A Combined Experimental and Computational Study of the LAPCAT II Supersonic Combustor

Abstract

Dual-mode ramjet propulsion systems are suggested for the next generation high-speed flight vehicles. Here, we combine experimental measurements of high-speed (subsonic and supersonic) combustion at different operating conditions in the LAPCAT-II dual-mode ramjet combustor with Large Eddy Simulations (LES) using finite rate chemistry models and new skeletal H2-air combustion chemistry. The LAPCAT II combustor consists of four sections, and experiments have been performed for wall injection of H2 in a Ma 2.0 vitiated air-flow for total pressures and temperatures of p0=0.40 MPa, 1414 K<T0<1707 K, and a fixed equivalence ratio of φ=0.15. For this p0 the combustor is over-expanded, and the transition from supersonic to subsonic flow occurs at the start of the fourth combustor section. The flow and combustion diagnostics include measurements of p0 and T0 upstream of the combustor, wall-pressure profiles and Schlieren and OH* chemiluminescence imaging. The computational set-up consists of the full combustor, from the nozzle to the dump-tank. The computational model is composed of a compressible finite rate chemistry LES model, using the mixed subgrid flow model and the Partially Stirred Reactor (PaSR) combustion model, together with a new 22 step H2-air reaction mechanism. Qualitative as well as quantitative comparisons between experiments and simulations show reasonable agreement, but also reveal a high sensitivity of both the LES predictions and the experiments to T0. The LES results are further used to describe the underlying mechanisms of flow, wall-injection, mixing, self-ignition and turbulent combustion, and how these interrelated processes are modified by increasing the total temperature under otherwise identical conditions.