JP2014047775A - Diffuser, and centrifugal compressor and blower including the diffuser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small chord-pitch ratio diffuser capable of keeping the effect of secondary flow of the small chord-pitch ratio diffuser, suppressing separation of guide vanes near a blade wall surface, and further suppressing generation of surging, generation of noise due to interference of a centrifugal impeller with the guide vanes, and generation of stall in revolution, and to provide a centrifugal compressor and a blower including the diffuser.SOLUTION: In a diffuser 4, a flow channel of a fluid sent from a centrifugal impeller 2 is formed between two side walls 4a and 4b, a plurality of guide vanes 5 for rectifying the fluid flowing in the flow channel, are formed to have a small chord-pitch ratio, and front edge portions 5a of the guide vanes 5 are disposed separately from a peripheral edge portion 2a of the centrifugal impeller 2. The guide vanes 5 are provided with extending portions 6 extending toward the peripheral edge portion 2a of the centrifugal impeller 2 from a side of the front edge portions 5 while connected with one of the side walls 4a and 4b. A centrifugal compressor 1 or a blower includes the diffuser 4.

Description

  The present invention relates to a diffuser, a centrifugal compressor and a blower provided with the diffuser.

FIG. 11 shows a conventional diffuser provided in the centrifugal compressor.
There are various types and shapes of the diffuser 104 that converts the dynamic pressure of the fluid delivered from the centrifugal impeller 102 of the centrifugal compressor 100 into a static pressure. Among them, the low chord joint ratio diffuser 104 is configured as shown in FIG. 11, for example, and the guide vane 105 hardly peels off on the negative pressure surface, and the occurrence of surging is suppressed and the operating range is wide. However, in the centrifugal compressor and the blower provided with such a low chord joint ratio diffuser 104, noise is generated due to interference between the guide vane 105 and the centrifugal impeller 102, and thus noise reduction is required. Therefore, a low chord ratio diffuser 104 that can suppress occurrence of surging and reduce noise is required.
As background art of this technical field, for example, Patent Document 1 discloses that “in a centrifugal compressor including an impeller 2 and a diffuser 4 with blades, the diffuser is composed of a guide blade 5 having the same leading edge radius and different length from the diffuser plate 4. It is configured, and one or more short guide vanes 6 are installed between adjacent long guide vanes 5 ”(see summary).

JP-A-6-288398

Transactions of the Japan Society of Mechanical Engineers (B) Volume 51, 472 3860-3865 "Effect of side wall secondary flow on stall limit of circular cascade"

The long guide vanes and the short guide vanes provided in the centrifugal compressor of Patent Document 1 have the same leading edge radius, and the short guide vanes are arranged between adjacent long guide vanes. With such a configuration, interference between the centrifugal impeller and the guide vanes (long guide vanes, short guide vanes) can be reduced, and the generation of noise due to pressure fluctuations can be reduced.
However, if a short guide vane is placed between long guide vanes, the distribution of isostatic lines between adjacent guide vanes of the small chord ratio diffuser changes, and the secondary flow in the small chord ratio diffuser changes. The characteristic changes. Therefore, peeling on the suction surface side of the guide vane is likely to occur, and the effect of suppressing the stall of the diffuser cannot be sufficiently obtained.
The secondary flow of the low chord ratio diffuser is described in detail in Non-Patent Document 1 described above.

Further, the technique disclosed in Patent Document 1 does not consider turning stall, which may occur on the larger flow rate side than surging and limit the operating range. Rotating stall is a phenomenon in which a reverse flow region generated in a centrifugal compressor and a blower turns in the circumferential direction. When a rotating stall occurs, pressure pulsation occurs, and thus operation may become impossible due to an increase in vibration and noise. In a space where no blade is formed between the peripheral edge portion 102a of the centrifugal impeller 102 and the front edge portion 105a of the guide blade 105 shown in FIG. 11 (bladeless space), the flow rate of the fluid sent from the centrifugal impeller 102 decreases. In this case, the radially outward dynamic pressure component is reduced. The radially outward dynamic pressure component is particularly small in the velocity boundary layer near the side walls 104a and 104b of the diffuser 104 due to the viscosity of the fluid. Rotating stall occurs when a reverse flow region that is generated when a radially outward dynamic pressure component in the vicinity of the side walls 104a and 104b overcomes a static pressure gradient radially inward is swirled in the circumferential direction.
Such turning stall can be suppressed by bringing the front edge portion 105a of the guide vane 105 closer to the peripheral edge portion 102a of the centrifugal impeller 102 (that is, reducing the radius of the front edge).

