Abstract:
A high drag vortex generator for inhibiting the formation of boundary layer gas flow is mounted in a duct having a strong adverse pressure gradient with high speed gas flow over a primary aerodynamic. The vortex generator includes a mounting for supporting the high drag vortex generator at a spatial interval in the high speed gas flow above the primary aerodynamic surface. The high drag vortex generator is supported from the mounting and extends from the mounting in the high speed gas flow less than the full distance to the primary aerodynamic surface. Each high drag vortex generator includes first and second vanes. The first and second vanes have flow confining components at substantial right angles to one another. The vanes flow confining components deflect fluid flow towards and/or away from the primary aerodynamic surface inhibiting boundary layer formation downstream of the vortex generator.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of US Provisional Patent Application entitled Externally Mounted Vortex Generators with Diffuser Flow Duct Passages filed by Thomas R. Norris as Ser. No. 60/560,951 on Apr. 9, 2004. 
     
    
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    NOT APPLICABLE 
       REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK 
       [0003]    NOT APPLICABLE 
         [0004]    This invention relates to vortex generators for improving flow over an aerodynamic surface using an improved vortex generator system. More particularly the improved vortex generators improve flow in zones that include unusually strong adverse pressure gradients and/or thick unstable boundary layers. 
         [0005]    The disclosed vortex generator set is positioned a short distance away from the aerodynamic surface. At this distance, the vortex generator system is expected to be out of the low energy boundary layer or any accumulations of stalled gas. The vortex generator system is ideal to improve flow internal to ducts that include wide angle and high area ratio diffusers, particularly in turbomachines; the back ends of sharply tapered annular diffuser center cones or other center body shape; or ducts having turns. 
       BACKGROUND OF THE INVENTION 
       [0006]    It is well known that vortex generators can improve flow over an aerodynamic surface by energizing the boundary layer at the aerodynamic surface. The aerodynamic surface defines a flow boundary, and thus dynamically guides flow, such as a duct wall or aircraft surface. 
         [0007]    The vortex generators provide a swirling flow mixing action that trails downstream of the vortex generator. Small vortex generator vanes are commonly seen on the upper, suction surfaces of wings of commercial aircraft. Vortex generators are commonly used in sets across an aerodynamic surface, such as a row across a wing, or around the interior of a duct having a bend with a low-angle diffuser. 
         [0008]    In this disclosure, the term “vortex generator” refers to a flow mixing device placed on or adjacent to an aerodynamic surface with the objective of preventing flow separation between high speed stream flow and the boundary layer, which can be stall gas. 
         [0009]    In the technical literature and some patents relating to burners, there is also mention of a vortex generator. The vortex generator in this case a very different device with a different objective. The burner vortex generator is a very high drag baffle plate oriented directly across the flow, in essence a multi-nozzle device with substantial solidity which squirts flow into a spiral. This device, having high solidity, severely restricts flow as well as developing an intense swirl necessary for proper burner flame holding and burner function. This is a totally different device than the vortex generators discussed in this patent, although in American English and American industrial practice, the name is unfortunately the same as the topic of this patent. 
         [0010]    Many types of vortex generators for boundary layer control have been devised. The most widely used vortex generator consists of a relatively small vane extending a short distance out from a much larger aerodynamic surface. In the usual case, the chord of the vane (line drawn between the vane leading and trailing edge) extends at a slight angle to the direction of flow expected during aircraft flight conditions where a flow separation might occur if the vortex generator was not present. These simple vortex generators are economical, have well-known performance characteristics, and are all combined with exceptionally low drag. They are suited for improving flow in relatively weak adverse pressure gradients. However, being of small size and fastened directly to the aerodynamic surface, these vortex generators can become wholly immersed in a thickened boundary layer or stalled flow accumulations, resulting in ineffectiveness. They must thus be placed where energetic free stream flow will be dependably incident against the aerodynamic surface, which usually is well upstream of where the benefit of their increased flow mixing is desired. Despite these severe limitations, the advantages are insurmountable in many weak adverse pressure gradient applications. No other vortex generator type is in as wide use. 
         [0011]    Many other types of vortex generators have been devised and tested. A classic discussion of experiments and data appears in G. B. Schubauer and W. G. Spanberg: “Forced Mixing in Boundary Layers,” Journal of Fluid Mechanics, 8 (1960). Both authors were with the U.S. National Bureau of Standards. Maintaining low drag is a major concern in this study. 
         [0012]    An excellent introduction to diffusers may be found in “The Design of High Efficiency Turbomachinery and Gas Turbines,” Chapter 4, by David Gordon Wilson, The MIT Press, Cambridge, Mass., Third Printing, 1988. 
         [0013]    A review of some U.S. patents concerning vortex generators follows: 
         [0014]    Van der Hoeven in U.S. Pat. No. 4,655,419 “Vortex Generator” (1984) describes a vortex generator vane size relative to the boundary layer thickness, shape, and application of a curved row of vortex generating vanes to a particular jetliner aircraft wing geometry. 
         [0015]    Bruynes, in a historic vortex generator patent, U.S. Pat. No. 2,558,816, “Fluid Mixing Device” (1947) discloses vanes similar to the van der Hoeven vortex generators, applied to improve flow in ducts, fans, diffusers, and wind tunnels. These vanes begin on a wall of the diffuser where boundary layer or stall gas is present. Vanes in diffusers have minimal effect if placed within such areas where rapidly thickening boundary layers are present. Specifically, the direction of gas flow is not always possible to ascertain in boundary layers; thus the direction of vane alignment cannot be properly chosen. 
