Abstract:
The present invention relates in general to vortex shedding flow meters with enhanced sensitivity for sensing and measuring vortex frequencies.

Description:
[0001]    The present application is a continuation of copending U.S. application Ser. No. 13/416,048, filed Mar. 9, 2012, which claims priority to U.S. Provisional Patent Application Ser. No. 61/451,200, filed on Mar. 10, 2011. Both of the aforementioned applications are incorporated herein by reference in their entirety for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates in general to vortex shedding flow meters. In particular, the invention relates to an improved vortex shedding flow meter with enhanced sensitivity for sensing and measuring vortex frequencies. 
       BACKGROUND OF THE INVENTION 
       [0003]    Vortex shedding flow meters have been used for many applications and are able to measure the flow rates of a variety of fluids, including steam, liquids, and gases. A vortex shedding flow meter operates on the principle that a bluff body, when placed in a moving fluid, produces an alternating series of vortices at a frequency that is directly related to the velocity of the moving fluid. Some vortex shedding flow meters detect the frequency of the shed vortices, thus the flow rates, by having a vane that is in communication with a piezoelectric material, positioned downstream from the bluff body. As the vortices pass over the vane, alternating lateral forces deflect the vane one way and then the other creating a surface charge about the piezoelectric material. The surface charge of the piezoelectric material is a function of the strain on the vane and therefore the velocity of the fluid may be measured. 
         [0004]    Based on the design of current vortex shedding flow meters, however, the piezoelectric materials, are susceptible to producing charge not only when there is a deflection of the vane but also through turbulence and noise within the measured system, yaw (strain in the direction of the flow) due to drag, and vibrations. 
         [0005]    There are a number of selection criteria for an appropriate piezoelectric material, including sensitivity, dynamic range, signal-to-noise ratio, temperature and cost. Sensitivity is directly related to the piezoelectric coefficient of the material. Dynamic range is a function of both sensitivity and mechanical robustness, meaning the material must generate a usable charge signal at low flow as well as remain mechanically sound at maximum strains, often a million times greater. Maximizing signal-to-noise requires that the piezoelectric material only respond to the specific mechanical strain vector being measured and reject all others. Further, bulk temperature and electromagnetic effects such as pyroelectric and ferromagnetic noise should preferably have little effect on the piezoelectric material Accordingly, there are a number of factors that should be considered before an appropriate and effective piezoelectric material is found. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention recognizes and addresses the foregoing considerations, and others, of prior art construction and methods. 
         [0007]    According to an aspect, the present invention provides a vortex shedding flow meter. The flow meter includes a housing and a bluff body having a first side that makes initial contact with the flow of a fluid. The flow meter further includes a detector wing oriented in a cantilever manner from the housing and is positioned spaced apart from the bluff body in relation to the flow of the fluid. The detector wing has a channel within the wing. In this aspect, the channel further includes a Y-cut lithium niobate crystal to sense deflections of the detector wing and at least two electrodes that make contact with the Y-cut lithium niobate crystal and that extend through the channel to the housing. 
         [0008]    According to another aspect, the present invention also provides a vortex shedding flow meter. The flow meter includes a housing and a hexagonal bluff body having a first side that makes initial contact with the flow of a fluid, the first side having a length at least two times the length of an opposite, parallel second side and at least five times the length of two adjacent perpendicular sides. The flow meter further includes an octagonal detector wing oriented in a cantilever manner from the housing and spaced apart from the bluff body in relation to the flow of the fluid. The detector wing further includes a first side proximate the bluff body with a length substantially equal to the length of an opposite parallel second side and substantially equal to the length of two perpendicular third sides. 
