Abstract:
Impeller and stator for use in a fluid machine and consisting, for reducing flow noise and for improving the stability of the characteristic curve between the flow input and output cross-sections, of a solid material matrix with a plurality of flow channels for deflecting the flow and increasing the pressure.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention.  
           [0002]    The invention, in general, relates to an impeller and to a stator for fluid machines and, more particularly, to an impeller and a stator for use in fans and compressors.  
           [0003]    The compression of gaseous fluids may be carried out by fans, hereinafter sometimes referred to as ventilators and blowers, providing a small pressure increase and by compressors providing a large pressure increase.  
           [0004]    Turbo-compressors operate on the principle of energy being supplied by changing the helix. The gas flows through a rotating impeller provided with a plurality of vanes or blades for supplying the energy. The gas flows through the impeller axially, diagonally and radially. Accordingly, compressors are known as radial, diagonal and radial fans or compressors.  
           [0005]    In addition to impellers, fixed flow direction devices, so-called stators or diffusors, equipped with individual vanes are used for improving the transmission of energy and the degree of efficiency in fans and compressors. The vanes of the impellers and of the stators are provided with an entry or front edge and with an exit or rear edge. The surfaces of the vanes between front and rear edge are known as pressure and suction sides.  
           [0006]    As regards the vanes of the impellers and stators, the mean pressure at the pressure side of the vanes is larger than at the suction side which causes forces to affect the vanes. The forces equal the forces exerted by the impellers and stators on the flow and which cause the change of the helix and the transmission of energy in the fans and compressors. In the prior art, the impeller vanes are affixed to a hub with an axial, diagonal or radial contour.  
           [0007]    At their outermost side opposite the impeller hub, the vanes may be connected and fastened by a ring, a covering tape. In diagonal and radial fans and compressors the ring is known as a cover disc. Toward the outside, the impellers and stators are enclosed by a housing. In the upstream and downstream direction the impeller hub may be extended by a stationary housing. For the sake of small flow losses, the gaps between the impeller or stator and the housing are configured to be as small as possible. As a rule, the impellers are driven by an electric motor by way of the hub of the impeller.  
           [0008]    An intensive noise is known to be generated when the impellers and the pressure fields tied to the vanes between pressure and suction side are rotating. The noise is known as rotary noise. Another significant source of the noise are pressure variations which are caused by the flow through the impellers and stators and the formation of small and large swirls connected therewith.  
           [0009]    Many measures of minimizing the noise are known in the prior art.  
           [0010]    A distinction is to be made between active measures, such as, for instance, the design of fans and compressors with small flow losses, the selection of irregular spaces between the vanes (division) as well, as disclosed by DE 196 04 638 A1, crescent-shaped vanes or co-rotating jets and diffusors.  
           [0011]    A blower is known from DE 42 05 925 A1in which the center portion of the vanes is made of a porous material. As a result of the porous material the vanes may be permeated from their pressure side to the suction side. This leads to lowered pressure differences and reduced noises otherwise generated by swirls and pressure difference. However, this causes the efficiency of the energy transmission and of the pressure increase to be reduced as well. As disclosed by U.S. Pat. No. 5,244,349, perforated vanes are used instead of porous material to reduce the mass of the vanes.  
           [0012]    The conditions are similar in an axial impeller with crescent-shaped vanes which as taught by DE 196 04 638 A1 are interrupted in the flow direction. It results in improved pressure distribution and an improved energy transmission as well as reduced noise generation.  
           [0013]    The prior art also teaches lowered noise emission by protrusions at the rear edges of impellers. In this connection, it is assumed that as well as the pressure fields the protrusions affect the swirls in the flow.  
           [0014]    A second group of measures is essentially directed to muffle the generated noises. These measures are known as passive measures.  
           [0015]    For instance, DE 100 19 237 A1 proposes to fabricate the hub and the housing of sound-attenuating material. A blower is described by DE 42 44 906 A1 in which a portion of the interior of the housing is made of sound-absorbing material. In connection with fans, DE 196 04 638 A1 proposes crescent-shaped vanes for reducing the generation of noise.  
