Cooling double seal and anti-backflow system based on external air entrainment and design method thereof

Abstract

This invention belongs to the field of aero-engine thermal management technology, and provides a cooling dual-sealing anti-backflow system based on bypass bleed air and its design method. It includes a streamlined bleed air duct on the inner wall of the bypass duct to draw in low-temperature airflow; a turbine rear support integrating bleed air cooling function and internally equipped with a cavity support plate and load-bearing strut; a collection chamber collecting the airflow passing through the turbine rear support; and a cooling-sealing distribution unit, including an afterburner inner cone, a low-pressure turbine disk, and a bearing cavity. The outlet of the collection chamber is connected to a bypass bleed air port, a shared channel for the labyrinth seal and the comb-honeycomb seal structure, and a film vent on the peripheral wall of the afterburner inner cone, achieving multi-module coordinated cooling, sealing, thermal insulation, and pressure regulation functions. This invention features high integration, compact structure, low flow resistance, and high energy efficiency. It eliminates the need for high-pressure bleed air or active control, effectively preventing gas backflow and improving the cooling effect and sealing reliability of key components.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine thermal management technology, and relates to a cooling dual-seal anti-backflow system based on bypass bleed air and its design method. Background Technology

[0002] The hot-end components of the aft body of an aero-engine operate in extremely harsh environments for extended periods. In particular, the inner cone of the afterburner is directly exposed to high-temperature exhaust gases and experiences extremely high heat flux. Its cooling efficiency directly determines the service life of these components. However, excessive flow resistance in the cooling channels can lead to a decrease in pressure within the channels, creating a pressure differential that drives the backflow of high-temperature exhaust gases. This can not only cause high-temperature exhaust gases to flow backward into the cooling channels, affecting the low detectability requirements of the afterburner inner cone, but in extreme cases, it can even lead to the ablation of the inner cone.

[0003] At the same time, the low-pressure turbine rotor-stator clearance area also faces the risk of high-temperature gas backflow. Once gas backflow occurs, it will directly heat the turbine rotor and support bearings, accelerating their low-cycle fatigue failure, and may invade the bearing cavity, causing high-temperature deterioration of the lubricating oil and seal failure, ultimately leading to serious mechanical failures such as bearing seizure.

[0004] Furthermore, the turbine rear support, as a core load-bearing component, must simultaneously withstand mechanical loads and the radiation and convective heat of high-temperature combustion gases. This high concentration of heat loads easily leads to problems such as inconsistent thermal deformation and structural stress concentration, severely impacting structural integrity and service life. Traditionally, cooling of the turbine rear support relies on core engine bleed air or an independent cooling circuit. This approach suffers from drawbacks such as high cooling air consumption, complex flow paths, and disconnection from other thermal management functions.

[0005] The main solution to the above problems currently relies on bleed air from the high-pressure compressor's afterstage to meet basic cooling and sealing requirements. However, this method consumes approximately 1% to 3% of the core engine's airflow, significantly sacrificing engine thrust and fuel economy. To overcome this drawback, some existing technologies attempt to use a cryogenic air source from the bypass duct as an alternative, but these solutions generally suffer from the following bottlenecks:

[0006] 1. The separate design of the bleed air device and the rear support of the turbine increases the length of the bleed air path and the number of turns, resulting in increased flow resistance loss; the lack of a two-way anti-backflow design for the cooling channel and the rear sealing cavity of the disc can easily lead to gas backflow and insufficient cooling of the casing.

[0007] 2. The various functional modules (cooling, rear disc seal, bearing seal, turbine rear support cooling) mostly use independent air sources and parallel flow paths, resulting in low overall utilization of cold air. To compensate for high flow resistance and low efficiency, it is often necessary to introduce more than 5% of the bypass flow, which has a negative impact on engine performance.

[0008] 3. The extensive use of regulating valves and complex electronic control systems for flow distribution increases the system's weight, cost, and complexity, and poses a risk of system failure due to actuator, sensor, or controller malfunctions. Furthermore, existing systems struggle to adaptively adjust to changes in thermal load under different operating conditions.

[0009] 4. It failed to effectively prevent backflow of gas from the cooling channel of the afterburner and the low-pressure turbine disk, and could not provide comprehensive and reliable backflow protection.

