Bend pipe and fluid machine

Abstract

A bend pipe and a fluid machine comprising: an inlet pipe part that has a linear shape; a bend pipe part that has a curved shape and is connected to the downstream end of the inlet pipe part; and an outlet pipe part that has a linear shape and is connected to the downstream end of the bend pipe part, wherein the bend pipe part has a first center-of-gravity line which is curved inward in the bending direction, a second center-of-gravity line curved outward in the bending direction, and an inflection point provided at an intersection of the first center-of-gravity line and the second center-of-gravity line.

Description

Bend Pipe and Fluid Machinery

[0001] The present disclosure relates to a bend pipe and a fluid machinery.

[0002] A centrifugal compressor as a fluid machinery is a compressor that compresses a fluid by using centrifugal force with a rotating impeller. The centrifugal compressor has a suction flow path connected to the inlet side and a discharge flow path connected to the outlet side. On the layout of the equipment, a bend pipe for changing the direction of fluid flow in the suction flow path may be applied.

[0003] The bend pipe is a pipe bent approximately 90 degrees, with a straight inlet pipe portion connected to one end in the longitudinal direction and an outlet pipe portion connected to the other end. When fluid flows into the bend pipe from the inlet pipe portion, flow separation may occur inside the bending direction due to the action of centrifugal force. When flow separation occurs in the fluid, pressure loss occurs and efficiency decreases. As a technique for solving such problems, for example, there is one described in Patent Document 1.

[0004] Japanese Patent No. 6605041

[0005] The bend pipe described in Patent Document 1 is provided with an inner inclined surface that inclines toward the downstream side on the inner side of the bending direction. Such a bend pipe can suppress flow separation by inclining the shape of the wall surface inward in the bending direction, but a predetermined length is required for the reattachment of the separated flow. Therefore, there is a problem that the length from the bend pipe to the centrifugal compressor becomes long and the equipment becomes large. Also, if a predetermined length cannot be ensured from the bend pipe to the centrifugal compressor on the layout of the equipment, the separated flow will flow into the centrifugal compressor, resulting in a decrease in performance.

[0006] The present disclosure solves the above-described problems, and an object thereof is to provide a bend pipe and a fluid machinery that can suppress flow separation and suppress the enlargement of the equipment.

[0007] To achieve the above objective, the bend pipe of the present disclosure comprises a straight inlet pipe section, a curved bend pipe section connected to the downstream end of the inlet pipe section, and a straight outlet pipe section connected to the downstream end of the bend pipe section, wherein the bend pipe section has a first centroid line that curves inward in the direction of curving, a second centroid line that curves outward in the direction of curving, and an inflection point provided at the intersection of the first centroid line and the second centroid line.

[0008] Furthermore, the fluid machine of this disclosure comprises the bend pipe and an impeller positioned downstream of the bend pipe.

[0009] The bend pipe and fluid machinery of this disclosure can suppress flow separation and also suppress the increase in size of the equipment.

[0010] Figure 1 is a front view of the bent pipe of the first embodiment. Figure 2 is a schematic diagram showing the swirling velocity distribution and axial velocity distribution in the bent pipe of Conventional Example 1. Figure 3 is a schematic diagram showing the swirling velocity distribution and axial velocity distribution in the bent pipe of Conventional Example 2. Figure 4 is a schematic diagram showing the swirling velocity distribution and axial velocity distribution in the bent pipe of the first embodiment. Figure 5 is a graph showing the compressor efficiency as a function of volumetric flow rate. Figure 6 is a graph showing the temperature rise coefficient as a function of volumetric flow rate. Figure 7 is a graph showing the compressor pressure ratio as a function of volumetric flow rate. Figure 8 is a front view of the bent pipe of the second embodiment. Figure 9 is a cross-sectional view of the bent pipe. Figure 10 is a front view of the bent pipe of the third embodiment. Figure 11 is a front view of the bent pipe of the fourth embodiment. Figure 12 is a schematic diagram of a centrifugal compressor to which the bent pipe is applied.

[0011] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure, and where there are multiple embodiments, they may be combinations of these embodiments. Furthermore, the components in the embodiments include those readily conceivable by those skilled in the art, those that are substantially identical, and those that are equivalent.

