US3508561A - Method of and means for controlling fluid flows - Google Patents

Description

187-1 f l S-tAKUHKUUM 'A ril 28, 1970 'J QJ. CORNISH III 5 5 I METHOD OF AND MEANS FOR CONTROLLING FLUID FLOWS Filed March 20, 196'? 4 Sheets-Sheet 1 Fle'l iNI/ NTOR. JOSEPH J. CORNISH,]1I

Agent I April 28, 1970, v .1. J. CO RNISH Ill METHOD OF AND MEANS FOR CONTROLLING FLUID FLOWS Filed March 20, 1967 k 4 Sheets-Sheet 2 FIG.5

I INVENTOR. JOSEPH). Cqamsmlll Agent April 28 1970 J.J. CORNISH m 33,503,561

METHOD OF AND MEANS FOR CONTROLLING FLUID FLOWS Filed March 20, 1967 4 sheets sheet s INVENTOR. JOSEPH J. CORNISH, 111

Agent P 8, 1970 .1. J; CORNIYSH 3,5 6 7' METHOD OF AND MEANS F0R CONTROLLING FLUID FLOWS Filed March 20, 1967 i 4 Sheets-Sheet INVENTOR. JOSEPH J: CORN'ISH, III

Agent United States Patent 3,508,561 METHOD OF AND MEANS FOR CONTROLLING FLUID FLOWS Joseph J. Cornish III, Marietta, Ga., assignor to Lockheed Aircraft Corporation, Burbank, Calif. Filed Mar. 20, 1967, Ser. No. 624,422 Int. Cl. Fc N08 US. Cl. 137-13 18 Claims ABSTRACT OF THE DISCLOSURE A method for influencing the growth and behavior of vortices is founded on the fact that a low energy core exists at the middle of the vortex which has a tendency for movement in an axial direction. This is coupled with a recognition that movement in the core is in different directions at different points along the core which, if not disturbed by other influences, causes an axial velocity fluctuation to exist in the core of the vortex. This periodic meeting or pumping is directly related to vortex shedding and alternations of the circumstances of the vortex core by removing the flow from the vortex by suction at the cores strongly influences the shedding behavior. This suction can be applied in such a manner as to prevent the vortex shedding and instead lock it to the surface where it may be used as an effective flow control mechanism, for example on flat surfaces, at the aft end of bluff bodies and either inside or outside of cylindrical exhaust as a jet engine. Alternately, the vortex shedding rate can be increased and even stimulated by injecting air into the vortex core.

This invention relates generally to techniques employed in controlling the flow of fluids and more particularly to a method of and means for controlling fluid flows by the removal of selected portions of fluid from the flow in such a way that turbulent motions such as vortices within the fluid not only cease to interfere with the flow but may also be actually employed to improve conditions and operations in the vicinity of such flow.

For example, fluids passing over a surface lose their momentum and energy Where they contact the surface and this low energy layer becomes thicker with the increase in distance, the fluid moves along the surface resulting in an objectionable resistance to relative movement therebetween. In order to overcome this, various schemes have been proposed to remove this low energy or boundary layer of air including suction'slots, air jets, etc.

It has also been known that a sharp discontinuity of the surface can produce a vortex which will act like a roller in the boundary layer air over the surface. The nature of vortices is such, however, that they will build up to a point as determined by the particular discontinuity and flow conditions and then peel off or flow aft. This results in a succession of vortices producing a turbulent wake and accompanying pressures with objectionable effects such as noise, percussion, vibration, etc.

Prior attempts have been made to stabilize vortices and the more effective have included means for bleeding or sucking some of the fluid comprising the vortex and disposing of it in an innocuous area. Some of these prior schemes have also attempted to maintain the vortex as a permanent condition so that the entrapped energy becomes available for use to improve the overall operation of the surface or body in that fluid medium. Such improvement is manifested by a low noise level when employed in the exhaust duct of a jet engine, reduced surface friction and/or drag and increased lift when employed on the aerodynamic surface of an airplane, and

other characteristics having utility in a variety of applications.