[0010] Therefore, there is an urgent need to design a system with high integration, simplified architecture, high energy efficiency and enhanced backflow prevention to fundamentally solve industry pain points such as high flow resistance loss, low cold air utilization rate and failure of gas backflow prevention and control, and fill the gap in the field of dual sealing technology for bleed air of aero-engines. Summary of the Invention

[0011] To address the technical problems existing in the cooling and sealing systems of hot-end components of aero-engine rear bodies, such as high flow resistance loss, low cold gas utilization, high risk of gas backflow, poor system integration, and insufficient reliability due to reliance on active control, this invention discloses a cooling dual-sealing anti-backflow system based on bypass bleed air and its design method.

[0012] Specifically, the technical solution for implementing the present invention is as follows: On the one hand, the present invention provides a cooling dual-seal anti-backflow system based on duct air intake, the system including a duct air intake unit, a turbine rear support with integrated duct air intake cooling function, and a cooling-seal distribution unit.

[0013] The duct air intake unit includes a streamlined air intake duct installed on the inner wall of the duct, used to draw low-temperature airflow from the duct. The turbine rear support is provided with a cavity support plate and a load-bearing column, which are used to guide the outer bypass airflow introduced by the streamlined air duct to pass through the wall for heat exchange and cooling, and to collect the cooled airflow into the air collection chamber located downstream of the turbine rear support. The cooling-sealing distribution unit includes an inner cone with added force, a low-pressure turbine disk, and a bearing cavity. The outlet of the gas collection cavity is connected to the following three paths: (a) Bypass air vent: The first low-temperature airflow is discharged from the gas collection chamber, forms a heat insulation and protective layer on the surface of the inner casing and merges into the main flow channel to regulate the local pressure and temperature field. (b) The labyrinth seal on the rear side of the low-pressure turbine disk and the comb-honeycomb sealing structure of the bearing cavity share a common channel. The second low-temperature airflow enters the labyrinth seal and the comb-honeycomb sealing structure respectively through the common channel, forming a double sealing barrier. (c) The air film holes opened on the peripheral wall of the inner cone of the force-adding body, through which the third low-temperature airflow is injected to form a cooling air film covering the surface of the inner cone; The system satisfies the following conditions: the total pressure loss coefficient of the low-temperature airflow from the streamlined air intake to the air collection chamber outlet is ≤5%, and the comprehensive utilization rate of cold air is ≥90%.

[0014] Furthermore, the amount of low-temperature airflow drawn by the streamlined air intake duct is 3% to 4% of the total flow rate of the outer bypass.

[0015] Furthermore, the peripheral wall at the rear end of the inner cone has multiple air film holes, and the inlet of the air film holes is a funnel-shaped diffuser structure; wherein, the total pressure loss coefficient of the cooling channel of the inner cone is ≤8%, and the comprehensive cooling efficiency is ≥0.85.

[0016] Furthermore, the labyrinth seal is disposed on the mating end face of the rotor and stator behind the low-pressure turbine disk, and its air inlet is connected to the gas collecting chamber. The pressure in the sealing chamber behind the low-pressure turbine disk is... With the mainstream gas pressure after the turbocharger satisfy: Cooling seal flow rate satisfy: ,in, Where A is the flow coefficient and A is the area of ​​the sealing annulus. To ensure the density of the sealed cold air.

[0017] Furthermore, the air inlet of the comb-honeycomb sealing structure is connected to the air collection chamber, and together with the labyrinth seal, forms a double sealing barrier.

[0018] On the other hand, the present invention provides a design method for the above-mentioned cooling dual-seal anti-backflow system based on duct air intake, the method comprising the following steps: S1: Set the air intake from the low-temperature airflow in the duct to 3% to 4% of the total flow rate of the duct, and design a streamlined air intake duct on the inner wall of the duct based on this air intake. S2: Based on the constraint that the total pressure loss coefficient from the streamlined air intake to the air collection chamber outlet is ≤5%, design the cooling channel structure inside the turbine rear support; S3: Based on the constraint that the ratio between the low-pressure turbine disk back sealing chamber pressure and the turbine back mainstream gas pressure is greater than 1.02, determine the gas supply capacity of the labyrinth seal and the comb-honeycomb seal structure. S4: Configure the outlet flow path of the gas collecting chamber to distribute the low-temperature airflow in the gas collecting chamber to the following three functional branches: (a) The air film cooling branch of the inner cone of the force-applying structure; (b) The rear panel seal and the bearing cavity sealing branch; (c) Bypass vent insulation and protection branch; S5: Based on the low-temperature airflow distribution ratio of the three functional branches and their corresponding heat-work conversion effect, calculate the comprehensive utilization rate of cold air; if the calculation result is less than 90%, adjust the intake air volume, cooling channel structure or outlet flow path configuration until the performance requirements are met.

