Quiet fan with non-radial elements

Abstract

In an air blower or axial compressor, such as employed in airplane power plants, ventilating systems, etc., a series of rotating vanes, stationary vanes, or supporting structure of streamline struts is oriented in circumferentially leaning relation to another series of blades in the machine so as to effect a reduction in noise.

Description

BACKGROUND OF THE INVENTION

An axial compressor, air blower or a fan can be described as a machine in which energy is imparted to the air flowing through it in a direction essentially along the axis of the machine. The essential components of such machines are rows of rotating blades which impart energy to the airstream and rows of stationary vanes which serve a dual purpose of turning the airflow in the desired direction as well as providing structural support. The row of rotating blades is usually called a rotor and the frame containing the stationary vanes is usually called a stator. The combination of a rotor and stator is usually called a stage. In some instances the combination of a rotor situated between two stators is called a one-and-a-half stage. In axial compressors used in jet engines one would find a plurality of stages. In a fan employed for propelling or providing lift for an airplane one would find only a few number of stages. For such applications one may also use a 11/2 or a single stage. In air blowers used in ventilating systems one may find only a rotor supported by framework of a few streamlined struts either in front or behind the rotor. In such cases these supporting struts do not serve the purpose of turning the flow as in the case of vanes in a stator. However, there is a similarity in the manner in which noise is generated in all of these various types of machines, so that the term stator will be employed in this specification to include the frame containing the supporting struts. Similarly the term vanes will be employed to include the supporting struts even though they do not perform any flow turning.

The primary source of noise generated in fans, air blowers, and axial compressors is the pulsations in airflow caused by the rotating blades moving past the stationary vanes or struts. The fundamental frequency of the noise thus generated is the product of the number of blades in the rotor and its speed as revolutions per second. In present day designs, actually in use, the rotor blades as well as the stator vanes are radially oriented in the manner of spokes of a wheel, causing strong pulsations in the airflow passing through them. Furthermore, such fluctuations or pulsations in the flow reach their peak values all along the length of blade or vane at the same instant.

In the prior patented art, the patent to Kappus, U.S. Pat. No. 3,216,654 illustrates a turbofan engine as one class of axial-flow assemblies including a compressor unit, involving the noise problem to which the invention is directed. Erwin U.S. Pat. No. 3,373,928 discloses a propulsion fan adaptable for a similar use which proposes to reduce noise by multiplying the number of fan blades to an extent such that the number of blades multiplied by the rotational speed, gives a frequency which is above the audible limit.

SUMMARY OF THE INVENTION

The present invention pertains to configurating the stationary vanes in a stator and/or the rotating blades of the rotor in a manner such as to achieve noise reduction without requiring the use of an unusually large number of fan blades or airfoils. The details of the rest of the engine, compressor, fan or blower will not be discussed here, since such omission does not detract from the usefulness or application of this invention. In this present invention the blades and/or vanes are oriented in non-radial configurations so as to provide vane-blade inter-actions in a manner similar to that in a pair of scissors. Specifically, a vane or blade interacts with the wake from an upstream vane or blade at an oblique angle and also such interaction proceeds gradually from hub to tip as the rotor blade moves past the stator vane. Of more importance is that for every vane leaning in one direction there is a corresponding vane leaning in the opposite direction. As the above referred to wake-interaction travels radially inwardly along one leaning vane, it will travel radially inwardly along another corresponding vane leaning in the opposite direction. The obliquity of the wake interactions, in conjunction with the phase differences in the occurrence of such interactions on the plurality of vanes provides the noise reduction.

OBJECTS OF THE INVENTION

The main object of the present invention is to provide a stator or rotor with non-radial vanes leading in alternate directions so as to reduce noise in fans, air blowers, and axial compressors.

Another object applicable to a stator is to provide for annular adjustment of the set of vanes leaning in one direction relative to the set of vanes leaning in the opposite direction.

Another object is to provide circumferentially leaning vanes in the stator located upstream of a rotor and vanes leaning in the opposite direction in the stator located downstream of the rotor, and to provide angular adjustment of either one of the stators relative to the other.

Another object is to provide a structural support frame of non-radial streamlined struts, adjacent struts leaning circumferentially in opposite directions, for supporting the rotating shaft of a fan consisting of rotating vanes.

The usefulness of the invention and the claims made are not limited to any specific application but includes all rotating machinery where rotors and stators are employed for imparting energy to the airstream. The term stator includes a frame containing streamlined supporting struts, which do not turn the flow passing through them.

DESCRIPTION OF THE INVENTION

Whereas the specification concludes with claims particularly delineated and distinctly claiming the subject matter of the invention, it is believed that the invention will be better understood from the following description along with the accompanying drawings in which:

FIG. 1 is a partial cross-sectional view showing one stage comprising rotor and stator configurations.

