Integrated Analysis of Scramjet Flowpath with Innovative Inlets

An overview is presented of fundamental and practical insights obtained on scramjet flowpaths during a three year Challenge Project utilizing high fidelity methodologies and advanced post-processing techniques. Simulations are employed to analyze the principal phenomena, including inlet distortion, fuel-air mixing, ignition and thrust generation at freestream Mach numbers between 6 and 8. In addition to guiding the evolution and execution of high-speed ground and flight experiments, the discovery objective of the project identifies trends and suggests optimization strategies for rapid response and kinetic kill hypersonic vehicles. Three inlet designs are considered, including the traditional rectangular cross-section configuration and two streamline traced variants denoted Scoop and Jaws, each attached to a corresponding cavity-based flame-holding combustor. The simulations reveal the characteristic distortion signature of each design. Parametric analyses provide insight into major performance issues, including the effects of distortion on combustion, injector port configurations and gaseous versus liquid (multi-phase) injection of simple and complex fuels. Some results are consistent with intuition: for example, streamwisestaggered and spanwise-interlaced injectors enhance diffusive mixing. Other findings are not intuitive and point to competing constraints. Injection strategies that enhance cavity circulation, or disturb the shear layer emanating from the step are superior. Numerical issues are also explored to understand the effect of chemistry model fidelity (frozen versus finite-rate kinetics of increasing complexity) and turbulence closure (Reynolds-Averaged Navier-Stokes and Large-Eddy Simulation [LES]). Small scales resolved with the superior LES method are essential in understanding the unsteady shock dynamics and ignition delay time.