         [0009]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    A full and enabling disclosure of the present invention, including the best mode thereof directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended drawings, in which: 
           [0011]      FIG. 1A  is a side view of a vortex shedding flow meter in accordance with an embodiment of the present invention; 
           [0012]      FIG. 1B  is a cross-sectional top view of a bluff body and detector wing viewed along line  1 B- 1 B of  FIG. 1A ; 
           [0013]      FIG. 2A  is a cross-sectional side view of a vortex shedding flow meter in accordance with an embodiment of the present invention; 
           [0014]      FIG. 2B  is an enlarged view of the portion indicated by circle  2 B of  FIG. 2A ; 
           [0015]      FIG. 3  is a perspective view of a vortex shedding flow meter in accordance with an embodiment of the present invention fitted within a cross-section of a pipe; 
           [0016]      FIG. 4A  is a partially transparent, side view of spacers fitted over piezoelectric material in accordance with an embodiment of the present invention; 
           [0017]      FIG. 4B  is a partially-transparent, top view of the spacers illustrated in  FIG. 4A ; 
           [0018]      FIG. 4C  is a perspective view of the spacers illustrated in  FIG. 4A ; 
           [0019]      FIG. 4D  is a partially transparent, top view of spacers fitted over piezoelectric material in accordance with an additional embodiment of the present invention; 
           [0020]      FIG. 5  is a partial cross-sectional view of a vortex shedding flow meter within a shroud in accordance with a second embodiment of the present invention; 
           [0021]      FIG. 6  is a partial cross-sectional view of the vortex shedding flow meter within a shroud of  FIG. 5 ; 
           [0022]      FIG. 7  is a transparent, side view of a channel fitted with piezoelectric material in accordance with the embodiment illustrated in  FIG. 5 ; 
           [0023]      FIG. 8  is a front view of the vortex shedding flow meter illustrated in  FIG. 5  with the shroud removed; 
           [0024]      FIG. 9  is a cross-sectional view taken along line A-A of  FIG. 8 ; 
           [0025]      FIG. 10  is an enlarged view of the portion indicated by circle  10  in  FIG. 9 ; 
           [0026]      FIG. 11  is a front view of the vortex shedding flow meter of  FIG. 8  with a cover; 
           [0027]      FIG. 12A  is a computational fluid dynamics model of a vortex shedding flow meter in accordance with a first embodiment of the present invention where water is passed at 0.1 ft/sec; 
           [0028]      FIG. 12B  is a computational fluid dynamics model of a vortex shedding flow meter in accordance with a first embodiment of the present invention where water is passed at 1.0 ft/sec; 
           [0029]      FIG. 12C  is a computational fluid dynamics model of a vortex shedding flow meter in accordance with a first embodiment of the present invention where water is passed at 10 ft/sec; 
           [0030]      FIG. 12D  is a computational fluid dynamics model of a vortex shedding flow meter in accordance with a second embodiment of the present invention where water is passed at 5 ft/sec; 
           [0031]      FIG. 12E  is a computational fluid dynamics model of a vortex shedding flow meter in accordance with a second embodiment of the present invention where water is passed at 10 ft/sec; 
           [0032]      FIG. 12F  is a computational fluid dynamics model of a vortex shedding flow meter in accordance with a second embodiment of the present invention where water is passed at 1 ft/sec; 
           [0033]      FIG. 12G  is a computational fluid dynamics model of a vortex shedding flow meter in accordance with a second embodiment of the present invention where water is passed at 0.5 ft/sec; 
           [0034]      FIG. 12H  is a computational fluid dynamics model of a vortex shedding flow meter in accordance with a second embodiment of the present invention where water is passed at 0.1 ft/sec; 
           [0035]      FIG. 12I  is a computational fluid dynamics model of a vortex shedding flow meter where a shroud having an obstruction is utilized; 
           [0036]      FIG. 13  is a graphical representation of the lift coefficient and drag coefficient of a detector wing of the present invention versus angles of attack as discussed in Example 2; and 
           [0037]      FIG. 14  is a graphical representation of the charge produced by a piezoelectric material in response to changes in velocity while positioned in a vortex shedding flow meter of the present invention, as discussed in Example 5. 
       
