Abstract:
A cooling fan for an engine in a vehicle. Ordinarily, a fan rotates within a shroud, which surrounds the fan. Leakage can occur between the tips of the fan blades and the shroud, wherein fan exhaust moves forward, and then passes through the fan again. The invention reduces leakage by placing a surface downstream of the fan. The surface employs the Coanda Effect, to urge fan exhaust to continue in the downstream direction, and not move forward as leakage air.

Description:
[0001]     The invention concerns an approach to reducing air which leaks upstream past fan blades that are moving air downstream.  
       BACKGROUND OF THE INVENTION  
       [0002]      FIG. 1  is a cross-sectional view of a prior-art cooling fan  3 , as used in motor vehicles, which cools a radiator (not shown), which extracts heat from engine coolant. A motor  4  rotates a cylindrical hub  5 , as indicated by arrow  6 , which hub  5  carries fan blades  3 . Arrows  7  indicate moving air streams.  
         [0003]     One feature of such a fan is that it increases static pressure at point A 1 , compared with point A 2 . This pressure differential causes leakage air, indicated by arrows  8  and  8 A, to flow in the space between the fan ring  9  and the shroud  12 .  
         [0004]     This leakage represents a loss in efficiency, since the leaked air was initially pumped or moved to the pressure at point A 1 , but then drops to the pressure at point A 2 , but with no work or other useful function being accomplished.  
         [0005]     It may appear that the airflow indicated by arrow  8  is penetrating a solid body, namely, the strut  18  which supports stator  21 . However, this appearance is an artifact of the cross-sectional representation of  FIG. 1 . In fact, spaces exist between adjacent stators  21 , as indicated schematically by space  24  in  FIG. 3 . Air can flow as indicated by arrow  27 , which corresponds in principle to arrow  8  in  FIG. 1 .  
         [0006]      FIGS. 2A-2D  are copies of the like-numbered Figs. in U.S. Pat. No. 5,489,186, and represent strategies proposed by that patent to (1) reduce the leakage and (2) accomplish other beneficial objects.  
       SUMMARY OF THE INVENTION  
       [0007]     In one form of the invention, a duct of increasing cross-sectional area is positioned in the exhaust of a fan, and upstream of stators used to straighten flow. Exhaust of the fan adheres to the walls of the duct because of the Coanda Effect, thereby reducing tendencies of the exhaust to reverse direction and leak upstream, past the tips of the fan blades.  
         [0008]     An object of the invention is to provide an improved cooling fan in a motor vehicle.  
         [0009]     A further object of the invention is to provide a cooling fan in a motor vehicle which employs the Coanda effect to entrain high pressure air in a flow path to thereby reduce the leakage illustrated in  FIG. 1 .  
         [0010]     In one aspect, one embodiment comprises a cooling system for a vehicle, comprising: a fan which produces exhaust which enters stator vanes downstream; and means, located entirely between the fan and the stator vanes, which increases fan efficiency. In one embodiment, efficiency is increased by at least three percent.  
         [0011]     In another aspect, one embodiment comprises a cooling system for a vehicle, comprising: a fan which produces exhaust which includes a leakage flow, which leaks upstream of the fan, past blades of the fan; and means downstream of the fan, which reduces the leakage flow.  
         [0012]     In yet another aspect, one embodiment comprises a cooling system for a vehicle, comprising: a fan having an exit diameter D; a Coanda ring surrounding fan exhaust which has an entrance diameter equal to D and which diverts fan exhaust radially outward by a mechanism which includes the Coanda effect; and a stator, entirely downstream of the Coanda ring, past which fan exhaust travels.  
         [0013]     In still another aspect, one embodiment comprises a cooling system for a vehicle, comprising: a fan having an exit diameter D; a duct immediately downstream of the fan, having an inlet diameter equal to D; and an exit diameter greater than D, which duct reduces torque required to power the fan.  
