Duration: 36 months
The outer skin of flight vehicles features surface defects that may appear after several missions in a reusability context. Questions regarding such defects include: how large can they be without a heat flux peak appearing on the vehicle skin or triggering other unwanted phenomena? Can we reduce the safety margins embedded in today’s tolerances through a deeper knowledge of the air flow response to surface defects and hence prolong the life-cycle? And ultimately, can we stabilize the flow past an obstacle by carefully choosing some skin properties? Evidently, the answers to these questions have implications in terms of cost-reduction, safety and sustainability. Yet at present, tolerances applied to the size of surface defects are dictated by correlations deduced from experimental databases – see [8-9] and references therein. We propose to analyse the flow over surface defects using numerical techniques belonging to the computationally most demanding yet physically most informative stability category: global stability analysis [24]. While the latter has already seen some use on smooth surfaces [25-27], it has not yet been applied to hypersonic flows over gaps, steps and fence-like arrangements in a systematic manner, providing a comprehensive database for realistic skin surfaces as seen in practice. The purpose of the activity is twofold. First, the database will contribute to identify if and when overly conservative safety margins can be updated into less stringent requirements. Second, it will guide us through a sensitivity analysis on what strategies can be devised to stabilise the flow after a surface defect. A possible route of progress is identified at this stage: imposing a space-dependent wall temperature. Recent studies over obstacle-free configurations have proven this concept [16,28]. We will investigate it over surface defects using optimization techniques imported from data science [29].
