An acoustic noise elimination assembly is disclosed which has a capability for disrupting the continuity of fields of sound pressures forwardly projected from fans or rotors of a type commonly found in the fan or compressor first stage for air-breathing engines, when operating at tip speeds in the supersonic range. The assembly includes a tubular cowl defining a duct for delivering an air stream axially into the intake for a jet engine. A sound barrier, defined by a number of intersecting flat plates or struts has a line of intersection coincident with a longitudinal axis of the tubular cowl, which serves to disrupt the continuity of rotating fields of multiple pure tonal components of noise

Burcham, F. W.

English

NASA Technical Reports Server

United States Patent 1191 
Burcham 
[111 4,300,656 
[45] NOV. 87, 1981 
1751 
1731 
17-11 
12-21 
1511 
1521 
1581 
1561 
MULTIPLE PURE TONE ELIMINATION 
STRUT ASSEMBLY 
Inventor: 
Assignee: 
Frank W. Burcham, Lancaster, Calif. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Appl. NO.: 185,869 
Filed: Sep. 11, 1980 
Int. (21.3 .............................................. B64D 33/02 
U.S. Cl. .................................................... 181/214 
Field of Search ., ............. 181/213, 214, 219, 224, 
415/119; 60/270 R 
181/229, 222, 215-218, 220; 137/15.1, 15.2; 
References Cited 
U.S. PATENT DOCUMENTS 
3,080,707 3/1963 Vetter ................................ 137A5.1 
3,363,421 1/1968 Ferri ............................. 60/270 R X 
3,426,981 2/1969 Allcock .......................... 137A5.1 X 
3,477,231 11/1969 Paulson ........................... 181/214 X 
3,483,881 12/1969 Pike et al. .......................... 137/15.2 
3,511,337 5/1970 Pease et al. ..................... 181/214 X 
3,583,417 6/1971 Clark et  al. ..................... 181/214 X 
3,610,262 10/1971 Wise ................................ 181/214 X 
3,710,889 1/1973 Lamy .................................. 181/214 
3,819,008 6/1974 Evans et al. ........................ 181/214 
3,829,237 8/1974 Chesstnutt ..................... 137A5.1 X 
3,908,683 9/1975 Demetrick ......................... 137A5.1 
Primary Examiner-L. T. Hix 
Assistant Examiner-Benjamin R. Fuller 
Attorney, Agent, or Firm-Paul F. McCaul; John R. 
Manning 
1571 ABSTRACT 
An acoustic noise elimination assembly having a capa- 
bility for disrupting the continuity of fields of sound 
pressures forwardly projected from fans or rotors of a 
type commonly found in the fan or compressor first 
stage for air-breathing engines, when operating at tip 
speeds in the supersonic range. The assembly incudes a 
tubular cowl 12 defining a duct for delivering an air- 
stream axially into the intake for a jet engine E and a 
sound barrier 14, defined by a plurality of intersecting 
flat plates or struts 14a-14d having a line of intersection 
coincident with a longitudinal axis of the tubular cowl, 
which serves to disrupt the continuity of rotating fields 
of multiple pure tonal components of noise. 
3 Claims, 2 Drawing Figures 
1 
https://ntrs.nasa.gov/search.jsp?R=19820008926 2020-03-21T16:15:41+00:00Z
U.S. Patent Nov. 17, 1981 4,300,656 
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4,300,656 
I I 
MULTIPLE PURE TONE ELIMINATION STRUT 
ASSEMBLY 
ORIGIN O F  T H E  INVENTION 
The invention described herein was made in the per- 
formance of work by employees of the United States 
Government and may be manufactured and used by or 
for the Government for Governmental purposes with- 
out the payment of any royalties thereon or therefor. 
BACKGROUND O F  THE INVENTION 1. Field of 
the Invention 
As is known, rotors or fans for the first stage of large 
jet engines operate at speeds such that the tips of the 
blades thereof attain a velocity or “tip speed” in the 
supersonic range. Moreover, from these fans or rotors, 
when operational at supersonic velocities, there emi- 
nates a rotating field of sound pressure containing pure 
tone components of noise. Simply by eliminating these 
tonal components it is possible to reduce the noise level 
for jet aircraft by several decibels. 
The invention generally relates to acoustic noise sup- 
pression devices for use in combination with air-breath- 
ing engines, and more particularly to a pure tone elimi- 
nation assembly adapted to be mounted upstream from 
the air intake for a jet engine and employed for disrupt- 
