JP2006009748A - Centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centrifugal compressor suppressing drop of efficiency with a little pressure loss. <P>SOLUTION: Height H of a blade 3 of an impeller 1 is formed in such a manner that the same gradually reduces from a front edge part 5 of the blade toward the rear edge part 6 side, and that change ratio of height of the blade gets relatively large in a vicinity of a rear edge part of the blade. The blade 3 can be constructed to make height H thereof large on the rear edge part 6 side under a design limitation that outlet width of the rear edge part 6 of the blade 3 is constructed in a predetermined design value L. Consequently, ratio Δb/H of width Δb of a clearance CL and height H of the blade 3 become relatively large. Since a ratio of flow passage area occupied by clearance flow CLF and flow passage area occupied by main flow is reduced and pressure loss is reduced, drop of efficiency can be prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a centrifugal compressor.

  As shown in FIG. 7, the centrifugal compressor 10 includes an impeller 1 that is rotationally driven by a motor (not shown) and the like, and a casing 2 that houses the impeller 1. The impeller 1 includes a hub (rotor) 4 formed in a substantially conical shape, and blades 3 attached to the hub 4 in a radial shape. The casing 2 is formed in a substantially conical cylinder shape so as to accommodate the impeller 1 with a predetermined clearance CL. From the front edge portion 5 to the rear edge portion 6 of the impeller 1, the clearance CL is a substantially constant value.

  The symbol H indicates the height of the blade 3, and the height H of the blade 3 is gradually decreased from the front edge 5 side of the impeller 1 toward the rear edge 6 side. Here, the height H of the blade 3 is the size of the protrusion of the blade from the hub surface in the direction orthogonal to the main air flow in the impeller. In the following, the value obtained by dividing the amount of change in blade height with respect to the meridional surface distance along the hub surface by the meridional surface distance is defined as the rate of change in blade height.

  In the impeller 1 of the centrifugal compressor 10, there is a clearance flow that flows from the clearance CL between the tip 7 of the blade 3 and the shroud casing 2. As shown in FIG. 10, the clearance flow CLF means that a part of the air on the pressure surface 3 a side of the blade 3 of the impeller 1 passes through the clearance CL between the blade 3 and the casing 2, and the negative pressure surface 3 b of the blade 3. The phenomenon that flows into the side.

  FIG. 8 and FIG. 9 show the modeled impeller internal flow when the clearance flow CLF ideally does not exist. FIG. 8 is a diagram corresponding to the AA arrow in FIG. 7. Assuming that there is no clearance CL between the blade 3 and the casing 2, as shown in FIG. 8, the flow velocity of the flow (main flow) flowing in the depth direction perpendicular to the paper surface on the cross section of the line BB in FIG. 9, the flow velocity gradually decreases from the suction surface 3b side to the pressure surface 3a side of the blade 3, as shown in FIG.

  On the other hand, what was modeled when the clearance flow CLF exists is shown in FIGS. As shown in FIG. 10, the clearance flow CLF flows in a direction substantially perpendicular to the main flow direction. Therefore, as shown in FIG. 11, in the inter-blade flow velocity distribution on the CC line in FIG. Is a mixture of an ideal flow velocity and a substantially zero flow velocity of the clearance flow CLF, which is halved with respect to the ideal flow velocity shown in FIG. The decrease in flow velocity in the main flow direction due to this mixing is pressure loss.

  As shown in FIG. 7, in the impeller 1 of the centrifugal compressor 10, the height H of the blades 3 decreases from the inlet to the outlet in the flow direction. 12A shows a case where the height H of the wing 3 is relatively high, and FIG. 12-2 shows a case where the height H of the wing 3 is relatively low. As described above, the clearance CL between the casing 2 and the casing 2 is substantially constant from the front edge portion 5 side to the rear edge portion 6 side of the blade 3, so that when the height H of the blade 3 decreases, the clearance CL width Since the ratio of Δb and the height H of the blade 3 (Δb / H) is relatively large, the clearance flow CLF occupies the area occupied by the mainstream as shown in FIGS. The ratio with the area increases and the pressure loss increases. That is, the pressure loss due to the clearance flow CLF is larger as the height H of the blade 3 is lower, and is larger on the rear edge 6 side than on the front edge 5 side of the blade 3.

JP 2000-64998 A

  An object of the present invention is to provide a centrifugal compressor that has little pressure loss and can suppress a decrease in efficiency.

