Abstract:
A collection apparatus is provided for receiving a portion of a medium that flows around the apparatus and directing the portion into a collector. The apparatus includes an axisymmetric streamline receiver and a support member. The streamline receiver includes a chamber as well as at least one opening into the chamber that receives the portion. The support member includes an axisymmetric conduit for directing the portion from the chamber towards the collector. An alternate apparatus includes a streamline receiver, a support member and a tail stabilizer. The receiver includes upper and lower members that form leading and trailing edges to define a chord. Along an exterior surface, one or both of the members provide at least one opening that receives the portion. The support member has a conduit that directs the portion from the opening towards the collector. The tail stabilizer is secured to the streamline receiver to orient the leading edge into the medium.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The invention is a Continuation of U.S. patent application Ser. No. 11/401,012 filed Mar. 29, 2006 and issued as U.S. Pat. No. 7,305,895 on Dec. 11, 2007, which is a Continuation-in-Part, claims priority to and incorporates by reference in its entirety U.S. patent application Ser. No. 11/134,603 filed May 19, 2005 and issued as U.S. Pat. No. 7,111,521 on Sep. 26, 2006. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore. 
    
    
     BACKGROUND 
     The invention relates generally to the sampling of moving fluids such as moving airflows, and more particularly to a sampling system that extracts samples of a moving fluid passing thereover. 
     Moving fluids such as airflows frequently must be sampled for a variety of flow monitoring applications. Such sampling may be performed to examine the ambient air for chemical, biological and/or radiological particulates. Other purposes may include inertial characteristics of the airflows, such as provided by pressure measurements. 
     A typical sampling system incorporates a housing having an inlet formed therein and a pump or fan. The inlet faces directly into the flowstream, and the fluid expands into a diffuser before being diverted to a collector. As fluid (e.g., air) moves over the housing, the pump draws the fluid into the housing through the inlet and toward the collector. The inlet and pump may be optimized for an expected set of external flow conditions. In particular, the system can be designed for appropriate pump power consumption and pump speeds under the expected fluid flow conditions. 
     However, if the fluid flow speed significantly exceeds the design parameters, the Bernoulli effect at the housing&#39;s inlet causes backpressure to develop in the housing. Bernoulli&#39;s principle concerns the relationship between static and dynamic pressures, such that P 0 =P+½ρ u 2 , where P 0  represents stagnation or total pressure (of fluid being at rest), P is static pressure (parallel to fluid flow), ρ is fluid density and u is fluid velocity. 
     In conventional inlets, the velocity decreases as the fluid enters the housing, thereby increasing static pressure inside the housing. The difference between the internal housing static pressure and the external static pressure in the ambient stream represents the backpressure. As the backpressure increases within the housing, the pump must rotate faster than its design operational levels to draw the moving fluid into the collector. Such continued beyond-design operation may yield decreased pump efficiency and increased risk of motor overheating. 
     SUMMARY 
     Conventional medium collection inlets yield disadvantages addressed by various exemplary embodiments of the present invention. In particular, various embodiments mitigate against backpressure inefficiency, as well as reduce inlet friction loss. Other various embodiments alternatively or additionally provide for omnidirectional flow receipt within a horizontal plane. 
     Various exemplary embodiments provide an axisymmetric collection apparatus for receiving a portion of a medium that flows around the apparatus and directing the portion into a collector. The apparatus includes an axisymmetric streamline receiver and a support member. The receiver contains a chamber and at least one opening into the chamber that receives the portion. The support member includes an axisymmetric conduit for directing the portion from the chamber towards the collector. 
     In various exemplary embodiments, the opening has an annular axisymmetric geometry. In alternate embodiments, the opening represents a plurality of openings angularly distributed along an exterior surface of the streamline receiver, each opening having a finite angular width. The axisymmetric conduit may direct a subportion of the portion to a diversion opening that encompasses an axial centerline of the streamline receiver. 
     Various exemplary embodiments also provide a planform collection apparatus for receiving a portion of a medium that flows around the apparatus and directing the portion into a collector. The apparatus includes a streamline receiver, a support member and a tail stabilizer. The receiver includes upper and lower members that form leading and trailing edges to define a chord. 
