NOTICE 

NASA Case No. LEW- 15,170-1 

PRINT FIG. 1 

.The invention disclosed in this document resulted from research in aero- - -- 

nautical and space activities performed under programs of the National 

Aeronautics and Space Administeration. ./ The invention is owned by NASA and is, 

therefore, avail able for 1 icensing in accordance with the NASA Patent 

Licensing Regulation (14 Code of Federal Regulations 1245.2). 

To encourage commercial utilization of NASA-owned inventions, it is NASA 

policy to grant licenses to commercial concerns. Although NASA encourages 

nonexclusive 1 icensing to promote competition and achieve the widest possible 

utilization, NASA will consider the granting of a limited exclusive license, 

pursuant to the NASA Patent Licensing Regulations, when such a license will 

provide the necessary incentive to the licensee to achieve early practical 

application of the invention. 

Address inquiries and all applications for 1 icense for this - -- invention to 

NASA Patent Counsel , Lewis Research Center, Mail Stop LE-LAW, 21000 Brookpark 

Road, Cleveland, OH 44135. Approved NASA forms for application -- -- for - -- 

nonexclusive or exclusive license are available from the above -- address. 

-- Serial No.: 046,256 - 

Filed Date: 04/14/93 

(NASA-Case-LEU-15170-I) JET MIXER 

NOISE SUPPRESSOR USING ACOUSTIC 

FEEDGACK Patent Application (NASA) 

20 P Unclas 

LeRC 
LEW - 15,1701 AWARDS ABSTRACT 

JET MIXER NOISE SUPPRESSOR USING ACOUSTIC FEEDBACK 

The present invention generally relates to providing 

an improved jet mixer noise suppressor for high 

speed jets that rapidly mixes high speed air flow 

with a lower speed air flow, and more particularly, 

relates to an improved'jet mixer noise suppressor 

that uses feedback of acoustic waves produced by the 

interaction of sheer flow instability waves with an 

obstacle downstream of the jet nozzle. 

Referring to Fig. 1, multiple primary high velocity 

nozzle jets are shown which emit high velocity jet 

flow into ejector shroud 4 through ejector inlet 6. 

In addition, lower velocity air is entrained into 

ejector shroud 4 through ejector inlet 6 due to the 

high velocity jet flow drawing the lower velocity 

air into the ejector shroud. The higher and lower 

velocity air stream are then mixed using acoustic 

feedback waves resulting from highly directional .- 

sound waves produced by the interaction of sheer 

, flow instability waves with obstacles down stream of 

nozzle 2. In Fig. 1, the multiple nozzle jets 2 are 

separated by a predetermined distance and emit high 

velocity jets which are in phase in order to obtain 

synchronous mixing of the higher and lower velocity 

air flow. 

The jet mixer noise suppressor of the present 

invention uses multiple jets, surrounded by 

entrained ambient air to flap in unison using the 

acoustic waves fed back from downstream of the jets 

to rapidly enhance the mixing of the jets. The jet 

mixer noise suppressor of the present invention uses 

the natural interaction of shear layer coherent 

structure with shock cells found in an imperfectly 

expanded supersonic jet which generates screech. 

The screech causes feedback of the acoustic waves to 

,the nozzel lip creating resonance and creating 

instability waves to enhance the mixing of the jet 

flow. 

Inventor: Edward J. Rice 

Home Address: 3116 Dover Center Road 

Westlake, OH 44145 

Employer: NASA Lewis Research Center 

Initial Evaluator: 

SerialNo.: 046,256 

Filed: 04/14/93 
Serial No. 046,256 

Filed: 04/14/93 

NASA CASE NO. LEU-15,170-1 PATENT APPLICATION 

JET MIXER NOISE SUPPRESSOR USING 

ACOUSTIC FEEDBACK 

Oriqin of the Invention 

5 The invent ion described herein was made by an employee of the U. S. 

Government and may be manufactured and used by or for the Government for 

governmental purposes, without the payment of any royal ties thereon or 

therefor. 

Technical Field 

10 The present invention generally relates to providing an improved jet 

mixer noise suppressor for high speed jets that rapidly mixes high speed 

air flow with a lower speed air flow, and more particularly, relates to an 

improved jet mixer noise suppressor that uses feedback of acoustic waves 

produced by the interaction of sheer flow instability waves to enhance the 

15 mixing of the higher and lower speed air flow, suppressing noise exiting 

from the jet nozzle. 

