Wind tunnel tests for gust load investigation in transonic flows – Part 1 : Development of an innovative test rig

The development of load predictions capabilities and load control strategies is a key axis for enhancing the design process of the next aircraft generation, with the aim of significantly reducing fuel consumption levels. Within the Clean Sky 2 AIRFRAME ITD framework, a specific objective is dedicated to addressing the gust load case, which is crucial for strength design and fatigue loading source for transport type aircraft particularly in the certification process. Building on the accomplishments of the Clean Sky SFWA-ITD project, a new experimental research program has been established, centred around Wind Tunnel Tests (WTT) conducted at the transonic ONERA S3Ch facility. The primary goals of this program were to deepen our understanding of gust effects, particularly in the non-linear domain, and to advance the maturity of load control approaches. The initial phase of these studies has been conducted within the framework of a project called GUDGET, aimed at developing an innovative test rig for investigating gust loads, particularly challenging in the transonic regime. Based on pre-design solutions provided by ONERA, new gust generation devices have been analysed, designed and manufactured in order to deliver deterministic vertical and harmonic gusts with larger amplitude and in a wide frequency range. Two main concepts consisting in a tandem of airfoils installed horizontally right upstream of the test section were studied, based on either dynamically moving airfoils or fixed vanes equipped with pulsed blowing slots. To investigate the effects of gusts on the aerodynamic and aeroelastic behaviour of a model, the test rig also included a wall-mounted half-wing model. This model was heavily instrumented and equipped with a suitable aileron located close to the wingtip, which was remotely actuated using a high-frequency actuation system to demonstrate real-time active gust load alleviation. Finally, the results of a first WTT campaign, carried out to qualify the unsteady flow induced by the various gust generation capabilities, are presented. The outcomes of a second WTT dedicated to analysing gust effects on the model aeroelastic behaviour for different structural and aerodynamic conditions, are presented in a companion paper [12].