JP2008163821A - Centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand the operational range of a centrifugal compressor with a simple structure. <P>SOLUTION: A plurality of channels 30 are composed of each side surface of each wedge block 39, a hub side wall surface 32, a shroud side wall surface in a diffuser 18. Each side surface of each wedge block 39 is bent to keep angle to a tangential direction of an impeller rotation circumference of each side surface in a downstream side of each bent parts 41, 42 smaller than angle to a tangential direction of an impeller rotation circumference of suction side wall surface 33 in an upstream side of each bent parts 41, 42. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a diffuser structure of a centrifugal compressor.

  A centrifugal compressor 10 is known as one of compressors for compressing gas. For example, as shown in FIG. 6, the conventional centrifugal compressor 10 includes a rotating shaft 12 to which an impeller 11 is attached, a housing 14 that rotatably supports the rotating shaft 12, a shroud 15, and a scroll 17. The impeller 11 includes a hub 13 having a cylindrical portion fitted on the rotary shaft 12, a disk-shaped portion extending radially from the cylindrical portion, and a rotary blade 19 fixed to the hub 13. Yes. The rotary blade 19 is composed of a plurality of blades extending from the inner peripheral side to the outer peripheral side. The shroud 15 has a minute gap between the impeller 11 and the rotor blade 19, and the inner surface shape thereof conforms to the outer shape of the rotor blade 19. A region surrounded by each rotor blade 19, the hub 13, and the shroud 15 constitutes a fluid flow path.

  The shroud 15 includes a suction port 16 on the fluid suction side of the impeller 11, and includes a diffuser 18 and a scroll 17 that recovers the pressure of the fluid that has passed through the impeller 11 on the fluid outlet side of the impeller 11. The diffuser 18 is a parallel flow passage provided in the outlet of the impeller 11 and directed in the radial direction, and includes a plurality of stationary blades 20 in the flow passage. The stationary blade 20 is provided along the direction of the fluid that enters the diffuser 18 from the impeller 11. The scroll 17 is a spiral duct that collects fluid discharged from the flow path between the plurality of stationary blades 20 of the diffuser 18 (see, for example, Patent Document 1).

  The flow of fluid in the centrifugal compressor 10 shown in FIG. 6 will be described. The fluid sucked into the centrifugal compressor 10 from the suction port 16 is sucked into the impeller 11. And it flows through the flow path comprised by the some rotary blade 19 provided in the impeller 11, the hub 13, and the shroud 15. FIG. This flow path is a flow path in which the direction of flow changes in the radial direction along the fluid side surface of the hub 13 toward the downstream, although the inlet side is coaxial with the rotary shaft 12. The rotating blade 19 is rotated by the rotating shaft 12 to apply a rotational force to the fluid flowing in the flow path, and the fluid flows in the radial direction along the flow path of the impeller 11 while rotating by the rotational force. Then, the fluid is discharged from the impeller 11 and flows into the diffuser 18. The fluid that has been decelerated by the diffuser and recovered in pressure flows into the scroll 17. The fluid that has passed through the flow passages of the plurality of diffusers 18 constituted by the plurality of stationary blades 20 is collected in the scroll 17, and the pressure is recovered and discharged from the discharge port to the outside.

  A flow velocity distribution at the outlet of the impeller 11 of the centrifugal compressor 10 is shown in FIG. The direction of the flow of the fluid sucked into the impeller 11 changes from the axial direction to the radial direction along the hub 13. This flow direction is called the meridional direction. At the exit of the impeller 11, the meridional direction is the radial direction. When the flow direction changes, the fluid is pressed against the hub 13 by centrifugal force. Therefore, the flow path in the impeller 11 near the hub 13 has a high flow rate and a high flow speed, but the reverse shroud. On the side close to 15, the flow rate is small and the flow rate is slow. For this reason, as shown in FIG. 7, at the impeller 11 outlet, the flow velocity of the portion in contact with both wall surfaces is decelerated by friction with the wall surface and is smaller than the flow velocity at the central portion, but fluid away from the wall surface flows. The hub side meridional surface direction velocity Vh is larger than the shroud side meridional surface direction velocity Vs.

