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Description
Prior velocimetric diagnoses of air-blasted sprays fail to measure the velocity of the carrier gas and dispersed liquid phases individually and simultaneously over broad, continuous areas of the spray flow field. An optically and digitally discriminating, simultaneous two-phase Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) method is applied to a simplified air-blast atomizer spray using existing techniques. Nebulized gas phase tracer particles doped with Rhodamine B fluorophore emitting a Laser Induced Fluorescence (LIF) signal is filtered using an optical filter to create a unique signal for the gas phase tracer. The two-phase Mie scattering signal of the liquid droplets and gas phase tracer particles is filtered using a minimum intensity filter to remove gas phase tracer signals from the image and allow for the PTV calculation of the dispersed liquid phase. Convergence of all gas phase PIV and liquid droplet PTV measurements are quantitatively confirmed. Uncertainties in the gas phase Laser Induced Fluorescence (LIF) PIV measurements are calculated and found to be less than 5% in the low turbulence region of the gas phase jet. The gas phase tracer LIF PIV technique was shown to capture mean gas phase velocities with less than 5% error in the low turbulence region of the gas phase jet as compared to simultaneous gas phase tracer Mie PIV measurements. Minimum intensity filtered image liquid droplet PTV results are validated against Particle Doppler Anemometry (PDA) results to within approximately 5% error. The velocimetric measurements of each phase allow for the local velocity ratio, or slip, to be resolved with good spatial resolution, showing the evolution of the two-phase velocity slip from between 3-4 decreasing towards unity along the spray axis from 1.2 to 4 diameters from the nozzle exit. Calculation of the Reynolds stresses in the gas phase also show an increase in gas phase turbulence with increase in liquid flow rate. The method is shown to successfully demonstrate the exchange of momentum between the carrier gas and dispersed liquid phases within the spray and identify two distinct spray modes within the region from 1.2 to 4 diameters from the atomizer nozzle.