[0012] [First Embodiment] <Bend Pipe> Figure 1 is a front view of the bend pipe according to the first embodiment. In the following description, dimensions such as the radius of curvature and radius refer to dimensions relative to the inner diameter shape of the bend pipe. The bend pipe is a pipe having a predetermined thickness, and its outer diameter shape is set according to the inner diameter shape.

[0013] As shown in Figure 1, the bend pipe 10 is a pipe for supplying fluid to a fluid machine. However, the bend pipe 10 may also be used as a pipe for discharging fluid from the fluid machine. The fluid flowing inside the bend pipe 10 is either a fluid at atmospheric pressure or an energy medium used for energy conversion by the fluid machine.

[0014] The bent pipe 10 comprises an inlet pipe section 11, a bent pipe section 12, and an outlet pipe section 13. The inlet pipe section 11 has a straight shape and is arranged along the center of gravity line G11. The outlet pipe section 13 has a straight shape and is arranged along the center of gravity line G31. The center of gravity line G1 of the inlet pipe section 11 and the center of gravity line G31 of the outlet pipe section 13 are perpendicular. The bent pipe section 12 has a curved shape and is arranged along the first center of gravity line 21 and the second center of gravity line 22. The impeller 14 is located downstream of the outlet pipe section 13 of the bent pipe 10. The fluid machine 15 is composed of the bent pipe 10 and the impeller 14.

[0015] The downstream end of the inlet pipe section 11 is connected to the upstream end of the bend pipe section 12, and the downstream end of the bend pipe section 12 is connected to the upstream end of the outlet pipe section 13. The flow direction of the fluid supplied from the inlet pipe section 11 to the bend pipe section 12 is changed by 90 degrees before being discharged to the outlet pipe section 13. However, the bend pipe 10 is not limited to a configuration in which the center of gravity line G11 of the inlet pipe section 11 and the center of gravity line G31 of the outlet pipe section 13 intersect at a 90-degree angle; they may intersect at an angle smaller than 90 degrees or at an angle larger than 90 degrees.

[0016] <Bent Pipe Section> The bent pipe section 12 has a first centroid line G21, a second centroid line G22, and an inflection point P. The first centroid line G21 curves inward in the direction of bending of the bent pipe section 12. The first centroid line G21 is a first radius of curvature R21 with a first center O21. The second centroid line G22 curves outward in the direction of bending of the bent pipe section 12. The second centroid line G22 is a second radius of curvature R22 with a second center O22. The first centroid line G21 and the second centroid line G22 intersect at the inflection point P. The inflection point P is the intersection of the first centroid line G21 and the second centroid line D22.

[0017] The first radius of curvature R21 of the first centroid line G21 and the second radius of curvature R22 of the second centroid line G22 are the same. However, the configuration is not limited to the first radius of curvature R21 of the first centroid line G21 and the second radius of curvature R22 of the second centroid line G22 being the same. Preferably, the second radius of curvature R22 of the second centroid line G22 is less than or equal to the first radius of curvature R21 of the first centroid line G21. For example, preferably, the second radius of curvature R22 of the second centroid line G22 is in the range of 1.0 to 0.9 times the first radius of curvature R21 of the first centroid line G21 (1.0R21 ≥ R22 > 0.9R21).

[0018] The first center of gravity line G21 of the bent pipe section 12 connects to the center of gravity line G11 of the inlet pipe section 11 on the upstream side and intersects with the second center of gravity line G22 at the inflection point P on the downstream side. On the other hand, the second center of gravity line G22 of the bent pipe section 12 intersects with the first center of gravity line G21 at the inflection point P on the upstream side and connects with the center of gravity line G31 of the outlet pipe section 13 on the downstream side. Here, the center of gravity line G31 of the outlet pipe section 13 is the rotation center of the impeller 14.

[0019] Furthermore, in the bent pipe section 12, the inflection point P and the centroid line G31 of the outlet pipe section 13 are offset in a direction along the centroid line G11 of the inlet pipe section 11. That is, the first centroid line G21 curves inward from the centroid line G11 of the inlet pipe section 11 in the direction of bending of the bent pipe section 12 to the inflection point P. The second centroid line G22 curves outward from the inflection point P in the direction of bending of the bent pipe section 12 to the centroid line G31 of the outlet pipe section 13. Therefore, a deviation δ is set between the inflection point P and the centroid line G32 in the direction along the centroid line G11. Preferably, the deviation δ between the inflection point P and the centroid line G31 of the outlet pipe section 13 is in the range of 5% to 10% of the inner diameter D of the outlet pipe section 13 (0.05D ≤ δ ≤ 0.1D).

