High-fidelity Flight Simulation Of Parachute-payload System:the Multibody Dynamics Approach And Fluid-structure Interaction Approach

Parachute is the most widely used aerodynamic decelerator and stabilizer in aerospace field.Due to the complicated aerodynamic characteristics of parachute and uncertain factors of flight environment,it is difficult to predict the dynamics behaviour of parachute-payload system(PPS),which caused a lot of trouble to the engineering application and design of PPS.With the help of numerical simulation,the performance of PPS can be accessed,which provides a reference to later evaluation,validation and optimization.On the other hand,compared to experiment,numerical simulation also reduces time and cost of the PPS design process.Most of current PPS simulation programs are in-house code for some specific PPS,which introduce a lot of hypothesis to simplify the programming task.These programs have poor versatility and scalability,as well as very low fidelity.The goal of current research is to develop better simulation algorithms and improve the software architecture,and both the multibody dynamics approach and the fluid-structure interaction(FSI)have been studied.The details are as follows:A modularized computational environment architecture based on dynamics components is given,which treats the basic objects(e.g.parachute,payload,deployment bag,et al.)and basic process(e.g.stripping,inflation,contact et al.)as standalone components.The complete flight process is composed of multiple components.Based on this approach,the more general basic environment models and high fidelity dynamics models for atmospheric flight are given,in which unreasonable hypothesis are eliminated.Typical airdrop process such as single small cargo drop and heavy cargo drop are analysed in detail,and then modeled by the given components.The state functions of complete PPS flight process are given,and the usage of dynamics components is demonstrated.The corresponding software architecture design scheme,module composition,execution flow,and the underlying dynamics algorithm and the implementation of the front-end user interface are given in detail.In addition,a parallel Monte Carlo simulation method and a flexible 3-D visulization method is presented.The PPS simulation software named PACE(PArachute-payload System Computational Environment)is developed,and the basic models such as environment models,dynamics models,et al.,are validated by several selected validation cases.Moreover,high-fidelity simulation of single small cargo drop,many small cargo drop,single heavy cargo drop and multiple heavy cargo drop are conducted.As the FSI approach,an adaptive moving mesh method to simulate the parachute flow in a finite mass scenario is presented.The method is based on Arbitrary Lagrangian-Eulerian(ALE)formulation and accounts both the parachute and payload motion during decelerating.The method is first validated by comparing parachute open force and descent velocity results with the USAF C-9 canopy drop test data(both single canopy and cluster),then this method is applied to the investigation of a smallscale parachute-payload system's performance.Three types of fabric with different permeability are considered as parachute canopy,the influence of canopy permeability on key performance parameters–openning characteristics,terminal descent characteristics,stability,etc.–is studied.Comparative analysis of the vortex structure and vorticity features under different canopy permeability is also conducted,and the FSI mechanism of unstable angle oscillation during parachute descent process is investigated.