    
    
       [0038]    Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0039]    Reference will now be made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0040]    A vortex shedding flow meter  100  in accordance with an embodiment of the present invention is shown in  FIG. 1A  through  FIG. 3 . Flow meter  100  includes a bluff body  102  and a detector wing  104  that both extend in a cantilever manner from a housing  106 . Detector wing  104  is fixedly attached to housing  106 . As shown in  FIGS. 2A and 2B , detector wing  104  further defines a channel  108  that extends upward into housing  106 . Channel  108  may allow an operative connection between detector wing  104  and housing  106  such that generated vortices from bluff body  102  may be detected and measured, as more fully discussed below. 
         [0041]    To further increase the efficacy of vortex shedding flow meter  100 , varying the size and shape of bluff body  102  and detector wing  104 , along with varying their orientation with respect to one another, results in improved measurement capabilities. For example, in some embodiments and as best illustrated in  FIG. 1B , bluff body  102  may be constructed as a hexagonal geometric shape. In such instances, bluff body  102  includes a first side  112  which makes initial contact with the fluid whose velocity is to be measured by vortex shedding flow meter  100 . Although  FIG. 1B  illustrates bluff body  102  as a hexagonal geometric shape, it should be understood that bluff body  102  may be constructed with any number of sides to effectively create measurable vortices. For example, in some embodiments, bluff body  102  may include three, four, five, six, seven, eight, or more sides. Additionally, the size or width of each side may vary to increase the measuring capabilities of vortex shedding flow meter  100 . For example, in some embodiments, each side may have an equal width, or in other embodiments, first side  112  of bluff body  102  may be of a greater width than any of the other sides. 
         [0042]    In some embodiments of the present invention, such as where bluff body  102  is a hexagonal geometric shape, bluff body  102  may include a first side  112  that is between about 0.1 and 0.5 inches in width. Additionally, in such embodiments, bluff body  102  may include a second side  114 , parallel to first side  112  that is between about 0.05 inches and 0.25 inches. Such embodiments of bluff body  102  may also include lateral sides  116  perpendicular to first side  112  and second side  114 , which are preferably between 0.025 and 0.1 inches. The configurations of bluff body  102  described above may be of appropriate size when used in a pipe having a diameter of between about 1 and 6 inches. Such sizes may also be varied proportionally to be utilized in pipes of different diameters. 
         [0043]    As also shown in  FIG. 1B , in some embodiments, detector wing  104  may be constructed as an octagonal geometric shape. Such a shape produces a low drag coefficient verses a lift coefficient for a number of attack angles as shown in  FIG. 13  and Example 2. It should be understood, however, that in further embodiments of the present invention, detector wing  104  could include any number of sides. For example, detector wing  104  may include three, four, five, six, seven, eight, nine, ten, or more sides. As also discussed with respect to bluff body  102 , the sides of detector wing  104  may be of any suitable size to increase the measuring capabilities of vortex shedding flow meter  100 . In some embodiments, each side of detector wing  104  may be of equal width, or, in further embodiments, each side of detector wing  104  may be of a different width. 
         [0044]    In some embodiments where detector wing  104  comprises an octagonal geometric shape, detector wing  104  may include a first side  118 , which is spaced apart from second side  114  of bluff body  102 , which is between about 0.05 and 0.2 inches in width. Additionally, such embodiments of detector wing  104  could include a second side  120 , opposite first side  118 , which may also have a width between about 0.05 and 0.2 inches. The sides  122  of detector wing  104  that are perpendicular to first and second end  118 ,  120  may also be of a length between about 0.05 and 0.2 inches. Such embodiments may prove advantageous when placed in a pipe having a diameter between about 1 and 6 inches. Again, as is true with bluff body  102 , the configurations and sizes of detector wing  104  described above may be varied proportionally based on the size of the pipe utilized. 
         [0045]    The spacing between bluff body  102  and detector wing  104  may also be varied to provide more accurate results in measuring flow rate by vortex shedding flow meter  100 . For example, in some embodiments, the distance between any portion of bluff body  102  and any portion of detector wing  104  may be between about 0.001 inch and 1 inch. In other embodiments, the distance between bluff body  102  and detector wing  104  may be between 0.01 inches and 0.5 inch. The distance between bluff body  102  and detector wing  104  should be such that the vortices created by bluff body  102  reach detector wing  104 . 
