WO2008035465A1 - Centrifugal compressor - Google Patents

Abstract

A centrifugal compressor having a diffuser structure in which gas flow is less likely to be separated from a hub-side wall surface on the downstream side in a diffuser path. The diffuser path (15) recovers static pressure by reducing the speed of gas flow discharged from the outer peripheral edge of an impeller rotating in a housing (11). The hub-side wall surface (15b) of the diffuser path (15) has a tilt flat surface (20) approaching the shroud side, and the tilt surface (20) is located at a position on the downstream side of that portion of the hub-side wall surface (15b) that is in parallel with the direction normal to a cross-section of an impeller exit.

Description

 Specification

 Centrifugal compressor

 Technical field

 [0001] The present invention relates to a centrifugal compressor such as a turbocharger.

 Background art

 Conventionally, a centrifugal compressor such as a turbocharger used for an internal combustion engine for automobiles is known.

 FIG. 5A is a cross-sectional view showing a main part of a conventional centrifugal compressor. The illustrated centrifugal compressor 10 compresses a fluid such as gas or air introduced from the outside of the housing 11 by rotating an impeller 13 having a large number of blades 12 in a housing 11. The fluid flow (air flow) formed in this way is sent to the outside through the impeller outlet (hereinafter also referred to as “diffuser inlet”) 14, the diffuser passage 15 and the scroll 16 which is the outer peripheral end of the impeller 13. . Note that reference numeral 17 in the figure denotes an axial center line around which the impeller 13 rotates.

[0003] The diffuser passage 15 described above is provided between the impeller outlet 14 and the scroll 16, and is a passage for recovering the static pressure by decelerating the airflow discharged from the impeller outlet 14. The diffuser passage 15 is usually formed by a pair of opposed wall surfaces. In the following description, one of the pair of opposed wall surfaces is referred to as a shroud side wall surface 15a, and the other is referred to as a groove side wall surface 15b.

 Since turbochargers for automobiles used in combination with internal combustion engines require a wide compressor operating range, a type of diffuser (vaneless diffuser) that does not normally have a vane is used. .

[0004] Incidentally, in recent years, the distortion of the airflow flowing into the diffuser passage 15 has become larger as the flow rate of the centrifugal compressor 10 increases and the pressure ratio increases. It is considered that a phenomenon called surging that determines the operation limit on the small flow rate side in the diffuser passage 15 occurs when a flow having a large strain enters the diffuser passage 15.

The mechanism for generating surging is considered to occur when the backflow region of the airflow reaches the outlet end of the diffuser passage 15. In addition, the above-described backflow region is generated. It is considered that the raw material is caused by the flow on the compressor shroud side in the diffuser passage 15, that is, the flow distortion along the shroud side wall surface 15a. Therefore, a diffuser for reducing such flow distortion is used. A structure has been proposed.

[0005] The flow distortion described above is a state in which the flow velocity distribution and the pressure distribution are non-uniform. As a conventional technique for making this uniform, the flow passage cross-sectional area of the diffuser passage 15 is changed, or A structure and a method using a circulation passage are employed. In the case of such conventional techniques, the emphasis is on reducing the distortion that occurs on the inlet side (impeller outlet 14 side) of the diffuser passage 15.

 As a conventional technique for reducing the above-described distortion, for example, it has been proposed to provide a convex portion or a concave portion on the wall surface of the diffuser passage 15 to change the cross-sectional area of the flow passage. Such protrusions and recesses change the shape of the passage in the circumferential direction to equalize the flow of air along the circumferential direction, which can improve the compression efficiency. (For example, see Patent Document 1)

 Patent Document 1: JP-A-10-176699

 Disclosure of the invention

 [0006] However, particularly in a small centrifugal compressor such as a turbocharger for automobiles, it is difficult to measure an internal flow such as an airflow flowing in the diffuser passage. Therefore, the distortion of the actual internal flow is not yet fully understood, and further, the phenomena leading to surging have been elucidated. It is necessary to develop means and expand the operating range of centrifugal compressors (wide range).

