Turbojet Engine Noise Reduction With Mixing Nozzle-Ejector Combinations Page: 2 of 34
This report is part of the collection entitled: National Advisory Committee for Aeronautics Collection and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
TECH LIBRARY KAFB, NM
ill1111IllIlll lillliIIIll
0067212
NATIONAL ADVISORY CO~ITEE FOR AERONAUTICS
TECHNICAL NOTE 4317
TURBOJET ENGINE NOISE REDUCTION WITH MIXING
N0ZZLE-EJECTOR COMBINATIONS
By Willard D. Coles, John A. Mihaloew
and Edmund E. Callaghan
SUMMARY
Several noise suppressors consisting of combinations of mixing noz-
zles and ejectors were tested on two full-scale turbojet engines. Maxi-
Smum sound pressure level reductions of 12 decibels and sound power level
reductions of 8 decibels were obtained. The ejectors provided 3 to 5
decibels of the sound power reduction. The effects of ejector dimensions
on noise suppression and engine performance were investigated. Ejector
lengths of approximately 2.0 standard nozzle diameters and ejector diam-
eters larger than 1.6 standard nozzle diameters provided the greatest
additional noise reduction to that obtained with the mixing nozzles alone.
The ejector can restore the static thrust loss caused by use of the mix-
ing nozzle or can provide static-thrust augmentation.
The noise reduction obtained from an ejector is a function of the
secondary airflow rate and results from the diffusion of the jet to lower
velocity. Velocity profiles at the ejector exit are compared with pre-
vious results obtained using conical nozzles and with calculated free-jet
boundaries resulting from normal spreading at equivalent downstream
distances.
Maximum probable noise reductions calculated from weighted local jet
velocity and area were not realized probably because the noise generated
inside the ejector is appreciable.
INTRODUCTION
Low-flying jet aircraft operating from municipal airports surrounded
by residential communities present a formidable noise annoyance problem.
In addition to the annoyance factor, however, the fluctuating pressures
of the high intensity noise are a source of structural damage to the air-
craft. Therefore, from the standpoint of both the annoyance and the
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Coles, Willard D.; Mihaloew, John A. & Callaghan, Edmund E. Turbojet Engine Noise Reduction With Mixing Nozzle-Ejector Combinations, report, August 1958; (https://digital.library.unt.edu/ark:/67531/metadc57100/m1/2/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.