  However, when the front edge portion 105a of the guide vane 105 of the diffuser 104 is brought close to the peripheral edge portion 102a of the centrifugal impeller 102, the interference between the guide vane 105 and the centrifugal impeller 102 is increased and noise increases.

  Therefore, the present invention maintains the effect of the secondary flow of the low chord joint ratio diffuser, so that separation near the suction surface of the guide vane can be suppressed, generation of surging can be suppressed, and the centrifugal impeller and the guide vane can be prevented. It is an object of the present invention to provide a low-string ratio diffuser capable of suppressing generation of noise due to interference and generation of turning stall, and a centrifugal compressor and a blower provided with the diffuser.

In order to solve the above-mentioned problems, the present invention forms a flow path for fluid delivered from a centrifugal impeller between two side walls, and a plurality of guide blades for rectifying the fluid flowing through the flow path have a small chord joint ratio. The diffuser is formed in such a manner that the front edge portion of the guide vane is spaced from the peripheral edge portion of the centrifugal impeller. And the protrusion part which enlarges the absolute flow angle near the side wall of the wingless space is characterized in that it is formed so as to stand on one side wall and not reach the other side wall.
Moreover, it is set as the centrifugal compressor and air blower provided with this diffuser.

  According to the present invention, the effect of the secondary flow of the low chord joint ratio diffuser is maintained, the stall of the guide vane near the blade wall surface is suppressed, the surging is generated, and the noise is generated by the interference between the centrifugal impeller and the guide vane. It is possible to provide a low-string ratio diffuser capable of suppressing the occurrence of turning stall, and a centrifugal compressor and a blower provided with the diffuser.

It is sectional drawing along the meridian surface of the centrifugal impeller with which a centrifugal compressor is equipped, and a diffuser. It is sectional drawing in Sec1-Sec1 of FIG. It is a figure which shows the static pressure distribution in the diffuser of a small chord ratio. It is a figure which shows typically the effect of an extending part. (A), (b) is a figure which shows the extension part formed in one side of a side wall. (A) is a figure which shows the extended part which inclines toward the downstream from upstream, and becomes high, (b) is a figure which shows the extended part which becomes circularly high from the upstream to the downstream. is there. FIG. 6 is a diagram illustrating a diffuser according to a second embodiment. (A), (b) is sectional drawing in Sec2-Sec2 of FIG. (A), (b) is sectional drawing which shows the rib formed in one of the side walls. (A) is sectional drawing which shows the rib which inclines toward the downstream from upstream, and height becomes high, (b) is sectional drawing which shows the rib whose height becomes circular arc shape from upstream to downstream. It is sectional drawing which shows the conventional diffuser with which a centrifugal compressor and an air blower are equipped.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

  Embodiment 1 describes an example of a diffuser provided in a centrifugal compressor that compresses a fluid such as gas or liquid with a centrifugal impeller.

FIG. 1 is a cross-sectional view taken along the meridian surface of a centrifugal impeller and a diffuser provided in the centrifugal compressor, and FIG. 2 is a cross-sectional view taken along Sec1-Sec1 in FIG.
FIG. 3 is a diagram showing a static pressure distribution in the low chord joint ratio diffuser.
As shown in FIG. 1, a centrifugal compressor 1 includes a centrifugal impeller 2 that rotates about a rotating shaft 3, and a diffuser 4 that forms a flow path through which a fluid sent from a peripheral portion 2 a of the centrifugal impeller 2 flows. , Including. The diffuser 4 converts the dynamic pressure sent from the rotating centrifugal impeller 2 into a static pressure and forms a flow path that reduces flow path wall surface friction.

As shown in FIG. 1, the centrifugal impeller 2 includes a hub 2b formed so as to spread from the rotating shaft 3 in the circumferential direction, a shroud 2c provided to face the hub 2b, and between the hub 2b and the shroud 2c. And blades 2d formed side by side in the circumferential direction at appropriate intervals.
The centrifugal impeller 2 that rotates about the rotation shaft 3 guides the fluid sucked from the suction port 2e that opens in the axial direction along the blade 2d, and is a centrifugal force generated in the fluid by the rotation, as shown in FIG. In this way, it is sent out from the peripheral edge 2a.