         [0016]    Hoadly in U.S. Pat. No. 2,650,752 “Boundary Layer Control in Blowers” (1949) discloses several types of vortex generator vanes installed in fans, on struts in ducts, diffusers, and on aircraft wings and control surfaces. In particular T-shaped vortex generators are disclosed, which T-shaped vortex generators do not have toward and away wall fluid diverting components. 
         [0017]    Alford in U.S. Pat. No. 2,844,001 “Flow Straightening Vanes for Diffuser Passages” (1953) discloses in a turbojet outlet annulus and duct various vanes whose length is a partial passage width. These vanes straighten flow to recover swirl energy to increase thrust, and also induce vortices. 
         [0018]    Birch in U.S. Pat. No. 4,298,089 “Vortex Generators for Internal Mixing in a Turbofan Engine” (1979) discloses vortex generators stated to reduce mixing noise of two separate flows as they merge, one cold flow from the fan and the other hot flow from the core engine. The vortex generators are mounted at the back of the core engine nozzle rim just upstream of the point of the flow confluence. 
         [0019]    Laskody in U.S. Pat. No. 4,217,756 “Vortex Mixers for Reducing the Noise Emitted by Jet Engines” (1977) discloses stacked airfoils mounted on a radial spine that attempted to mix a hot core and cold annular flow within a nozzle. These are located just downstream of the confluence of the two streams, all in a quest for lower noise. 
         [0020]    Ealba in U.S. Pat. No. 4,971,768 “Diffuser with Convoluted Vortex Generator” discloses a circumferential strip with, for vortex generation, a convoluted downstream edge. The application is in a pipe leading toward a diffuser. 
         [0021]    I have experimented with this specific shape of diffuser. I have found that the convoluted downstream edge causes deflection along the circumference of the convoluted downstream edge; it does not cause efficient deflection towards and away from the diffuser walls so as to have an efficient effect on boundary layers downstream of the disclosed diffuser. 
         [0022]    In what follows, I describe a vortex generator system that is especially useful on an aerodynamic surface that includes along its length a strongly adverse pressure gradient, such as a diffusing flow passage. A diffusing flow passage is one in which the pressure gradient increases in the direction of flow. Examples of a diffusing flow passage in a turbomachine are those diffusers found downstream of blade sections, near and in combustors, between or within compressor blade sections, and the flow path through an axial or radial compressor. Portions of turns or bends may be diffusing. In some diffusing flow passages, there may be sections where the static pressure locally stays the same or decreases in the direction of flow. However, in the diffusing flow passages here considered, for the duct as a whole, the static pressure increases in the direction of flow. 
         [0023]    In the following discussion about diffusing flow passages, the term coefficient of pressure rise, or Cpr, is defined as: 
         [0024]    Cpr=static pressure rise through the diffuser/dynamic pressure at the low pressure location of reference. 
         [0025]    This low pressure reference is usually chosen at the diffuser smallest area or the diffuser inlet. The Cpr is always between 0 and 1. 
         [0026]    The “diffuser effectiveness” is defined as the actual static pressure rise in the diffuser divided by the static pressure rise that would ideally occur in the absence of any flow losses for the duct area change of the diffuser. The diffuser effectiveness is also always between 0 and 1, but is always greater than the Cpr. 
       Discovery 
       [0027]    I have discovered that the proper introduction of comparatively high drag vortex generators inhibits flow separations in areas of strong adverse pressure gradient on an aerodynamic surface where flow separations would otherwise occur. Particularly, in compact diffusers with an effectiveness of up to about 0.90, the high drag vortex generators can produce a net improvement in flow efficiency for a given diffuser area ratio, despite the high drag. This result appears to be counterintuitive and unexpected, given the high drag penalty of the vortex generator itself. 
         [0028]    “Strong adverse pressure gradient” is defined in this application as a decelerating flow within a duct sufficient to produce losses within the incoming flow of kinetic energy of the gas exceeding 10%. Such pressure gradients are commonly found in diffusers having divergences exceeding 8° with area ratios (Outlet/Inlet) exceeding 1.75. 
         [0029]    A “high drag vortex generator system” is a device for exchanging momentum between high speed flow and slow boundary layer flow in the high speed or free stream gas flow found away from the walls of a flow passage or the walls of a duct with a strong adverse pressure gradient. “High drag vortex generator” is defined as a vortex generators placed in a diffuser with at least one vane of each vortex generator substantially within the free stream with an effectiveness no greater than 0.90. Most of these high drag vortex generators will be in the form of intersecting vanes, often cruciform or ladder shaped. 
         [0030]    “Free stream” or “high speed gas flow” is defined in this application as that portion of the gas flowing between a duct wall and the central portion of a duct that has a speed of 0.65 or greater than the average speed across the duct. 
         [0031]    A “turbomachine with high speed gas flow” is defined for this patent as a gas flow housing or duct enclosing a spinning, dynamically acting impeller, that produces or consumes power, and a maximum gas velocity averaged through any plane across the flow through the machine with a bladed section of at least Mach 0.10 or a pressure ratio of highest pressure divided by lowest pressure of at least 1.1. 
