, the indicial method was integrated i nto a three-dimensional rotor simulation, and the near- and far-field acoustics were computed using the Ffowcs Williams-Hawkins equation. Go od agreement was found with simultaneously measured airloads and acous tics data.