Shock enhancement and control of hypersonic mixing and combustion

Abstract

The possibility that shock enhanced mixing can substantially increase the rate of mixing between coflowing streams of hydrogen and air has been studied in experimental and computational investigations. Early numerical computations indicated that the steady interaction between a weak shock in air with a coflowing hydrogen jet can be well approximated by the two-dimensional time-dependent interaction between a weak shock and an initially circular region filled with hydrogen imbedded in air. An experimental investigation of the latter process has been carned out in the Caltech 17 Inch Shock Tube in experiments in which the laser induced fluorescence of byacetyl dye is used as a tracer for the motion of the helium gas after shock waves have passed across the helium cylinder. The flow field has also been studied using an Euler code computation of the flow field. Both investigations show that the shock impinging process causes the light gas cylinder to split into two parts. One of these mixes rapidly with air and the other forms a stably stratified vortex pair which mixes more slowly; about 60% of the light gas mixes rapidly with the ambient fluid. The geometry of the flow field and the mixing process and scaling parameters are discussed here. The success of this program encouraged the exploration of a low drag injection system in which the basic concept of shock generated streamwise vorticity could be incorporated in an injector for a Scramjet combustor at Mach numbers between 5 and 8. The results of a substantial computational program and a description of the wind tunnel model

Investigation of a contoured wall injector for hypervelocity mixing augmentation

“…Large-scale stirring of the flow field will result directly in increased molecular-scale mixing as the interfacial area between the two gases in increased and species gradient dimensions decreased. Further, Marble et al 5 showed that the time-scale on which the mixing occurs is short enough to be of interest for combustion enhancement in scramjet applications.…”

“…A geometry was conceived in April 1987 and presented by Marble et al 5 • A diagram of the injection geometry is shown in Figure I. The injector consists of alternate compression ramps and expansion troughs.…”

Experimental Investigation on Flameholding Mechanism and Combustion Performance in Hydrogen-Fueled Supersonic Combustors

“…Such influences can subsequently lead to the interactions of a shock-mixing layer and shock-boundary layer inside the combustor. While the shockmixing layer interactions may enhance the overall mixing rate (Marble, 1990), the shock-boundary layer interactions may induce boundary layer separation and hence form a low-speed recirculation flow (Shapiro, 1953). Obviously, the induced boundary layer separation would cause problems for most hypermixer fuel injectors mounted on the combustor wall, since the local flow is preferred to be supersonic without separation (Drummond, 1991).…”

Interaction of Vortex with Bow Shock Wave: Computational Model, Experimental Validation, Enhanced Mixing

“…Such flow situations with high velocities and short residence times require that fuel and air mix and burn quickly to avoid excessively long combustors. It is well known that the shearlayer growth rate diminishes significantly with increasing convective Mach numbers, and as such, the mixing in high-speed flow is slow [1][2][3][4][5]. Various studies on slot injection into a supersonic flow have been reported in an attempt to enhance the mixing efficiency.…”

“…Such transverse injection schemes have undergone diverse modifications to enhance the mixing characteristics. Novel techniques such as shock enhancement [2][3][4][5], two-stream injection [6,7], oscillating shock wave [8], hypermixing nozzles [9], controlled swirling injectors [10,11], and aeroramps [12,13] have been considered with varying success. A rather comprehensive review of various injection schemes has been carried out [14].…”