         [0014]     These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  illustrates leakage in a prior-art fan system;  
         [0016]      FIGS. 2A, 2B ,  2 C, and  2 D are copies of like-numbered Figs. in U.S. Pat. No. 5,489,186;  
         [0017]      FIG. 3  illustrates a space  24  between struts  18  and explains that struts  18  in  FIG. 1  are not present at all circumferential positions along shroud  12 , so that flow path  8  in  FIG. 1  can actually be present;  
         [0018]      FIG. 4  illustrates one form of the invention;  
         [0019]      FIG. 5  is an enlarged view of part of  FIG. 4 ;  
         [0020]      FIGS. 6A and 6B  are simplified schematics of a water glass  39  and a water faucet  45 , to explain the Coanda Effect;  
         [0021]      FIG. 7  illustrates how leakage flow  69  is accompanied by flow reversal and eddies  73 , which effectively reduce the cross-sectional area of total exhaust  63  from the fan;  
         [0022]      FIG. 8  illustrates how the invention reduces or eliminates the flow reversal and eddies  73 , thereby increasing the cross-sectional area of total exhaust from the fan;  
         [0023]      FIGS. 9, 10 , and  11  are plots of performance parameters, and compare fan performance with, and without, the Coanda ring  30  of the invention;  
         [0024]      FIG. 12  is a copy of  FIG. 2D , with annotations;  
         [0025]      FIG. 13  illustrates how exhaust of a fan follows a helical, or corkscrew, path;  
         [0026]      FIGS. 14A and 14B  illustrate how the prior-art apparatus of  FIG. 2D  blocks swirl;  
         [0027]      FIGS. 15A and 15B  illustrate how the invention does not block swirl as in  FIG. 14 ; and  
         [0028]      FIGS. 16A, 16B ,  16 C,  16 D and  16 E illustrate exit angles of the Coanda ring  30 ;  
         [0029]      FIG. 17  is a schematic cross-sectional view of one form of the invention.  
         [0030]      FIG. 18  is a schematic perspective view of Coanda ring  100 , with stiffening ribs  105 .  
         [0031]      FIG. 19  is a schematic perspective cut-away view, showing the Coanda ring  100  installed within shroud  12 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]      FIG. 4  is a cross-sectional view of one form of the invention, wherein an annular ring  30 , termed a Coanda ring, is stationed downstream of the fan ring  9 , and upstream of stator  21 . The fan ring  9  is a ring which connects the tips of neighboring fan blades.  
         [0033]     The inner diameter D 1  of the Coanda ring  30  is equal to the inner diameter D 2  of the fan ring  9 . Further, as shown in  FIG. 5 , the inner surface  33  of the Coanda ring  30 , at the point P 1  where fan exhaust enters the Coanda ring  30 , is tangent to the fan airflow  34 . The inner surface  33  of the Coanda ring  30  then curves away from the central axis  36  in  FIG. 4  of the fan, acting somewhat as a diffuser, but while maintaining attached flow along the Coanda ring  30 , as discussed later.  
         [0034]     The Coanda ring  30  utilizes the Coanda effect. The Coanda effect can be easily demonstrated, using an ordinary water faucet and a water glass, held horizontally, both shown in  FIGS. 6A and 6B . On the left side of  FIG. 6A , the water glass  39  stands outside the water stream  42  emanating from the faucet  45 , and the water stream  42  does not contact the glass  39 . On the right side of the  FIG. 6B , the rightmost wall  48  of the glass  39  touches the water stream  42 . Because of the Coanda effect, the water stream  42  adheres to the surface of the glass  39 , and follows the contour of the glass  39 , until the water stream  42  drops off, at point P 2 .  
         [0035]     The particular location of point P 2  will change as conditions of the water stream  42  change. For example, if velocity of the water stream  42  changes, the location of point P 2  will, in general, also change.  
         [0036]     This example of the Coanda Effect involved a liquid. However, the Coanda Effect also occurs in gases.  
         [0037]      FIG. 5  is an enlargement of part of  FIG. 4 . The Coanda ring  30  entrains airstreams  34  exiting the fan  3  so that the airstreams  34  follow the surface  33  of the Coanda ring  30 .  
         [0038]     Point P 1  in  FIG. 5 , at the tangent point of the Coanda ring  30 , corresponds in principle to the rightmost wall  48  of the water glass  39  in  FIG. 6B .  
         [0039]     Ideally, the flow along the Coanda ring  30  in  FIG. 5  is attached along the entire axial length of the Coanda ring  30 , that is, from the tangent point P 1  to the exit point PB.  
         [0040]     The Coanda ring  30  creates a significant improvement in cooling over that found in the prior art, especially when the exhaust of the fan blades  3  in  FIG. 4  is obstructed by an object located downstream, such as an engine block. This will be explained.  
         [0041]      FIG. 7  shows a prior-art cooling fan  3 , which may draw air through a radiator, or heat exchanger,  60  and directs exhaust  63  toward an engine block  66 , or other major component of the engine. The presence of leakage air  69  requires that a reversal of flow direction of the exhaust  63  occur. Dashed line  72  represents a boundary of the primary stream tube of the fan exit flow. The flow below line  72  is part of the main exit flow of the fan. The flow above line  72  is the region of reversing flow, indicated by loops  73 .  
