A steam turbine exhaust cylinder with an asymmetric diffuser and volute structure

Abstract

A steam turbine exhaust cylinder with an asymmetric diffuser and volute structure, the rear wall of the upper cavity is inclined, so that the distance between the rear wall of the upper cavity and the front wall of the upper cavity gradually decreases from the bottom of the upper cavity to the top of the upper cavity; the lower cavity further includes an inverted frustum-shaped contraction cavity arranged at the bottom of the columnar cavity; the outer guide ring of the diffuser is coaxially sleeved outside the inner guide ring; the outer guide ring and the inner guide ring are horn-shaped; the profile lines of the inner guide ring and the outer guide ring are Bessel curves; the outlet end face of the inner guide ring is a folded surface structure, including a semi-circular plane and an arc-shaped inclined surface, and the arc-shaped inclined surface is inclined from the upper end of the semi-circular plane towards the diffuser inlet end; the circumference of the semi-circular plane is fixed to the inner side of the rear wall of the lower cavity and the frustum-shaped contraction cavity, and the circumference of the arc-shaped inclined surface is fixed to the inner side of the rear wall of the upper cavity. The structure of the present invention is simple, can fully improve the utilization rate of the residual velocity kinetic energy of the exhaust cylinder, and improve the static pressure recovery coefficient; at the same time, reduce the exhaust steam vortex loss inside the exhaust cylinder and reduce the total pressure loss coefficient.

Description

Technical Field

[0001] The invention relates to the technical field of steam turbines, in particular to a steam turbine exhaust cylinder with an asymmetric diffuser and a volute structure. Background Art

[0002] The steam entering the steam turbine flows through each stage to perform work, then enters the exhaust cylinder through the last stage blade of the steam turbine, and finally flows to the condenser. The steam flow passes through the diffuser area formed by the inner and outer guide rings in the exhaust cylinder, the flow velocity is reduced, and the kinetic energy is converted into pressure energy, forming an effective static pressure recovery; but due to the friction, vortex, steering and other resistance effects, the pressure is reduced. This part of the pressure drop loss is called the exhaust resistance loss of the steam turbine. Therefore, a low-pressure exhaust cylinder with good aerodynamic performance can effectively reduce the exhaust resistance loss and improve the static pressure recovery.

[0003] The diffuser and volute are two key structures of the exhaust cylinder. The diffuser formed by the flow area between the inner and outer guide rings is the main source of static pressure recovery in the exhaust cylinder and has an important impact on the performance of the exhaust cylinder. After the steam flows out of the diffuser, it enters the exhaust volute, where it turns and converges to flow toward the downstream condenser. In the process of flowing in the volute, part of the kinetic energy continues to be converted into pressure energy. At the same time, the turning and convergence of the steam flow leads to the appearance of obvious channel vortices, end wall vortices, separation vortices and other vortex groups inside the volute, causing flow losses inside the exhaust cylinder.

[0004] At present, for the exhaust cylinder diffuser, the existing designs mostly use multi-section welded guide rings or smaller guide ring components. The impact of the vortex generated by the nonlinear guide ring profile on the diffuser performance and the insufficient diffusion capacity caused by the small size of the diffuser are ignored, which limits the static pressure recovery capacity of the exhaust cylinder. In addition, the design process of the diffuser should also pay attention to the overall coupling design with the volute to ensure that the diffuser outflow is fully developed and the vortex loss is minimized. For the exhaust cylinder volute, the existing design focuses on the overall size of the volute and the impact of the relative position size of the volute and the diffuser on the exhaust cylinder performance. However, the flow characteristics of the mainstream area inside the exhaust cylinder volute still have obvious asymmetric characteristics and severe vortex losses, which should be taken into consideration in the volute design process to alleviate the vortex loss, thereby further improving the aerodynamic performance of the exhaust cylinder. Summary of the invention

[0005] The object of the present invention is to provide a steam turbine exhaust cylinder with an asymmetric diffuser and a volute structure, which can effectively reduce flow losses and improve static pressure recovery effects.

