A medium variable bypass ratio turbofan engine configuration based on a dual-fan structure

Abstract

The present invention proposes a medium variable bypass ratio turbofan engine configuration based on a dual-fan structure, specifically relating to a turbofan engine structure with dual fans and adjustable nozzles with adjustable inlet blades. By adopting a dual-fan structure, a low-pressure fan and a high-pressure fan are provided to intake and pressurize air separately, which is conducive to expanding the bypass ratio adjustment range and reducing the working variation amplitude of a single-stage fan; by providing a variable splitter cone and adjustable blades on the inlet of the high-pressure fan, and by controlling their angles, the flow ratio of the outer duct and the inner duct is adjusted to achieve different bypass ratios, which is the key to achieving a medium variable bypass ratio; by providing a second duct, part of the inner duct flow is introduced into the outer duct, which further increases the bypass ratio adjustment range and is conducive to achieving a medium variable bypass ratio within the range of 3 to 6. The present invention has the advantages of a large bypass ratio adjustment range, strong high-altitude climbing capability, and low high-altitude cruising fuel consumption, and is suitable for the power requirements of high-altitude long-endurance unmanned aerial vehicles.

Description

Technical Field

[0001] The present invention belongs to the field of aviation engine technology, in particular to the field of aviation turbofan engine technology, and relates to a medium variable bypass ratio turbofan engine structure, and specifically to an aerodynamic layout structure form of a dual-fan dual-duct used in a medium variable bypass ratio dual-shaft turbofan engine. Background Art

[0002] A high-altitude, long-endurance unmanned aerial vehicle (HALE UAV) is a type of drone capable of flying at high altitudes and remaining aloft for extended periods. Generally, these drones fly at altitudes above 15,000 meters, can remain aloft for days or even longer, and possess high stealth capabilities. Compared to traditional manned aircraft or satellites, HALE UAVs typically offer advantages such as low cost, high flexibility, reusability, and the ability to carry a variety of payloads. They can meet the military and civilian needs for long-term, wide-area, high-precision surveillance and reconnaissance, communications coverage, meteorological observation, environmental monitoring, and search and rescue. To improve their information acquisition capabilities, mission execution efficiency, and battlefield survivability, HALE UAVs are flying at increasingly higher altitudes, requiring them to remain aloft for longer periods, and possessing increasingly advanced stealth capabilities.

[0003] To achieve longer flight times and stronger stealth, high-altitude, long-endurance UAVs (UAVs) place higher demands on engine performance and design. This increased fuel efficiency is increasingly demanded, necessitating the adoption of low-fuel-consumption engine designs to maximize UAV flight time. This typically requires efficient combustion and thrust output, as well as low specific fuel consumption. For example, turbofan engines are typically more efficient at high altitudes because they exploit the rarefaction of the atmosphere and air currents, reducing air resistance and energy consumption. To achieve stronger stealth, smaller engines and fully shielded inlet and outlet designs are often required, reducing the overall size and radar cross-section of the UAV and enhancing its stealth. To achieve this, strict engine diameter requirements are often imposed to ensure full shielding of the inlet and outlet to minimize reflected signals. Furthermore, factors such as engine reliability and maintenance costs must also be considered.

[0004] To meet the stringent requirements of high-altitude, long-endurance UAVs, engines must utilize the highest possible bypass ratio to reduce fuel consumption. Bypass ratio is a key performance metric for aircraft engines and refers to the ratio of the airflow in the outer bypass to the airflow in the inner bypass. Generally speaking, the higher the bypass ratio, the lower the fuel consumption of the aircraft engine. This is because the greater the airflow bypassing the engine core and entering the propeller, the lower the exhaust velocity, improving propulsion efficiency and reducing fuel consumption while producing the same thrust. A higher bypass ratio improves engine fuel efficiency and thrust output, but also increases engine weight and size. Under strict size and weight requirements, the thrust of a high-bypass ratio engine is limited, which can easily result in a UAV lacking sufficient thrust to achieve high-altitude climbs, limiting its climb altitude. Furthermore, the engine's thrust may not be sufficient to support high-speed flight. Therefore, significantly increasing the engine's thrust level in both of these conditions necessitates the development of a medium-variable bypass ratio turbofan engine. A smaller bypass ratio is used during aircraft climbing and high-speed flight to provide greater thrust to support flight and increase the aircraft's climbing altitude and speed; a larger bypass ratio is used during high-altitude cruising to reduce fuel consumption throughout the entire journey, thereby increasing the aircraft's airborne time and further extending the range.

