An exhaust system and design method based on a reversible power turbine including a turbine outlet working condition adaptive switching structure

Abstract

The purpose of the present invention is to provide an exhaust system and design method based on a reversible power turbine, including an adaptive switching structure for turbine outlet working conditions, including an adaptive transition baffle structure, a support plate structure, a turbine section, and an exhaust volute section. The adaptive transition baffle structure is located at the outlet end of the turbine middle casing. The working state of the adaptive transition baffle structure rotates and changes automatically with the blowing of the airflow in different flow channels of the turbine. The support plate structure is located between the turbine section and the exhaust volute section. When the reversing turbine of the present invention is in the forward working condition, the baffle opens outward to block the forward flow channel airflow from flowing back into the reverse flow channel, effectively reducing flow losses; when the reversing turbine is in the reverse working condition, the baffle contracts inward, which can also reduce the backflow loss to a certain extent. The exhaust volute can further expand the turbine outlet airflow to slow down and cool it down, and rotate the airflow direction by 90° to discharge vertically upward to meet emission standards.

Description

Technical Field

[0001] The present invention relates to a turbine, in particular to an exhaust system and a design method of the turbine. Background Art

[0002] As a leader in today's power equipment industry, gas turbines have garnered widespread attention from researchers and technicians since their inception. Regarded as the "Mount Everest" of the machinery manufacturing industry, gas turbines hold a strategic position in a country's national economy, energy, power, and machinery.

[0003] Gas turbines cannot reverse directly, requiring additional power transmission equipment to match the power turbine for reverse operation. The installation of this power transmission equipment increases the size, weight, and sailing resistance of the power system. Furthermore, the power transmission equipment has a power transmission limit, exceeding which comes at a significant cost. To address this shortcoming, Niu Xiying et al. (CN 109505664A) from the 703rd Research Institute of China Shipbuilding Industry Corporation invented and patented a dual-ducted integrated power turbine capable of direct reverse operation (comprising an inner duct forward turbine and an outer duct reverse turbine). This turbine significantly reduces the ship's reverse radius and significantly improves its maneuverability. However, due to the direct connection between the forward and reverse turbine flow paths, airflow backflow can occur during operation. The reverse volute (CN 109578141A) invented by Yu Shunwang et al. from the 703rd Research Institute, while well-suited to the turbine, does not address this backflow phenomenon or its solution.

[0004] The exhaust volute of a marine gas turbine is a critical component connecting the power turbine and the exhaust system, and is crucial to the overall performance of the gas turbine. Exhaust gas from the power turbine expands and deflects 90 degrees within the volute before being discharged into the exhaust system. The flow within the power turbine and the non-axisymmetric exhaust volute is tightly coupled and inherently unsteady. The flow interaction between the power turbine and the exhaust volute significantly influences the aerodynamic forces acting on the power turbine blades. Therefore, a well-designed flow profile within the exhaust volute is crucial. Summary of the Invention

[0005] The purpose of the present invention is to provide an exhaust system and design method based on a reversible power turbine that can solve problems such as backflow loss, leakage loss, and high-temperature deformation, including a turbine outlet working condition adaptive switching structure.

[0006] The object of the present invention is achieved like this:

[0007] The present invention is based on an exhaust system of a reversible power turbine and includes an adaptive switching structure for turbine outlet working conditions. The system is characterized in that it includes an adaptive transition baffle structure, a support plate structure, a turbine section, and an exhaust volute section. The adaptive transition baffle structure is located at the outlet end of the middle casing of the turbine. The working state of the adaptive transition baffle structure automatically rotates and changes with the blowing of airflow in different flow channels of the turbine. The support plate structure is located between the turbine section and the exhaust volute section.

[0008] The exhaust system of the present invention based on a reversible power turbine and including a turbine outlet working condition adaptive switching structure may also include:

[0009] 1. The adaptive transition baffle structure includes independent baffles, which are divided into two layers in a staggered arrangement. Each independent baffle is adjacent to an independent baffle on a different layer, and is separated from the baffles on the same layer by a baffle on a different layer. The independent baffles are arranged in a circumferential circle as a whole.

[0010] 2. The independent baffle includes a baffle body, a baffle sealing ring, a baffle limiting ring, and a baffle fixing base. The end of the baffle body is located in the baffle sealing ring, and the two are connected by a baffle connecting bolt. A baffle limiting ring is set between the end of the baffle body and the baffle sealing ring, and the baffle fixing base is connected to the baffle limiting ring.