[0006] The technical solution adopted by the present invention to solve the problems of the prior art: A steam turbine exhaust cylinder with an asymmetric diffuser and volute structure, including an exhaust cylinder volute formed by splicing and fixing an upper cavity and a lower cavity that are interconnected. The front wall of the exhaust cylinder volute is provided with a steam inlet, and the bottom of the exhaust cylinder volute is provided with a steam outlet; a diffuser is arranged inside the exhaust cylinder volute; the inlet end of the diffuser is located at the steam inlet and is coaxial with the steam inlet; the upper cavity includes an upper cavity front wall, an upper cavity rear wall, and an arc-shaped side wall fixedly arranged between the upper cavity front wall and the upper cavity rear wall; the lower cavity includes a columnar cavity; the upper cavity rear wall is inclined from the bottom of the upper cavity to the top of the upper cavity, and the distance between the upper cavity rear wall and the upper cavity front wall gradually decreases from the bottom of the upper cavity to the top of the upper cavity, so as to form an asymmetric volute structure that is thinner at the top and thicker at the bottom; the lower cavity further includes an inverted frustum-shaped contraction cavity arranged at the bottom of the columnar cavity; the diffuser includes an inner guide ring and an outer guide ring; the outer guide ring is coaxially sleeved outside the inner guide ring; the outer guide ring and the inner guide ring are in the shape of a horn that expands from the inlet end to the outlet end of the diffuser; the profile lines of the inner guide ring and the outer guide ring are both Bezier curves; the outlet end face of the inner guide ring is a folded surface structure, including a semi-circular plane located below the axis of the diffuser and an arc-shaped inclined plane located above the semi-circular plane. The arc-shaped inclined plane is inclined towards the inlet end of the diffuser from the upper end of the semi-circular plane, and the angle between the arc-shaped inclined plane and the axis of the diffuser is the same as the angle between the upper cavity rear wall and the axis of the diffuser; the circumference of the semi-circular plane is fixed to the inner side of the lower cavity rear wall and the frustum-shaped contraction cavity, and the circumference of the arc-shaped inclined plane is fixed to the inner side of the upper cavity rear wall, so that the inner guide ring forms an upper and lower asymmetric structure.

[0007] A first arc-shaped baffle is arranged between the front wall of the upper cavity and the arc-shaped side wall inside the exhaust cylinder volute; a second arc-shaped baffle is arranged between the rear wall of the upper cavity and the arc-shaped side wall; and the first arc-shaped baffle, the upper cavity front wall, and the arc-shaped side wall enclose an arc-shaped cavity with a triangular cross-section; the second arc-shaped baffle, the upper cavity rear wall, and the arc-shaped side wall enclose an arc-shaped cavity with a triangular cross-section; first baffles are arranged between the two sides of the front wall of the lower cavity inside the exhaust cylinder volute and the adjacent side walls; second baffles are arranged between the two sides of the rear wall of the lower cavity and the adjacent side walls, and the first baffle, the front wall of the lower cavity, and the adjacent side wall enclose a prismatic cavity with a triangular cross-section; the second baffle, the rear wall of the lower cavity, and the adjacent side wall enclose a prismatic cavity with a triangular cross-section.

[0008] The inverted frustum-shaped contraction cavity includes a contraction cavity front wall, a contraction cavity rear wall, and a contraction cavity side wall. The contraction cavity rear wall is a vertical plate body, and the contraction cavity front wall and the contraction cavity side wall are both inclined plate bodies that incline from the bottom of the columnar cavity towards the axis direction of the steam outlet, so as to form an asymmetric contraction structure on the front and rear walls of the lower cavity.

[0009] A condenser connection section extends from the bottom of the inverted frustum-shaped contraction cavity, and the condenser connection section is a columnar pipe section.

[0010] The steam inlet is connected to the inlet end of the diffuser via a stepped inlet wall.