  The centrifugal compressor of the present invention is formed such that the blade height of the impeller changes so as to gradually decrease from the front edge portion side to the rear edge portion side of the blade, and the change rate of the blade height Is configured to be relatively large in the vicinity of the trailing edge of the blade.

  In the centrifugal compressor of the present invention, the shroud line of the shroud surface facing the casing housing the impeller is provided at the tip of the impeller blade from the hub surface on the trailing edge of the blade from the point of exit width. It protrudes in the direction of increasing the height of the blade on the trailing edge side of the blade from the intersection of the virtual tangent and the shroud line, rather than the virtual tangent drawn on the shroud line toward the inside. It is characterized by being formed. Here, the exit width point from the hub surface on the trailing edge of the blade may be a point separated from the hub surface on the trailing edge of the blade by the exit width.

  In the centrifugal compressor according to the present invention, a hub line, which is a boundary line with a hub to which the blade is attached, at a proximal end portion of the impeller blade, a radial direction of the impeller from an intersection of the rear edge portion of the blade and the hub line It is characterized by being formed so as to be concave in the direction of increasing the height of the wings than the imaginary radius line drawn in (1).

  In the centrifugal compressor according to the present invention, a hub line, which is a boundary line with a hub to which the blade is attached, at a base end portion of the blade is arranged in a radial direction of the impeller from an intersection of the trailing edge portion of the blade and the hub line. It is characterized by being formed to be concave in the direction of increasing the height of the wings than the drawn virtual radius line.

  The centrifugal compressor of the present invention is formed such that the impeller blade height gradually decreases from the leading edge toward the trailing edge, and the blade height change rate has at least one inflection point. It is characterized by being configured.

  According to the centrifugal compressor of the present invention, it is possible to suppress a decrease in efficiency with little pressure loss.

Hereinafter, an embodiment of the centrifugal compressor of the present invention will be described in detail with reference to the drawings.
In the present embodiment, portions common to the above-described conventional technology are denoted by common reference numerals, and detailed description thereof is omitted.

  In the present embodiment, as described with reference to FIGS. 12A and 12B, the pressure loss on the trailing edge 6 side of the blade 3 having a relatively large pressure loss is reduced, and the centrifugal compressor The purpose is to effectively suppress the decrease in efficiency.

(First embodiment)
The first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a side view showing an impeller 1 of a centrifugal compressor 20 of the present embodiment, and FIG. 2 is an enlarged view of a main part of FIG.

  As shown in FIG. 1, a line (shroud line) 12 of the shroud surface 11 of the blade 3 facing the casing (not shown) on the tip 7 side of the blade 3 is the same as that of the conventional centrifugal compressor 10 of FIG. Compared to the shroud line 13, the blade 3 is formed so as to bulge in a direction in which the height H of the blade 3 increases. The swelled portion (convex portion) of the wing 3 is denoted by reference numeral 14. The wing | blade 3 has the convex part 14, and the height H of the wing | blade 3 is formed larger than before.

  In FIG. 2, reference numeral TA <b> 1 is a shroud in the blade 3 of the centrifugal compressor 20, starting from a point P on the shroud side of the outlet width L from the hub line on the trailing edge of the blade 3, toward the upstream side inside the blade 3. A tangent drawn on line 12 is shown. Point P is also the intersection of the shroud line 12 and the trailing edge of the wing 3. The blade 3 of the centrifugal compressor 20 has a convex portion 14 that bulges in the direction in which the height H of the blade 3 is larger than the tangent TA1 on the trailing edge 6 side from the intersection of the shroud line 12 and the tangent TA1. is doing. On the trailing edge 6 side of the blade 3 of the conventional centrifugal compressor 10, the height H of the blade 3 is relatively low, and pressure loss due to the clearance flow CLF is particularly problematic. The convex portion 14 is provided on the rear edge 6 side of the wing 3. Thereby, the pressure loss by the clearance flow CLF is effectively reduced.

  A symbol TA2 indicates a tangent line drawn from the point P to the shroud line 13 of the conventional centrifugal compressor 10 of FIG. Since the blade 3 of the centrifugal compressor 10 does not have a convex portion that bulges in the direction in which the height H of the blade 3 is larger than the tangent TA2, the blade 3 of the centrifugal compressor 20 has a higher height than the blade 3 of the centrifugal compressor 20. The height H is low and the pressure loss due to the clearance flow CLF is large.

