Low-bypass-ratio turbofan engine with adjustable bypass ratio

Abstract

An adjustable bypass ratio low-bypass turbofan engine comprises a fan, an outer bypass duct, an axial compressor, a combustion chamber, a turbine, and an exhaust nozzle. The fan has three stages. The first two stages have blades of equal length, with an airflow ratio to the inner bypass duct not exceeding 1.3. The third stage blades are longer than the first two stages. Adjustable guide vanes are also present, either behind the second-stage blades or in front of or behind the portion of the third-stage blades that are longer than the first two stages. During startup, by opening or closing the adjustable guide vanes, the flow area of ​​the third-stage fan blades is changed, or the airflow of the outer bypass duct is adjusted. This allows the engine to operate at a maximum bypass ratio of 0.3 or higher but not exceeding 1.0 during subsonic cruise, and at a minimum bypass ratio of 0.3 or less during supersonic flight. This improves the engine's thrust and fuel efficiency at subsonic and supersonic speeds, but without requiring a core drive fan system or a three-bypass duct.

Description

Technical Field

[0001] This invention relates to an adjustable bypass ratio low-bypass turbofan engine, belonging to the technical field of military low-bypass turbofan engines. Background Technology

[0002] Conventional turbofan engines have a fixed bypass ratio. For fighter jets, low-bypass turbofan engines benefit from higher bypass ratios during subsonic cruise, while lower bypass ratios are better for supersonic flight, especially when the bypass ratio is below 0.3, resulting in high thrust and low fuel consumption. For example, my country's WS15, the US's F119, and Russia's AL-51F1 are currently the most advanced military low-bypass turbofan engines, with bypass ratios below 0.3. During supersonic flight, they exhibit low drag, high thrust, and low fuel consumption, but during subsonic cruise, the smaller bypass ratio leads to a significant drop in thrust and high fuel consumption. Conversely, military low-bypass turbofan engines with bypass ratios above 0.3 but below 1.0 offer high thrust and low fuel consumption during subsonic cruise, but... Supersonic flight results in high drag, significant thrust reduction, and high fuel consumption. Currently, conventional low-bypass turbofan engines for military use cannot increase the bypass ratio at subsonic speeds and decrease it at supersonic speeds. While the US YF120 and XA100 turbojet / turbofan variable cycle engines have experimentally demonstrated the ability to change the bypass ratio and improve thrust and fuel consumption at subsonic and supersonic speeds, the YF120's multiple adjustment devices—including mode selection valves, front variable geometry ejectors, rear variable geometry ejectors, and the core drive fan system—are located in different positions. Changing the bypass ratio in the YF120 is complex and carries the risk of overflow. Its maintainability and technical risk control are inferior to the conventional F119 turbofan engine, leading to its abandonment by the US military. Although the XA100 adaptive variable cycle engine does not have the risk of overflow, its complex three-duct design may affect its thrust-to-weight ratio and reliability. Summary of the Invention

[0003] The purpose of this invention is to provide a coreless drive fan system and a three-duct, adjustable-bypass-ratio low-bypass turbofan engine that increases the bypass ratio at subsonic speeds and decreases the bypass ratio at supersonic speeds.

[0004] The present invention is implemented as follows: a low-bypass turbofan engine with adjustable bypass ratio, the structure of which includes a fan, an outer bypass duct, an axial compressor, a combustion chamber, a turbine, and an exhaust nozzle. The fan has three stages, the first two stages of which have blades of the same length and the ratio of their airflow to the airflow of the inner duct does not exceed 1.3. The third stage of the fan is characterized by having blades that are longer than the first two stages and also having adjustable guide vanes, etc.

[0005] The adjustable guide vanes are located behind the second-stage fan blades and in front of the portion of the third-stage fan blades that is longer than the first two stages.

[0006] The adjustable guide vane is located behind the portion of the third-stage fan blade that is longer than the first two stages.

[0007] The adjustable guide vanes are located behind the second-stage fan blades, in front of the portion of the third-stage fan blades that is longer than the first two stages, and behind the portion of the third-stage fan blades that is longer than the first two stages.