[0011] The beneficial effects of the present invention are as follows: the present invention has a simple structure, and by improving the volute structure and the diffuser structure, the utilization rate of the residual kinetic energy of the exhaust cylinder is fully improved, and the static pressure recovery coefficient is improved; at the same time, the exhaust vortex loss inside the exhaust cylinder is reduced, and the total pressure loss coefficient is reduced, and finally the economy of the entire steam turbine unit is improved, which is mainly reflected in the following aspects:

[0012] 1. The present invention adopts an asymmetric volute structure according to the flow development characteristics of the mainstream area inside the volute when the exhaust cylinder is working. For the upper cavity of the volute, the rear wall of the upper cavity is set to be an inclined plate that is inclined from the bottom of the upper cavity to the top of the upper cavity, so that the distance between the rear wall of the upper cavity and the front wall of the upper cavity gradually decreases from the bottom of the upper cavity to the top of the upper cavity, so as to form an asymmetric volute structure that is thin on the top and thick on the bottom, that is, a geometric design with unilateral contraction treatment is adopted, which conforms to the flow characteristics of the fluid inside the exhaust cylinder flowing in with pre-swirl along the axial direction and gradually converging and flowing downward, that is, the fluid gradually converges from the top, and the flow increases and flows downstream. Due to the asymmetric cross-sectional geometric design of the upper cavity, which is thin on the top and thick on the bottom, the fluid is fully developed in each area inside the exhaust cylinder volute, avoiding the situation that the fluid at the exhaust cylinder top and the diffuser outlet is not full of the flow channel, which leads to flow separation, reduced effective flow area and increased flow loss; for the volute structure of the lower cavity, in order to match the downstream condenser, it is necessary to limit the contraction size of the exhaust cylinder outlet, and a chamfered cone-shaped contraction cavity is set at the bottom of the original cylindrical cavity, that is, the rear wall of the contraction cavity of the lower cavity is a vertical plate, and the front wall and side walls of the contraction cavity are both inclined plates inclined from the bottom of the columnar cavity toward the axis of the steam outlet. The asymmetric contraction structure, therefore, effectively guarantees the flow area at the outlet end of the diffuser flow channel of the lower cavity, ensures a large inlet and outlet area ratio, increases the pressure diffusion effect, and improves the static pressure recovery capacity of the exhaust cylinder.

[0013] 2. The present invention appropriately adds baffle structures on the front wall of the upper cavity and the rear wall of the upper cavity, the front wall of the lower cavity and the rear wall of the lower cavity of the exhaust cylinder volute to reduce the end wall vortex formed by the swirling flow of the fluid at the corner, thereby reducing the eddy current loss, reducing the total pressure loss coefficient of the exhaust cylinder, and at the same time increasing the strength, stiffness and stability of the exhaust cylinder volute.

[0014] 3. In terms of the structural improvement of the diffuser: The present invention adopts a large-size asymmetric guide ring geometry with a cubic Bézier curve as the profile line, enabling the fluid to flow more smoothly and steadily within the diffuser, effectively reducing the flow loss; the upper and lower asymmetric inner guide rings cooperate with the asymmetric volute structure, making the flow channel structures at various positions more in line with the internal flow development characteristics of the exhaust cylinder; for the outer guide ring, a large-size guide ring structure is adopted, which can separate the different pressure regions on the inner and outer walls of the guide ring, enabling the mainstream to rotate orderly along the inner wall surface of the guide ring, effectively restricting the development of the mainstream vortex in the volute, and reducing the total pressure loss; moreover, the large-size guide ring geometry ensures a sufficient inlet and outlet area ratio for the diffuser, effectively and reliably improving the pressure-increasing performance of the diffuser and ensuring the static pressure recovery effect of the exhaust cylinder. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of the exhaust cylinder volute structure and steam flow of the present invention.

[0016] Figure 2 is a side view of the exhaust cylinder volute of the present invention.

[0017] Figure 3 is a schematic diagram of the diffuser structure of the present invention.

[0018] Figure 4 is Figure 3 an enlarged view of part B of

[0019] Figure 5 is a schematic diagram of the structure of the present invention.

[0020] Figure 6 is Figure 5 a sectional view taken along line A-A of

[0021] Figure 7 is a bottom view of the upper cavity of the present invention.

[0022] Figure 8 is a schematic diagram of the structure of the lower cavity of the present invention.