     At least one of the members incorporates along an exterior surface at least one opening that receives the portion. The support member has a conduit that directs the portion from the opening towards the collector. The tail stabilizer may be secured to the streamline receiver for orienting the leading edge into the medium. 
     In various embodiments, the opening includes an interior surface recessed from the exterior surface. In further embodiments, the interior surface slants to deepen with the distance from the leading edge. In additional embodiments, the opening includes boundary walls that define the varying width, and the boundary walls connect to the interior surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and various other features and aspects of various exemplary embodiments will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like or similar numbers are used throughout, and in which: 
         FIG. 1  is an isometric cross-section view of an axisymmetric mushroom inlet assembly; 
         FIG. 2  is a plan cross-section diagram of an inlet assembly having an axisymmetric airfoil; 
         FIGS. 3A and 3B  are cross-section isometric views of an inlet assembly having an axisymmetric airfoil and Bernoulli-effect inlets; 
         FIG. 4  is an isometric view of a weathervane inlet system; and 
         FIGS. 5A and 5B  are isometric views of a weathervane inlet airfoil having Bernoulli-effect inlets, with  FIG. 5B  representing a cross-section view. 
     
    
    
     DETAILED DESCRIPTION 
     Conventional inlet designs for fluid sample collection housings are subject to the following limitations: First, Bernoulli-effect backpressure in a housing at off-design fluid flowspeeds reduces collection efficiency and may adversely affect pump operational life. Second, boundary layer thickness development within the inlet influences fluid flow into the housing. Third, an inertial response time for weathervane directional alignment to the fluid flow. Fourth, non-isokinetic conditions may reduce inlet efficiency. Various exemplary embodiments address these limitations in the conventional configurations. 
       FIG. 1  shows an isometric cross-sectional view of a first omni-directional sampling inlet structure  100  that is axisymmetric about a substantially vertical symmetry axis. An outer mushroom-shape aeroshell  110  presents a streamline plan profile over which a medium (e.g., especially ambient air, but alternatively water, oil and other gasses or liquids) passes as a flowfield from a horizontal transverse direction within a substantially horizontal omnidirectional plane. An outer-under rim  115  forms a lower lip connecting to the streamline body or aeroshell receiver&#39; 110  at a joining circumference  120  along the maximum outer diameter. 
     The passing medium impinges the structure  100  at a leading edge within the flowfield approximately at the joining circumference  120 . An inner-under planform  125  provides a surface under which the flowfield passes along the transverse direction. The volume substantially enclosed above by the aeroshell  110  and below by the rim  115  and the planform  125  forms a chamber  130  into which the medium may enter. 
     The planform  125  may be supported by a cylindrical outer stem  140  substantially parallel to the symmetry axis. A cylindrical inner stem  150 , also substantially parallel to the symmetry axis may support the aeroshell  110 . The sterns  140 ,  150  may be tilted together in association with the symmetry axis in an off-vertical direction for reorienting the structure  100 . 
     As the flowfield passes over and under the structure  100 , a flow portion of the medium passes into an annular inlet  160  formed between the rim  115  and the planform  125  into the chamber  130 . The outer and inner stems  140 ,  150  form an annular channel  170  directing the flow portion from the chamber  130  therethrough. 
     The aeroshell  110  may be represented geometrically by an upper (or top) profile having a first radius of curvature. A contiguously assembled surface containing the rim  115 , the inlet  160  and the planform  125  may be represented geometrically by a lower (or bottom) profile having a second radius of curvature. To minimize back pressure within the chamber  130 , the structure  100  may enable a higher static pressure below the structure and adjacent the inlet  160  than above the structure. Under the Bernoulli principle then, the flowfield velocity over the aeroshell  110  preferably exceeds the velocity under the contiguously assembled surface. Consequently, the first radius of curvature may preferably be smaller than the second radius of curvature, such that the lower profile appears flatter than the upper profile. The upper and lower profiles are revolved about the symmetry axis to form the axisymmetric structure  100 . 
     Particulate matter entrained within the flow portion may sweep on (downward) past the annular inlet  170  into a collector (not shown) by inertia and drag of the individual particles. The collector may represent a “dry filter unit” (DFU) used to detect selectable particulates for chemical or biological analysis. The remaining flow portion may be redirected (upward) towards a tube  180  formed by the inner stem  150  and ejected from the structure  100  through an outlet  185 . An example streamline  190  traces a path through which an entering portion of the medium may traverse. 
