Numerical investigation of the role of hyper-mixers in supersonic mixing

Abstract

Hypersonic air-breathing engines are considered to be the most appropriate alternative device to rocket based propulsion systems in reusable space vehicles within the lower atmospheric regime. Supersonic combustion ramjet (scramjet) engine is the key enabling technology for such sustained hypersonic flights. In scramjet engines, since the residence time of the mixture is of the order of a millisecond (for flight Mach numbers from 6 to 8) owing to the short combustor length, generation of useful thrust over the vehicle drag through heat addition at such high speeds is a challenging task. This is due to the fact that the fuel has to mix and burn completely within the short combustor length. Consequently, this places a severe limitation on the mixing time scale. This emphasises the importance of fuel injectors and mixing enhancement devices in supersonic combustors. ABSTRACTIn this numerical study, the role of hyper-mixers on supersonic mixing is investigated for six different strut configurations. To this end, 3D, compressible, turbulent, non-reacting flow calculations with air as the secondary injectant have been carried out. A qualitative comparison of the predictions with experimental results is made through Schlieren and Mie scattering images. A quantitative evaluation of the predictions is made by comparison with experimentally measured exit stagnation pressure, wall static pressure and the degree of unmixedness. Based on these results, three strut configurations have been selected for carrying out simulations with hydrogen as the injectant. Results from the hydrogen simulations are compared with the predictions using air and also across the strut configurations. The results clearly demonstrate that castellated strut configurations are very effective in enhancing mixing in such high speed flows.

Numerical investigation of the effect of strut geometries on the flow characteristics in a model combustor

“…It was found that the 14° ramp angle gave maximum mixing, and three relieved strut gave the least degree of unmixedness due to the generation of streamwise vortices. The effect of hypermixers in improving the mixing characteristics of strut-based combustors was numerically studied by Desikan et al (2010). Five strut geometries were considered in their model combustor which was studied numerically with air as an injectant and compared to the baseline wedge-shaped strut.…”

A Numerical Study on the Characteristics of Air–Fuel Mixing Using a Fluidic Oscillator in Supersonic Flow Fields

“…Passive methods use a specific structure inside the combustion chamber or change the configuration of the wall to form a vortex and recirculation zone in the flow, which result in improved air-fuel mixing performance for higher combustion performance. Various methods have been studied, such as pylons [3][4][5][6], cavities [7][8][9][10][11][12][13][14], hyper-mixers [15][16][17][18][19][20][21], injector locations [22], angles [23,24], and outlet shapes [25]. A pylon is a slim structure on the wall of the combustion chamber that generates a recirculation zone and vortex to promote air-fuel mixing and stabilize the flame.…”

“…A hyper-mixer is a system where a part of the wall of a combustion chamber has a form such as a ramp or a step. The shape generally induces a counter-rotating vortex, which helps to improve the mixing efficiency and expansion of the mixed area [15][16][17][18][19][20][21]. Studies have been carried out on adjusting the angle, arrangement, and shape of the injector [23-25] and using a swirler or counterflow nozzle [26,27].Unlike passive methods, active methods actively intervene in the flow of combustion chambers.…”