Model deformation measurements at ARA

There are a number of reasons for the increasing interest in recent years in the determination of true model shapes in industrial wind tunnels. The primary goal at the Aircraft Research Association (ARA) is to provide validation data for fluid-structure interaction simulation capabilities, both in-house and for our customers, which combine finite element structural analysis tools with traditional computation fluid dynamics codes. As commercial and industrial techniques such as RANS approaches have increased in accuracy, the impact of deformation on, for example, section pressure profiles, has become clearer and, if not properly accounted for, results from CFD will not match up with experimental data. This then feeds in to an ultimate goal of building aircraft wind tunnel models that deform in the same fashion as the true aircraft structure. This is an increasing motivation as new, lightweight materials are sought to reduce fuel burn. A further driver follows the rising trend in wind tunnel testing to move beyond mean static measurements towards dynamic, time-resolved data that can offer greater insight, especially for off-design conditions, which manufacturers are now committing more resources to investigating as they strive for the best possible performance. These off-design conditions can include a variety of complex flow patterns, such as transonic buffet onset, exploration of flutter boundaries & stall-flutter and even unsteady phenomena such as gust loading. Better understanding of these limits can avoid the extra structures of overly conservative designs necessary due to lack of information and surety about the onset and dynamics of these highly unsteady flow regimes.