[0020] The deviation δ between the inflection point P and the centroid line G32 is equal to the deviation δ between the second centroid line G22 and the centroid line G31. Since the second centroid line G22 curves from the inflection point P to the centroid line G31, the deviation δ between the second centroid line G22 and the centroid line G31 decreases from the inflection point P towards the upstream end of the outlet pipe section 13.

[0021] The inner diameter shape (outer shape) of the bent pipe section 12 is determined by the first centroid line G21, the second centroid line G22, and the inflection point P. The bent pipe section 12 has a circular cross-sectional shape, and the cross-sectional area of ​​the internal flow path is the same along the flow direction. Here, the cross-sectional area of ​​the flow path is the cross-sectional area of ​​the flow path perpendicular to the first centroid line G21 and the second centroid line G2. Therefore, on the upstream side of the bent pipe section 12, a first inner curved surface 21a forming an arc shape with a radius of curvature R21a is provided on the inside in the direction of curvature, and a first outer curved surface 21b forming an arc shape with a radius of curvature R21b is provided on the outside in the direction of curvature. The radii of curvature R21a and R21b are set with respect to the first center O21. Furthermore, the bent pipe section 12 is provided with a second inner curved surface 22a on the downstream side, forming an arc shape with a radius of curvature R22a on the inside in the direction of curvature, and a second outer curved surface 22b on the outside in the direction of curvature, forming an arc shape with a radius of curvature R22b. The radii of curvature R22a and R22b are set to the second center O22. The inner and outer arc shapes of the bent pipe section 12 are connected to the outlet pipe section 13 without any steps by the arc shapes.

[0022] In the above description, the bent pipe section 12 was described as being composed of a first centroid line G21, a second centroid line G22, and an inflection point P, but the configuration is not limited to this. For example, the bent pipe section 12 may have a straight centroid line between the centroid line G11 of the inlet pipe section 11 and the curved first centroid line G21. Also, the bent pipe section 12 may have a straight centroid line between the second centroid line G22 and the centroid line G31 of the outlet pipe section 13.

[0023] <Operation of the bent pipe> The fluid flows from the inlet pipe section 11 along the direction of the center of gravity line G11 and into the bent pipe section 12. The fluid that flows into the bent pipe section 12 flows along the directions of the first center of gravity line G21 and the second center of gravity line G22, is discharged into the outlet pipe section 13, and reaches the impeller 14.

[0024] When a fluid flows along the first inner curved surface 21a in the bent pipe section 12, flow separation occurs. However, the bent pipe section 12 is provided with a second inner curved surface 22a that curves outward, following the first inner curved surface 21a that curves inward. Therefore, when the fluid flows from the first inner curved surface 21a to the second inner curved surface 22a, the direction of the flow reverses, preventing the development of the separation region A, which is the low-pressure region of the fluid, and thus suppressing flow separation.

[0025] Furthermore, the bent pipe section 12 has a deviation δ in the direction along the center of gravity G11 between the inflection point P and the center of gravity G31. As a result, when the fluid flows from the first inner curved surface 21a to the second inner curved surface 22a, a step is formed in the flow, and the development of the separation region A downstream is suppressed.

[0026] As a result, the flow at the inlet of the impeller 14 is straightened by the bent pipe section 12, a uniform fluid velocity distribution can be obtained, and the fluid machine 15 can achieve high efficiency and pressure ratio.

[0027] <Velocity Distribution of Fluid in a Bend Pipe> Figure 2 is a schematic diagram showing the swirling velocity distribution and axial velocity distribution in a bend pipe of Conventional Example 1, Figure 3 is a schematic diagram showing the swirling velocity distribution and axial velocity distribution in a bend pipe of Conventional Example 2, and Figure 4 is a schematic diagram showing the swirling velocity distribution and axial velocity distribution in a bend pipe of the first embodiment. Figures 2, 3, and 4 show the fluid velocity distribution when the inside of the bend pipe is viewed from the upstream side with the impeller in the direction of the center of gravity of the outlet pipe.

