US3695388A

US3695388A - Quiet jet discharge nozzle

Info

Publication number: US3695388A
Application number: US152696A
Authority: US
Inventors: Vincent B Paxhia; Franklin B Bossler
Original assignee: Textron Inc
Current assignee: Textron Inc
Priority date: 1971-06-14
Filing date: 1971-06-14
Publication date: 1972-10-03
Anticipated expiration: 1989-10-03
Also published as: GB1378943A; CA953755A; FR2141913B1; FR2141913A1

Abstract

An improved air/gas jet nozzle of multiple orifice form is disclosed, the output of which is substantially inaudible to the human ear. The nozzle comprises an airfoil-shaped plenum having discharge orifices in its trailing edge. Sheaths of inaudible range vibrating air are induced to surround the discharge streams from the nozzle orifices and mask the audible range sound therein.

Description

United States Patent Paxhia et al.

[541 QUIET JET DISCHARGE NOZZLE [72] Inventors: Vincent B. Paxhia, Tonawanda; Franklin B. Bossler, Williamsville,

both ofN.Y.

[73] Assignee: Textron lnc., Providence, R.l.

[22] Filed: June 14, 1971 [21] Appl. No.: 152,696

[52] US. Cl ..l81/33 F, 181/33 HC, 181/60, 239/265.l7, 181/72 [51] Int. Cl ..B64d 33/06, FOln l/l4, FOln 7/20 [58] Field of Search..18l/33 F, 33 H, 33 HA, 33 HB, 181/33 HC, 33 HD, 46, 56, 60, 72;

[56] References Cited UNITED STATES PATENTS 2,845,775 8/1958 Tyler et al,; ..l8l/33 F [451 Oct. 3, 1972 FOREIGN PATENTS OR APPLICATIONS 859,272 6/1940 France ..l8l/60 514,913 11/1939 'GreatBritain ..l8l/6O Primary ExaminerRobert S. Ward, .lr. Att0mey.lohn B. Bean et a1.

[57] ABSTRACT An improved air/gas jet nozzle of multiple orifice form is disclosed, the output of which is substantially inaudible to the human ear. The nozzle comprises an airfoil-shaped plenum having discharge orifices in its trailing edge. Sheaths of inaudible range vibrating air are induced to surround the discharge streams from the nozzle orifices and mask the audible range sound therein.

7 Claims, 6 Drawing Figures PATENTEDucrs 1912 BY FRANKLIN B. BOSSLER @wazm ATTORNEYS 4 QUIET JET DISCHARGE NOZZLE The quiet and efficient discharge of air or other gases or fluids (hereinafter referred to as air) via jet devices for thrust generation purposes has long been a sought-for goal in various industries. Such devices would improve any air discharge system operating in an environment where acoustic vibrations at audible levels are intolerable or undesirable. The invention differs from the heretofore popular theory of blending into a jet stream relatively large amounts of ambient or secondary air for the purpose of avoiding undesirable perceived noise effects and/or to obtain thrust augmentation. The present invention provides surprisingly improved advances in this technology. Examples of prior patents dealing with the problem include US. Pat. Nos. 2,955,418; 3,227,240; 3,524,588; 3,572,463; 3,572,466; 3,572,960. Whereas previously respected theories in connection with this problem has been based upon belief that noise at undesirable levels is generated as a result of shearing action between colliding streams of relatively high and low velocity air, we have ascertained that such theories are inadequate and erroneous, and that surprisingly improved results may be attained by forcing the acoustic wavelengths of the exiting jet stream to be so small that the resulting sound may be rapidly attenuated by molecular absorption into a temporary sound masking envelope of relatively viscous ambient atmosphere, until such time as it becomes attenuated and inaudible to the human ear. In order to achieve this result (while still maintaining efficiency of the nozzle for propulsion purposes) the invention contemplates a multiple-orifice nozzle embodying novel orifice positional relationships and jet stream velocities which are as high as possible without'being supersonic; the nozzle orifices being small as possible without producing excessive thrust losses due to viscosity effects.

It is the object of the present invention to provide an improved multiple orifice nozzle system applicable to the aforesaid problems.

