Abstract:
A rotary jet including a core-flow arrangement minimizes flow separation of primary and induced secondary flows over the afterbody of the jet rotor. By discharging a small portion of the primary jet through a central opening in the afterbody concentric with the nozzled rotor, a favorable pressure gradient is generated over the surface of the afterbody, which helps reduce or prevent flow separation thereover.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to thrust augmenters, and more particularly to rotary jet ejectors incorporating a core flow arrangement. 
     U.S. Pat. No. 3,046,732 to Foa, incorporated herein by reference, discloses a method and apparatus for effecting a highly efficient direct energy transfer between a primary or driving fluid and a secondary fluid. One arrangement set forth, the axial flow rotary jet, contemplates a rotor carrying nozzles oriented so that they are skewed relative to the axis of the rotor and communicating with a source of primary fluid under pressure. The region occupied by the driving fluid emerging from the rotor rotates about the same axis and at the same angular velocity as the rotor. The boundaries of this region are interfaces separating the driving fluid from the driven fluid with the relation of the interfaces to the induced flow pattern dynamically substantially like that of blade or vane surfaces of the same shape rotating at the same angular velocity. Thus the driving fluid forms &#34;pseudo-blades&#34;, the action of which on the driven fluid is somewhat similar to the flow induction process of solid vanes or blades in dynamic flow machines. Where the stream issuing from the rotating orifice has an axial component such that its axis in its rotation describes a hyperboloid which is nearly a cylindrical surface, and the interaction space is shrouded, substantial thrust augmentation is typically produced by the resultant induced secondary fluid flow. 
     One of the main obstacles to the attainment of the maximum potential performance of axial-flow, rotary jet energy exchange mechanisms, of the kind disclosed in U.S. Pat. No. 3,046,732, has been found to be the occurrence of fluid flow separation over the trailing surface of the rotor casing (also known as the afterbody) where the pressure increases in the direction of the flow of fluid. Flow separation results in not only an increase of the pressure drag, but also a recirculation of flow of secondary fluid induced by the primary jet flow. This latter result is particularly undesirable inasmuch as it produces a loss of pumping effectiveness of the &#34;pseudo-blades&#34;. Well known methods exist for retarding or preventing flow separation in regions of adverse pressure gradient, e.g., boundary layer suction or injection, &#34;vortex generators&#34;, and others, but all such methods entail either flow losses or mechanical complications, or both. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides for a rotary jet thrust augmenter which diverts a portion of the primary flow from the path through the rotor nozzles and discharges that portion through a central passage. Pressurized primary fluid is carried, via a supply duct, from a source to nozzles circumferentially spaced about a rotor rotatably supported on a fixed shell. The shell is concentrically disposed within the rotor, and includes a truncated substantially conical afterbody attached rearwardly thereof, and a central passage therethrough communicating the supply duct with an interaction space within a shroud. The primary fluid emanating from the rotating nozzles generates a helical flow pattern over the afterbody and through the shroud. This primary fluid flow interacts with ambient secondary fluid and is induced into and through the shroud. The portion of the primary fluid diverted through the central passage emanates therefrom in the form of a central jet, and acts to entrain primary and secondary flows entering the shroud along the outer surface of the afterbody. 
     OBJECTS OF THE INVENTION 
     It is therefore an object of this invention to minimize flow separation in rotary jet thrust augmenters to thereby maximize the transfer of energy from one flowing fluid to another fluid. 
     Another object of the present invention to improve performance from an axial flow rotary jet thrust augmenter by reducing flow separation over the surface of the afterbody. 
     Another object of the invention is to retard or prevent flow separation over the surface of the afterbody by substituting a centrally disposed fluid jet for a portion of the separation region of the afterbody. 
     Yet another object is to increase thrust augmentation in a rotary jet ejector through the injection of air or other fluid into the central stream. 
     Still another object is to maintain a favorable pressure gradient over the afterbody through entrainment of primary and secondary flows along the afterbody outer surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and many of the attendant advantages of this invention will readily be appreciated as the same becomes understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein: 
     FIG. 1 depicts the prior art rotary jet disclosed by U.S. Pat. No. 3,046,732. 