ing the continuity of forwardly projected, rotating 
fields of pure tonal sound pressure as they eminate from 
the engine. 
2. Description of the Prior Art 
During the course of a search conducted ,for the in- 
vention, hereinafter more fully described and claimed, 
the following patents were discovered: 
5 
10 
15 
20 
25 
30 
35 
3,080,707 
3,363,421 
3,426,981 
3,477,231 
3,483,881 
3,511,337 
3,583,417 
3,610,262 
3,710,889 
3,829,237 
3,908,683 
Vetter March 12, 1963 
Ferri January 16, 1968 
Allcock February 11, 1969 
Paulson November 11, 1969 
Pike et al December 16, 1969 40 
Pease et a1 May 12, 1970 
Clark June 8, 1971 
Wise October 5, 1971 
Lamy January 16, 1973 
Chestnutt August 13, 1974 
Demetrick September 30, 1975 45 
As is known, the noise produced by jet engines oper- 
ating with supersonic relative tip speeds, in the fan or 
compressor first stage thereof includes multiple pure 
tone components forwardly propagated as a rotating 
field of sound pressure. Previously, such multiple pure 
tone noise has been attenuated with devices such as 
liners provided in the inlet. Such techniques, at best, 
tend to be partially effective and thus fail to meet exist- 
ing needs. 
Substantially all of the patents discovered during the 
course of the search contain disclosures of plates, vanes, 
or struts disposed in an intake flow path for a jet engine, 
excepting the patents to Pease et a1 and Ferri. However, 
in each instance, the purpose of the plates or vanes, as 
disclosed, is to “choke” or vary the velocity of the air 
flow for purposes of imparting supersonic speed to the 
flow for thus creating a sound barrier, particularly 
when the engine is operating at low power settings. 
This technique also fails to meet existing needs for vari- 
ous reasons, not the least of which are those which can 
be expected to attend the reduction in intake capacity 
for the engine. The patent to Pease et al, of course, 
2 
discloses a noise attenuator for a gas turbine, wherein 
attenuation is effected by sound absorbing plates having 
off-set sections for deflecting the noise path, and the 
patent to Ferri discloses a ram-jet engine. The teachings 
of these patents are not deemed relevant. It is, therefore, 
believed that the prior art is devoid of any suggestion of 
the invention hereinafter more specifically described 
and claimed. 
It is the general purpose of the instant invention to 
provide a practical, pure tone elimination assembly in 
combination with the upstream or air intake for a jet 
engine, having a bladed rotor characterized by tip 
speeds in the supersonic range. 
OBJECTS AND SUMMARY O F  THE 
INVENTION 
It is an object of the instant invention to provide an 
improved, acoustic noise elimination assembly for use in 
combination with jet engines. 
It is another object to provide a pure-tone elimination 
assembly having a capability for disrupting the continu- 
ity of a forwardly projected, rotating field of sound 
pressure developed by fans or rotors, commonly found 
in the fan or compressor first stage for air-breathing 
engines, when operating at tip speed in the so-called 
supersonic range. 
These and other objects and advantages are achieved 
through the use of a pure-tone elimination assembly 
including a tubular cowl defining a duct for delivering 
an air stream axially into the air intake for a jet engine or 
the like, and a plurality of flat, plate-like members ar- 
ranged in mutually intersecting planes having a line of 
intersection coincident with the longitudinal axis of said 
tubular cowl for disrupting the continuity of a rotating 
field of multiple pure tone components of noise, as will 
become more readily apparent by reference to the fol- 
lowing description and claims in light of the accompa- 
nying drawings. 
DESCRIPTION O F  THE DRAWINGS 
FIG. 1 is a perspective view depicting a jet or similar 
air-breathing engine having mounted thereon a multi- 
ple, pure-tone elimination assembly embodying the 
principles of the instant invention. 
FIG. 2 is a fragmented, perspective view, on some- 
what of an enlarged scale more clearly illustrating the 
assembly shown in FIG. 1. 
DESCRIPTION O F  THE PREFERRED 
EMBODIMENT 
Referring now to the drawings, with more particular- 
ity, wherein like reference characters designate like or 
corresponding parts throughout the several views, 
55 there is shown in FIG. 1 a jet engine, generally desig- 