[0028] Conventional Example 1 is a bent pipe having a bent section curved at 90 degrees. In Conventional Example 1, as shown in Figure 2, the fluid swirls at high speed in a clockwise direction on the inside of the curve, and the axial flow of the fluid is non-uniform in the circumferential direction. Conventional Example 2 is a bent pipe having a bent section curved at 90 degrees and an inner inclined surface on the inside of the curve (Patent Document 1). In Conventional Example 2, as shown in Figure 3, the fluid swirls at high speed in a clockwise direction on the inside of the curve, and the axial flow of the fluid is non-uniform in the circumferential direction.

[0029] The first embodiment is a bent pipe 10 having a bent pipe section curved at 90 degrees, with a first centroid line G21, a second centroid line G22, and an inflection point P set thereon. In the first embodiment, as shown in Figure 4, the fluid swirls clockwise at a low speed on the inside of the curve, and the axial flow of the fluid is uniform in the circumferential direction. That is, in the bent pipe 10 of the first embodiment, the flow at the inlet of the impeller 14 is straightened by the bent pipe section 12, and the fluid has a uniform velocity distribution in the circumferential direction.

[0030] <Performance Characteristics> Figure 5 is a graph showing the compressor efficiency as a function of volumetric flow rate, Figure 6 is a graph showing the temperature rise coefficient as a function of volumetric flow rate, and Figure 7 is a graph showing the compressor pressure ratio as a function of volumetric flow rate. In Figures 5, 6, and 7, Conventional Example 1 is represented by a short dotted line, Conventional Example 2 by a long dotted line, and the first embodiment by a solid line.

[0031] As shown in Figure 5, in Conventional Example 1 (short dotted line), Conventional Example 2 (long dotted line), and the First Embodiment (solid line), the compressor efficiency increases with increasing volumetric flow rate and decreases at the design point. Also, as shown in Figure 6, in Conventional Example 1 (short dotted line), Conventional Example 2 (long dotted line), and the First Embodiment (solid line), the temperature rise coefficient decreases with increasing volumetric flow rate and drops sharply at the design point. As shown in Figure 7, in Conventional Example 1 (short dotted line), Conventional Example 2 (long dotted line), and the First Embodiment (solid line), the compressor pressure ratio decreases with increasing volumetric flow rate and drops sharply at the design point.

[0032] As shown in Figures 5, 6, and 7, the compressor efficiency, temperature rise coefficient, and compressor pressure ratio are highest in the first embodiment (solid line) at the design point. In other words, the fluid machine 15 having the bend pipe 10 of the first embodiment (solid line) achieves higher efficiency and pressure ratio compared to the fluid machines having the bend pipes of Conventional Example 1 (short dotted line) and Conventional Example 2 (long dotted line).

[0033] [Second Embodiment] Figure 8 is a front view of the bend pipe according to the second embodiment, and Figure 9 is a cross-sectional view of the bend pipe. Note that components having the same function as those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions are omitted.

[0034] As shown in Figures 8 and 9, the bent pipe 10A comprises an inlet pipe section 11, a bent pipe section 12A, and an outlet pipe section 13. The bent pipe section 12A has a curved shape and has a first centroid line G21, a second centroid line G22, and an inflection point P. The first centroid line G21 curves inward in the bending direction of the bent pipe section 12A and has a first radius of curvature R21 with a first center O21. The second centroid line G22 curves outward in the bending direction of the bent pipe section 12A and has a second radius of curvature R22 with a second center O22. The first centroid line G21 and the second centroid line G22 intersect at the inflection point P. In addition, the bent pipe section 12A is offset in a direction along the centroid line G11 of the inlet pipe section 11 between the inflection point P and the centroid line G31 of the outlet pipe section 13. A deviation δ is set between the inflection point P and the centroid line G32 in the direction along the centroid line G11.

[0035] The bent pipe section 12A has a first inner curved surface 21a on the upstream side, forming an arc shape with a radius of curvature R21a on the inside in the direction of curvature, and a second inner curved surface 22a on the downstream side, forming an arc shape with a radius of curvature R22a on the inside in the direction of curvature. The first inner curved surface 21a is provided along the first centroid line G21, and the second inner curved surface 22a is provided along the second centroid line G22. The first inner curved surface 21a curves toward the side approaching the first centroid line G21, and the second inner curved surface 22a curves toward the side moving away from the second centroid line G22, and the first inner curved surface 21a and the second inner curved surface 22a are smoothly continuous without any steps.