         [0046]    Referring now particularly to  FIG. 2A , vortex shedding flow meter  100  includes channel  108  which may allow an operative connection between detector wing  104  and housing  106 . As shown in  FIG. 2B , channel  108  includes a first end  124 , proximal housing  106 , and a distal second end  126  located further along the length of detector wing  104 . In some embodiments, a piezoelectric material  128  is placed in channel  108  adjacent second end  126 . Piezoelectric material  128  produces a surface charge in response to deflections within detector wing  104  caused by vortices created by bluff body  102 . This surface charge can be measured to provide the velocity of the moving fluid within the pipe. The placement of piezoelectric material  128  is done such that piezoelectric material  128  is in an area of maximum imparted strain for proper detection of all movements of detector wing  104 . 
         [0047]    Piezoelectric materials suitable for use in the present invention may include piezoelectric ceramics, such as barium titanate, lead ziconate titanate, and lead titanate, along with polymer films including polyvinylidene fluoride. Other piezoelectric materials suitable for use with the present invention may also include monocrystalline materials, including quartz, lithium niobate, potassium niobate, and lithium tantalate, among others. The preferred piezoelectric material may depend on the requirements of the application. For example, monocrystalline materials may provide better resistance to changes in temperature of the fluid to be measured, if such is the case in the user&#39;s application. 
         [0048]    In an embodiment of the present invention, lithium niobate may be utilized as piezoelectric material  128 . It has been found that lithium niobate has an advantageous piezoelectric constant d 33 , which increases the sensitivity of the piezoelectric material in detecting strain. In further embodiments of the present invention, the piezoelectric material  120  may be a “Y-cut” lithium niobate crystal. The coordinate system used to describe the physical tensor properties of lithium niobate is neither hexagonal nor rhombohedral but rather a Cartesian XYZ system. The accepted conventional coordinate system can be chosen as follows: the Z-axis is along the c-axis (i.e. the spontaneous polarization direction), the X-axis is perpendicular to the mirror plane and the Y-axis is chosen to form a right-hand system. Thus, the Y-axis must lie in a plane of mirror symmetry. Based on the lithium niobate&#39;s coordinate system, a “Y-cut” lithium niobate crystal is one that is cut perpendicular to the Y-axis. 
         [0049]    Such a crystal is produced by cutting perpendicular to the crystal&#39;s Y-axis providing it with a “Y”-crystallographic orientation. A Y-cut lithium niobate crystal avoids pyroelectric effects (typically present in Z-axis oriented crystals), while still utilizing an advantageous piezoelectric sensitivity. In some embodiments, the “Y-cut” lithium niobate crystal of the present invention allows for the crystal to have a continuous operating range up to 450° C. and is immune to thermal shock below 100° C/s. When a Y-cut lithium niobate crystal is utilized in the present invention, in some embodiments, the crystal is placed within channel  108  such that its Y-axis is perpendicular to the deflection of the wing. 
         [0050]    Prior to insertion within channel  108 , in some embodiments, piezoelectric material  128  may be fitted between two spacers  130  as shown in  FIGS. 4A through 4D . Spacers  130  may serve to properly hold piezoelectric material  128  within channel  108 . Spacers  130  for use in the present invention may be constructed of any suitable material in the art capable of properly securing piezoelectric material  128  while vortex shedding flow meter  100  is in use. For example, forsteire ceramics may be used due to their acceptable thermal expansion coefficient. The needs of a particular application, however, may dictate the appropriate material of spacers  130 . 
         [0051]    In this embodiment, within spacers  130  is a metalized layer  132  that makes direct contact with piezoelectric material  128 . In some embodiments, metalized layer  132  may be constructed of silver or silver palladium. Metalized layer  132  of spacers  130  may also include wire electrodes  134  that are fused to metalized layer  132 . Such electrodes  134  may be made of any appropriate metal material, including, in some embodiments, silver. The metalized layers  132 , electrodes  134  and the piezoelectric material  128  act together to create a capacitor to relay the charge produced to housing  106  for determination of the flow rate. Spacers  130  may further define electrode notches  136  for proper placement of electrodes  134 . Electrode notches  136  may be located to oppose one another, as shown in  FIG. 4A , or may be offset as illustrated in  FIG. 4D . By providing offset electrode notches, a user may avoid the risk of contact between electrodes which could lead to shorting. 
         [0052]    Piezoelectric material  128  may fit securely within spacers  130 . In some embodiments, however, a material, for example, potting compound, may provide a strain relief at a point of contact between spacers  130  and piezoelectric material  128 . The potting compound may also make contact with electrodes  134  and aid in maintaining their placement. 
