JP2012202242A - Exhaust diffuser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust diffuser controlling an exhaust gas flow to be more ideal.SOLUTION: A manhole 14 includes: a front edge 14a located in an upstream side in a main flow direction where an exhaust gas E flows; and a rear edge 14b located in a downstream side in a flow direction of a combustion gas G. An inner cylinder 11 includes a diameter-reduced part 11b where the diameter is reduced from a predetermined start position St in the main flow direction to an end position En at an end in the downstream side. The front edge 14a and the start position St, and the rear edge 14b and the end position En are set to be coincide with each other.

Description

  The present invention relates to an exhaust diffuser.

As shown in FIG. 7, the gas turbine (axial turbine) 100 compresses the air taken in from the front entrance with the compressor 120, heats it in the combustion chamber 130, and further regulates the flow with the turbine 140 at the rear to adjust the power. Finally, exhaust is performed through the rear exhaust diffuser 150.
FIG. 8 is a schematic partial cross-sectional view of the gas turbine 100 showing an example of the positional relationship between the moving blades of the turbine 140 and the exhaust diffuser 150. The gas turbine 100 includes a turbine casing 110 on the outside, and a plurality of stages of combinations of stationary blades 111 and moving blades 112 are arranged therein. A bearing (journal bearing) 115 housed in a bearing housing 114 supports the rear end of the rotor 113 to which the moving blade 112 is attached. The bearing housing 114 is supported concentrically with the center of the turbine casing 110 by a plurality of struts 153 arranged radially so as to cross the flow of exhaust gas.
Here, an example in which a single-stage strut 153 is provided in the direction in which the exhaust gas flows is shown, but another single-stage strut called a manhole may be provided downstream. Since this manhole also functions as a strength member that plays a supporting role, in the present invention, the manhole and the manhole are collectively referred to as a strut.

  An arrow F in FIG. 8 indicates the flow of exhaust gas. The exhaust gas exiting the final stage moving blade 112 is exhausted through the exhaust diffuser 150. The exhaust diffuser 150 has a hub side tube (inner cylinder) 151 and a tip side tube (outer cylinder) 152 concentrically disposed around the hub side tube (inner cylinder) 151, and an annular flow path is formed between the tubes. The hub side tube 151 has a cylindrical shape, but the tip side tube 152 has a truncated cone shape whose diameter increases toward the downstream side. Therefore, the exhaust diffuser 150 has a gradually increasing cross-sectional area from the upstream side toward the downstream side. It is a so-called conical diffuser. It is also the role of the struts 153 to maintain the shape of the annular flow path by keeping the distance between the hub side tube 151 and the tip side tube 152 and to support it in the turbine casing 110.

  Although a strut is indispensable in an exhaust diffuser, it causes a relatively large pressure loss when the exhaust gas passes through the area where the strut is disposed and for the exhaust gas. On the other hand, the present applicant has proposed an exhaust diffuser structure capable of reducing pressure loss in Patent Document 1 and Patent Document 2.

JP-A-2005-290985 JP 2011-32900 A

However, according to the study by the present inventors, there is room for improvement in the flow of exhaust gas.
Therefore, an object of the present invention is to provide an exhaust diffuser that can bring the flow of exhaust gas closer to an ideal one.

According to the study by the present inventors, the exhaust flow is separated at the downstream end of the hub side tube (inner cylinder) and a vortex is generated. Therefore, the exhaust flow passes through the struts and circulates greatly. Therefore, the flow is difficult to be uniform, and the actual pressure recovery amount is considerably smaller than the pressure recovery amount in the exhaust duct. In addition, a considerable axial distance is required to eliminate the vortex. Furthermore, eddy currents are accompanied by noise and vibration. By eliminating these problems, the flow of the exhaust flow can be made closer to an ideal one.
The exhaust diffuser of the present invention made there is an inner cylinder, an outer cylinder that is disposed around the inner cylinder, and an exhaust passage is formed between the inner cylinder, an inner cylinder, A strut connecting the outer cylinders.
The strut includes a front edge located on the upstream side in the direction in which the exhaust gas flows through the exhaust flow path, and a rear edge located on the downstream side in the direction in which the exhaust gas flows.
The inner cylinder includes a reduced diameter portion whose diameter decreases from a predetermined start position on the upstream side in the direction in which the exhaust gas flows to an end position on the downstream end.
Each of the leading edge and the starting position and the trailing edge and the ending position are set to coincide with each other in the direction in which the exhaust gas flows.

  In the exhaust diffuser of the present invention, it is preferable that the strut is inclined so that the rear edge descends from the outer cylinder toward the inner cylinder in order to flow the exhaust gas toward the shaft of the exhaust diffuser.