  In the present embodiment, in the meridional shape of the outlet portion of the impeller 1 of the centrifugal compressor 20, the conventional shroud line 13 is concave in the shroud direction from the hub 4 in the height H direction of the blade 3. The shroud line 12 of the present embodiment is a convex type. In contrast to the conventional impeller 1 having the same outlet width L (FIGS. 2 and 7) as the impeller 1 of the centrifugal compressor 20, by making the shroud line 12 convex, it is intermediate from the inlet of the impeller 1 to the outlet. It is possible to increase the height H of the blade 3 in the portion (in the present embodiment, particularly on the outlet side where the pressure loss is large).

  Therefore, in the centrifugal compressor 20 of the present embodiment, the ratio (Δb / H) between the width CL of the clearance CL and the height H of the blade 3 is relatively larger than that of the conventional centrifugal compressor 10. . As a result, the ratio between the channel area occupied by the clearance flow CLF and the channel area occupied by the main flow is reduced and the pressure loss is reduced, so that a reduction in efficiency can be prevented.

  Also in the centrifugal compressor 20 of the present embodiment, the clearance CL between the casing and the impeller 1 is the rear edge portion from the front edge portion 5 side of the blade 3 as in the conventional centrifugal compressor 10 shown in FIG. It is set to a substantially constant value over the 6 side. In the present embodiment, the casing of the centrifugal compressor 20 is configured in accordance with the shape of the blade 3 such that the blade 3 has the convex portion 14 and the height H of the blade 3 is higher than that of the conventional blade (blade 3 in FIG. 7). The clearance CL from the front edge 5 side to the rear edge 6 side of the wing 3 is formed in a shape that has a substantially constant value (not shown).

  In the embodiments of the present invention to be described later, the height H of the blade 3 of the impeller 1 gradually increases from the front edge 5 side to the rear edge 6 side of the impeller 1 in the same manner as in the past. Although it is formed to change so as to become smaller, the blade 3 also has a sufficient blade height so that the ratio occupied by the clearance flow CLF is reduced on the trailing edge side of the blade 3, and smoothly moves toward the impeller outlet that is relatively narrow. In order to guide the air to the blade, the blade height change rate is characterized by having an inflection point. In other words, when taking the blade height on the vertical axis and the meridional distance from the blade leading edge along the hub surface on the horizontal axis, the conventional blade shape becomes a monotonously decreasing curve convex downward, In each embodiment of the present invention, a curve having an inflection point in the middle is convex downward on the front edge side and upward convex on the rear edge side (possibly further convex near the rear edge).

  The present embodiment described above can be summarized as follows.

(Basic principle)
The basic principle of this embodiment is that the leakage loss is reduced and the efficiency is improved by reducing the ratio of the clearance CL with respect to the height H of the blade 3. Conventionally, the absolute value of the clearance CL is reduced, 1) the absolute value of the leakage amount is reduced, and 2) the ratio of the clearance CL and the height H of the blade 3 is reduced. On the other hand, in the present embodiment, the absolute value of the clearance CL can be reduced by the above-described conventional approach. Therefore, the height H of the blade 3 is further increased in order to reduce leakage loss. Therefore, the ratio between the clearance CL and the height H of the blade 3 is reduced.

(Additional effect)
In this embodiment, the following additional effects can be obtained.

  FIG. 3 shows a blade 3 of a conventional centrifugal compressor 10. In FIG. 3, symbol U indicates the rotational speed of the impeller 1, symbol W indicates the relative velocity of the flow, and symbol C indicates the absolute velocity of the flow. As a result, a velocity triangle as shown in FIG. 3 is formed. FIG. 4 shows the speed triangle of the impeller 1 of the centrifugal compressor 20 of the present embodiment, and the speed triangle of the impeller 1 of the conventional centrifugal compressor 10 is indicated by a broken line in FIG.

  As shown in FIGS. 3 and 4, in the impeller 1 of the centrifugal compressor 20, when the height H of the blade 3 is increased by the amount of the convex portion 14, Cm in the speed triangle decreases when the same flow rate is flowed. And Cm ′. In order to keep the work amount constant (keep the pressure constant), it is necessary to set Cu ′ = Cu. For this reason, the blade angle βk ′ <βk is corrected so that the flow angle β ′ <β (FIG. 3).

