A numerical study of mixing enhancement in supersonic reacting flow fields

Abstract

Work has been underway for a number of years at the NASA Langley ResearchCenter to develop a supersonic combustion ramjet or scramjet that is capable of propelling a vehicle at hypersonic speeds in the atmosphere or beyond. A recent part of that research has been directed toward the optimization of the scramjet combustor, and in particular the efficiency of fuel-air mixing and reaction in the engine. A supersonic, spatially developing and reacting mixing layer serves as an excellent physical model for the mixing and reaction processes that take place in a scramjet combustor. This paper describes a study of fuel-air mixing and reaction in a supersonic mixing layer and discusses several techniques that were applied for enhancing the mixing processes and the overall combustion efficiency in the layer. Based on the results of this study, an alternate fuel injector configuration was computationally designed, and that configuration significantly increased the amount of fuel-air mixing and combustion over a given combustor length that was achieved.

Hybrid LES of Detonations in Reacting Multi-Phase Mixtures

“…However, the impact of shock interactions with mixing regions is of considerable importance and needs to be understood.Past studies show that mixing is significantly reduced in free shears as the convective Mach number is increased. This consideration led Drummond and Mukunda [1989] to study the gain in mixing and combustion efficiency obtained by simulating a dual shock interaction with a reacting free shear layer, but observed moderate improvements only. This configuration was later considered analytically by Buttsworth [1996] who estimated the vorticity gain through the interaction to be only about 16%.…”

“…This configuration was later considered analytically by Buttsworth [1996] who estimated the vorticity gain through the interaction to be only about 16%. The original study of Drummond and Mukunda [1989] was a two-dimensional simulation, and the shocks impacted the shear layer before it had developed a fully unstable and self-similar state. Also, the analytical method treated the flow in the laminar limit, so that the turbulence amplification that occurs during the interaction was not included.…”

“…A primary grid of 250 x 80 x 40 cells is used to discretize the domain of 17 cm x 10 cm x 3 cm. The grid is clustered towards the centerline, to provide a proper resolution of the mixing layer, with a minimum spacing in the vertical direction of 0.1 mm, following the spatial resolution reported in the numerical simulation of Drummond and Mukunda [1989]. A refined simulation is performed to assess the accuracy of the coarser resolution.…”

DNS, LES and Stochastic Modeling of Turbulent Reacting Flows

“…The vorticity then interacts with the layer and results in a significant increase of the degree of mixing and reaction. Drummond et al (1989) and Drummond et al (1991) continued this investigation further by studying fuel-air mixing in a supersonic combustor. They describe a technique using swept-wedge fuel injectors (Northam et al, 1989) to enhance the mixing processes…”

“…Drummond and Mukunda (1988) have studied fuel-air mixing and reaction in a supersonic mixing layer and have applied I several techniques for enhancing mixing and combustion in the layer. They show that when the mixing layer, with its large gradients in velocity and species, is processed through a shock with strong cur-U vature, vorticity is produced.…”