JP3601958B2 - Turbo machinery - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a turbomachine, and more particularly, to a high or medium specific speed, high efficiency and compact turbomachine.
[0002]
[Prior art]
For example, as shown in FIG. 10, the flow path of the axial flow pump is provided with an impeller 12 rotating around an axis and a diffuser portion 18 having a hub 14 and a diffuser blade 16 inside a cylindrical casing 10. It is configured. The fluid sucked into the pump from the suction channel 20 is energized by the rotational motion of the impeller 12 to increase the total pressure, and the swirling speed of the fluid is reduced in the diffuser unit 18 to reduce the kinetic energy of the swirling flow. It is structured to recover as static pressure. That is, in the diffuser section 18, the static pressure increases in the flow direction as the speed decreases.
[0003]
At this time, if the shape of the flow path is inappropriate, the fluid will flow backward due to the reverse pressure gradient in the flow direction, resulting in a significant reduction in pump performance. In particular, it is known that when the turbomachine is made compact, the blade load on the blades increases and the reverse pressure gradient increases, which is likely to cause such a separation phenomenon, which is a factor that hinders the efficiency and compactness of the turbomachine. It has become.
[0004]
The flow path shape of the diffuser section 18 is defined by both the meridional plane shape and the blade shape. Of these, the meridional plane shape defines a change in the cross-sectional area of the flow passage between the diffuser flow passage inlet and outlet, and thus has a great influence on the realization of an appropriate deceleration process inside the diffuser. In the mixed flow pump, the flow path cross-sectional area increases even if the flow path width is constant due to the increase in the radius from the inlet of the diffuser section to the maximum diameter section of the diffuser section. Can be.
[0005]
On the other hand, in a high specific speed turbomachine represented by an axial pump, since the hub 14 and the casing 10 are designed so that the radius of the inlet 22 and the radius of the maximum diameter portion are substantially constant as shown in FIG. Most of the operations depend on changes in the blade angle.
[0006]
[Problems to be solved by the invention]
However, if the deceleration action is performed only by the turning action of the blade as in the above-described conventional axial flow turbomachine, the blade may be overloaded and large-scale separation may occur. For example, FIG. 12 shows a velocity vector diagram of a conventional axial flow pump blade surface predicted by a three-dimensional viscous flow analysis, and a large-scale separation from a corner between a blade negative pressure surface of a diffuser portion and a hub surface is shown. This can be confirmed to cause the pump performance to be significantly reduced.
[0007]
Therefore, in the axial flow pump with a high load, it is not possible to reduce the friction loss by decelerating the flow early in the first half of the flow path of the diffuser section 18 having a large flow velocity, and to maintain high efficiency and an operation range. It was difficult to achieve high compactness.
[0008]
An object of the present invention is to suppress the separation phenomenon inside the diffuser portion of a high specific speed turbo machine represented by an axial flow pump, and to realize a high efficiency and high compactness of the high specific speed turbo machine. is there.
[0009]
[Means for Solving the Problems]
The invention according to claim 1 is a turbo machine provided with an impeller rotating around an axis and a diffuser portion having a hub and diffuser blades inside a cylindrical casing, wherein the diffuser portion has an inlet and a diffuser portion. and have a depression cross between meridional shapes of the outlet, the inlet annular flow area between the up recesses the increases from the annular flow passage area of the position where the recess is a maximum, the inlet of the diffuser portion The turbomachine is characterized in that the area is larger than the annular flow path area and not more than 1.25 times the area . As a result, the flow path cross-sectional area of the diffuser portion is increased without greatly increasing the outer diameter of the casing, and the deceleration effect due to the increase in the flow path cross-sectional area of the diffuser portion is used in addition to the turning action of the blade. Even in a loaded turbomachine, the flow can be efficiently decelerated. If the increase in the flow path area due to the depression is excessive, the flow is excessively decelerated and the flow may be separated.Therefore, the annular flow path area at the position where the depression is the maximum is the annular flow area at the inlet of the diffuser portion. It needs to be 1.25 times or less of the road area.
[0010]
The invention according to claim 2 is the turbomachine according to claim 1, wherein an annular flow passage area is reduced between the recess position and the blade outlet.
[0011]
The invention according to claim 3 is the turbomachine according to claim 1 or 2, wherein the depression is formed on a hub surface.
