Abstract
Efficient mixing and combustion in supersonic flow is critical for developing hypersonic airbreathing propulsion systems such as scramjet engines. The short residence time of a few milliseconds of inflow air in a scramjet combustor make it very difficult to achieve efficient and fast fuel/air mixing. In supersonic flow, the compressibility effect suppresses the development of planar free shear layers, which play an important role in low-speed turbulent mixing. For this reason, a mixing strategy based only on planar shear layers cannot be effective, as it requires the use of impractically long engines that result in weight and heat transfer penalties. One of the efficient methods to enhance and accelerate mixing in supersonic flow is to induce streamwise vortices. Because streamwise vortices swirl perpendicular to the airflow, they are less susceptible to compressibility effects and are advantageous for enhancing the mixing process between the injectant and the airflow. Experimental and computational studies on mixing enhancement by streamwise vortices have been extensively conducted over several decades. Therefore, this paper reviews and summarizes research progress on mixing enhancement using streamwise vortices for four widely studied physical devices: lobed mixers, ramp injectors, pylon injectors, and strut injectors. In addition, the mechanisms for generating streamwise vortices, the flow structures of these physical devices, and the effect of streamwise vortices on mixing enhancement are provided.
Published Version
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