Supersonic Combustion Testing with Laser Optical Diagnostics

Abstract

Achieving a fundamental understanding of the mechanism for fuel/air mixing in compressible mixing flows is vital to the combustion efficiency of supersonic ramjets (Scramjets). In order to study this fuel/air mixing process an experimental investigation of the behavior of the growth rate of compressible mixing layers has been performed in a Mach 2.0 supersonic ramjet model combustion chamber using planar laser Rayleigh and Mie scattering visualizations. Hydrogen was injected parallel to the free air stream of a rectangular test section through the base of a plate injector centered in the test chamber. The investigations have been performed for hree different flow conditions at convective Mach numbers of 0.8, 0.9 and 1.0 and have been compared to existing dta from literature. The experiments generally show that the mixing layer growth rate is a decreasing function with increasing level of compressibility, leading to much less mixing and entrainment of the compressible mixing layer in comparison to the incompressible case. In order to test new methods for mixing enhancement we have conducted shock-mixing layer interaction studies in dependence of the compressibility level, expressed by the convective Mach number Mc. A variable wedge plate (wedge angle of 7° and 15°) was located at the top wall of the combustion chamber initiating shock waves which were reflected into the mixing layer. The effect of the shock impingement on the mixing layer growth rate has been measured by the visual mixing layer thickness downstream the interaction region. Depending on the shock strength and on the shock-mixing layer interaction region slight but significant mixing layer growth rate enhancement has been measured.