A Front-Tracking Technique for Computing Inflatable Structures in Supersonic Flows with Shocks

In recent years, both NASA and ESA have run Technology Demonstration Missions employing Hypersonic Inflatable Aerodynamic Decelerators (HIADs), an inflatable structure cov- ered by a flexible heat shield which is used to decelerate and protect space vehicles entering the atmosphere at hypersonic speed. This paper describes a recently developed numerical technique to simulate the Fluid-Structure interaction between the hypersonic stream and the flexible structure of the HIAD. We do so by using a front-tracking/shock-fitting technique that models both the bow shock and the thin membrane of the HIAD as double-sided surfaces of negligible thickness. Shock-motion is governed by the Rankine-Hugoniot jump relations, whereas a non-linear membrane model is used to simulate the deformation of the HIAD under the combined effect of the inflation and aerodynamic pressure. Local re-meshing is used to ensure that the surface triangulations used to geometrically describe both the material interfaces and the bow-shock are conforming with the background tetrahedral grid that fills the fluid domain. The computational examples cover three different HIADs of increasing geometrical complexity. We also show that fitting, rather than cap- turing, the bow shock allows to preserve the design order of the spatial discretization scheme in the entire shock-downstream region.