Evolving one-dimensional transient jet modeling by integrating jet breakup physics

Abstract

High-speed optical measurements of unsteady liquid fuel jets under engine-like conditions have shown that the initial penetration of the jets does not follow the behavior predicted by previously introduced one-dimensional jet models based on gas-jet principles. The experimental data indicate that the transient jet penetration velocity is initially controlled by the jet exit velocity, transitioning to gas-jet like mixing-dominated penetration further downstream. This behavior is consistent with the common description of high-pressure fuel jets as containing a liquid core surrounded by entrained gas and fuel droplets. In this paper, a new one-dimensional modeling methodology is introduced that couples the transport equations for the evolution of the liquid core of the jet and the surrounding sheath of droplets resulting from breakup. This allows for the penetration of the jet to be initially governed by the liquid core, which is relatively unaffected by the ambient gas, transitioning to spray penetration dominated by the entrained ambient gas. The model also provides a defined jet centerline velocity, which allows for the shape of the radial profiles of fuel velocity and fuel volume fraction to be solved for directly, without the need for a steady-jet assumption, as was used in previous one-dimensional models. This change removes the need for a constant momentum flux assumption, improving the transient nature of the model. The results of the model are validated against the aforementioned optical transient jet measurements. The model and all associated experimental data have been made available for use at rothamer.erc.wisc.edu/dlp .