As a result, in the centrifugal compressor 20 of the present embodiment, the absolute flow velocity C ′ is also reduced as compared with the conventional centrifugal compressor 10. Since this absolute flow velocity C ′ causes a friction loss with the casing, the loss of the impeller 1 is reduced by decreasing the absolute flow velocity C ′.
Therefore, as an additional effect of the present embodiment, by reducing the blade angle βk, friction loss can be reduced, and reduction in the efficiency of the centrifugal compressor 20 can be suppressed.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG.
In the second embodiment, description of parts common to the first embodiment will be omitted, and only characteristic parts of the second embodiment will be described.

  As shown in FIG. 5, in the centrifugal compressor 30 according to the second embodiment, the hub line 17 on the base end 16 side, which is the side attached to the hub 4 in the blade 3, is the same as the conventional centrifugal compressor 10 of FIG. 7. Compared to the hub line 15, the height H of the blade 3 is formed so as to be recessed. In the wing 3, the different part (concave portion) is indicated by reference numeral 18. The wing | blade 3 has the convex part 18, and the height H of the wing | blade 3 is formed larger than before. The hub line 17 is a boundary line between the base end portion 16 of the blade 3 of the impeller 1 and the hub 4 to which the base end portion 16 of the blade 3 is attached.

  In FIG. 5, the conventional hub line indicated by reference numeral 15 is a radial line segment (radial line) of the hub 4 passing through the point Q on the hub 4 side of the outlet width L of the trailing edge 6 of the blade 3 at the same time. Point Q is the intersection of the hub line 17 and the trailing edge 6 of the wing 3. The blade 3 of the centrifugal compressor 30 has a convex portion 18 that bulges in a direction in which the height H of the blade 3 is larger than the radius line 15 passing through the point Q. On the trailing edge 6 side of the blade 3 of the conventional centrifugal compressor 10, the height H of the blade 3 is relatively low, and pressure loss due to the clearance flow CLF becomes a particular problem. The portion 18 is provided on the trailing edge 6 side of the wing 3. Thereby, the pressure loss by the clearance flow CLF is effectively reduced. Since the conventional centrifugal compressor 10 does not have a convex portion that bulges in the direction in which the height H of the blade 3 is larger than the hub line 15, the height of the blade 3 is higher than that of the blade 3 of the centrifugal compressor 30. The height H is low, and the pressure loss due to the clearance flow CLF is large.

  In the impeller 1 of the conventional centrifugal compressor 10, in the meridional shape, with respect to the hub line 15, the front edge 5 of the impeller 1 and the axial length Z 1 from the front edge 5 to the rear edge 6 of the impeller 1 The axial length Z2 from the front edge portion 5 of the impeller 1 at the intermediate portion between the rear edge portions 6 is Z1 ≧ Z2. On the other hand, in 2nd Embodiment, with respect to the axial direction length Z1 from the front edge part 5 of the impeller 1 to the rear edge part 6, it is the axial direction length from the front edge part 5 of the impeller 1 in an intermediate part. The maximum value Z2max of Z2 is Z1 <Z2max.

  In the second embodiment, the maximum value of the axial length of the impeller 1 at the intermediate portion between the front edge portion 5 and the rear edge portion 6 of the impeller 1 is set to Z1 <Z2max, whereby the front edge of the impeller 1 is set. The height H of the wing 3 at the intermediate portion between the portion 5 and the trailing edge portion 6 can be increased. Therefore, the ratio (Δb / H) between the width Δb of the clearance CL and the height H of the blade 3 is relatively large. As a result, the ratio between the channel area occupied by the clearance flow CLF and the channel area occupied by the main flow is reduced and the pressure loss is reduced, so that a reduction in efficiency can be prevented. Also in the second embodiment, the additional effect of the first embodiment can be obtained.

  As shown in FIGS. 1 and 5, in the first embodiment and the second embodiment, in common, the height H of the blade 3 of the impeller 1 is from the front edge 5 side of the blade 3 in the same manner as in the related art. In this case, the rate of change of the height H of the blade 3 is relatively close to the vicinity of the rear edge 6 of the blade 3. It has the feature of being configured to be large. That is, both the first embodiment and the second embodiment have a configuration in which H of the blade 3 is ensured to the maximum just before the outlet of the impeller 1 and the flow path is narrowed sharply in the vicinity of the outlet as compared with other parts. Have. According to this configuration, the height H of the blade 3 is increased on the trailing edge 6 side under the design constraint that the exit width of the trailing edge 6 of the blade 3 is configured to a predetermined design value L. can do.

