科研之友
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摘要
The disruption of simulated fuel droplets in supersonic flow is examined experimentally in a drawdovvn supersonic wind tunnel. The droplets are accelerated in the supersonic flow, achieving supersonic velocities relative to the surrounding air with relative Mach numbers as high as 1.8 and Weber numbers as high as 300. Monodisperse 100-mu m-diam fluid droplets are generated using a droplet-on-demand generator upstream of the tunnel entrance. The droplets are imaged by direct close-up single- and multiple-exposure imaging. Three test liquids were employed: 2-propanol and tetraethylene glycol dimethyl ether as nonvolatile fluids, and a more volatile 50/50 hexanol-pentane mixture. The decreased static pressure in the supersonic stream had the potential to give rise to superheating of the droplet fluid, as in some eases, the static pressure became significantly lower than the vapor pressure of the droplet liquid. Droplet lifetimes for the hexanol/pentane mixture appear to be shorter due to accelerated vaporization consistent with superheating, although little impact is observed on the droplet velocity and relative Mach number. Droplet-disruption patterns for these supersonic flow conditions can be classified into four different flow regions by considering the changes in the Weber number with downstream distance as the droplets accelerate. The drag coefficients associated with the droplet disruption under locally supersonic conditions are generally higher than those expected for solid spheres, largely due to the cross-sectional area change associated with droplet deformation/breakup.
- 出版日期2012-8
