Numerical Simulation Study Of Fluid-solid Interaction Of Supersonic Mars Capsule-parachute System

The parachute system is the most common aerodynamic decelerator in Mars exploration missions.It plays a key role in the Entry,Descent,and Landing of exploration vehicles.In the low-density Martian environment and supersonic flow field,the flexible canopy often produces violent oscillations,and instability such as wrinkles,swings and overturns appear on the edge of canopy,which greatly affects the aerodynamic deceleration performances of the parachute sy stem.However,there is a lack of understanding of the interaction process of unsteady shock waves,turbulent wakes and vortices in supersonic flow field of Mars capsule-parachute system,as well as the instability phenomenon caused by the fluid-solid coupling of flexible passive deformed canopy and suspension lines.Therefore,it is extremely challenging to study the fluidsolid interaction of the supersonic capsule-parachute system.It's also an urgent need in the field of deep-space planetary exploration,and has important theoretical research value and great engineering application significance.In this paper,a Berger-Oliger type of three-dimensional multi-layer block-structured adaptive mesh refinement strategy,a hybrid TCD(Tuned Center Difference)and WENO(Weighted Essentially Non-oscillatory)numerical algorithm and the large-eddy simulation method based on the stretched vortex subgrid model is used to deal with the strong shock waves and turbulent large scale vortex structures in supersonic flow.In addition,the flexible canopy solver of the mass-spring-damping model combined with Kirchhoff-Love thin-shell theory model and the suspension line solver similar to the two-dimensional spring model have been developed,and they have successfully been loosely coupled with the unsteady compressible fluid solver of open source VTF(Virtual Test Facility).The aerodynamic performances and flow features of supersonic Mars capsule rigid disk-gap-band parachute system and capsule flexible BoP(Break-out patch)parachute system are numerically simulated.The simulation results show that only by ensuring the resolution of the adaptive refinement grids of flow field,can the aerodynamic performances and flow features of supersonic Mars capsule rigid disk-gap-band parachute system be accurately simulated.The importance of adaptive mesh refinement resolution for numerical simulation of complex flow field is verified.Lay the foundation for further research on the fluid-solid coupling of supersonic Mars capsule flexible parachute system.It is found that the turbulent wake behind the capsule is the main reason for the flow instability of the rigid disk-gap-band parachute system.The turbulent wake behind the capsule interacts with the bow shock wave front the canopy,resulting in the formation of a low velocity backflow area and extremely unstably flow filed inside the canopy.The vortex structure formed by the periodic reverse overflowing from the inside of the canopy falls off the edge of the canopy and enters the canopy turbulent wake area.It mixes with multiple physical quantities such as turbulence and supersonic jets,resulting in a highly turbulent and enhanced disturbance in flow field,thereby reducing the aerodynamic deceleration performances of the parachute system.The influence of the presence or absence of capsule,the trailing distance ratio and flow initial Mach number on the aerodynamic performances of the flexible BoP parachute system is studied.The results show that the flexible canopy exhibits obvious periodic "breathing motion"phenomenon in supersonic flow.The trailing ratio of the capsule-parachute system is the main parameter that affects the lateral deviation of the flexible canopy,and found the relatively good aerodynamic deceleration performance parameters of the parachute system.The aerodynamic drag coefficient of the capsule flexible BoP parachute system obviously increases and the flow oscillation disturbance is the smallest,the aerodynamic performances is the best at initial Mach number 1.8 and the trailing ratio 10.51.Finally,it was found that the turbulent wake behind the capsule caused the unstable oscillation of the flexible parachute system according to the vortex dynamic analysis.The vortex structures in the wake area behind the capsule is rich,and the interaction of its movement withe the shock wave structure in the front of the canopy caused an increase in the disturbance of the flow field inside the canopy.It makes the flexible canopy produce periodic "breathing motion"phenomenon.The multi-physical interaction with turbulent flow and separated flow makes the flow vortex structure full and affects the aerodynamic deceleration performances of the parachute system.