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This paper concentrates on the fuel regression rate characteristics of hybrid rocket motor with helical grain and attempts to overcome the low regression rate shortcoming of conventional hybrid rocket motor. Both three-dimensional numerical simulations and lab-scale firing tests are conducted to analyze the regression behavior of solid helical fuel grain. Gaseous oxygen and polyethylene are utilized as the propellants. Head axial injection method and Laval nozzle are adopted in the motor. A steady numerical model based on pure-gas-phase reaction assumption is established. Flow field characteristics of the hybrid rocket motor with helical grain are identified through three-dimensional numerical simulations. Simulation results show that the helical structure can both increase turbulence kinetic energy and swirl number in the flow field. These two factors both contribute to the increase of the fuel regression rate. Geometric factors influencing the fuel regression rate are thread pitch, groove depth and groove width. Experimental results reveal that the fuel regression rate increases with the increase of the groove depth and the groove width. The thread pitch can also obviously influence the regression behavior of the helical grain. Overall, the helical grain can effectively increase the fuel regression rate of hybrid rocket motor. [ABSTRACT FROM AUTHOR]

This paper attempts to research and predict the effect of the convention aluminum particle additives on the performance of the HTPB/98HP hybrid rocket motor with the numerical approach. The aluminum particle is injected to the flow field in form of droplet from the grain surface, and then simulated by the discrete phase model. A CFD code has been developed to solve the coupling mass, momentum and energy equations of gas and solid at the grain surface, as well as the initial parameters of the aluminum droplet. A good agreement exists between the calculated regression rate from numerical model and the experimental data, indicating that the accuracy of applying numerical approach to predict the characteristics of aluminum metallized HRM is acceptable. Series of static numerical simulation have been conducted to determine the effect of aluminum particle property on the combustion and specific impulse performance of the HRM. The regression rate increases with the weight fraction of convention aluminum particle, but shows no distinguished correlation with the particle diameter. The characteristic velocity and vacuum specific impulse display a strong dependence on the particle diameter. The results illustrate that the proposed numerical approach is potentially an effective tool for predicting and investigating the enhancement of the regression rate and performance of the HRM with the addition of aluminum particle. [ABSTRACT FROM AUTHOR]

Hybrid rocket motors (HRMs) easily achieve variable thrust by changing oxidizer mass flow rate. This paper represents numerical and experimental studies on the throttleable HRM with aerospike nozzle, which can enhance the performances of the throttleable HRM theoretically. By comparing the performance of the throttleable HRM with the aerospike nozzle and that with the de Laval nozzle, the characteristics of the aerospike nozzle applied to the throttleable HRM are explored. Both numerical and experimental investigations are conducted. In the simulation part, characteristic velocity, combustion efficiency, thrust coefficient and specific impulse of the HRM with the two types of nozzles at different oxidizer mass flow rate are obtained. Comparing with the HRM with the de Laval nozzle, the HRM with the aerospike nozzle can improve specific impulse by about 8.9%∼23.4% when the working pressure ratio is lower than the design pressure ratio. The combustion efficiency of the throttleable HRM with the aerospike nozzle is 3.9%∼8.6% higher than that with the de Laval nozzle because of the core structure of the aerospike nozzle. When the oxidizer mass flow rate is 50 g/s, the thrust coefficient of the aerospike nozzle is increased by 12.3% relative to that of the de Laval nozzle which flow separation occurs in. The corresponding firing tests are performed by the lab-scale motor with 90% hydrogen peroxide (HP) and polyethylene (PE) grain. The numerical and experimental results agree well. The combination of the throttleable HRM and the aerospike nozzle has the advantages to improve the performance of HRMs. [ABSTRACT FROM AUTHOR]