A Model for the Design and Analysis of Thrust Optimized Scramjets

The dual mode scramjet is a promising air breathing engine concept that is capable of powering any aircraft in the Mach number range of 3 through 12. This paper describes the inverse design of a tip-to-tail dual mode ramjet-scramjet engine that is derived from the exact solution of 1D and Quasi-1D flow fields. Through the coupled use of the exact solutions of shock waves in an ideal gas, and the exact representations of planar and axisymmetric geometric shapes, a series of elementary configurations are developed and analyzed. The design process is accomplished through the use of specially developed subroutines, programmed in FORTRAN, to manipulate and assemble these elementary configurations into completed engine configurations. The elementary shapes of interest to this study include the star-shaped leading edges, the caret-shaped inlets, cylindrical combustors, convergent and divergent nozzles, and plug nozzle after-bodies. An integral part of this research effort is the development of a FORTRAN code. As its output, the design code generates an engine configuration and analyzes its thrust characteristics. Further, the algorithms used to evaluate the resulting engine performance, such as its Isp, its thrust, and its maximum operating temperatures, are based on established engineering correlations. In general, the code developed as part of this research effort was used to conduct the following studies: to generate propulsion systems configurations from prescribed 2-D shock waves; to evaluate the resulting engine geometric characteristics; to evaluate the thrust performance of the engine, and; to identify the design parameters that affect the engine’s overall shape and performance. The outcome of this research can be classified in the following two categories. First, the propulsion system design and assembly process led to the discovery of engineering parameters that directly influence the aerodynamic performance of the resulting scramjet engine configuration. Second, these engineering parameters were manipulated to generate configurations with superior thrust and Isp characteristics.