[0023] In the figures: 1 - steam inlet, 2 - diffuser, 3 - inlet wall surface, 4 - front wall of the upper cavity, 5 - rear wall of the upper cavity, 6 - circular arc side wall, 7 - rectangular columnar cavity, 8 - inverted frustum-shaped contraction cavity, 9 - columnar pipe section, 10 - first arc-shaped baffle, 11 - second arc-shaped baffle, 12 - first baffle, 13 - second baffle, 14 - arc-shaped cavity with an isosceles triangle cross-section, 14a - arc-shaped cavity with a triangle cross-section, 15 - inner wall profile, 16 - prismatic cavity, 201 - inner guide ring, 202 - outer guide ring, 201a - semi-circular plane, 201b - arc-shaped inclined plane, 801 - front wall of the contraction cavity, 802 - rear wall of the contraction cavity, 803 - side wall of the contraction cavity. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention will be described below in conjunction with the accompanying drawings and specific embodiments:

[0025] Figure 1 It is a schematic structural diagram of a steam turbine exhaust cylinder with an asymmetric diffuser and volute structure. A steam turbine exhaust cylinder with an asymmetric diffuser and volute structure includes an exhaust cylinder volute formed by splicing and fixing an upper cavity and a lower cavity that are interconnected. At the front wall surface of the exhaust cylinder volute, there is a steam inlet 1 for inputting the steam flow from the last-stage blade row. At the bottom of the exhaust cylinder volute, there is an outlet connected to the condenser; so that the steam flow from the upstream last-stage blade row enters the exhaust cylinder axially along the steam inlet 1, and after being turned and collected by the diffuser 2, it flows to the downstream condenser through the outlet at the bottom of the exhaust cylinder volute; inside the exhaust cylinder volute, there is a diffuser 2; the inlet end of the diffuser 2 is located at the steam inlet 1 and is coaxial with the steam inlet 1, and between the steam inlet 1 and the inlet end of the diffuser 2, it is connected by a stepped inlet wall surface 3 corresponding to the steam seal structure and extraction structure of the steam turbine; specifically: the upper cavity includes an upper cavity front wall 4, an upper cavity rear wall 5, and an arc-shaped side wall 6 fixedly arranged between the upper cavity front wall 4 and the upper cavity rear wall 5; as Figure 2 shown: the upper cavity rear wall 5 is inclined from the bottom of the upper cavity to the top of the upper cavity, and the distance between the upper cavity rear wall 5 and the upper cavity front wall 4 gradually decreases from the bottom of the upper cavity to the top of the upper cavity, that is, a geometric design of unilateral contraction is adopted at the rear wall position of the upper cavity to form an asymmetric volute structure with a thinner upper part and a thicker lower part. Such a structure enables the fluid to fully develop in each area inside the exhaust cylinder volute, avoiding the fluid at the top of the exhaust cylinder and the outlet position of the diffuser 2 not filling the flow passage, thereby generating flow separation, reducing the effective flow area, and increasing the flow loss.

[0026] The lower cavity includes a rectangular columnar cavity 7 that is open at the top and bottom and an inverted frustum-shaped contraction cavity 8 arranged at the bottom of the columnar cavity. At the bottom of the inverted frustum-shaped contraction cavity 8, there extends a columnar pipe section 9, and this columnar pipe section 9 is connected to the condenser as a condenser connection transition section. Among them, the inverted frustum-shaped contraction cavity 8 adopts an asymmetric inverted "frustum" contraction structure that conforms to the flow characteristics: including a contraction cavity front wall 801, a contraction cavity rear wall 802, and a contraction cavity side wall 803, where as Figure 2 shown: the contraction cavity rear wall 802 is a vertical plate body, while the contraction cavity front wall 801 and the contraction cavity side wall 803 are both inclined plate bodies that are inclined from the bottom of the columnar cavity towards the axis of the outlet. So that the front and rear walls of the lower cavity form an asymmetric contraction structure, ensuring the flow area at the outlet end of the diffuser 2 flow passage in the lower cavity, ensuring a large inlet and outlet area ratio, increasing the diffusing effect, and enhancing the static pressure recovery ability of the exhaust cylinder.