[0011] 3. The baffle body is a curved baffle with an arc, and the baffle limiting ring is clearance-matched with the baffle body and the baffle sealing ring.

[0012] 4. The support plate structure includes a leading edge, a middle connecting section, and a trailing edge. The middle connecting section is a streamlined spline and is tangent to the leading edge and the trailing edge respectively. The leading edge and the trailing edge are in an arc shape.

[0013] 5. The exhaust volute section includes a diffuser section, a volute section, and a transition section. The inlet of the diffuser section is provided with a flange and bolt holes connected to the reverse turbine casing. The volute section is provided with a volute tongue structure, and its exterior is provided with ribs.

[0014] The present invention is based on a reversible power turbine and is characterized by an exhaust system design method including a turbine outlet working condition adaptive switching structure.

[0015] (1) Obtaining turbine design point operating parameters and turbine geometric parameters. The turbine design point operating parameters include speed, inlet total temperature and total pressure, and mass flow rate. The turbine geometric parameters include the casing and hub dimensions of the forward and reverse turbines.

[0016] (2) The relevant aerodynamic parameters of the turbine outlet are obtained through CFD numerical calculation, including the total temperature, total pressure and mass flow rate of the turbine outlet airflow;

[0017] (3) Preliminary design of exhaust volute;

[0018] (4) Establish a volute model and a turbine overall model, perform a combined CFD simulation of the turbine and volute, and obtain the flow field parameters related to the turbine outlet and the flow field near the exhaust volute outlet;

[0019] (5) Design the turbine outlet transition baffle. Determine the baffle length and thickness based on the flow field velocity. Determine the baffle rotation angle based on the flow field velocity direction. Then determine the number of baffles, the baffle upper and lower layered arrangement, and the shape of the restriction ring.

[0020] (6) Re-establish the overall flow model of the turbine and volute and perform joint CFD simulation calculations to obtain the complete exhaust system flow state, analyze the overall flow loss of the volute, analyze the turbine efficiency and loss under forward and reverse conditions, and analyze whether there is a more obvious atmospheric recirculation phenomenon near the exhaust volute airflow outlet;

[0021] (7) Based on the analysis of step (6), it is concluded whether the exhaust system flow requirements are met. If not, return to step (3) to optimize the volute design, return to step (5) to optimize the turbine outlet baffle design, and if so, proceed to step (8);

[0022] (8) Design the flange at the volute inlet, and match the size, thickness, and screw holes to the turbine casing outlet. Perform an overall strength analysis of the volute, including the shear stress on the volute caused by the internal fluid flow pressure and the external atmospheric pressure, and the thermal stress caused by the high-temperature airflow inside the volute. Select the material based on the maximum stress and thermal stress. Further analyze and determine the number, size, and layout of the support plates, the number of ribs at the volute tongue, and the thickness of the volute shell based on the properties of the selected material.

[0023] The exhaust system design method of the present invention based on a reversible power turbine including a turbine outlet operating condition adaptive switching structure may also include:

[0024] 1. Step (3) is specifically:

[0025] The design of the volute requires knowledge of the exhaust system's design requirements, including the exhaust system's total axial length L0, the exhaust system's upper height limit H0, and exhaust gas emission requirements, including exhaust temperature and velocity requirements. When designing the volute, allowance should be made for the turbine outlet transition baffle and support plate (L1). The total axial length of the volute is then calculated as L2 = L0 - L1.

[0026] Diffuser section: The volute expansion section is preliminarily designed based on the turbine outlet airflow velocity and the required exhaust speed. According to the mass flow conservation and expansion ratio definition, the following formula is used:

[0027]

[0028] Among them, v1 and v2 are the turbine outlet velocity and the expansion section outlet velocity respectively; S1 and S2 are the volute inlet cross-sectional area and the transition section outlet cross-sectional area respectively, and S1 to S2 is the expansion ratio; r1 is the turbine hub radius, r2 is the turbine casing radius, and r3 is the volute expansion section outlet casing radius; the total length of the expansion section is selected between 0.5L2 and 0.6L2;

[0029] Volute section: Based on the geometric parameters related to the reverse turbine outlet and the diffuser outlet, a three-segment broken line is preliminarily designed. The total length of the volute section is the total length of the volute minus the length of the diffuser section. The end height H1 of the vertical line is greater than the radius r3 of the diffuser section outlet. The volute tongue structure further expands the airflow, leaving a margin for the contraction section of the transition section.

