US3209775A

US3209775A - Bias device for pure fluid amplifier

Info

Publication number: US3209775A
Application number: US243097A
Authority: US
Inventors: Edwin M Dexter; Jones Donnie Roland
Original assignee: Bowles Engineering Corp
Current assignee: Bowles Engineering Corp
Priority date: 1962-12-07
Filing date: 1962-12-07
Publication date: 1965-10-05
Anticipated expiration: 1982-10-05

Description

' Oct. 5,1965 DEXTER ETAL 3,209,775

BIAS DEVICE FOR PURE FLUID AMPLIFIER Filed Dec. '7, 1962 Spring Was/fer 32 37 31 fly 5 1 7 25 INVENTOR S [mm M 05x75? c2 0. {om/v0 JO/VES ATTORNEYS United States Patent BIAS DEVICE FOR PURE FLUID AMPLTFEER Edwin M. Dexter, Silver Spring, and Donnie Roland Jones, Hyattsvilie, MIL, assignors to Eowles Engineering Corporation, Silver Spring, Md, a corporation of Maryland Filed Dec. 7, 1962, Ser. No. 243,097 10 Claims. (Cl. 137-8L5) This invention relates generally to pure fluid amplifying systems and more specifically, to a mechanism for selectively nullifying or creating a variable bias condition in a pure fluid amplifying system.

It was discovered recently that a fluid-operated system having no moving parts could be constructed so as to provide a fluid amplifier in which the proportion of the total energy pressure or mass flow of a fluid stream delivered to an output orifice or utilization device is controlled by a further fluid stream of lesser total energy pressure or mass flow. These systems are generally referred to as pure fluid amplifiers, since no moving mechanical parts are required for their operation.

A typical pure fluid amplifier may comprise a main fluid nozzle extending through an end wall of an interaction region defined by a sandwich-type structure consisting of an upper plate and a lower plate which serve to confine fluid flow to a planar flow pattern between the two plates, two side walls (hereinafter referred to as the left and right side walls), and one or more dividers disposed at a predetermined distance or distances from the end wall. The leading edges or surfaces of the dividers are disposed relative to the main fluid nozzle centerline so as to define separate areas in a target plane. The side walls of the dividers in conjunction with the interaction region side walls establish the receiving apertures which are entrances to the amplifier output channels. Completing the description of the apparatus, left and right control orifices may extend through the left and right side walls respectively. In the complete unit, the region bounded by top and bottom plates, side walls, the end wall, receiving apertures, dividers, control orifices and a main fluid nozzle, is termed an interaction chamber region.

Two broad classes of pure fluid amplifiers are-(I) Stream interaction or momentum exchange and (II) Boundary Layer Control. Class I amplifiers include devices, in distinction to the devices of Ciass II, in which there are two or more streams which interact in such a way that one or more of these streams (control streams) deflects another stream (power stream) with little or no interaction between the side walls of the interaction region and the streams themselves. Power stream deflection in such a unit is continuously variable in accordance with control signal amplitude. Such a unit is referred to as a continuously variable amplifier or computer element. In an amplifier or computer element of this type, the detailed contours of the side walls of the interaction chamber are of secondary importance to the interacting forces between the streams themselves. Although the side walls of such units can be used to contain fluid in the interacting chamher, and thus make it possible to have the control and power streams interact in a region at some desired ambient pressure, the side walls are so placed that they are somewhat remote from the high velocity portions of the interacting streams and the power stream does not ap proach or attach to the side walls. Under these conditions the power stream flow pattern within the interacting chamber depends primarily upon the size, speed and direction of the power stream and control streams and upon the density, viscosity, compressibility and other properties of the fluids in these streams.

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(II) The second broad class of fluid amplifier and computer elements comprises units in which the main power stream flow and the surrounding fluid interact in such a way with the interaction region side walls that the resulting flow patterns and pressure distributions within the interaction region are greatly affected by the details of the design of the chamber walls. In this broad class of units, the power stream may approach or may contact the interaction region side walls. The effect of the side wall configuration on the flow patterns and pressure distribution, which can be achieved with single or multiple streams, depends upon the relation between: the width of the interacting chamber near the power nozzle, the width of the power nozzle, the position of the center line of the power nozzle relative to the side walls (symmetrical or asymmetrical), the angles that the side walls make with respect to the center line of the power nozzle; the length of the side walls or their effective length as established by the spacing between the power nozzle exit and the flow dividers, side wall contour and slope distribution; and the density, viscosity, compressibility and uniformity of the fluids used in the interaction region. It also depends on the aspect ratio and therefore to some extent on the thickness of the amplifying or computing element in the case of two-dimensional units. The interrelationship between the above parameters is quite complex and is described subsequently. Response time characteristics are a function of size of the units in the case of similar units.