  In the exhaust diffuser of the present invention, the reduced diameter portion can be reduced in diameter over the entire circumferential direction of the inner cylinder, but the reduced diameter portion is formed with a reduced diameter region only at the portion where the strut is joined and the periphery thereof. be able to. The flow of the exhaust gas hitting the strut is pushed to the wall surface side such as the outer peripheral surface of the inner cylinder. For this reason, in the area near the strut, the exhaust gas is difficult to peel off on the outer peripheral surface of the inner cylinder. Therefore, only the joint portion between the strut and the inner cylinder and the surrounding area are reduced in diameter.

  According to the present invention, it is possible to provide an exhaust diffuser that can bring the flow of the exhaust flow closer to an ideal one.

It is sectional drawing which shows the exhaust diffuser vicinity of the gas turbine which concerns on 1st Embodiment. It is a figure which shows FIG. 1 typically. It is sectional drawing which shows the exhaust diffuser vicinity of the gas turbine which concerns on 2nd Embodiment. It is a figure which shows FIG. 3 typically. It is sectional drawing which shows the exhaust diffuser vicinity of the gas turbine which concerns on 3rd Embodiment. (A) is a figure which shows FIG. 5 typically, (b) is 6b-6b arrow sectional drawing of (a), (c) is 6c-6c arrow sectional drawing of (a). It is a half sectional view showing a schematic structure of a conventional gas turbine. It is sectional drawing which shows the exhaust diffuser vicinity of the conventional gas turbine.

[First Embodiment]
Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
As shown in FIG. 1, the exhaust diffuser 10 is connected to a cylindrical inner cylinder 11 that houses a journal bearing 7 and the like that pivotally supports the rotor 5, and a turbine casing 4 a, and is disposed around the inner cylinder 11. A cylindrical outer cylinder 12.
The exhaust diffuser 10 extends from the outer cylinder 12 to the inside of the inner cylinder 11 and is provided on the downstream side of the struts 13 for holding the journal bearings 7 from the periphery. Maintenance of the journal bearings 7 and the like is provided. And a manhole 14 provided for the purpose. In the exhaust diffuser 10, the direction of the rotation center axis A is the main flow direction (the direction in which the exhaust gas flows) along the main flow of the exhaust gas E.

The inner cylinder 11 is provided coaxially with the exhaust diffuser 10 and extends in the main flow direction from the upstream side to which the turbine 4 is connected toward the downstream side. The inner cylinder 11 includes an equal-diameter portion 11a having an equal diameter, a diameter-reduced portion 11b that is connected to an end portion on the downstream side of the equal-diameter portion 11a, and whose diameter decreases toward the downstream side, and a diameter-reduced portion And a sealing end 11c that closes the downstream end of 11b. The provision of the reduced diameter portion 11b may hereinafter be referred to as element 1.
The outer cylinder 12 has an inner peripheral wall surface (wall surface) 12b that gradually increases in diameter in the main flow direction from the upstream side to which the turbine 4 is connected toward the downstream side.

  Between the inner cylinder 11 and the outer cylinder 12, an exhaust passage P having an annular shape is formed by the inner peripheral wall surface 12b of the outer cylinder 12 and the outer peripheral wall surface 11d of the inner cylinder 11. The exhaust flow path P has an outer peripheral wall surface 11d of the inner cylinder 11 formed to have substantially the same diameter, while the inner peripheral wall surface 12b of the outer cylinder 12 gradually increases in diameter toward the downstream side. As it progresses from the upstream side to the downstream side, the opening area that intersects the mainstream direction gradually increases.

The struts 13 are arranged radially around the rotation center axis A of the rotor 5 at an angle of 120 ° to each other. That is, in this example, the journal bearing 7 is supported by the three struts 13.
Each strut 13 includes a strut body 13a that holds the journal bearing 7, and a strut cover 13b that covers the strut body 13a with combustion gas G and protects it by heating. The strut cover 13 b extends from the inner cylinder 11 toward the outer cylinder 12.
The strut cover 13b extends in a direction intersecting the main flow, and in order to reduce the main flow resistance in the exhaust flow path P, the cross-sectional shape is a wing shape (streamline type). The strut cover 13b has a front edge 13c and a rear edge 13d.

Similarly to the struts 13, the manholes 14 are arranged radially around the rotation center axis A of the rotor 5 at an angle of 120 °.
The manhole 14 connects the inner cylinder 11 and the outer cylinder 12 and communicates the outside of the outer cylinder 12 and the inside (accommodating space) of the inner cylinder 11.
The manhole 14 also extends in a direction crossing the mainstream, and in order to reduce the resistance of the mainstream in the exhaust passage P, the cross-sectional shape is a wing shape (streamline type).