[0005] To achieve a change in the bypass ratio of a turbofan engine, it is mainly necessary to change the ratio of the flow rate of the outer and inner bypass. When the total inlet flow remains unchanged, increasing the flow rate of the inner bypass can improve the quality of the air working medium entering the combustion chamber and enhance the thrust of the engine. In order to achieve the change in the flow rate of the inner and outer bypass of a turbofan engine, it is necessary to change the geometric structure of the engine compression system and exhaust system to achieve the purpose of changing the bypass ratio. In the prior art, the "Wide Speed ​​Range Variable Cycle Engine Based on Interstage Combustion Chamber Driving Low-Pressure Turbine Rotor" disclosed in Chinese invention patent application CN202210488043.3 and the "A Three-Bypass ACE Engine with Flade Fan and Core Engine Driving Fan Stage" disclosed in CN202110937625.0 can achieve the adjustment and change of the engine bypass ratio to a certain extent. However, existing technologies including the above-mentioned patents still face certain difficulties and challenges in achieving changes in the bypass ratio of turbofan engines (for example, achieving a medium-variable bypass ratio of 3 to 6). These difficulties and challenges are mainly manifested in the following aspects: the operating range of turbofan engines is relatively wide, and they need to meet both low-speed and high-speed operating conditions. This requires that key components such as the compression system, combustion chamber, and expansion system all have good adaptability, otherwise it will affect the engine performance and increase the difficulty of achieving a medium-variable bypass ratio. At the same time, the intake volume and pressure ratio corresponding to the medium-range bypass ratio vary greatly, requiring a complex control system to accurately adjust the fan and other components to achieve different bypass ratios, which undoubtedly increases the difficulty of achieving a medium-variable bypass ratio. In addition, the operating conditions of turbofan engines will vary greatly at different bypass ratios, which requires good matching of the various engine components, otherwise it will affect the operating stability of the engine and increase the difficulty of achieving a medium-variable bypass ratio. Summary of the Invention

[0006] (1) Purpose of the invention

[0007] In response to the power requirements of high-altitude, long-endurance unmanned aerial vehicles (UAVs) and the difficulties and challenges faced by existing technologies in achieving moderate bypass ratio variation, the present invention proposes a medium-variable bypass ratio turbofan engine configuration based on a dual-fan structure. Specifically, it relates to a turbofan engine structure with dual fans and an adjustable nozzle, each with adjustable inlet blades. The dual-fan structure employs a low-pressure fan and a high-pressure fan for separate intake and pressurization, which helps expand the bypass ratio adjustment range and reduce the operating range of a single-stage fan. A variable splitter cone and adjustable inlet blades on the high-pressure fan are provided, and their angles are controlled to adjust the flow ratio between the outer and inner ducts, achieving different bypass ratios. This is the key to achieving moderate variable bypass ratios. A second duct is provided to divert part of the inner duct flow into the outer duct, further expanding the bypass ratio adjustment range and facilitating the achievement of a moderate variable bypass ratio within the range of 3 to 6. The engine configuration proposed by the present invention has the advantages of a wide bypass ratio adjustment range, strong high-altitude climb capability, and low high-altitude cruising fuel consumption, making it suitable for the power requirements of high-altitude, long-endurance UAVs.

[0008] (2) Technical solution

[0009] To achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] A medium variable bypass ratio turbofan engine configuration based on a dual-fan structure includes at least one air inlet located at its head, an inner casing extending axially along the center of rotation of the engine is provided downstream of the air inlet, the inner casing divides the flow channel into an outer duct located radially outside and extending axially and an inner duct located radially inside and extending axially, the outer side of the outer duct is the outer casing, at least one low-pressure fan assembly is provided in the air inlet, at least one high-pressure fan assembly and a core engine assembly are provided in sequence along the flow direction in the inner duct, at least one adjustable tail nozzle is provided at the downstream tail of the outer casing, and at least one lobe mixer is provided at the downstream tail of the inner casing, characterized in that,

[0011] The inner casing includes at least an inlet section located upstream and a main body section located downstream of the inlet section along the flow direction. The high-pressure fan assembly is arranged in the inlet section of the inner casing, and the core engine assembly is arranged in the main body section of the inner casing.

[0012] Moreover, a second duct is formed between the inlet section and the main section of the inner casing to connect the inner flow channel and the outer flow channel. The second duct is located between the high-pressure fan assembly and the high-pressure compressor in the core engine assembly in the flow direction.

[0013] In addition, a variable diverter cone is provided at the upstream leading edge of the inlet section of the inner casing, and the variable diverter cone is connected to the upstream leading edge of the inlet section of the inner casing through a diverter cone rotating shaft in a radially adjustable angle manner. When the variable diverter cone is adjusted to flip outward, the air flow rate entering the outer duct is reduced and the air flow rate entering the inner duct is increased. Conversely, when the variable diverter cone is adjusted to flip inward, the air flow rate entering the inner duct is reduced and the air flow rate entering the outer duct is increased.

