Abstract
Numerical studies of droplet-laden spatially developing shear layers are conducted with a high convective Mach number (Mc = 1.0), in which a high-order hybrid weighted essentially nonoscillatory scheme is used for the turbulence as well as shock capturing. The evaporating droplets are tracked as point mass in the Lagrangian manner, and the two-way coupling between the flow and droplets is considered by adding the source terms to the governing equations of the gas-phase. This research focuses on the preferential concentration of droplets and the interactions between droplets and eddy shocklets in the shear layers with high flow compressibility and analyzes the underlying mechanisms of momentum and thermal response behaviors of droplets to eddy shocklets. The segregation of droplets exhibits the strongest spatial preference in the highly compressible shearing vortices, and droplets tend to accumulate as stripes behind the shocklets, associated with the coherent structures. The high flow compressibility results in the strong spatiotemporal variations of pressure and temperature, and the distributions of the expansion zones with low temperature and the compression zones with high temperature occur alternately in the shear layer. The relaxation response behaviors of the droplets to the change of momentum and thermal features of the surrounding carrier gas result in the delay of droplet evaporation in the high temperature region and then the enhancement of droplet-vapors in the low temperature region. The present observations can be ascribed to the interactions between the dispersed droplets and the distributed eddy shocklets in the shear flows with high compressibility.
Highlights
The multiphase compressible/supersonic flows laden with dispersed droplets occur commonly in various natural and engineering applications, such as spray combustion of liquid fuel in engines, atmospheric dispersion of pollutants, and so on
Numerical studies of droplet-laden spatially developing shear layers are conducted with a high convective Mach number (Mc = 1.0), in which a high-order hybrid weighted essentially nonoscillatory scheme is used for the turbulence as well as shock capturing
Scitation.org/journal/adv with the acoustic time.[29]. This feature leads to the strong change of the gas pressure, and the fluctuating amplitude could be the same order with the dynamic pressure during the turnover of the large eddies in the shear layer
Summary
The multiphase compressible/supersonic flows laden with dispersed droplets occur commonly in various natural and engineering applications, such as spray combustion of liquid fuel in engines, atmospheric dispersion of pollutants, and so on. These research areas involve the transportation and dispersion of the dispersed phase as well as the droplet evaporation in the carrier phase, which are fundamental topics in the research of multiphase flow and combustion.[1] In particular, the combustion in a high-speed propulsion system such as supersonic combustion ramjets (scramjets) often faces flow compressibility. Both the rotational motion of fluid and the flow compressibility are found to become important as turbulence is highly compressible in supersonic flows. It is important to consider the physics and mechanisms of the interphase interactions between scitation.org/journal/adv droplets and compressible flows, and the research could be used to improve the design and operation of the combustion chamber of scramjets
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