Amplifying and computing devices of this second broad category which utilize boundary layer effects; i.e., effects which depend upon details of side wall configuration and placement, can be further subdivided into three sub-types:

(a) Boundary layer units in which there is no lock on effect.

(b) Boundary layer units in which lock on effects are appreciable.

(c) Boundary layer units in which lock on effects are dominate and which have memory.

(a) Boundary layer elements in which there is no lock on efiect.

Such a unit has a gain as a result of boundary layer effects. However, these effects do not dominate the control signal but instead combine with the control flows to provide a continuously variable output signal responsive to control signal amplitude. In these units the power stream remains diverted from its initial direction only if there is a continuing flow out of or into one or more of the control orifices.

(b) Boundary layer units in which lock on effects are appreciable. In these units, the boundary layer effects are sufficient to maintain the power stream in a particular deflected flow pattern through the action of the pressure distribution arising from asymmetrical boundary layer effects and require no additional streams, other than the power stream to maintain that flow pattern. Naturally in this type unit continuous application of a control signal can also be used to maintain a power stream flow pattern. Such flow patterns can be changed to a new stable flow pattern, however, either by supplying or removing fluid through one or more of the control orifices, or through a control signal introduced by altering the pressures at one or more of the output apertures, as for example by blocking of the output channel to which flow has been directed.

(c) Boundary layer control units which have memory; i.e., wherein lock-on characteristics dominate control signals resulting from complete blockage of the outlet to which flow has been commanded.

In memory type boundary layer units, the flow pattern can be maintained through the action of the power stream alone without the use of any other stream or continuous application of a control signal. In these units, the flow pattern can be modified by supplying or removing fluid through one or more of the appropriate control orifices. However, certain parts of the power stream flow pattern, including lock-on to a given side wall, are maintained even though the pressure distribution in the output channel to which flow is being delivered is modified, even to the extent of completely blocking this output channel.

The power stream deflection phenomena in boundary layer units is the result of a transverse pressure gradient due to a difference in the effective pressures which exist between the power stream and the opposite interaction region side walls; hence, the term Boundary Layer Control. In order to explain this effect, assume initially that the fluid stream is issuing from the main nozzle and is directed toward the apex of a centrally located divider. The fluid issuing from the nozzle, in passing through the chamber, entrains some of the surrounding fluid in the adjacent interaction regions and removes this fluid therefrom. If the fluid stream is slightly closer to, for instance, the left side wall than the right side wall, it is more effective in removing the fluid in the interaction region between the stream and the left wall than it is in removing fluid between the stream and the right wall since the former region is smaller. Therefore, the pressure in the left interaction region between the left side wall and power stream is lower than the pressure in the right interaction region and a differential pressure is set up across the power jet tending to deflect it towards the left side wall. As the stream is deflected further toward the left side wall, it becomes even more eflicient in entraining fluid from the left interaction region and the effective pressure in this region is further reduced. In those units which exhibit lock-on features or characteristics, this feedback-type action is self-reinforcing and results in the fluid power stream being deflected toward the left wall and predominantly entering the left receiving aperture and outlet channel. The stream attaches to and is then directly deflected by the left side wall as the power stream effectively intersects the left side wall at a predetermined distance downstream from the outlet of the main orifice; this location being normally referred to as the attachment location. This phenomena is referred to as boundary layer lock-on. The operation of this type of apparatus may be completely symmetrical in that if the stream had initially been slightly deflected toward the right side wall rather than the left side wall, boundary layer lock-on would have occurred against the right side wall.

Control of these units can be effected by controlled flow of fluid into the boundary layer region from control orifices at such a rate that the pressure in the associated boundary layer region becomes greater than the pressure in the opposing boundary layer region located on the opposite side of the power stream and the stream is switched towards this opposite side of the unit.