[0030] Transition section: preliminarily designed according to the overall size requirements of the exhaust system and volute, the transition section is in the shape of a quadrangular pyramid with a total height of H2=H0-H1. The transition section adopts a contraction section to ensure that the airflow outlet has a speed that prevents atmospheric backflow.

[0031] The advantages of the present invention are:

[0032] 1. A transition baffle designed to adapt to the operating conditions is located at the outlet of the reversing power turbine casing. This effectively blocks airflow from the forward flow channel into the reverse flow channel during forward operation. It also partially blocks backflow during reverse operation.

[0033] 2. The transition baffle is designed with a limiting ring to limit the baffle's rotation angle. The baffle is relatively thin and made of low-density, lightweight, and heat-resistant material, so that the baffle can complete its rotation only by the airflow and the limiting ring.

[0034] 3. The cross-section of the support plate is streamlined, which can minimize flow loss while maintaining support strength;

[0035] 4. Summarize the exhaust system design optimization methods, including the transition section baffle, support plate, and volute design optimization methods. Combining CFD simulation calculations and strength analysis makes the design optimization process more reasonable and faster. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the meridian plane of the overall model;

[0037] Figure 2 This is a cross-sectional view of the turbine outlet transition section baffle;

[0038] Figure 3 This is the end view of the turbine outlet transition section;

[0039] Figure 4 The relative position of the baffle and the airflow state under the forward working condition;

[0040] Figure 5 The relative position of the baffle and the airflow state in the reverse working condition;

[0041] Figure 6 The baffle status under forward working condition;

[0042] Figure 7 It indicates the baffle status in reverse working condition;

[0043] Figure 8a The support plate layout and cross-section diagram are shown in Figure 1. Figure 8b It is AA view;

[0044] Figure 9 This is a cross-sectional view of the volute;

[0045] Figure 10 This is the axial view of the volute;

[0046] Figure 11 Flowchart of the design optimization method. DETAILED DESCRIPTION

[0047] The present invention will be described in more detail below with reference to the accompanying drawings:

[0048] Combine Figure 1-11 The exhaust system of the present invention, based on a reversible power turbine and including a turbine outlet operating condition adaptive switching structure, comprises a turbine transition baffle 1, a support plate 2, and an exhaust volute section 3. The turbine section 4, which coordinates with the entire model, includes a forward flow channel 4-1 and a reverse flow channel 4-2.

[0049] The turbine outlet adaptive baffle 1 is located at the outlet end of the turbine's intermediate casing and is composed of several independent baffles. The baffles are arranged in a circumferential circle and divided into two staggered layers. Each baffle is adjacent to a baffle on a different layer, and each baffle on the same layer is separated by a baffle on a different layer. The baffle's operating state automatically rotates and changes with the airflow in different turbine flow paths, achieving an adaptive effect. A method for optimizing the overall design of the exhaust system, including the baffles, is also provided.

[0050] The working mode of the turbine outlet transition section baffle: Figure 2 、 Figure 3As shown, a single baffle consists of a baffle body 1-1, a baffle sealing ring 1-2, a baffle restraining ring 1-3, baffle connecting bolts 1-4, and a baffle fixing base 1-5. The baffle body is an inwardly curved, curved plate-like structure that can rotate along its central axis. The baffle internal restraining ring and the baffle fixing base are fixed structures. The baffle fixing base is fixed to the gas turbine casing, and the baffle internal restraining ring is fixed to the baffle fixing base. The baffle internal restraining ring ensures the baffle can rotate within a certain angular range, while the baffle fixing base also fixes the circumferential position of the baffle. The baffle sealing ring is connected to the baffle via bolts 1-4 and rotates with the baffle, ensuring that the baffle is fixed to the restraining ring and can rotate within the angle limited by the restraining ring.