  As shown in FIG. 8, the impeller 11 is fixed to a rotating shaft and rotates at a predetermined rotational speed, and the rotational speed of the fluid outlet or the tip of the impeller 11 is u. The direction of the flow of the fluid flowing through the fluid flow path formed between the plurality of rotor blades 19 of the impeller 11 at the outlet of the impeller 11 is the direction of the outlet of the rotor blade 19. Since the hub side meridional surface direction velocity Vh is larger than the shroud side meridional surface direction velocity Vs, the hub side outlet flow velocity Wh in the direction along the hub side rotor blade 19 is applied to the shroud side rotor blade 19. It is faster than the shroud side outlet flow velocity Ws in the direction along. Since the rotation speed of the impeller 11 is the same on both the hub side and the shroud side, the fluid in the flow path of the impeller 11 moves with the rotation speed u in the rotation direction of the impeller 11. Accordingly, the hub-side outlet flow velocity Wh in the direction along the rotor blade 19 inside the impeller 11, the shroud-side outlet flow velocity Ws, and the rotation speed u in the rotation direction are combined, and the resultant velocity vectors Ch on the hub side and the shroud side. , Cs are shifted in each direction as shown in FIG. The shroud-side outflow angle αs, which is the angle of the shroud-side composite speed vector Cs with respect to the tangential direction of the impeller rotation circumference, is the hub-side outflow, which is the angle of the hub-side composite speed vector Ch with respect to the tangential direction of the impeller rotation circumference. It becomes smaller than the angle αh. Further, since the gap between the outer periphery of the impeller 11 and the inlet side inner periphery of the diffuser 18 is small, the shroud side outflow angle αs and the hub side outflow angle αh are respectively the shroud side inflow angle βs and the hub side inflow angle βh. Is approximately equal to

  In addition, it is known that the fluid is equiangular when there is no diffuser loss inside the diffuser 18 provided between the parallel walls as shown in FIG. The equiangular line is a curve such that the angle formed by the streamline with respect to the tangential direction of the inner periphery of the diffuser at the inlet of the diffuser 18 is equal to the angle formed by the streamline with respect to the tangential direction of the outer periphery of the diffuser at the outlet of the diffuser 18. Since the radius is large between the inner periphery and the outer periphery of the diffuser, this equiangular line is a curve that is bent to the inner periphery side from the straight line that extends from the inner periphery to the outer periphery of the diffuser. For this reason, the fluid on the hub side that has flowed into the diffuser 18 does not flow linearly toward the outlet of the diffuser 18 as indicated by the streamline 51 in FIG. 8 after flowing into the diffuser 18 at the hub-side inflow angle βh. Furthermore, it flows in a curved shape inclined toward the inner peripheral side of the diffuser 18. Similarly, the shroud side also flows into the inlet of the diffuser 18 at the shroud side inflow angle βs, and then flows in a curved line inclined toward the inner peripheral side of the diffuser 18 as indicated by a streamline 52 in FIG.

JP 2004-27932 A

  Since the shroud side inflow angle βs is smaller than the hub side inflow angle βh, the fluid flowing on the shroud side flows in a direction away from the suction side wall surface 33 of the stationary blade 20 rather than the fluid flowing on the hub side. As described above, since the fluid flow line is directed away from the suction side wall of the stationary blade 20, the flow is easily separated on the suction side of the stationary blade 20, and a surge phenomenon is likely to occur. In particular, when the flow rate decreases, the shroud-side outlet flow velocity Ws decreases more than the hub-side outlet flow velocity Wh, so that a surge phenomenon is more likely to occur, and the operating range of the centrifugal compressor is narrowed. was there. Further, there is a problem that the efficiency of the diffuser 18 is reduced due to the separation of the flow even if the surge phenomenon does not occur.

  Therefore, in order to solve such a problem, in the prior art described in Patent Document 1, by changing the mounting angle between the hub side and the shroud side of the stationary blade 20 of the diffuser 18, the suction side of the stationary blade 20 is changed. In this way, the separation of the flow at the point is reduced and the occurrence of surge phenomenon is reduced. However, since the stationary blade 20 of the diffuser 18 is often manufactured by integrating a plurality of blade rows, the structure in which the inlet angle is changed on the hub side and the shroud side in this way is troublesome to manufacture. there were.