Further, as shown in FIG. 1, the diffuser 4 is a space sandwiched between two side walls 4 a and 4 b having a portion substantially parallel to a rotation plane on which the hub 2 b of the centrifugal impeller 2 rotates. A flow path through which a fluid flows is formed between the side walls 4a and 4b, and a guide vane 5 for rectifying the fluid is further provided. In Example 1, the side wall on the hub 2b side of the centrifugal impeller 2 is 4a, and the side wall on the shroud 2c side is 4b.
The distance from one side wall 4a (4b) forming the diffuser 4 to the other side wall 4b (4a) is referred to as the height Hd of the diffuser 4.

As shown in FIG. 2, a plurality of guide vanes 5 of the diffuser 4 are arranged in a circular cascade on the radially outer side of the centrifugal impeller 2. The guide blade 5 is formed so as to spread outward from the peripheral edge 2 a of the centrifugal impeller 2, and has an appropriate angle with respect to the radial direction of the centrifugal impeller 2. This angle is determined as appropriate, for example, an angle that coincides with the angle of the flow of fluid (absolute flow angle α) delivered from the centrifugal impeller 2 rotating at the rated rotational speed at the rated flow rate.
In addition, about the shape and number of the guide blades 5, a known technique regarding the diffuser can be applied, and is appropriately set depending on the performance required for the centrifugal compressor 1.

Moreover, the diffuser 4 of Example 1 is a low chord ratio ratio diffuser, and the distance L of the front edge part 5a of the adjacent guide blade 5 and the length of the guide blade 5 along the meridian plane (hereinafter referred to as a blade length C). ) And the chordal joint ratio σ is smaller than 1. That is, the guide blades 5 are formed so that the following expression (1) is established.

σ = C / L <1 (1)

The front edge 5a of the guide vane 5 is the end of the guide vane 5 on the centrifugal impeller 2 side.

Further, the front edge portion 5 a of the guide blade 5 is formed on a circumference having a radius r <b> 1 centering on the rotation center of the centrifugal impeller 2. Hereinafter, the radius r1 of the circumference where the leading edge portion 5a is formed is referred to as a leading edge radius.
The leading edge radius r1 is set larger than the radius of the peripheral edge 2a of the centrifugal impeller 2 (hereinafter referred to as the impeller radius r2) (r1> r2). With this configuration, the front edge portion 5 a is disposed away from the peripheral edge portion 2 a of the centrifugal impeller 2.
The leading edge radius r1 is a design value set to a length suitable for suppressing interference between the leading edge portion 5a of the guide blade 5 and the rotating centrifugal impeller 2.

The diffuser 4 configured in this way converts the dynamic pressure generated in the fluid by the centrifugal force of the rotating centrifugal impeller 2 into a static pressure. The fluid delivered from the peripheral edge 2a of the rotating centrifugal impeller 2 includes a velocity component (radial velocity component Vr) that extends radially outward from the centrifugal impeller 2 and a velocity component (circumferential) along the circumferential direction. Direction velocity component Vs) is generated, and the fluid has a velocity component (absolute velocity component Vf) in a direction in which the radial velocity component and the circumferential velocity component are added, and is sent out from the peripheral portion 2a. In the first embodiment, an angle formed by the absolute velocity component Vf and the circumferential velocity component Vs is defined as “absolute flow angle α”.
This absolute flow angle α decreases as the flow rate of the fluid delivered from the centrifugal impeller 2 decreases due to the relationship of the speed triangle at the outlet from which the fluid is delivered from the centrifugal impeller 2.

A velocity boundary layer that is affected by resistance due to the viscosity of the fluid is formed on the side of the diffuser 4 on the side walls 4a and 4b (see FIG. 1). In the velocity boundary layer, the flow velocity of the fluid flowing through the diffuser 4 is lowered by the frictional force generated between the viscosity of the fluid and the side walls 4a and 4b, and accordingly, the dynamic pressure near the side wall of the diffuser 4 is lowered. The dynamic pressure here refers to the pressure generated by the radial velocity component Vr of the fluid.
Thus, when the flow rate of the fluid delivered from the centrifugal impeller 2 decreases, the radial velocity component Vr decreases and the absolute flow angle α decreases. Thereby, the dynamic pressure of the fluid flowing between the guide vanes 5 is reduced.
That is, in the velocity boundary layer formed in the diffuser 4, the dynamic pressure decreases due to the viscosity of the fluid, the influence of friction, and the decrease in the flow rate of the fluid sent from the centrifugal impeller 2 (see FIG. 1).

