Flow characteristics of viscous high-speed jets in axial /swirl injectors

Hongbok Park, Purdue University


A fully nonlinear model incorporating a weak viscous treatment has been developed to assess the time-dependent evolution of axisymmetric axial/swirl liquid jets using a boundary element method (BEM). By using this model, substantial efforts have been made so far in assessing the instability and unsteady atomization processes in liquid jets. By focusing on the boundary layer instability mechanism, simulations are compared against experimental/theoretical results. Results show that the boundary layer thickness is the dominant factor affecting the nonlinear wave growth near the exit plane of the orifice. In addition, virtually every ligament which is formed from the jet core breaks into smaller ligaments and this secondary instability would reduce effective SMD values. A classical swirl injector, or simplex atomizer, has also been studied. The free surface is simulated both inside/outside the swirl injector. A potential vortex is superposed on the bulk flow to simulate the swirl in modifying the current fully-nonlinear model for use in assessing its static and dynamic characteristics. For the unforced inflow condition, the static characteristics such as core radius, film thickness, spray angle and droplet size are computed for a variety of design conditions. These results show the influence of injector geometry to flow characteristics is very small. This work is expanded to dynamic characteristic analysis for a swirl injector. Calculated dynamic response for a forced inflow disturbance shows well the behavior of a swirl injector. Similar to other present works, droplet tracking algorithms have been developed to account for aerodynamic drag subsequent to ring formation. The 3-dimensional trajectory simulation for each droplet shed from the jet core shows the physical process well from drop formation to dispersion, and helps understanding of the atomization process and the formation of the spray cone in axial/swirl liquid jets.




Heister, Purdue University.

Subject Area

Aerospace materials

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