THE DRAWINGS The invention is illustrated and described herein by way of example by the accompanying drawing wherein:

FIG. 1 is a side elevational view of one form of multiple orifice nozzle of the present invention;

FIG. 2 is a rear end view thereof;

FIG. 3 is a fragmentary sectional view thereof, on enlarged scale, taken as suggested by line 33 of FIG. 1 and illustrating operation of the invention;

FIG. 4 is a rear elevational view of another form of thereof have been attenuated into inaudible levels. Thus. in one form of the invention, a single jet blast or jet stream" would be sheathed by an envelope of ambient air flowing alongside-360 of the periphery of the jet stream; but only within other specific parameters as explained hereinafter.

However, in order to convert the concept of the present invention into practical hardware, a very large number of small jet orifices are required, and it is at this point that our invention further distinguishes from the prior art. We have found that multiple jets will produce the predicated small wavelength noise in almost any arrangement, but that undesirable long wavelength noise is also produced as a by-product unless the nozzle orifices are arranged so that each issuing jet is permitted to act and react with the ambient air as though it were an isolated jet. The purposes of the invention may be attained either by providing a single row of properly spaced apart (as will be explained hereinafter) orifices, or two or more parallel rows of alternately staggered and properly spaced and directionally divergent orifices, as will be explained hereinafter.

For example, the nozzle plenum may be constructed as shown in the accompanying drawing, and as shown therein a preferred form of the nozzle of the invention is provided to comprise a hollow shell 10 which is elongated in at least two directions so as to provide a plenum for supplying and accommodating a plurality of jet stream discharge orifices 12. The shell 10 is externally airfoil-shaped as illustrated at FIG. 3, and is mounted in flow communication with any preferred form of pressured fluid supply conduit such as illustrated at 14.

As shown in FIGS. 3, 5, the rear edge portion of the shell 10 is ogive-shaped and terminates in a trailing edge 18. As shown at FIGS. 2, 3, the orifices 12 may be arranged in a single vertical row, exiting directly through the trailing edge portion 18 of the nozzle. Or, as shown at FIGS. 4, 5, herewith, another preferred form of the invention a plurality of orifices 12 are relatively positioned and arrayed so as to be staggered alternatively in parallel rows at opposite sides of the trailing edge 18, and are canted in their directions of discharge as best shown at FIG. 5. In any case it will be apparent from examination of FIGS. 3, 5, of the drawing herewith that the ejector action of the air through the orifices 12 will induce flow of ambient air 20 around the shell 10 and then around each high velocity jet 22 of air so as to envelop it while it travels a substantial distance away from the nozzle. The air flows to the orifices are through specifically designed and shaped conduits 16 which receive air/gas under pressure from the plenum 14, as will be further described hereinafter.

As stated hereinabove, the invention contemplates that each ultra-sonic jet stream 22 issuing from an orifice 12 will induce flow therearound of an external shell of sound-masking subsonic ambient air 20 about the entire 360 of its sectional periphery; the orifices 12 being so relatively spaced that the induced air flow streams avoid interference with each other. FIG. 3 herewith illustrates this feature of the invention; and it is by reason of this arrangement that maximum noise supression is obtained. Various patterns of multiple port arrangements have been tested with this object in mind, whereupon it was discovered that when working relative to the median camber line of the shell 10, so as to relatively diverge approximately 4.

In practical terms the jet stream discharge orifices are drilled through the trailing edge wall section of the nozzle asshown; and it has been determined that the orifice diameters should be such that air will be discharged therethrough at a rate less than Mach 1, and preferably between Mach .6 and .8 or thereabove, approaching but never reaching Mach 1. Such results are attained for example by furnishing air/gas to orifices of about 0.040 inches diameters at pressures up to about psi. The orifice exits should then be relatively spaced apart within the range of 1.5 to 4.3 times the orifice diameters. A preferred positional arrangement for an array of orifices as shown in FIGS. 2, 4,6, herewith would locate the orifices on centers approximately two orifice diameters apart in all directions.