[0036] The bent pipe section 12A is provided with a bulge 31 that bulges out toward the upstream side of the inlet pipe section 11 on the second inner curved surface 22a. The bulge 31 is preferably located downstream of the first inner curved surface 21a, but a part of it may be located toward the first inner curved surface 21a. The bulge 31 is provided along the circumferential direction. The bulge 31 is provided at the downstream end of the bent pipe section 12A, in the lower half in the circumferential direction, over a range of 180 degrees. However, the position of the bulge 31 is not limited to a range of 180 degrees in the lower half of the bent pipe section 12A, but may be in a range of 180 degrees or less.

[0037] The bulging portion 31 has a curved surface 31a with respect to the fluid flow direction. The curved surface 31a has a curved shape that protrudes inward in the bending direction so as to be spaced apart from the second inner curved surface 22a. The bulging portion 31 bulges upstream of the inlet pipe portion 11 from the outer surface of the downstream end of the bend pipe portion 12 by a length of 2 to 4 times the radius of curvature R21a of the first inner curved surface 21a.

[0038] When the fluid flowing through the bent pipe 10A flows along the first inner curved surface 21a in the bent pipe section 12A, flow separation occurs. However, the bent pipe section 12A has a first inner curved surface 21a that curves inward followed by a second inner curved surface 22a that curves outward, and a bulge 31 is provided on the second inner curved surface 22a. Therefore, when the fluid flows from the first inner curved surface 21a along the second inner curved surface 22a, the separated flow enters and is contained in the bulge 31. As a result, the fluid separation region A does not develop, and flow separation is suppressed at the location of the bulge 31.

[0039] [Third Embodiment] Figure 10 is a front view showing a bend pipe of the third embodiment. Components having the same function as those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions are omitted.

[0040] As shown in Figure 10, the bent pipe 10B comprises an inlet pipe section 11, a bent pipe section 12B, and an outlet pipe section 13. The bent pipe section 12B has a curved shape and has a first centroid line G21, a second centroid line G22, and an inflection point P. The first centroid line G21 curves inward in the bending direction of the bent pipe section 12B and has a first radius of curvature R21 with a first center O21. The second centroid line G22 curves outward in the bending direction of the bent pipe section 12B and has a second radius of curvature R22 with a second center O22. The first centroid line G21 and the second centroid line G22 intersect at the inflection point P. In addition, the bent pipe section 12B is offset in a direction along the centroid line G11 of the inlet pipe section 11 between the inflection point P and the centroid line G31 of the outlet pipe section 13. A deviation δ is set between the inflection point P and the centroid line G32 in the direction along the centroid line G11.

[0041] The bent pipe section 12B has a first inner curved surface 21a on the upstream side, forming an arc shape with a radius of curvature R21a on the inside in the direction of curvature, and a second inner curved surface 22B on the downstream side, forming an arc shape with a radius of curvature R22B on the inside in the direction of curvature. The first inner curved surface 21a is provided along the first centroid line G21, and the second inner curved surface 22a is provided along the second centroid line G22. The first inner curved surface 21a curves toward the side approaching the first centroid line G21, and the second inner curved surface 22a curves toward the side moving away from the second centroid line G22, and the first inner curved surface 21B and the second inner curved surface 22B are smoothly continuous without any steps.

[0042] The bent pipe section 12B is provided with a bulge 32 that bulges out toward the upstream side of the inlet pipe section 11 on the second inner curved surface 22a. The bulge 32 is preferably located downstream of the first inner curved surface 21a, but a part of it may be located toward the first inner curved surface 21a. The bulge 32 is preferably provided along the circumferential direction, similar to the bulge 31 in the second embodiment (see Figure 9).

[0043] The bulging portion 32 has an opposing surface 32a against which the fluid flowing along the first inner curved surface 21a collides, and a guiding surface 32b continuous with the first inner curved surface 21a. The bulging portion 32 has a channel shape such that the opposing surface 32a and the guiding surface 32b face each other with a predetermined length therebetween. The opposing surface 32a and the guiding surface 32b are parallel, but the channel shape may be a tapered shape. The angle of the opposing surface 32a with respect to the center-of-gravity line G31 of the outlet pipe portion 13 is preferably 45 degrees or more and 135 degrees or less, but is not limited to this angle range.