(Third embodiment)
The third embodiment will be described with reference to FIG.
In the third embodiment, description of parts common to the above embodiment is omitted, and only characteristic parts in the third embodiment are described.

  In the centrifugal compressor 40 according to the third embodiment, the blade 3 has both the convex portion 14 of the first embodiment and the convex portion 18 of the second embodiment. Thereby, in 3rd Embodiment, there can exist the effect of the said 1st Embodiment and 2nd Embodiment.

  As described above, in the first to third embodiments, the width of the clearance CL and the height H of the blade 3 are changed by changing the shape of the outlet of the impeller 1 and increasing the height H of the blade 3 at the intermediate portion. (Δb / H) becomes relatively small. As a result, the ratio of the flow path area occupied by the clearance flow CLF and the flow path area occupied by the main flow is reduced, and the occurrence of pressure loss is reduced, so that a reduction in the efficiency of the centrifugal compressor can be prevented.

It is a sectional side view of the impeller of the centrifugal compressor of 1st Embodiment of this invention. It is an enlarged view of FIG. It is a figure which shows the speed triangle regarding the conventional impeller. It is a figure which shows the speed triangle regarding the impeller of 1st Embodiment. It is a sectional side view of the impeller of the centrifugal compressor of 2nd Embodiment of this invention. It is a sectional side view of the impeller of the centrifugal compressor of 3rd Embodiment of this invention. It is a sectional side view of the impeller of the conventional centrifugal compressor. FIG. 8 is a diagram corresponding to the AA arrow in FIG. 7 and modeled when there is ideally no clearance flow. It is a figure which shows the blade | wing flow velocity distribution on the BB line of FIG. It is the figure modeled when the clearance flow exists corresponding to the AA arrow view of FIG. It is a figure which shows the blade | wing flow velocity distribution on the CC line of FIG. It is a figure which shows the ratio of the area which a clearance flow occupies when a blade height is high, and the area which a mainstream occupies. It is a figure which shows the ratio of the area which a clearance flow occupies when a blade height is low, and the area which a mainstream occupies.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Impeller 2 Casing 3 Blade | wing 3a Pressure surface 3b Negative pressure surface 4 Hub 5 Front edge part 6 Rear edge part 7 Tip part 10 Centrifugal compressor 11 Shroud surface 12 Shroud line 13 Shroud line 14 Convex part 15 Hubline 16 Base end part 17 Hubline 18 Convex 20 Centrifugal compressor 30 Centrifugal compressor 40 Centrifugal compressor CL Clearance CLF Clearance flow △ b Clearance width H Blade height TA1 Tangent TA2 Tangent P point Q point U Impeller rotational speed W Flow relative velocity C Flow Absolute speed of

Claims (5)

The height of the impeller blade is formed so as to gradually decrease from the front edge side to the rear edge side of the blade,
The absolute value of the change rate of the blade height is configured to be relatively large in the vicinity of the trailing edge of the blade. A shroud line of a shroud surface facing a casing accommodating the impeller at a tip portion of the impeller blades is formed on the shroud line from the hub surface on the trailing edge of the blade toward the inside of the blades from the point of exit width. It is formed so as to be convex in the direction of increasing the height of the blade on the trailing edge side of the blade from the intersection of the virtual tangent and the shroud line rather than the drawn virtual tangent. And centrifugal compressor. A hub line, which is a boundary line with a hub to which the blade is attached, at a proximal end portion of the impeller blade, is more than the virtual radius line drawn in the radial direction of the impeller from the intersection of the rear edge of the blade and the hub line. A centrifugal compressor characterized by being formed to be concave in the direction of increasing the height of the blade. The centrifugal compressor according to claim 2,
A hub line, which is a boundary line with a hub to which the blade is attached, at a base end portion of the blade is more than a virtual radius line drawn in the radial direction of the impeller from an intersection of the trailing edge of the blade and the hub line. A centrifugal compressor characterized by being formed to be concave in the direction of increasing the height. The impeller wing height is formed so that it gradually decreases from the leading edge to the trailing edge,
The centrifugal compressor is characterized in that the change rate of the height of the blade has at least one inflection point.

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