As shown in FIG. 5B, the conventional diffuser passage 15 generally has a shroud side wall surface 15a and a nove side wall surface 15b, which are a pair of opposing wall surfaces, in a parallel shape. The axial flow width W of the is constant in the circumferential direction. For the conventional diffuser passage 15 configured in this way, we measured the internal flow using the model and confirmed the flow pattern until surging. As a result, the reverse flow region (indicated by arrow A in the figure) showed the diffuser passage 15 Before the flow field reaches the end of the diffuser outlet 18 side, the flow is separated from the side wall surface 15b near the diffuser outlet 18 and the reverse flow area (arrow in the figure) It was found that it was formed with a mark B). In other words, not the shroud side reverse flow region A but the reverse flow region B is considered to cause surging.

[0008] In this way, the separation of the flow from the hub side wall surface 15b that occurs in the vicinity of the diffuser outlet 18 can be achieved by changing the shape of the passage in the circumferential direction as described in Patent Document 1, for example. It is thought that this cannot be suppressed by the conventional technology in which the flow of the air along is uniform.

 The present invention has been made in view of the above circumstances, and its object is to separate the flow from the hub side wall surface downstream of the hub side wall surface in the diffuser passage (near the diffuser outlet). It is to provide a centrifugal compressor having a diffuser structure that is difficult to perform.

 The present invention employs the following means in order to solve the above problems.

 The centrifugal compressor according to the present invention is provided with a diffuser passage that restores static pressure by decelerating the airflow discharged from the outer peripheral end force of the impeller rotating in the housing. In the centrifugal compressor, the hub of the diffuser passage The side wall surface is provided with an inclined region approaching the shroud side at a position downstream of the portion parallel to the normal direction of the impeller outlet cross section.

 [0010] According to such a centrifugal compressor, the hub side wall surface of the diffuser passage is provided with an inclined region that approaches the shroud side at a position downstream of the portion parallel to the normal direction of the impeller outlet cross section. Therefore, in the inclined region, the radial velocity in the low speed region generated on the side wall of the hub increases, and the radial velocity distribution in the diffuser passage becomes uniform.

 In this case, the inclined region is, for example, an inclined flat surface, a curved surface or a stepped portion formed on the nove side wall surface, and in this inclined region, the closer to the downstream side wall surface, the closer to the downstream side. The axial wall width of the diffuser passage may be narrowed from the upstream side to the downstream side by inclining the hub side wall surface.

 [0011] In the above invention, a preferred position in the length direction of the diffuser passage where the inclined region is provided is a ratio of 0.3 to 0.3 of the diffuser passage from the diffuser inlet to the diffuser outlet (1) with the base point (0) as a base point. This is the range on the downstream side (exit side) from 0.7.

In the above invention, the inclined region provided in the diffuser passage is the hub side wall surface. It is preferable to set so that the maximum amount of protrusion toward the side wall of the shroud is about 1Z3 to 1Z5 of the passage width that is equivalent to the size of the backflow area measured.

 In the above invention, when the inclined region is a plane, a preferable inclination angle is a force that is 20 degrees or less with respect to the normal line of the impeller outlet cross section. A more preferable inclination angle is a method of the impeller outlet cross section. It is 2 degrees or more and 10 degrees or less with reference to the line. If the angle of inclination is excessive, the air flow is accelerated again by reducing the passage area, which is not preferable.

[0012] According to the present invention described above, the hub side wall surface of the diffuser passage is provided with an inclined region that approaches the shroud side at a position downstream of a portion parallel to the normal direction of the impeller outlet cross section. Therefore, in this inclined region, the radial speed of the low speed region generated on the hub side wall surface increases. For this reason, the radial velocity distribution in the diffuser passage is made uniform and local separation is less likely to occur, so that the surge flow rate can be reduced and a wide range operation can be achieved to widen the compressor operating range.

 Further, the present invention described above is suitable for a wide range of a small centrifugal compressor equipped with a vaneless diffuser, such as an automotive turbocharger that requires a wide compressor operating range.

 Brief Description of Drawings

 FIG. 1 is a cross-sectional view of a diffuser passage showing a first embodiment of a centrifugal compressor according to the present invention.

 2 is a cross-sectional view showing a first modification of FIG.

 3 is a cross-sectional view showing a second modification of FIG.

 FIG. 4 is a cross-sectional view of a diffuser passage showing a second embodiment of the centrifugal compressor according to the present invention.

