WO2017030164A1

WO2017030164A1 - Turbo device

Info

Publication number: WO2017030164A1
Application number: PCT/JP2016/074101
Authority: WO
Inventors: 修作香川; 高幹櫻井; 学辻村; 香織佐々木; 貴司松村
Original assignee: 株式会社荏原製作所
Priority date: 2015-08-19
Filing date: 2016-08-18
Publication date: 2017-02-23
Also published as: JP2017040188A; JP6624846B2

Abstract

The present invention is a turbo device in which the vanes have an outwardly convex shape as viewed in longitudinal section, wherein unstable characteristics produced due to re-circulating flow are effectively improved. Provided is a turbo machine provided with a casing, and an impeller disposed in the casing and having a plurality of vanes. In the turbo device, the plurality of vanes has an outwardly convex shape as viewed in cross-section that includes the rotating shaft of the impeller, the internal peripheral surface of the casing has an inwardly concave shape as viewed in cross-section of the interval facing the plurality of vanes, and a plurality of grooves is formed on the internal peripheral surface of the casing in at least a portion of the interval.

Description

Turbo machine

The present invention relates to a turbomachine.

Turbomachine is a general term for machines that use an impeller provided in a casing to realize conversion between mechanical energy of rotation of the impeller and energy of fluid flowing in the casing. For example, a turbo pump is a turbo machine that applies pressure to a liquid flowing in a casing by rotationally driving an impeller. There are other turbomachines (eg, blowers and compressors) that apply pressure to the gas, and turbomachines (eg, water turbines, windmills, and turbines) that convert fluid pressure into impeller rotation.

In the turbo machine as described above, unstable characteristics may occur in the flow of fluid in the machine due to various factors. For example, in the case of a turbo pump, the head usually decreases with an increase in the flow rate, which makes it possible to operate stably. A so-called right-up characteristic is generated in which the lift is also increased. Operation may become unstable in the flow rate region where the upward-sloping characteristic occurs, and surging may occur in which the fluid mass self-oscillates in the machine. One of the causes of such unstable characteristics is the recirculation flow generated near the inlet of the impeller in the low flow region.

As a method for suppressing such a phenomenon, conventionally, a method called a casing treatment in which a plurality of deep grooves are formed on the inner peripheral surface of the casing in the blade existing region has been known. Further, for example, Patent Documents 1 to 3 propose techniques for forming a plurality of shallow grooves on the inner peripheral surface of the casing in a region including the inlet of the impeller. According to the techniques described in Patent Documents 1 to 3, by extending the groove to the recirculation flow generation location near the entrance of the impeller, an effect of sufficiently suppressing the generation of the recirculation flow can be obtained even in a shallow groove. it can. In this technique, since the groove is formed shallower than in the conventional casing treatment, the reduction in the maximum efficiency of the turbomachine due to the formation of the groove can be reduced.

Japanese Patent No. 3888880 Japanese Patent No. 3862135 Japanese Patent No. 3841391

However, as apparent from, for example, FIG. 5 of Patent Document 1, the above-described technique is such that the outer shape of the blade in the longitudinal section (the section including the rotation shaft of the impeller) is straight or inward. Applicable when Although not explicitly disclosed in Patent Documents 1 to 3, in this case, the blade mounting angle cannot be made variable. On the other hand, when the attachment angle of the blade is variable, the shape of the blade in the longitudinal section is convex outward, and the shape of the inner peripheral surface of the casing is concave inward correspondingly. When the shapes of the blades and the inner peripheral surface change as described above, the state of occurrence of the recirculation flow also changes. Therefore, for example, in a turbo machine in which the blade mounting angle is variable, the unstable characteristics cannot always be effectively improved by conventional techniques as described in Patent Documents 1 to 3.

The present invention has been made in view of the above points. One of the objects of the present invention is a new and improved capable of effectively improving the unstable characteristics caused by recirculation flow in a turbomachine having blades with outwardly convex shapes in a longitudinal section. Is to provide an improved turbomachine.

According to an aspect of the present invention, a turbomachine including a casing and an impeller provided in the casing and having a plurality of blades is provided. In the turbomachine, the plurality of blades have an outwardly convex shape in a cross section including the rotation shaft of the impeller, and an inner peripheral surface of the casing is inwardly concave in a section of a section facing the plurality of blades. And a plurality of grooves are formed on the inner peripheral surface of the casing in at least a part of the section.