  An object of the present invention is to widen the operating range of a centrifugal compressor with a simple structure.

  The centrifugal compressor of the present invention is a centrifugal compressor that includes a suction side wall surface, a pressure side wall surface, a shroud side wall surface, and a hub side wall surface, and includes a channel type diffuser that recovers the flowed-in fluid and discharges it. Each angle of the suction side wall surface and the pressure side wall surface with respect to the tangential direction of the impeller rotation circumference is smaller than each angle of the suction side wall surface and the pressure side wall surface with respect to the tangential direction of the impeller rotation circumference. Features. In the centrifugal compressor of the present invention, the suction side wall surface has a smaller angle with respect to the tangential direction of the impeller rotation circumference at a position where the flow channel area is approximately 1.1 times the throat portion, and the pressure side wall surface has the flow channel area. It is also preferable that the angle of the impeller rotation circumference with respect to the tangential direction becomes small at a position where is approximately 1.2 times the throat portion.

  In the centrifugal compressor of the present invention, each wall surface of the diffuser on each extension of the shroud side wall surface or the hub side wall surface of the impeller is directed toward the shroud side, the hub side, or both sides between the throat portion and the fluid outlet, respectively. The wall surface of the diffuser on the respective extension of the shroud side wall surface or the hub side wall surface of the impeller is a position where the flow passage area is approximately 1.1 times the throat portion. It is also preferable that it spreads toward the shroud side, the hub side or both sides between the fluid outlet and the fluid outlet.

  The present invention has an effect that the operating range of a centrifugal compressor can be expanded with a simple structure.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the centrifugal compressor 10 of the present embodiment includes an impeller 11, a rotating shaft 12 to which the impeller 11 is attached, a housing (not shown) that rotatably supports the rotating shaft 12, and rotation of the impeller 11. A shroud 15 provided with a minute gap along the surface, a diffuser 18 that recovers the pressure of the fluid that has passed through the impeller 11, and a scroll 17 that is a spiral pipe that collects fluid discharged from the diffuser 18. And.

  The impeller 11 is fixed to the rotating shaft 12, and includes a hub 13 that changes the flow path from the rotating shaft direction toward the radial direction, and a rotary blade 19 fixed to the hub 13. The side of the rotor blade 19 fixed to the hub 13 is the hub side end 23 of the rotor blade 19, and the open end on the shroud 15 side is the shroud side end 21. A shroud 15 is provided on the surface of the rotor blade 19 facing the hub 13 at the shroud side end 21 with a minute gap, and the rotor blade 19, the hub 13 and the shroud 15 constitute a fluid flow path. Each rotor blade 19 is twisted from the fluid inlet to the outlet so that the rotor 19 can efficiently discharge the fluid sucked in the axial direction from the suction port 16 of the shroud 15 in the radial direction. The height of each rotor blade 19 gradually decreases in inverse proportion to the diameter of the rotor blade 19 that becomes the flow path width from the fluid inlet toward the fluid outlet, and substantially decreases from the fluid inlet toward the outlet. It is comprised so that it may become a fixed channel area.

  The diffuser 18 includes a disk-shaped hub side wall 31 fixed to the housing on the hub 13 side, a flat plate-shaped wedge block 39 fixed to the hub side wall surface 32 that is the inner surface of the hub side wall 31, and a wedge-shaped block 39. And a disk-shaped shroud side wall 37 configured to be continuous with the shroud 15. The plurality of wedge-shaped blocks 39 are fixed to the hub side wall surface 32 so that the tips thereof face the inner peripheral side of the diffuser 18 and the side surfaces are in the fluid flow direction. Each wedge-shaped block 39 is arranged at equal intervals in the circumferential direction, and each side surface of each wedge-shaped block 39, a hub side wall surface 32 that is an inner surface of the hub side wall 31, and a shroud side wall surface 38 that is an inner surface of the shroud side wall 37. Thus, a plurality of channel-type flow paths 30 are formed. The surface of each wedge-shaped block 39 on the rotation direction side of the impeller 11 forms a suction side wall surface 33, and the opposite surface forms a pressure side wall surface 35.