[0008] During startup and operation, the adjustable guide vanes open during subsonic cruise, engaging all third-stage fan blades and increasing airflow in the bypass duct. The engine operates at a maximum bypass ratio of 0.3 or higher but not exceeding 1.0, entering a high-efficiency mode and reducing fuel consumption and noise. During supersonic flight, the adjustable guide vanes close, preventing the portion of the third-stage fan blades that is longer than the first two stages from participating in operation, or reducing airflow in the bypass duct. The engine operates at a minimum bypass ratio of 0.3, entering a high-thrust mode. By adjusting the adjustable guide vanes, the flow area of ​​the third-stage fan blades can be changed, or the bypass ratio of the engine at subsonic and supersonic speeds can be adjusted to improve thrust and fuel consumption, but without using the core drive fan system and the three-stage bypass duct. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the first structure of the adjustable bypass ratio low bypass ratio turbofan engine of the present invention.

[0010] Figure 2 This is a schematic diagram of the second structure of the adjustable bypass ratio low-bypass turbofan engine of the present invention.

[0011] Figure 3 This is a schematic diagram of the third structure of the low-bypass turbofan engine with adjustable bypass ratio according to the present invention.

[0012] In the diagram: 1. Fan; 2. Adjustable guide vanes; 3. Outer bypass duct; 4. Axial compressor; 5. Combustion chamber; 6. Turbine; 7. Tail nozzle. Detailed Implementation

[0013] See attached document Figure 1 , 23. The structure of the adjustable bypass ratio low bypass ratio turbofan engine of the present invention includes a fan 1, adjustable guide vanes 2, an outer bypass duct 3, an axial compressor 4, a combustion chamber 5, a turbine 6, and an exhaust nozzle 7; wherein the fan 1 has three stages, the first two stages have blades of the same length, and the ratio of their airflow to the airflow of the inner bypass duct does not exceed 1.3, the third stage blades are longer than the first two stages, and the adjustable guide vanes 2 are located behind the second stage blades of the fan 1 and in front of the portion of the third stage blades that are longer than the first two stages, or behind the portion of the third stage blades that are longer than the first two stages, or behind the second stage blades of the fan 1 and in front of the portion of the third stage blades that are longer than the first two stages, and at the portion of the third stage blades that are longer than the first two stages. Following the turbine 1, the number of adjustable guide vanes 2 are 1, 1, or 2 turns respectively. These adjustable guide vanes 2 can be either rotatable guide vanes controlled by a rotatable guide vane mechanism or variable-camber guide vanes controlled by a variable-camber guide vane mechanism, which can be selected as needed. The outer bypass duct 3 is located after the third stage blades of fan 1 and outside the inner bypass duct; it is a low-bypass ratio outer bypass duct, which can be selected as needed. The number of stages in the axial compressor 4 and turbine 6 can be selected as needed. The combustion chamber 5, i.e., the combustion chamber in the core engine, can be selected as needed. The exhaust nozzle 7 is located after turbine 6, and may or may not contain an afterburner. When the turbofan engine with the above structure starts and runs, it opens during subsonic cruise. Figure 1 , 2 The adjustable guide vanes 2 in fan 1 allow all the third-stage blades of fan 1 to participate in operation, increasing the airflow in the outer bypass duct 3. The engine operates at a maximum bypass ratio of 0.3 or higher but not exceeding 1.0, entering a high-efficiency mode and reducing fuel consumption and noise. During supersonic flight, such as acceleration, climb, dogfighting, and supersonic cruise, the fan is shut down. Figure 1 , 2 The adjustable guide vanes 2 in section 3 prevent the portion of the third-stage blades of fan 1 that is longer than the first two stages from participating in the operation, or reduce the airflow in the outer bypass duct 3. The engine operates at a minimum bypass ratio of no more than 0.3, enters a high-thrust mode, with high thrust and low fuel consumption, as described above.