Further, the diffuser 4 converts dynamic pressure into static pressure by the enlarged flow path. Therefore, as shown by the isostatic line shown by the solid line PL in FIG.
Then, a force (static pressure gradient Fs) is generated from a large static pressure on the downstream side to a small static pressure on the upstream side.
The upstream side of the diffuser 4 is the centrifugal impeller 2 (see FIG. 2) side, and the downstream side is the downstream of the flow of fluid along the guide vane 5 (see FIG. 2). Further, the surface facing the upstream in the guide vane 5 becomes the negative pressure surface 50a, and the surface facing the downstream becomes the pressure surface 50b.

  As described above, when the dynamic pressure decreases in the velocity boundary layer and the force from upstream to downstream decreases due to the dynamic pressure, the force from upstream to downstream may be smaller than the static pressure gradient Fs. In this case, a backflow is generated in the velocity boundary layer near the side wall of the diffuser 4 due to the static pressure gradient Fs from the downstream to the upstream. Furthermore, the generated reverse flow sequentially moves in the circumferential direction of the centrifugal impeller 2 to cause a turning stall.

Since the diffuser 4 according to the first embodiment is a low chord joint ratio diffuser, as shown in FIG. 3, an angle β formed by a streamline indicating a fluid flow and an isostatic pressure line is an obtuse angle. From this, the static pressure gradient Fs in the direction orthogonal to the isostatic pressure line from the downstream to the upstream turns the flow with a small dynamic pressure between the guide blades 5 toward the upstream. In FIG. 3, the static pressure gradient Fs turns the low energy fluid between the guide vanes 5 counterclockwise.
In particular, in the velocity boundary layer where the flow velocity becomes slow, the low energy fluid near the blade wall surface of the guide vane 5 is turned by the static pressure gradient Fs, and as shown by the broken line FL in FIG. 3, the suction surface 50a of one guide vane 5 A secondary flow from the side toward the pressure surface 50b side of the adjacent guide vane 5 is generated.

When the secondary flow as shown in FIG. 3 is generated in the diffuser 4, the velocity boundary layer on the suction surface 50a side is swept out to the pressure surface 50b side, so that separation near the blade wall surface of the guide blade 5 can be suppressed.
With this configuration, on the suction surface 50a side of the guide vane 5 formed with a small chord ratio, separation near the blade wall surface in the velocity boundary layer when the flow rate of the fluid delivered from the centrifugal impeller 2 is small is suppressed. The occurrence of surging is suppressed.

  As described above, the experimental results show that the effect of suppressing the occurrence of separation near the blade wall on the suction surface 50a side is higher in the small chord ratio diffuser having the chord ratio σ of “0.5 to 0.95”. As obtained. Therefore, the diffuser 4 according to the first embodiment is preferably a small chord ratio diffuser in which the chord ratio σ is in the range of “0.5 to 0.95”.

Further, in the first embodiment, the leading edge of the guide vane 5 is suppressed as shown in FIGS. 1 and 2 in order to suppress the turning stall that occurs in the vaneless space of the diffuser 4 in which the guide vane 5 is formed with a small chordal ratio. It was set as the structure provided with the extension part 6 extended toward the peripheral part 2a of the centrifugal impeller 2 from the part 5a.
As shown in FIG. 2, the extending portion 6 is formed in a shape in which the guide blade 5 extends from the front edge portion 5 a upstream, that is, toward the peripheral edge portion 2 a of the centrifugal impeller 2. Further, as shown in FIG. 1, the height Ht of the extending portion 6 is formed lower than the height Hd of the diffuser 4.
That is, the extended portion 6 is formed as a protruding portion that stands on one side wall 4a (4b) and does not reach the other side wall 4b (4a). And the extending part 6 formed in one side wall 4a and the extending part 6 formed in the other side wall 4b are configured to face each other, and a blade is formed between the two extending parts 6 facing each other. An unbladed space (interblade space 6a) is formed. In addition, the code | symbol 6b shows the extended part front edge.