  The figure which looked at the impeller 11 and the diffuser 18 of the centrifugal compressor 10 of this embodiment from the suction side in FIG. 2 is shown. As shown in FIG. 2, each blade 19 attached to the hub 13 has a blade height that gradually decreases from the fluid inlet side toward the outlet side. Further, each rotor blade 19 is configured to bend toward the opposite side with respect to the rotation direction, and the rotation speed of the impeller 11, the outer diameter, and the blade blades with respect to the tangential direction of the rotation circumference of the impeller 11 of each rotor blade 19. A predetermined pressure ratio and flow rate are configured to be output by an outlet blade angle that is an angle.

  As shown in FIGS. 2 and 3, the channel-type flow path 30 formed between the wedge-shaped blocks 39 is directed from the fluid inlet on the inner peripheral side of the diffuser 18 toward the fluid outlet on the outer peripheral side. The flow path width is configured to increase toward the outer peripheral side with an opening angle δ. The flow path 30 constituted by the pressure side wall surface 35, the suction side wall surface 33, the hub side wall surface 32, and the shroud side wall surface 38 of the wedge-shaped block 39 is the most flow path on the inner peripheral side of the diffuser 18. The cross-sectional area is narrow. The portion of the minimum channel cross-sectional area is the throat portion. In the present embodiment, since the hub side wall surface 32 and the shroud side wall surface 38 are parallel to each other, the distance between the pressure side wall surface and the suction side wall surface 33 is the minimum distance d1 in the throat portion. . Then, the distance between the wall surfaces is increased in proportion to the opening angle δ toward the downstream.

  A suction side wall surface bent portion 41 is provided in a portion where the distance between the pressure side wall surface 35 and the suction side wall surface 33 is d2 which is 1.1 times the minimum distance d1 toward the downstream of the flow path 30. ing. The suction side wall surface bent portion 41 has an angle with respect to the tangential direction of the impeller rotation circumference of the suction side wall surface 33 on the downstream side of the flow from the suction side wall surface bent portion 41, and the upstream side of the flow from the suction side wall surface bent portion 41. This is the portion where the suction side wall surface 33 is bent toward the inner peripheral side of the diffuser 18 so as to be smaller than the angle of the impeller rotation circumference of the suction side wall surface 33 with respect to the tangential direction. Thereby, each angle with respect to the tangential direction of the impeller rotation circumference of the suction side wall surface 33 at the fluid outlet of the diffuser 18 is smaller than an angle with respect to the tangential direction of the impeller rotation circumference of the suction side wall surface 33 at the fluid inlet of the diffuser 18. ing.

  Further, toward the downstream side of the flow path 30, the pressure side wall surface bent portion 42 is formed in a portion where the distance between the pressure side wall surface 35 and the suction side wall surface 33 is d3 which is 1.2 times the minimum distance d1. Is provided. The pressure side wall surface bent portion 42 has an angle with respect to the tangential direction of the impeller rotation circumference of the pressure side wall surface 35 on the downstream side of the flow from the pressure side wall surface bent portion 42, and is upstream of the pressure side wall surface bent portion 42. This is a portion where the pressure side wall surface 35 is bent toward the inner peripheral side of the diffuser 18 so as to be smaller than the angle with respect to the tangential direction of the impeller rotation circumference of the pressure side wall surface 35. Thereby, each angle with respect to the tangent direction of the impeller rotation circumference of the pressure side wall surface 35 at the fluid outlet of the diffuser 18 is smaller than an angle with respect to the tangential direction of the impeller rotation circumference of the pressure side wall surface 35 at the fluid inlet of the diffuser 18. ing.

  The suction side wall surface bent portion 41 and the pressure side wall surface bent portion 42 cause the flow path 30 on the outlet side of the diffuser 18 to bend toward the rotation direction of the impeller 11 by θ with respect to the inlet side. The bending angle θ may be about 2 to 5 degrees, and the angle formed by the streamline with respect to the tangential direction of the inner periphery of the diffuser at the inlet of the diffuser 18 is the angle formed by the streamline with respect to the tangential direction of the outer periphery of the diffuser at the outlet of the diffuser 18. It is good also as an angle along the equiangular line which is a curve which becomes equal.