In the above turbomachine, the groove suppresses the generation of a recirculation flow in the clearance between the blades and the inner peripheral surface of the casing, and the loss due to the interference of the recirculation flow with the main flow can be reduced. In a turbomachine with blades protruding outward, the loss due to the recirculation flow generates an unstable characteristic. Therefore, the unstable characteristic can be effectively improved by reducing the loss. .

The above turbo machine may further include an angle variable mechanism that changes the mounting angle of the plurality of blades. The above-described problems are caused by the shapes of the inner peripheral surfaces of the blades and the casing. Therefore, it is not essential that the blade mounting angle is variable in the turbomachine, and the configuration of the turbomachine can be effective even when the blade mounting angle is not variable.

In the turbo machine, the plurality of grooves may not be formed on the inner peripheral surface of the casing except for the section. It is possible to suppress the occurrence of recirculation flow near the inlet of the impeller by extending the groove to the outside of the above section, for example, the outer side of the impeller inlet, but the reduction in the maximum efficiency of the turbomachine is minimized. From the standpoint of achieving this, the groove is formed with a minimum length, and the groove may not be formed on the inner peripheral surface except for the above section.

In the above turbomachine, the width of each of the plurality of grooves is 6 mm or more, and the total width is 15% of the peripheral length of the inner peripheral surface of the casing at the end of the plurality of grooves on the inlet side of the impeller. It may be up to 35%. The depth of each of the plurality of grooves may be greater on the exit side of the impeller than on the entrance side of the impeller. Since the maximum efficiency of the turbomachine decreases as the volume of the groove increases, the groove may be shallower than the outlet side on the inlet side of the impeller, for example, where the influence of the groove depth on the suppression of recirculation flow is small. .

In the above turbomachine, the plurality of grooves may be formed to be inclined with respect to a plane including the rotating shaft of the impeller. In this case, the plurality of grooves may be formed to form an angle corresponding to an angle formed by the plurality of blades with respect to the plane including the rotation axis of the impeller. As a result, it is possible to reduce the maximum efficiency drop while improving the unstable characteristics caused by the recirculation flow in the turbomachine.

1 is a longitudinal sectional view of a turbo machine according to a first embodiment of the present invention. It is a see-through | perspective perspective view of the turbomachine shown in FIG. It is a graph for demonstrating improvement of the right-up characteristic in the 1st Embodiment of this invention. It is a see-through | perspective perspective view of the turbomachine which concerns on the 2nd Embodiment of this invention. It is a graph of the characteristic curve which shows the relationship between the flow volume and the head in the 1st Example of this invention. FIG. 6 is a graph in which a characteristic curve indicating efficiency and shaft power is further superimposed on the graph shown in FIG. 5. It is a graph of the characteristic curve which shows the relationship between the flow volume in the 2nd Example of this invention, a head, efficiency, and shaft power.

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

(First embodiment)
FIG. 1 is a longitudinal sectional view of a turbo machine according to a first embodiment of the present invention. Referring to FIG. 1, a turbo pump 1 that is a turbo machine according to the present embodiment includes a casing 2, an impeller 3, and an angle variable mechanism 5. The impeller 3 provided in the casing 2 has a plurality of blades 4. The blade 4 has an outwardly convex shape in the illustrated longitudinal section, that is, a section including the rotation axis RA. On the other hand, the inner peripheral surface 2 s of the casing 2 has a concave shape on the inner side in the section SC facing the blade 4 in the longitudinal section. As illustrated, in the section SC, the convex shape of the blades 4 and the concave shape of the inner peripheral surface 2s correspond to each other. In this specification, the side closer to the rotation axis RA is referred to as the inner side, and the side farther from the rotation axis RA is referred to as the outer side. The angle variable mechanism 5 changes the attachment angle of the blade 4. Furthermore, in the turbo pump 1, a plurality of grooves 6 are formed in the inner peripheral surface 2s at the center of the section SC.

FIG. 2 is a perspective view of the turbo machine shown in FIG. In FIG. 2, the casing 2 is not shown except for the inner peripheral surface 2s of the section SC. FIG. 2 shows the length L, width W, and depth D of the groove 6 formed in the inner peripheral surface 2s. The length L of the groove 6 is defined in a plane including the rotation axis RA, and the width W is defined in a direction perpendicular to the plane. The plurality of grooves 6 are arranged in the circumferential direction of the inner peripheral surface 2s. Therefore, when viewed in the direction along the rotation axis RA, the groove 6 is formed on the radiation centered on the rotation axis RA.

