JPH0615879B2 - Diff user of centrifugal fluid machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a diffuser of a centrifugal fluid machine such as a centrifugal compressor or a blower, and more particularly to a diffuser of a model that requires a wide operating range and high efficiency.

[Conventional technology]

Centrifugal compressors or blowers generally generate a radial airflow by rotation of the impeller 1. Since the air flow that flows out from the impeller has a large velocity energy, a diffuser with stationary blades is installed on the outer peripheral part of the impeller, which is the downstream side of the impeller, and the velocity energy of the fluid discharged from the impeller is compressed. It is designed to be converted into energy. A plurality of stationary blades constituting the diffuser are radially provided on the outer peripheral portion of the impeller, and a diffuser flow path is formed between the blades of these stationary blades.

In such a compressor or blower, there is a problem that a separation flow region occurs on the negative pressure surface of the stationary blade under a low flow rate condition, and a surge phenomenon occurs in which a sufficient pressure increase cannot be obtained. As a diffuser for a centrifugal compressor or a blower which solves this problem and is less likely to cause a surging phenomenon even in a small flow rate state, as disclosed in Japanese Patent Laid-Open No. 57-159998, it is rotatable at the inlet of the diffuser. There is known an invention in which an auxiliary blade is provided to control a fluid flowing through a diffuser. Further, as disclosed in JP-A-53-119411, the diffuser with vanes is composed of a double circular blade row, and the blade length of the inner circular blade row is 0.9
Proposals to reduce the number of times to less than double are known.

[Problems to be Solved by the Invention]

However, in JP-A-57-159998, the diffuser flow path formed between the stationary blades is rapidly expanded immediately downstream of the auxiliary blades, so that not only pressure loss occurs but also downstream of the auxiliary blades. A vortex flow is generated on the side, which promotes the development of a boundary layer generated on the flow passage surface of the diffuser casing, and there is a problem that the performance of the diffuser is deteriorated.

Further, in the case of Japanese Patent Laid-Open No. 53-119411, since the chord length of the inner circular blade row is short, strength problems occur when the number of blades is large or the blade height is large.

The object of the present invention is to control the development of the boundary layer generated in the diffuser flow passage and to allow the flow along the stationary blade to the leading edge of the stationary blade even at a low flow rate, so that the operating range is wide. Another object is to obtain a diffuser for a centrifugal fluid machine that has high performance.

[Means for Solving the Problems]

In order to achieve the above object, the present invention is a centrifugal fluid in which a plurality of stationary blades are arranged on the outer circumference of an impeller, and the kinetic energy of the fluid discharged from the impeller is converted into pressure energy by the action of the stationary blades. In a diffuser of a machine, a portion of an inlet intermediate blade that is provided to extend upstream of the leading edge of the stationary blade and has a chord length and height smaller than that of the stationary blade, and a downstream side of the portion of the inlet intermediate blade. An intermediate blade having a portion of the straightening vane that is arranged at a lower height than the inlet intermediate blade, and further has a portion of the outlet intermediate blade that is higher than the height of the straightening blade downstream of the portion of the straightening blade. It is characterized in that it is provided between the plurality of stationary blades.

[Action]

According to the present invention, with the above configuration, the following effects can be obtained.

(1) At the portion of the inlet intermediate blade that is provided between the stationary blades and extends upstream of the leading edge of the stationary blades, the flow from the impeller is guided along the stationary blades. The flow along the stationary blade can be given to the leading edge of the stationary blade even at a low flow rate.

(2) Giving a flow along the stationary blade to the leading edge of the stationary blade,
By developing the boundary layer generated on the surface of the stationary blade from the leading edge of the stationary blade, the thickness of this boundary layer can be minimized and the pressure recovery performance of the diffuser can be improved.

(3) When only the inlet intermediate blade is provided, a vortex is generated from the downstream end and the root end of this inlet intermediate blade,
In the present invention, the straightening vane, which is lower in height than the inlet intermediate blade and is continuous with the inlet intermediate blade, is provided on the downstream side of the inlet intermediate blade. Therefore, generation of vortex flow from the root end of the inlet intermediate blade can be prevented. . Therefore, the generation of this vortex does not promote the development of the boundary layer on the surface of the diffuser casing flow path.