None of these previously proposed techniques and systems have been employed to any appreciable extent due to their low efliciency and high cost in terms of power, complexity, weight, etc. This has been found to be due in most part to a misconception of the vortex characteristics as evidenced by an improper location of suction requiring unduly large power and flow quantities. Moreover, these known and previously proposed schemes are all predicated on a mitigating philosophy and overlook the prospect of preventing the generation of vortices in situations where they are undesirable but have been tolerated, sometimes with the help of compensating means.

The present invention contemplates the control of vortices whereby they may be created or quickly disposed of as desired. Where created, they are maintained permanently so as to become in effect an integral part of the fluidynamic surface or body with which they are associated and thereby contribute to the high performance thereof. Where destroyed or disposed of, they are removed before they have had a chance to actually form and for all intents and purposes may be said to be avoided rather than disposed of since the associated structure or surface is virtually unaffected thereby and retains its designed configuration and air flow characteristics.

In its broadest aspects, the instant invention contemplates control of the fluid flow by manipulation of the vortex or vortices therein. This is accomplished essentially by applying a pressure to the vortex at a preselected point or points in the cross-stream length thereof. This particular type of pressure, as well as the source of means producing it, will vary depending upon the particular application. In every case, however, this agency is effective at and along the core of the vortex to remove the low energy fluid that tends to collect and build there at a predetermined rate relative to that of its build up. In this way, the vortex may be perpetuated by the removal of fluid at substantially the same rate that it enters the core, or it may be destroyed or eliminated by the addition of fluid to the core accelerating the core build-up and vorteX shedding.

While this removal of the vortex core fluid to either perpetuate or destroy the vortex can be accomplished by any tangible or intangible moving force such as a passirig body or pressure respectively, the latter is presently preferred. In this case, there are provided pressure producing units disposed in a preselected location with resepct to each other and to the vortex so that when pressure is applied thereby it is made to act on the core of the vortex. In the case of a negatively applied pressure, a suction is created and the core fluid is drawn into it and conveyed by it from the vortex, while a positive pressure produces a fluid jet that blows the core fluid from the mainstream.

Where a vortex is desired, it is herein proposed to create one by providing a discontinuity which may be a depression in, or an obstruction on, a surface exposed to a fluid flow. The dimensions of this discontinuity are such both as to size and orientation that a vortex is produced. At a preselected point or points along the cross-stream length of the vortex thus created, a suction duct is provided'with its opening or inlet disposed in the preselected position with respect to the core of the vortex. At its other end, each suction duct is connected to an appropriate suction or a negative pressure source so that predetermined quantities of low energy fluid is extracted from the vortex core by the duct when operative. In this way, the low energy fluid area or core of the vortex is prevented from growing as it otherwise will do, and the additional high energy fluid constantly entering the outer periphery of the vortex tangentially will be absorbed thereby. A permanent air roller" in effect is thereby produced so as to define the limits of the associated fluidynamic surface.

The number and spacing of the openings provided in the fluid duct will be determined by the dimensions of the vortex and its cross-stream length and shape or curvature. Generally, where the vortex has a length or a potential length less than its diameter, only one such opening is required.

The location of each suction duct opening is critical to the extent that best results are obtained when one is located in the area of each cross-stream node of the vortex since it has been determined that a cross flow exists in the length of the vortex. The characteristics of this cross flow are such that vortex shedding normally exists at regularly spaced intervals, hence the nodes, the length and location of which is a function of the diameter of the vortex, the free stream velocity, and the fluid viscosity and density.

Where a vortex is not desired, it is herein proposed to destroy or eliminate it by a positive rather than a negative pressure. While this may be effected in a number of ways, some means are better suited for certain applications. For example, the same type of device used to perpetuate a vortex may be employed. More specifically, in such embodiment a fluid duct is provided at a preselected point or points along the cross-stream length of the vortex with its opening or outlet appropriately disposed with respect to the core of the vortex. At its other end, each duct is connected to a suitable positive pressure source so that fluid discharged through the duct forces predetermined quantities of low energy fluid into the vortex core. In this case, unlike the first described, fluid discharges supplement the normal axial fluid oscillations or pumping within the core to accelerate vortex shedding. If desired, nozzles may be associated with each fluid opening to facilitate this operation and the speed of vortex shedding established in a predetermined manner.