Here, in the illustrated example, the groove 6 has a rectangular cross section. The depth D is constant from the inlet side to the outlet side of the impeller 3. However, the present embodiment is not necessarily limited to such an example. For example, the depth D may be larger on the outlet side than on the inlet side of the impeller 3. The maximum efficiency of the turbo pump 1 decreases as the volume of the groove 6 increases. Therefore, for example, if the influence of the depth D of the groove 6 on the suppression of the recirculation flow is small on the inlet side of the impeller 3, by making the groove 6 shallower on the inlet side than on the outlet side, The amount of decrease in maximum efficiency may be reduced.

FIG. 3 is a graph for explaining the improvement of the right-up characteristic in the first embodiment of the present invention. FIG. 3 shows a characteristic curve showing the relationship between the flow rate Q and the head H of the turbo pump. The actual characteristic curve of the pump head H _pump, in low flow rate zone than the flow rate Q is a limit flow rate Q _R, right up characteristic lift H _pump is increased with an increase of the flow rate Q is observed. Here, the cause of the occurrence of such characteristics will be described using the following formula (1) in which the head H _pump is expressed using the theoretical head H _th and the head loss H _loss .

In the above formula (1), the theoretical head H _th can be expressed by the following formula (2). Where g is the acceleration of gravity, u ₁ and u ₂ are the peripheral speeds at the inlet and outlet of the impeller of the turbo pump (product of impeller radius and rotational angular velocity), and v _u1 and v _u2 are the impellers, respectively. It is the circumferential turning speed of the fluid at the entrance and exit of the car.

When no recirculation flow is generated near the entrance of the impeller, v _u1 = 0 in the above equation (2). On the other hand, when a recirculation flow having a swirl speed is generated near the entrance of the impeller, v _u1 > 0, and the theoretical head H _th is reduced as compared with the case where no recirculation flow is generated. The graph of FIG. 3 shows the reduction amount ΔH _{th of the} theoretical head that may occur due to such a cause. Reduction [Delta] H _th theoretical lift due to the recycle stream flow rate Q is generated in the low flow rate zone than the limit flow rate Q _R will cause upward-sloping characteristics of lift H _pump.

On the other hand, the head loss H _loss is caused by the frictional resistance between the flow path formed by the casing and the impeller and the fluid. The head loss H _loss is also caused by interference between the recirculation flow generated in the flow path and the main flow. In the graph of FIG. 3, such a head loss H _loss is shown as a difference between the theoretical head H _th and the head H _pump . A small flow rate region than the flow rate Q is a limit flow rate Q _R, if the frictional resistance in addition to the recycle stream and the interference increases lift loss H _loss by generation of mainstream, right up characteristic of which is also lifting height H _pump Cause.

Here, as a result of the fluid numerical analysis performed by the present inventors, in the turbo pump 1 according to the present embodiment, since the blades 4 have an outwardly convex shape in the longitudinal section, they are more than near the entrance of the impeller 3. It has been found that the occurrence of recirculation flow in the clearance between the blade 4 and the inner peripheral surface 2s of the casing 2 is significant. Therefore, in the turbo pump 1, the increase in the head loss H _loss due to the recirculation flow interfering with the main flow is a main cause of the upward rising characteristic of the head H _pump .

According to this knowledge, in the turbo pump 1, it is not always effective to suppress the generation of the recirculation flow in the vicinity of the inlet of the impeller 3 in order to improve the right-up characteristic of the head H _pump . Rather, by reducing the head loss H _loss caused by the recirculation flow generated by the clearance between the blades 4 and the inner peripheral surface 2s interfering with the main flow, the head H _{pump is} effectively raised to the right. It is thought that the characteristics can be improved.

Therefore, the present inventors devised that the groove 6 is formed in the inner peripheral surface 2s of the casing 2 in the section SC facing the blade 4 in the turbo pump 1. The groove 6 suppresses the occurrence of a recirculation flow in the clearance between the blades 4 and the inner peripheral surface 2s, and reduces the head loss H _loss that occurs when the recirculation flow interferes with the main flow.