 FIG. 5A is a cross-sectional view showing the main parts of a centrifugal compressor.

 FIG. 5B is a cross-sectional view showing a conventional structure of a diffuser passage.

 Explanation of symbols

[0014] 10 Centrifugal compressor

 11 Housing

12 Impeller 14 Impeller exit (diffuser entrance)

 15, 30 Diffuser passage

 15a, 30a shroud side wall

 15b, 30b Hub side wall

 16 scronore

 18 Diffuser outlet

 20 Inclined plane (Inclined area)

 21 Inclined curved surface (inclined area)

 22 Inclined fold line (inclined area)

 33 Shroud side slope (slope area)

 BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, an embodiment of a centrifugal compressor according to the present invention will be described with reference to the drawings.

 As shown in FIG. 5A, the centrifugal compressor 10 includes a diffuser passage 15 that recovers static pressure by decelerating the airflow discharged from the outer peripheral end of the impeller 13 that rotates in the housing 11. The diffuser passage 15 is provided so as to connect between the impeller outlet (diffuser inlet) 14 and the scroll 16, and is formed between a pair of opposing wall surfaces including the shroud side wall surface 15a and the nozzle side wall surface 15b. Has been.

 FIG. 1 is a cross-sectional view of the diffuser passage 15 showing the first embodiment. This diffuser passage 15 also introduces the air flow (indicated by the white arrow in the figure) from which the outer peripheral end force of the impeller 13 is also discharged into the diffuser inlet 14 force between the shroud side wall surface 15a and the hub side wall surface 15b. The airflow guided to the formed flow path is caused to flow from the diffuser outlet 18 to the scroll 16.

In the illustrated embodiment, the hub side wall surface 15b of the diffuser passage 15 is provided with an inclined plane 20 approaching in the direction of the shroud side wall surface 15a at a position downstream of a portion parallel to the normal direction of the impeller outlet cross section. ing. This inclined plane 20 is an inclined area formed on the hub side wall surface 15b of the diffuser passage 15, and is closer to the shroud side wall surface 15a as it is separated from the diffuser inlet 14 and closer to the diffuser outlet 18, and between the opposing wall surfaces. The axial flow path width W, which is the distance, is reduced to Wa. [0017] That is, the inclined region formed by the inclined wall surface 20 is upstream of the passage in the diffuser passage 15 in which the flow path length in the normal direction is L and parallel to the normal direction and the flow path length is La. Is inclined toward the shroud side wall surface 15a, and is provided in the downstream portion where the flow path length is Lb. Here, if the flow path length L is 1, a suitable length of the downstream portion Lb that becomes the inclined region is set to a length La of the upstream portion parallel to the normal direction of 0.3 to 0.7. The remaining part on the downstream side. In other words, the preferred position for providing the inclined region in the length direction of the diffuser passage 15 is that the flow path length from the diffuser inlet 14 to the diffuser outlet 18 that is the base point (0) to the end point (1) is L ( If L = 1), the length La of the upstream portion is set to a ratio of 0.3 to 0.7, and the length Lb of the downstream portion is set to a ratio of 0.7 to 0.3. That's fine. Therefore, the flow path length L is the sum of the upstream length La and the downstream length Lb (L = La + Lb), so the upstream length La and the downstream length L The total value L with Lb is always “1”.

 [0018] In addition, the inclined region provided in the diffuser passage 15 is about 1Z3 to 1Z5 of the passage width at the diffuser outlet 18 where the protruding amount force Wb of the inclined wall surface 20 from the hub side wall surface 15b to the shroud side wall surface 15a becomes the maximum value Wb. It is preferable to set so that. That is, the maximum value Wb of the protruding amount is about 1Z3 to: LZ5W (Wb ^ lZ3 to: LZ5W), so that the axial channel width Wa narrowed by the inclined wall surface 20 is equal to the axial channel width W. It is set to be about 2Z3 to 4Z5 (Wa = 2Z3 to 4Z5W).

 In addition, as in the case of the inclined wall surface 20 described above, the inclination angle Θ when the inclined region is a plane is preferably set to 20 degrees or less with reference to the normal line of the impeller outlet cross section. However, the more suitable inclination angle Θ is 2 degrees or more and 10 degrees or less with respect to the normal line of the impeller outlet cross section.