[0014] For example, in a low-bypass turbofan engine, the fan blades have three stages. The first two stages have blades of equal length, with a flow rate to the internal duct ratio of 1.25. The third stage blades are longer than the first two stages. Adjustable guide vanes are located behind the second-stage blades and in front of or behind the portion of the third-stage blades that are longer than the first two stages, or both behind the second-stage blades and in front of and behind the portion of the third-stage blades that are longer than the first two stages. The bypass ratio is 0.57, and the structure is as follows: Figure 1 , 2As shown in Figure 3; after engine start-up, during subsonic cruise, all adjustable guide vanes are opened, allowing all third-stage fan blades to participate in operation, increasing airflow in the bypass duct, and the engine operates at its maximum bypass ratio of 0.57, entering a high-efficiency mode, reducing fuel consumption and noise; during supersonic flight, such as acceleration, climb, dogfighting, and supersonic cruise, all adjustable guide vanes are closed, preventing the portion of the third-stage fan blades that is longer than the first two stages from participating in operation, or reducing airflow in the bypass duct, and the engine operates at its minimum bypass ratio of 0.25 or no more than 0.3, entering a high-thrust mode, with high thrust and low fuel consumption. That is, at subsonic speeds, the bypass ratio is the same as that of the WS10 series, and at supersonic speeds, the bypass ratio is the same as that of the WS15, improving the engine's thrust and fuel consumption at both subsonic and supersonic speeds.

[0015] In the above implementation process, if it is necessary to operate at any bypass ratio between the maximum and minimum bypass ratio, the adjustable guide vanes can be adjusted; because the low-pressure turbine driving the fan will bear a greater load after increasing the bypass ratio, the low-pressure turbine can be used with 1 or 2 stages as needed.

[0016] This invention provides an adjustable bypass ratio low-bypass turbofan engine with no overflow risk, simple structure, and reliable operation. It can be used in various low-bypass ratio military turbofan engines. For military turbofan engines with a bypass ratio of 1.0 or higher and a maximum flight speed of supersonic speed, such as the Russian NK-32, the structure of this invention can also be adopted to increase thrust and reduce fuel consumption by reducing the bypass ratio during supersonic flight.

Claims

1. A low-bypass turbofan engine with adjustable bypass ratio, comprising a fan (1), an outer bypass duct (3), an axial compressor (4), a combustion chamber (5), a turbine (6), and a tail nozzle (7). The fan (1) has three stages, with the first two stages having blades of equal length and a flow rate to the inner bypass duct of no more than 1.

3. The characteristic feature is that the third stage blade of the fan (1) is longer than the first two stages, and it also has adjustable guide vanes (2). During operation after startup, when cruising at subsonic speeds, the adjustable guide vanes (2) are opened, allowing all the third stage blades of the fan (1) to participate in the operation, and the air in the outer bypass duct (3) to be drawn into the outer bypass duct. With increased airflow, the engine operates at a maximum bypass ratio of 0.3 or higher but not exceeding 1.0, entering a high-efficiency mode and reducing fuel consumption and noise. When flying at supersonic speeds, the adjustable guide vanes (2) are closed, so that the portion of the third stage blade in the fan (1) that is longer than the first two stages does not participate in the operation, or the airflow in the outer bypass duct (3) is reduced, and the engine operates at a minimum bypass ratio of not more than 0.3, entering a high-thrust mode. By adjusting the adjustable guide vanes (2), the flow area of ​​the third stage blade of the fan is changed or the bypass ratio of the engine at subsonic and supersonic speeds is adjusted, thereby improving its thrust and fuel consumption.

2. The adjustable bypass ratio low bypass ratio turbofan engine according to claim 1, characterized in that the adjustable guide vane (2) is located behind the second stage blade of the fan (1) and in front of the portion of the third stage blade that is longer than the first two stage blades.

3. The adjustable bypass ratio low bypass ratio turbofan engine according to claim 1, characterized in that the adjustable guide vane (2) is located behind the portion of the third stage blade of the fan (1) that is longer than the first two stage blades.

4. The adjustable bypass ratio low bypass ratio turbofan engine according to claim 1, characterized in that the adjustable guide vane (2) is located behind the second stage blade of the fan (1), in front of the portion of the third stage blade that is longer than the first two stage blades, and behind the portion of the third stage blade that is longer than the first two stage blades.

Images