[0044] When the fluid flowing through the bend pipe 10B flows along the first inner curved surface 21B in the bend pipe portion 12B, flow separation occurs. However, the bend pipe portion 12B is provided with a second inner curved surface 22a that bends outward following the first inner curved surface 21a that bends inward, and the bulging portion 32 is provided on the second inner curved surface 22a. Therefore, when the fluid flows along the first inner curved surface 21a to the second inner curved surface 22a, the separated flow enters and is accommodated in the bulging portion 32. That is, the separated flow collides with the opposing surface 32a of the bulging portion 32 and becomes difficult to exit from the bulging portion 32. Then, the separation region A of the fluid does not develop, and flow separation is suppressed at the position of the bulging portion 31.

[0045] [Fourth Embodiment] FIG. 11 is a front view showing a bend pipe of the fourth embodiment, and FIG. 12 is a schematic view of a centrifugal compressor to which the bend pipe is applied. Members having the same functions as those of the first embodiment described above are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

[0046] As shown in FIG. 11, the bend pipe 10B includes an inlet pipe portion 11, a bend pipe portion 12B, and an outlet pipe portion 13. The bend pipe portion 12B has a curved shape and has a first center-of-gravity line G21, a second center-of-gravity line G22, and an inflection point P. The first center-of-gravity line G21 and the second center-of-gravity line G22 intersect at the inflection point P. Also, in the bend pipe portion 12B, the inflection point P and the center-of-gravity line G31 of the outlet pipe portion 13 are displaced in the direction along the center-of-gravity line G11 of the inlet pipe portion 11. A deviation δ in the direction along the center-of-gravity line G11 is set between the inflection point P and the center-of-gravity line G32.

[0047] The bend pipe portion 12B is provided with a first inner curved surface 21a having an arc shape with a radius of curvature R21a on the inner side in the bending direction on the upstream side, and a second inner curved surface 22B having an arc shape with a radius of curvature R22B on the inner side in the bending direction on the downstream side. The first inner curved surface 21B and the second inner curved surface 22B are smoothly continuous without a step. The bend pipe portion 12B is provided with a bulging portion 32 that bulges toward the upstream side of the inlet pipe portion 11 on the second inner curved surface 22a. The bulging portion 32 has the same shape as that in the above-described third embodiment. However, the bulging portion 32 may have the shape of the bulging portion 31 or other shapes described in the above-described second embodiment.

[0048] A connecting pipe 33 that is connected to the inlet portion of the fluid machine disposed on the upstream side of the inlet pipe portion 11 is connected to the bulging portion 32. As shown in FIG. 12, the two-stage compressor 50 as a fluid machine has a low-pressure compressor 51 and a high-pressure compressor 52. The low-pressure compressor 51 is connected to a suction passage 61, the low-pressure compressor 51 and the high-pressure compressor 52 are connected by a connecting passage 62, and the high-pressure compressor 52 is connected to a discharge passage 63. The low-pressure compressor 51 compresses the fluid sucked from the suction passage 61 and supplies the low-pressure fluid to the high-pressure compressor 52 through the connecting passage 62. The high-pressure compressor 52 compresses the low-pressure fluid supplied through the connecting passage 62 and discharges it as a high-pressure fluid from the discharge passage 63.

[0049] The bend pipe 10B is applied as the connecting passage 62 for the two-stage compressor 50. The bend pipe portion 12B has the bulging portion 32 and the connecting pipe 33. In the bend pipe portion 12B, the bulging portion 32 is connected to the suction passage 61 through the connecting pipe 33.

[0050] As shown in FIGS. 11 and 12, when the fluid flowing through the bend pipe 10B flows along the first inner curved surface 21B in the bend pipe portion 12B, flow separation occurs, and the fluid enters and is accommodated in the bulging portion 32. The fluid that has entered the bulging portion 32 returns from the bulging portion 32 through the connecting pipe 33 to the inlet portion of the low-pressure compressor 51, that is, the suction passage 61. Since the fluid flowing through the bend pipe portion 12B is a low-pressure fluid and the fluid flowing through the suction passage 61 is at atmospheric pressure, the low-pressure fluid in the bulging portion 32 is returned to the suction passage 61 by the connecting pipe 33 due to the differential pressure. Therefore, the fluid separation region A does not develop, and flow separation is suppressed at the position of the bulging portion 31.

