Unsteady Ballistic Code for Performance Predictions
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Abstract
The Solid Propellant Rocket Engine by its very nature embodies, in its chemical properties and geometry, the whole history of thermofluid‐dynamic and characteristic quantities from ignition to burn‐out.
Thus prediction is one of the most critical means for its management and utilization, in terms of guaranteeing performance and other elements, such as cost‐effectiveness.
Especially in the context of space propulsion, the typical dimensions and power of these engines and the fact that they are not reusable in most instances, make them very expensive systems, as do their full scale ground static tests, which obviously require facilities and a logistical preparation on a grand scale. These are inevitable and necessary both for the qualification in the design phase and for the verification of changes implemented during the years of service as boosters of the first stage of a launcher. However a limitation of such tests would allow a significant lowering of the costs in both phases. Hence reliable predictions can be critically important.
This is the perspective from which the present work is conceived; its purpose is the creation and development from first principles of an unsteady ballistic numerical code able to calculate the performance of solid propellant rocket engines from ignition to burn‐out.
The request of such a project from Avio is motivated by the necessity to have a single and reliably based code, that represents a safe starting point for the development of a more complex one, to be enriched in time with changes dictated by later needs. At present two separate codes are used for numerical
Unsteady Ballistic Code for Performance Predictions
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predictions, one for the ignition transient and the other for the stationary phase, respectively. Currently there is not one single code, which can be used and modified according to necessity, capable of simulating the whole rocket operation history.
The difficulties of developing a suitable model deal with the choice of the numerical solver and its management in relationship to the complexity of the problem under consideration; the simulation of the entire phenomenon requires, in fact, the modeling of a number of rather complex processes and phenomena (combustion of the propellant grain, exchange of heat, erosive burning, etc.), which all play an important role; for this reason it is inevitable that the mathematical model adopted represents a significant simplification of the real problem.
The present work describes the problems faced and the aspects considered for the realization of the code, starting from the analysis of a simple physical problem like the realization of a core module capable of resolving basic problems whose exact solution is known (this is in fact the main requirement of Avio); the results obtained will serve for the validation of the same code. In the following chapters two further aspects of the work are presented, namely (i) the treatment of the more general problem related to the phenomenology of the combustion of a propellant grain in a rocket motor and (ii) the realization of a more complex code able to deal with the problem as a whole.
Finally, in order to assess its effectiveness and accuracy, the final program has been tested on the MPS of Ariane 5. This is the most complex motor for its geometry and is well known by Avio, given its current and frequent use in a number of flights since 1996 as the booster of the European launcher.
As a last validation run, to be considered secondary given the shortage of data currently available, a test has been conducted on an experimental motor
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(Zefiro16) fired on the ground during the development phases of the new VEGA launcher, which will be completed in the next few years and will join the Arianespace fleet as a more economic and flexible solution for low Earth orbit injection of small payloads.