         [0042]     The reversing flow is characterized by flow separation from adjacent surfaces and also turbulence and eddies. The average exit velocity of the reversing flow, above line  72 , is much less than the velocity within the stream tube of the fan exit flow, below line  72 . That is, the air molecules in the reversing flow are traveling in random directions, compared with the air molecules below line  72 . Thus, the reversing air molecules above line  72  do not add vectorially to a single vector in a single direction having a relatively large velocity, as they do below line  72 . Consequently, the reversing molecules above line  72  can be viewed as stationary or slowly moving compared with the molecules and airflow below the line  72 .  
         [0043]     From another point of view, the reversing flow (above line  72 ) has a lower average exit velocity than the rest of the flow (below line  72 ) exiting the fan  3 . As a result, the effective cross-sectional area of total exiting flow is, in effect, limited to that below line  72 . The total exiting flow, in effect, is limited to that between points point P 3  and P 4  in  FIG. 7 .  
         [0044]     In contrast, under the invention as shown in  FIG. 8 , the Coanda ring  30  reduces the reversing flow. The separated flow above line  72  in  FIG. 7  is significantly reduced, or eliminated. Now the cross-sectional area of the flow exiting the fan is increased because of the reduction or elimination of the reversing flow and extends from point P 5  to point P 6  in  FIG. 8 .  
         [0045]     The Coanda ring  30  has increased flow output by reducing or eliminating the reversing flow shown above line  72  in  FIG. 7 .  
         [0046]      FIGS. 9-11  illustrate experimental results obtained using the Coanda ring  30 . In all results, the horizontal axis represents PHI, non-dimensional flow rate through the fan.  FIG. 9  illustrates pressure rise, PSI, plotted against PHI. The pressure rise from point A 2  to A 1  in  FIG. 1  represents one such pressure rise.  
         [0047]      FIG. 10  illustrates ETA, efficiency, plotted against PHI.  FIG. 11  illustrates LAM, non-dimensional torque required to drive the fan, plotted against PHI.  
         [0048]     In each plot, a vertical line is drawn at PHI=0.116, which represents vehicle idle condition. This condition is taken as significant because it represents a condition of low fan airflow, yet at a time when high engine cooling can be required, as in bumper-to-bumper traffic on a hot day.  
         [0049]      FIG. 9  indicates that, at this idle condition, fan pressure increases in the presence of the Coanda ring  30 , which is beneficial.  FIG. 11  indicates that torque absorbed by the fan decreases in the presence of the Coanda ring  30 , meaning that less power is required by the motor driving the fan  3 , which is also beneficial.  FIG. 10  indicates an increase in efficiency at this idle condition of about 4 percent, which is considered highly significant.  
         [0050]      FIGS. 17-19  illustrate an additional embodiment. Fan blade  3  rotates about axis  36 , as in  FIG. 4 . In  FIG. 17 , Coanda ring  100  is hollow, as indicated in  FIG. 18 . Stiffening ribs  105  in  FIGS. 17 and 18  connect the Coanda ring  100  with the shroud  12 .  FIG. 19  is a perspective cut-away view, showing the Coanda ring  100  installed in the shroud  12 .  
         [0051]     Some significant differences exist between the prior art structure of  FIG. 2  and the embodiment of  FIGS. 17-19 .  FIG. 12  shows one prior art structure, with added labels. One difference is that the vane  28 D in  FIG. 12  is present in the annular gap between the fan ring  24 D and the shroud housing  26 D. No such vane is present in  FIG. 17 .  
         [0052]     Another difference is that the vane  28 D extends into the hollow interior of curved surface  48 D. In  FIG. 17 , no vane which is present in the annular gap between the fan ring  9  and the shroud  12  extends into the hollow interior of the Coanda ring  100 . Instead, the stiffening ribs  105  lie completely within the hollow interior of the Coanda ring  100 , and do not extend beyond the axial limits of the Coanda ring.  
         [0053]     Another difference is that the vanes  28 D in  FIG. 12  are intended to control direction of recirculation airflow which passes into the annular gap between fan ring  24 D and shroud  26 D. The stiffening ribs  105  in  FIG. 17  do not perform this function.  
         [0054]     Another difference is that it is clear that the vanes  28 D in  FIG. 12  are symmetrically distributed about the fan axis (not shown). The stiffening ribs  105  in  FIG. 17  need not be symmetrically distributed.  
         [0055]     Another difference lies in the fact that, in one form of the invention, the stiffening ribs  105  are adjacent the stators  21  in  FIG. 17 , and provide mechanical stiffness at the points where the stator  21  is supported by the shroud  12 . For example, if a stator is located at the one o&#39;clock position, a stiffening rib  105  is also located at that position. In some designs, the stiffening ribs are used to support the motor  4  of  FIG. 1 .  