         [0053]    Once piezoelectric material  128  is properly situated within spacers  130 , spacers  130  may be placed within channel  108 . In some embodiments, and as shown in  FIGS. 2A and 2B , spacers  130  and channel  108  may be slightly tapered. Such tapering may allow the walls of channel  108  to force spacers  130  together, so that spacers  130  and piezoelectric material  128  will press fit in channel  108  to maintain a secure connection. 
         [0054]    Spacers  130  and channel  108  may include a high surface finish. For example, in some embodiments, spacers  130  and channel  108  may have a surface finish between about 0.1 and 2.0 μm. In further embodiments, spacers  130  and channel  108  may have a surface finish between about 0.2 and 0.8 μm. Such a surface finish may be necessary to avoid any unnecessary stress on spacers  130  while situated within channel  108 . If such stresses are present and reach an undesirable level, spacers  130  may fail structurally as they are moved into channel  108 . 
         [0055]    After spacers  130  are properly placed within channel  108 , mechanical force may be applied to spacers  130  (which carry piezoelectric material  128 ) to secure them in position. In some embodiments, and as illustrated in  FIG. 2B , this may be accomplished using a screw  138  and a stressing ring  140 . In such embodiments, a portion of channel  108  may be threaded such that screw  138  will move downward as it is rotated and come in contact with stressing ring  140 . Stressing ring  140  may provide sufficient force to spacers  130  to maintain the proper placement of piezoelectric material  128 . If a screw is utilized, it may be equipped with a through hole  142  such that electrodes  134  may pass to housing  106 . 
         [0056]    Once electrodes  134  have been extended to housing  106 , devices (not shown) within (or external to) housing  106  may detect the charge transmitted by electrodes  134  to determine a flow rate. For example, in some embodiments, electrodes  134  pass to housing  106 , which includes a charge amplifier and an analog to digital converter. A signal processor may be utilized to determine the frequency of the vortices. This frequency may be converted to and outputted as a flow rate. 
         [0057]      FIGS. 5-11  illustrate vortex shedding flow meter  100   a  in accordance with an additional embodiment of the present invention. As shown, flow meter  100   a  includes a shroud  110   a  which may aid in producing proper vortices in pipes of larger diameters, for example, pipes having a diameter between about 1 inch and 80 inches. The shroud  110   a  may increase the signal to noise ratio and protect the measured vortices from surrounding noise in the flow pipe. 
         [0058]    In such embodiments, however, shroud  110   a  does not include an obstruction at the upstream end of the shroud such as shroud lip  144   a  as shown in  FIG. 12I . It has been found that such obstructions too often create secondary vortices that are detected by the detector wing and are not indicative of the vortices created by the bluff body. The impact on the efficacy of a vortex shedding flow meter when used with a shroud having such an obstruction  144   a  can best be seen in  FIGS. 12A through 12I . In some instances, as best illustrated in  FIG. 12I , the obstruction  144   a  of shroud  110   a  influences the ability of a bluff body to create any vortices, and often, leaves only laminar flow within the shroud. The obstruction  144   a  produces vortices around the outside of the shroud, which are outside of the detector area and, therefore, unreadable. The only readable vortices read by the bluff body are secondary effects from the obstruction  144   a  of the shroud  110   a,  which may be unreliable. Accordingly, the absence of obstructions on the shroud, as shown in the  FIGS. 12A-12H , allows the detector wing  104   a  to more properly detect the vortices produced by bluff body  102   a  and not to be influenced by secondary flow turbulence profiles. 
         [0059]    The embodiment illustrated in  FIGS. 5-11  generally includes a bluff body  102   a  and a detector wing  104   a  which are sized in a similar manner as the bluff body and detector wing described above. In addition, the detector wing  104   a  is situated in a similar place on the housing  106   a  as described above. The bluff body  102   a,  however, as shown in  FIG. 5 , may extend vertically inside the opening of shroud  110   a  rather than being cantilevered from the housing  106   a.  In such embodiments, the bluff body  102   a  may extend the entire inner diameter of the shroud  110   a,  or in additional embodiments, the bluff body  102   a  may only extend a portion of the diameter of the shroud  110   a.    
         [0060]    Vortex shedding flow meter  100   a,  as shown in  FIGS. 5 and 6 , may be placed within an aperture  146   a  defined in shroud  110   a.  In such embodiments, the shroud  110   a  may also include an arcuate structure(s)  148   a  that fully or partially surrounds the housing  106   a  and in which housing  106   a  is seated to ensure a secure fit of the vortex shedding flow meter  100   a  within the shroud  110   a.  Such a configuration may be utilized with the earlier described embodiment as well when the vortex shedding flow meter  100  is placed within a larger pipe or tube. 