It is also possible to extend the groove 6 to the outside of the inlet of the impeller 3 and suppress the occurrence of recirculation flow near the inlet of the impeller 3 as in Japanese Patent No. 3884880. However, the longer the groove 6, the lower the maximum efficiency of the turbo pump 1. In addition, as described above, in the turbo pump 1, the increase in the head loss H _loss is greater than the theoretical head decrease amount ΔH _{th in the} upward rising characteristic of the head H _pump . Accordingly, if the reduction in the maximum efficiency of the turbo pump 1 is minimized while improving the right-up characteristic of the head H _pump , the groove 6 has a minimum length L for suppressing the occurrence of recirculation flow. The groove 6 may not be formed on the inner peripheral surface 2s except for the section SC.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The configuration of the present embodiment is the same as that of the first embodiment except for the arrangement of grooves described below. Accordingly, duplicate descriptions, for example, descriptions with reference to longitudinal sectional views as in FIG. 1, are omitted by giving common reference numerals to corresponding components.

FIG. 4 is a perspective view of a turbo machine according to the second embodiment of the present invention. In FIG. 4, as in FIG. 2, the casing 2 is not illustrated except for the inner peripheral surface 2 s of the section SC. Referring to FIG. 2, in the turbo pump 11 according to the present embodiment, a plurality of grooves 16 are formed on the inner peripheral surface 2 s of the casing 2 at the center of the section SC. As illustrated, the groove 16 extends in a direction inclined with respect to a plane including the rotation axis RA. Here, the angle formed by the groove 16 with respect to the plane including the rotation axis RA may correspond to the attachment angle of the blade 4. More specifically, the groove 16 may be formed with respect to a plane including the rotation axis RA so as to form an angle corresponding to an angle formed by the blade 4 with respect to the plane. Here, in this embodiment, the attachment angle of the blade | wing 4 can change with the angle variable mechanism 5 (not shown in FIG. 4). Therefore, the angle formed by the groove 16 with respect to the plane including the rotation axis RA is, for example, the attachment angle of the blade 4 is a median value, an average value of the variable range, or an arbitrary reference angle set within the variable range. The blade 4 is determined based on the angle formed with respect to the plane including the rotation axis RA.

FIG. 4 also shows the length L, width W, and depth D of the groove 16. As described above, since the groove 16 is formed to be inclined with respect to the plane including the rotation axis RA, the length L is also defined in a direction inclined with respect to the plane. The width W defined in the direction perpendicular to the length L is also inclined with respect to the plane including the rotation axis RA. Also in this embodiment, the plurality of grooves 16 are arranged in the circumferential direction of the inner peripheral surface 2s as in the first embodiment. However, since each groove 16 is inclined, it is different from the first embodiment. The plurality of grooves 16 are not arranged in the direction of the width W. In the illustrated example, the groove 16 has a rectangular cross section like the groove 6 of the first embodiment, and the depth D is constant from the inlet side to the outlet side of the impeller 3. However, the present embodiment is not necessarily limited to such an example. Also in the present embodiment, as in the first embodiment, for example, the depth D may be larger on the outlet side than on the inlet side of the impeller 3.

The groove 16 formed in the turbo pump 11 according to the present embodiment also suppresses the occurrence of a recirculation flow in the clearance between the blade 4 and the inner peripheral surface 2s, similarly to the groove 6 of the first embodiment. In addition, the head loss H _loss caused by the recirculation flow interfering with the main flow is reduced. Also in this embodiment, it is possible to extend the groove 16 to the outside of the inlet of the impeller 3 and suppress the occurrence of recirculation flow near the inlet of the impeller 3. However, if the reduction in the maximum efficiency of the turbo pump 11 is to be minimized, the groove 16 is formed with the minimum length L for suppressing the generation of the recirculation flow, and the inner peripheral surface 2s except for the section SC. It is not necessary to form the groove 16 on the surface.

The first and second embodiments of the present invention have been described above. In these embodiments, the turbo pump 1 and the turbo pump 11 described as examples of the turbo machine are both mixed flow pumps. However, embodiments of the present invention may also include other types of turbo pumps, such as axial flow pumps, and turbomachines other than pumps. In such other types of turbomachines, similarly to the above-described embodiment, by forming a plurality of grooves in a section where the inner peripheral surface of the casing faces the blades, the blade and the inner peripheral surface of the casing are formed. It is possible to suppress the occurrence of a recirculation flow in the clearance between them and to reduce the loss caused by the recirculation flow interfering with the main flow.

Further, in the above embodiment, the angle variable mechanism for changing the blade attachment angle is provided, but in the turbomachine according to another embodiment, the blade attachment angle is not necessarily variable. In the above embodiment, the problem solved by forming a plurality of grooves on the inner peripheral surface of the casing is that the blade has a convex shape outward in the longitudinal section, and the inner peripheral surface corresponds to the inner side. This is caused by having a concave shape. That is, this problem occurs regardless of whether or not the blade mounting angle is variable. Therefore, in another embodiment of the present invention, the blade mounting angle may not be variable as long as the inner peripheral surfaces of the blade and the casing have the shape as described above.