FIG. 4 is a diagram illustrating the effect of the extending portion.
When the extending portion 6 is provided as shown in FIGS. 1 and 2, the absolute flow angle α2 (α <α2) indicated by the solid line indicates the absolute flow angle α that decreases as the fluid flow rate decreases, as shown by the one-dot chain line in FIG. It can be turned greatly like this.
As a result, the fluid flows against the static pressure gradient Fs (see FIG. 3), and the occurrence of backflow near the side wall of the bladeless space can be suppressed. Therefore, the occurrence of backflow in the bladeless space is suppressed, and the occurrence of turning stall is suppressed. That is, by providing the extending portion 6, it is possible to prevent the occurrence of a reverse flow region and to suppress the occurrence of a rotating stall.

The extending portion 6 is formed so as to stand on one side wall 4a (4b) and not reach the other side wall 4b (4a). Therefore, since it does not affect the characteristics of the isostatic pressure line between the guide vanes 5 of the small chord ratio diffuser 4, the secondary flow characteristic of the small chord ratio diffuser 4 can be maintained, and the guide vane 5 has a negative pressure surface 50a. Backflow is suppressed.
Furthermore, as described above, when the extending portion 6 is brought close to the peripheral edge portion 2a of the centrifugal impeller 2, the occurrence of a backflow near the side wall of the bladeless space can be suppressed.
That is, by providing the extending portion 6 on the guide vane 5 of the diffuser 4 having a small chord joint ratio, the peeling of the negative pressure surface 50a of the guide vane 5 and the occurrence of the backflow near the side wall of the bladeless space are effectively suppressed. It is possible to effectively suppress surging and turning stall.

However, since the extending portion 6 extends to the vicinity of the peripheral edge portion 2a of the centrifugal impeller 2, the centrifugal impeller 2 and the extending portion 6 are likely to interfere with each other and noise is likely to be generated.
Therefore, as shown in FIG. 1, the height Ht of the extended portion 6 formed on the side walls 4a and 4b is formed to be lower than the height Hd of the diffuser 4 so as to have an interblade space 6a.
With this configuration, the height of the extended portion front edge 6b facing the centrifugal impeller 2 in the extended portion 6 can be reduced, and interference between the centrifugal impeller 2 and the extended portion 6 can be reduced. And the noise by interference of the centrifugal impeller 2 and the extending part 6 can be reduced.

  In addition, since the decrease in dynamic pressure occurs in the velocity boundary layer where friction between the fluid and the side walls 4a and 4b occurs, the backflow of the fluid is also likely to occur in the velocity boundary layer. Therefore, it is sufficient if the absolute flow angle α is turned in the vicinity of the side walls 4a and 4b. That is, even the extended portion 6 formed lower than the height Hd of the diffuser 4 can favorably turn the absolute flow angle α in the velocity boundary layer and suppress the occurrence of backflow. As a result, generation | occurrence | production of turning stall can be suppressed.

In addition, the extension part 6 should just be the structure extended close to the centrifugal impeller 2 side in the range which can suppress the noise by interference with the centrifugal impeller 2 to an acceptable level. That is, the length of the extended portion 6 toward the centrifugal impeller 2 may be a design value determined by experimental measurement or the like.
Further, the height of the extending portion 6, that is, the length from the one side wall 4a (4b) to the other side wall 4b (4a) is appropriately set according to the size of the velocity boundary layer generated in the diffuser 4 and the like. Design values may be used.

<Modification>
5 and 6 are diagrams showing modifications of the first embodiment.
As a modification of the first embodiment, for example, as shown in FIGS. 5A and 5B, the extending portion 6 of the guide blade 5 may be formed on one of the side walls 4 a and 4 b. .
In FIGS. 5A and 5B, the arrows indicate the flow velocity distribution (distribution of the radial velocity component Vr) of the fluid, and the longer the flow velocity, the higher the flow velocity (radial velocity component Vr).
Depending on the shape of the centrifugal impeller 2, as shown in FIG. 5A, the fluid flow rate may increase on the shroud 2 c side of the peripheral edge 2 a and the fluid flow rate may decrease on the hub 2 b side.
In this case, even if the flow rate of the fluid delivered from the centrifugal impeller 2 decreases, the decrease in the absolute flow angle α is small on the shroud 2c side, and the decrease in dynamic pressure in the velocity boundary layer is small. Therefore, it is not necessary to turn the absolute flow angle α at the extended portion 6, and the extended portion 6 may not be provided on the side wall 4 b on the shroud 2 c side.