         [0032]    In the disclosure that follows, certain of my high drag vortex generator systems in diffusers appear similar to or are identical with low drag vortex generator systems in diffusers utilized in the prior art. It will be understood that in these instances, the prior art never considered the placement of these vortex generators in diffusers having a high drag environment with strong adverse pressure gradients. 
         [0033]    In so far as the prior art does not disclose this type of high drag vortex generator alone or in a system in the turbomachinery environment, invention is claimed. 
       Further Background 
       [0034]    In addition, a higher area ratio is made possible per given length of diffuser utilized. It is well known that diffusers with small included angles between walls, about 6 to 7 degrees, produce the highest effectiveness of all, but are rarely feasible because of their excessive length. Thus, the vortex generators of this invention will see most application to improving diffusers of the usual case, with their larger angles of 8 degrees and over, and accompanying high adverse pressure gradients. 
         [0035]    Stated in other terms, the ratio between inlet and outlet on conventional diffusers seldom exceeds 1 to 2.5 or 2.6. In utilizing some of the following constructions of this disclosure, I am able to exceed these limits and approach ratios in the range of 1 to 3.0. 
         [0036]    It is to be understood that the vortex generator of this invention differs from those vortex generator vanes of conventional design and that are commonly affixed to the wings of aircraft in at least three respects. 
         [0037]    First, wings normally operate with relatively high efficiency aerodynamic surfaces. These high efficiency aerodynamic surfaces have relatively thin boundary layers and only mild adverse pressure gradients on the aft portions of wings and similar aerodynamic surfaces on aircraft tails. In passing through the air, such wings may have loss coefficients of just 1 or 2 percent at low angle of attack, excluding drag used to create lift. Diffusers do not include high efficiency aerodynamic surfaces. 
         [0038]    Second, the range of flow direction of the boundary layer flow is predictable during normal flight. This is to be contrasted with turbomachines having diffusing flow passages and their sometimes the thick boundary layers and potentially unstable accumulations of boundary layers gases, in which direction of flow can be more than 45 degrees to the direction of free stream flow, often in varying and unpredictable angles. 
         [0039]    Third, such vortex generators are fastened directly to the aerodynamic surface and are typically within a distance from the aerodynamic surface of less than 3 percent of the length, or chord, of the aerodynamic surface. This is to be distinguished from the device herein described. I attach the vortex generator vanes to a mount distanced from the aerodynamic surface that positions the vortex generator vanes at a spatial separation from the aerodynamic surface. 
         [0040]    Fourth, conventional vortex generators usually have the junction of the vanes and mounting, and all or a substantial part of their surface area, within the low velocity boundary layer. In the low velocity boundary area, such vortex generators are low drag. My high drag vortex generator system has reduced surface area in the boundary layer, and the attachment of vanes to their mounting at a distance from the wall in the high velocity area or free stream area. This is an advantage if the boundary layer is unstable or if boundary layer flow direction is uncertain or variable. 
         [0041]    Fifth, conventional vortex generators do not have structure and vanes with multiple or structurally redundant attachments to the flow passage walls or structure. The high drag vortex generators of this invention do. 
         [0042]    Sixth, the high drag vortex generators may enclose the area through which the gas flows. Conventional vortex generators do not. 
         [0043]    Most importantly, the vortex generator of my invention is not foreseen as suited to be mounted onto any substantial span of the wing of an aircraft, replacing conventional vortex generators in the usual case, because of high drag, weight, and complexity. 
       BRIEF SUMMARY OF THE INVENTION 
       [0044]    In a turbomachine with a high speed gas flow section having a strong adverse pressure gradient with high speed free stream gas flow over a primary aerodynamic surface for confining the high speed gas flow, a high drag vortex generator for inhibiting the formation of boundary layer gas flow is mounted. The high drag vortex generator includes a mounting for supporting the high drag vortex generator at a spatial interval in the high speed gas flow above the primary aerodynamic surface confining duct flow. The high drag vortex generator is supported from the mounting and extends from the mount in the high speed gas flow equal to or less than the full distance to the primary aerodynamic surface confining diffuser flow. Each high drag vortex generator includes first vanes and second vanes, in which either the first and second vanes can be the mount. The first vanes have first flow confining components and the second vanes have second flow confining components at substantial right angles with respect to the first flow confining components of the first vanes. The first vane flow confining components deflect fluid flow from the free stream gas flow towards and/or away from the primary aerodynamic surface. The flow confining components of the second vane maintain the deflected fluid flow along a path towards and/or away from the primary aerodynamic surface. The second vanes flow confining components prevent the excessive sideways deflection parallel to the primary aerodynamic surface, enabling penetration through undeflected free stream gas flow. This enables boundary layer formation downstream from the vortex generator to be inhibited by mixture of the deflected free stream gas flow into the volume adjacent the primary aerodynamic surface where the boundary layers might otherwise thicken excessively or accumulate. 
         [0045]    The flow confining components of the vanes are sufficiently adjacent one another to prevent appreciable sideways displacements parallel to the primary aerodynamic surface and to confine the displaced free stream high speed gas flow with a path leading towards and/or away from the primary aerodynamic surface. Normally, this is determined emphirically. 