  In the present embodiment, the flow path 30 is a rectangular channel type, and the hub side wall surface 32 and the shroud side wall surface 38 are parallel to each other. Therefore, the suction side wall surface bent portion 41 and the pressure side wall surface bent portion 42 are arranged on the pressure side. Although the distance between the wall surface 35 and the suction side wall surface 33 is set to be 1.1 times and 1.2 times the distance of the throat portion, the shape of the flow path 30 may be a shape other than a rectangular shape, or the hub side wall surface 32 and the shroud side wall surface 38 are not parallel to each other, the positions of the suction side wall surface bent portion 41 and the pressure side wall surface bent portion 42 are 1.1 times the flow path area of the throat portion, respectively. It is preferable that the position is doubled.

  Further, the suction side wall surface 33 and the pressure side wall surface 35 may be bent planes bent by the suction side wall surface bent portion 41 and the pressure side wall surface bent portion 42, respectively, or the suction side wall surface bent portion 41 and the pressure side wall surface bent portion 42. You may comprise as a curved surface bent by.

  The operation of the centrifugal compressor configured as described above will be described with reference to FIG. As shown in FIG. 4, the impeller 11 rotates counterclockwise at a rotational speed u. Since the fluid sucked into the impeller 11 changes its axial direction from the axial direction to the radial direction along the hub 13, the fluid is pressed to the hub 13 side by centrifugal force, and the flow path hub in the impeller 11. The side close to 13 has a high flow rate and a high flow rate, and the side close to the reverse shroud has a low flow rate and a low flow rate. Therefore, at the outlet of the impeller 11, the hub side meridional surface direction velocity Vh is larger than the shroud side meridional surface direction velocity Vs, and the hub side outlet flow velocity Wh is larger than the shroud side outlet flow velocity Ws. Further, since the rotational speed of the outlet of the impeller 11 is constant at u on both the hub side and the shroud side, the direction of the combined speed vector Cs of the shroud side outlet flow speed Ws and the rotational speed u is the hub side outlet flow speed Wh and the rotational speed. It is inclined toward the inner peripheral side of the diffuser 18 with respect to the combined velocity vector Ch with u. For this reason, the fluid on the shroud flows in a direction away from the suction side wall surface 33 than the fluid on the hub side. Further, since the flow tends to flow along equiangular lines, the fluid on the shroud side flows like the streamline 54 and the fluid on the hub side flows like the streamline 53.

  However, the suction side wall surface 33 and the pressure side wall surface 35 constituting the flow path 30 are the suction side wall surface bent portion 41 and the pressure side wall surface bent portion 42, respectively, and the angles of the respective wall surfaces 33 and 35 with respect to the tangential direction of the impeller rotation circumference. Therefore, the fluid flows along the suction side wall surface 33 and the pressure side wall surface 35 and is discharged from the outlet of the diffuser 18.

  As a result, the separation of the fluid from the suction side wall surface on the hub side is reduced, and the occurrence of a surge phenomenon in the diffuser 18 due to the separation of the fluid is suppressed. In particular, when the flow rate of a centrifugal compressor is reduced, the flow rate on the hub side is significantly lower than that on the shroud side, so that separation of fluid from the suction side wall surface on the hub side increases, and surge is likely to occur. According to the present embodiment, it is possible to reduce the separation of the fluid from the suction side wall surface on the hub side. Therefore, it is possible to effectively reduce the occurrence of a surge in the diffuser 18 and to operate without the occurrence of a surge. There is an effect that the operation area can be expanded.

  Further, the difference between the direction of the fluid flow in the diffuser 18 and the direction of the suction side wall surface 33 and the pressure side wall surface 35 can be reduced, loss due to separation of the fluid inside the diffuser 18 can be reduced, and the diffuser 18. It is possible to improve the efficiency.

  In this embodiment, the surge phenomenon of the diffuser 18 is reduced by a simple configuration of a channel-type diffuser having a channel-type flow path constituted by a flat wedge block 39, a hub side wall 31, and a shroud side wall 37. There exists an effect that the operation area | region can be expanded.

  Another embodiment will be described with reference to FIG. FIG. 5 shows a cross section in the flow direction of the flow path 30 of the diffuser 18. In the present embodiment, the hub side wall surface 32 and the shroud side wall surface 38 sandwiching the wedge-shaped block 39 are not parallel but extend by a dimension A toward the hub side and the shroud side, respectively. Moreover, it is thick toward the fluid outlet side according to the spreading shape of each wall surface 32,38 of a flow path. The spreading start point is preferably located at the position of the suction side wall surface bent portion 41 having a flow passage area 1.1 times the flow passage area of the throat portion. The spread angle is a minute angle of about 0.5 to 2 degrees.