Alternatively instead of having flow into the boundary layer region to control the unit, fluid may be withdrawn from this opposite control orifice to effect a similar control by lowering the pressure on this opposite side of the stream instead of raising the pressure on the first side. The control flow may be at such a rate and volume as to defleet the power stream partially by momentum interchange so that a combination of the two effects may be employed. However, it is not essential, and in many cases is undesirable, that the control flow have a momentum component transverse to the power stream when the control fluid issues from its control orifice.

Only a small amount of energy is required in the control signal fluid flow to alter the power jet path so that some or all of the power jet becomes intercepted by the load device or output passage. For a continuously applied control signal, the power gain of this system can be considered equal to the ratio of the change of power delivered by the amplifier to its output channel or load to the change of control signal power required to effect this associated change of power delivered to the output channel or load. Similarly, the pressure gain can be considered equal to ratio of the change of output pressure to the change of control pressure required to cause the change, or, the ratio of the change of output channel mass flow rate to the associated change of control signal mass fiow rate required defines the mass flow rate gain.

It is apparent that this second broad class of pure fluid amplifiers and components and systems provide units which can be interconnected with other units (for example, either class I or II elements) so that the output signal. of one unit can provide the control or power jet supply of a second unit.

The term input signal is defined as the fluid signal which is intentionally supplied to the fluid logic component for the purpose of instructing or commanding the component to provide a desired output signal. Preferably each input signal is of some pre-established relatively constant magnitude. The term output signal used herein is the fluid signal which is produced by the fluid logic component. The input and output signals can be in the form of time or spatial variations in pressure, density, flow velocity, mass flow rate, fluid composition, transport properties, or other thermodynamic properties of the input fluid individually or in combination thereof. The term fluid as used herein includes compressible as well as incompressible fluids, fluid mixtures and fluid combinations.

Pure fluid amplifying systems are usually constructed of two or three flat plates sandwiched together and held in a fluid-tight relationship by machine screws, clamps, adhesives or any other suitable means. If only two flat plates are used, the passages, cavities and orifices needed to form the fluid amplifier component are created in one plate by etching, molding, milling, casting or other conventional techniques, and the other plate is sealed to the one plate to cover these passage, cavities and orifices. When the sandwich type structure comprises three plates, the center plate usually is cut out or shaped by other means to provide the desired configuration of the fluid amplifier component and the remaining two plates provide upper and lower covering plates for sandwiching the center plate therebetween.

Although conventional techniques for forming cavities, passages and orifices are capable of providing relatively close dimensional tolerances, the fluid output in the amplifying system oftentimes reflects slight dimensional deviations in either the size, shape or position of the elements forming the system from the true design dimensions. For example, in the absence of an input signal, deviations in the dimensions of the passages, cavities or orifices from the determined design dimensions may cause the system to have an inherent bias so that the flow or pressure pattern in the output passages is either undesirably asymmetrical or undesirably symmetrical in comparison to the desired flow or pressure pattern. If the system were to provide a null bias output signal from the output passages in the absence of a control signal, an unequal flow or pressure condition in these passages would be undesirable, whereas if a bias output signal were desired equal flow or pressure in the output passages would be undersirable. In either instance, it is usually important that the bias of the particular fluid amplifier be either present or absent and in any event be known to those who wish to use the system either as a single component or in combination with other pure fluid components, or with other types of fluid systems.

The amount of bias in a particular pure fluid amplifying system may be readily ascertained by applying a power stream to the power nozzle of the amplifier and sensing the differentials in mass flow, energy or pressure from the output passages by suitable fluid sensing instruments.

.Since this determination is preferably made after the plates have been sealed in fluid-tight relation, one to the other, the problem then arises of being able to increase, decrease or eliminate the bias of the system.

Hitherto, when a pure fluid component was found to be undesirably biased, the component would be discarded as a reject because known methods for correcting this condition involved excessive expenditures of time and effort. Those working in the art will appreciate the problems of initially locating the reason for the bias condition and thereafter attempting to correct the condition. When the plates are bonded together by a high pressure resistant adhesive, they ordinarily cannot be separated without changing or destroying their shapes and thus the possibility of being able to satisfactorily separate the plates so that they could be used again is virtually hypothetical. Thus, there appeared to be no feasible solution to the problem of eliminating or providing a desired bias to the enclosed pure fluid system in the absence of a control stream flow from a control nozzle.