         [0046]    The preferred mounting for the disclosed vortex generator is a parallel or U-shaped mounting. The preferred form of the disclosed vortex generator system is linked “U” shaped elements, in turn positioned by narrow rods, tubes, or aerodynamic shapes attached as required to the aerodynamic surface, an adjacent duct wall, or an opposite duct wall. The attachment point of these rods, tubes, or aerodynamic shapes may be upstream, downstream, or even with the high drag vortex generator system. If appropriate, positioning structure may be anchored to a turbomachine structural element. 
         [0047]    Optimum placement of the vane members may have to be determined by experiment, so that positioning members do not produce excessive wakes, particularly at the aerodynamic surface, that initiate stalls or unavoidable large wakes that grow in the downstream direction. 
         [0048]    The high drag vortex generator system diverts portions of the flow and may also assist in changing the average direction of flow. If the entire flow in a duct is diverted, in effect, the high drag vortex generators act in place of turning vanes, but of course, with some portions of flow diverted more than others. Uses of the high drag vortex generator system include increasing or reducing swirl angle, or turning the flow through a bend in a duct, or aiding flow in conforming to curves in a duct wall, such as a change in wall taper angle or radius in an annular duct, or a bend in a rectangular or square exhaust duct. In these cases, the curved elements of the high drag vortex generator will in general approximately trace the intended average curvature of the flow, plus or minus the diversion angles of the individual elements. 
         [0049]    A preferred placement of the vortex generator can be in a duct having high speed free stream gas flow over a primary aerodynamic surface for confining the high speed gas flow and having the formation of a boundary layer between the primary aerodynamic surface of the duct and the free stream gas flow. Preferably the duct would be a diffuser having a divergence exceeding 8° and an area ration exceeding 1.75 (outlet area/inlet area). The greatest benefit will be in diffusers with area ratios between about 2.25 and 4:1, and total diversion angles between 10 and 18 degrees. 
         [0050]    Placement of the vortex generator can be over the primary aerodynamic surface of a deflecting duct, within a diffuser, between stator blades in a turbo machine, and around mounting struts and central housings, such as bearing housings, in a turbo machine. 
         [0051]    The mounting preferably consists of two or more U-shaped or channel-shaped elements, and extensions thereof linked so as to form a vortex generator set, with the U-shaped elements working in concert. They create a trailing vortex action by having one or more of the various surfaces of each element at an appropriate angle to oncoming flow. 
         [0052]    The preferred aspect ratio of the legs and crosses of the “U” shaped elements is in the range of 1:4 to 4:1, depending on the desired direction of flow deflection. In general, the longer elements should be more or less perpendicular to the plane which contains the incident and deflected directions of flow. 
         [0053]    If elements are linked side-by-side with the “legs” of the U&#39;s in contact, then the U-shaped elements will be said to function in parallel, in general producing a number of small vortices that extend widely across the aerodynamic surface. Physically, the vortex generator set forms a line cross-wise to oncoming flow and generally adjacent to and parallel to the aerodynamic surface. The parallel vortex generator set is particularly well suited for use in strong adverse pressure gradients or where boundary layers are thin to thick, but stable. 
         [0054]    If instead the elements are linked with the tips of the legs joining the corners of the next U-shaped element and forming a stack, then the elements will be said to function in series, in general producing one or two strong, large vortices per stacked set which are confined to a downstream, comparatively narrow streak along the aerodynamic surface. With elements in series, the vortex generator set is suited for extremely strong adverse pressure gradients where flow separation is possible. In these cases, the boundary layer can be very thick and flow can be unstable. In these same cases, there is a more energetic flow a substantial distance from the aerodynamic surface. These types of flows are common in some types of turbomachines. 
         [0055]    In the parallel sets or the series sets, one leg, both legs, and/or the cross of the “U” may be extended partially downstream and partially crosswise or parallel to the direction of flow to help guide the deflection and vortex action to where it is most useful. These extensions will be called vortex guides. If they are long, they may require additional bracing. 
         [0056]    In general, for manufacturing ease and best structural integrity, the vortex generator sets will be made as one or more large pieces, as opposed to making the U shaped elements separately and then joining. However, the form and function is well described using the terms “U” shape, element, set, legs, guide, cross piece, series, and parallel. Two additional terms are parallel mounting frame and radial mounting frame, defined next. 
         [0057]    For U shaped elements acting in parallel, the cross pieces of the U shaped elements are in a line, which will usually be a structural element and to which the legs are attached. This structural element will be termed the “parallel mounting frame” for the legs. This mounting strut is, as previously stated, also more or less parallel to the adjacent aerodynamic surface. 
         [0058]    For U shaped elements acting in series, their legs will touch and be in a line, which line will usually be made as a structural element and to which the cross pieces will be attached. This long structural element will be termed the “radial mounting frame,” because of its usual approximate radial orientation if installed in a turbomachine diffusing flow passage. It will normally be within 45 degrees of perpendicular to the aerodynamic surface, or, in a turbomachine, a duct or diffuser wall. 