[0019] Furthermore, when calculating the heat-work conversion effect of the air film cooling branch, the aperture, inclination angle and spacing of the air film holes are configured so that the total pressure loss coefficient of the cold air flowing through the inner cone cooling channel is ≤8% and the overall cooling efficiency is ≥0.85.

[0020] Furthermore, when determining the air supply capacity of the rear-disc seal and bearing cavity sealing branch, the flow area of ​​the labyrinth seal and the comb-honeycomb seal structure are configured, and the pressure of the low-pressure turbine rear-disc seal cavity is determined. With the mainstream gas pressure after the turbocharger satisfy: Cooling seal flow rate satisfy: ,in, Where A is the flow coefficient and A is the area of ​​the sealing annulus. To ensure the density of the sealed cold air.

[0021] Furthermore, when configuring the outlet flow path of the air collection chamber, the flow distribution ratio of the three functional branches is coordinated to ensure that the overall utilization rate of the system's cooling air is ≥90%.

[0022] Compared to traditional aircraft engine cooling and sealing systems, this invention possesses significant technical advantages and engineering value. The system of this invention has the following advantages: 1. Simplified architecture and extremely low flow resistance: This invention adopts a centralized cooling and multi-path parallel integrated architecture, eliminating redundant throttling components and complex flow paths, resulting in smoother airflow delivery, a lighter system structure, significantly reduced processing and assembly costs, and wider adaptability. The total pressure loss coefficient from the induced draft fan inlet to the air collection chamber outlet is ≤5%, demonstrating excellent system flow resistance control.

[0023] 2. Improved energy efficiency and energy saving: By establishing a direct quantitative relationship between flow resistance and air utilization rate, the traditional qualitative design barrier is broken through. The comprehensive utilization rate of air is ≥90%, which is significantly improved compared with the traditional solution. It does not require the consumption of high-pressure compressor working fluid, effectively reduces engine thrust loss, and greatly improves fuel economy.

[0024] 3. Dual-sealing protection, high reliability: Adopting a pressure-flow coordinated management mechanism, the flow rate is adaptively distributed through the full flow path flow resistance network. Combined with dual sealing and pressure margin constraints, the backflow channel of the gas is completely blocked, ensuring efficient cooling of the inner cone of the booster, reliable sealing behind the low-pressure turbine disk, and stable sealing of the bearing cavity, thus extending the service life of key hot-end components.

[0025] 4. Optimize pressure distribution and suppress gas backflow: By using the bypass air vent, the regulated cold air is reinjected into the inner casing cooling channel, which increases the local pressure after the turbine, suppresses the formation of local low-pressure areas, weakens the pressure driving conditions for gas backflow, and improves the overall machine operation stability.

[0026] 5. The entire system has quantifiable and controllable indicators and strong engineering applicability: The system indicators are quantifiable and measurable, and the parameters are adjustable. There is no need for a complex active control unit. It is compatible with multiple types of engines, facilitates engineering modification and mass production application, and has extremely high promotion value. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of a cooling double-seal anti-backflow system based on duct air intake disclosed in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the design method of a cooling dual-seal anti-backflow system based on duct air intake disclosed in an embodiment of the present invention. Among them, 1. outer bypass duct; 2. streamlined duct air duct; 3. turbine rear support; 4. cavity support plate; 5. reinforcing inner cone; 6. film gas vent; 7. low-pressure turbine disk; 8. grate-honeycomb sealing structure; 9. bypass duct air vent; 10. bearing cavity; 11. labyrinth seal; 12. main duct; 13. gas collection cavity; 14. load-bearing support; 15. inner casing. Detailed Implementation

[0029] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0030] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features of the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] This invention provides a cooling dual-seal anti-backflow system based on duct air intake, the system including a duct air intake unit, a turbine rear support 3 with integrated duct air intake cooling function, and a cooling-seal distribution unit.