           [0016]    Further attempts at solving the noise problem of impellers and stators are the subject of Swiss patent CH 409 225 which provides a flow grid structured as a fibrous body with elongated fibrous individual bodies.  
           [0017]    German patent 174,180 utilizes zig-zig rings and tapes which are flowed through in a direction oblique to the shafts.  
           [0018]    In GB 2,065,773 A disks of rigid porous materials forming sturdy impellers for the transmission of energy.  
           [0019]    DE 195 45 977 A1 is addressed to a similar aspect, viz.: the cost-efficient fabrication of impellers where conventional impellers with vanes are replaced by inexpensive bent strips of sheet metal.  
           [0020]    For evaluating the level of noise of fans, the specific A-valued noise power level is utilized which is related to predetermined values of total pressure increase, volume flow and number of rotations. If the specific noise levels are correlated, for instance, to the diameter as a parameter of the type of fans, a range will result which embraces acceptable fans as regards their degree of efficiency and specific noise power level. Very good radial and axial fans attain specific total noise power levels of about 20 dB (A) and 32 dB (A), respectively.  
           [0021]    Nevertheless, the development in recent years has shown that intensive efforts notwithstanding, it has not been possible further to reduce the minimum specific noise power levels. Hence, in spite of the intensive efforts, the prior art suffers from the disadvantage that the noise pollution from fans and compressors is still unacceptably high.  
           [0022]    Fans of flow technologically favorable properties and compressors providing large pressure increases and large volume flows at a predetermined number of rotations and diameter often suffer from the fact that they have no stable characteristic curve. This characteristic curve, derived from applying increased pressure as a function of the volume flow does not monotonously drop at an increasing volume flow. This characteristic is caused by irregular separations from the impeller and stator vanes—rotating separation—and leads to reduced efficiency, increase noise emission and an additional mechanical load on the vanes. For that reason, fans must not be operated in an unstable operating range. Several stabilizing devices are known for preventing an unstable operation.  
         OBJECT OF THE INVENTION.  
         [0023]    It is a primary object of the invention to provide impellers and stators for axial, diagonal and radial fans or compressors which have a significantly lower specific noise power level than conventional fans and compressors.  
           [0024]    Another object of the invention resides in improving the stability of the characteristic curve of such fans and compressors.  
           [0025]    Other objects will in part be obvious and will in part appear hereinafter.  
         BRIEF SUMMARY OF THE INVENTION.  
         [0026]    In the accomplishment of these and other objects, the invention provides an impeller and a stator for fluid machines, more particularly fans and compressors, which for reducing flow noise and for improving the stability of the characteristic curve between the flow input and output cross-section are formed by a solid material matrix with a plurality of flow channels where a deflection of the flow and the pressure increase connected therewith occur.  
           [0027]    In accordance with an advantageous embodiment of the invention the solid material matrix is not isotropically structured of segments spaced from each other and which form the flow channels for the fluid.  
           [0028]    In the direction of flow, the segments are of polygonal cross-sections, for instance, and are formed by tapes.  
           [0029]    In another advantageous embodiment the segments are formed with a honey-comb, square or trapezoid cross-section. Preferably, the segments are formed by tapes of plastic or metal and are fabricated by a molding process.  
           [0030]    In accordance with a further embodiment of the invention the solid material matrix consist of isotropic porous materials provided with flow channels for the fluid. Advantageously, the porous materials are foams. Metal or plastic foams are especially suitable.  
           [0031]    In accordance with a further embodiment of the invention the solid material matrix is formed of fibrous structures or of sieves arranged transversely of the flow direction.  
           [0032]    The object of the invention is accomplished by structuring the solid material matrix, in the direction of flow, of at least two layers, the first layer being made of fibrous structures or of an isotropic porous material and the second layer being formed of segments.  
           [0033]    It is generally advantageous to provide cover tapes for mechanically stabilizing the solid material matrix or, in the case of a radial structure of the impeller, to form a supporting disc and a covering disc.  