[0012]
The invention according to claim 4 is characterized in that the depression is maximum at a position 60% or less of the meridional blade length from the leading edge of the diffuser blade . It is a turbo machine. The swirling flow at the diffuser section inlet has a high flow velocity, and to minimize the occurrence of friction loss due to this, it is necessary to complete the deceleration in the first half of the diffuser section as soon as possible. Therefore, with the above configuration, the flow can be decelerated early in the first half of the flow path of the diffuser portion having a high flow velocity, the friction loss can be reduced, and the efficiency can be improved.
[0014]
Before SL may be from smaller comb radius of the outlet side of the radius of the hub surface at the inlet.
[0015]
The outer diameter before Symbol casing may be decreased in the diffuser rear half portion.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a high specific speed turbomachine according to one embodiment of the present invention. An impeller 12 rotating around an axis, a hub 14 and a diffuser are provided inside a cylindrical casing 10 having a constant diameter. A diffuser section 18 having the blade 16 is provided. The diffuser portion 18 is formed such that the meridian plane of the hub 14 has the same radius of the inlet 22 and the radius of the outlet 24, and has a recess 26 between the inlet 22 and the outlet 24. The recess 26 is made from the entrance of the total length L _g of the diffuser portion 18 to a maximum at a point L _m.
[0017]
The diffuser blade 16 has a structure bent in the circumferential direction as in the conventional case. In the latter half of the diffuser section 18, since the boundary layer is in a developed state, excessive deceleration may cause flow separation. Therefore, in the latter half, the depressed surface of the hub 14 is returned to the same radius as the inlet portion 22 again, so that the speed is gradually reduced only by the blade action.
[0018]
In the meridional plane shape of the axial flow pump shown in FIG. 1, if the flow path areas at the diffuser section 18 inlet, maximum depression position, and outlet are defined as A ₁ , A ₂ , and A ₃ respectively, these areas are given by the following equations. Can be
A ₁ = πD ₁ B ₁ , A ₂ = πD ₂ B ₂ , A ₃ = πD ₃ B ₃
Since D ₁ = D ₃ and B ₁ = B ₃ , A ₁ = A ₃ . Also, since the 26 recess in the hub 14 side it is _provided, which is _A 2> A _1.
The position of the maximum depression, i.e., the maximum flow area position L _m, to the blade length L _g of the above hub 14 side is positioned upstream of the 60% position. That has a _L m <0.6L _g, so that to complete sufficient deceleration quickly.
[0019]
FIG. 2 is a graph in which a change in the flow state of the suction surface of the diffuser section 18 due to the maximum area ratio A ₂ / A _{1 is} predicted by flow analysis . In FIG. 12 , the flow of the diffuser section 18 that has caused large-scale flow separation has occurred. However, it can be confirmed that this is improved by an appropriate hub depression (maximum area ratio A ₂ / A ₁ = 1.2) and the flow separation phenomenon can be suppressed. In addition, when A ₂ / A ₁ = 1.3, the flow field deteriorates rapidly, and it can be seen that an excessive increase in the area causes excessive deceleration in the first half of the flow path, and the flow separates.
[0020]
FIG. 3 shows the result of examining the effect of the maximum area on the efficiency improvement by predicting the pump efficiency by flow analysis. As is apparent from this figure, the maximum area ratio _A 2 / _{A 1} there is an optimum _value, 1.0 _<A 2 / _A 1 compared to efficiency improvement to conventional Katachiko meridional shapes at <1.25 give Can be
[0021]
FIG. 4 shows another embodiment of the present invention. In this example, the diameter of the hub 14 on the outlet 24 side is larger than that of the recess 26 but smaller than that of the inlet 22 side. Accordingly, the flow path cross-sectional area _{A 3} of the outlet 24 side is larger than the inlet 22 side _{A 1.} In the above example, by setting A ₃ = A ₁ , excessive deceleration is avoided in the latter half of the flow channel in which the boundary layer has been developed, and separation is suppressed. However, if the blade load is relatively small and further deceleration is possible, A ₃ > A ₁ may provide additional pressure recovery.
[0022]
FIG. 5 shows still another embodiment of the present invention. If the diameter of the hub 14 is too large, there may occur a rapid expansion loss diffuser downstream, whereas, reducing the diameter of the outlet 24 side of the hub 14 of the diffuser portion 18 becomes excessively large exit area A _3, the second half blade Peeling may occur at the part. In this embodiment, in the meridional shape of the rear half of the diffuser portion 18, the inner diameter of the casing 10 is reduced in the rear half, and at the same time, the hub diameter is also reduced in the rear half in order to secure a flow path area in the blade rear half. By doing so, these problems have been solved.