[0027] Figures 3 - 4Shows the specific structure of the diffuser: The diffuser 2 includes an inner guide ring 201 and an outer guide ring 202; the outer guide ring 202 is coaxially sleeved outside the inner guide ring 201; the outer guide ring 202 and the inner guide ring 201 are in a horn shape that expands from the inlet end to the outlet end of the diffuser; the profile lines of the inner guide ring 201 and the outer guide ring 202 are both cubic Bézier curves. Taking the outer guide ring 202 as an example: As Figure 4 shown, the outer guide ring 202 is formed by an initial cubic Bézier curve (i.e., the connection line of the hollow control points in the figure) by adjusting each hollow control point to finally form the inner wall profile line 15, and rotating one week on the basis of the inner wall profile line 15. The inner walls of the inner guide ring 201 and the outer guide ring 202 are smooth and conform to the flow mechanism, thus avoiding the flow loss caused by the separation vortex in the diffuser 2; As Figure 3 、 Figure 5 shown: The outlet end face of the inner guide ring 201 is a folded surface structure, including a semi-circular plane 201a located below the axis of the diffuser 2 and an arc-shaped inclined plane 201b located above the semi-circular plane 201a. The arc-shaped inclined plane 201b is inclined from the upper end of the semi-circular plane 201a towards the inlet end of the diffuser 2, and the included angle between the arc-shaped inclined plane 201b and the axis of the diffuser 2 is the same as the included angle between the rear wall 5 of the upper cavity and the axis of the diffuser 2; The circumference of the semi-circular plane 201a is fixed to the rear wall of the lower cavity and the inner side of the frustum-shaped contraction cavity, and the circumference of the arc-shaped inclined plane 201b is fixed to the inner side of the rear wall 5 of the upper cavity. Due to the length limitation of the end of the inner guide ring 201 by the inclined plate structure of the rear wall 5 of the upper cavity, the inner guide ring 201 forms an asymmetric structure in the up and down directions. The large-sized guide ring structure effectively separates the different pressure regions between the wall surfaces of the outer guide ring 202 in the diffuser 2, enables the steam flow to flow orderly and controllably along the wall surfaces of the inner and outer guide rings 201 and 202, restricts the development of the steam flow vortex in the exhaust cylinder volute, and reduces the total pressure loss; At the same time, it ensures a sufficient inlet and outlet area ratio of the diffuser 2, effectively improves the pressure boosting performance of the diffuser 2, and ensures the static pressure recovery effect of the exhaust cylinder.

[0028] As Figure 5 、 Figure 7 shown: A first arc-shaped baffle 10 is provided between the front wall of the upper cavity and the arc-shaped side wall 6 in the exhaust cylinder volute; a second arc-shaped baffle 11 is provided between the rear wall of the upper cavity and the arc-shaped side wall 6. And the first arc-shaped baffle 10 and the front wall of the upper cavity and the arc-shaped side wall 6 enclose an arc-shaped cavity 14 with an isosceles triangle cross-section, and the second arc-shaped baffle 11 and the rear wall of the upper cavity and the arc-shaped side wall 6 enclose an arc-shaped cavity 14a with a triangle cross-section.

[0029] As Figure 8As shown in the figure: First baffles 12 are provided between the two sides of the front wall of the lower cavity in the exhaust cylinder volute and the adjacent side walls; second baffles 13 are provided between the two sides of the rear wall of the lower cavity and the adjacent side walls, and a prismatic cavity 16 with a triangular cross-section is formed between the first baffle 12 and the front wall and the adjacent side walls of the lower cavity. Similarly, a prismatic cavity 16 with a triangular cross-section is formed between the second baffle 13 and the rear wall and the adjacent side walls of the lower cavity. By adding the first arc-shaped baffle 10, the second arc-shaped baffle 11, the first baffle 12 and the second baffle 13, the eddy current loss caused by the end wall vortex formed by the fluid at the corner of the volute is reduced.