The present invention expeditiously overcomes the problem by incorporating in the system an externally adjustable airfoil which is positioned upstream of the throat of the power nozzle so that power stream bias adjustment can be made during the testing of the device or system. After adjustment, the airfoil will provide the desired bias to the system and will remain stationary during subsequent operations so that the system still retains the capability of functioning without moving mechanical parts.

Broadly, therefore, it is an object of this invention to provide a pure fluid amplifying system having an adjustable bias in the absence of a control input signal.

Another object of this invention is to provide a pure fluid amplifying system including a stream interaction chamber and a power nozzle for discharging a power stream into one end of the interaction chamber, wherein an xternally adjustable airfoil is located upstream of the throat of the power nozzle for producing the desired bias of the power stream and the system.

Yet another object is to provide a power nozzle for use in a fluid amplifying system that incorporates an airfoil located upstream of the power nozzle throat, the airfoil deflecting the fluid in the power nozzle upstream of the throat so that a biased power jet issues from the power nozzle.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a plan view of the pure fluid amplifying system of this invention;

FIGURE 2 is an enlarged plan view of an airfoil located upstream of the throat of a power nozzle incorporated in the amplifying system; and

FIGURE 3 is an enlarged partial sectional view of FIGURE 1 taken on line 33 of that figure.

Referring now to FIGURES 1 and 2 of the accompanying drawings for a more complete understanding of the invention, there is illustrated the configuration of a typical fluid amplifier formed in a flat plate 11 by conventional techniques, described hereinabove. A further flat plate 12 covers the plate 11 to provide a planar surface for confining the fluid to the delineated cavities, passages and orifices in the plate 11, the plate 12 being preferably bonded in fluid-tight relation to the plate 11 by adhesives, etc. For the purpose of clarity, the plates 11 and 12 are illustrated as composed of a clear plastic material or glass, although it should be understood that generally the plates may be composed of any material that is compatible with the fluid or fluids employed in the system 10.

The plate 11 is formed with the configuration shown in FIGURE 1 in order to provide a power nozzle 13, a control nozzle 14, a jet interaction chamber 15, and left and

right output passages

16 and 17, respectively. The

diverging sides of a flow splitter 18 define adjacent sides of the

output passages

16 and 17. The nozzles '13 and 14 receive power and control streams, respectively, from suitable sources (not shown) connected to the walls defining the bores 2d and 21 formed in the plate 11. The power nozzle 13 is formed with a power nozzle orifice 22 which extends through the end wall 23 of the chamber 15; the orifice 22 being of any conventional shape.

The chamber 15 is provided with left and

right side walls

24 and 25, respectively, which may be set back remotely from the orifice 22 as shown by the solid lines in FIGURE 1 so that boundary layer effects are not created by flow in the interaction chamber 15. The

side walls

24 and 25 might also be positioned sufliciently close to the orifice 22 as indicated by the dotted lines 24' and 25' in FIGURE 1, so that boundary layer effects would be created between the power stream issuing from the orifice 22 and either side wall 2 1 or 25. Alternatively, one of the

side walls

24 or 25 may be set back remote from the orifice 22 while the other side wall is positioned sufficiently close to the orifice 22 so that boundary layer effects are created only along the one

side wall

24 or 25 that is positioned closer to the orifice 22.

The function of the control nozzle 14 is to issue input signals into the interaction chamber 15 and thereby effect amplified directional displacement of the power stream issuing from the orifice 22 from the left output passage 16 to the right output passage 17. It will be apparent to those working in the art that a plurality of opposed or adjacent control nozzles may be employed, or the amplifier otherwise modified in accordance with known techniques to achieve a desired result.