[0051] like Figure 4 、 Figure 6 As shown, the baffles are arranged in two compact layers, 1-6-1, each consisting of four separate, complete baffles, spaced 45° apart from each other, 1-6-3, for a total of eight baffles across the two layers. Each baffle has a 60° circumferential angle, overlapping the baffles on either side by 15°, 1-6-3. This ensures a tight seal in both open and closed states. Figure 4 It shows that the relative position when the vehicle is working is 1-6-1, and the airflow working state is 1-6-2. Figure 5 When working in reverse, the relative position is 1-7-1, and the airflow working state is 1-7-2. When working in forward working state, the airflow flows out from the forward turbine flow channel and blows the baffle upward. Figure 6 As shown in the figure. Due to the rotation angle limit of the limiting ring, the baffle position will be limited to a fixed angle. Similarly, when working in reverse mode, the airflow flows out from the reverse turbine flow channel and blows the baffle downward. The baffle state is as follows Figure 7 shown.

[0052] How the support plate works: The cross-section of the support plate is shown in Figure 8. Both the leading edge 2-1 and the trailing edge 2-2 are arc-shaped. The intermediate connecting section 2-3 is composed of streamlined splines, tangent to the leading and trailing edges to minimize flow disruption. The support plate's primary purpose is to support the volute's strength and, secondarily, to provide some flow regulation at the turbine outlet.

[0053] The working mode of the exhaust volute: Figure 9 and Figure 10As shown, the exhaust volute consists of a diffuser section 3-1, a volute section 3-2, and a transition section 3-3. The diffuser section inlet is designed with a flange and bolt holes 3-4 to facilitate connection to the reverse turbine casing. The ratio of the diffuser section's outlet cross-sectional area to its inlet cross-sectional area is called the diffusion ratio. The diffuser section further expands the turbine outlet airflow, slowing and cooling it. Due to the presence of the volute tongue structure 3-5, the volute section is designed with ribs 3-6 on the outer shell to increase its strength. The airflow changes direction as it passes through the volute section. The continuous zigzag design of the volute section's inner shell reduces flow losses and facilitates manufacturing. The transition section connects to the outside atmosphere. After the airflow is decelerated and cooled in the diffuser section and the volute section changes its direction, it essentially meets emission requirements in the transition section. During variable operating conditions of the gas turbine, the transition section prevents some atmospheric backflow.

[0054] Based on the above model, the exhaust system design optimization method is summarized as shown in the figure.

[0055] (1) The turbine design point operating parameters (speed, inlet total temperature and pressure, mass flow rate) and turbine geometric parameters (casing and hub dimensions of the forward and reverse turbines) are known.

[0056] (2) The relevant aerodynamic parameters of the turbine outlet (total temperature, total pressure, and mass flow rate of the turbine outlet airflow) are obtained through CFD numerical calculation.

[0057] (3) Preliminary design of exhaust volute.

[0058] Volute design requires knowledge of exhaust system design requirements, including the system's total axial length (L0), the system's maximum height (H0), and exhaust gas emission requirements, including exhaust temperature and velocity. The volute design requires space (L1) for the turbine outlet transition baffle and support plate. Therefore, the total axial length of the volute is calculated as L2 = L0 - L1.

[0059] Diffuser section: The volute expansion section is preliminarily designed based on the turbine outlet airflow velocity and the required exhaust velocity. Based on the mass flow conservation and the definition of the expansion ratio, the following formula is used:

[0060]

[0061] Where v1 and v2 are the turbine outlet (volute inlet) and expansion section outlet velocities, respectively; S1 and S2 are the volute inlet and transition section outlet cross-sectional areas, respectively. The ratio of S1 to S2 is the expansion ratio; r1 is the turbine hub radius, r2 is the turbine casing radius, and r3 is the volute expansion section outlet casing radius. The expansion section outlet velocity does not need to strictly meet the required exhaust speed. The total expansion section length should be selected to be approximately 0.5L2 to 0.6L2.

[0062] Volute section: Based on the geometric parameters related to the outlet of the reverse turbine and the outlet of the diffuser, three broken lines are preliminarily designed. It should be noted that the second straight line should be kept at about 45° as much as possible, and the first and third straight lines should have basically the same angles with the horizontal and vertical directions respectively and should be selected moderately. The lengths of the three straight lines are selected according to the geometric requirements of the exhaust casing outlet. Since the volute section is between the diffuser section and the transition section, special attention should be paid to matching the two. The total length of the volute section should be the total length of the volute minus the length of the expansion section. The end height H1 of the vertical line should be greater than the outlet radius r3 of the expansion section. The volute tongue structure further expands the airflow to reserve a margin for the contraction section of the transition section.