On the other hand secondary vortex generating units may be provided at preselected points along the crossstream length of the principal vortex to establish a plurality of vortices each having a core disposed substantially perpendnicular to the core of the principal vortex. Thus, the cross-flow characteristics or pumping action within the secondary vortex cores is used as pressure generators in drawing or sucking the principal vortex core and thereby dispose of it.

The instant invention is equally applicable to vortices of continuous length as would be associated with an oval or circular surface as it is to those of fixed length as would be associated with a planar, curved or horizontal surface. Thus, the cross-flow characteristics of pumping action of a vortex is essentially the same regardless of the shape of a particular surface with which it is associated. The single difference resides in the distance between nodes, and in each case it is important that the pressure producing units or generators be properly located.

With the above and other objects in view as will be apparent, this invention consists in the several procedural steps as well as the construction, combination and arrangement of parts all as hereinafter more fully described, claimed and illustrated in the accompanying drawings wherein preferred embodiments of the invention are shown as it would be applied to particular applications where it is desired to control fluid flows and more specifically described as follows:

FIGURE 1 is a series of isometric views of a segment of a vortex showing initially the formation thereof and then the development of cross flow within the vortex core resulting in a pumping action whereby an enlarged core diameter is produced at regularly spaced intervals to a point Where shedding will occur and finally means illustrated schematically by a phantom line located at and axially along the vortex center to stabilize, for example, the vortex diameter and maintain the vortex permanently, a fixed length, horizontal vortex being shown to facilitate an understanding of the phenomenon, which would be the same for a continuous length or circular vortex configuration;

FIGURE 2 is an isometric view of a segment or length of preferred vortex stabilizing means in the form of a fluid duct appropriately connected to a pressure source and including a plurality of laterally disposed tubes terminating in one or more openings to be located in a predetermined relative position with respect to the core of the vortex;

FIGURE 3 is a section taken along line 3 3 of FIGURE 2 to show the configuration of each of the laterally disposed tubes;

FIGURE 4 is an end view thereof; g I

FIGURE 5 is a perspective view ofa fragment of an aircraft wing adjacent the trailing edge thereof to show a specific application of the vortex stabilizing means of FIGURE 2, the wing having been provided with a discontinuity in the form of a spanwise recess to produce a vortex which the stabilizing means is designed and adapted to maintain therein;

FIGURE 6 depicts a different application of the invention showing a perspective view of an aerodynamic body such as an aircraft nacelle formed or otherwise provided with a series of transverse discontinuities producing peripheral recesses to create vortices and in which stabilizing means like that shown in FIGURE 2 is located to perpetuate and maintain such vortices as permanent air rollers which define the external aerodynamic surface of the body;

FIGURE 7 is a fragment of the same body shown'in FIGURE 6 incorporating alternate vortex stabilizing means comprising suction openings in the base of each peripheral recess in spaced relation to one another corresponding to and in lieu of the tubes employed in the stabilizing means of FIGURE 6;

FIGURE 8 depicts another application of the invention showing a longitudinal section through the aft end of an exhaust duct or tailpipe from a jet engine which is provided with an annular cusp-like discontinuity on its inner surface to create a vortex and in which the alternate stabilizing means of FIGURE 7 are located to secure or lock the vortex as a permanent air roller, the exhaust efllux pattern corresponding to the on and ofl conditions of the stabilizing means being shown in solid and broken lines respectively;

FIGURE 9 depicts still another application of the in-' vention showing a similar portion of a tailpipe incorporating another alternate vortex stabilizing means in the form of triangular tabs on the inner wallof the tailpipe in spaced relation to one another corresponding to and in lieu of the tubes of FIGURE 2 and the openings of FIGURE 6, such tabs being shown in the inoperative position whereby the exhaust efiiux leaves the tailpipe in the conventional form of successive vortices having cores that grow and eventually disintegrate, only a few of such successive vortices being shown prior to their disintegration; V

FIGURE 10 is a similar view with the tabs in their operative position extending transversely into the tailpipe to constitute localized discontinuities therein and create a; plurality of secondary, streamwise vortices having cores with cross-stream characteristics or pumping action permoving it aft or downstream to prevent the growth there of; and

FIGURE 11 is an isometric view of a fragment of the tailpipe of FIGURES 9 and 10 and associated tabs to show in greater detail the construction and mounting of the tabs and their interconnection for movement in unison.