(4) The portion of the flow straightening vanes provided between the stationary blades prevents the secondary flow from the suction surface to the pressure surface of the stationary blade, so that the loss due to this secondary flow can be reduced.

(5) Since the intermediate blade is composed of the portion of the inlet intermediate blade having a large height and the portion of the flow straightening blade having a height lower than that of the inlet intermediate blade, it is possible to obtain a sufficient flow straightening action for the intermediate inlet blade. The height of the rectifier vanes can be increased and the height of the rectifying vanes can be minimized, so that the increase in friction loss caused by the provision of the intermediate vanes can be minimized. be able to.

(6) Since the height of the inlet intermediate blade is lower than that of the stationary blade, the flow blocking effect due to the presence of the inlet intermediate blade is mitigated.

(7) By having the portion of the outlet intermediate blade, the flow on the side close to the outer periphery between the stationary blades can be guided in the direction along the stationary blades, and the performance of the diffuser can be improved.

In the present invention, by virtue of the above actions (1) to (7), surging does not occur even at a considerably low flow rate, and therefore the operating range can be greatly expanded and the development of the boundary layer and the secondary flow can be improved. It is possible to obtain a diffuser for a centrifugal fluid machine having high controllability.

〔Example〕

Embodiments of a diffuser of a centrifugal compressor according to the present invention will be described below with reference to the drawings.

1 to 3 show an embodiment of the present invention, in which 1 is an impeller including a blade 1A and a core plate 1B, and 2 is a rotating shaft thereof, which is a driving machine (not shown). 3 is a casing, 4 is a suction pipe, 5 is a diffuser portion, and 6 is a scroll casing. The above-mentioned diffuser portion 5 includes the blade-side diffuser casing 5A,
The core plate side diffuser casing 5B, a plurality of stationary blades 7 provided between the diffuser casings 5A and 5B as shown in FIG. 2, and the blades so as to project into the diffuser section flow path between the stationary blades 7. The intermediate diffuser 8 provided in the side diffuser casing 5A is provided.
As shown in FIGS. 2 and 3, the intermediate blade 8 has an inlet intermediate blade 8A whose chord and height are smaller than those of the stationary blade.
A straightening vane 8B connected to this and having a height smaller than the height of the inlet intermediate vane 8A; and an outlet intermediate vane 8C continuous to this straightening vane 8B and having the same size as the inlet intermediate vane 8A. .

Next, the operation of the above-described embodiment of the present invention will be described.

By the rotation of the impeller 1, the fluid passes through the suction pipe 4 and the impeller 1
While passing through the inside, energy is applied to form a high-speed flow, which flows into the diffuser section 5. In the diffuser section 5, the fluid flowing out from the impeller 1 flows into the scroll casing 6 while converting its velocity energy into pressure energy. Therefore, the fluid, which has been further converted from the velocity energy to the pressure energy, becomes a flow collected by the scroll casing 6 and flows out from a discharge port (not shown).

Since the inlet intermediate blade 8A in the above-mentioned intermediate blade 8 guides the flow in the direction along the stationary blade 7, the flow is along the stationary blade 7 even under a low flow rate condition, so that the surging phenomenon does not easily occur and the operating range of the impeller 1 is reduced. Can be expanded. Since the action of the inlet intermediate blade 8A is as described above, it is desirable that the blade height is about 50% of the stationary blade 7. Since the inlet intermediate blade 8A is supported in a cantilever manner from the blade-side diffuser casing 5A, it is desirable that the height is small in terms of strength, and the height is lower than that of the stationary blade 7. Since the presence of the inlet intermediate blade 8A narrows the flow path, when the compressor flow rate is larger than the design value, the inlet intermediate blade 8A acts as resistance. From this point as well, it is desirable that the blade height is low, and 70% or less of the stationary blade 7 is desirable.