[0030] The above content is a further detailed description of the present invention in combination with specific preferred technical solutions, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A steam turbine exhaust cylinder with an asymmetric diffuser and volute structure, comprising an exhaust cylinder volute formed by splicing and fixing an upper cavity and a lower cavity that communicate with each other. An inlet port is provided on the front wall surface of the exhaust cylinder volute, and an outlet port is provided at the bottom of the exhaust cylinder volute. A diffuser is provided inside the exhaust cylinder volute. The inlet end of the diffuser is located at the inlet port and is coaxial with the inlet port. The upper cavity includes an upper cavity front wall, an upper cavity rear wall, and an arc-shaped side wall fixedly provided between the upper cavity front wall and the upper cavity rear wall. The lower cavity includes a columnar cavity. It is characterized in that, The rear wall of the upper cavity is inclined from the bottom of the upper cavity body to the top of the upper cavity body, and the distance between the rear wall of the upper cavity and the front wall of the upper cavity gradually decreases from the bottom of the upper cavity body to the top of the upper cavity body, so as to form an asymmetric volute structure with a thinner upper part and a thicker lower part; the lower cavity body further includes an inverted frustum-shaped contraction cavity arranged at the bottom of the columnar cavity; The inverted frustum-shaped contraction cavity includes a front wall of the contraction cavity, a rear wall of the contraction cavity and a side wall of the contraction cavity. The rear wall of the contraction cavity is a vertical plate body, and the front wall of the contraction cavity and the side wall of the contraction cavity are both inclined plate bodies inclined from the bottom of the columnar cavity towards the axis direction of the steam outlet, so as to form an asymmetric contraction structure on the front and rear walls of the lower cavity body; The diffuser includes an inner guide ring and an outer guide ring; the outer guide ring is coaxially sleeved outside the inner guide ring; the outer guide ring and the inner guide ring are trumpet-shaped that expand from the inlet end to the outlet end of the diffuser; the profile lines of the inner guide ring and the outer guide ring are both Bezier curves; the outlet end face of the inner guide ring is a folded surface structure, including a semi-circular plane located below the axis of the diffuser and an arc-shaped inclined plane located above the semi-circular plane. The arc-shaped inclined plane is inclined towards the inlet end direction of the diffuser from the upper end of the semi-circular plane, and the included angle between the arc-shaped inclined plane and the axis of the diffuser is the same as the included angle between the rear wall of the upper cavity and the axis of the diffuser; the circumference of the semi-circular plane is fixed to the inner side of the rear wall of the lower cavity and the frustum-shaped contraction cavity, and the circumference of the arc-shaped inclined plane is fixed to the inner side of the rear wall of the upper cavity, so that the inner guide ring forms an upper and lower asymmetric structure.

2. The steam turbine exhaust cylinder with an asymmetric diffuser and volute structure according to claim 1, wherein, A first arc-shaped baffle is arranged between the front wall of the upper cavity body and the arc-shaped side wall in the volute of the exhaust cylinder; a second arc-shaped baffle is arranged between the rear wall of the upper cavity body and the arc-shaped side wall; and the first arc-shaped baffle and the front wall of the upper cavity body and the arc-shaped side wall enclose an arc-shaped cavity with a triangular cross-section; the second arc-shaped baffle and the rear wall of the upper cavity body and the arc-shaped side wall enclose an arc-shaped cavity with a triangular cross-section; on both sides of the front wall of the lower cavity body in the volute of the exhaust cylinder, a first baffle is arranged between the front wall of the lower cavity body and the adjacent side wall; on both sides of the rear wall of the lower cavity body, a second baffle is arranged between the rear wall of the lower cavity body and the adjacent side wall, and the first baffle and the front wall of the lower cavity body and the adjacent side wall enclose a prismatic cavity with a triangular cross-section; The second baffle and the rear wall of the lower cavity body and the adjacent side wall enclose a prismatic cavity with a triangular cross-section.

3. The steam turbine exhaust cylinder with an asymmetric diffuser and volute structure according to claim 1, characterized in that, A condenser connection section extends from the bottom of the inverted frustum-shaped contraction cavity, and the condenser connection section is a columnar pipe section.

4. A steam turbine exhaust cylinder having an asymmetric diffuser and volute structure according to claim 1, characterized in that, The steam inlet is connected to the inlet end of the diffuser through a stepped inlet wall surface.

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