New Method for Computing Performance of Choked Reacting Flows and Ram-to-Scram Transition

An improved method has been developed to compute the thrust of a dual-mode scramjet, which is an engine with a combustor that operates both subsonically and supersonically. This strategy applies to any internal flow that can be modeled one-dimensionally. To handle the mathematical singularity at the location of thermal choking, the simple Shapiro method is expanded to create a new method that includes finite-rate chemistry and high-temperature gas properties. A forward shooting method is employed to find appropriate initial conditions for integration of the governing equations, which results in a unique transonic (choked) condition capable of reaching a supersonic state at the end of the domain. Solutions of the governing equations are computed using the propulsion code MASIV, which has been integrated into a hypersonic vehicle flight dynamics code. Computations for both ram-mode and scram-mode operations are compared to experimental results. Predictions are made for flight conditions of a hypersonic vehicle built around the given flowpath. Benefits of a pseudo-one-dimensional approach are that computational time is small and physical reasons for observed engine performance are easy to determine. Limitations include the fact that behavior of oblique shocks and other two-dimensional and three-dimensional phenomena in the combustor cannot be computed directly.