[0063] Transition section: Preliminary design based on the exhaust system and overall volute size requirements. The transition section is in the shape of a quadrangular pyramid, with a total height of H2 = H0 - H1. The transition section uses a tapered cross-section to ensure a certain airflow velocity at the outlet, effectively preventing atmospheric backflow.

[0064] (4) Based on (3), a preliminary volute design has been obtained, and a volute model and a turbine overall model have been established. A combined CFD simulation of the turbine and volute is performed to obtain the relevant parameters of the turbine outlet flow field and the flow field near the exhaust volute outlet (transition section).

[0065] (5) Based on the turbine outlet flow field parameters obtained in (4), the turbine outlet transition baffle design begins. The baffle length and thickness are determined based on the flow field velocity, and the baffle rotation angle is determined based on the flow field velocity direction. The number of baffles, the upper and lower layered arrangement of the baffles, and the shape of the confinement ring are then determined.

[0066] (6) The turbine outlet transition baffle model has been obtained through (5). The overall flow model of the turbine and volute is re-established and a joint CFD simulation is performed to obtain the complete exhaust system flow state. The overall flow loss of the volute is analyzed, and the turbine efficiency and loss under forward and reverse conditions are analyzed respectively. It is analyzed whether there is a more obvious atmospheric recirculation phenomenon near the exhaust volute airflow outlet (transition section).

[0067] (7) Based on the analysis in (6), conclude whether the exhaust system flow requirements are met. If not, return to (3) to optimize the volute design and return to (5) to optimize the turbine outlet baffle design. If so, proceed to (8).

[0068] (8) Design the flange at the volute inlet, and make sure that its size, thickness, and screw holes match those of the turbine casing outlet. Perform an overall strength analysis of the volute, including the shear stress on the volute caused by the internal fluid flow pressure and the external atmospheric pressure, and the thermal stress caused by the high-temperature airflow inside the volute. Select materials based on the maximum stress and thermal stress. Either traditional nickel-based high-temperature resistant alloys or new carbon fiber materials can be selected. Further analysis is performed based on the properties of the selected materials to determine the number, size, and layout of the support plates, the number of ribs at the volute tongue, and the thickness of the volute casing. It should be noted that the influence of the support plate timing effect on the flow must also be considered in the design of the support plates to minimize flow losses.

[0069] The turbine in step (1) is a known turbine that requires an exhaust system. The flow field analysis is based on CFD simulation calculations, and the main parameters are the turbine outlet mass flow rate, total temperature, total pressure, and outlet airflow angle.

[0070] Step (2) The design of the volute requires knowledge of the exhaust system design requirements, including the total axial length of the exhaust system L0, the upper limit of the exhaust system height H0, and the exhaust gas emission requirements: including the exhaust temperature requirements and the exhaust velocity requirements. When designing the volute, it is necessary to reserve the space L1 required for the turbine outlet transition section baffle and support plate, so the total axial length of the volute is L2 = L0-L1. The volute expansion section is preliminarily designed based on the turbine outlet airflow velocity and the required exhaust speed. According to the mass flow conservation and the definition of the expansion ratio, the following formula is obtained:

[0071]

[0072] Where v1 and v2 are the airflow velocities at the turbine outlet (volute inlet) and the expansion section outlet, respectively; S1 and S2 are the cross-sectional areas of the volute inlet and the transition section outlet, respectively, with the ratio of S1 to S2 being the expansion ratio; r1 is the turbine hub radius, r2 is the turbine casing radius, and r3 is the volute expansion section outlet casing radius. The expansion section outlet airflow velocity does not need to strictly meet the exhaust requirement. The total expansion section length should be approximately 0.5L2 to 0.6L2.

[0073] The inner shell of the volute section consists of three fold lines and a vertical line. The angle of the middle fold line should be maintained between 30° and 60°, and the turning angles of the front and rear fold lines should be as consistent as possible. The total length of the volute section should be the total length of the volute minus the length of the expansion section. The end height H1 of the vertical line should be greater than the radius r3 of the expansion section outlet. The overall shape of the transition section is a square pyramid, with a total height of H2 = H0 - H1.

[0074] In step (3), the position of the outlet transition baffle is selected according to the position of the turbine middle casing, the number and size of the baffles are selected according to the combined CFD simulation calculation of the turbine and volute, and the axial length of the baffle is selected according to the flow field streamline.