         [0059]    A less preferred series arrangement has only a single spine mounting for the vanes, created by deleting one leg of the “U” shaped elements, and the spine joining the crosses of the “U”&#39;s in their mid-section or ends. This arrangement reduces drag slightly, but is less robust structurally, and the deflected gas will not penetrate as easily either through the high energy free stream gas or into a boundary layer as with the full “U” shaped elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0060]      FIG. 1  is a perspective view of a vortex generator according to this invention illustrating the primary aerodynamic surface of a duct, a strut across the duct constituting the mount for the vortex generators, and oppositely inclined vortex generators extending from the strut towards (but not to the primary aerodynamic surface) illustrating deflection of gases relative to aerodynamic surface, the deflection here being alternately towards and away from the aerodynamic surface as it extends across the duct; 
           [0061]      FIG. 2A  is a side elevation view of the vortex generator of this invention mounted to a strut extending across a duct, the strut being provided with the vortex generators of this invention; 
           [0062]      FIG. 2B  is a view along lines  2 B- 2 B of  FIG. 2A  looking at the vortex generator from upstream to downstream; 
           [0063]      FIG. 2C  is a view along lines  2 C- 2 C of  FIG. 2A  looking across the strut illustrating the vortex generators in section; 
           [0064]      FIG. 3A  is a vortex generator and mount having flow through the vortex generator from the vicinity of a aerodynamic surface through the generators of and into the free stream gas flow; 
           [0065]      FIG. 3B  is a vortex generator and mount having flow through the vortex generator from the free stream gas flow to the vicinity of the aerodynamic surface; 
           [0066]      FIG. 4A  is a vortex generator having first and second downwardly extending sections with the first section constituting a conventional airfoil shaped vortex generator with a smaller group of vortex generators mounted to an inverted U-shaped extension which stands partially towards but not to the aerodynamic surface; 
           [0067]      FIG. 4B  is a vortex generator where respective pairs of vortex generators alternatively deflect fluid flow in the free stream; 
           [0068]      FIG. 5  is a vortex generator shown detached from the primary aerodynamic surface, the vortex generator having conventional vortex generator vanes placed on the surface of the vanes of the vortex generator; 
           [0069]      FIG. 6A  is a view from the inlet, compressor portion of a turbo machine illustrating the vortex generators of this invention placed around the periphery of a confining circular duct, on struts supporting a central bearing housing from the periphery of the circular duct, and about the central bearing housing of the turbo machine; 
           [0070]      FIG. 6B  is an illustration of a turbomachine downstream of  FIG. 6A  illustrating portions of the turbomachine where the high drag vortex generator of this invention may be placed (the drawings being labeled  6 B- 1  and  6 B- 2  respectively); 
           [0071]      FIGS. 7A and 7B  illustrate offset overlying and underlying vortex generators with respect to a strut standing across a turbo machine; 
           [0072]      FIGS. 8A and 8B  illustrate the high drag vortex generator of this invention mounted between two stator blades for preventing the formation of boundary layers in the interstitial spatial interval between the tips of rotor blades and the sidewalls of the confining duct of the turbo machine; 
           [0073]      FIG. 9A  is a side elevation section of a turbo machine at the beginning of a diffuser annulus illustrating a mounting placed in the high speed streamflow with vortex generators of this invention attached thereto; 
           [0074]      FIG. 9B  is a cross section taken and the diffuser mounting schematically illustrating deflections produced by the vanes; 
           [0075]      FIG. 9C  is an expanded cross-sections similar to  FIG. 9   b  illustrating a diffuser with an annular disposition within the beginning of the diffuser annulus, this diffuser being provided with numerous vertical vanes to prevent sideways displacement of high-speed gas flow; 
           [0076]      FIG. 10A  is a side elevation taken at the diffuser end of a turbo machine illustrating placements of the vortex generator of this invention at the terminus of the flow annulus and the beginning of the conventional diffuser; 
           [0077]      FIG. 10B  is view of the diffuser of  FIG. 10   a  taken along lines  10   b - 10   b  of  FIG. 10   a;    
           [0078]      FIG. 11A through 11D  are various embodiments of vortex generators having U-shaped configurations; 
           [0079]      FIG. 12A  is a view of the beginning of a diffuser in a turbo machine illustrating the high drag vortex generators of this invention placed between structural struts in a grid like array; and, 
           [0080]      FIG. 12B  is a section taken across a diffuser similar to that shown in  FIG. 12   a  one immediately behind a moving blade row in a turbo machine. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0081]    Referring to  FIG. 1 , one half of a U-shaped duct  10  constituting the primary aerodynamic surface P is shown. Utilizing this example, the reader will understand that the duct in which the gas flow is confined does not necessarily have to be a closed duct. For example the duct may be a flow diverting duct of U-shape or compressor discharge diffuser placed within the exhaust of a turbo machine. 
         [0082]    A mounting strut M is mounted to one wall of U-shaped duct  10  and is shown extending across U-shaped duct  10 . Mounting M is the surface to which vortex generators G are mounted. It is important to understand that mounting M and vortex generators G are in the free stream gas flow. Further, vortex generators G stand from the underside of mounting M and extend to and toward primary aerodynamic surface P. These vortex generators G may never reach the primary aerodynamic surface; instead they may stop short of the primary aerodynamic surface P. In this extension to and toward primary aerodynamic surface P, vortex generators G can extend into the boundary layer, although this is not preferred. The reason this extension is not preferred is that I have found that the prediction of the direction of flow of boundary layers, including any stalled gases is not possible. Boundary layer flow direction in turbomachine diffusers with struts and having efficiencies in the range of less than 70 percent is often completely unpredictable. 
