JP2021080870A - Centrifugal fluid machine - Google Patents

Abstract

To reduce, in a diffuser of a centrifugal fluid machine, a pressure loss caused by a leak flow, which is generated in a gap formed on an end face of a diffuser vane whose formation is difficult to avoid due to restrictions on manufacture.SOLUTION: A centrifugal fluid machine includes a diffuser part 103, and a flow passage of the diffuser part includes a side wall 105A on a shroud side, a side wall 105B on a hub side, and a plurality of vane members. The vane member has a first vane member 104A projecting from the side wall on the shroud side and a second vane member 104B projecting from the side wall on the hub side, and the first and second vane members are arranged opposite to each other. In the first vane member and the second vane member opposite to the first vane member, a gap c between the opposed surfaces of the first vane member and the second vane member is a combination of heights near the side wall on the hub side or near the side wall on the shroud side.SELECTED DRAWING: Figure 1

Description

The present invention relates to a centrifugal fluid machine, and more particularly to the structure of a diffuser portion of a centrifugal fluid machine.

A conventional diffuser provided in a centrifugal fluid machine is shown in FIG. The diffuser 103 mounted on the centrifugal fluid machine is a deceleration flow path for converting the dynamic pressure of the fluid delivered from the rotating centrifugal impeller 102 fastened to the rotating shaft 101 into static pressure, and is boosted. A plurality of blade members 104 for decelerating and rectifying the fluid project from the diffuser side wall 105A on the shroud side at intervals on the outer diameter side of the centrifugal impeller 102 with the rotation shaft 101 as the center. Has a structure. The blade member 104 has various shapes, and for example, there is a case where a small chord ratio diffuser described in Non-Patent Document 1 is mounted, in which the blade is less likely to stall on the small flow rate side and the operating range is wide. In the conventional example shown in FIG. 5, the wing member 104 has a structure that protrudes from the side wall 105A on the shroud side. Here, since it is difficult to integrally mold the side wall 105B on the hub side and the wing member 104, they are often manufactured separately. As shown in FIG. 5, the side wall 105B on the hub side and the wing member 104 are manufactured separately. In many cases, a gap c is formed between the 104 and the end face 106.

In FIG. 5, the wing member 104 has a structure like a cantilever protruding from the shroud side side wall 105A, and a gap c is formed between the hub side side wall 105B and the end surface 106 of the wing member 104. However, there are other prior art techniques with different configurations. For example, in Patent Document 1, a first wing member projecting from the shroud side side wall and a second wing member projecting from the hub side side wall are formed in the diffuser flow path, and the end faces of these two wing members are formed. It is configured to face each other in the diffuser flow path. At this time, the gap c is formed in the vicinity of the center of the diffuser flow path where the speed of the fluid is relatively high, not near the side wall of the diffuser portion where the speed of the pressurized fluid is slow, so that the gap c is mixed in the fluid. The aim is to suppress the accumulation of dust and the like in the gap c (see paragraph number 0034 of Patent Document 1). Further, in Patent Document 2, similarly, a first wing member protruding from the shroud side side wall and a second wing member protruding from the hub side side wall are formed in the diffuser flow path, and these two wing members are formed. The end faces are opposed to each other in the diffuser flow path (see FIG. 1 of Patent Document 1). Further, an overlapping portion is formed on each of the end faces of these two blade members, and the overlapping portion has a wedge shape in which the tapered surfaces face each other, and is configured to face each other in the diffuser flow path. By doing so, the blade height of the protruding blade member is reduced to increase the natural frequency, and the vibration frequency of the fluid due to the passage of the blades of the impeller and the resonance of the blade member are prevented and opposed to each other. By forming an overlapping portion on the end faces of the two blade members, it is aimed to reduce the leakage flow from the gap portion (see paragraphs 0023 and 0026 of Patent Document 2). Also in Patent Document 2, in order to maximize the effect of increasing the natural frequency of the wing member, it is necessary to set the gap forming position near the center of the diffuser flow path.

