Effects of properties and location in the plume on droplet diameter for injection in a supersonic stream

The mean droplet diameter in the spray resulting from transverse injection of liquid jets into supersonic airstream was investigated in detail by the use of the diffractively scattered light method. The effects of viscosity, surface tension, jet/freestream dynamic pressure ratio, injector diameter, and location in the plume on the mean droplet diameter were determined. AH tests were performed at A/^ =3.0, with P0 4.2 atm and T0 = 300 K. The injectants used were water, various solutions of glycerine and ethanol in water, and Fluorinert to produce wide variations in viscosity and surface tension. The important results can be summarized as follows: 1) the droplet size has an inverse relation with respect to jet/freestream dynamic pressure ratio, 2) the droplet diameter decreases as the measurement station moves downstream, 3) the smallest droplets are formed at the outer edge of the spray plume, 4) droplet size has a direct relation with respect to surface tension and viscosity of the injectant, and 5) at very high viscosities the jet does not break up into nominally spherical particles. For a certain range of viscosity and dynamic pressure ratio, the breakup of the jet is into ligaments rather than droplets.