[0032] Specifically, such as Figure 1 The outer duct air intake unit includes a streamlined air intake fan 2 installed on the inner wall of the outer duct 1, which is used to draw low-temperature airflow from the outer duct 1.

[0033] The turbine rear support 3 is provided with a cavity support plate 4 and a load-bearing column 14 inside, which are used to guide the outer bypass airflow introduced by the streamlined air duct 2 to directly exchange heat and cool through the wall, thereby achieving targeted cooling of the cavity support plate 4 and the load-bearing column 14. At the same time, the airflow is rectified and initially distributed, and finally the cooled airflow is collected into the air collection chamber 13 located downstream of the turbine rear support 3. The air collection chamber 13 can be an annular pressure stabilizing chamber.

[0034] The cooling-sealing distribution unit includes an inner cone 5, a low-pressure turbine disk 7, and a bearing cavity 10. The outlet of the gas collecting cavity 13 is connected to the following three paths: (a) Bypass air vent 9, the first low-temperature airflow is led out from the gas collection chamber 13, forms a heat insulation protective layer on the surface of the inner casing 15 and flows into the main flow channel 12; (b) The labyrinth seal 11 on the rear side of the low-pressure turbine disk 7 and the comb-honeycomb sealing structure 8 of the bearing cavity 10 share a common channel. The second low-temperature airflow enters the labyrinth seal 11 and the comb-honeycomb sealing structure 8 through the common channel, forming a double sealing barrier. (c) The air film hole 6 opened on the peripheral wall of the inner cone 5 is used to spray a third low-temperature airflow to form a cooling air film covering the surface of the inner cone. The system satisfies the following conditions: the total pressure loss coefficient of the low-temperature airflow from the inlet of the streamlined air duct 2 to the outlet of the air collection chamber 13 is ≤5%, and the comprehensive utilization rate of cold air is ≥90%.

[0035] like Figure 2 As shown, this embodiment of the invention also provides a design method for the above-mentioned cooling dual-seal anti-backflow system based on duct air intake, the method comprising the following steps: S1: Set the amount of low-temperature airflow drawn from the outer bypass 1 to 3% to 4% of the total flow of the outer bypass, and design a streamlined air duct 2 on the inner wall of the outer bypass 1 based on this amount of airflow. S2: Based on the constraint that the total pressure loss coefficient from the inlet of the streamlined air duct 2 to the outlet of the air collection chamber 13 is ≤5%, the cooling channel structure inside the turbine rear support 3 is designed. S3: Based on the constraint that the ratio between the low-pressure turbine disk back sealing chamber pressure and the turbine back mainstream gas pressure is greater than 1.02, determine the gas supply capacity of the labyrinth seal 11 and the comb-honeycomb sealing structure 8. S4: Configure the outlet flow path of the gas collecting chamber 13 so that the low-temperature airflow in the gas collecting chamber 13 is distributed to the following three functional branches: (a) The air film cooling branch of the inner cone 5; (b) The rear-disc seal and bearing cavity sealing branch, wherein the low-temperature airflow enters the labyrinth seal 11 after the low-pressure turbine disk 7, and forms a positive gas seal at the labyrinth seal 11 through pressure matching, blocking the high-temperature combustion gas of the main channel 12 from entering the rear-disc cavity, thus protecting the turbine rotor and bearing components. A portion of the low-temperature airflow enters the grate-honeycomb sealing structure 8, providing a stable sealing gas source for the bearing cavity, maintaining the pressure balance in the cavity, preventing high-temperature deterioration of the lubricating oil and seal failure, and ensuring the reliable operation of the bearing system.

[0036] (c) Bypass vent 9 heat-insulated and protected branch; S5: Based on the low-temperature airflow distribution ratio of the three functional branches and their corresponding heat-work conversion effect; if the calculation result is less than 90%, adjust the intake air volume, cooling channel structure or outlet flow path configuration until the performance requirements are met and calculate the comprehensive utilization rate of cold air.

[0037] In one embodiment, by configuring the outlet flow path of the air collection chamber 13, the flow distribution ratio of the three functional branches is coordinated so that the overall utilization rate of the system's cooling air is ≥90%.