           [0034]    An embodiment of the invention which in terms of minimizing flow noise is particularly advantageous is provided with flow channels which for a partial pressure balance are partially connected to each other in the radial or circumferential direction thereby to reduce the noise pollution.  
           [0035]    As conceived by the invention, the impeller and the stator are not in the conventional manner provided with individual vanes. In accordance with the invention, the impeller and stator are formed by a solid material matrix with a plurality of flow channels. As here understood, a solid material matrix are structured materials with fluid flow channels for deflecting the flow. When structured as an axial fan, the solid material matrix of the impeller or stator is formed in the manner of a disc, for instance.  
           [0036]    The invention offers the advantageous set forth hereinafter:  
           [0037]    In the manner of turbo-machines, the transmission of energy takes place by a change of the helix. New Parameters assume the place of polars of the vanes, of the grid affects and of the marginal losses. These are primarily the forces (3 components) per unit of volume exerted on the flow by the solid material matrix or the structured materials.  
           [0038]    The swirling noise tied to the impeller and stator vanes as well as struts and the like as well as the noise of rotation and the siren sound are eliminated. For that reason the noise spectrum in the center frequency range which defines the fan noise, is of an extremely low level. The flow noise at very large frequencies is increased. This does not, however, adversely affect the A-value level.  
           [0039]    In the partial load range “rotational separation” and thus a continuous intensive noise occurs in high-load fans. Rotational separation is based upon the laminar separation and upon the formation of large structures extending beyond individual vanes of a wheel. Such effects hardly occur in the case of a solid material matrix made of structured material; i.e. all characteristic curves are stable, special sensitizers are eliminated.  
           [0040]    The degrees of efficiency of the novel fans are not substantially worse than those of conventional fans the losses of which are compound of planar, margin, gap and mixing losses. In the case of vanes of structured material the losses resulting from the deflection (analogously to planar losses) are substantially greater than is usually the case. Margin losses, gap losses and mixing losses are reduced.  
           [0041]    All struts, e.g. for mounting the machine, are advantageously made either of a structured material are they are integrated into it for minimizing the size of the separation swirls.  
           [0042]    For achieving good partial load performance, two or more basic structures may be used to the impeller and stator. Thus, for minimizing impact losses, an isotropic fibrous structure is particularly advantageous at the entrance of the wheel as a honey-comb structure at the exit of the wheel for lowering frictional losses.  
           [0043]    Stepped pressure values of about 1 are required (e.g. vacuum cleaner blower) for many applications with an axial feed direction. Hitherto, this has been possible only with radial stages, often with a follow-up stator and return-feed grids. Axial fans with correspondingly large pressure values suffer from unstable characteristic curves with all the disadvantages resulting therefrom. This disadvantage does not arise with axial stages of structured materials.  
           [0044]    Because of the stability of their characteristic curves the impellers and stators in accordance with the invention are used in smoke-removal fans.  
           [0045]    Because of its reduced noise emission, the concept in accordance with the invention is used in fans for computers. A further exemplatory field of applications is the use of the concept for water vapor turbo compressors.  
           [0046]    The mentioned number of possible applications demonstrates that the principle in accordance with the invention may be applied to many differently dimensioned fans and compressors. 
