ID 362

Effect of modulation of the liquid and gas flow rates and of the gas swirl ratio on the structure of a spray produced by a two-fluid coaxial atomizer under the effect of strong electric fields

 

Abstract:

The effect of modulating the gas swirl ratio, and the liquid and gas flow rates on the droplet size and number density distributions is experimentally studied. A coaxial two-fluid atomizer with laminar liquid turbulent gas jets is investigated using two-camera high-speed stereo visualizations, as well as interferometry droplet size and velocity measurements. The liquid mass loading is kept small, while the gas momentum ratio is varied from 5 to 125, and the swirl ratio ranges from zero to 1 (equal stream-wise and cross-stream flow rates). The flow rates are perturbed via harmonic sonic and ultrasonic forcing of the gas and liquid injection rates. The effect of the flow rate modulation, frequency and amplitude, on both the spray primary instabilities and the drop size distribution are characterized. We also investigate how the swirl ratio can be used to finely tune external perturbations, aimed at achieving better spray control. The laminar liquid stream is charged by the strong local electric field created between the metallic injection needle used as the anode, and a ring located on the streamwise end of the coaxial gas chamber used as the cathode. The electric charge in the liquid depends on the liquid and gas flow rates, and affects the primary instabilities, thus feeding into the variables modulated in the overall spray control strategy.