Patent Publication Number: US-9903387-B2

Title: Ring fan and shroud assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. application Ser. No. 12/594,017, filed Sep. 30, 2009 (now U.S. Pat. No. 8,475,111 issued on Jul. 2, 2013), which is a national phase entry of PCT/US2008/059515, filed Apr. 5, 2008, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/910,271, filed Apr. 5, 2007. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a ring fan and shroud assembly and more particularly to a ring fan and shroud assembly with improved air flow characteristics. 
     BACKGROUND OF THE INVENTION 
     Axial type fans move air, or other fluids, using rotating impeller blades. As the impeller blades rotate, different pressures on opposite sides of the blades are developed. The discharge sides of the impeller blades typically develop a high pressure while the intake sides develop a low pressure. The pressure differential between these two sides causes the fluid to flow from the high-pressure discharge side to the low-pressure intake side near the tips of the impeller blades creating an undesirable back flow of some of the fluid flow passing through the fan. It is well-known that this backflow can decrease the efficiency of the fan and may lead to undesirable noise generation. 
     Engine cooling fans develop static pressure across the fan such that the regions ahead of the fan are at significantly lower pressure than regions behind the fan. Many engine cooling fans have cowlings or shrouds positioned circumferentially around them in order to assist in directing the air flow in the desired direction. Practical operation of fans used in motor vehicle cooling systems dictate minimum clearances between the rotating fan members and stationary shroud members in order to ensure safe, durable functioning throughout the life of the vehicle. 
     Many of the cooling fan members used in such systems are ring-type fans, i.e. the fans have a circumferential ring member positioned on the tips of the fan blades. The pressures developed across the cooling fans drive leakage flow through the gaps occurring between the fan&#39;s blade tips or any rotating ring, and the stationary surfaces of the shroud. 
     In ring fans, the leakage flow encounters the tip gap at the trailing edge of the rotating ring and enters the gap region having a very high tangential velocity component. As the leakage flow progresses through the gap region, the viscous drag of the rotating ring continues to strengthen this vortical flow until finally it reaches the exit of the gap region, which is just upstream of the tips of the blades of the fan. 
     When the recirculating leakage flow reenters the main fan air flow passage, it possesses a very high tangential component, which is at odds with the velocity and direction of the primary incoming air flow of the fan. As the tangentially-oriented recirculating flow mixes with the passage of the primary air flow which is mostly axial, a vortex is formed adjacent the front of the leading edge at the tips of the fan blades. Since the leading edges of fan blades are designed for the primary flow velocity condition, the vortex encountered by the blades is misaligned relative to the intended inlet vector. This can cause the tip region to stall and the resulting low relative-momentum flow can “hang up” in the region of the blade tips and fan ring. This reduces the air flow rate of the fan, as well as its static pressure, and also increases the drag. 
     It would therefore be desirable to have a ring fan and shroud assembly that was effective in reducing these complications. It would further be desirable to minimize or eliminate the tangential velocity component prior to reinducing the leakage flow back into the primary air stream flowing through the fan. It would further be desirable to minimize the tip gap leakage flow and prevent tip stall. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a ring fan and shroud assembly which minimizes the tip gap leakage flow and prevents tip stall. It is a further object of the present invention to provide a ring fan and shroud assembly with improved efficiency and reduced noise generation. 
     It is an additional object of the present invention to provide a ring fan and shroud assembly in which the shroud and guide vanes can be easily formed in a conventional two-piece mold injection molding process 
     In accordance with the objects of the present invention, a ring fan and shroud guide assembly is provided. The fan assembly includes a plurality of impeller blades positioned within and attached to a conical outer ring. A portion of the stationary shroud member can overlap radially inwardly a portion of the fan&#39;s rotating ring. The shroud member and ring member form an annular recirculation nozzle adjacent the primary inlet air flow passage of the fan. A plurality of curved guide vanes are provided in the shroud member which act on the back flow of air entering the tip gap. The axially extending guide vanes have a substantially tangential leading edge orientation which align with the air flow entering the air gap. The curved guide vanes minimize or eliminate the tangential velocity component of the back flow air stream prior to reinducing that leakage flow back into the air stream through the recirculation nozzle. 
     The tip-gap has an entrance area substantially larger than the area of the recirculation nozzle. This, together with a converging exit region increases the velocity of the air flow injection of the leakage flow back into the fan&#39;s air stream. 
     Other features, benefits and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the attached drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a vehicle engine having a cooling system according to a preferred embodiment of the present invention. 
         FIG. 2  illustrates a fan assembly in accordance with a preferred embodiment of the present invention. 
