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Noise reduction with lobed mixers: nozzle-length and free-jet speed effects
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Dalton, William N. Mengle, Vinod G. Bridges, James C. Boyd, Kathy C. |
| Copyright Year | 1997 |
| Description | Acoustic test results are presented for 1/4th-scaled nozzles with internal lobed mixers used for reduction of subsonic jet noise of turbofan engines with bypass ratio above 5 and jet speeds up to 830 ft/s. One coaxial and three forced lobe mixers were tested with variations in lobe penetration, cut-outs in lobe-sidewall, lobe number and nozzle-length. Measured exit flow profiles and thrusts are used to assist the inferences from acoustic data. It is observed that lobed mixers reduce the low-frequency noise due to more uniformly mixed exit flow; but they may also increase the high-frequency noise at peak perceived noise (PNL) angle and angles upstream of it due to enhanced mixing inside the nozzle. Cut-outs and low lobe penetration reduce the annoying portion of the spectrum but lead to less uniform exit flow. Due to the dominance of internal duct noise in unscalloped, high-penetration mixers their noise is not reduced as much with increase in free-jet speed as that of coaxial or cut-out lobed mixers. The latter two mixers also show no change in PNL over the wide range of nozzle-lengths tested because most of their noise sources are outside the nozzle; whereas, the former show an increase in noise with decrease in nozzle-length. |
| File Size | 1009861 |
| Page Count | 14 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_19980000198 |
| Archival Resource Key | ark:/13960/t6644p98c |
| Language | English |
| Publisher Date | 1997-11-01 |
| Access Restriction | Open |
| Subject Keyword | Acoustics Gas Jets Penetration Acoustic Properties Bypass Ratio Jet Aircraft Noise Multiphase Flow Noise Reduction Subsonic Flow Dominance Uniform Flow Low Frequencies Thrust Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
