CFD Analysis of an Inlet-Isolator Combination for Dual Mode Scramjet Applications

The dual mode scramjet is a promising high-speed air breathing engine concept with great potential of powering any aircraft in the Mach number range of 3 through 12. This paper describes an inverse design method for the construction of a morphing dual mode ramjet-scramjet engine forebody configuration. The configuration is carved from the exact solutions of 2D flow fields. Through the coupled use of the exact solutions of shock waves in an ideal gas, and the exact representations of planar stream surfaces, a series of elementary configurations are developed and pieced together to form stream tubes. Further, these tubes are pieced together to form the complete scramjet inlet configuration. Once configurations of reasonable shapes are derived, they are analyzed through the use of explicit engineering correlations. An integral part of this research is the development of a FORTRAN F90 code, where the design process is accomplished through the use of specially developed subroutines. In addition, the program is very flexible, and allows for the manipulation and assembly of the elementary planar stream surfaces into stream tubes, and even into full engine forebody configurations. In this study, the elementary shapes of interest include the star-shaped leading edges and the caret-shaped waveriders. Viscous aerodynamic engineering correlations were used to develop algorithms that evaluate the performance of the scramjet forebody, including its inlet and its isolator performances. Studies that include the engine maximum operating conditions, such as, dynamic pressures, temperatures and back-pressure ratios, were also conducted. This paper not only documents the design procedure, but also attempts to validate the design concept through the use of independent CFD packages. As part of this effort, a Mach 5 scramjet forebody configuration was evaluated using both Fluent and AVUS in an attempt to validate its performance. The results of these studies are documented in this paper. In addition, parametric studies were conducted on the 4-point star configuration with respects to its performance over the entire hypersonic flight corridor. Preliminary findings indicate that the inverse design process is fairly accurate, and that the performance of the resulting configuration offers very attractive qualities to the scramjet designers.