The primary goals of this study are to investigate turbulent combustion dynamics in high Mach number flows and to understand the influence of turbulence on the high-speed combustion phenomena. To conduct this unprecedented experimental investigation, an arc-heated hypersonic wind tunnel facility with 1-second test time is used for generating high Mach number (Mach 4.5, 6 and 9) and high-enthalpy flows of total temperature up to 3,500 K. An integrated model scramjet is installed in the test section of the hypersonic tunnel for experimental investigations in well-defined flows.
The freestream turbulence is manipulated using various combinations of meshes and a turbulence damper (a component enforcing slow flow expansion and rapid contraction). It is well known that fine meshes can break large-scale flow structures into small-scale structures to facilitate turbulence dissipation. In addition, the contraction component (turbulence damper) is designed to accelerate gas mixtures toward sonic point at the C/D nozzle throat while dampening the streamwise velocity fluctuations. The turbulence levels in flows are measured qualitatively and quantitatively using Rayleigh scattering and Pitot probe, respectively.
Flow field visualizations in a model scramjet are conducted in room temperature flows at different turbulence levels using CO2-seeded Rayleigh scattering method. The three-dimensional flow structures are acquired by scanning the two-dimensional laser sheet for Rayleigh scattering over the entire scramjet flow volume. Flow structures visualized using this novel technique depict that the jet-induced secondary flows significantly affect the subsequent flow structures. In addition, it is obvious that the increased turbulence level in freestream triggers earlier boundary layer transition and separation. Although these investigations on the 3D flow structures in the model scramjet are conducted in low-enthalpy flows, numerous important insights on the rather generic flow behaviors that will appear also in high-enthalpy flows are provided with various turbulent levels and inlet geometries.
Planar laser induced fluorescence (PLIF) method is used as the most important tool for investigating the turbulent flame in supersonic flows. Ethylene (C2H4) is directly injected into the model scramjet under various freestream turbulence conditions. The effects of the freestream turbulence, inlet geometries, and other flow properties including total pressure/temperature are studied.