This paper presents a dynamic model to numerically simulate the parachute deployment for space vehicle recovery system. In the proposed dynamic model, the deployment bag and the space vehicle are treated as a six-degree-of-freedom rigid body with mass varied and a regular six-degree-of-freedom rigid body, respectively. The parachute system is considered as the mass spring damper model, in which the canopy, suspension lines, risers and bridles are discretized into some three-degree-of-freedom segments with their centralized mass on the end points. During the deployment a notable phenomenon can be observed and so-called line sail. The line sail generally occurs during a deployment in which the relative wind is not parallel to the deployment direction. The line sail has been known to cause or contribute to the following problems: increased deployment times, changes in snatch load, asymmetrical deployment, friction damage, and unpredictable canopy inflation. To understand its mechanisms, the effects of aerodynamics such as angle of flight path, deployment bag ejection velocity, Mach number, air density and wind velocity are numerically investigated.
In order to study the safe distance between twin-parachute during their inflation process for fighter ejection escape, the fighter was equipped with two canopies and two seats, two types of parachute were used to numerically simulate their inflation process, respectively. One of them is C-9, the other a slot-parachute (S-P). Their physical models were built, then the meshes inside and around both parachutes were generated for fluid-structure interaction (FSI) simulation. The penalty function and the arbitrary Lagrangian-Eulerian (ALE) method were employed in the FSI simulation. To validate the numerical model for FSI simulation, at first the single parachute of the twin-parachute was used for the FSI simulation, the predicted inflation times for both types of parachute were compared with the experimental data. The computed results are in good agreement with experimental data. As a result, the inflation times were predicted with twin-parachute for both kinds of parachute. On the basis of the locations of ejected seats after the separation of seat and pilot, the initial locations and orientations of twin-parachute were also obtained. The numerical simulations for both kinds of parachute were performed by the FSI method, respectively. Our results illustrate that when the interval time for two seats ejected is greater than 0.25s, two pilots attached the twin-parachute are safe, and the twin-parachute would not interfere each other. Moreover, our results also indicate that the FSI simulation for twin-parachute inflation process is feasible for engineering applications and have a great potential for wide use.
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