         [0061]    In this embodiment, vortex shedding flow meter  100   a  may also include a temperature sensor  150   a  as shown in  FIG. 5 . The temperature sensor  150   a  may be placed within the housing  106   a,  which includes a temperature sensor channel  152   a.  The temperature sensor channel  152   a  may allow for the proper placement of the temperature sensor  150   a,  and may be filled with potting compound once the temperature sensor  150   a  is in place. The temperature sensor  150   a  may also include an electrode  154   a  or series of electrodes that can communicate the measured temperature to a display device. The temperature sensor  150   a,  in some embodiments, may be a resistance temperature detector and may include carbon resistors, film thermometers, wire wound thermometers, coil elements, or other types of suitable temperature detectors known in the art. The specific application of the vortex shedding flow meter  100   a  may dictate the particular temperature sensor utilized. 
         [0062]    In the embodiment illustrated in  FIG. 5 , the piezoelectric material  128   a  is not situated within spacers, but instead is inserted into channel  108   a,  which is then filled with ceramic potting compound. In such embodiments, as shown in  FIG. 7 , piezoelectric material  128   a  may be equipped with metalized layers  132   a  on opposing sides of piezoelectric material  128   a,  which are fused with electrodes  134   a.  As discussed above, metalized layers  132   a  and electrodes  134   a  may be made of any appropriate metal, for example, silver or silver palladium. 
         [0063]    In some embodiments, and as illustrated in  FIG. 5 , the electrodes  134   a  may pass through a ceramic insulator  156   a  that includes respective passages  158   a  for each electrode  134   a.  Such construction may allow for the passing of the electrodes  134   a  through the housing  106   a  without having them come in contact with one another. Although the embodiment is described with a ceramic insulator, it should be noted that other insulators may also prove useful and may be utilized with additional embodiments of the present invention. 
         [0064]    In embodiments where a shroud is utilized and as shown in  FIGS. 8-10 , the housing  106   a  may include an extension  160   a  and neck  161   a  to cover the piezoelectric material electrodes  134   a  and the temperature sensor electrodes  154   a  so they are not damaged as they extend outside of the shroud  110   a  to an outer surface of the larger pipe or tube. As shown in  FIGS. 9 and 10 , the housing  106   a  includes a threaded portion  162   a  defining inner threads to engage outer threads on a threaded portion  164   a  at a first end  163   a  of extension  160   a.  In additional embodiments, the extension  160   a  may be secured within the housing with the use of an adhesive rather than with treaded portions. Once the extension is properly in place, a stop  166   a  may be installed above the treaded portions  162   a  and  164   a  to prevent the fluid within the tube from entering the housing  106   a.  For example, in some embodiments, a heat shrink tube may serve as the stop  166   a  within the housing  106   a.  The neck  161   a,  as shown in  FIG. 9 , may be placed over a second end  165   a  of the extension  160   a  and secured with, in some embodiments, welding or adhesives. The neck  161   a  is of a suitable diameter such that the exit passage (not shown) of the larger pipe or tube may be relatively small and may still accommodate the neck  161   a  of the vortex shedding flow meter  100   a.    
         [0065]    In embodiments with an extension, the vortex shedding flow meter  100   a  may also include a cover  168   a  to enclose the extension  160   a  as shown in  FIG. 11 . The cover  168   a  provides an additional barrier between the fluid within the pipe (tube) and the electrodes that extend from the housing  106   a  and out of the pipe. In such embodiments, the cover  168   a  could include a recessed end  170   a  that is suitable to fit within the housing  106   a  and the stop  166   a.  The cover  168   a  can be welded into the housing  106   a  to ensure that no additional fluid is allowed to seep into the housing  106   a.  The cover  168   a  may be constructed of any metal or other appropriate material that is suitable to protect the electrodes  134   a  and  154   a  from the fluid that is passing through the pipe. For example, in some embodiments, the cover  168   a  may be constructed of a stainless steel or other type of metal. 
         [0066]    The following examples describe various embodiments of the present invention. Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from consideration of the specification or practice of the invention as disclosed herein. It is intended that the specification, together with the examples, be considered to be exemplary only, with the scope and spirit of the invention being indicated by the claims which follow the examples. 
       EXAMPLES 
     Example 1 
       [0067]    An improved vortex shedding flow meter of the present invention was constructed and tested for efficiency in determining flow rates. The shape of the bluff body and the detector wing of the vortex shedding flow meter used for testing is illustrated in  FIG. 1B . The bluff body and detector wing were further sized in accordance with Table 1 shown below. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Dimensions of experimental bluff body and detector wing 
               