         [0083]    I prefer the vortex generator vanes to have two components. The first of these components is a vaned surface is essentially parallel to the local free stream flow. The second of these components is vanes for deflecting gas flow towards and away from the primary aerodynamic surface P. Both of these vane surfaces must act in tandem. Further, one of the vane surfaces can also be the mount. 
         [0084]    Referring further to  FIG. 1 , vortex generators G are airfoil shaped and inclined with respect free stream gas flow in opposite directions with vortex generators  11  deflecting flow a way from wall of U-shaped duct  10  and vortex generators  12  deflecting flow toward wall of U-shaped duct  10 . Vortex generators  11 ,  12  form a converging flow volume with respect to the free stream duct flow. As such, they tend to deflect the flow downwardly towards primary aerodynamic surface P. Vortex generators  12 ,  11  form a diverging flow volume with respect to free stream duct flow. As such, they tend to deflect the flow upwardly with respect to primary aerodynamic surface P. Both deflections relative to primary aerodynamic surface P have been found beneficial with respect to the reduction of boundary layer accumulation on primary aerodynamic surface P downstream from vortex generators  11 ,  12 . 
         [0085]    Optionally, further flow deflection can be provided by extensions  13 ,  14  to mounting M; extensions  13  deflect fluid toward the wall of duct  10 ; extension  14  deflects fluid away from the wall of duct  10 . 
         [0086]    As can be seen, vortices are schematically illustrated. These vortices emanate from that portion of the vanes  11 ,  12  which is nearest to but slightly separated from primary aerodynamic surface P. Thus, it will be understood that mount M independently supports vanes  11 ,  12  so that the tips of the respective vanes are just overlying primary aerodynamic surface P. 
         [0087]    Referring to  FIG. 2A , strut  20  standing across annular duct  22  is shown. Strut  20  defines primary aerodynamic surface P. Overlying front edge of strut  20  is mounting M which is here shown as two smaller struts  24 . Referring to  FIGS. 2B and 2C , vortex generators G can be seen mounted underlying struts  24  extending to and towards primary aerodynamic surface P. It can be thus seen, that the vortex generator is suitable for mounting to struts. 
         [0088]    Referring to  FIG. 3A , an airfoil shaped strut  30  with an overlying mounting strut  32  is shown having vortex generators G mounted on either side of mounting strut  32 . Here, vortex generators G are hollow to permit fluid flow from the vicinity of primary aerodynamic surface P, through mounting strut  32  to upper vortex generator G to the main free stream gas flow. 
         [0089]    Referring to  FIG. 3B , an airfoil shaped strut  30  with an overlying mounting strut  32  is shown having underlying vortex generators G. One vortex generator is shown fastened to primary aerodynamic surface P to permit flow of free stream gas from the high speed stream to and toward primary aerodynamic surface P of strut  30 . Free stream gas enters from a hole in strut  32  and exits of immediately adjacent primary aerodynamic surface P. From the views of  FIGS. 3A and 3B , the reader will understand that the vortex generators G can be hollowed to permit fluid flow. 
         [0090]    The preferred direction and location of gas insertion into the free stream flow is downstream, and the preferred position is into the low pressure zone associated with the trailing vortices at the tips of vanes G. A short tube extending from the vane tip trailing corner and projecting into the vortex may be found by experiment to improve performance. 
         [0091]    Referring to  FIG. 4A , primary aerodynamic surface P is shown having a mounting M with a two-part vortex generator G depending from the mounting toward primary aerodynamic surface. The first part of the vortex generator  40  is a conventional airfoil shaped deflector. The second part of the vortex generator  42  is a U-shaped deflector depending from the end of conventional airfoil shaped deflector  40 . Again, vortex generator G does not have contact with primary aerodynamic surface P. 
         [0092]    Referring to  FIG. 4B , conventional airfoil shaped vortex generators  44  are shown depending from a mounting M and inclined in a first direction with respect to passing free stream gas flow. Conventional air foil shaped vortex generators  45  are shown depending from a mounting M and inclined in a second direction with respect to passing high-speed gas flow. It can be seen that the vortex generators  44 ,  45  can be arrayed in deflecting pairs, which deflecting pairs may or may not be parallel to one another. It will again be noted that the vortex generators as suspended from mounting M, do not come into contact with the primary aerodynamic surface P. Further, the vortices are typically generated from lowermost, protruding, and trailing portion of the respective vortex generators. 
         [0093]    Referring to  FIG. 5 , mounting M has converging vortex generators  51  mounted on the upper surface of mounting M and diverging vortex generators  52  mounted on the lower surface of mounting M. These respective converging and diverging vortex generator pairs  51 ,  52  can be arrayed on opposite sides of mounting M. Remembering the example of  FIG. 1 , it will be understood that vortex generator pairs  51  overlying vortex generator pairs  52  cause fluid in the wake of mounting M to move in the same direction. Here, converging vortex generators  51  will deflect fluid upwardly away from the wake of mounting M; diverging vortex generators  52  will deflect fluid upwardly toward the wake of mounting M. The respective overlying and underlying deflections will be complementary causing over all fluid flow to move upwardly with respect to the perspective view of  FIG. 5 . 