A strong vortex 11 flows out from the tip of the inlet intermediate blade 8A and the end of the root, that is, the downstream side, as shown in FIG.
The energy of these vortices changes to thermal energy and becomes a loss, but the vortex flowing out from the downstream side of the root disturbs the flow in the diffuser part 5 in particular, and thus causes a large loss. In the present invention, the flow straightening blade 8B provided on the downstream side of the inlet intermediate blade 8A suppresses the generation of the vortex flow from the root side of the inlet intermediate blade 8A, so that the loss can be prevented. Straightening vane 8B
Since the purpose is to prevent eddy currents, its height may be lower than that of the inlet intermediate blade 8A.

Next, the flow near the outer circumference between the stationary blades 7 is generally
The flow does not follow the direction of, but is close to the circumferential direction. Therefore, the outlet intermediate blade 8C guides the flow in the direction along the stationary blade 7 to enhance the performance of the diffuser. The height of the outlet intermediate blade 8C is preferably about 50% of that of the stationary blade 7, and is preferably 70% or less from the viewpoint of ensuring rigidity.

FIG. 4 shows a second embodiment of the present invention. This embodiment is an example in which the flow straightening vanes 8B are provided on both sides of the surface facing the intermediate blade 8 and the surface facing the same. In this case, both the downstream end of the inlet intermediate blade 8A and the eddy current generated at the root can be eliminated, so that the performance can be further improved.

FIG. 5 shows a third embodiment of the present invention, in which an intermediate blade 8 is provided between the stationary blades 7 so as to face each other. Even with this configuration, the same effect as that of the above-described embodiment can be obtained. In this case, the height of the intermediate blade 8 is about half that of the intermediate blade 8 shown in the first and second embodiments.

〔The invention's effect〕

According to the present invention, between the stationary blades of the diffuser, a portion of the inlet intermediate blade, which is provided to extend to the upstream side of the leading edge of the stationary blade and has a relatively large height, and a height lower than the inlet intermediate blade. Since the intermediate blade having the straightening vane portion and the outlet intermediate blade portion having a height higher than the height of the straightening vane is provided on the downstream side of the straightening vane portion, the flow along the stationary blade even when the flow rate is low. Can be applied to the leading edge of the stationary blade, the boundary layer developed on the surface of the stationary blade and the surface of the diffuser casing flow path can be suppressed, and the friction loss due to the provision of the intermediate blade can be minimized. There is an effect that a diffuser for a centrifugal fluid machine having a wide operating range and high performance can be obtained.

[Brief description of drawings]

1 is a longitudinal sectional view showing an embodiment of a diffuser of a centrifugal compressor according to the present invention, FIG. 2 is a view taken along the line II-II of FIG. 1,
FIG. 3 is a perspective view thereof, and FIGS. 4 and 5 are enlarged views of essential parts showing another embodiment of the present invention. 1 ... Impeller, 2 ... Rotation axis, 3 ... Diffuser, 7
...... Stationary wing, 8 …… Middle wing, 8a …… Inlet middle wing, 8b
...... Rectifier blade, 8c …… Middle blade at exit.

Claims (2)

[Claims] 1. A diffuser of a centrifugal fluid machine, wherein a plurality of stationary blades are arranged on the outer circumference of an impeller, and the kinetic energy of fluid discharged from the impeller is converted into pressure energy by the action of the stationary blades. A portion of the inlet intermediate blade that is provided to extend upstream of the leading edge of the stationary blade and has a chord length and a height smaller than that of the stationary blade, and is disposed downstream of the portion of the inlet intermediate blade. A plurality of stationary blades, each of which has a straightening vane portion having a height lower than that of the inlet intermediate blade, and an outlet intermediate blade portion having a height higher than the height of the straightening vane downstream of the straightening vane portion; A diffuser for a centrifugal fluid machine characterized by being provided between blades. 2. The centrifugal fluid machine according to claim 1, wherein the intermediate blades are provided on the flow passage surfaces of both the diffuser casings on the blade side and the core plate side so as to face each other. Diffuser.