FIG. 2 is an exploded perspective view of a portion of the rotor and stator of FIG. 1 showing the orientation of the blades and vanes in the planes of the rotor and the stator respectively.

FIG. 3 is an exploded perspective view of portions of tandem frames in a stator.

FIG. 4 is a partial cross-sectional view of a rotor located between two stators.

FIG. 5 is a partial cross-sectional view of a frame containing non-radial streamlined struts, and

FIG. 6 is a perspective view showing portions of the non-radial streamlined struts.

FIGS. 1, 2, and 3 disclose a stator downstream of a rotor in a single stage of a multistage compressor, in the way of an example only, and in no manner do they limit the scope of the application of the invention. FIGS. 5 and 6 disclose a structural frame of streamlined struts supporting a rotor employed in a ventilating fan. The scope of the invention is not limited to any particular axial position of this supporting frame in relation to the location of the rotor.

Referring to FIG. 1, there is shown a partial cross section of a single stage in a multistage compressor. The rotor, consisting of suitably pitched radial blades 11 of airfoil cross section attached to the hub 12, rotates and imparts velocity to the airstream flowing between the hub and outer casing 13. Downstream of the rotor is located a stator 14 consisting of a plurality of stationary vanes 15 and 16 with pitch, attached to the hub and the outer casing. The air flow leaving the rotor is turned into a direction suitable for the following stage, not included in the figure, by employing suitable airfoil cross sections for the stationary vanes in the stator. In addition to performing the required flow turning, these stationary vanes also provide structural support between the hub and the outer casing. In specific applications where no flow turning is required, the stator may consist of few supporting streamlined struts without pitch. The direction of flow is indicated by arrows in the figure.

Referring next to FIG. 2, there is shown a perspective view of portions of rotor and stator of FIG. 1. For the sake of clarity, the rotor and stator are shown in an exploded view in this figure, but in any practical application they will be close to each other. The rotor contains radially oriented blades 11 having suitable airfoil sections and pitch as in conventional axial compressor rotors. The means of securing the rotor blades to the rotating hub 12 and the means of providing torque to the rotor are not shown in the figure, as such omission does not detract from the usefulness of the invention. The perspective view of the stator 14 depicts the arrangement of the stationary vanes. There is one set of vanes 15 all located in one cross-sectional plane followed by another set of vanes 16 all of which are located in an adjacent cross-sectional plane. These stationary vanes 15 and 16 are of suitable airfoil shapes with pitch such as to provide the required turning angle to the flow passing through the duct formed by the hub and the outer casing. With respect to radial direction, the vanes 15 lean circumferentially in one direction, whereas the vanes 16 lean in an opposite direction. The details of securing the vanes 15 and 16 to the inner rim 17 or to the outer rim 18 are not shown in the figure, as they do not affect the use of and advantages provided by the present invention.

In FIG. 3 is shown a partial view of the tandem frames of a stator. All the stationary vanes 19 leaning in one direction are secured to an inner rim 20 and outer rim 21. All the stationary vanes 22 leaning in the other direction are secured to an inner rim 23 and outer rim 24. Only for the sake of clarity these tandem frames are shown far apart from each other, but in any practical application they are close to each other, e.g. as in FIG. 1. On the outer rim 24 is arranged a worm-gear 25 to provide a means for rotatably adjusting the position of vanes 22 with respect to the vanes 19. The drive for the worm-gear and its control are not shown in the figure as they are not an essential feature of the invention. Other means for providing a similar relative motion can be employed without affecting the use and claims of this invention. The means for securing the rims 23 and 24 to the hub and outer casing of the compressor are not shown in the figure. To provide structural rigidity and prevent vibration of the vanes 19, a circular ring 26 is attached to all the vanes at a suitable radial location between the hub and tip. This ring 26 is secured to a portion or all of the airfoil cross section employed for the vanes. Similarly a ring 27 is attached to all the vanes 22 to provide the structural support referred to above. In FIG. 4 is shown an alternate use of the stator frames comprising the non-radial vanes. This is a partial view of the tandem frames shown in FIG. 3, axially spaced with a rotor between. The rotor 28 containing rotating blades is located between stators 29 and 30 containing stationary vanes. The stationary vanes in stator 29 are made to lean in a direction opposite to those in the stator 30 as described in FIG. 3. The rotor vanes 11 are radial and pitched as in FIG. 2. Furthermore, a worm-gear such as shown at 25 in FIG. 3 is attached to either of the stators 29 and 30 to provide a means of altering their angular disposition as discussed in FIG. 3.