         [0094]    It will also be understood that vanes  51  can have their own subset of vortex generators. These are shown on the leading edge of one of the vortex generators  51 . 
         [0095]      FIG. 6A  is a front view of a turbo machine illustrating the vortex generators G of this invention in three discrete locations. First, vortex generators  60  are placed about the circular periphery of the turbo machine. Second, vortex generators  61  are aligned to the struts of the turbo machine. Finally, vortex generators  62  are placed about the central bearing housing of the turbo machine. All vanes are schematically shown by broken lines. 
         [0096]      FIG. 6B  is a perspective illustration of a turbomachine illustrating areas of the machine where the high drag vortex generators of this invention may be placed. Those areas are diffuser  601 , the vortex generator here shown as part of a silencer on the silencer inlet; diffusing duct  602 , the vortex generator here shown as a part of the compressor mounted on two stages of blades; diffusing duct  603 , the vortex generator here shown mounted on two stages of stators; compressor outlet  604 , the vortex generator here shown mounted on a blade row; duct bend  604 . 5 , the vortex generator here shown directing annular segments of flow to follow the contour of the duct; compressor outlet  605 , the vortex generator here shown mounted on a stator row; entrance to compressor inlet  606 , the vortex generator here shown mounted in an annular flow duct; compressor inlet  607 , the vortex generator here shown mounted on a blade row; compressor inlet  608 , the vortex generator shown mounted on a stator row; compressor  609 , the vortex generator here shown mounted on a stator row; compressor  610 , the vortex generator here shown mounted on a blade row; compressor outlet  611 , the vortex generator here shown mounted on a blade row; compressor outlet  612 , the vortex generator here shown mounted on a turning vane or stator row; diffuser  613 , the vortex generator here at the entrance to the combustor; turbine  614 , the vortex generator here shown mounted on a blade row upstream of a diffuser; turbine  615 , the vortex generator here shown mounted on a stator row upstream of a diffuser; exhaust diffuser  616 , the vortex generator here shown mounted between struts; more or less annular diffuser  617 , the vortex generator here shown guiding flow along the cone of the tapered center body; duct bend  618 , the vortex generator here shown as extensions of turning vanes; and, duct bend  619 , the vortex generator here shown that the leading edge in front portion of the turning vane. 
         [0097]      FIGS. 7A and 7B  illustrate offset of vortex generators  70 ,  71  with respect to strut  72 . In  FIG. 7A  vortex generators  70  is downstream the relative to strut  72  from vortex generators  71 . In  FIG. 7B , vortex generators  70  are offset in overlying strut  72  (not shown) with respect to vortex generators  71 . Mounting struts  70  and  71  can be positioned upstream of the strut  72 , as well. This is true if the free stream direction is not aligned parallel to the chord of the strut. 
         [0098]      FIG. 8A  is a perspective view of a turbo machine having rows of stator blades  80  and rotating rows of rotor blades  81  immediately behind stator blades  80 . The view illustrated is immediate to the primary aerodynamic surface P which is the conical converging casing  82  of a turbo machine. Extending across the respective stator blades  80  are vortex generators  84  aligned in the high-speed gas flow in deflecting pairs. It is known that the interstitial volume between the tips of rotor blades  81  and conical diverging casing  82  of a turbo machine are areas where boundary layer gas can have particularly large consequences. By the introduction of my high drag vortex generators  84 , boundary layer gas accumulation in this interstitial volume can be mitigated, albeit at the cost of losses due to varying angles of attack on the rotating blade. 
         [0099]    In  FIG. 8B , side-by-side structure of the vortex generators  84  is illustrated. Specifically, vertical structures  80  are shown interconnected by arcuate deflecting surfaces  84 . These respective surfaces  84  typically have alternating deflections of their arcuate surfaces between the vertical members  80  of the vortex generators. These arcuate shapes, properly sized, can keep the available area constant for the flow enclosed by the vanes, which reduces flow losses, especially at the intersections. 
         [0100]    Some guidelines in the design of high drag vortex generators follow. The preferred initial design choice is high drag vortex generators acting in parallel. In an annular or round diffuser, the number of elements on a circumference may be from about five to over 50, with 12 to 24 being a good first trial, to be refined by physical or computational experiment. The available passage width, if small with respect to the circumference may dictate a higher number than otherwise would be used. The vane and mounting elements, if uncurved, may be sloped up to about 8 degrees in the direction of flow, without producing unduly large wakes. For vortex generator elements acting in series, this angle may be increased to between 8 and 10 degrees, as experiment shows to be acceptable. For vanes with curvature (camber) and substantial thickness along the direction of flow, much greater flow deflections are possible without large unstable wakes. The vane tips, as a first trial, should extend toward the aerodynamic surface about half of the distance between the mounting and the aerodynamic surface. If experiment shows that a stronger vortex action would be desired, then vortex generators in acting series, or adding more curvature for increased flow deflection may be added. This will extend the benefit of stable flow farther downstream. With the series arrangement, it may be practical to shorten or even delete the vane portions between the mounting and the aerodynamic surface, but not with the purely parallel arrangement. For annular and more or less circular or oval diffusing flow passages, it is beneficial to maintain a flow swirl angle of from about 6 to 12 degrees, with the lower swirl appropriate for low angle diffusers and for converging flow along the convergent tapering portions of center bodies in annular diffusers. 
