Lifting Surface Approach . . to the Estimation of Gust Response of Finite Wings

Abstract

Unsteady response of finite wings flying though turbulence is investigated using linearized lifting surface theory. The NLR method, extended to the unsteady case, is employed for the numerical calculation of the lift force arising from oscillatory gusts for a wide range of frequencies. An efficient numerical procedure is presented for the estimation of the response to random turbulence. It takes into consideration the instantaneous variation of the vertical velocity of turbulence along the span as well as the spanwise distribution of the aerodynamic influence function. This procedure uses the relation between the output power spectral density and the spanwise cross-spectrum of turbulence, defined in terms of the spanwise correlated frequency response function, which in turn is derived from the aerodynamic transfer matrix for the modified upwash field. The results computed by means of this method with a model of turbulence uniform in span, and with a model of isotropic turbulence, exhibit considerable differences.