  In this manner, by expanding the hub side wall surface 32 and the shroud side wall surface 38 of the channel type diffuser 18 toward the downstream side, in addition to the effects of the above-described embodiment, the pressure recovery in the diffuser 18 can be effectively performed. There is an effect that it can be performed.

  Further, in the present embodiment, the hub side wall surface 32 and the shroud side wall surface 38 are described as expanding toward the hub side and the shroud side, respectively, but only the hub side wall surface 32 is expanded toward the hub side. It is also preferable that only the shroud side wall surface 38 expands toward the shroud side.

It is a perspective view showing a centrifugal compressor concerning an embodiment of the present invention. It is the top view which looked at the impeller and diffuser of the centrifugal compressor concerning embodiment of this invention from the axial direction. It is a perspective view showing a channel type diffuser in a centrifugal compressor concerning an embodiment of the present invention. It is explanatory drawing which shows the flow of the impeller and diffuser of the centrifugal compressor concerning embodiment of this invention. It is sectional drawing of the diffuser in the centrifugal compressor concerning other embodiment of this invention. It is sectional drawing of the centrifugal compressor in a prior art. It is a distribution map of meridional surface direction speed in the impeller exit of a centrifugal compressor. It is a figure which shows the direction of the flow of the impeller and diffuser of the centrifugal compressor in a prior art.

Explanation of symbols

  10 Centrifugal Compressor, 11 Impeller, 12 Rotating Shaft, 13 Hub, 14 Housing, 15 Shroud, 16 Suction Port, 17 Scroll, 18 Diffuser, 19 Rotating Blade, 20 Stator Blade, 21 Shroud Side End, 23 Hub Side End, 30 Channel, 31 hub side wall, 32 hub side wall surface, 33 suction side wall surface, 35 pressure side wall surface, 37 shroud side wall, 38 shroud side wall surface, 39 wedge-shaped block, 41 suction side wall surface bent portion, 42 pressure side wall surface bent portion, 51 to 54 Streamlines, d1 to d3 distance, u rotation speed, Vh hub side meridional direction speed, Vs shroud side meridional direction speed, Wh hub side outlet flow velocity, Ws shroud side outlet flow velocity, αh hub side outflow angle, αs Shroud side outflow angle, βh Hub side inflow angle, βs Shroud side inflow , [Delta] opening angle, theta flexion.

Claims (4)

In a centrifugal compressor including a channel-type diffuser that includes a suction side wall surface, a pressure side wall surface, a shroud side wall surface, and a hub side wall surface, and recovers the inflowing fluid to recover the pressure.
Each angle with respect to the tangential direction of the impeller rotation circumference of the suction side wall surface and the pressure side wall surface at the fluid outlet is smaller than each angle with respect to the tangential direction of the impeller rotation circumference of the suction side wall surface and the pressure side wall surface at the fluid inlet. thing,
Centrifugal compressor characterized by. The centrifugal compressor according to claim 1,
The suction side wall surface has a smaller angle with respect to the tangential direction of the impeller rotation circumference at a position where the flow passage area is approximately 1.1 times the throat portion, and the pressure side wall surface has a flow passage area of approximately 1.2 times the throat portion. The centrifugal compressor is characterized in that the angle with respect to the tangential direction of the impeller rotation circumference becomes small at a certain position. The centrifugal compressor according to claim 1 or 2,
Each wall surface of the diffuser on the respective extension of the shroud side wall surface or the hub side wall surface of the impeller extends toward the shroud side, the hub side, or both sides between the throat portion and the fluid outlet, respectively. Centrifugal compressor. The centrifugal compressor according to any one of claims 1 to 3,
Each wall surface of the diffuser on each extension of the shroud side wall surface or hub side wall surface of the impeller is shroud side or hub side between the position where the flow path area is approximately 1.1 times the throat part and the fluid outlet. Alternatively, the centrifugal compressor is characterized by spreading toward both sides.

Images