         [0056]     Another difference is that the number, K, of stiffening ribs  105  present is sufficiently low that, if the same number, K, of vanes  28 D in  FIG. 12  were present, that number, K, of vanes  28 D would be ineffective to accomplish the optimal re-direction desired by the prior art device. One reason is that, because of the small number, K, of vanes  28 D, the space between them is large, so that air flowing midway between a pair of vanes  28 D is not subject to diversion by the vanes  28 D, because the vanes are too distant.  
         [0057]     In one embodiment, the total number of stiffening ribs  105  equals any number from one to ten, and no more. In another embodiment, the stiffening ribs  105  do not form a symmetrical array, or no mirror-image symmetry is present.  
       Additional Considerations  
       [0058]     1. Several differences exist between one form of the invention and the prior-art apparatus of  FIG. 2D , which is repeated in  FIG. 12 , with annotations. In  FIG. 12 , the curved surface  48 D is hollow, and no barrier to entry by air into the hollow interior is present. That is, air can enter, as indicated by arrow A. The air can circulate within curved surface  48 D after entering.  
         [0059]     Further, a turning vane  28 D is present, and this vane  28 D extends into the hollow interior of curved surface  48 D.  
         [0060]     Further still, much of the curved surface CS lies at the same axial station AS as does the stator vane  37 D.  
         [0061]     In contrast to these three features, the Coanda ring  30  of  FIG. 5  contains a forward barrier  90 , which blocks entry of air to any hollow interior. That is, no airstream A as in  FIG. 12  can enter the interior of the Coanda ring  30  in  FIG. 54 . In one form of the invention, the Coanda ring  30  can be formed of a solid material, or of an expanded foam-like material, either of which prevent entry of air into the interior of the Coanda ring  30 .  
         [0062]     Also, there is no vane present within any hollow interior of the Coanda ring, unlike the vane  28 D of  FIGS. 2D and 12 .  
         [0063]     In addition, the Coanda ring  30  of  FIG. 8  lies entirely forward of the stator  21 , unlike the situation of  FIG. 12 .  
         [0064]     2. Another difference between the invention and the prior-art apparatus of  FIGS. 2D and 12  is that it is unknown whether the prior-art apparatus utilizes the Coanda Effect to maintain attached flow along the outside of curved surface  48 D in  FIG. 12 . That is, it is not known whether flow separation occurs, for example, at point P 7  in  FIG. 12 . Such separation could occur at very high airflows, and the fan could be designed to produce such high airflows. The Coanda Effect would not be present at such separation.  
         [0065]     3. Yet another difference between the invention and the prior art apparatus of  FIGS. 2D and 12  is that under the invention, a swirl component of the fan exhaust will travel along the Coanda ring  30 . In the prior-art apparatus of  FIGS. 2D and 12 , the stator  37 D blocks the swirl.  FIGS. 13-15B  illustrate the situation.  
         [0066]      FIG. 13  illustrates a simple, single-bladed fan  100 , which rotates in the direction of arrow  105 . The exhaust of the fan  100  follows a helical or corkscrew path  110 . The circular, or tangential, component of this helical flow is commonly called swirl.  
         [0067]     In  FIGS. 14A and 14B , which are schematics of the prior-art device of  FIGS. 2D and 12 , the stator  37 D blocks the swirl. More precisely, the swirl surrounded by the ring  48 D is blocked when it encounters the stator  37 D because the stator  37 D is also surrounded by the ring  48 D. The bottom of  FIG. 14B  illustrates the sequential arrangement of the fan  22 D, the ring  48 D, and the stator  37 D. This sequence is also shown in  FIG. 2D .  
         [0068]     In contrast, as in  FIG. 15A , blockage of swirl within the Coanda ring  30  by the stator  21  is not present. One reason is that the stator  21  is not surrounded by the Coanda ring  30 . Stator  21  is not present within the Coanda ring  30 .  
         [0069]     Of course, under the invention, stator  21  in  FIG. 15B  may modify the swirl. However, stator  21  is entirely downstream of the Coanda ring  30 . The swirl still exists unmodified by the stator  21  within the Coanda ring  30 .  
         [0070]     4. A significant feature of the invention is the increase in effective cross-sectional area of fan exhaust, as indicated in  FIG. 8 , in the presence of a downstream obstruction. In one example, the obstruction is located less than D 14  from the outlet  93  of the fan, wherein D is a fan diameter. In other examples, the obstruction is located D/K downstream of the outlet of the fan, wherein D is a fan diameter and K is a number ranging from, for example, 1 to 10, but the number could range higher.  