Referring now to FIGURES 2 and 3, the power nozzle 13 is constricted upstream of the orifice 22 to provide a preferably symmetrically converging throat section of rectangular cross section, referred to generally by the numeral 27, and a symmetrically tapering airfoil 28 is positioned wholly upstream of the narrowest constriction of said throat section, hereinafter referred to as throat 29. The downstream end of the airfoil 28 is mounted to the cylindrical head 30 of a bolt 31 having a threaded shaft 32 extending from the head 31), the threaded shaft 32 being threadedly mounted in the plate 11 perpendicularly to the direction of movement of the power stream in the nozzle 13. The lower edge 34, FIGURE 3, of the airfoil 28 may terminate flush with the planar bottom surface of the nozzle 13 or the airfoil 28 may be recessed in a circular groove (not shown) formed in the bottom surface of the nozzle 13 and having a diameter slightly greater than the length of the airfoil 28. The upstream edge of the airfoil 28 terminates adjacent the longitudinal axis of the threaded shaft 32, and the axis of the shaft 32 preferably intersects a centerline CL located equidistances from opposite side walls of the orifice 22 and the nozzle 13. A spring washer 36 is positioned between the head 34) and the plate 11 and serves to lock the bolt 31 and the airfoil 28 against pivotal movement caused by fluid under normal operating pressures flowing over and against the surfaces of the airfoil 28.

A transverse slot 37 is provided in the outermost end of the threaded shaft 32 which preferably does not extend from the planar surface of the base of the plate 11. The slot 37 is designed to receive the blade of a screwdriver or any other suitable device capable of imparting rotation to the shaft 32.

After the plates 11 and 12 are sealed one to the other and fluid supplied to the power nozzle 13,. the airfoil 28 can be rotated, if necessary, by rotation of the shaft 32, to vary the deflection of the power stream upstream of the throat 29 and thereby increase, reduce or eliminate the bias of the output signals from the

output passages

16 and 17. The spacing between the upper edge 38 of the airfoil 28 and the adjacent surface of the plate 12 should be made large enough so that the small axial movement imparted to airfoil 28 by rotation of the shaft 7 32 during adjustment of the bias will not cause the airfoil 28 to abut the plate 12.

As shown in FIGURE 2, a counterclockwise angular position of the airfoil 28 relative to the centerline CL of the power nozzle 13 produces boundary layer forces causing deflection of the power stream towards the left wall defining the throat 29 so that the power stream issuing from the orifice 22 is biased more towards the left side wall 24 of the interaction chamber 25 than towards the right side wall 25 of the interaction chamber 15. Conversely, a clockwise angular position of the airfoil 28, FIGURE 2, relative to the centerline CL of the power nozzle 13 produces boundary layer forces causing the power stream to be biased more towards the right side wall 25 than towards the left side wall 24. When the airfoil is positioned parallel to the centerline CL of the nozzle 13, the flow from the orifice 22 is symmetrical, providing the nozzle 13 is symmetrical. The airfoil 28 can be continuously adjusted during testing of the component 10 until the proper bias or absence of bias in the output fluid signal is achieved. The airfoil 28 is symmetrically tapered at both ends to minimize turbulence and reduce friction losses in the boundary layers during system operation.

For the purposes of this invention, the airfoil 28 has the most desired deflecting effect on the power stream when positioned wholly upstream of the throat 29 proximate the entrance thereof. The closer the airfoil 28 is located to the input end of the nozzle 13, the less the ultimate deflecting effect of the airfoil on the power stream flow from the nozzle 13. The effectiveness of the airfoil decreases as the nozzle length increases, and therefore relatively short nozzles are generally preferable. Once the desired bias is established by movement of the airfoil 28, the threaded engagement between the bolt 30 and the plate 11 and the expansion of the spring washer 36 between the head 31 and the plate 11 will maintain the airfoil in the required power stream deflecting position. Once the bias is adjusted the system 10 will function without any moving mechanical parts.

It should also be understood that the airfoil 28 may be of any conventional aerodynamic shape capable of deflecting fluid flow with a minimum of turbulence and energy loss, and that the nozzle 13 may also assume other conventional configurations. For example, the sidewalls forming the throat of the nozzle might be planar and converge symmetrically to an orifice communicating with the end wall of the interaction chamber with the upstream tip of the airfoil being located centrally of the nozzle orifice.

We claim:

1. In a fluid amplifying system including a power nozzle having a constricted throat and a chamber for receiving a power stream from said throat, the improvement comprising an airfoil positioned wholly upstream of said throat and mounted for rotative movement about an axis perpendicular to the direction of flow in said nozzle and means connected to said airfoil for effecting angular displacement thereof, said airfoil generating boundary layer forces in said throat to deflect said stream according to the angular position of said airfoil.

