Numerical Analyses of Discrete Gust Response for a Flexible Aircraft

Abstract

Based on Navier -Stokes equations and structural and flight dynamic equations of motion, dynamic responses in vertical discrete gust flow perturbation are investigated for a supersonic transport model. A tightly coupled method was developed by the subiteration between aerodynamic equations and dynamic equations of motion. First, und er the assumption of rigid -body and single freedom of motion in the vertical plunging, the results of direct -coupling method are compared with the results of quasi -steady model method. Then gust responses for the one -minus -cosine gust profile are analyzed with two freedoms of motion in plunging and pitching for the rigid and flexible airplane configurations . considered in aircraft structure design. Due to its multidisciplinary nature with aero dynamics, flight dynamics, aeroelasticity and atmospheric turbulence, up to now, only the doublet -lattice, unsteady linear aerodynamic code (DLM) coupled with the equation of motion of flexible vehicle was used for the gust response analysis [1 -3]. Gusts in nature tend to random. The early design methods for gust loads were based on a single discrete gust having one -minus -cosine velocity profile. Recently the statistical discrete gust (SDG) method and the power spectral density (PSD) method [4] in the freq uency domain are used to define the gust loads, however, which are still difficult to combine with the modern Navier -Stokes numerical method. In the paper, the fully implicit multiblock Navier Stokes aeroelastic solver implemented by the authors [5], coupled with the flight and structural dynamic equations of motion, has been developed to simulate gust dynamic responses for the supersonic transport (SST) designed by National Aerospace Laboratory of Japan (NAL) [6]. To study the effects of dynamic respon se due to flow perturbation and airplane motion, only the consideration of vertical plunging motion, a comparative study was first done for the rigid airplane in the harmonic flow perturbation with the direct -coupling method and the quasi -steady model meth od. Then the gust responses in a one -minus -cosine gust velocity profile are analyzed with two freedoms of motion in plunging and pitching for the rigid and flexible airplane models.