       
    
    
     DESCRIPTION OF THE SEVERAL DRAWINGS  
       [0047]    The novel features which are considered to be characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, in respect of its structure, construction and lay-out as well as manufacturing techniques, together with other objects and advantages thereof, will be best understood from the following description of preferred embodiments when read in connection with the appended drawings, in which:  
         [0048]    [0048]FIG. 1 is an axial section of an axial fan for mounting in a pipe;  
         [0049]    [0049]FIG. 2 a, b  is an axial sectional view of the axial fan for mounting in a pipe;  
         [0050]    [0050]FIG. 3 depicts an unwound coaxial section through impeller and stator of an axial fan for mounting in a pipe;  
         [0051]    [0051]FIG. 4 depicts an axial section of the axial fan with free aspiration;  
         [0052]    [0052]FIG. 5 depicts an unwound coaxial sectional view through impeller and stator of an axial fan of fibrous and cellular material;  
         [0053]    [0053]FIG. 6 is an axial sectional view through a radial fan with an impeller of precisely structured material;  
         [0054]    [0054]FIG. 7 depicts different cellular structures for an impeller for a radial fan (radial section);  
         [0055]    [0055]FIG. 8 is an unwound coaxial sectional view through the impeller and stator of a radial fan in which the cellular structure is formed by many undulating and profiled discs;  
         [0056]    [0056]FIG. 9 is an unwound coaxial section through the impeller and stator of a radial fan in which the cellular structure is formed by many ribbed discs;  
         [0057]    [0057]FIG. 10 is an unwound coaxial section through the impeller and stator of a radial fan in which the cellular structure is formed by many ribbed discs;  
         [0058]    [0058]FIG. 11 is an axial view of the ribbed discs of FIG. 10;  
         [0059]    [0059]FIG. 11  a, b  depict unwound coaxial sections through an impeller and stator of the axial fan with covers; and  
         [0060]    [0060]FIG. 12 is a radial section of the structure of an impeller of a radial fan with covers. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0061]    [0061]FIG. 1 depicts an axial fan  23  provided with an impeller  1 , a stator  2  and an impeller hub  3  for mounting the impeller  1  on the shaft of a drive motor  5 . As a rule, the drive motor  5  will be an electric motor, but other machines may be used whenever circumstances favor it. In addition to their function suitably to deflect the flow, the vanes of the rector serve to support the motor  5  within a housing  6 . For reasons of stability and assembly, the center of the stator  2  is limited or defined by a stator hub  4 . The shaft of the drive motor  5  has been identified as  22 .  
         [0062]    In accordance with the invention, impellers and stators of a solid material matrix of preferably precisely structured material are used rather than conventional impellers and stators with profiled twisted vanes or blades. The wall thickness of the materials forming the segments may be very thin. In this manner the effect of the power which the vanes or blades otherwise exert on the flow in conventional fans, is distributed over many small segments of “structural elements” of the matrix. The structure lends a very high stability to the impeller  1  and stator  2 . Where special requirements demand it, supportive elements are integrated into the impeller  1  and stator  2 .  
         [0063]    In the direction of the flow  11 , the segments are of polygonal cross-section, honey-comb cross-section  15 , or square or trapezoidal cross-section.  
         [0064]    The segments are formed from tapes  19  of plastic or metal. Preferably, all struts, links, brackets and the like are either also made of structured material or they are integrated into it. The direction of the incoming flow  11  of the fluid and the rotational axis  10  of the shaft of the drive motor  5  and of the impeller  1  have also been shown.  
         [0065]    In accordance with a preferred alternative embodiment of the invention, the impeller  1  and stator  2  are made of isotropic foams for reducing running and flow noise. Advantageously, the isotropic foams are metal or plastic foams.  
         [0066]    In an equally advantageous embodiment the impeller  1  and stator  2  are made of fiber-like structures  14 .  
         [0067]    [0067]FIG. 2 represents and enlarged sectional view of the axial fan in the flow direction  11 . The structure of the segments is formed, for instance, by winding and connecting a tape  19  with prefabricated struts  20 . At a strong helical change and for reasons of reducing losses, the pitch of the structure is usually larger in the radial direction than in the circumferential direction in view of the fact that with the deflection and circumferential direction the losses of the secondary flow increase. For velocity and pressure balancing, the structure may be provided with openings in the radial as well as circumferential direction.  
         [0068]    [0068]FIG. 3 results from a coaxial section and its flattening onto a planar. The flow channels  21  may be seen to be different for the impeller  1  and the stator  2 . For purposes of explaining the geometry of the section, the directions of the incoming flow  11  and of the rotation  12  of the impeller  1  have been shown. The flow channels  21  may as shown be uninterrupted, or they may consist of several sections. The dimensions of the flow channels  21  must be selected so as to result in the formation of boundary layers at Reynold values slightly below the change-over to turbulent boundary layers.  