Backsround Art 

Presently, there does not exist any jet mixer which is designed to 

specifically utilize acoustic feedback from downstream of a jet nozzle to 

20 enhance the mixing of jet air exiting from a jet nozzle. Rather, a 

variety of mixers/suppressors have been developed to provide enhanced 

mixing of two different jet or velocity streams. These improved mixers, 

for example, have reduced the dimension of the high speed flow passage of 

the ejector resulting in mechanical and performance limitations. Accord25 ingly, the conventional turbulent mixing process has been used to perform 

the mixing using the smaller high speed flow passage. 
NASA CASE NO. LEN-15,170-1 

Other jet mixer noise suppressors which have been used to provide 

mixing of two different velocity streams have been constructed of multiple 

lobed, radially aligned, alternate passages of higher and lower velocity 

5 streams for annular or ring-1 i ke geometries. Additional mixer noise 

suppressors have been constructed using parallel alternate passages for 

rectangular nozzle geometries. Further, mixer noise suppressors have been 

constructed using single vortex generators which mix fan air with primary 

exhaust flow across the engine exhaust area. However, these prior art 

10 mixer noise suppressors have involved less than optimum flow mixing rates 

and poor noise reduction due to noise radiation. In addition, the prior 

art mixer noise suppressors have been complex, bulky and of considerable 

length resulting in a mixer which is heavier and more expensive to incorporate into a jet engine. 

The jet mixer noise suppressor of the present invention is more 

suitable than the prior art jet mixer noise suppressors since, by using 

the feedback of acoustic waves received from the down stream side of the 

nozzle, the jet mixer noise suppressor of the present invention is able to 

provide excellent mixing of jet streams while being relatively short in 

20 length, lighter in weight and less expensive than the prior art jet 

mixers. In addition, many applications requiring jet mixer noise suppressors require lower noise output from the device than the prior art mixer 

noise suppressors can provide. Accordingly, the present invention can be 

used in these types of applications since the present invention is able to 

25 provide greatly enhanced mixing of jet flow streams, thus greatly reducing 
NASA CASE NO. LEW-15,700-1 

the noise output from the jet engine. 

Summary of the Invention 

It is, therefore, an object of the present invention to provide an 

5 improved mixer which is smaller in size, lighter in weight and lower in 

cost. 

It is another object of the present invention to provide an improved 

mixer which will provide thorough mixing in significantly shorter distances and which will render the mixing produced noise more amenable to 

10 reduction using acoustic treatment. 

It is an additional object of the present invention to provide an 

improved jet mixer noise suppressor which utilizes acoustic feedback 

resulting from sound waves produced by the interaction of sheer flow 

instability waves with multiple structured obstacles down stream of the 

15 nozzle. 

The jet mixer noise suppressor of the present invention uses multiple 

jet nozzles, surrounded by entrained ambient air to flap in unison using 

the acoustic waves fed back from downstream of the nozzles to rapidly 

enhance the mixing of the jets. The jet mixer noise suppressor of the 

20 present invention uses the natural interaction of shear layer coherent 

structure with shock cells found in an imperfectly expanded supersonic jet 

which generates screech. The screech causes feedback of the acoustic 

waves to the nozzle lip creating resonance and creating instability waves. 

The presen.t invention uses a nozzle which outputs high velocity air flow 

25 that i s i n phase with airflow exiting from an adjacent nozzle to cause the 
NASA CASE NO. LEN-15,170-1 

jet air flow to flap in unison and mixes these jet air flows with the 

instability waves to enhance the mixing of the jet flow. 

In an alternative embodiment, the jet mixer noise suppressor of the 

5 present invention uses small paddles or obstacles in the path of the jet 

flow near the shear layer edge. The jet coherent structure interacts with 

these obstacles causing feedback of the acoustic waves to the nozzle lip 

which excites the coherent structure, thereby closing the feedback loop. 

In carrying out the above objects of the present invention, there is 

10 provided a jet mixer noise suppressor which includes a first nozzle 

outputting a first air stream generating feedback of a first acoustic wave 

from downstream of the first nozzle and a second nozzle outputting a 

second air stream, synchronous with the first air stream, generating 

feedback of a second acoustic wave from downstream of the second nozzle. 

