An Investigation of Twin Supersonic Jet Coupling

Abstract

The closely spaced twin-jet configuration often seen in military aircraft is distinct from the single jet in both the flow and acoustic fields. The twin-jet plumes interact with each other weakly or strongly varying with the jet operating flow regime and Mach number. The interaction mechanisms of the supersonic twin-jet exhausting from bi-conical convergingdiverging nozzles with design Mach number of 1.23 at a separation distance of two nozzle exit diameters are investigated using near-field pressure measurements and phase-locked flow visualization to explore the twin-jet coupling. Across a series of jet operating Mach numbers, the twin-jet plumes feature three major jet motions: axisymmetric, helical, and flapping modes. The jet flapping motion is strongly augmented in the twin-jet configuration compared to the single jet case. Along the twin-jet plane, which is also the jet flapping direction, the coherent flow structures are observed to displace back and forth laterally. Because of the nature of the jet flapping motion, the near-field pressure fluctuations are markedly amplified at low Strouhal numbers, particularly along the twin-jet plane for far downstream locations. Localized arc filament plasma actuators were implemented as an active flow control tool on the twin-jet plumes to explore the coupling mechanisms. The results show that decoupling and coupling of twin-jet plumes can both be achieved, depending on the jet operating condition and the excitation parameters employed.