In FIG. 5 is shown a partial cross-sectional view of a stationary frame which serves the purpose of a supporting structure for the rotating shaft connected to a suitable rotor. The rotor containing the rotating blades is not shown in the figure and can be upstream or downstream of the supporting struts 31 shown in the figure. All of the streamlined struts 31 extending non-radially outward, are attached to an inner hub 32 and outer rim 33, and are contained in the same cross-sectional plane. A suitable bearing, not shown in the figure, is utilized within the hub to carry the rotating shaft of a compressor, fan or air blower.

In FIG. 6 is shown a view of the structural frame of FIG. 5 depicting the non-radial and alternately leaning configuration of the streamlined struts. Half of the streamlined struts 34 are all similarly oriented and lean in one direction. The remaining struts 35 are all similarly oriented and lean in a direction opposite to that of the struts 34. All the struts are secured to an inner hub 32 and an outer rim 33 to form a rigid supporting structure. The details of means of securing the struts to the inner and outer rims are not shown in the figure. One or more circular rings 36 can be attached to part or the entire cross sections of the struts at suitable radial locations to provide additional rigidity to the streamlined struts.

Having described the orientation and structural arrangements of the plurality of non-radial vanes in a stator, some of the definite characteristics can be observed. Since all the vanes such as 15 or 16 shown in FIG. 2, lying in one cross-sectional plane are oriented in the same direction, the distance between any two adjacent vanes measured along the circumference at any specific radius remains constant. Consequently, presently available design methods can be employed to choose the airfoil cross sections and pitch for the vanes. The vanes 15 and vanes 16 will have suitably designed airfoil sections so that the required flow turning is partially accomplished in the row of vanes 15 and the remainder in the row of vanes 16.

Any structural vibrations of the vanes 15 or 16 shown in FIG. 2 can be damped by securing the trailing edges of each forward vane 15 to the leading edges of rear vane 16 at the points of intersection.

In another form of application of the invention, the vane configuration shown for the stator in FIG. 2 can be employed for a rotor. In such application the stationary vanes of the adjacent stator are radially configured in a manner similar to the rotor blades shown in rotor of FIG. 2. Each rotating leaning blade together with a corresponding rotating blade leaning in the opposite direction and portions of the inner and outer rims connecting them form a rigid structure. Consequently, the rotating blades in spite of their non-radial configuration are not subjected to excessive bending stresses under the effect of centrifugal force.

The vanes 19 and 22 shown in FIG. 3 may have a short chord in comparison to their length. Any structural vibrations of the vanes are damped by one or more suitable circumferential rings located between the inner and outer rims and connected to all or part of the airfoil sections of the vanes.

The specific purpose of providing means for angular displacement between tandem frames as shown in FIG. 3 is to optimize the noise reduction with changes in the rotor speed. The worm-gear 25, schematically shown in FIG. 3, can be driven by a mechanism controlled by the rotor speed. In an application where optimum noise reduction is desired at a specific speed or where the speed does not appreciably change, a fixed position of the vanes, as in FIG. 2, can be chosen to simplify the structural design of the inner and outer rims of the stator.

The invention as described here in terms of stationary vanes lends itself easily for modifications to existing machinery to reduce their noise. For example, whatever aerodynamic or structural duties an existing stator is required to perform can be easily done by the two rows of stationary vanes 15 and 16 together as shown in FIG. 2.

While certain preferred forms of the invention are described, modifications and variations are obviously possible. It is therefore to be understood that within the scope of the claims, the invention may be practiced otherwise than specifically described.

The effectiveness of the invention in reducing noise as intended has been established by me through tests on an experimental fan.

In the appended claims, the term "vane" is used in a generic sense to designate both the stator vanes and the rotor blades of the foregoing description.

Claims

I claim:

1. In an axial flow apparatus of the type described, in combination:

a rotor unit and a stator unit each comprising a circumferential array of vanes;

said rotor unit being rotatable in axial adjacency to said stator unit for imparting energy to an axial flow through the apparatus;

one of said units having a frame comprising inner and outer supports;

said vanes of one unit including a plurality of non-radial vanes of airfoil cross-section which are similarly oriented in non-radial positions leaning circumferentially away from the radial in a common direction throughout their radial extent; said vanes being secured between said supports;

the vanes of the other unit being oriented in positions angularly related to the positions of said non-radial vanes;

said non-radial vanes comprising a first circumferential array of vanes all similarly oriented in positions leaning circumferentially away from the radial in one direction and a second circumferential array of vanes leaning away from the radial in an opposite direction;

whereby the pulsations created by the vanes of said rotor unit passing the vanes of said stator unit will be attenuated by the radial progressions of the crossings of the relatively moving vanes, thereby reducing noise.

2. An axial flow apparatus as defined in claim 1;

said first and second circumferential arrays being disposed in respective axially adjacent planes and all secured between the same inner and outer support members.

3. An axial flow apparatus as defined in claim 1;

said first and second circumferential arrays being disposed in respective planes which are separated by an axial space in which the other unit is received.