Development of Hybrid-Rocket Solid Fuel Grain with a Star-Fractal Counter-Swirl Port

Abstract

Hybrid-rocket solid fuel grain with a star-fractal swirl port was developed in our previous study to improve the fuel regression rate. The effectiveness of this grain has been demonstrated by ground combustion experiments and ballistic launch experiments. However, its characteristic-exhaust-velocity (c^*) efficiency was insufficient, and the swirl geometry of the port caused roll torque in the fuselage. In order to improve c^* efficiency and reduce roll torque, hybrid-rocket solid fuel grain with a star-fractal counter-swirl port was developed here. Combustion experimental results showed that the developed grain improves the c^* efficiency and fuel regression rate. Numerical results using computational fluid dynamics suggested that a double vortex structure (inner clockwise flow and outer counterclockwise flow) may enhance the mixing of fuel gas and oxidizer and that, compared with the original swirl geometry of the port, the counter-swirl geometry decreases the exhausted circumferential momentum flow rate from the nozzle. This may also reduce roll torque.