         [0071]     5. The invention maintains attached flow along the Coanda ring  30 , as indicated in  FIG. 5 , during at least one operating mode of the fan, such as the idle operating mode discussed above. In another form of the invention, attached flow is maintained during substantially all modes of operation of the fan. In another form of the invention, attached flow is maintained along the Coanda ring  30 , as indicated in  FIG. 5 , during at least one operating mode of the fan, such as the idle operating mode discussed above. In yet another form of the invention, attached flow is maintained during substantially all modes of operation of the fan  
         [0072]     6.  FIG. 16A , top left, illustrates a standard cylindrical coordinate system. The coordinate system is superimposed on the Coanda ring  30  of  FIG. 5  in the upper right part of  FIG. 16B . As the lower right part of  FIG. 16C  indicates, flow entering the Coanda ring  30  enters at zero degrees, and exits at about 58 degrees.  
         [0073]     It is expected that the exiting angle will determine the point of separation of fluid from the Coanda ring  30 . That is, for example, if no separation occurs for a given flow velocity and the exit angle of 58 degrees shown, separation may occur if the exit angle is changed to 90 degrees.  FIGS. 16D and 16E  show other illustrative exiting angles.  
         [0074]     To determine the limiting exit angle, in one form of the invention, the shape of the Coanda ring  30  is determined experimentally. That is, for example, a desired flow rate of fan exhaust is first established, and then different Coanda rings are tested. All Coanda rings have the same entrance angle, namely, zero degrees, which is tangent to the fan exhaust. But the different Coanda rings have different exit angles, such as the two rings shown in lower left part of the  FIG. 16C . Progressively increasing exit angles are tested until an exit angle is found at which flow separation occurs. This testing can be done in a wind tunnel with smoke visualization.  
         [0075]     The exit angle causing flow separation is taken as identifying the limiting Coanda ring. One of the Coanda rings having a smaller exit angle is chosen for use in production.  
         [0076]     7. One form of the invention includes the apparatus of  FIG. 4  or  8 , together with a motor vehicle in which the apparatus is installed. The apparatus cools a radiator (not shown) which extracts heat from engine coolant.  
         [0077]     8.  FIG. 5  shows a Coanda ring  30  having a curved, convex surface. However, part of the surface (not shown) may be flat. Also, a flat surface (not shown), such as one extending directly between points P 1  and PB, can be used.  
         [0078]     9. In  FIG. 3 , the part of ring  12  spanning between struts  18  blocks radial flow. That is, this part of the ring  12  acts as a barrier to radial flow. In contrast, in one form of the invention, there is no corresponding barrier between tips T of stator blades  21 . Radial flow is possible past tips T, between adjacent stator blades  21 .  
         [0079]     10. In  FIG. 4 , the Coanda Ring  30  has an inner surface S 1 , which is a surface of revolution about axis  36 . In  FIG. 5 , the inner surface S 1  has an inner radius (or diameter) RA at an axial station AS 1 , and an inner radius (or diameter) RB at an axial station AS 2 . Axial station AS 2  is closer to the stator vanes  21  than is axial station AS 1 . Radius RA is smaller than radius RB. From another perspective, the diameter and cross sectional area of the channel bounded by surface S 1  both increase as one approaches the stator vanes  21 , and both increase in the downstream direction.  
         [0080]     11. In  FIG. 5 , an entrance can be defined at the left side, that is, the upstream side, of the Coanda Ring  30 . An exit can be defined at the right side, that is, the downstream side. The exit diameter is larger than the entrance diameter.  
         [0081]     12. One form of the invention comprises one or more of the following: the stationary ring  12  in  FIG. 4 , the Coanda Ring  30 , and the stator vanes  21 . It is possible that these components will be manufactured by a plastics fabrication supplier, which will not manufacture the motor  4 , or the associated fan. The components in  FIG. 4 , obtained from different suppliers, will then be assembled together.  
         [0082]     One form of the invention resides in the unitary molded article, constructed of plastic resin, which includes the structure of  FIG. 18 , together with all of shroud  12  in  FIG. 17 .  FIG. 19  is a schematic view of this structure.  
         [0083]     Another form of the invention is the unitary structure shown in cross section within dashed box  120  in  FIG. 17 . It includes the structure of  FIG. 18 , surrounded and attached to part of shroud  12  of  FIG. 17 , but no other components.  
         [0084]     Numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention. What is desired to be secured by Letters Patent is the invention as defined in the following claims.