     As a consequence of the flow paths into the inlet and ejected through the outlet  185 , the backpressure equilibrates to the ambient conditions, thereby reducing flow inefficiency. Moreover, the axisymmetric design of the structure  100  permits medium reception from omnidirectionally within the substantially horizontal flow plane. 
       FIG. 2  shows a plan cross-sectional view of a second omni-directional sampling inlet structure  200  that is axisymmetric about a substantially vertical symmetry axis  205 . An upper airfoil shell  210  presents a plan profile over which the medium passes as a flowfield from a horizontal transverse direction substantially perpendicular to the symmetry axis  205 . A lower airfoil shell  215  presents a plan profile under which the medium passes and connects to the upper airfoil shell  210  at a joining circumference  220  along the maximum outer diameter. 
     The passing medium impinges the structure  200  at a leading edge within the flowfield approximately at the joining circumference  220 . The volume substantially enclosed by the shells  210 ,  215  forms a chamber  230  into which the medium may enter. In context of the exemplary embodiments described herein, the term “airfoil” denotes a streamline shape within a flowfield in which the medium may preferably be but not limited to atmospheric air. 
     A cylindrical outer stem  240  parallel to the symmetry axis may support the lower airfoil shell  215 . The stem  240  may be tilted in association with the symmetry axis  205  in an off-vertical direction for reorienting the structure  200 . As the flowfield passes over and under the structure  200 , a flow portion of the medium passes into at least one annular inlet  250 . 
     Each inlet  250  may form either a substantially annular opening circumferentially around the symmetry axis  205 . Alternatively, each inlet  250  may represent a series of openings into the chamber  230  having finite angular width and being angularly distributed around the symmetry axis  205 . 
     The inlets  250  may be characterized by an effective radial length d in  locally tangent to the structure  200 . The radial length is normal to the flow direction  255  and must be at least equal an absolute velocity |v| of the flow times a characteristic time constant τ. The inlets  250  may additionally, or in the alternative, employ Bernoulli-effect principles described further below. 
     The upper airfoil shell  210  may include an inlet  250   a , as above described for an annular ring or a series. The lower airfoil shell  215  may include an inlet  250   b , also as an annular ring or a series. The outer stem  240  may include, near its juncture with the lower airfoil shell  215 , an inlet  250   c , also as an annular ring or a series. 
     As the medium flows around the structure  200 , a portion of the flow enters the chamber  230  through the inlets  250 , traveling radially inward. A baffle or diverter  260  redirects the flow portion downward into the outer stem  240  towards a tube channel  265  to enter a collector (not shown). Example streamlines  270  show the path of the flow portion entering the inlets  250  and diverting to the tube channel  265  for analysis. 
       FIGS. 3A and 3B  show isometric cross-sectional views of a second omni-directional sampling inlet structure  300  that is axisymmetric about a substantially vertical symmetry axis. A circumferential upper shell  310  exhibits an airfoil cross-section about the symmetry axis extending along a top surface of the structure  300 . A circumferential lower shell  315  presents a comparatively flat cross-section about the symmetry axis extending along a bottom surface of the structure  300 . 
     The upper and lower shells  310 ,  315  converge to join along a circumferential rim  320 , thereby enclosing a chamber  325  for the structure  300 .  FIGS. 3A and 3B  present the views of the structure  300  from below and above the rim  320 , respectively. The medium can flow from any horizontal direction transverse to the symmetry axis over the upper shell  310  and under the lower shell  315 . The lower shell  315  may be supported by a cylindrical stem  330  and joined circumferentially along a fillet  335  to form a tube  340  parallel to the symmetry axis. 
     Several inlets  350  may be circumferentially distributed along the lower shell  315  to permit the medium to flow into the chamber  325 . Alternatively, the inlets  350  may be circumferentially distributed along the upper shell  310 , particularly for collective inclusion of precipitation. Each inlet  350  includes a recessed surface  355  within the chamber  325 . The recessed surface  355  may be substantially perpendicular to the symmetry axis, thereby being approximately parallel to streamlines entering the inlet  350 . 
