A Computational Fluid-Structure Interaction Study of Inflation Cycles of a Tension Cone Decelerator

Abstract

Inflatable aerodynamic decelerators present potential advantages for planetary entry in missions of robotic and human exploration. The design of these structures face many engineering challenges, including complex deformable geometries, anisotropic material response, and coupled shockturbulence interactions. In this paper, we describe a comprehensive computational fluid-structure interaction study of an inflation cycle of a tension cone decelerator in supersonic flow and compare the simulations with earlier published experimental results. The aeroshell design and flow conditions closely match recent experiments conducted at Mach 2.5. The structural model is a 16-sided polygonal tension cone with seams between each segment. The computational model utilizes adaptive mesh refinement, large-eddy simulation, and shell mechanics with self-contact modeling to represent the flow and structure interaction. This study focuses on the dynamics of the structure as the inflation pressure varies gradually, and the behavior of forces experienced by the flexible and rigid (the payload capsule) structures. I.Introduction Theoretical point-designs suggest that an inflatable aerodynamic decelerator (IAD) is a promising means for deceleration of a heavy payload into a planetary atmosphere. It offers a low mass to dragproducing area ratio for a reduced ballistic coefficient and large deceleration rates at high planetary altitudes, where atmospheric density is low. This enables higher elevation landing sites along with reduced vibration and oscillation during the entry process. Preliminary experimental results from the 1960’s along with recent experiments [1,2] indicate that the IAD may offer advantages over supersonic parachutes for high-payload deceleration, avoiding well-known instabilities encountered in these parachutes within the Mach number range of interest [3]. The aeroshell also serves as a heat shield, reducing the total weight, and cost of the mission. To date, only reduced-scale versions of these concepts have been tested in the laboratory or in test campaigns in Earth’s atmosphere [4]. Given the large number of material and flow parameters involved, there is substantial uncertainty regarding the process that should be followed to rescale the experimental drag and moments to full-scale geometries. The same uncertainties prevail in the design of representative small scale experiments. For example, how should an experiment be designed such that material anisotropies and nonlinearities of the flexible coated fabrics used in the IAD experience the same physical conditions (or regime) as in a full vehicle? Similar uncertainty arises when considering Reynolds number effects on the interaction between eddies in the flow and the fine-scale wrinkling of the fabric. In this paper, we continue results presented earlier [5,6], using a structured computational fluid dynamics (CFD) solver with adaptive mesh refinement (AMR) that is coupled with a large-deformation thin-shell/membrane finite-element solver to investigate the stability and aerodynamic behavior of a tension cone inflatable aerodynamic decelerator in supersonic flow with varying inflation pressure. The main progress discussed here is the use of an accurate structural model that closely approximates the flexible experimental model used in [1], which includes seams between the segments of the 16-sided polygonal tension cone. Two simulation sequences are performed to examine inflation and deflation of the IAD. Particular focus is given to comparison between earlier experimental and computational results and new simulations using this polygonal model.