15 In addition, the jet mixer noise suppressor includes an ejector having an 

inlet, outlet and shroud, receiving the first and second air streams from 

the first and second nozzles through the inlet, receiving entrained air 

produced from the first and second air streams being received by the 

ejector, receiving the first and second acoustic waves fed back from 

downstream of the first and second nozzles through the outlet, and mixing 

the first and second air steams and the entrained air responsive to the 

first and second acoustic waves in the shroud. Further, the first and 

second nozzles of the present invention are positioned so that the first 

and second acoustic waves are out of phase with each other. 

These objects, together with other objects and advantages which will 
NASA CASE NO. LEN-15,170-1 

be subsequently apparent, reside in the details of construction and 

operation, as more fully hereinafter described and claimed, reference 

being had to the accompanying drawings forming a part hereof, wherein like 

5 reference numerals refer to like parts throughout. 

Brief Descri~tion of the Drawinqs 

Fig. 1 is a basic structural diagram of the first embodiment of the 

present invention; 

Fig. 2 is a top view of multiple jets emitting high speed jet flows 

10 of Fig 1; 

Fig. 3 is a diagram of the phase plot of the acoustic field resulting 

from the interaction of the flow coherent structure with the downstream 

shock structure; 

Figs. 4(a) and 4(b) are diagrams illustrating the mixer element 

15 spacing to obtain enhanced mixing using resonant mixing of jet flows; 

Fig. 5 is a diagram of the second embodiment of the present invention 

illustrating a beveled nozzle used to provide an external repetitive shock 

structure to create the desired acoustic feedback; 

Fig. 6 is a diagram of the general structure of the third embodiment 

20 of the present invention which uses obstacles in the path of the jet flow 

to enhance mixing of resonant jet flow; and 

Fig. 7 is a diagram of the fourth embodiment of the present invention 

which illustrates a beveled nozzle of the second embodiment of the present 

invention used together with mu1 tiple obstacles of the third embodiment of 

25 the present invention to obtain enhanced mixing of the jet flow. 
NASA CASE NO. LEW-15,170-1 

Descri~tion of the Preferred Embodiments 

Referring to Fig. 1, a basic structural description of the first 

embodiment of the present invention is shown. In Fig. 1, multiple primary 

5 high velocity nozzle jets 2 used in an imperfectly expanded supersonic jet 

are shown which emit high velocity jet flow into ejector shroud 4 through 

ejector inlet 6. In addition, lower velocity air 8 is entrained into 

ejector shroud 4 through ejector inlet 6 due to high velocity jet flow 

drawing lower velocity air 8 into ejector shroud 4. The higher and lower 

10 velocity air streams are then mixed using acoustic waves fed back from 

downstream of nozzles 2 resulting from highly directional sound waves 

produced by the interaction of sheer flow instability waves with obstacles 

down stream of nozzles 2. In Fig. 1, multiple nozzle jets 2 are separated 

by a predetermined distance and emit high velocity jets which are in phase 

15 in order to obtain synchronous mu1 tiple mixing processes by mixing the 

higher and lower velocity air flow. Nozzles 2 may a1 ternatively be 

positioned in an annular configuration as well. Fig. 2 shows in more 

detail multiple nozzles 2 emitting high velocity jets which are in phase 

with each other as indicated with respect to Fig. 1 to obtain the enhanced 

20 mixing. The enhanced mixing moves the mixing process back toward the 

nozzles exits and this moves the source of downstream propagating acoustics waves back up toward the nozzle exits. As a result of the longer 

propagation length the acoustic treatment of the shroud walls can be more 

effective., 
NASA CASE NO. LEN-15,170-1 

Fig. 3 shows an exemplary screech phase plot for an imperfectly 

expanded supersonic jet using a conventional converging nozzle run at a 

high pressure resulting in acoustic feedback or screech from the down5 stream of the converging nozzle. As shown in Fig. 3, the shock pattern 

which returns from downstream of nozzle 12 has several contours of constant phase with respect to pressure in comparison to a reference point. 