 The above-mentioned normal line and normal direction of the impeller outlet cross section mean a straight line extending in the radial direction from the axial center line 17 around which the impeller 13 rotates through the impeller outlet cross section and its direction. It is similar to the air flow direction.

[0019] As described above, the diffuser passage 15 including the inclined region formed by the inclined wall surface 20 has the shroud side wall surface 15a and the hub side wall surface 15b both parallel to the normal direction and the axial flow path width W. The axial flow path width W is toward the diffuser outlet 18 side due to the upstream region where the is constant and the inclined wall surface 20 where the hub side wall surface 15b is inclined toward the shroud side wall surface 15a. It is narrowed and has an inclined area on the downstream side.

 For this reason, the airflow introduced from the diffuser inlet 14 is decelerated by flowing through the diffuser passage 15 to recover the static pressure.At this time, on the downstream side approaching the diffuser outlet 18, it is generated near the wall surface. A low-speed region air flow, which is considered to cause separation from the side wall surface 15b, is gradually guided toward the shroud side wall surface 15a by being guided to the inclined wall surface 20.

 In this case, the low speed region is a region where the velocity component in the radial direction from the diffuser inlet 14 toward the diffuser outlet 18 is low. In the example shown in the figure, the radial direction and the normal direction described above coincide.

 [0021] As a result, the velocity component in the radial direction increases in the airflow in the low speed region generated near the wall surface of the hub side wall surface 15b. For this reason, in the diffuser passage 15, the radial velocity distribution is made uniform, so that local peeling does not occur.

 As described above, when local separation occurs in the diffuser passage 15, the surge flow rate can be reduced, so that a wide range expansion that extends the operating range of the centrifugal compressor can be achieved. In particular, when applied to a small centrifugal compressor equipped with a vane-less diffuser, such as an automobile turbocharger, where a wide compressor operating range is required, it is easy to achieve a wide range.

 By the way, considering the case where a similar inclined region is provided on the shroud side wall surface 15a, the axial flow path width W is conversely narrowed toward the diffuser outlet 18 side. However, in the vicinity of the diffuser outlet 18 on the shroud side wall surface 15a, there is no low-speed region in the vicinity of the wall surface that is considered to be a cause of separation, so the airflow guided to the inclined wall surface 20 gradually flows toward the hub side wall surface 15b. It is accelerated by following. For this reason, the velocity distribution in the radial direction is force! This increases the speed difference between the speed shroud side wall surface 15a and the hub side wall surface 15b where the low speed region exists, thereby further increasing non-uniformity.

 Next, a first modification of the above-described inclined area will be described based on FIG. In addition, the same code | symbol is attached | subjected to the part similar to embodiment mentioned above, and the detailed description is abbreviate | omitted.

In this first modification, an inclined region is formed by an inclined curved surface 21 instead of the inclined plane 20 of FIG. This inclined curved surface 21 is in the length direction of the diffuser passage that provides the inclined region. The preferred position (ratio of length Lb) and the maximum protrusion Wb from the wall side wall surface 15b to the shroud side wall surface 15a are the same as those of the inclined plane 20, and are appropriately curved to satisfy this condition. Etc. may be set. In this case, the curved surface may be either a concave curved surface or a convex curved surface as viewed from inside the diffuser passage 15.

[0024] Even if such an inclined region by the inclined curved surface 21 is provided, the velocity component in the radial direction of the airflow in the low speed region generated in the vicinity of the wall surface of the hub side wall surface 15b increases, so in the diffuser passage 15, The radial velocity distribution becomes uniform and local delamination is less likely to occur.

 Therefore, it is possible to reduce the surge flow rate and achieve a wide range that expands the operating range of the centrifugal compressor. In particular, a small centrifugal compressor equipped with a vaneless diffuser requires a wide compressor operating range. If applied to the case, wide range can be easily achieved.

 Next, a second modification of the above-described inclined region will be described based on FIG. In addition, the same code | symbol is attached | subjected to the part similar to embodiment mentioned above, and the detailed description is abbreviate | omitted.

