Large-Amplitude Gusts on the NASA Common Research Model

Abstract

Up to date, there is only little knowledge on the topic of unsteady nonlinear transonic flow, which results from large-amplitude excitations. The Certification Specifications for Large Aeroplanes, however, demand loads computations for large-amplitude excitations e.g. for gust encounters of an aircraft. In this paper, numerical solutions to the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations will be used to analyze gust responses of a transport aircraft configuration for a variety of monofrequent gusts with different lengths and amplitudes. It is shown that the unsteady nonlinear responses can lead to lower maximum lift values and lower lift derivatives compared to their time-linearized reference. These nonlinear effects diminish with increasing frequency (i.e. decreasing gust length). Though the turbulence model of Spalart and Allmaras shows completely different separation patterns than the differential Reynolds-stress model used, the variation of the turbulence model does not alter the overall qualitative findings, but has an effect on the quantitative values only.