             
          
           
               
                   
                 Number Designation (from FIG. 1B) 
                 Length (in) 
               
               
                   
                   
               
               
                   
                 112 
                 0.250 
               
               
                   
                 114 
                 0.125 
               
               
                   
                 116 
                 0.050 
               
               
                   
                 117 
                 0.098 
               
               
                   
                 118 
                 0.100 
               
               
                   
                 120 
                 0.100 
               
               
                   
                 122 
                 0.100 
               
               
                   
                 123 
                 0.121 
               
               
                   
                   
               
               
                   
                 Distance between 114 and 118: 0.081 inches 
               
             
          
         
       
     
       Example 2 
       [0068]    The drag coefficient and lift coefficient of the improved detector wing described in Example 1 were tested against a wide range of angles of attack. From the detected drag and lift coefficients, a moment coefficient was measured. The results of the testing are shown below in Table 2 and are graphically represented in  FIG. 13 . 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Experimental results of testing drag coefficient and lift coefficient 
               
             
          
           
               
                   
                 Angle of 
                 Lift 
                 Drag 
                 Moment 
               
               
                   
                 Attack 
                 Coefficient 
                 Coefficient 
                 Coefficient 
               
               
                   
                   
               
             
          
           
               
                   
                 0 
                 0 
                 0.0141 
                 0 
               
               
                   
                 10 
                 0.586 
                 0.0224 
                 0.037 
               
               
                   
                 20 
                 0.973 
                 0.0498 
                 0.055 
               
               
                   
                 30 
                 1.124 
                 0.1007 
                 0.072 
               
               
                   
                 40 
                 1.085 
                 0.1447 
                 0.086 
               
               
                   
                 50 
                 0.946 
                 0.1197 
                 0.057 
               
               
                   
                 60 
                 0.877 
                 0.1828 
                 0.05 
               
               
                   
                 70 
                 0.852 
                 0.26 
                 0.037 
               
               
                   
                 80 
                 0.87 
                 0.3595 
                 0.02 
               
               
                   
                 90 
                 0.989 
                 0.3061 
                 0 
               
               
                   
                 100 
                 0.913 
                 0.2369 
                 −0.02 
               
               
                   
                 110 
                 0.893 
                 0.157 
                 −0.037 
               
               
                   
                 120 
                 0.92 
                 0.0969 
                 −0.05 
               
               
                   
                 130 
                 0.992 
                 0.0525 
                 −0.057 
               
               
                   
                 140 
                 1.138 
                 0.118 
                 −0.086 
               
               
                   
                 150 
                 1.187 
                 0.0794 
                 −0.072 
               
               
                   
                 160 
                 1.023 
                 0.0407 
                 −0.055 
               
               
                   
                 170 
                 0.585 
                 0.023 
                 −0.037 
               
               
                   
                 180 
                 0 
                 0.0141 
                 0 
               
               
                   
                   
               
             
          
         
       
     
         [0069]    As indicated from Table 2 and  FIG. 13 , the design of the detector wing of Example 1 minimizes the drag coefficient over the lift coefficient over a wide range of angles of attack. Such design maximizes the sensitivity to vortex generation created by the bluff body. 
       Example 3 
       [0070]    The improved vortex shedding flow meter of Example 1 was properly fitted in a 3 inch diameter PVC pipe with water as the measuring fluid. Water, with a viscosity of 8.90 E −04 Pa·s, was then passed through the pipe at various velocities to measure the Reynolds number which resulted from the varying velocities. A visual representation of each trial is shown in  FIGS. 12A through 12C . 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Experimental results relating to changes in velocity 
               
             
          
           
               
                 Trial 
                 Velocity 
                 Calculated 
                 Measured 
               
             
          
           
               
                 Figure 
                 Ft/s 
                 m/s 
                 Reynolds Number 
                 Reynolds Number 
               
               
                   
               
             
          
           
               
                 12A 
                 0.1 
                 0.03048 
                 2.61E+03 
                 3.0238E+03 
               
               
                 12B 
                 1 
                 0.3048 
                 2.61E+04 
                 3.0238E+04 
               
               
                 12C 
                 10 
                 3.048 
                 2.61E+05 
                 3.0238E+05 
               
               
                   