[0014] Preferably, the low-pressure fan assembly comprises at least a low-pressure fan rotor and a low-pressure fan stator located downstream of the low-pressure fan rotor, and the low-pressure fan stator is arranged adjacent to the outlet position of the air inlet duct.

[0015] Preferably, the high-pressure fan assembly is arranged in the inlet section of the internal flow channel, and at least includes a high-pressure fan inlet guide vane, a high-pressure fan rotor and a high-pressure fan stator arranged in sequence along the flow direction.

[0016] Furthermore, in the high-pressure fan assembly, the outlet angle of the high-pressure fan inlet guide vane is adjustable. When it is necessary to improve the engine bypass ratio and increase the external bypass flow and reduce the internal bypass flow, the high-pressure fan inlet guide vane is adjusted to increase its outlet angle, thereby reducing the gas flow entering its downstream high-pressure fan assembly. Correspondingly, the angle of the variable diverter cone is adjusted to flip it inward to reduce the gas flow diverted to the internal flow channel.

[0017] Furthermore, when it is necessary to reduce the engine bypass ratio to increase the internal flow and reduce the external flow, the high-pressure fan inlet guide vane is adjusted to reduce its outlet angle, thereby increasing the gas flow entering its downstream high-pressure fan assembly. Correspondingly, the angle of the variable diverter cone is adjusted to flip it outward to reduce the gas flow diverted to the external flow channel.

[0018] Preferably, a control valve with adjustable opening is provided in the second duct, and the opening of the control valve is adjusted according to the working condition of the engine.

[0019] Preferably, the core engine assembly is arranged in the main section of the internal flow channel, and includes at least a high-pressure compressor, a combustion chamber, a high-pressure turbine assembly, and a low-pressure turbine assembly arranged in sequence along the flow direction. The axial space between the high-pressure turbine assembly and the low-pressure turbine assembly is a high-low-pressure turbine transition section. The high-pressure turbine assembly is connected to the high-pressure fan assembly and the high-pressure compressor through a high-pressure shaft and provides driving power. The low-pressure turbine assembly is connected to the low-pressure fan assembly through a low-pressure shaft and provides driving power.

[0020] Furthermore, the high-pressure turbine assembly at least includes a high-pressure turbine guide vane and a high-pressure turbine rotor arranged in sequence along the flow direction, the high-pressure turbine rotor is transmission-connected to the high-pressure fan assembly and the rotor part of the high-pressure compressor through a high-pressure shaft and provides driving power, the low-pressure turbine assembly at least includes a first-stage low-pressure turbine and a second-stage low-pressure turbine arranged in sequence along the flow direction, the first-stage low-pressure turbine at least includes a first-stage low-pressure turbine guide vane and a first-stage low-pressure turbine rotor arranged in sequence along the flow direction, the second-stage low-pressure turbine at least includes a second-stage low-pressure turbine guide vane and a second-stage low-pressure turbine rotor arranged in sequence along the flow direction, the first-stage low-pressure turbine rotor and the second-stage low-pressure turbine rotor are both transmission-connected to the low-pressure shaft and transmission-connected to the rotor part of the low-pressure fan assembly through the low-pressure shaft and provide driving power.

[0021] The medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention has the following working process: during the operation of the engine, air is sucked in by a low-pressure fan arranged in the air inlet duct, and after being pressurized by the low-pressure fan, it is divided into two streams by a variable splitter cone, one stream enters the outer duct and the other stream enters the inner flow channel. The flow direction is adjusted by the high-pressure fan inlet guide vanes in the inlet section of the inner flow channel, and then enters the high-pressure fan rotor and stator for pressurization, and then further split, one stream continues to flow forward and enters the high-pressure compressor, and the other stream enters the outer duct through the second duct. The airflow after being pressurized by the high-pressure compressor enters the combustion chamber, and after combustion to increase the temperature, it enters the high-pressure turbine to perform work, and then enters the low-pressure turbine to perform work. The exhaust gas is mixed with the airflow in the outer duct in the lobe mixer, and the evenly mixed airflow is ejected through the adjustable nozzle to generate thrust.

[0022] (3) Technical effects

[0023] Compared with the prior art, the medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention has the following beneficial and significant technical effects:

[0024] (1) The medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention, by adopting the dual-fan structure, enables the engine to have a higher bypass ratio adjustment potential and a wider operating range, which is conducive to achieving a medium variable bypass ratio.

[0025] (2) The medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention can significantly reduce the difficulty of achieving a medium variable bypass ratio by providing an adjustable splitter cone and adjustable blades at the high-pressure fan inlet, which is a simple and effective means of achieving different bypass ratios.

[0026] (3) The medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention can further increase the bypass ratio adjustment range by setting a second bypass, which makes it possible to achieve a medium variable bypass ratio in the range of 3 to 6.