As is also shown in Fig. 3, the shock pattern returning from the downstream side of nozzle 12 to the left of nozzle 12 has contours of constant 

10 phase which are 180° out of phase with the contours on the right side of 

nozzle 12. This screech phase plot was generated at one mach speed, and 

additional phase plots can be generated at other desired mach speeds to 

operate the supersonic jet. 

In order to generate the flapping wave motion of the jet, i.e., the 

15 instability waves for enhanced mixing of the higher and lower velocity air 

flows, the acoustic waves between the nozzles should be out of phase with 

each other. Thus, the acoustic waves returning from the down steam of the 

right side or edge of nozzle 12 in Fig. 3 should be out of phase with the 

acoustic waves returning from the down stream side of the left side of 

20 nozzle 14. Similarly, the acousticwaves generated from thedown stream 

of the left side of nozzle 12 should be out of phase with the acoustic 

waves returning from the'down stream of the right edge of nozzle 16. 

Thus, the phase differences between the acoustic waves will generate 

instability waves which will enhance the mixing between the higher and 

25 lower velocity air flows. Based upon the phase plot of Fig. 3, it can 
NASA CASE NO. LEW-15,170-1 

readily be seen for the specific mach speed which this data was observed, 

that the left side of nozzle 14 should be placed approximately 3" to the 

right of the center of nozzle 12 since the right side of nozzle 12 is at 

5 the O0 phase contour and the left side of nozzle 14 is at the 180° phase 

contour on the curve X=O, X being the vertical distance from the nozzle 

axis of nozzle 12. Thus, nozzles 12 and 14, if placed as indicated above, 

will be out of phase with each other thereby generating the instability 

waves which provide resonant mixing of the higher and lower velocity 

10 airflow. 

Figs. 4(a) and 4(b) are graphs showing observed actual data which may 

be used to determine the spacing between nozzles to obtain the instability 

waves with reference to different mach numbers for a specific jet engine. 

Fig. 4(a) shows that the nozzles are separated by a distance s for a given 

15 nozzlewidth h. In Fig. 4(b), at mach speed 1.5, for a 1/2" nozzle, curve 

18 shows that the ratio of distance between the nozzles (s) over nozzle 

width (h) is approximately 8.75. If the same nozzle was to be used at, 

for example, mach 1.3, the ratio between the distance between the nozzles 

over the nozzle width would be approximately 6.3. Fig. 4 also shows data 

20 recorded for a 1/4" nozzle along curve 20. Thus, Fig. 4(b) shows observed 

data for two different sized nozzles at various mach speeds. To further 

verify that the observed data was correct, theoretical data was also 

plotted on Fig. 4(b) for when the source of the shock emanated from the 

third shock cell as we1 1 as from the second shock cell of the shock 

25 pattern of the instability waves. From Fig. 4(b) it appears that the 
NASA CASE NO. LEN-15,170-1 

source of the shock wave emanates from approximately the fourth shock cell 

according to the observed data for that particular jet nozzle. Thus, Fig. 

4(b) can be used to determine the appropriate spacing between nozzles 

5 based upon the mach speed which the jet nozzle is to operate. 

Fig. 5 shows a second embodiment of the present invention which 

involves a beveled nozzle 22 generating a multiple shock pattern which is 

approximately paral lel to beveled nozzle 1 ip 24. Thus, beveled nozzle 22 

redirects the mixing generated noise of the acoustic wave toward an 

10 enclosing wall to control the form of the acoustic wave and thereby 

achieve enhanced noise reduction. The beveled nozzle preferably includes 

internal contours which provide external repetitive shock structure which 

is nearly paral lel to the 1 ip of beveled nozzle 22 in order to redirect 

the acoustic wave from downstream of nozzle 22. In this second embodi15 ment, since nozzle 22 is expected to generate instability waves, it is 

preferable that a converging nozzle operated at a high pressure be used in 

conjunction with beveled lip 24 of nozzle 22. Thus, the second embodiment 

of the present invention modifies the nozzle opening shape to cause the 

natural instabilities of the shear flow between the nozzle jets and the 

20 surrounding air to propagate at an angle oblique to the jet axis which 

would be larger than that occurring in the prior art jet nozzles. This 

propagation of the natural instabilities at an oblique angle further 

contributes to the enhanced mixing of the higher and lower velocity air 

flows, further decreasing the exiting noise. The proper spacing between 

25 the beveled nozzles to provide enhanced mixing can be determined by 
NASA CASE NO. LEW-15,170-1 

collecting data as described in the first embodiment of the present 

invention with respect to Figs. 3 and 4. 