Further, depending on the shape of the centrifugal impeller 2, as shown in FIG. 5B, the fluid flow rate may increase on the hub 2b side of the peripheral edge 2a, and the fluid flow rate may decrease on the shroud 2c side. .
In this case, even if the flow rate of the fluid delivered from the centrifugal impeller 2 decreases, the decrease in the absolute flow angle α is small on the hub 2b side, and the decrease in dynamic pressure in the velocity boundary layer is small. Therefore, it is not necessary to turn the absolute flow angle α at the extended portion 6, and the extended portion 6 may not be provided on the side wall 4 a on the hub 2 b side.

Further, as another modification of the first embodiment, as shown in FIGS. 6A and 6B, a configuration in which an extending portion 6 whose height increases from the upstream toward the downstream may be provided.
In the diffuser 4, the influence of the friction between the fluid and the side walls 4 a and 4 b propagates in the height direction and the velocity boundary layer becomes thicker in the height Hd direction as the downstream side. Therefore, by using the extended portion 6 having a higher downstream side, it is possible to effectively suppress the occurrence of backflow in the thick velocity boundary layer.
Moreover, the height of the extending part 6 is low upstream of the diffuser 4, and interference between the extending part 6 and the centrifugal impeller 2 can be effectively reduced.
For example, as shown to (a) of FIG. 6, it may be the extension part 6 which inclines along a meridian surface from upstream to downstream and becomes high.
Further, as illustrated in FIG. 6B, for example, the extending portion 6 may be an arcuate shape that increases from the upstream toward the downstream and extends along the meridional surface.
In addition, although not shown in figure, the extension part 6 which becomes high stepwise along the meridian surface from upstream to downstream may be sufficient, for example.

As described above, in the first embodiment, as shown in FIGS. 1 and 2, the leading edge side 5 a of the guide vane 5 provided in the low-string ratio diffuser 4 extends toward the centrifugal impeller 2, and extends. 6 is formed. With this configuration, it is possible to suppress the occurrence of backflow in the velocity boundary layer and to prevent the occurrence of turning stall.
Further, the extending portion 6 is formed with a height Ht lower than the height Hd of the diffuser 4, and an inter-blade space 6a is formed between the extending portion 6 on the side wall 4a side and the extending portion 6 on the side wall 4b side. . With this configuration, the length of the extended portion front edge 6b facing the centrifugal impeller 2 in the extended portion 6 can be shortened. Therefore, the effect of the secondary flow between the blades of the guide blade 5 can be maintained, the separation near the blade wall surface, the interference between the centrifugal impeller 2 and the extending portion 6 can be reduced, surging, the centrifugal impeller 2 and Noise due to the interference of the extended portion 6 can be reduced.

FIG. 7 is a diagram illustrating the diffuser according to the second embodiment, and FIGS. 8A and 8B are cross-sectional views taken along Sec2-Sec2 in FIG.
The centrifugal impeller 2 and the diffuser 4 according to the second embodiment have substantially the same configuration as that of the first embodiment, and the same components as those of the centrifugal impeller 2 and the diffuser 4 shown in FIG. Detailed description is omitted.
In addition, the diffuser 4 in Example 2 is also a low chord ratio diffuser.
And the diffuser 4 which concerns on Example 2 is replaced with the extension part 6 shown in FIG. 1, and the rib 7 formed discontinuously with the guide blade 5 is provided.

As shown in FIG. 7, the guide blade 5 is formed such that the front edge portion 5 a is positioned at a front edge radius r <b> 1 that is larger than the impeller radius r <b> 2 of the centrifugal impeller 2. 5 a is formed so as to be separated from the peripheral edge 2 a of the centrifugal impeller 2. As a result, a bladeless space S1 in which no guide vane 5 exists is formed between the impeller radius r2 and the leading edge radius r1, that is, in the region on the side of the peripheral edge 2a surrounded by the leading edge 5a. In the second embodiment, the rib 7 is provided in the bladeless space S1.
The rib 7 is erected on the side walls 4a and 4b of the diffuser 4, and its height Ht2 is formed to be lower than the height Hd of the diffuser 4, that is, a configuration connected to one of the side walls 4a and 4b is preferable. . With this configuration, the rib 7 is formed as a protruding portion having a height that stands on one side wall 4a (4b) and does not reach the other side wall 4b (4a).

  The rib 7 preferably has a function of rectifying the fluid flowing through the diffuser 4 and guiding the fluid flowing near the side wall of the bladeless space S1 to the negative pressure surface 50a of the adjacent guide vane 5. The planar shape (the shape when projected onto the side walls 4a and 4b) is not particularly limited. For example, the shape is gradually widened from the upstream and further narrowed toward the downstream (blade shape). )And it is sufficient. In addition, the planar shape of the rib 7 may be appropriately determined according to the performance required for the centrifugal compressor 1.