[0075] Step (4) Establish an overall flow model of the turbine and exhaust system for CFD simulation. Optimization includes parameters such as the number, length, size, and thickness of the transition baffles; and the position of the volute transition section and volute tongue. This ensures that the volute exhaust parameters meet the standards while minimizing atmospheric backflow at the volute outlet.

[0076] Step (5) simulates the strength of the exhaust system, including the pressure caused by the internal and external pressure difference and the thermal stress caused by the internal and external temperature difference. Then, the volute material is selected, considering the material's thermal conductivity, thermal expansion coefficient, and allowable stress. Based on the selected material, the support plate, volute body, and ribs at the volute tongue are further designed. In addition, after fully considering the strength factor, the support plate design must also consider the timing effect caused by the turbine outlet airflow to minimize airflow loss.

[0077] Example:

[0078] The overall layout of the baffles is divided into two layers of baffles 1-6-1 and 1-7-1 arranged compactly above and below, each consisting of 4 to 6 separate complete baffles, for a total of 8 to 12 baffles. The circumferential angle of each baffle is 25° to 70°, overlapping with the baffles of different layers on both sides by 5° to 15°, 1-6-3 and 1-7-3, respectively, to ensure that the baffle as a whole can fully block backflow when opening and closing. When the baffle is open, it is the forward working state of the turbine, and when the baffle is closed, it is the reverse working state of the turbine. The working state switching relies on the airflow in different flow channels of the turbine to make the baffle move, so as to achieve the effect of the baffle adapting to the working conditions.

[0079] This new turbine outlet transition section design effectively prevents backflow from the forward flow path into the reverse flow path during forward operation. It blocks approximately 0.8 kg / s of backflow, reduces blower power loss by approximately 98.59 kW, and improves efficiency by approximately 0.39%. The baffle is constructed of a new, high-temperature-resistant, low-density material to ensure it remains actuated.

Claims

1. An exhaust system based on a reversible power turbine including a turbine outlet operating condition adaptive switching structure, characterized by: It includes an adaptive transition baffle structure, a support plate structure, a turbine section, and an exhaust volute section. The adaptive transition baffle structure is located at the outlet end of the middle casing of the turbine. The working state of the adaptive transition baffle structure rotates and changes automatically with the blowing of airflows in different flow channels of the turbine. The support plate structure is located between the turbine section and the exhaust volute section. The baffle can be blown up and down, and the working state switching depends on the blowing of airflows in different flow channels of the turbine to make the baffle move, so as to achieve the effect of the baffle adapting to the working condition. The baffle material adopts high-temperature resistant and low-density material to ensure that the baffle can be blown.

2. The exhaust system based on a reversible power turbine and including a turbine outlet operating condition adaptive switching structure according to claim 1, characterized in that: The adaptive transition baffle structure includes independent baffles, which are divided into two layers in an upper and lower layer arranged in a staggered manner. Each independent baffle is adjacent to an independent baffle on a different layer, and is separated from a baffle on the same layer by a baffle on a different layer. The independent baffles are arranged in a circumferential circle as a whole.

3. The exhaust system based on a reversible power turbine and including a turbine outlet operating condition adaptive switching structure according to claim 2, characterized in that: The independent baffle includes a baffle body, a baffle sealing ring, a baffle limiting ring, and a baffle fixing base. The end of the baffle body is located in the baffle sealing ring, and the two are connected by a baffle connecting bolt. A baffle limiting ring is arranged between the end of the baffle body and the baffle sealing ring, and the baffle fixing base is connected to the baffle limiting ring.

4. The exhaust system based on a reversible power turbine and including a turbine outlet operating condition adaptive switching structure according to claim 3, characterized in that: The baffle body is a curved baffle with an arc, and the baffle limiting ring is clearance-matched with the baffle body and the baffle sealing ring.

5. The exhaust system based on a reversible power turbine and including a turbine outlet operating condition adaptive switching structure according to claim 1, characterized in that: The support plate structure includes a leading edge, a middle connecting section, and a trailing edge. The middle connecting section is a streamlined spline and is tangent to the leading edge and the trailing edge respectively. The leading edge and the trailing edge are in an arc shape.

