Abstract
The computational fluid dynamics of hybrid rocket internal ballistics is becoming a key tool for reducing the engine operation uncertainties and development cost as well as for improving experimental data analysis. Nevertheless, its application still presents numerous challenges for the complexity of modeling the phenomena involved in the fuel consumption mechanism and its coupling with the chemically reacting flowfield. This paper presents a review of the computational thermo-fluid-dynamic models developed for the internal ballistics of hybrid rockets burning gaseous oxygen with classical polymeric or paraffin-based fuels, with a special focus on the interaction between the fluid and the solid fuel surface. With the purpose of predicting the local fuel regression rate, which is the main parameter needed for the hybrid rocket design, the model is coupled with an improved gas/surface interface treatment based on local mass, energy and mean mixture-fraction balances, combined to either a pyrolysis-rate equation in the case of classical polymers, or to an additional equation for the liquid paraffin entrainment fraction of the total fuel consumption rate. A number of experimental test cases obtained from the static firing of two different laboratory-scale rockets are simulated to determine the models’ capabilities, showing very good agreement between the calculated and measured fuel regression rates with both standard pyrolyzing and liquefying fuels. The prediction of the chamber pressure measured with paraffin fuel resulted in it being more cumbersome for the single-phase flow assumption. The advantages and limitations of the models are discussed.
Highlights
The hybrid rocket is a chemical propulsion engine in which the fuel and oxidizer are separated in different physical states [1]
This paper presents the computational fluid dynamic (CFD) models defined by the authors for simulating the internal ballistics of a hybrid rocket burning either classical polymeric or paraffin-based fuels with gaseous oxygen, with an eye to their evolution
The The numerical model presented in Section 3.3.2 has been applied to the simulation of several test test cases obtained from the static firing of the sub-scale hybrid rocket burning paraffin-based fuels; cases obtained from the static firing of the sub-scale hybrid rocket burning paraffin-based fuels; the the results are discussed
Summary
The hybrid rocket is a chemical propulsion engine in which the fuel and oxidizer are separated in different physical states [1]. Analytical models later developed for liquefying fuels [7,20] are essentially modifications of the classical hybrid boundary-layer combustion theory for the entrainment mass transfer from the fuel grain and, yield the same limits as the original theory. In this framework, the numerical modeling of the rocket internal thermo-fluid-dynamics, with predictive capabilities of the fuel regression rate and overall engine performance, is becoming a key tool both in the system design process and in the experimentally measured performance-analysis stage. Numerical results are summarized and compared to the experimental data gathered by static firings of two laboratory-scale engines
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