Flame Structures in a Model Solid Fuel Ramjet with Increasing Reynolds Numbers

This paper takes a step toward understanding the complex nature of the combustion dynamics within a solid fuel ramjet operating at a variety of altitudes, outlining viable strategies for performing physically accurate numerical simulations at reasonable computational costs. First, simulations of one-dimensional solid fuel diffusion flames were performed to demonstrate the effects of scaling system pressure on the flame structure. Next, a series of parametric two-dimensional numerical simulations of a planar solid fuel ramjet with hydroxyl-terminated polybutadiene as fuel were performed. A grid convergence study established a relationship between upstream flow conditions and resolution requirements at the grain surface. Simulations with increasing operating pressures were performed to analyze the altitude effects on flame dynamics. Proper orthogonal decomposition, spectral proper orthogonal decomposition, flame brush probability density functions, flame curvature, and mean field analyses were used to compare the numerical solutions each of the simulated conditions. The results showed that increasing the operating pressure (decreasing altitude) of the solid fuel ramjet combustor caused an increase in fuel regression rate and flame curvature. However, other parameters such as the flame brush and flame temperature were insensitive to the operating pressure, which indicated that combustor performance was largely self-throttling and dictated by the combustor geometry.