[0023]
The axial flow diffuser according to the present invention can be used not only in combination with an axial impeller, but also in combination with a high specific speed impeller having a diagonal flow angle on the hub 14 surface. FIG. 6 shows such an embodiment.
[0024]
FIG. 7 shows an embodiment in which the present invention is applied to a mixed flow turbomachine having a medium specific speed. In the guide of the mixed flow turbomachine, the radius of the meridional plane generally increases to the maximum diameter portion 27, and then the radius decreases toward the outlet 24 in general. In this case, even if the flow path width B is constant, the radius increases, so that the flow path cross-sectional area of the maximum diameter portion 27 is larger than the flow path cross-sectional area of the guide inlet 22, and deceleration due to an increase in meridional plane area. The effect occurs. However, when the pump outer diameter is reduced in size, there is a possibility that the area increase due to the increase in the radius cannot be sufficiently secured. Even in such a case, according to the present invention, the depression 26 is provided in the vicinity of the maximum diameter portion, and the increase in the flow path area due to the increase in the radius and the increase in the area due to the depression 26 are used together, so that the efficiency is not impaired. The maximum diameter of the flow diffuser can be reduced.
[0025]
8 and 9 show an example in which the present invention is applied to a multi-stage turbomachine. Each stage is constituted by an impeller and a diffuser portion , and the flow flowing from the suction passage 20 passes through the first stage impeller 12a and the diffuser blade 16a, and then from the second stage impeller 12b to the diffuser blade. After passing through each stage to 16b, it flows out to the outlet channel 24. FIG. 8 shows a case of a high specific speed turbo machine which handles an incompressible fluid such as a pump, and FIG. 9 shows a case of a high specific speed turbo machine which handles a compressible fluid such as an axial compressor. In the latter case, the flow path height decreases because the volume of the fluid decreases as the pressure increases toward the subsequent stage due to the compressibility of the fluid. In this case, there are a case where the hub side radius is increased and a case where the casing radius is reduced. In any case, a depressed portion 26 is provided in the stationary blade hub portion, and a deceleration effect due to an increase in the flow path cross-sectional area is generated. It is similar to the case of
[0026]
【The invention's effect】
As described above, according to the present invention, the flow path cross-sectional area of the diffuser portion is increased without greatly increasing the outer diameter of the casing, and the flow is efficiently decelerated while suppressing the separation phenomenon, thereby achieving high efficiency. And compact high specific speed turbomachinery can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a meridional shape of an axial pump according to an embodiment of the present invention.
FIG. 2 is a diagram showing a change in a flow field depending on an area ratio of the axial flow pump of the present invention.
FIG. 3 is a graph showing the effect of the maximum area on the efficiency improvement.
FIG. 4 is a diagram showing a meridional plane shape of a high specific speed turbomachine according to another embodiment of the present invention.
FIG. 5 is a diagram showing a meridional plane shape of a high specific speed turbomachine according to still another embodiment of the present invention.
FIG. 6 is a diagram showing a meridional plane shape of a high specific speed turbomachine according to still another embodiment of the present invention.
FIG. 7 is a diagram showing a meridional plane shape of a high specific speed turbomachine according to still another embodiment of the present invention.
FIG. 8 shows an example in which the present invention is applied to a multi-stage turbomachine.
FIG. 9 shows an example in which the present invention is applied to a multi-stage turbomachine.
FIG. 10 is a diagram illustrating a general shape of a high specific speed turbomachine.
FIG. 11 is a diagram showing a meridional plane shape of a conventional high specific speed turbomachine.
FIG. 12 is a velocity vector diagram of a conventional axial flow pump blade surface.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Casing 12 Impeller 14 Hub 16 Diffuser blade 18 Diffuser part 20 Suction channel 22 Diffuser part inlet 24 Diffuser part outlet 26 Depression

Claims (4)

In a turbomachine provided with an impeller rotating around an axis and a diffuser portion having a hub and diffuser blades inside a cylindrical casing,
The diffuser unit may have a depression cross between meridional shapes of the inlet and outlet, the annular flow area between the inlet to said depression is increased, an annular flow path of the position where the recess is maximum A turbo machine characterized in that the area is larger than the area of the annular flow passage at the inlet of the diffuser portion and is 1.25 times or less thereof . The turbomachine according to claim 1, wherein an annular flow passage area is reduced between the depression position and the blade outlet. The turbomachine according to claim 1, wherein the depression is formed on a hub surface. The turbomachine according to any one of claims 1 to 3, wherein the depression is maximum at a position 60% or less of a meridional blade length from a leading edge of the diffuser blade .

Images