 In the second modification, an inclined region is formed by an inclined folding line 22 instead of the inclined plane 20 of FIG. The inclined fold line 22 is composed of a flat inclined portion 22a and a parallel portion 22b on the diffuser outlet 18 side. In this case, the parallel portion 22b is parallel to the shroud side wall surface 15a and the hub side wall surface 15b. The

 In addition, the inclined folding line 22 is a suitable position in the length direction of the diffuser passage where the inclined region is provided (the ratio of the length Lb) and the maximum value Wb of the protrusion amount from the side wall wall surface 15b to the shroud side wall surface 15a. Is the same as the inclined plane 20.

 [0026] Even if such an inclined region by the inclined fold line 22 is provided, the air velocity in the low speed region generated near the wall surface of the hub side wall surface 15b increases the velocity component in the radial direction. Therefore, in the diffuser passage 15, The radial velocity distribution becomes uniform and local delamination is less likely to occur.

Therefore, it is possible to reduce the surge flow rate and achieve a wide range that expands the operating range of the centrifugal compressor. In particular, a small centrifugal compressor equipped with a vaneless diffuser requires a wide compressor operating range. If applied to the case, wide range can be easily Can be achieved.

 In addition, the inclined folding line 22 shown in the figure may be combined with an inclined portion 22a having a force of two or more steps, which is a combination of the inclined portion 22a and the parallel portion 22b, or may be combined with a curved surface.

 FIG. 4 is a cross-sectional view showing a second embodiment of the centrifugal compressor according to the present invention. In addition, the same code | symbol is attached | subjected to the part similar to 1st Embodiment mentioned above, The detailed description is abbreviate | omitted In this embodiment, the diffuser channel | path 30 is divided | segmented into three area | regions. That is, in order from the upstream side, the hub side inclined portion 31, the parallel portion 32 parallel to the normal direction of the impeller outlet cross section, and the shroud side inclined portion 33 are integrally connected. For this reason, a hub-side inclined portion 31 is added to the most upstream side with respect to the first embodiment shown in FIG. 1, and at the shroud-side inclined portion 33, the shroud side wall surface 30a and the hub side wall surface 30b are parallel to each other. It is arranged and inclined toward the shroud side at the same inclination angle.

[0028] Even if such a configuration is adopted, in the shroud side inclined portion 33 of the diffuser passage 30, the hub side wall surface 30b is downstream of the parallel portion 32 that is a portion parallel to the normal direction of the impeller outlet cross section. An inclined region approaching the shroud side is provided at a position on the side. That is, when the hub side wall surface 30b of the shroud-side inclined portion 33 approaches the shroud side, an inclined region having substantially the same function as the inclined plane 20 described above is formed.

 For this reason, the hub side wall surface 30b having an inclined plane similar to the inclined plane 20 increases the velocity component in the radial direction in the low speed region generated near the wall surface of the hub side wall surface 30b. In addition, the velocity distribution in the radial direction becomes uniform, and local peeling is less likely to occur.

 Therefore, it is possible to reduce the surge flow rate and achieve a wide range that expands the operating range of the centrifugal compressor. In particular, a small centrifugal compressor equipped with a vaneless diffuser requires a wide compressor operating range. If applied to the case, wide range can be easily achieved.

[0029] In this manner, the hub side wall surface 15a of the diffuser passage 15 is provided with an inclined region that approaches the shroud side at a position downstream of the portion parallel to the normal direction of the impeller outlet cross section. Therefore, the radial speed in the low speed region generated on the hub side wall surface 15a increases, and the radial speed distribution in the diffuser passage 15 becomes uniform. Therefore, in the vicinity of the diffuser outlet 18 in the diffuser passage 15, local air flow separation from the wall surface occurs, so that the surge flow can be reduced and a wide range operation that widens the compressor operating range is achieved. it can.

 It should be noted that the present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope without departing from the gist of the present invention.

Claims

The scope of the claims  No., a centrifugal compressor provided with a diffuser passage that restores static pressure by decelerating the airflow discharged from the outer peripheral end of the impeller that rotates in the udging, wherein the hub side wall surface of the diffuser passage has an impeller outlet cross-section A centrifugal compressor comprising an inclined region approaching the shroud side at a position on the downstream side of a portion parallel to the normal direction.