[0038] In one embodiment, the peripheral wall at the rear end of the inner cone 5 has multiple air film cooling holes 6. The holes have a diameter of 1.0 mm, an inclination angle of 30°, and a spacing of 4 mm to 8 mm. The inlet of each air film cooling hole 6 is a funnel-shaped diffuser structure. Through the funnel-shaped diffuser structure, the cooling gas can achieve thermal insulation cooling by forming a continuous air film on the surface. Furthermore, it ensures that the internal pressure is higher than the gas pressure in the main flow channel, preventing backflow of gas. When calculating the heat-work conversion effect of the air film cooling branch, the diameter, inclination angle, and spacing of the air film cooling holes 6 are configured such that the total pressure loss coefficient of the cold gas flowing through the cooling channel of the inner cone 5 is ≤8%, and the overall cooling efficiency is ≥0.85.

[0039] In one embodiment, the labyrinth seal 11 is disposed on the stator end face behind the low-pressure turbine disk 7, and its air inlet is connected to the gas collecting chamber 13. When determining the air supply capacity of the rear seal and bearing cavity sealing branch, the flow area of ​​the labyrinth seal 11 and the comb-honeycomb sealing structure 8 is configured to adjust the pressure in the rear seal cavity of the low-pressure turbine disk. With the mainstream gas pressure after the turbocharger satisfy: Cooling seal flow rate satisfy: ,in, Where A is the flow coefficient and A is the area of ​​the sealing annulus. To ensure the density of the sealed cold air.

[0040] In one embodiment, the air inlet of the comb-honeycomb sealing structure 8 is connected to the air collection chamber 13, and together with the labyrinth seal 11, it forms a double sealing barrier with a sealing reliability of ≥99.9%.

[0041] In one embodiment, the system of the present invention achieves a total pressure loss coefficient of ≤5% for the low-temperature airflow from the inlet of the streamlined air duct 2 to the outlet of the air collection chamber 13, and a comprehensive utilization rate of ≥90% for the cold air, as follows: 1) Design of flow resistance constraints: To ensure the overall system performance, this invention achieves precise quantification of flow resistance through the pressure loss coefficient, the calculation formula of which is as follows: ; In the formula: —Total flow resistance coefficient from the air intake at the windshield to the air collection chamber; —Total pressure loss from the air intake to the air collection chamber, in kPa. ; —Total pressure at the duct air inlet, in kPa, is a constant; —Total outlet pressure of the air collection chamber, in kPa. The airflow loss in this section is only caused by wall friction and guiding disturbance, with no functional energy loss. The total pressure loss coefficient from the wind tunnel inlet to the air collection chamber is strictly limited to ≤5%, ensuring efficient delivery of cold air energy from the source and laying the foundation for efficient operation of subsequent functional branches.

[0042] 2) Design constraints on the overall utilization rate of the cooling system: Based on the law of conservation of energy, the total energy of the cooling system = energy with no functional losses + effective functional energy of each branch. The engineering quantification formula is as follows: ; In the formula: —Effective cooling work of the turbine rear casing, in kJ; —Effective work of cooling the inner cone with added force, in kJ; —Effective work of the low-pressure turbine disc rear seal, in kJ; —Effective work of bearing cavity sealing, unit: kJ; —Effective thermal insulation performance of the inner casing, in kJ; —Total effective work of external duct entrainment, in kJ.

[0043] The calculation formulas are as follows: ; ; ; ; ; ; In the above formula, The corresponding flow path cold air mass flow rate is expressed in kg / s. The specific heat capacity of air at constant pressure is taken as 1.005 kJ / (kg·K); To correspond to the cold air inlet temperature of the flow path, The corresponding cold air outlet temperature, in K; The average temperature of the branch air outlet, in K, is calculated using the following formula: ; 3) Design of technical indicators for double-sealing backflow prevention: This invention abandons the traditional single-sealing mode and constructs a comprehensive gas backflow prevention system through dual-path flow loss control, accurately defines the performance threshold of each branch, completely blocks the gas backflow channel, and ensures the safety of the engine's core components.

[0044] 1.1) Cooling flow path of the inner cone with added force: Design pressure loss constraints: ; In the formula, This is to account for the total pressure loss of the inner cone cooling channel. This constraint ensures that the pressure inside the cooling channel is always higher than the mainstream gas pressure.