  As shown in FIG. 8A, the rib 7 in the second embodiment is formed, for example, so as to be shifted toward the negative pressure surface 50a side of the guide blade 5 in the bladeless space S1. Moreover, the rib 7 is arrange | positioned so that it may spread toward the outer side from the peripheral part 2a of the centrifugal impeller 2, and has an appropriate angle with respect to the radial direction of the centrifugal impeller 2, for example. This angle is appropriately determined, for example, an angle that coincides with the absolute flow angle α of the flow of the fluid delivered at the rated flow rate from the centrifugal impeller 2 that rotates at the rated rotational speed. Here, the rated flow rate and the rated rotation speed are values determined as design values of the centrifugal compressor 1.

According to this configuration, the absolute flow angle α (shown by the alternate long and short dash line in FIG. 8A) that has become smaller due to the flow rate of the fluid delivered from the centrifugal impeller 2 is reduced by the rib 7. The fluid is turned to α2 (α <α2) (shown by a solid line in FIG. 8A), and the fluid can be suitably guided to the suction surface 50a of the adjacent guide vane 5.
Further, the rib 7 is formed close to the peripheral edge 2a of the centrifugal impeller 2, but the height Ht2 (see FIG. 7) is formed lower than the height Hd (see FIG. 7) of the diffuser 4, Interference with the centrifugal impeller 2 can be reduced. Therefore, generation of noise due to interference can be suppressed.
In addition, the thick arrow of Fig.8 (a) shows the flow of a fluid.

  In addition, the rib 7 is formed at a position shifted toward the negative pressure surface 50 a of the guide vane 5, whereby the fluid sent from the centrifugal impeller 2 can be efficiently guided to the negative pressure surface 50 a side of the guide vane 5. . With this configuration, the thickness of the velocity boundary layer (the length in the height direction of the diffuser 4) on the suction surface 50a side of the guide vane 5 can be reduced, and separation of the suction surface 50a near the blade wall surface can be suppressed.

As shown in FIG. 8B, the length along the meridian surface of the rib 7 is defined as a blade length C2. Further, the outer shape of the guide vane 5 and the rib 7 is such that the circumference of the inscribed circle is continuous, and an extension line of the warp line L2 (line connecting the center of the inscribed circle) of the guide vane 5 and the rib 7 An interval between the sled lines L3 (interval along the circumferential direction of the centrifugal impeller 2) is defined as an inter-rib pitch Pt.
In this case, it has been obtained as an experimental result that when the rib pitch Pt is in the range of “0 × C2 to 0.65 × C2”, the fluid can be efficiently guided to the negative pressure surface 50a side of the guide vane 5. . Therefore, in the second embodiment, it is preferable that the ribs 7 are configured so that the rib pitch Pt is in the range of “0 × C2 to 0.65 × C2”.

In addition, the external shape of the guide blade 5 and the rib 7 is not limited to a shape in which the circumference of the inscribed circle is continuous. For example, the guide blades 5 and the ribs 7 may be flat blades having a constant thickness, or may be blades having warpage.
For example, in the case of a flat plate blade having a constant thickness, the arrangement of the guide blades 5 and the ribs 7 and the rib pitch Pt are determined based on a camber line (not shown) of the flat plate blade instead of the warp lines L2 and L3. And it is sufficient.

<Modification>
9 and 10 are diagrams showing modifications of the second embodiment.
As a modification of the second embodiment, as shown in FIGS. 9A and 9B, a rib 7 may be formed on one of the side walls 4a and 4b. In this case, when the fluid flow velocity (radial velocity component Vr) increases on the shroud 2c side of the peripheral edge 2a of the centrifugal impeller 2, as shown in FIG. What is necessary is just the structure in which the rib 7 is formed. When the fluid flow velocity (radial velocity component Vr) increases on the hub 2b side of the peripheral edge 2a of the centrifugal impeller 2, as shown in FIG. 9B, ribs are formed on the side wall 4b on the shroud 2c side. 7 may be used.