Patent No. 5488717 JP-A-2009-19563

Proceedings of the Japan Society of Mechanical Engineers (Vol. B) Vol. 51, No. 472 PP. 3860-3856 "Effect of side wall secondary flow on stall limit of circular blade row"

By the way, in the case of the diffuser structure described in Patent Document 1 and Patent Document 2, both ends of the first wing member protruding from the shroud side side wall and the second wing member protruding from the hub side side wall face each other. The gap c formed by the surface is formed near the central portion of the diffuser flow path as described above. The velocity of the fluid flowing in the diffuser flow path is faster in the vicinity of the central portion than in the vicinity of the side wall. Here, considering the flow field around the blade member, the faster the fluid velocity, the more the blade works (the blade load increases), so the static between the pressure surface and the negative pressure surface of the blade. The pressure difference increases. Therefore, when the gap is formed near the central portion of the diffuser flow path, there is a problem that the leakage flow from the pressure surface to the negative pressure surface of the blade through the gap is strengthened and the pressure loss is increased. It was.

In view of the above, the present invention provides a diffuser structure for a centrifugal fluid machine, which makes it possible to reduce the pressure loss caused by the leakage flow generated in the gap formed on the end face of the diffuser blade.

A feature of the present invention that achieves the above object is
A centrifugal fluid machine having a diffuser portion, the flow path of the diffuser portion includes a side wall on the shroud side, a side wall on the hub side, and a plurality of blade members, and the blade member is projected from the side wall on the shroud side. It has a first wing member and a second wing member protruding from the side wall on the hub side, and the first and second wing members are arranged to face each other, and the first wing member and the first wing member are arranged to face each other. The second wing member facing the wing has a combination of heights such that the gap between the facing surfaces of the first wing member and the second wing member is near the side wall on the hub side or near the side wall on the shroud side. A centrifugal fluid machine characterized by that.

According to the above configuration, the pressure loss due to the leakage flow of the diffuser is reduced.

It is a figure which shows the diffuser in 1st Example of this invention. It is a figure which looked at the blade member of the diffuser part in 1st Example of this invention from the upstream side in the impeller rotation axis direction. It is a figure which showed the relationship between the diffuser blade tip clearance ratio and the amount of efficiency reduction. It is a schematic diagram of the internal flow in the diffuser flow path between two adjacent blades of a chord ratio diffuser. It is a figure which shows the conventional diffuser provided in a centrifugal fluid machine.

Hereinafter, examples of the multi-stage centrifugal fluid machine according to the present invention will be described with reference to the drawings.

FIG. 1 shows the diffuser in the first embodiment of the present invention. In the figure, the parts with the same reference numerals as those in FIG. 5 represent the same parts. As shown in FIG. 1, the basic configuration of the centrifugal fluid machine in this embodiment is almost the same as that of the conventional centrifugal fluid machine shown in FIG. On the other hand, in this embodiment, the blade member 104 installed in the diffuser 103 and for converting the dynamic pressure of the fluid sent from the centrifugal impeller 102 into static pressure is projected from the side wall 105A on the shroud side. It is composed of a wing member 104A of 1 and a second wing member 104B protruding from the side wall 105B on the hub side, and the end faces 106A and 106B of these two wing members 104A and 104B are opposed to each other in the diffuser flow path to form a gap. It is a feature that the diffuser is formed by forming c and setting the formation position of the gap c in the vicinity of the side wall 105B on the hub side.

The effect of this configuration will be described. FIG. 1 also shows a schematic view 107 of the flow velocity distribution in the diffuser 103 upstream of the diffuser blade members 104A and 104B. As shown in the flow velocity distribution 107, since a velocity boundary layer is formed near the side wall 105A on the shroud side and the side wall 105B on the hub side, the fluid is compared with the mainstream velocity flowing near the center of the flow path. The speed is low. Here, in this embodiment, the formation position of the gap c is brought close to the side wall 105B on the hub side where the speed of the fluid is low. FIG. 2 shows a view of the first blade member 104A as viewed from the upstream side in the impeller rotation axis direction. Although a plurality of the blade members 104A are installed at arbitrary intervals in the circumferential direction, only three of them are shown in this figure. In this embodiment, since the formation position of the gap c is close to the side wall 105B on the hub side where the fluid velocity is low, the velocity of the fluid flowing near the blade surface of the diffuser blade member 104A shown in FIG. 2 is high. The wing loading is reduced, and the static pressure difference between the pressure surface PS and the negative pressure surface SS is reduced. Therefore, it is possible to weaken the leakage flow 108 indicated by the arrow in the figure from the pressure surface PS of the blade to the negative pressure surface SS through the gap c, and the pressure loss due to the leakage flow is reduced.