In addition to the single beveled nozzle 22, a double beveled nozzle 

5 could also be used which would have a converging 1 ip forming a pyramid 

shape and generate external repetitive shock structures which are nearly 

parallel to each beveled portion of the nozzle 1 ip in order to redirect 

the acoustic wave from downstream of the nozzle. 

Fig. 6 shows a third embodiment of the present invention which can 

10 also be used to redirect the instability waves and provide proper phasing 

of the acoustic waves to produce enhanced mixing of the higher and lower 

velocity air flows. It is preferable, as shown in Fig. 6, that paddles 11 

are grouped in pairs and placed in the path of the higher velocity air 

flow exiting from the nozzles for each nozzle 2. Paddles 11 are a1 so 

15 preferably connected to the top and bottom of ejector shroud 4. The jet 

coherent structure interacts with paddles 11 causing an acoustic feedback 

to the nozzle 1 ip which excites the coherent structure and closes the 

feedback loop. Additionally, oblique propagation angle of the instability 

waves could a1 so be accompl ished by mounting paddles 11 at an angle with 

20 respect to the jet axis. The proper spacing between nozzle to provide 

enhanced mixing can be determined by collecting data as described in the 

first embodiment of the present invention with respect to Figs. 3 and 4. 

Finally, Fig. 7 shows a fourth embodiment of the present invention 

which includes a beveled nozzle of the second embodiment with paddles 11 

25 of the third embodiment where paddles 11 are preferably parallel to the 
NASA CASE NO. LEN-15,170-1 

beveled lip of the nozzle. The use of obstacles in the third and fourth 

embodiments of the present invention is especially important when the 

nozzles do not emit a substantial amount of shock waves such as a properly 

5 expanded shock free nozzle. In addition, the use of the obstacles causes 

the sheer flow instability waves to have a propagation direction which is 

oblique to the jet axis so that the downstream acoustic waves generated by 

the mixing process is more amenable to the use of acoustic treatment which 

thereby enhances the reduction of noise produced by the mixing of the 

10 higher and lower velocity air flows. 

The many features and advantages of the invention are apparent from 

the detailed specification and, thus, it is intended by the appended 

claims to cover all such features and advantages of the invention which 

fall within the true spirit and scope of the invention. Further, since 

15 numerous modifications and changes will occur to those skilled in the art, 

it is not desired to limit the invention to the exact construction and 

operation i 11 ustrated and described, and, accordingly, a1 1 suitable 

modifications and equivalents may be resorted to falling within the scope 

of the invention. 
NASA CASE NO. LEW-15,170-1 

Abstract of the Disclosure 

JET MIXER NOISE SUPPRESSOR USING ACOUSTIC FEEDBACK 

5 The present invention generally relates to providing an improved jet 

mixer noise suppressor for high speed jets that rapidly mixes high speed 

air flow with a lower speed air flow, and more particularly, relates to an 

improved jet mixer noise suppressor that uses feedback of acoustic waves 

produced by the interaction of sheer flow instability waves with an 

10 obstacle downstream of the jet nozzle. 
10 EJECTOR OUTLET 

Fig. 1 
VIOLENT MIXING REGION 

2 

GROWING INSTABILITY WAVE 

-- -- - i- f 

HIGH ---- SPEED JET 

- \ 

\ 

\ 

/ / 

* LOWER SPEED FLOW 1- // 

Fig. 2 
Fig. 3 

SCREECH PHASE EXPERIMENTAL DATA 

DISTANCE ALONG 

NOZZLE AXIS, INCHES 
1'1 2 E'L P'L S'l 9'1 L'L 8'1 
MULTIPLE SHOCK PATTERN 

. I 

PROPAGATION DIRECTION 

OF INSTABILITY WAVES 

Fig. 5 
10 EJECTOR OUTLET 

Fig. 6 
1 1 MULTIPLE OBSTACLES 

IN SHEAR LAYER 

INSTABILITY WAVES 

- SHEAR LAYER 

INSTABILITY 

PROPAGATION 

Fig. 7