nated E and having a bladed rotor R, equipped with a 
pure tone elimination assembly, generally designated 
10, which embodies the principles of the instant inven- 
tion. 
With reference to FIG. 2, it can be seen that the 
multiple pure tone elimination assembly 10 includes a 
tubular cowl 12 projected forwardly from the blades of 
the rotor R for the engine E. Hence, it should be appre- 
ciated that the air stream entering the inlet of the engine 
65 E first is caused to flow axially through a tubular cowl 
, 12. 
Within the cowl 12 there is disposed a sound barrier, 
generally designated 14. The barrier 14 is affixed or 
50 
60  
4,300,65 6 
3 4 
anchored in the cowl 12 and is employed to disrupt the noise level for the engine E is reduced on the order of 
continuity of the rotating noise field propagated from several decibels. 
the tips of the rotor R. Thus the barrier serves to elimi- In view of the foregoing, it is believed to be readily 
nate the multiple pure tones as they eminate from the apparent that the multiple pure tone elimination device 
engine E. As a practical matter, the barrier 14 is, where 5 provides a practical solution to the problems heretofore 
so desired, employed also for purposes of mechanically encountered in eliminating pure tone noise developed 
supporting the cowl, and thus the barrier renders a dual by larger jet engines, such as those employed as power 
function. plants for large transport aircraft. 
As shown in the drawings, the barrier 14 includes 
four struts, designated 14a-14d. These struts are ar- 10 
ranged to form a cruciform and intersect along a line 
coincident with the longitudinal axis of symmetry for 
the cowl 12. In practice, it has been found that the 
dimension of the struts along their lines of intersection 
preferably is equal to the diameter of the rotor R. 
It should also be apparent that in many instances it 
may be more advantagous to use three or even two 
struts of greater lengths for purposes of achieving a 
similar result while yet reducing weight. In any event, 
tthe barrier 14 is positioned upstream from the rotor R 20 
and is of a length sufficient to disrupt the rotating field 
of multiple pure tones, sufficiently for preventing the 
field from redeveloping upstream from the barrier 14. 
Thus the noise developed by the tips of the rotor R, at 
supersonic speeds, is attenuated fro thereby greatly 25 
reducing the level of the objectionable noise which 
attends the operation of the rotors or fans employed in 
jet engines, particularly those commonly referred to as 
“larger” jet engines for “heavy” aircraft. 
tion, the operation of the inveption herein disclosed and 
claimed readily is apparent as it suffices to understand 
that a rotating field of multiple pure tones propagated 
by the tips of the rotor R, operating at supersonic 
speeds, is disrupted and then prevented from reassem- 35 rotor. 
What is claimed is: 
1. A pure-tone elimination assembly adapted to be 
mounted upstream from the air intake for a jet engine 
characterized by a bladed rotor having operational tip 
speeds in the supersonic range, whereby the engine is 
further characterized by a forwardly projected rotating 
15 field of multiple pure-tone noise at operational speeds, 
comprising: 
A. a tubular cowl defining a duct for delivering an 
airstream axially into the air intake for said engine; 
and 
B. a plurality of struts for disrupting the continuity of 
a rotating field of multiple pure-tone components 
of noise comprising a plurality of flat, plate-like 
members arranged in mutually intersecting planes 
and having a line of intersection coincident with 
the longitudinal axis of said cowl. 
2. A pure-tone sound elimination device as defined in 
claim 1 wherein said plurality of struts comprise at least 
four flat, plate-like members arranged in an intersecting 
configuration conforming to a cruciform and having an 
It is believed that in view of the foregoing descrip- 30 axis of intersection coincident with the longitudinal axis 
of said cowl. 
3. A pure-tone sound elimination assembly, as defined 
in claim 2 having a dimension along said axis of intersec- 
tion at least as great as the diametric dimension of said 
bling upstream from the barrier 14, whereby the total * * * * *  
40 
45 
50 
55 
60  
65 


Multiple pure tone elimination strut assembly

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