Although the gap c is formed in FIG. 1 close to the side wall 105B on the hub side, the gap c may be formed close to the side wall 105A on the shroud side. However, the configuration closer to the side wall 105B on the hub side has a greater effect of reducing the pressure loss due to the leakage flow. The reason for this will be explained. Dotted arrows 110A and 110B shown in FIG. 1 indicate a leak flow leaking from the outlet side of the centrifugal impeller 102 into the back cavity 109A on the shroud side, and from the rear cavity 109B on the hub side to the outlet side of the centrifugal impeller 102. The leak flow that leaks is shown respectively. Here, on the side of the side wall 105A on the shroud side, the low velocity fluid near the wall surface is sucked into the back cavity 109A on the shroud side by the leak flow 110A, so that the velocity of the fluid is relatively high. On the other hand, on the side of the side wall 105B on the hub side, the low velocity fluid in the back cavity 109B on the hub side leaks toward the diffuser 103 due to the leak flow 110B, so that the velocity of the fluid is the lowest. Therefore, the velocity of the fluid is lower on the side of the side wall 105B on the hub side than on the side of the side wall 105A on the shroud side, so that the vicinity of the side wall 105B on the hub side is closer to the vicinity of the side wall 105A on the shroud side. The wing loading of the wing member 104 is reduced, and the static pressure difference between the pressure surface PS and the negative pressure surface SS is reduced. Therefore, when the formation position of the gap c is brought closer to the side wall 105B on the hub side, the pressure loss due to the leakage flow in the gap c is reduced.

The smaller the size of the gap c, the more the pressure loss due to the leak flow can be reduced. However, considering the assembly error at the time of assembling the fluid machine, the gap c is unnecessarily. Cannot be made smaller. FIG. 3 shows the gap c =, which is the ratio of the gap c to the diffuser flow path width b shown in FIG. 1, which was examined using three-dimensional computational fluid dynamics, with the gap ratio c / b as the horizontal axis. It is a figure which showed the relationship between the gap ratio and the efficiency reduction amount, which took the amount of efficiency reduction at the time of changing the gap ratio c / b with respect to the case of 0 on the vertical axis. As shown in the figure, the larger the gap ratio c / b is, the larger the efficiency reduction amount becomes. However, when c / b <3%, the efficiency reduction amount is approximately within 1.5%, and the c at the right end in the figure. Even if / b becomes larger than that, the efficiency reduction amount can be reduced to about half of the efficiency reduction amount (approximately 3%) in the vicinity where the efficiency reduction amount does not increase remarkably. Therefore, it is desirable that the gap ratio c / b <3%.

The diffuser structure of the centrifugal fluid machine of the present invention is not limited to the above illustrated example, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

Hereinafter, another embodiment for carrying out the present invention will be described. In this embodiment, the basic configuration is almost the same as that of the first embodiment, but the first wing member 104A projecting from the side wall 105A on the shroud side and the second wing projecting from the side wall 105B on the hub side. It is a feature that the member 104B and the member 104B are each composed of a small chord ratio diffuser. The effect of this configuration will be described. FIG. 4 is a schematic view of the internal flow in the diffuser flow path between two adjacent blades of the small chord ratio diffuser, which was created with reference to the above-mentioned Non-Patent Document 1. In the small chord ratio diffuser, as shown in FIG. 4, the shape of the isostatic pressure line 111 between the adjacent blade members 104 changes, and the angle β formed by the streamline 112 and the isostatic pressure line 111 in the mainstream changes. It becomes an obtuse angle. Therefore, the force 113 due to the static pressure gradient perpendicular to the isostatic pressure line 111 acts so as to face inward in the radial direction with respect to the direction of the streamline 112 in the mainstream. Therefore, the low velocity flow in the velocity boundary layer near the side walls 105A and 105B in the small chord ratio diffuser flows in the direction of being pushed back inward in the radial direction by the force 113 due to the static pressure gradient. Therefore, in the vicinity of the side walls 105A and 105B of the chord ratio diffuser, a secondary flow is generated from the negative pressure surface SS of the blade to the upstream side of the pressure surface PS of the adjacent blade as shown in 114 of FIG. Since this secondary flow acts to suck out the boundary layer of the negative pressure surface SS of the blade, the diffuser blade negative pressure surface SS is unlikely to peel off to the small flow rate side in the small chord ratio diffuser, and the operating range on the small flow rate side. Spreads.