6. The exhaust system based on a reversible power turbine and including a turbine outlet operating condition adaptive switching structure according to claim 1, characterized in that: The exhaust volute section includes a diffuser section, a volute section, and a transition section. The inlet of the diffuser section is provided with a flange and bolt holes connected to the reverse turbine casing. The volute section is provided with a volute tongue structure, and its exterior is provided with ribs.

7. A design method for an exhaust system based on a reversible power turbine, including a turbine outlet operating condition adaptive switching structure, characterized by: (1) Obtaining turbine design point operating parameters and turbine geometric parameters. The turbine design point operating parameters include speed, inlet total temperature and total pressure, and mass flow rate. The turbine geometric parameters include the casing and hub dimensions of the forward and reverse turbines. (2) The relevant aerodynamic parameters of the turbine outlet are obtained through CFD numerical calculation, including the total temperature, total pressure and mass flow rate of the turbine outlet airflow; (3) Preliminary design of exhaust volute; (4) Establish a volute model and a turbine overall model, perform a combined CFD simulation of the turbine and volute, and obtain the flow field parameters related to the turbine outlet and the flow field near the exhaust volute outlet; (5) Design the adaptive transition baffle at the turbine outlet. Determine the baffle length and thickness based on the flow field velocity, determine the baffle rotation angle based on the flow field velocity direction, and then determine the number of baffles, the upper and lower layered arrangement of the baffles, and the shape of the restriction ring. The working state of the adaptive transition baffle structure rotates and changes automatically with the blowing of airflow in different flow channels of the turbine; (6) Re-establish the overall flow model of the turbine and volute and perform joint CFD simulation calculations to obtain the complete exhaust system flow state, analyze the overall flow loss of the volute, analyze the turbine efficiency and loss under forward and reverse conditions, and analyze whether there is a more obvious atmospheric recirculation phenomenon near the exhaust volute airflow outlet; (7) Based on the analysis of step (6), it is concluded whether the exhaust system flow requirements are met. If not, return to step (3) to optimize the volute design, return to step (5) to optimize the turbine outlet baffle design, and if so, proceed to step (8); (8) Design the flange at the volute inlet, and match the size, thickness, and screw holes to the turbine casing outlet. Perform an overall strength analysis of the volute, including the shear stress on the volute caused by the internal fluid flow pressure and the external atmospheric pressure, and the thermal stress caused by the high-temperature airflow inside the volute. Select the material based on the maximum stress and thermal stress. Further analyze and determine the number, size, and layout of the support plates, the number of ribs at the volute tongue, and the thickness of the volute shell based on the properties of the selected material.

8. The exhaust system design method based on a reversible power turbine including a turbine outlet operating condition adaptive switching structure according to claim 7, characterized in that: Step (3) is specifically as follows: The design of the volute requires knowledge of the exhaust system's design requirements, including the exhaust system's total axial length L0, the exhaust system's upper height limit H0, and exhaust gas emission requirements, including exhaust temperature and velocity requirements. When designing the volute, allowance should be made for the turbine outlet transition baffle and support plate (L1). The total axial length of the volute is then calculated as L2 = L0 - L1. Diffuser section: The volute expansion section is preliminarily designed based on the turbine outlet airflow velocity and the required exhaust speed. According to the mass flow conservation and expansion ratio definition, the following formula is used: Among them, v1 and v2 are the turbine outlet velocity and the expansion section outlet velocity respectively; S1 and S2 are the volute inlet cross-sectional area and the transition section outlet cross-sectional area respectively, and S1 to S2 is the expansion ratio; r1 is the turbine hub radius, r2 is the turbine casing radius, and r3 is the volute expansion section outlet casing radius; the total length of the expansion section is selected between 0.5L2 and 0.6L2; Volute section: Based on the geometric parameters related to the reverse turbine outlet and the diffuser outlet, a three-segment broken line is preliminarily designed. The total length of the volute section is the total length of the volute minus the length of the diffuser section. The end height H1 of the vertical line is greater than the radius r3 of the diffuser section outlet. The volute tongue structure further expands the airflow, leaving a margin for the contraction section of the transition section. Transition section: preliminarily designed according to the overall size requirements of the exhaust system and volute, the transition section is in the shape of a quadrangular pyramid with a total height of H2=H0-H1. The transition section adopts a contraction section to ensure that the airflow outlet has a speed that prevents atmospheric backflow.

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