It will be recognized that while every effort is made to reduce pressure losses in the orifices and the associated ducting, such losses to some degree will be encountered. However, it has been found that the effect of such losses on propulsion system performance can be minimized in accordance with the present invention. In addition to the external arrangement of the nozzle orifices as shown herein, it is important that the internal forms of the orifice bores must be such that no excessive turbulence be created in the throat sections thereof such as would result from the presence of sharp corners and edges interiorly of the bore. The flow of air/gas must completely fill the orifice bores in order to generate the required thrust with minimum losses. It is also important that the plenum casing 10 be of an external shape of aerodynamic smoothness, so that the performance of the nozzle is not adversely affected either as to noise production or thrust efficiency, as a result of motion of the ambient air relative to the nozzle assembly.

Nozzle efficiency is defined as the ratio of the actual thrust obtained to the thrust that could be theoretically obtained by isentropic expansion for the same mass flow rate and pressure ratio. This distinction is very important. In practice, duct and nozzle losses may be lar.- gely offset by providing slightly larger nozzle areas, to restore the mass flow rate to the ideal flow. The loss of thrust is then proportional to the square root of the pressure loss instead of being directionally proportional to it.

For sound abatement purposes the sound pressure from the jet orifices should be predominately at frequencies at the upper range of audibility and beyond. In addition, the influence of nozzle-exit diameters and relative spacings apart as well as nozzle-exit velocities, are critical. For example, it has been determined that .04 inch diameter jet bores provide relatively low power spectral densities when operating at efficient pressure ratios. Although smaller jet bores provide a,lower,overall noise level eir fabrica ion and operative maintenance 18 more I icult. There ore, the

largest diameter consistent with minimum audible frequency noise requirements should be employed.

Although we have shown herein certain preferred embodiments of multiple row orifice arrangements, it will be understood that other arrangements may be employed depending upon the thrust distribution requirements.

We claim:

1. An inaudible thrust producing discharge nozzle device comprising an externally airfoil-shaped plenum having a trailing edge and air discharge orifice means extending through the wall portion of said trailing edge,

said orifice means including a row of separate orifices of circular section directing discharge of high speed air jet streams from said plenum rearwardly of said trailing edge and being relatively spaced apart so as to induce flows of air from the ambient atmosphere encasing each high speed dis-charge jet stream within a non-turbulent sheath of inaudible range vibrating air, thereby masking the audible range sound propogations of said jet streams until they are attenuated and reduced to inaudible levels.

2. A nozzle as set forth in claim 1 wherein said orifice means comprises two rows of orifices exiting at opposite sides of said trailing edge at staggered spaced apart positions symmetrically thereof.

3. A nozzle as set forth in claim 2 wherein said orifices are directed to discharge from opposite sides of said trailing edge jet streams travelling in divergent directions.

4. A nozzle as set forth in claim 1 wherein the ratio of the diameters of said orifices to the rate of flow therethrough is such that the velocity of jet stream flow at the orifice exits is less than Mach 1.

5. A nozzle as set forth in claim 4 wherein the velocity of jet stream flow at the orifice exits is between .6 to .8 Mach.

6. A nozzle as set forth in claim 4 wherein the rate of jet stream flow at the orifice exits is greater than .5

Claims

1. An inaudible thrust producing discharge nozzle device comprising an externally airfoil-shaped plenum having a trailing edge and air discharge orifice means extending through the wall portion of said trailing edge, said orifice means including a row of separate orifices of circular section directing discharge of high speed air jet streams from said plenum rearwardly of said trailing edge and being relatively spaced apart so as to induce Flows of air from the ambient atmosphere encasing each high speed dis-charge jet stream within a non-turbulent sheath of inaudible range vibrating air, thereby masking the audible range sound propogations of said jet streams until they are attenuated and reduced to inaudible levels.

6. A nozzle as set forth in claim 4 wherein the rate of jet stream flow at the orifice exits is greater than .5 Mach and less than Mach 1.

7. A nozzle as set forth in claim 1 wherein said orifice means comprises a plurality of rows of orifices arranged parallel to said trailing edge, said orifices being at staggered spaced apart positions symmetrically thereof.