Aeroacoustics of Three-Stream High-Speed Jets from Coaxial and Asymmetric Nozzles

Abstract

The development of three-stream variable-cycle turbofan engines for tactical aircraft provides an opportunity for noise reduction by shaping the exhaust of the secondary and tertiary streams. The paper reviews an experimental study of subscale three-stream jets operating at high specific thrust and issuing from rapid-prototyped nozzles. Exhaust conditions at four set points, with variable tertiary pressure ratio and bypass ratio, were determined using thermodynamic cycle analysis. Nozzles were fabricated for each set point and featured coaxial and non-coaxial exit geometries. The operating conditions were simulated using precisely metered helium-air mixtures, and far-field noise surveys were collected using a 24-microphone array. For a low-bypass ratio, a coaxial configuration offers no significant noise benefit compared to the single-stream primary jet. Configurations with offset secondary or tertiary streams offer significant noise reduction in the direction of the thicker flow. For an overall bypass ratio around 0.5, reductions of 5.1 dB in overall sound pressure level and 4.2 dB in effective perceived noise level were attained.

Influences of nozzle pressure ratio on flow characteristics of serpentine multi-stream supersonic nozzle

“…The stealth performance heightens utilizing the serpentine configuration [5]. The jet noise is signally reduced by shielding the high-speed main flow from the low-speed third flow [6]. In addition, the rectangular nozzle exit has the unique advantages in the integration with aircraft, infrared suppression and thrust vector control [7].…”

Imprint of Vortical Structures on the Near-Field Pressure of a Turbulent Jet

“…[6] and [7]. In a time-averaged sense, the action of the turbulent eddies that dominate sound production is represented by the statistics on the surface of peak Reynolds stress, abbreviated here as SPS.…”