INDICIAL LIFT APPROXIMATIONS FOR 2-DIMENSIONAL SUBSONIC FLOW AS OBTAINED FROM OSCILLATORY MEASUREMENTS

An approach is described to obtain generalized approximations to the i ndicial lift response due to angle of attack and pitch rate in two-dim ensional subsonic flow. Starting from an assumed representation, the a pproximations are accomplished by means of a nongradient optimization algorithm in which the coefficients of the approximation are free para meters. The optimization is subject to prescribed constraints in terms of the known initial and asymptotic behavior of the indicial response , and by requiring the response duplicate the known exact (analytic) s olutions at earlier values of time. The approach is applied to extract the intermediate forms of the indicial lift response, generalized in terms of Mach number and pitch axis location, from experimental measur ements of the unsteady lift in the frequency domain.