(First embodiment)
Subsequently, a first embodiment of the present invention will be described. In the first example, in the turbo pump 1 according to the first embodiment described above, any one of three types of grooves 6 having different widths W is formed on the inner peripheral surface 2s of the casing 2 (implementation). A fluid numerical analysis was performed on Examples 1 to 3) and a comparative example in which the groove 6 was not formed on the inner peripheral surface 2s. In this embodiment, the turbo pump 1 is a mixed flow pump having a specific speed of 680, and the number N, the length L, the depth D, and the width W of the grooves 6 are as shown in Table 1 below. W _Σ / CL shown in Table 1 is the sum of the widths W of the plurality of grooves 6 (that is, W × N) at the end of the groove 6 on the inlet side of the impeller 3 and the inner peripheral surface of the casing 2. It is a ratio to the circumferential length CL of 2s. In the present embodiment, the inner radius of the casing 2 in the above portion was 142 mm, and the peripheral length CL of the inner peripheral surface 2s was 2π × 142≈892 mm.

FIG. 5 is a characteristic curve graph showing the relationship between the flow rate Q and the head H in the first embodiment of the present invention. 5 to 7, the numerical values on the vertical axis and the horizontal axis are expressed as relative values. Therefore, the absolute value of each value is not expressed, but the relative magnitude relationship is expressed accurately. In FIGS. 5 to 7, the vertical axis and the horizontal axis are not logarithmic scales but are equally spaced scales. Referring to the graph of FIG. 5, in the comparative example in which the groove 6 is not formed, the flow rate Q is at a small flow rate region than the limit flow rate Q _R0, right up characteristic lift H is observed. On the other hand, in Example 1, although the upwardly rising characteristic of the head H is still observed, the critical flow rate decreases to _QR1 . That is, in the first embodiment, as a result of the improvement in the right-up characteristic of the head H in the flow rate range of Q _R1 to Q _R0 , the flow rate range where the turbo pump 1 can be stably operated is expanded. Further, in Example 2 and Example 3, almost no upward characteristic of the head H is observed in the entire flow rate range.

That is, in the result of the present embodiment shown in the graph of FIG. 5, a significant improvement in the right-up characteristic of the head H is observed at the time of Example 1 (W _Σ /CL=13.4%), and W _Σ In Example 2 (W _Σ /CL=33.6%) and Example 3 (W _Σ /CL=53.8%) where / CL is larger, the right-up characteristic is further improved. Therefore, in this example, it can be said that significant improvement was seen in the right-up characteristic of the head H when W _Σ / CL is 13.4% or more.

FIG. 6 is a graph showing the efficiency Eff. It is the graph which superimposed the characteristic curve which shows shaft power Ps. Referring to the graph of FIG. 6, it is shown that the shaft power Ps of Examples 1 to 3 exceeds the comparative example, particularly in the flow rate region where the flow rate Q is smaller than the limit flow rate Q _R0 . On the other hand, in the flow rate region where the flow rate Q is greater than or _equal to the limit flow rate Q _R0 , the efficiency Eff. Is shown to be lower than that of the comparative example. More specifically, before and after the flow rate Q _BEP at which the maximum efficiency of the turbo pump 1 is achieved, the efficiency Eff. Is about 97% in Example 1 (W _Σ /CL=13.4%), about 95% in Example 2 (W _Σ /CL=33.6%), and Example 3 (W _Σ /CL=53.8%) is about 92%.

Here, as shown in the graph of FIG. 6, the characteristic curves of the head H are substantially the same for Example 2 and Example 3, and the right-up characteristic is almost eliminated in both examples. . In other words, although the maximum efficiency is lower in the third embodiment than in the second embodiment, there is almost no difference in the effect of improving the right-up characteristic of the lift H. Therefore, in the present embodiment, it is sufficient to set W _Σ / CL to about 35% at most, and from the viewpoint of minimizing the reduction in the maximum efficiency of the turbo pump 1, W _Σ / CL is larger than that. It can be said that it was shown that it is not necessary to set.