         [0069]    [0069]FIG. 4 depicts an axial fan provided with a suction nozzle. To achieve a good partial load performance, this advantageous embodiment of the invention provides for two different structure layers are used in the impeller  1 . This is possible for the stator as well. The first layer in the direction of the incoming flow is of a fiber-like isotropic structure  14  for minimizing shock losses at the entrance to the impeller. The following second layer as the exit of the impeller is formed of a honey-comb structure  15  and is advantageous for reducing frictional losses.  
         [0070]    Furthermore, the fiber-like isotropic structure  14  makes a radial flow balance possible. The centrifugal and centripetal channel design in the structure of the impeller  1  and stator  2  may advantageously be used for attaining a desirable radial pressure and velocity distribution. With reference to the precisely structured impeller  1  the radius of curvature of the suction nozzle  13  is very small. For ensuring the stability of the impeller  1  a covering tape  7  is used which also keeps the different layers in engagement with each other.  
         [0071]    [0071]FIG. 5 depicts the fiber-like isotropic structure  14  of the entrance of the impeller  1  and of the stator in a flattened coaxial sectional view, as well as the honey-comb structure  15  at the exit of the impeller  1  and of the stator  2 .  
         [0072]    [0072]FIG. 6 is an axial sectional view of a radial fan  24  provided with an inventive impeller  1  made of precisely structured material. The impeller  1  of precisely structured honey-comb material is connected to the drive motor  5  by a support disc  16  and by the hub  3  of the impeller. A cover disc  8  limits the impeller  1  at its side opposite the support disc  16 . The impeller  1  is enclosed by a spiral housing  9 . In different applications it may be advantageous to insert a stator  2  (not shown) also made of precisely structured material behind the radial impeller  1 .  
         [0073]    Depending upon its intended use, the impeller  1  is constructed with different fiber-like structures  14  or different honey-comb cellular structures  15 . In the four quadrants of a radial section of the impeller  1  of a radial fan, FIG. 7 shows different combinations and structures formed of one or more straight or bent honey-comb structures and combination fiber and honey-comb structures. The desired precise structure is formed by the compartmentation of the impeller in axial and circumferential directions.  
         [0074]    In the first quadrant of FIG. 7 a ) a dual-layered impeller is shown. It consists of a first layer of a fiber-like structure  14  and of a second layer of a honey-comb structure  15 .  
         [0075]    In the second quadrant of FIG. 7 b ) there are shown two layers, the first layer consisting of a honey-comb structure  15  of obliquely disposed segments and the second layer consisting of a honey-comb structure with radially disposed segments.  
         [0076]    The fourth quadrant  7   c ) depicts a layer consisting of a honey-comb structure with obliquely arranged segments. In the third quadrant of FIG. 7 d ) a layer is shown which consists of a honey-comb structure  15  with bent or curved segments.  
         [0077]    [0077]FIG. 8 and FIG. 9 depict the structure of a precisely structured radial impeller of many thin, profiled and prefabricated discs  17  having ribs. The discs are placed axially adjacent and connected to each other. The result is a radial impeller  1  of high rigidity which may axially be further strengthened by stays.  
         [0078]    [0078]FIG. 10 depicts a flattened coaxial section of an impeller  1  and a stator  2  of a radial fan  24  in which the cellular structure is made up of many ribbed discs  17 . The cellular structure is limited by the support disc  16 . In accordance with this advantageous embodiment of the invention the depicted arrangement of the segments results in mechanical stability since forces can circumferentially be better absorbed by segments arranged in this manner.  
         [0079]    [0079]FIG. 11 a  and FIG. 11 b  respectively depict a coaxial section and an axial section of an axial impeller or stator in which the flow channels  21  are formed by tongues  26  made by punching out and peening of tapes. Closures  25  are being used for reducing radial flow compensation.  
         [0080]    [0080]FIG. 12 discloses a disc provided with ribs formed by two rows of tongues  26  of different inclinations in the circumferential direction. Another advantageous embodiment of the invention would be to use of more than two rows of tongues  26 .