Referring more particularly to FIGURE 1 of the draW-.

ings, 10 designates a fluid or air flow culminating in a vortex 11. The nature of every vortex including the vortex 11 is such that the air flow is drawn radially inward producing a core 12 of relatively low momentum air which collects there and grows diametrically until it becomes unstable and the vortex sheds. Conventionally, th.'s air flow, usually referred to as a vortex street, is treated and discussed as two-dimensional, i.e., as having a uniform transverse dimension and being shed in a continuous length. On the contrary, experiments conducted in connection with the present invention have shown that within the vortex street a cross flow exists establishing linear shifting or oscillating nodes 13 and 14 with an inherent pumping action causing the shedding to occur at predeterminated, equally spaced points.

In some of its forms, this invention contemplates the application of an applied pressure P, either positive or negative, adjacent the center 15 of each node 13 and 14 so as to be effective on the core 12 at and along its centerline. As illustrated in FIGURE 1, P is negative so as to stabilize the core, i.e., efiectively eliminate the pumping action so that the core diameter remains substantially constant to form a permanent air roller. In the various applications illustrated in FIGURES 5 through 8, such negative pressure is made to have a force matched to that of the air flow 10 as applied to the periphery of the vortex 11. Hence, low momentum air moving into the core 12 is removed therefrom at a rate substantially equal to that at which it is entering whereby the stable core as illustrated schematically at 16 of FIGURE 1 is produced.

To the above ends, as shown in FIGURES 2, 3, and 4 a duct or manifold 17 is provided having a series of spaced tubes 18 projecting laterally therefrom. The duct 17 is adapted to be disposed transversely of the air flow 10 with a tube 18 located adjacent the center 15 of each node 13 and 14. Each tube 18 communicates internally with the duct 17 and is pierced at its outer end by an opening 19 in each side wall. The several openings 19 are located at and along the centerline of the core 12 when the duct 17 and the tubes 18 are disposed as aforesaid with respect to the air flow 10.

FIGURE 5 shows a specific application of the invention wherein the device illustrated in FIGURE 2 is incorporated in a structure such as the fixed wing of an aircraft to prevent air flow separation from the surface thereof. In this case a movable control surface or flap 20 is hinged in conventional manner to the aft end of the immovable wing structure 21. Adjacent and along the hinge line, a spanwise recess 22 is formed or otherwise provided constituting a discontinuity in the surface defined by the wing structure 21 and flap 20 which generates a corresponding vortex equivalent to the vortex 11.

A duct or manifold 17 is mounted within the wing structure 21 with its tubes 18 projecting through the end wall thereof anddisposed in the recess 22 at the centers 15 of the nodes 13 and 14. With the proper suction applied by means of and through an appropriate source of fluid pressure such as, for example, a conventional pump illustrated generally at 17', FIGURE 2, the vortex 11 created within the recess 22 is perpetuated acting as a constant or permanent roller so long as an air flow passes over the surface of the wing structure 21 and flap 20. This serves among other things to facilitate the move ment of the air fiow 10 over the flap surface and prevent its separation therefrom.

FIGURE 6 shows another application of the invention wherein the device illustrated in FIGURE 2 is incorporated in an aerodynamic body or nacelle 23 not only to prevent the separation of air flow from the external surface thereof but also, in efliect to establish such external surface through the use of multiple parallelly disposed rows or rings of such tubes 18. More specifically, the aerodynamic body 23 is formed by a nose cone 24 and a tail cone 25 separated by a series of circumferential recesses 26 in the base of each of which is mounted a duct or manifold the equivalent of that shown at 17 in FIGURE 2 with projecting tubes 18. The openings 19 in the end of each tube 18 are adapted to be located in the core 12 of a vortex 11 created by the recess and through which the pressure is applied, in this case, negative pressure or suction through means such as the pump 17 appropriately connected to one end of the duct 17 and housed within end cone 24 or 25. The several vortices 11 are thereby maintained or locked within their resective recesses 26 forming a circle, as at 27, therearound with the outer surfaces of the several vortices 11 coacting one with the other and with the associated surfaces of the cones 24 and 25 to establish and maintain the external configuration of the aerodynamic body 23. This construction is designed and intended to substantially reduce the size and weight of the aerodynamic body 23.