[0051] [Effects of this embodiment] The bend pipe according to the first embodiment comprises a straight inlet pipe section 11, bend pipe sections 12, 12A, and 12B that are curved and connected to the downstream end of the inlet pipe section 11, and an outlet pipe section 13 that is straight and connected to the downstream ends of the bend pipe sections 12, 12A, and 12B. The bend pipe sections 12, 12A, and 12B have a first centroid line G21 that curves inward in the direction of bending, a second centroid line G22 that curves outward in the direction of bending, and an inflection point P provided at the intersection of the first centroid line G21 and the second centroid line G22.

[0052] In the first embodiment of the bent pipe, when the fluid flows along the inner surface in the direction of the bend in the bent pipe section 12, flow separation occurs. However, when the fluid flowing along the inner surface in the direction of the bend in the bent pipe sections 12, 12A, and 12B separates, the direction of the flow reverses from the inside in the direction of the bend to the outside in the direction of the bend, thereby suppressing the development of the fluid separation region A and preventing flow separation. As a result, flow separation can be suppressed at an early stage, and the size of the equipment can be reduced by shortening the length of the downstream side of the bent pipe sections 12, 12A, and 12B.

[0053] The bend pipe according to the second embodiment is the same as the bend pipe according to the first embodiment, further wherein the second radius of curvature R22 of the second centroid G22 is less than or equal to the first radius of curvature R21 of the first centroid G21. This makes it possible to shorten the length corresponding to the second centroid G22 in the bend pipe sections 12, 12A, and 12B.

[0054] The third embodiment of the bend pipe is a bend pipe according to the first or second embodiment, further characterized in that the inflection point P and the centroid line G31 of the outlet pipe section 13 are offset in a direction along the centroid line G11 of the inlet pipe section 11. As a result, when the fluid flows along the inside of the bending direction of the bend pipe sections 12, 12A, and 12B, a step in the flow is formed, which can suppress the downstream development of the separation region A.

[0055] The bend pipe according to the fourth embodiment is the same as the bend pipe according to the third embodiment, and furthermore, the deviation δ between the second centroid line G22 and the centroid line G31 of the outlet pipe section 13 decreases from the inflection point P toward the upstream end of the outlet pipe section 13. This allows fluid to flow smoothly from the bend pipe sections 12, 12A, and 12B to the outlet pipe section 13.

[0056] The bend pipe according to the fifth embodiment is a bend pipe according to the third or fourth embodiment, further wherein the deviation δ between the inflection point P and the centroid line G31 of the outlet pipe section 13 is 5% to 10% of the inner diameter D of the outlet pipe section 13. By limiting the deviation δ to a predetermined range, the occurrence of flow separation can be suppressed.

[0057] The sixth embodiment of the bend pipe is a bend pipe according to any one of the first to fifth embodiments, further comprising a first inner curved surface 21a along the first centroid line G21 and a second inner curved surface 22a along the second centroid line G22 on the inside in the bending direction, and bulging portions 31 and 32 that bulge toward the upstream side of the inlet pipe portion 11 on the second inner curved surface 22a. As a result, when the fluid flows from the first inner curved surface 21a along the second inner curved surface 22a, the separated flow enters the bulging portions 31 and 32, suppressing the development of the fluid separation region A and preventing flow separation in the vicinity of the bulging portions 31 and 32.

[0058] The bend pipe according to the seventh embodiment is the same as the bend pipe according to the sixth embodiment, and further, the bulge portion 31 has a curved surface 31a. This allows the separated flow to be smoothly guided to the bulge portion 31.

[0059] The bend pipe according to the eighth embodiment is a bend pipe according to the seventh embodiment, further comprising a bulge 31 that bulges out from the outer surface of the downstream end of the bend pipe sections 12, 12A, and 12B to the upstream side of the inlet pipe section 11 by a radius of at least twice the radius of the first inner curved surface 21a. By providing a bulge 31 of a predetermined size, flow separation can be effectively suppressed.