[0045] Active cooling and passive sealing: This invention employs a composite cooling structure of impact + convection + air film to enhance the cooling effect and set an overall cooling efficiency. At the same time, it ensures that the pressure in the cooling channel is always higher than the mainstream gas pressure, forming a gas film barrier to block the backflow of gas into the engine from the front end; 1.2) Cooling efficiency quantification formula: ; In the formula: —Inner cone wall temperature, K; —Mainstream gas temperature, K; —Cooling gas inlet temperature, K.

[0046] 4) Back panel sealing flow path design: Adopting a comb-honeycomb composite sealing structure, optimizing the sealing gap and structural form, setting the sealing cavity to maintain a slight positive pressure relative to the mainstream gas, forming a stable pressure barrier, and accurately blocking the gas from entering from the gap between the back panel and the stator.

[0047] 4.1) The slight positive pressure is ensured by the pressure ratio constraint, and the pressure ratio formula is: ; In the formula, The pressure of the low-pressure turbine disk rear sealing chamber. This is the mainstream combustion gas pressure after the turbine (typically a constant). This constraint is the backflow prevention core threshold. Minimum cold air seal flow rate. Calculation formula: ; In the formula: —Flow coefficient, with a value of 0.9; —Area of ​​the sealing annular gap, m²; —Density of sealed cold air, kg / m³.

[0048] 4.2) Bearing cavity sealing flow path: A labyrinth seal structure is adopted, with a sealing reliability of ≥99.9%. Combined with the low-pressure turbine disk rear sealing branch, a secondary protection is formed to completely eliminate problems such as gas intrusion into the bearing cavity, lubricating oil leakage, and high-temperature deterioration.

[0049] The cooling dual-seal anti-backflow system of this invention is a low-loss, high-utilization integrated flow path for duct cooling air intake, cooling, and sealing. This system draws low-temperature, low-pressure cooling airflow from the main duct flow through streamlined air intake ducts installed on the inner wall of the duct. The airflow then flows through a cooling channel formed by a hollow support plate and a load-bearing column integrated within the turbine rear support, effectively exchanging heat with the support structure while limiting its own temperature rise. The cooled airflow converges into the downstream air collection chamber for pressure stabilization and rectification, and is then adaptively and unthrottledly distributed to three functional branches: The air flows through the cooling channel of the inner cone and is ejected through the air film holes on its rear wall to form an air film cooling layer. The labyrinth seal behind the low-pressure turbine disk and the comb-honeycomb seal structure of the bearing cavity form a double sealing barrier. One path passes through the bypass vent, forming a heat-insulating protective layer on the surface of the inner casing and then flows into the main channel to regulate the local pressure field and suppress the tendency of gas backflow.

[0050] The design of this invention uses the gas collection chamber as a pressure stabilizing hub to achieve on-demand, undisturbed diversion of cold air; at the same time, by precisely matching the flow capacity and performance requirements of each branch (such as the sealing chamber pressure being more than 1.02 times higher than the mainstream gas pressure), a backflow prevention barrier is naturally formed without relying on an active control valve, and the cold air's work capacity is maximized.

[0051] Obviously, those skilled in the art should understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations of the embodiments of the present invention are possible for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cold anti-inversion system based on an external-bleed air cooling double seal, characterized in that, The system includes: The duct air intake unit includes a streamlined air intake duct (2) installed on the inner wall of the duct (1) for drawing low-temperature airflow from the duct (1); The turbine rear support (3) with integrated bleed air cooling function has a cavity support plate (4) and a load-bearing column (14) inside, which are used to guide the outer bypass bleed air introduced by the streamlined bleed air hood (2) through the wall for heat exchange and cooling, and to collect the cooled air flow into the gas collection chamber (13) located downstream of the turbine rear support (3). The cooling-sealing distribution unit includes an inner cone (5), a low-pressure turbine disk (7), and a bearing cavity (10). The outlet of the gas collection cavity (13) is connected to the following three paths: Bypass air vent (9), the first low-temperature airflow is led out from the air collection chamber (13), forms a heat insulation protective layer on the surface of the inner casing (15) and merges into the main flow channel (12). The labyrinth seal (11) on the rear side of the low-pressure turbine disk (7) and the comb-honeycomb sealing structure (8) of the bearing cavity (10) share a common channel. The second low-temperature airflow enters the labyrinth seal (11) and the comb-honeycomb sealing structure (8) respectively through the common channel, forming a double sealing barrier. The gas film hole (6) opened on the peripheral wall of the inner cone (5) allows a third low-temperature airflow to be sprayed through the gas film hole (6) to form a cooling gas film covering the surface of the inner cone. The system satisfies the following conditions: the total pressure loss coefficient of the low-temperature airflow from the inlet of the streamlined air duct (2) to the outlet of the air collection chamber (13) is ≤5%, and the comprehensive utilization rate of cold air is ≥90%. The labyrinth seal (11) is located on the rear stator mating end face of the low-pressure turbine disk (7), and its air inlet is connected to the gas collecting chamber (13). The pressure of the rear sealing chamber of the low-pressure turbine disk is... With the mainstream gas pressure after the turbocharger satisfy: Cooling seal flow rate satisfy: ,in, Where A is the flow coefficient and A is the area of ​​the sealing annulus. To ensure the density of the sealed cold air.