         FIG. 3  illustrates a shroud member in accordance with a preferred embodiment of the present invention. 
         FIG. 4  shows a ring fan and shroud assembly in accordance with a preferred embodiment of the present invention. 
         FIG. 5  is a cross-sectional view of the ring fan and shroud assembly as shown in  FIG. 4 , the cross-section being taken along lines  5 - 5  in  FIG. 4 . 
         FIG. 6  is an enlarged view of a portion of the ring fan and shroud assembly cross-section as shown in  FIG. 5 . 
         FIG. 7  is an illustration similar to  FIG. 6  and showing the components and air flows in a schematic manner. 
         FIGS. 8 and 9  illustrate an embodiment of the guide vanes in accordance with the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a ring fan and shroud assembly  10  constructed in accordance with the teachings of the present disclosure. Although it is contemplated that the ring fan and shroud assembly  10  can be used in a variety of applications, the ring fan and shroud assembly  10  of the particular example shown in the drawings and described herein is employed with a radiator cooling system in a truck or other vehicle. It is to be understood, however, that the present teachings can be used in many applications, and that the present teachings are not to be limited only to trucks or other vehicles. 
     The ring fan and shroud assembly  10  can include a fan member  15  and a shroud member  10 . The fan member  15  has a central hub member  13 , a plurality of blade members  12  (also called “impeller” members) and a circumferential outer ring member  14  that is positioned at and connected to the ends (or tips) of the blade members  12 . The use of impeller blades and a rotating ring element to form a fan assembly is well known in the art, and these fans assemblies are commonly referred to as “ring fans”. 
     While the fan member  15  of the present example is illustrated and described as having a solid, complete annular outer ring member  14  that is positioned at the tips of the blade members  12 , it is also possible that the outer ring member  14  (or discontinuous portions thereof) can be positioned radially inwardly slightly from the ends of the blade members  12 . 
     The outer ring member  14  can be integrally formed with the remainder of the fan member  15  and thus can be fixedly attached to the tips of the blade members  12 . The outer ring member  14  can have a frusto-conical shape, as shown in the drawings. The outer ring member  14  has a smaller diameter at the air inlet or low pressure side  16  of the fan member  15  and a larger diameter at the air discharge side, or high pressure side  17  of the rotating fan member  15 . 
     The shroud member  20  is cylindrical in shape and is positioned circumferentially around, or substantially circumferentially around, all or a principal portion of the rotating fan member  15 . 
     The shroud member  20  also has a portion or component  22  that is positioned radially inward of a leading edge  24  of the outer ring member  14  and axially overlaps a corresponding portion  26  of the outer ring member  14 . The portion  26  is spaced a radial distance D-1 from the outer ring member  14  and forms a nozzle  30  with an annular cross-sectional area. This nozzle  30  is called the “recirculation nozzle” as it re-injects into the primary fan air stream  32  the back flow of air  34  that enters into the tip gap  36  (defined below). 
     A trailing edge  38  of the outer ring member  14  and a second portion or surface  40  of the shroud member  20  are spaced apart by a radial distance D-2. The radial space between the trailing edge  38  of the outer ring member  14  and the surface  40  of the shroud member  20  is referred to as being a tip gap  36 —or tip gap region—and is the area where a portion of the air flow (see arrows  34  in  FIG. 7 ) flows back in the opposite direction of the main air flow of the fan member  15 . The tip gap  36  also has an annular cross-sectional area. 
     The distance D-2 is larger than the distance D-1, and similarly the annular cross-sectional area of the tip gap region  36  is larger than the annular cross-sectional area of the recirculation nozzle  30 . Preferably, the distance D-2 is substantially larger than distance D-1, by 50% or more. 
     A plurality of guide vanes  42  are provided in the shroud member  20 . The space in between the guide vanes  42  may be varied to modify the frequency of pressure pulses relative to a point on the fan member  15  as it proceeds through a full revolution in an effort to reduce fan noise and vibration (NVH). The number of guide vanes  42  as well as the number of blade members  12  also preferably correspond with a prime numbering system in order to help reduce NVH. In this regard, one possible ring fan and shroud assembly can have thirteen blade members  12  and thirty-one guide vanes  42 . 
     As noted above, the shroud member  20  forms a recirculation nozzle  30  which defines a flow passage adjacent to the primary incoming flow stream. The larger entrance area of the tip gap region  36  in conjunction with a converging exit region of the area of the recirculation nozzle  30  effectively provides high velocity injection of the leakage air flow (i.e., the back flow) back into the fan air stream. This also minimizes the tip gap leakage flow. The tip gap leakage flow  50  and the upstream primary flow  32  are merged together and align with each other as shown in  FIG. 7 . This is in proper incidence with respect to the leading edge angle of the tip of the blade members  12  near the outer ring member  14 . 