     The inlet  350  benefits from the Bernoulli effect by employing a narrow shallow opening at an outer radius end  360  and a wide deep opening at an inner radius end  365 . The outer and inner radii refer to structure  300  from the symmetry axis. The widths between these openings  360 ,  365  may vary linearly, or nonlinearly, such as the flat-Gaussian curve shown. This geometry enables the boundary layer within the inlet  350  to remain substantially uniform, thereby reducing pressure losses into the structure  300 . This design opening is labelled a “Bernoulli-effect inlet” herein. 
     A boundary layer develops along the surface  355  as the medium flows into the inlet  350 . Expansion of the depth and width of the inlet  350  as the medium to flow progressively into the chamber  325  reduces viscous drag losses, thereby reducing pressure drop across the inlet as well as turbulence. The medium flows towards the radial center of the structure  300  and turns downward into the tube  340  to enter a collector (not shown). 
       FIG. 4  shows an isometric view of a weather-vane sampling inlet assembly  400 . The assembly  400  features an airfoil  410  having slit inlets  415  supported on a strut  420  leading into a collector (not shown). The strut  420  may be oriented in a substantially vertical direction to enable the airfoil  410  to rotate toward any direction in a substantially horizontal plane. The inlets  415  have lengths at least an order of magnitude greater than the corresponding widths. 
     The assembly  400  may further include a tail  430  that orients the assembly  400  to direct the airfoil  410  towards windward by connection to a stiff linkage or rod  440  in the manner of a weathervane. The airfoil  410  may represent cross-section planforms documented by the former National Advisory Committee for Aeronautics (NACA). Many NACA planforms are bilaterally symmetric across the chord. This embodied configuration is described in U.S. patent application Ser. No. 11/134,603 incorporated by reference. 
       FIGS. 5A and 5B  shows isometric views of a weather-vane sampling inlet system  500  in similar fashion to the assembly  400  shown in  FIG. 4  but absent explicit illustration of the tail  430  and the rod  440 .  FIG. 5A  represents an airfoil  510  supported on a stem  520  as viewed from above. In a similar view,  FIG. 5B  represents a chord-wise cross-section of the airfoil  510  showing its interior across its midspan. 
     The airfoil  510  provides an upper surface  530  and a lower surface  535  exposed to the medium. At a forward end, the surfaces  530 ,  535  may be joined at a leading edge  540 . Similarly at the aft end, the surfaces  530 ,  535  may be joined at a trailing edge  545 . These surfaces and edges may represent NACA planforms. The leading and trailing edges  540 ,  545  form a chord of the airfoil  510 . 
     The system  500  differs from the assembly  400  primarily by employment of Bernoulli-effect inlets  550 .  FIG. 5A  shows the inlets  550  on the upper surface  530 , although the inlets may also be employed on the lower surface  535 . Each inlet  550 , as shown in  FIG. 5B , employs a narrow shallow forward end  555  and a wide deep aft end  560 . The aft end  560  is farther downstream from the leading edge  540  than the forward end  555 . 
     A portion of the medium that flows over the airfoil  510  may enter the inlet  550 . The portion flows between recessed walls  565  that define the forward and aft ends  555 ,  560  and along a recessed surface  570  to contain a boundary layer region of the portion. The recessed surface  570  may be substantially parallel to the chord, or alternatively may be slanted to provide a deeper channel at the aft end  560  than the forward end  555 . The widths between these ends  555 ,  560  may vary linearly, or nonlinearly, such as the flat-Gaussian curve shown. 
     A chute  575  connected downstream (i.e., aft) of the associated inlet  550  directs the flow portion into a channel  580  within the strut  520 . The chute  575  may join contiguously with the recessed walls  565  and the recessed surface  570 . The channel  580  leads to a conduit  585  into a collector (not shown). 
     A chamber  590  represents interior regions not in communication with the inlet  550 , the chute  575  or the channel  580 . Thus, in the depicted exemplary version, the flow portion does not enter the chamber  590 , which may be vented to equilibrate with an appropriate pressure level relative to ambient conditions to maintain structural integrity and/or internal chamber pressure for optimal inlet flow performance. 
     While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.