Numerical Study of Start Strategy for Ram Accelerator at the Time of Low Injection Pressure.

Abstract

A numerical tool is used to study the role of an ignition tube in the Hiroshima University ram accelerator (named HURAMAC), a unique rectangular shape ram acceleration tube utilized the optical visualization of flow fields. The finite difference method is used to obtain the solution for the reactive gas flow field. An adaptive multi-level grid system is employed for the purpose of effectively using fine mesh points. A detailed methane and oxygen reaction model is considered for the calculation of combustible mixtures. As shown in the simulation results, the process of shock induced ignition and flame propagation is achieved in the ignition tube. After the projectile is moved into the ram acceleration tube where the gas is diluted with a large amount of carbon dioxide, the combustion becomes weak. According to this simulation, it was found that the flame on the projectile surface becomes thinner and the front shock isn't strong enough to pass over the shoulder which is the throat of the supersonic diffuser. The results also show that the flame is held at a stable state in the boundary layer of the projectile surface when burning in a low energetic mixture injected into the ram acceleration tube, successfully starting the ram accelerator at an early stage. The result is a sub-detonative operation mode.