Dynamics of sonic jet injection into supersonic crossflow

Abstract

The interaction between a sonic air jet and a supersonic air crossflow is simulated using large-eddy simulation (LES). A hybrid numerical methodology is used here to capture shock waves locally with minimal dissipation of the turbulent structures. The dynamic subgrid closure model employed for the LES permits a fully localized evaluation of the closure coefficients, such that there are no ad hoc adjustable parameters. Simulation of the experimental study of Santiago and Dutton (J. Propul. Power, vol. 13, 1997, pp. 264–273), where detailed measurements of the mean velocity and turbulent fluctuations have been acquired, is reported. The LES results show fairly good agreement with the experimental data for the mean and statistical fluctuations of the velocity field. The numerical study is then extended to two other jets in crossflow conditions to study the impact of the free-stream Mach number and of the jet to free-stream momentum ratio on the structure of the jet and on the dynamics of the interaction.

The vortical structures of the time-averaged fields are identified and related to their equivalent in subsonic jet in crossflow. Horseshoe, counter-rotating, and steady wake vortices and also hanging vortices and windward vortex pairs are highlighted from the statistical results of all three cases. An analysis of the dynamics of the unsteady interaction is presented next. Similar to the low-speed jet in crossflow, vortex generation through Kelvin–Helmholtz instabilities is observed on the windward side of the jet. Furthermore, an unsteady deformation of the windward barrel shock is identified and found to induce the ejection of pockets of unshocked jet fluid, and highly vortical shear vortices are formed. Hanging vortices, generated by the skewed mixing layer on the sides of the jet, are found to remain quasi-steady in the course of the interaction. Large-scale and unsteady vortices along the sides of the jet column are highlighted for the lower jet to free-stream momentum ratios, whereas these instabilities appear weaker for higher momentum ratio. In this case, however, the presence of windward vortices is clearly identified. These structures form at the boundaries of the recirculation zone ahead of the shock and are convected along the upper boundary of the jet. Finally, wake vortices are observed but appear to play a minor role in the mixing process.

Keywords:

• LES
• compressible flow dynamics
• unsteady vortical structures

Acknowledgements

The first author would like to thank Dr. Santiago for providing the experimental data for comparison. The authors gratefully acknowledge the support from the Air Force Office of Scientific Research (grant number FA9550-06-1-0056), with Dr. Fariba Fahroo as the technical monitor.