[0060] The bend pipe according to the ninth embodiment is a bend pipe according to the sixth embodiment, further having an opposing surface 32a upon which the fluid flowing along the first inner curved surface 21a collides, and the angle θ of the opposing surface 32a with respect to the centroid line G31 of the outlet pipe portion 13 is 45 degrees or more and 135 degrees or less. As a result, the separated flow collides with the opposing surface 32a, thereby suppressing flow separation in the vicinity of the bulges 31 and 32.

[0061] The bend pipe according to the tenth embodiment is a bend pipe according to any one of the sixth to ninth embodiments, and furthermore, the bulging sections 31 and 32 are connected to a connecting pipe 33 which is connected to the inlet of a low-pressure compressor (fluid machine) 51 located upstream of the inlet pipe section 11. This makes it possible to suppress flow separation in the vicinity of the bulging sections 31 and 32 by discharging the separated flow to the outside of the bulging sections 31 and 32.

[0062] The fluid machine according to the eleventh embodiment comprises bend pipes 10, 10A, and 10B, and an impeller 14 positioned downstream of the bend pipes 10, 10A, and 10B. This allows for early suppression of flow separation and reduces the size of the equipment by shortening the length of the downstream sections of the bend pipes 12, 12A, and 12B.

[0063] In the embodiments described above, a centrifugal compressor was used as the fluid machine, but the invention is not limited to a centrifugal compressor.

[0064] 10, 10A, 10B Bend pipe 11 Inlet pipe part 12, 12A, 12B Bend pipe part 13 Outlet pipe part 14 Impeller 15 Fluid machine 21a First inner curved surface 21b First outer curved surface 22a Second inner curved surface 22b Second outer curved surface 31, 32 Swelling part 31a Curved surface 32a Opposing surface 32b Guide surface 33 Connecting pipe A Separation area G11 Center of gravity G21 First center of gravity G22 Second center of gravity G31 Center of gravity R21 First radius of curvature R22 Second radius of curvature O21 First center O22 Second center P Point of inflection

Claims

1. A bent pipe comprising: an inlet pipe section having a straight shape; a bent pipe section having a curved shape and connected to the downstream end of the inlet pipe section; and an outlet pipe section having a straight shape and connected to the downstream end of the bent pipe section, wherein the bent pipe section has a first centroid line that curves inward in the direction of curving; a second centroid line that curves outward in the direction of curving; and an inflection point provided at the intersection of the first centroid line and the second centroid line.

2. The bend pipe according to claim 1, wherein the second radius of curvature of the second centroid is less than or equal to the first radius of curvature of the first centroid.

3. The bend pipe according to claim 1, wherein the inflection point and the center of gravity of the outlet pipe are offset in a direction along the center of gravity of the inlet pipe.

4. The deviation between the second centroid line and the centroid line of the outlet pipe section decreases from the inflection point toward the upstream end of the outlet pipe section, as described in claim 3.

5. The bend pipe according to claim 3, wherein the deviation between the inflection point and the centroid line of the outlet pipe is 5% to 10% of the inner diameter of the outlet pipe.

6. The bent pipe section is provided with a first inner curved surface along the first center of gravity and a second inner curved surface along the second center of gravity on the inside in the direction of curvature, and the second inner curved surface is provided with a bulge that bulges toward the upstream side of the inlet pipe section, as described in claim 1.

7. The bend pipe according to claim 6, wherein the bulging portion has a curved surface.

8. The bend pipe according to claim 7, wherein the bulging portion bulges out from the outer surface of the downstream end of the bend pipe portion toward the upstream side of the inlet pipe portion by a radius of at least twice the radius of the first inner curved surface.

9. The bend pipe according to claim 6, wherein the bulging portion has an opposing surface upon which a fluid flowing along the first inner curved surface collides, and the angle of the opposing surface with respect to the center of gravity of the outlet pipe portion is 45 degrees or more and 135 degrees or less.

10. The bend pipe according to claim 7, wherein the bulging portion is connected to a connecting pipe which is connected to the inlet portion of a fluid machine located upstream of the inlet pipe portion.

11. A fluid machine comprising: a bend pipe according to claim 1; and an impeller disposed downstream of the bend pipe.

Images