Cavitation in Two-Dimensional Asymmetric Nozzles

Diesel fuel spray characteristics are thought to depend on cavitation inside the fuel injector nozzles. These nozzles are very small and the fuel flow is very fast, making experimental observation very difficult. Numerical simulation of the two-phase flow is hindered by the severe density difference between the liquid and vapor as well as the existence of complex free surfaces. Recent experimental and numerical advances are now permitting visual observation of real-scale cavitating flow and two-dimensional simulation of the cavitating flow. In contrast to past work, we have chosen to study asymmetric nozzle flow. Asymmetry is more representative of real injector geometry than symmetric nozzles and may yield more reproducible results.

Experimental runs of 1 mm long nozzles were made at upstream pressures up to 120 bar with downstream pressures from 1 to 50 bar. Photographs of planar asymmetric nozzles revealed complex transient structures on the fuel-vapor interface. The nature of these structures depended on both the upstream and downstream pressure. Numerical simulation of selected experimental cases predicted nearly identical vapor location. The numerical simulation also provided predictions of the velocity and pressure field. Numerical simulations of a different geometry with an upstream pressure of 1000 bar predicted a strong, chaotic cavity oscillation with a frequency of about 26 to 33 kHz.