Now, in the exhaust diffuser 10, the manhole 14 and the inner cylinder 11 provided with the reduced diameter portion 11b have the following relationship.
The position of the front edge 14a of the manhole 14 and the boundary between the equal diameter portion 11a and the reduced diameter portion 11b (the reduced diameter start position St) of the inner cylinder 11 are set to coincide with each other in the main flow direction. Hereinafter, this configuration may be referred to as element 2.
Further, the position of the rear edge 14b of the manhole 14 and the position of the rear end of the inner cylinder 11 (the reduced diameter portion 11b) (the end position En of the reduced diameter) are set to coincide with each other in the mainstream direction. Hereinafter, this configuration may be referred to as an element 3.

Since the exhaust diffuser 10 includes the element 1, the flow of the exhaust gas E can be guided toward the rotation center axis A (see FIG. 2).
However, even if the element 1, that is, the reduced diameter portion 11b is provided, there is a component that peels off from the outer peripheral surface of the reduced diameter portion 11b in the flow of the exhaust gas E, and this forms a vortex. Therefore, the exhaust diffuser 10 can effectively guide the flow of the exhaust gas E toward the rotation center axis A by including the element 2.
In order to suppress separation of the exhaust gas E from the inner cylinder 11 (outer peripheral surface), it is ideal that the flow path (opening) area of the exhaust flow path P is constant. However, since the manhole 14 is provided in the exhaust passage P, the passage area on the downstream side of the upstream side of the manhole 14 is reduced. In order to compensate for the decrease in the flow path area, it is desirable to provide the reduced diameter portion 11b. Therefore, if the diameter of the inner cylinder 11 is reduced in accordance with the presence of the manhole 14 that causes the reduction of the flow path area, that is, the front edge 14a, the flow area on the upstream side can be easily maintained. Therefore, by providing the element 2, exfoliation of the exhaust gas E can be suppressed.

  Furthermore, by providing the element 3, separation of the flow of the exhaust gas E from the outer peripheral surface of the inner cylinder 11 is reduced. That is, if the reduced diameter portion 11b of the inner cylinder 11 protrudes downstream of the rear edge 14b of the manhole 14, separation may occur at the protruding portion. Therefore, the occurrence of peeling is suppressed by setting the element 3, that is, the rear edge 14 b and the rear end of the reduced diameter portion 11 b to coincide with each other. As a result, noise and vibration due to eddy current generation are reduced.

  As described above, by providing the element 1 and the element 2, the exhaust diffuser 10 can effectively guide the flow of the exhaust gas E downstream from the manhole 14 toward the rotation center axis A. The downstream circulation region can be reduced, and the flow can be made uniform over a short distance. As a result, pressure recovery can be increased and the axial distance can be shortened. Moreover, by providing the element 3, the exhaust diffuser 10 can reduce noise and vibration.

  In this embodiment, the specifications of the manhole 14 and the inner cylinder 11 are set according to the gas turbine in which the exhaust diffuser 10 is used. As one guideline, the inclination angle (θ) of the reduced diameter portion 11b is 5 The ratio (T / L) between the height T of the flow path and the length L in the direction of the rotation center axis A from the front edge 14a to the rear edge 14b of the manhole 14 is 0. It is preferably set in the range of .5 to 2.0.

  In the present embodiment, the position of the front edge 14a and the start position St of the inner contraction diameter are set to coincide with each other. The position of the front edge 14a and the start position St of the inner contraction diameter physically match. It is not limited to doing. The same applies to the relationship between the position of the rear edge 14b and the end position En of the rear end of the reduced diameter portion 11b. For example, even if there is an inevitable misalignment that occurs when the exhaust diffuser 10 is actually manufactured, the above-described effects can be obtained if the effects described above are obtained. The positional deviation allowed in this case is 10% or less of the length L, preferably 5%.

[Second Embodiment]
Hereinafter, an exhaust diffuser 20 according to a second embodiment of the present invention will be described.
Since the exhaust diffuser 20 has the same basic configuration as that of the first embodiment, the following description will focus on differences from the first embodiment. In addition, the same code | symbol is attached | subjected to the same structure as the exhaust diffuser 10 of 1st Embodiment.

  As shown in FIG. 3, the exhaust diffuser 20 is different from the first embodiment in the form of a manhole 24. That is, the manhole 24 inclines the rear edge 24b so as to descend from the outer cylinder 12 to the inner cylinder 11 and downstream. By doing so, as shown in FIG. 4, the pressure on the inner cylinder 11 side can be made lower than the pressure on the outer cylinder 12 side. Therefore, the exhaust gas E can be more effectively guided toward the rotation center axis A. The front edge 24a is orthogonal to the direction of the rotation center axis A (the same applies to the first embodiment).

