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Local drop-size, velocity, and liquid flux profiles were measured within conical steady sprays using a phase/Doppler velocimeter. The coflowing gas mean velocity, gridinduced turbulence intensity and length scale, and its temperature and pressure were each varied using a wind tunnel facility (gas velocity from 3 to 22.2 m/s, turbulence intensity from 2.7 to 8.6%, length scale from 8.4 to 17.8 mm, gas temperature from 300 to 750K, gas pressure from 101 to 610 kPa, and a differential injection pressure of 689 kPa). The results show that the turbulence in the gas influences the drop-size and velocity distributions. Drop mean and fluctuating velocity components were found to be close to the gas mean and turbulence velocities in regions where the drop-size-velocity correlation coefficient was low. The drop-size-velocity correlation decreased with increasing gas density and gas velocity. Drop-size distributions broadened, and the total amount of liquid vaporized increased when the turbulence intensity and scale were increased. At a given gas temperature, the amount of vaporization increased when the gas density was increased and the overall drop size (a flux-weighted Sauter mean over the spray cross-section) also decreased. However, local drop sizes were larger in vaporizing sprays than in nonvaporizing sprays at the same gas density. This interesting result could be due to the fact that the gas viscosity increases with increasing gas temperature and this increases the drop-drag coefficient, leading to reduced radial penetration of the spray. An additional factor is that, although vaporization reduces the size of all drops, smaller drops vaporize faster and drop-size averages are weighted towards larger drops.
fuel sprays, drops (liquids), particle-size distribution, vaporizing, turbulent flow, two-phase flow
Associate professor, University of Wisconsin, Madison, WI