Further, as another modified example of the second embodiment, as illustrated in FIG. 10A, a rib 7 that is inclined from the upstream toward the downstream and is increased along the meridian surface may be used. Alternatively, as shown in FIG. 10 (b), a rib 7 whose height increases in a circular arc shape along the meridional surface from upstream to downstream may be used. In addition, although not shown in figure, the rib 7 which becomes high stepwise along the meridian surface from the upstream to the downstream may be used, for example.
As described above, in the diffuser 4, the velocity boundary layer becomes thicker in the height Hd direction toward the downstream. Therefore, by using the rib 7 having a higher downstream, it is possible to effectively suppress the occurrence of backflow in the thick velocity boundary layer.
Moreover, the height of the rib 7 is low upstream of the diffuser 4, and interference between the rib 7 and the centrifugal impeller 2 can be effectively reduced.

As described above, in the second embodiment, as shown in FIGS. 7 and 8, the rib 7 is provided in the bladeless space S <b> 1 where the guide blade 5 is not formed. With this configuration, the occurrence of a reverse flow region in the velocity boundary layer can be suppressed, and the occurrence of a rotating stall can be prevented.
Further, the rib 7 is formed so as to be shifted toward the negative pressure surface 50a side of the guide vane 5, and can efficiently guide the fluid sent from the centrifugal impeller 2 to the negative pressure surface 50a side. With this configuration, it is possible to reduce the thickness of the velocity boundary layer on the suction surface 50a side of the guide vane 5 and to suppress separation of the suction surface 50a near the blade wall surface. And generation | occurrence | production of surging can be suppressed.
Further, the rib 7 is formed with a height Ht2 lower than the height Hd of the diffuser 4, and the length of the end of the rib 7 facing the centrifugal impeller 2 can be shortened. Therefore, interference between the centrifugal impeller 2 and the rib 7 can be reduced, and noise due to interference between the centrifugal impeller 2 and the rib 7 can be reduced.

In addition, this invention is not limited to an above-described Example. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described.
Further, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment.

For example, in the first embodiment, the extended portion 6 (see FIG. 1) is formed on the side walls 4a and 4b (see FIG. 1), but the extended portion 6 is formed on one of the side walls 4a and 4b. The rib 7 (refer FIG. 7) may be formed in the other. That is, the structure which Example 1 and Example 2 combined suitably may be sufficient.
In the second embodiment, one rib 7 is formed for one guide blade 5 (see FIG. 8A). However, two or more ribs are provided for one guide blade 5. 7 may be formed.
In addition, the rib 7 is configured to be discontinuous with the guide blade 5, but the rib 7 may have a shape connected to the guide blade 5. In this case, it is preferable that the configuration does not hinder the flow of fluid.
Moreover, although demonstrated as the diffuser 4 (refer FIG. 1) of the centrifugal compressor 1 (refer FIG. 1), this invention is not limited to the centrifugal compressor 1, It is applicable also to the diffuser with which an air blower and another apparatus are equipped. .
In addition, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention.

DESCRIPTION OF SYMBOLS 1 Centrifugal compressor 2 Centrifugal impeller 2a Peripheral part 4 Diffuser 4a, 4b Side wall 5 Guide vane 5a Front edge part 6 Extension part 7 Rib S1 Bladeless space (area | region of the peripheral part side enclosed by the front edge part)

Claims (6)

Two side walls that form a flow path for fluid delivered from the centrifugal impeller;
A plurality of guide vanes formed such that a leading edge portion thereof is arranged away from a peripheral portion of the centrifugal impeller to rectify a fluid flowing through the flow path and have a small chord node ratio;
An extending portion that extends from the front edge side of the guide vane toward the peripheral edge of the centrifugal impeller and is connected to one of the side walls;
A diffuser characterized by comprising:   The diffuser according to claim 1, wherein the extending portion is formed on one of the two side walls forming the flow path. Two side walls that form a flow path for fluid delivered from the centrifugal impeller;
A plurality of guide vanes formed such that a leading edge portion thereof is arranged away from a peripheral portion of the centrifugal impeller to rectify a fluid flowing through the flow path and have a small chord node ratio;
A plurality of the guide blades are formed so as to stand from one side of the side wall to the other side and are connected to one side of the side wall, and flow through the region. A rib for guiding fluid between adjacent guide vanes;
A diffuser characterized by comprising:   The diffuser according to claim 3, wherein the rib is formed on one of the two side walls forming the flow path.   A centrifugal compressor comprising the diffuser according to any one of claims 1 to 4.   A blower comprising the diffuser according to any one of claims 1 to 4.

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