2. The cooling double-seal anti-backflow system based on duct air intake as described in claim 1, characterized in that, The low-temperature airflow of the streamlined air duct (2) is 3% to 4% of the total flow of the outer duct.

3. The cooling double-seal anti-backflow system based on duct air intake as described in claim 1, characterized in that, The peripheral wall at the rear end of the inner cone (5) has multiple air film holes (6), and the inlet of the air film hole (6) is a horn-mouth diffuser structure; wherein, the total pressure loss coefficient of the cooling channel of the inner cone is ≤8%, and the comprehensive cooling efficiency is ≥0.

85.

4. The cooling double-seal anti-backflow system based on duct air intake as described in claim 1, characterized in that, The air inlet of the comb-honeycomb sealing structure (8) is connected to the air collection chamber (13), and together with the labyrinth seal (11), they form a double sealing barrier.

5. A design method for a cooling double-seal anti-backflow system based on duct air intake as described in any one of claims 1 to 4, characterized in that, The design method includes: The amount of low-temperature airflow drawn from the outer bypass (1) is set to 3% to 4% of the total flow of the outer bypass, and a streamlined air duct (2) is designed on the inner wall of the outer bypass (1) based on this amount of airflow. Based on the constraint that the total pressure loss coefficient from the inlet of the streamlined air duct (2) to the outlet of the air collection chamber (13) is ≤5%, the cooling channel structure inside the turbine rear support (3) is designed. Based on the constraint that the ratio between the low-pressure turbine disk back sealing chamber pressure and the turbine back mainstream gas pressure is greater than 1.02, the gas supply capacity of the labyrinth seal (11) and the comb-honeycomb sealing structure (8) is determined. Configure the outlet flow path of the gas collecting chamber (13) so that the low-temperature gas flow in the gas collecting chamber (13) is distributed to the following three functional branches: (a) The air film cooling branch of the inner cone (5) with added force; (b) The rear panel seal and the bearing cavity sealing branch; (c) Bypass vent (9) Thermal insulation branch; Based on the low-temperature airflow distribution ratio of the three functional branches and their corresponding heat-work conversion effect, the overall utilization rate of cold air is calculated; if the calculation result is less than 90%, the intake air volume, cooling channel structure or outlet flow path configuration is adjusted until the performance requirements are met.

6. The design method of the cooling double-seal anti-backflow system based on duct air intake according to claim 5, characterized in that, When calculating the heat-work conversion effect of the air film cooling branch, the aperture, inclination angle and spacing of the air film holes (6) are configured so that the total pressure loss coefficient of the cold air flowing through the cooling channel of the inner cone (5) is ≤8% and the overall cooling efficiency is ≥0.

85.

7. The design method of the cooling double-seal anti-backflow system based on duct air intake according to claim 5, characterized in that, When determining the air supply capacity of the rear sealing section of the turbine disk and the bearing cavity sealing branch, the flow area of ​​the labyrinth seal (11) and the comb-honeycomb sealing structure (8) are configured, and the pressure of the low-pressure turbine rear sealing cavity is determined. With the mainstream gas pressure after the turbocharger satisfy: Cooling seal flow rate satisfy: ,in, Where A is the flow coefficient and A is the area of ​​the sealing annulus. To ensure the density of the sealed cold air.

8. The design method of the cooling double-seal anti-backflow system based on duct air intake according to claim 5, characterized in that, When configuring the outlet flow path of the air collection chamber (13), coordinate the flow distribution ratio of the three functional branches so that the overall utilization rate of the cold air of the system is ≥90%.

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