Dynamics of Self-Pulsation in Gas-Centered Swirl Coaxial Injector: An Experimental Study

Experimental investigations on the self-pulsation dynamics in a gas-centered swirl coaxial atomizer are conducted using water and air. Experiments are performed in the pulsation regime by precisely varying the momentum flux ratio for different values of swirl number, recess length, and lip thickness. High-speed imaging is used to understand the underlying mechanism of the onset of pulsation. While the transition to the pulsation regime takes a route of intermittency in a nonrecessed injector, the transition in a recessed injector is seen to be spontaneous. The spray width fluctuates significantly in the pulsation regime, and hence the temporal variation in the spray width is used to characterize the pulsation frequencies. Three factors, the constrained shear layer instability between the liquid and the gas streams inside the recess region, the spread rate of the gas jet, and its interaction location with the liquid stream, are shown to dictate the presence of dominant pulsation frequencies and even their higher harmonics in many recessed configurations. It is further shown that the nondimensional pulsation frequency depends only on the lip thickness and is independent of the flow and other geometrical parameters of the injector considered in the present paper.