An Investigation of Twin Supersonic Jets' Near-field

Abstract

The near-field of twin-jets is investigated to study the twin-jet plumes’ interaction at a nozzle separation distance of two nozzle exit diameters. The linear microphone array was located close to the twin-jet plumes with various azimuthal angles relative to the twin-jet axes to record the near-field twin-jet effect. The twin-jet plumes interact and contribute to the near-field pressure amplification at different levels (weak or strong) depending on the dominant azimuthal mode motion (varying with jet Mach number). The level of twin-jet plumes’ interaction was evaluated by comparing to the equivalent single jet (with one of the twin-jet nozzles blocked). Among three azimuthal mode (axisymmetric, helical, and flapping) motions examined in this study, the twin-jet plumes (whose natural mode is determined by the jet Mach number) featuring the dominant flapping motion result in the most amplified near-field pressure response. Given by the nature of the flapping motion, the strong twin-jet plumes’ interaction is found in the preferred directivity along the flapping direction. In the twin jet this preferred direction is in the plane of the twin-jet axes. Localized arc filament plasma actuators were used as a flow diagnostic tool to confirm the understanding of the interaction phenomenon of twin-jet plumes.