Research and Technology | NASA Glenn Research Center

The journal article, “Computational Analyses of Offset-Stream Nozzles for Noise Reduction,” received the award of Best Paper by a Young Professional from the American Institute of Aeronautics and Astronautics Northern Ohio Section. The article, published in the Journal of Propulsion and Power (Jan.-Feb. 2009, Vol. 25, No. 1), was authored by NASA GRC’s Vance Dippold and Lancert Foster (Inlet & Nozzle Branch); and NASA Langley’s Michael Wiese (Analytical Systems and Materials).

The work described includes usage of the Wind-US code was to perform Reynolds-averaged Navier-Stokes calculations on two offset-stream-nozzle concepts for jet noise reduction. The analyses were completed in preparation for a series of experimental tests in which noise and flowfield measurements were made. The offset-stream nozzles demonstrated good performance and reduced the amount of turbulence on the lower side of the jet plume.

These computer analyses proved instrumental in guiding the development of the final test configurations and giving insight into the flow mechanics of offset-stream nozzles. The computational predictions were compared with flowfield results from the jet-rig testing and showed excellent agreement. This work was in support of the previous Advanced Subsonic Technology program.

Computational fluid dynamics (CFD) was used to evaluate the flow field and thrust performance of a promising concept for reducing the take-off noise of dual-stream turbofan nozzles. The concept, offset stream technology, reduces the jet noise observed on the ground by diverting (offsetting) a portion of the fan flow below the core flow, thickening and lengthening this layer between the high-velocity core flow and the ground observers. WIND, a Reynolds averaged Navier-Stokes (RANS) code, was used to analyze the flow field of the exhaust plume and to calculate nozzle performance.

The CFD predictions are in very good agreement with experimental flow field data, demonstrating that RANS CFD can accurately predict the velocity and turbulent kinetic energy fields. While this initial design of a large-scale wedge nozzle did not meet noise reduction or thrust goals, this study identified areas for improvement and demonstrated that RANS CFD can be used to improve the concept.

An article documenting these results, written by RTE/Jim DeBonis, has been recently published in the American Society of Mechanical Engineers (ASME) Journal of Fluids Engineering, Vol. 131 (April 2009). This work was in support of the Quiet Aircraft Technology (QAT) program and subsequently the Subsonic Fixed Wing project under the Fundamental Aeronautics program.