As an alternate to the stabilizing means illustrated in FIGURE 6-, the apparatus of FIGURE 7 may be employed. In this case, the duct or manifold 17 includes no tubes 18 but merely openings 19 which communicate with the base of each recess 26. As in the case with the tubes 18, the openings 19 must be precisely spaced one from the other; and when negative pressure or suction is applied, the core 12 of the associated vortex 11 is drawn into the openings 19 so that its cross-stream configuration becomes scalloped, as at 28, rather than in the form of a circle 27 when the openings 19 are disposed in the core 12 rather than adjacent thereto. Radially outward, the cross-stream vortex configuration straightens into a circle, for all intents and purposes identical to that of FIGURE 6. Thus, in either form of FIGURE 6 or 7 a series of air rollers constitutes a substantial portion of the aerodynamic body 23 with the outer periphery of all such rollers coacting with the external surfaces of end cones 23 and 24 to define the body 23.

This alternate stabilizing means has definite advantages over the tubes 18 in those cases where due to the particular application it is desirable to render the same inoperative at times. One such case is illustrated by way of example in FIGURE 8. In this case, while either form of vortex stabilizing means is equally effective, the alternate form of FIGURE 7 is preferred inasmuch as during normal cruise flight of the aircraft, it is desirable to render the device inoperative.

Referring more specifically to FIGURE 8, the invention is applied to the exhaust or aft end of a tailpipe 29 of a jet engine. Adjacent its terminus, this tailpipe 29 is formed with a discontinuity produced by an obstruction on its interior surface preferably in the general shape of an annular cusp 30. This has the effect of directing the efllux gases from the engine radially inward of the tailpipe 29 and establishing a turbulent exhaust flow therefrom defined by an envelope illustrated by broken lines V With the provision of spaced openings 19- within the cusp 30 each connected to a source of negative pressure equivalent to pump 17, the vortex 11 that is established by and within the cusp .30 is maintained and perpetuated therein when suction is applied. Thus, the efllux is made to adhere to the periphery of this constant air roller thereby produced establishing an exhaust envelope having a configuration illustrated by solid lines V By means of and through this embodiment, the velocity of the exhaust efilux may be substantially reduced corresponding to take-01f and landing and ground operations of the airplane which is not only beneficial to such operation but substantially reduces the accompanying noise level. During normal cruise flight, however, the device may be turned off so that the efflux pattern illustrated in broken lines V is produced, accompanied by an increased veloc ity and greater thrust beneficial during this mode of operation of the airplane when the attendant noise level is unimportant.

FIGURES 9, 10 and 11 show another application of the invention wherein an embodiment specific to the noise problem of jet engine is employed. The noise accompanying the operation of a jet engine has been determined to be the result of pressures within the efllux as established by the successive vortices produced when the exhaust leaves the tailpipe 29, and as depicted in FIGURE 9 builds to a point where it disintegrates substantially aft of the tailpipe terminus. Each such vortex 31 is annular in form and disposed with its core 32 transversely of the exhaust stream normally producing an exhaust pressure envelope P with a corresponding noise level.

In order to stabilize each such vortex 31, it is herein proposed to produce a plurality of parallelly disposed secondary-vortices 33 as depicted in FIGURE 10, each with its core 34 parallel to the exhaust stream (perpendicular to the principal vortices 31). The pumping action Within each of the secondary vortices 33 is thereby employed to pick up fluid developing in the core 32 of each principal vortex 31 as it is formed and pass it in the aft direction. The principal vortices 31 are thereby prevented from growing as would otherwise be the case and are in fact made to disintegrate rapidly producing an exhaust pressure envelope P of appreciably lower level with an attendant reduction in noise.