         [0101]    Referring to  FIGS. 9A and 9B , flow annulus  90  of a turbo machine is illustrated in section. Mount M is placed about and within annulus  90  and has mounted thereto the vanes  91 ,  92 . These vanes  91 ,  92  protrude from mount M toward annulus walls  94 ,  95  respectively. It is to be noted, that the respective vanes  91 ,  92  do not contact the walls. Further, adjacent vanes  91 ,  92  can deflect in the same direction or alternate directions, as schematically illustrated. 
         [0102]    Typically adjacent vanes are canted in differing directions with respect to the flow through annulus  90 . This produces boundary layer destroying mixing and turbulence in the wakes of fluid passage through the vortex generators. However, it may be found by experiment that having two or three adjacent vanes deflecting flow in one direction, and then two or three vanes deflecting flow in another direction may produce better results. 
         [0103]    Referring to  FIG. 9C , a variation of this vortex generator is shown. Specifically, metal strip  98  is formed as a continuum and mounted interior of the turbo machine diffuser  90 . Respective sections of metal strip  98  are bent in different deflecting directions with portions  96  deflecting fluid flow towards inner wall  95  and portions  97  deflecting fluid flow towards outer walls  94 . Mounting of the vortex generator occurs at mounts  99  fastened here to inner annulus walls  95 . In practice, the strip would have smooth curves for flow efficiency, rather than the angular construction necessary for illustration understanding shown in the drawings. 
         [0104]    Referring to  FIGS. 10A and 10B , placement of the annulus vortex generators in pairs is illustrated.  FIG. 10A  illustrates in section the exhaust of a turbo machine. Flow annulus  100  terminates at turbo machine inner housing  101 . Vortex generators V 1  and V 2  are placed around outer annulus surface  102  and inner annulus surface  103 , respectively. As illustrated in the side elevation of  FIG. 10A , boundary layer accumulation downstream of the annulus  100  is presented by mixing caused by the vortices. 
         [0105]    Referring to  FIG. 11A , an annularly arrayed vortex generator is illustrated. Specifically, radially arrayed (or vertically arrayed) vertical members  110  are connected by respective upwardly deflecting members  111  and downward deflecting members  112 . In the preferred embodiments here shown, upwardly deflecting members  111  alternate between downwardly deflecting members  112  to produce alternating deflections. 
         [0106]    Referring to  11 B, square arrays  113 ,  114  are shown having respective parallel deflecting surfaces inclined at 30 degrees with respect to the direction of fluid flow. The axis of fluid flow bifurcates the general deflection of arrays  113 ,  114 . Thus square arrays  113  will deflect the fluid upwardly while square arrays  114  will deflect the fluid downwardly. 
         [0107]    Referring to  FIG. 11C , a vortex generators such as that found near the outlet of a compressor is illustrated. Specifically, a compressor will have high-speed flow adjacent the outer annulus of a turbo machine. The vortex generator  115  here illustrated, deflects high-speed gas flow from near the exterior surface of the turbo machine annulus and channels that high-speed gas flow adjacent the inner annular surface, energizing the boundary layers near the shafting and shaft covers of the turbo machine. 
         [0108]    Referring to  FIG. 11D , paired series of vanes  116 ,  117  are shown on opposite sides of a single vertical member  118 . The respective vanes are canted at 30 degrees one with respect to another. At the same time, fluid flow is incident upon the vanes at angles of 15 degrees. Thus, one said of vanes  116  will deflect the flow upwardly; the other set of vanes  117  will deflect the flow downwardly. 
         [0109]    It will be understood that the illustrations of  FIGS. 11A-D  are all exemplary. Numerous other deflecting shapes will work as well. What is needed is the first vane flow confining components for deflecting fluid flow from the high speed gas flow towards and/or away from the primary aerodynamic surface. The second vane flow confining components for maintaining the deflected free stream fluid flow along a path towards and/or away from the primary aerodynamic surface. It is designed to avoid, or at least control flow gas motion parallel to the primary aerodynamic surface. Thus, control is attained by the vertically extending or radially extending second main flow confining components. This has the result that boundary layer formation downstream from the vortex generator is inhibited by mixing of the high speed free stream gas flow into the volume adjacent the primary aerodynamic surface where the boundary layers might otherwise thicken excessively. 
         [0110]    Referring to  FIG. 12   a , a turbine annulus  120  has inner wall  121  spatially separated from outer wall  122  by respective struts  123 , these respective struts  123  being placed at intervals around annulus  120 . Into the interstitial volume defined between respective inner wall  121  and outer walls  122  there are placed vortex generator grids R. These vortex generator grids include mount M which here is a grid having circumferential components  125  and radial components  126 . On the exterior of mount deflection vanes  127  protrude toward inner wall  121 , struts  123  and outer wall  122 . Interior of the respective grids there are placed deflection vanes  128  for supplying gas flow deflection towards outer wall  122  and deflection vanes  129  for supplying gas flow deflection towards inner wall  121 . 
         [0111]    Referring to  FIG. 12   b , the placement of vortex generator grid R one immediately behind moving blade row B is illustrated. 
         [0112]    Vanes  130  having differing degrees of deflection of the main gas flow stream are mounted so as to prevent the accumulation of boundary layer and/or stall gas downstream of the moving blade row B.