2. A fluid amplifying system comprising an interaction chamber, a power nozzle for issuing a defined fluid stream into one end of said chamber, plural output passages having the entrances thereof located downstream of said chamber for receiving fluid therefrom, said power nozzle and chamber having opposed and intersecting sidewalls and common substantially planar top and bottom walls, a throat section formed in said nozzle by converging side walls for constricting the fluid stream supplied to said nozzle, a pair of opposed side walls extending downstream from said converging side walls forming a throat for maintaining the constricted stream in a defined flow pattern of substantially rectangular cross section, an airfoil located wholly upstream of said throat and a shaft connected to 8 said airfoil, said shaft secured in said bottom wall perpendicularly thereof for angularly positioning said airfoil with respect to the direction of flow of the fluid stream in said nozzle, said airfoil being located intermediate said side walls of said nozzle for deflecting the stream according to the angular position of said airfoil.

3. A nozzle for issuing a stream in a fluid system, said nozzle including a throat section formed by symmetrical pair of converging concave side walls and substantially planar top and bottom walls and a throat for receiving fluid from said throat section, an airfoil located wholly upstream of said throat and mounted at its downstream edge in said bottom wall for angular displacement therein about an axis perpendicular to the direction of fluid flow in said nozzle, said airfoil deflecting fluid in said throat section according to its angular displacement thereby generating boundary layer forces in said throat to bias said stream.

4. A nozzle for use in a fluid system, said nozzle having opposed sidewalls and substantially planar top and bottom walls, a throat section formed in said nozzle by converging side walls for constricting the fluid stream supplied to said nozzle, a pair of opposed side walls extending downstream from said converging side walls forming a throat for maintaining the constricted stream in a defined flow pattern of substantially rectangular cross section, an airfoil located wholly upstream of said throat and a threaded shaft connected to the downstream edge of said airfoil, said threaded shaft secured in said bottom wall perpendicularly thereof for limited axial movement and for angularly positioning said airfoil with respect to the fluid stream in said nozzle to deflect said stream, said airfoil being located substantially intermediate said side walls.

5. The nozzle as claimed in claim 4, wherein locking means are located between said bottom wall and said airfoil for fixing the angular position of said airfoil.

6. The nozzle as claimed in claim 4, wherein said downstream edge of said airfoil and the longitudinal axis of said shaft are in substantial alignment.

7. In a fluid amplifier element having a power nozzle terminating in a constricted throat for issuing a power stream, control means downstream of said nozzle for deflecting said stream and plural output passages directed toward said nozzle for receiving said power stream, the improvement comprising bias means wholly upstream of said throat for generating boundary layer forces in said throat to deflect said power stream.

8. The combination according to claim 7 wherein said stream bias means comprises an airfoil mounted for rotative movement about an axis perpendicular to the direction of flow in said nozzle and adjustment means connected to said airfoil for effecting angular displacement thereof, said stream being deflected according to the angular position of said airfoil.

9. The combination according to claim 8 wherein said adjustment means comprises a shaft mounted for rotation and connected to the downstream edge of said airfoil.

10. The combination according to claim 9, wherein said shaft is a screw that is threadedly mounted for limited axial movement.

References Cited by the Examiner UNITED STATES PATENTS 2,702,986 3/55 Kadosch et al. 6035.54 2,763,125 9/56 Kadosch et al. 6035.54 2,825,204 3/58 Kadosch et al. 60-356 3,039,490 6/62 Carlson 137610 3,080,886 3/63 Severson 137597 3,093,306 6/63 Warren 23561 3,102,389 9/63 Pedersen et al 60-3554 LAVERNE D. GEIGER, Primary Examiner.

Claims

1. IN A FLUID AMPLIFYING SYSTEM INCLUDING A POWER NOZZLE HAVING A CONSTRICTED THROAT AND A CHAMBER FOR RECEIVING A POWER STREAM FROM SAID THROAT, THE IMPROVEMENT COMPRISING AN AIRFOIL POSITIONED WHOLLY UPSTREAM OF SAID THROAT AND MOUNTED FOR ROTATIVE MOVEMENT ABOUT AN AXIS PERPENDICULAR TO THE DIRECTION OF FLOW IN SAID NOZZLE AND MEANS CONNECTED TO SAID AIRFOIL FOR EFFECTING ANGULAR DISPLACEMENT THEREOF, SAID AIRFOIL GENERATING BOUNDARY LAYER