Consider a case where the diffuser blade member 104 is applied with the small chord ratio diffuser in order to secure a wide operating range on the small flow rate side. When the diffuser blade is composed of only one blade member 104 and a gap is provided between the blade end surface 106 of the blade member 104 and the side wall 105B on the hub side as in the conventional diffuser shown in FIG. 5, the blade end surface is provided. The wings will not be present on the hub-side side wall 105B facing the 106, and the preferred secondary flow on the side wall of the small chord ratio diffuser as described in FIG. 4 will not be formed. Therefore, even if the small chord ratio diffuser is applied, the stable operating range on the small flow rate side cannot be sufficiently secured.

On the other hand, as in this embodiment, the first wing member 104A protruding from the side wall 105A on the shroud side and the second wing member 104B protruding from the side wall 105B on the hub side have a small chord ratio, respectively. When the diffuser is used, the small chord ratio diffuser blades protrude from both the side wall 105A on the shroud side and the side wall 105B on the hub side. The next flow is maintained, and a wide stable operating range can be secured on the small flow rate side. Therefore, it is possible to reduce the pressure loss by weakening the leakage flow from the pressure surface PS of the blade to the negative pressure surface SS through the gap c, and to maintain a wide operating range on the small flow rate side.

The diffuser structure of the centrifugal fluid machine of the present invention is not limited to the above illustrated example, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

101 ... Rotating shaft, 102 ... Centrifugal impeller, 103 ... Diffuser, 104 ... Diffuser wing member, 104A ... First wing member protruding from the side wall on the shroud side, 104B ... First wing member protruding from the side wall on the hub side 2 wing members, 105A ... shroud side side wall, 105B ... hub side side wall, 106A ... end face of first wing member protruding from shroud side side wall, 106B ... second side wall protruding from hub side side wall End face of blade member, 107 ... Flow velocity distribution in diffuser, 108 ... Leakage flow from pressure surface to negative pressure surface of blade through gap of end surface of diffuser blade member, 109A ... Shroud side back cavity, 109B ... Hub side back cavity , 110A ... Leakage flow leaking from the outlet side of the centrifugal impeller to the rear cavity on the shroud side, 110B ... Leakage flow leaking from the rear cavity on the hub side to the outlet side of the centrifugal impeller, 111 ... Adjacent to the small chord ratio diffuser 2 Isostatic pressure line in the diffuser flow path between blades, 112 ... Streamline in the mainstream in the diffuser flow path between two adjacent blades of the small chord ratio diffuser, 113 ... Diffuser flow between two adjacent blades of the small chord ratio diffuser Force due to static pressure gradient perpendicular to isostatic pressure line in the road, 114 ... Secondary flow on the sidewall of the chord ratio diffuser,
b ... Diffuser flow path width, c ... Gap formed near the end face of the diffuser blade member, PS ... Pressure surface of the diffuser blade member, SS ... Negative pressure surface of the diffuser blade member, β ... Adjacent two blades of the diffuser with a small chord ratio The angle between the streamline in the mainstream and the isostatic pressure line in the diffuser flow path between them,

Claims (3)

It is a centrifugal fluid machine equipped with a diffuser part.
The flow path of the diffuser portion includes a side wall on the shroud side, a side wall on the hub side, and a plurality of blade members.
The wing member
The first wing member protruding from the side wall on the shroud side,
It has a second wing member protruding from the side wall on the hub side, and the first and second wing members are arranged to face each other.
In the second wing member facing the first wing member and the first wing member, the gap between the facing surfaces of the first wing member and the second wing member is near the side wall on the hub side or the side wall on the shroud side. A centrifugal fluid machine characterized by a combination of heights that are close to each other. The centrifugal fluid machine according to claim 1, wherein the ratio of the gap to the width of the diffuser flow path is less than 3%. The centrifugal hydraulic machine according to claim 1 or 2, wherein the first wing member and the second wing member are each composed of a chord ratio diffuser.

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