The Inverse Design and Performance Evaluation of Star-shaped Hypersonic Inlets

Abstract

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 coupled forebody-inlet-isolator configuration for possible dual mode ramjet-scramjet engine application. Flow fields derived from the exact solutions of the 2D, Quasi-1D and 1D Euler equations are used as the basis from which stream lines and stream surfaces are created. Moreover, 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 Fortran90, 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. A design code was developed which delivers as its output; engine configurations along with their performance characteristics. I. Introduction I.A: MotivationAircraft designers are focusing on a revolutionary engine technology that is capable of not only propelling vehicles to hypersonic speeds, but also one that can facilitate integrated air-to-space operations. The SCRAMJET, abbreviated from the words; Supersonic Combustion Ramjet, is the latest evolution of the jet engine family. The scramjet, like its predecessor, the ramjet, is a natural extension of the jet engine concept. However, unlike the ramjet, the scramjet uses no rotating parts. The scramjet is basically an air-breathing engine designed to fly at hypersonic speeds between Mach four and twelve or speeds in the range of 2700 to 6700 mph. The scramjet engine captures its airflow from the atmosphere and compresses it by deceleration to lower supersonic speeds. Fuel is injected into the combustor and burns in the supersonic airflow. The hot, high-pressure gas leaving the combustor is accelerated to high velocities in the nozzle to produce thrust. Scramjets will enable three categories of hypersonic craft; namely, weapons, such as cruise missiles; aircraft, such as those designed for global strike and reconnaissance missions; and space-access vehicles that will take off and land like conventional airliners 1-2 .While the physical concepts behind the scramjet are very simple, the practical ramifications of constructing such an engine are quite formidable. A few of the challenges are: supersonic fuel-air mixing, aero-thermodynamic heat dissipation from both skin friction and internal combustion, and other thermal management problems associated with operating an engine at exceedingly high temperatures for extended periods of time 3 . Consequently, the flow path of the incoming air needs to be extremely precise to minimize hot spots. However, by far, the biggest challenges ar...