Parachute-Payload System Flight Dynamics and Trajectory Simulation

Hindawi Publishing Corporation International Journal of Aerospace Engineering Volume 2012, Article ID 182907, 17 pages doi:10.1155/2012/182907 Research Article Parachute-Payload System Flight Dynamics and Trajectory Simulation Giorgio Guglieri Dipartimento di Ingegneria Meccanica e Aerospaziale, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy Correspondence should be addressed to Giorgio Guglieri, Received 15 November 2011; Revised 2 February 2012; Accepted 14 March 2012 Academic Editor: C. B. Allen Copyright © 2012 Giorgio Guglieri. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The work traces a general procedure for the design of a flight simulation tool still representative of the major flight physics of a parachute-payload system along decelerated trajectories. An example of limited complexity simulation models for a payload decelerated by one or more parachutes is given, including details and implementation features usually omitted as the focus of the research in this field is typically on the investigation of mission design issues, rather than addressing general implementation guidelines for the development of a reconfigurable simulation tool. The dynamics of the system are modeled through a simple multibody model that represents the expected behavior of an entry vehicle during the terminal deceleration phase. The simulators are designed according to a comprehensive vision that enforces the simplification of the coupling mechanism between the payload and the parachute, with an adequate level of physical insight still available. The results presented for a realistic case study define the sensitivity of the simulation outputs to the functional complexity of the mathematical model. Far from being an absolute address for the software designer, this paper tries to contribute to the area of interest with some technical considerations and clarifications. 1. Introduction The purpose of a parachute is to decelerate and provide stability to a payload in flight. The aerodynamic and stability characteristics of the parachute system are governed by the geometry of the parachute as such careful consideration is paid to this in the design process. The effects of deployment and opening force are critical in the safe operation of the parachute and the integrity of the payload. The opening characteristics also feature heavily in the selection of geometry and other parameters in the design process. Parachutes for aerospace applications [1–4] are in general symmetric about the canopy axis. This axis passes through the center of the canopy and the confluence point of the suspension lines. The canopy is the cloth surface that inflates to provide the desired lift, drag, and stability. The suspension lines transmit the retarding force from the canopy to the payload either directly or through a riser attached below the confluence point of the suspension lines. The deceleration force may be distributed on the payload over more than one mechanical joint linked to the riser by a set of short hardly extensible strips (bridles). There are a number of different kinds of parachutes that have been designed for various applications. The different applications parachutes are typically used for pilot, drogue, deceleration, descent, extraction, supersonic drogue and stabilization, flight termination, and landing. The dynamics of parachutes are complex and difficult to model accurately. During both the inflation process and the terminal descent stage, the dynamics of a parachute are governed by a coupling between the structural dynamics of the parachute system and the surrounding fluid flow. Both of these dynamic systems must be addressed as a coupled system to gain a proper representation of the dynamic system as a whole. When the parachute is in a steady state, the air flowing around the decelerator will separate at some location on the canopy. The shedding of the vortices from the canopy can affect the stability and cause a periodic motion of both parachute and payload. The wake from a porous parachute consists of air that flowed around the canopy and air that flowed through the canopy. A payload body in the speed range of parachute usage sheds a very turbulent wake. Part of the flow that is entering the parachute is therefore of a 2 disturbed nature and should be considered regarding the aerodynamic performance of the parachute. For many types of parachutes, this change in oncoming airflow can be quite significant during the time required for the parachute to inflate. The implication of a rapid deceleration is that second-order effects are likely to be present. To summarize, calculation of parachute deployment, inflation, and deceleration requires the numerical solution to the equations of motion for a viscous, turbulent, separated airflow. The parachute is also a flexible body having dynamic behavior coupled with the behavior of the flow, which passes through and around it. From the above description it is obvious that a full-time dependent solution of this system is far from being easily feasible. To make a mathematical model that is feasible, simplifications must be made, as long as the model can be validated satisfactorily by experiment or by comparison with reference data. The overall behavior of parachutes is related to various parameters: added masses, filling time, parachute shape (inflated canopy elongation), porosity, suspension line length, reefing, clustering, snatch loads at deployment, and aero-mechanical and inflation instability. In the past, most of these effects could be generally modeled in an imprecise way by simulation tools. A comprehensive computational technique is presented in [5–7] for carrying out threedimensional simulations of parachute fluid-structure interactions, and this technique is applied to simulations of airdrop performance and control phenomena in terminal descent. The technique uses a stabilized space-time formulation of the time-dependent, three-dimensional NavierStokes equations of incompressible flows for the fluid dynamics part. A finite-element formulation derived from the principle of virtual work is used for the parachute structural dynamics. The parachute is represented as a cablemembrane tension structure. Coupling of the fluid dynamics with the structural dynamics is implemented over the fluidstructure interface, which is the parachute canopy surface. According to the different missions, several types of payloads have been used in combination with aerodynamic decelerators: paratroops, equipment, hardware, materiel, weapons, missiles, aircraft, unmanned aerial vehicles, aerospace lifting, and nonlifting spacecraft. The present analysis is focused on aerospace applications for planetary and atmospheric entry vehicles, where the payload is typically a blunt body. (...truncated)