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Improved Inlet Noise Attenuation by Alteration of Boundary Layer ProfilesAcoustic liners are an essential component of technology used to reduce aircraft engine noise. Flow affects attenuation due to the liner in several ways, one of which is that boundary layers adjacent to the liner refract the sound. In the case of inlet noise, the boundary layer causes sound to be refracted away from the liner, thus degrading attenuation. A concept to improve attenuation by the liner by alteration of inlet boundary layer profiles is presented. The alteration of profiles is achieved by inlet blowing. Computational fluid dynamics and duct mode propagation theory for ducts carrying a parallel sheared flow have been used to design experiments to explore such a possibility in the NASA Langley Research Center Grazing Incidence Tube using an inlet blowing scheme developed at General Electric Global Research. The effects of inlet blowing on two liner configurations were evaluated. Calculated results will be shown for blowing ratios (injected flow/duct flow) of approximately 12% and frequencies up to 3 kHz. These results emphasize changes of attenuation achieved by blowing for the two liners. Experimental results of measured flow profiles (with and without blowing) in the Grazing Incidence Tube, and of corresponding changes in attenuation by the liner due to blowing will be presented.
Document ID
20040139251
Acquisition Source
Langley Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Mani, Ramani (NASA Langley Research Center Hampton, VA, United States)
Luedke, Jon (General Electric Co. Niskayuna, NY, United States)
Jones, Michael G. (NASA Langley Research Center Hampton, VA, United States)
Nark, Douglas M. (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
September 7, 2013
Publication Date
January 1, 2004
Subject Category
Aircraft Design, Testing And Performance
Meeting Information
Meeting: ACTIVE 04: 2004 International Symposium on Active Control of Sound and Vibration
Location: Williamsburg, VA
Country: United States
Start Date: September 20, 2004
End Date: September 22, 2004
Funding Number(s)
OTHER: 781-30-14
Distribution Limits
Public
Copyright
Public Use Permitted.

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