(Second embodiment)
Next, a second embodiment of the present invention will be described. In the second example, in the turbo pump 11 according to the second embodiment described above, any one of the three types of grooves 16 having different widths W is formed on the inner peripheral surface 2s of the casing 2 (implementation). A fluid numerical analysis was performed on Examples 4 to 6) and a comparative example in which no groove was formed on the inner peripheral surface 2s. In this embodiment, the turbo pump 11 is a mixed flow pump having a specific speed of 680, and the number N, the length D, and the width W of the grooves 16 are as shown in Table 2 below.

FIG. 7 shows a flow rate Q, a head H, and an efficiency Eff. It is a graph of the characteristic curve which shows the relationship with shaft power Ps. Referring to the graph of FIG. 7, in the comparative example in which the groove 16 is not formed, the flow rate Q is at a small flow rate region than the limit flow rate Q _R0, right up characteristic lift H is observed. On the other hand, in Examples 4 to 6 in which the grooves 16 having the widths W of 6 mm, 15 mm, and 24 mm are formed, the critical flow rate decreases as the width W increases, and the turbo pump 11 is stably operated. The operable flow range has been expanded. From this result, it can be said that in this embodiment, the right-up characteristic of the head H is improved even when the groove 16 inclined with respect to the plane including the rotation axis RA is formed.

On the other hand, with respect to the shaft power Ps, although it is shown that the shaft power of the fourth to sixth embodiments is slightly higher in the flow rate range where the flow rate Q is smaller than the limit flow rate _QR0, Compared with Examples 1 to 3, the difference from the comparative example is small. Further, the efficiency Eff. In the flow rate region where the flow rate Q is _{equal to} or higher than the limit flow rate QR0, the efficiency Eff. Is lower than that of the comparative example, but the difference from the comparative example is small compared to the above-described Examples 1 to 3. More specifically, before and after the flow rate Q _BEP at which the maximum efficiency of the turbo pump 11 is achieved, the efficiency Eff. Is 100%, the efficiency Eff. Exceeds 94%. From this result, it can be said that in the present embodiment, when the inclined groove 16 is formed, the right-up characteristic of the head H is improved, and the reduction in the maximum efficiency of the turbo pump 11 is smaller. .

Although some embodiments of the present invention have been described above, the above-described embodiments of the present invention are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes the equivalents thereof. In addition, any combination or omission of each component described in the claims and the specification is possible within a range where at least a part of the above-described problems can be solved or a range where at least a part of the effect is achieved. .

This application claims priority based on Japanese Patent Application No. 2015-161769 filed on Aug. 19, 2015. The entire disclosure including the specification, claims, drawings, and abstract of Japanese Patent Application No. 2015-161769 is incorporated herein by reference in its entirety. All of the specifications, claims, drawings and abstracts of Japanese Patent No. 3848880 (Patent Document 1), Japanese Patent No. 3862135 (Patent Document 2), and Japanese Patent No. 3841391 (Patent Document 3) The disclosure is incorporated herein by reference in its entirety.

DESCRIPTION OF

SYMBOLS

1,11 Turbo pump 2 Casing 2s Inner peripheral surface 3 Impeller 4 Blade 5 Angle variable mechanism 6,16 Groove

Claims

A turbomachine comprising a casing and an impeller provided in the casing and having a plurality of blades,
The plurality of blades have an outwardly convex shape in a cross section including a rotation axis of the impeller,
The inner peripheral surface of the casing has a concave shape inward in the cross section of the section facing the plurality of blades,
The turbomachine in which a plurality of grooves are formed on the inner peripheral surface of the casing in at least a part of the section.
The turbomachine according to claim 1, further comprising an angle variable mechanism that changes an attachment angle of the plurality of blades.
The turbo machine according to claim 1 or 2, wherein the plurality of grooves are not formed on an inner peripheral surface of the casing except in the section.
Each of the plurality of grooves has a width of 6 mm or more,
The total of the widths is 13.4% to 35% of the circumferential length of the inner peripheral surface of the casing at the ends of the plurality of grooves on the inlet side of the impeller. The turbo machine according to item 1.
The turbomachine according to any one of claims 1 to 4, wherein a depth of each of the plurality of grooves is larger on an outlet side of the impeller than on an inlet side of the impeller.
The turbo machine according to any one of claims 1 to 5, wherein the plurality of grooves are formed to be inclined with respect to a plane including a rotation axis of the impeller.
The turbo according to claim 6, wherein the plurality of grooves are formed so as to form an angle corresponding to an angle formed by the plurality of blades with respect to a plane including a rotation axis of the impeller. machine.