     FIG. 2 illustrates a preferred embodiment of the rotary-jet of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein like characters and reference numerals designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a thrust augmenting rotary jet substantially as disclosed in U.S. Pat. No. 3,046,732 wherein supply duct 1 carries primary or driving fluid under pressure from a source into rotor 2 where the fluid exits through circumferentially spaced nozzles 3, although only one is shown in the Figure. As the primary fluid exits, rotor 2, as a result of nozzles 3 being skewed relative to the axis of rotation of the rotor, is maintained in a state of rotation. The issuing primary fluid, as a result of the rotor rotation, forms helical pseudo-blades PB which rotate at the same angular velocity as nozzles 3 helically about, and axially along, afterbody 4. By such action of the pseudo-blades, a low pressure region is created at the leading (leftmost in FIG. 1) edge of shroud 5, and axial flow of the surrounding secondary fluid is induced into and through the shroud. 
     FIG. 2 illustrates the modified rotary jet of the present invention in which supply duct 1&#39; carries primary or driving fluid P under pressure from a source into the rotatable rotor 2&#39; where a major portion of the primary fluid exits through circumferentially spaced, skewed nozzles 3&#39; on rotor 2&#39;. In this way, as the fluid exits from the nozzle the rotor is maintained in a state of rotation. And as a result of this rotor rotation, the issuing primary fluid forms helical pseudo-blades in the same manner as set forth for the rotary jet of FIG. 1. Stationary, non-rotating support shell 7 is firmly held in concentric alignment with supply duct 1&#39; by radially arranged streamlined arms 9 or other suitable means. Rotor 2&#39; is rotatably supported about shell 7 through bearing assembly 8. Bearing assembly 8 is disposed in a circumferential recess 6 in the outer surface of the shell. Passage 10, associated with, and disposed concentrically within shell 7, extends longitudinally through both shell 7 and afterbody 4&#39;, the latter having the shape of a truncated cone with the larger diameter end being attached to the shell behind bearing assembly 8 just forwardly of the leading edge of shroud 5&#39;, central passage 10 communicating the interaction space within shroud 5&#39; at the smaller diameter. Other variations are possible, e.g. afterbody 4&#39; can also be unitary, and therefore rotatable with, the rotor. Central passage 10 permits a small portion of primary fluid P to bypass rotor nozzles 3&#39; and be discharged instead in the form of central jet j. 
     The percentage of primary flow that is diverted from rotor nozzles 3&#39; to central passage 10 may be controlled in a number of ways, e.g. through the use of nozzles, valves, variable-geometry arrangements, etc. A particularly effective control method, which is possible in some cases, is accomplished through the injection of fluid, e.g. compressed air, into the central stream through wall openings or orifices 11, as shown in FIG. 2. The fluid being injected is supplied from a source external to shell 7 and is interconnected with that source by tubes or pipes (not shown) which are carried internally of arms 9. Orifices 11 may be disposed forwardly of afterbody 4&#39;, preferably adjacent the forward or leading portion of rotor 2&#39;, and rearwardly of the leading edge of shell 7. Where the primary fluid is water and the injected fluid is air, the resulting central jet will be an air-augmented water jet, which will contribute to the overall thrust augmentation of the rotary jet. Very simply, the compressed air expands and causes an increase in the velocity of the water-and-air mixture through the shell central passage thereby resulting in thrust augmentation. A more complete discussion of this phenomenon is found in &#34;Thrust of an Air-Augmented Waterjet&#34;, by R. G. Amos, G. Maples &amp; D. G. Dyer, Journal of Hydronautics, Volume 7, April 1973, pages 64-71. 
     There has therefore been described an axial flow rotary jet thrust augmenter having rotating nozzles driven by pressurized primary fluid flow and a central passage for diverting a portion of the primary flow therethrough so that performance is improved. The central passage produces a jet which overcomes the flow separation difficulties inherently present when using the rotary jets of U.S. Pat. No. 3,046,732, by not only eliminating the most critical aspects of the boundary layer control portion of the afterbody but also, through an entrainment effect, maintaining a favorable pressure gradient, or at least reducing the unfavorable pressure gradient, over the remaining portion of the afterbody.