The result is preferably accomplished by a provision of properly spaced tabs 35 which are triangular in section with the apex thereof pointed upstream so that the engine exhaust is interrupted thereby. At its base, each tab 35 is hinged as at 36 to the adjacent wall of the tailpipe 29 being disposed and adapted to swing to and from extreme positions where it forms a smooth and uninterrupted internal surface of the tailpipe 29 constituting the inoperative position (FIGURE 9) and where its apex extends radially inwardly of the tailpipe 29, constituting the operative position (FIGURE The vortices 33 are created by the corners of each tab 35 when disposed in the operative position as they interrupt the exhaust stream, and once created these vortices 33 pass downstream where they intersect the cores 32 of the several principal vortices 31.

Movement of each tab 35 to and from its extreme position may be effected by means of and through a conventional actuator 39. Appropriate interconnecting means such as a ring 38 forming a common connector for the several links 37 associated with the several tabs 35 swings them in unison into and out of their extreme positions.

While particular embodiments of the invention are illustrated and described in connection with specific applications of the invention for purposes of a better understanding thereof, it is to be understood that various modifications and adaptations may be made in these preferred embodiments without departing from the invention. The appended claims are intended to cover all such variations as fairly fall within the true spirit and scope of the invention and define the sole limitations to be placed thereon.

What is claimed is:

1. The method of controlling a fluid flow having a vortex therein consisting essentially in establishing the location of each cross-stream node in the length of said vortex, and applying a pressure to said vortex in the area of each said node.

2. The method of claim 1 wherein said pressure is applied to said vortex in the core thereof.

3. The method of claim 1 wherein said fluid flow is associated with a surface and said applied pressure is a positive one directed along the cross-stream length aforesaid.

4. The method of claim 1 wherein each said node is established at a predetermined location. i

- 5. The method of claim 1 including the additional step of creating said vortex and wherein said applied pressure is a negative one with respect to said vortex.

v 6. The method of claim 5 wherein said fluid flow is associated with a surface and said vortex is created by producing at least one discontinuity on said surface.

7. The method of claim 1 wherein said applied pressure is produced by creating a plurality of secondary vortices having their cross-stream length disposed in a horizontal plane and perpendicular to the first mentioned vortex to intersect the same.

8. The method of claim 7 wherein at least each pair of said secondary vortices are created simultaneously.

9. Means for controlling a fluid flow containing a vortex comprising a fluid pressure source, and an outlet from said source located proximate each point corresponding to a cross-stream node in the length of said vortex whereby preselected quantities of fluid are removed from said vortex. 10. The means of claim 9 wherein each said outlet opens substantially perpendicular to said fluid flow whereby said preselected quantities of fluid are removed in an axial direction relative to said vortex.

11. The means of claim 9 wherein said fluid flow is adjacent an aerodynamic body, and including at least one recess in the surface of said body adapted to create said vortex.

12. The means of claim 9 wherein said fluid pressure source is a negative one whereby fluid is withdrawn thereby from said core. 13. The means of claim 9 wherein each said outlet is disposed in a predetermined, spaced location.

14. The means of claim 9 wherein said fluid flow is adjacent a surface, and including a discontinuity associated with said surface adapted to create said vortex.

15. The means of claim 14 wherein said discontinuity is a cusp. I

16. Means for controlling a fluid flow containing a vortex disposed transverse thereto comprising a fluid pressure generator effectively disposed with respect to the core of said vortex to act thereon ateach point corresponding to a cross-stream node in the length thereof and move fluid within said core in a preselected direction relative to said fluid flow, said generator including a plurality of retractable tabs projecting into said fluid flow upstream of said vortex to produce streamwise, secondary vortices therein.

17. The means of claim 16 wherein said fluid flow is adjacent a surface, and said tabs define localized areas and uninterrupted continuations of said surface when disposed in the retracted position.

18. The means of claim 16 including actuating means for the movement of said tabs in unison to and from their retracted position.

References Cited UNITED STATES'PATENTS

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