NTRS - NASA Technical Reports Server

Back to Results
Aeroacoustic Analysis of Fan Noise Reduction With Increased Bypass Nozzle AreaAn advanced model turbofan was tested in the NASA Glenn 9-by 15-Foot Low Speed Wind Tunnel (9x15 LSWT) to explore far field acoustic effects of increased bypass nozzle area. This fan stage test was part of the NASA Glenn Fan Broadband Source Diagnostic Test, second entry (SDT2) which acquired aeroacoustic results over a range of test conditions. The baseline nozzle was sized to produce maximum stage performance at cruise condition. However, the wind tunnel testing is conducted near sea level condition. Therefore, in order to simulate and obtain performance at other operating conditions, two additional nozzles were designed and tested one with +5 percent increase in weight flow (+5.4 percent increase in nozzle area compared with the baseline nozzle), sized to simulate the performance at the stage design point (takeoff) condition, and the other with a +7.5 percent increase in weight flow (+10.9 percent increase in nozzle area) sized for maximum weight flow with a fixed nozzle at sea level condition. Measured acoustic benefits with increased nozzle area were very encouraging, showing overall sound power level (OAPWL) reductions of 2 or more dB while the stage thrust actually increased by 2 to 3 percent except for the most open nozzle at takeoff rotor speed where stage performance decreased. Effective perceived noise levels for a 1500 ft engine flyover and 3.35 scale factor showed a similar noise reduction of 2 or more EPNdB. Noise reductions, principally in the level of broadband noise, were observed everywhere in the far field. Laser Doppler Velocimetry measurements taken downstream of the rotor showed that the total turbulent velocity decreased with increasing nozzle flow, which may explain the reduced rotor broadband noise levels.
Document ID
Document Type
Technical Memorandum (TM)
Woodward, Richard P. (NASA Glenn Research Center Cleveland, OH, United States)
Hughes, Christopher E. (NASA Glenn Research Center Cleveland, OH, United States)
Podboy, Gary G. (NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
September 7, 2013
Publication Date
July 1, 2005
Subject Category
Report/Patent Number
AIAA Paper 2005-3075
Meeting Information
11th Aeroacoustics Conference cosponsored by the American Institute of Aeronautics and Astronautics and the Confederation of European Aerospace Societies(Monterey, CA)
Funding Number(s)
WBS: WBS 22-781-30-58
Distribution Limits
Work of the US Gov. Public Use Permitted.

Available Downloads

NameType 20050201796.pdf STI