               
             
          
         
       
     
         [0071]    By utilizing an embodiment of the present invention, the vortex shedding flow meter, first, provides proper vortices for measurement as shown in the above-referenced figures. Additionally, the embodiment of the present invention results in consistent measurements to produce accurate readings of the fluid flow rate in the pipe. 
       Example 4 
       [0072]    The improved vortex shedding flow meter of having a bluff body and detector wing sized in accordance with the embodiment illustrated in Example 1 was properly fitted with a shroud having an inner diameter of 1.063 inches and a pipe with an inner diameter of 3.063 inches. Water, with a viscosity of 8.90 E −04 Pa·s, was then passed through the pipe at various velocities to measure the Reynolds number which resulted from the varying velocities. A visual representation of each trial is shown in  FIGS. 12D through 12H . 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Experimental results relating to changes in velocity 
               
             
          
           
               
                 Trial 
                 Velocity 
                 Calculated 
                 Measured 
               
             
          
           
               
                 Figure 
                 Ft/s 
                 m/s 
                 Reynolds Number 
                 Reynolds Number 
               
               
                   
               
             
          
           
               
                 12D 
                 5 
                 1.524 
                 1.248E+05 
                 1.248E+05 
               
               
                 12E 
                 10 
                 3.048 
                 2.497E+05 
                 2.497E+05 
               
               
                 12F 
                 1 
                 0.3048 
                 2.497E+04 
                 2.497E+04 
               
               
                 12G 
                 0.5 
                 0.1524 
                 1.248E+04 
                 1.248E+04 
               
               
                 12H 
                 0.1 
                 0.03048 
                 2.496E+03 
                 2.496E+03 
               
               
                   
               
             
          
         
       
     
         [0073]    By utilizing an embodiment of the present invention, the vortex shedding flow meter, first, provides proper vortices for measurement as shown in the above-referenced figures. Additionally, the embodiment of the present invention results in consistent measurements to produce accurate readings of the fluid flow rate in the pipe. 
       Example 5 
       [0074]    The embodiment of the present invention discussed in Example 1 was tested to determine whether the pressure variation from the vortices created by the bluff body could be sensed by the detector wing and translated into charge from a piezoelectric material located within a channel as shown in  FIG. 2 . The piezoelectric material&#39;s surface area was measured at 4.00 E −06 m 2 . The results of the test are shown in Table 5 and are graphically represented in  FIG. 14 . 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Measured stress and charge of invention at varying velocities 
               
             
          
           
               
                   
                 Velocity (ft/sec) 
                 Stress (Pa) 
                 Force (N) 
                 Charge (pC) 
               
               
                   
                   
               
             
          
           
               
                   
                 2 
                 5210 
                 2.08E−02 
                 0.129 
               
               
                   
                 4 
                 21219 
                 8.49E−02 
                 0.526 
               
               
                   
                 6 
                 49024 
                 1.96E−01 
                 1.216 
               
               
                   
                 8 
                 86441 
                 3.46E−01 
                 2.144 
               
               
                   
                 10 
                 1.34E+05 
                 5.37E−01 
                 3.330 
               
               
                   
                 12 
                 1.94E+05 
                 7.75E−01 
                 4.803 
               
               
                   
                   
               
             
          
         
       
     
         [0075]    As shown from the graphical representation in  FIG. 14 , the plot of velocity of flow versus the charge produced by the piezoelectric material shows quadratic behavior. These results are desired, as a specified increase in velocity produces a consistent increase in the charge obtained by the piezoelectric material. Again, these results indicate the improved measuring capabilities of vortex shedding flow meters of the present invention. 
         [0076]    All references cited in this specification, including without limitation, all papers, publications, patents, patent applications, presentations, texts, reports, manuscripts, brochures, books, internet postings, journal articles, and/or periodicals are hereby incorporated by reference into this specification in their entireties. The discussion of the references herein is intended merely to summarize the assertions made by their authors and no admission is made that any reference constitutes prior art. The right to challenge the accuracy and pertinence of the cited references is reserved. 
         [0077]    These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims. Therefore, the spirit and scope of the appended claims should not be limited to the description of the versions contained therein.