Analysis of inertial gust load relief characteristics of high aspect ratio wings

ifasd2024 Tracking Number 166

With its promise of enabling enhanced aerodynamic characteristics, the implementation of High Aspect Ratio Wings (HARWs) continues to be a key driver behind the development of novel aircraft configurations. However, due to their inherent non-classical properties associated with increased structural slenderness, HARWs are susceptible to a multitude of adverse aeroelastic phenomena related to gust load responses and aeroelastic instability. The analysis the gust responses of elastic aircraft dates to 1932, to the works of Küssner. During discrete gust encounters, an elastic structure exhibits responses comprising of several aeroelastic modes. The complexity of these multi-modal responses is exacerbated by the considerably low natural frequencies of HARWs. This is a result of the increased number of modes being stimulated by the excitation defined within the frequency range determined by a given flight speed and a gust gradient. Among approaches developed to reduce loads during gust encounters, various reconfigurable and hinged concepts have gained increased prominence recently. Extensive wind tunnel experimentation and numerical work has demonstrated their effectiveness in reducing incremental wing root loads, particularly under wider gusts. Further scope for this development includes the exploitation of the inertial shear load relief from the angular acceleration as originally observed in the context of rigid hinged and bird wings [Stevenson et al., 2023]. Whilst the above principle is strictly limited to hinged rigid bodies, the notable flexibility of HARWs still retains the possibility of exploiting the inertial load relief aspect. This research intends to explore this idea using the numerical model of a flexible cantilevered wing. The inertial shear load alleviation qualities associated with various low frequency aeroelastic modes will be explored. To enable this, classical techniques related to modal decomposition will be used to develop the study. In view of varying excitation frequency bands under discrete gusts, the inertial load relief qualities under an aggregation of the low frequency aeroelastic modes of the HARW will be examined. The insights generated will be illustrated with a focus on passive tailoring of inertial properties of HARWs (e.g., mass distribution, inertial amplification mechanisms) to improve the wing root load responses during gust encounters.