     Also, the high velocity tip gap leakage flow  50  that re-enters the tip air stream of the fan member  15  through the reduced area in the nozzle  30  utilizes the Coand{hacek over (a)} effect to stay attached to the rotating outer ring member  14 . This helps to energize the low relative momentum flow existing in the blade tip/rotating ring region and prevents tip stall. 
     The guide vanes  42  preferably have a curved configuration. As shown in  FIG. 8 , the guide vanes  42  also have substantially tangential leading edges  62  (i.e., each of the leading edges  62  is substantially tangential to an annular portion of the shroud member  20  at a point at which the leading edge  62  intersects the shroud member  20 ), which initially direct and orient the air flow entering the tip gap region  36 , and have substantially radial trailing edges  60  (i.e., each of the trailing edges  60  is oriented substantially toward a rotational axis of the fan member  15 ) that are adjacent the recirculation nozzles  30 . The guide vanes  42  minimize or eliminate the tangential velocity component of the air flow as it passes through the shroud member  20  and prior to introduction of the leakage flow back into the air stream flowing into the fan member  15 . 
     It is also possible for the shroud member  20  to have guide vanes  42  that have configurations that are different from that which is depicted in the drawings and described herein. 
     The guide vanes  42  on the shroud member  20  smoothly “capture” the leakage flow as it enters the tip gap region  36 . This is aided by the substantial tangential leading edge  62  of the guide vanes  42 , along with the substantially radial trailing edge  60  of the guide vanes  42 . Configuration in this manner gently turns the flow direction from tangential to radial and axial. A meridional air flow is created as the guide vanes  42  effectively remove the tangential component from the recirculation flow. A meridional air flow is one having only radial and axial velocity components without a tangential component present. 
     The introduction of the recirculation flow at high velocity energizes the low relative momentum fluid and utilizes the Coand{hacek over (a)} effect to help keep the primary flow attached to the surface of the rotating outer ring member  14 . The Coand{hacek over (a)} effect is a well-known aerodynamic effect discovered in 1930 by Henri-Marie Coand{hacek over (a)}. Coand{hacek over (a)} observed that a stream of air emerging from a nozzle tends to follow a nearby surface as long as the curvature or angle of the surface does not vary sharply from the flow direction. The present teachings employ this effect since the flow emerging from the recirculation nozzle  30  is directed along the inner surface of the rotating outer ring member  14 , helping to prevent tip stall. Additionally, in one embodiment, air flows past the discharge surface and along the shroud exit surface without recirculating back through the tip gap  36 . 
     In one embodiment, the shroud exit element is substantially parallel and coincident with the trailing edge  38  of the rotating outer ring member  14 . The decrease in flow area between the tip gap region entrance and exit, and the converging nature of the nozzle  30  promote acceleration of the flow as it reenters the fan passage. This promotes a significant pressure drop across the nozzle  30  which in turn improves the capacity of the fan member  15  to sustain high static pressure differential across the fan member  15 . 
     In a preferred embodiment, the guide vanes  42  are characterized by the following features: the dimension D-2 of the tip gap  36  ranges from ¼ inch to 1 inch, the inlet angle A ranges from 0 to 20 degrees, and the exit angle B ranges from −20 degrees to +20 degrees. See  FIGS. 8-9 . 
     In addition, the recirculation nozzle  30  can be characterized by the following features: the nozzle gap D-1 ranges from ⅛ inch to ½ inch, the overlap  24  of the shroud member  20  at the nozzle  30  ranges from 0.1 inch to 1 inch, and the nozzle angle C of the nozzle exit edge ranges from 0 degrees to 20 degrees. 
     A ring fan and shroud assembly constructed in accordance with the present teachings can provide a significantly improved pressure rise, together with stability and static efficiency. In general, the low relative momentum fluid trapped under the inside of the outer ring member  14  at the blade tips is energized and the recirculation flow is introduced back into the flow passage with the swirl removed. This helps to move the flow through the blade tip region and ensure that the recirculating flow encounters the leading edges of the blade members  12  aligned with the inlet angle A of the blade members  12 . 
     The ring fan and shroud assembly  10  can be manufactured using a two-piece injection molding tool. It is not necessary to utilize expensively machined channels in the casing walls as apparently employed in some current compressor tip casing treatments. 
     While preferred embodiments of the present invention have been shown and described herein, numerous variations and alternative embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention is not limited to the preferred embodiments described herein but instead limited to the terms of the appended claims.