[Third Embodiment]
Hereinafter, an exhaust diffuser 30 according to a third embodiment of the present invention will be described with reference to FIGS.
Since the exhaust diffuser 30 has the same basic configuration as that of the first embodiment, the following description will focus on differences from the first embodiment. In addition, the same code | symbol is attached | subjected to the same structure as the exhaust diffuser 10 of 1st Embodiment.

  The exhaust diffuser 30 is different from the first embodiment in the form of the inner cylinder 31. That is, the inner cylinder 31 includes a reduced diameter portion 31b that is connected to the downstream end portion of the equal diameter portion 31a and in which a reduced diameter region 31c is formed only at and around the portion where the manhole 14 is joined. The diameter-reduced region 31c starts from the front edge 14a of the manhole 14 and continuously deepens, and shows a form of inclination that becomes the largest at the rear edge 14b of the manhole 14. The rear edge 14b of the manhole 14 may be orthogonal to the rotation center axis A as in the first embodiment, or may be inclined so as to descend toward the downstream as in the second embodiment. Further, the inclination of the reduced diameter region 31c from the front edge 14a to the rear edge 14b may be linear or curvilinear. The outer shape in the cross section of the portion excluding the reduced diameter region 31c forms an arc as shown in FIG. 6, and the shape of the entire cross section resembles a petal pattern. The inner cylinder 11 of the first embodiment has a circular outer shape in cross section.

  The manhole 14 provided in the exhaust diffuser 30 prevents the flow of the exhaust gas E. The flow of the exhaust gas E hitting the manhole 14 is pushed to the wall surface side such as the outer peripheral wall surface 31 d of the inner cylinder 31. For this reason, in the area near the manhole 14, the exhaust gas E is difficult to peel off on the outer peripheral surface of the inner cylinder 31. Therefore, by inclining the joint portion of the manhole 14 with the inner cylinder 31 and the region including this (the reduced diameter region 31c) toward the rotation center axis A along the axial direction, the flow in this region can be efficiently performed. The circulation region downstream of the manhole 14 is made smaller toward the rotation center axis A. By doing so, the flow of the exhaust gas E becomes uniform earlier downstream of the manhole 14, and the pressure recovery increases.

The embodiment described above includes the strut 13, the manhole 14 (manhole 24), and the two-stage strut in the direction of the rotation center axis A, but the present invention is not limited to this and does not include the manhole 14. The present invention can be applied to an exhaust diffuser. In other words, the present invention is applied to both the exhaust diffuser having a single-stage strut in the axial direction and the exhaust stage diffuser having a plurality of struts in the axial direction, particularly to the last-stage strut through which the exhaust gas passes.
In the present invention, the number of struts including manholes arranged in the circumferential direction is not limited to 3 described above, and any number such as 2 or 4 can be adopted.
In addition to this, as long as it does not depart from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

4 Turbine 4a Turbine casing 5 Rotor 7 Journal bearing 10, 20, 30 Exhaust diffuser 11, 31 Inner cylinder 11a, 31a Equal diameter part 11b, 31b Reduced diameter part 11c Sealed end 11d, 31d Outer peripheral wall surface 31c Reduced diameter area 12 Outer cylinder 12b Inner peripheral wall surface 13 Strut 13a Strut body 13b Strut covers 14, 24 Manholes 14a, 24a Front edges 14b, 24b Rear edge A Rotation center axis P Exhaust flow path St Start position En End position

Claims (3)

An inner cylinder,
An outer cylinder disposed around the inner cylinder and having an exhaust passage formed between the inner cylinder;
A strut provided in the exhaust passage and connecting the inner cylinder and the outer cylinder;
The strut is
A leading edge located upstream of the exhaust gas flow direction in the exhaust flow path;
A rear edge located on the downstream side in the direction in which the exhaust gas flows, and
The inner cylinder is
A diameter-reducing portion whose diameter is reduced from a predetermined start position on the upstream side in the direction in which the exhaust gas flows to an end position on the downstream end,
Each of the front edge and the start position, and the rear edge and the end position are set to coincide with each other in a direction in which the exhaust gas flows.
Exhaust diffuser characterized by that. The strut is
The trailing edge is inclined so as to descend from the outer cylinder toward the inner cylinder;
The exhaust diffuser according to claim 1. The reduced diameter portion is
Formed only at and around the part where the struts are joined,
The exhaust diffuser according to claim 1 or 2.