[0027] (4) The medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention can achieve continuous adjustment of the bypass ratio, meeting the fine control requirements of the bypass ratio of high-altitude and long-endurance UAVs.

[0028] (5) The medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention can realize relatively independent control of the low-pressure fan and the high-pressure fan, which is conducive to achieving the required bypass ratio change while ensuring the engine operating performance.

[0029] (6) The medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention can effectively reduce the difficulty of achieving a medium variable bypass ratio by adopting a dual-fan structure and setting an adjustable diversion device and other technical means, and achieve fine adjustment of the bypass ratio in the range of 3 to 6. This has important application value for the power requirements of high-altitude and long-endurance unmanned aerial vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the medium variable bypass ratio turbofan engine based on a dual-fan structure of the present invention;

[0031] Figure 2 Schematic diagram of the rotor system of a medium variable bypass ratio turbofan engine of the present invention;

[0032] Figure 3 Schematic diagram of the flow path of the compression system of the medium variable bypass ratio turbofan engine of the present invention;

[0033] Figure 4 This is a schematic diagram of the adjustment of the high-pressure fan inlet guide vanes of the medium variable bypass ratio turbofan engine of the present invention.

[0034] Description of reference numerals:

[0035] Rotation center 1, low-pressure shaft 2, high-pressure shaft 3, low-pressure fan rotor 4, low-pressure fan stator 5, variable splitter cone 6, splitter cone rotating shaft 7, outer duct 8, high-pressure fan inlet guide vane 9, high-pressure fan rotor 10, high-pressure fan stator 11, second duct 12, high-pressure compressor 13, combustion chamber 14, high-pressure turbine guide vane 15, high-pressure turbine rotor 16, high- and low-pressure turbine transition section 17, first-stage low-pressure turbine guide vane 18, first-stage low-pressure turbine rotor 19, second-stage low-pressure turbine guide vane 20, second-stage low-pressure turbine rotor 21, lobe mixer 22, adjustable tail nozzle 23, inner duct 24. DETAILED DESCRIPTION

[0036] In order to better understand the present invention, the contents of the present invention are further explained in conjunction with the embodiments below. In the accompanying drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be understood as limiting the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The structure and technical solution of the present invention are further described in detail below in conjunction with the accompanying drawings, and an embodiment of the present invention is given.

[0037] like Figures 1 to 3As shown, the medium variable bypass ratio turbofan engine configuration based on a dual-fan structure of the present invention includes at least one air inlet located at its head. An inner casing extending axially about the engine's rotation center 1 is disposed downstream of the air inlet. The inner casing divides the flow path into an outer duct 8 located radially outward and extending axially, and an inner duct 24 located radially inward and extending axially. The outer side of the outer duct 8 is the outer casing. At least one low-pressure fan assembly is disposed within the air inlet. The low-pressure fan assembly includes at least a low-pressure fan rotor 4 and a low-pressure fan stator 5 located downstream of the low-pressure fan rotor 4, and the low-pressure fan stator 5 is disposed near the outlet of the air inlet. At least one high-pressure fan assembly and a core engine assembly are disposed sequentially along the flow direction within the inner duct 24. At least one adjustable tail nozzle 23 is disposed downstream of the outer casing, and at least one lobe mixer 22 is disposed downstream of the inner casing. The high-pressure fan assembly is arranged in the inlet section of the inner flow channel 24, and includes at least a high-pressure fan inlet guide vane 9, a high-pressure fan rotor 10 and a high-pressure fan stator 11 arranged in sequence along the flow direction. The core engine assembly is arranged in the main section of the inner flow channel 24, and includes at least a high-pressure compressor 13, a combustion chamber 14, a high-pressure turbine assembly, and a low-pressure turbine assembly arranged in sequence along the flow direction. The axial space between the high-pressure turbine assembly and the low-pressure turbine assembly is a high-low-pressure turbine transition section 17. The high-pressure turbine assembly is connected to the high-pressure fan assembly and the high-pressure compressor 13 through a high-pressure shaft 3 and provides driving power. The low-pressure turbine assembly is connected to the low-pressure fan assembly through a low-pressure shaft 2 and provides driving power. The high-pressure turbine assembly includes at least a high-pressure turbine guide vane 15 and a high-pressure turbine rotor 16 arranged in sequence along the flow direction. The high-pressure turbine rotor 16 is connected to the high-pressure fan assembly and the rotor part of the high-pressure compressor 13 through the high-pressure shaft 3 and provides driving power. The low-pressure turbine assembly includes at least a first-stage low-pressure turbine and a second-stage low-pressure turbine arranged in sequence along the flow direction. The first-stage low-pressure turbine includes at least a first-stage low-pressure turbine guide vane 18 and a first-stage low-pressure turbine rotor 19 arranged in sequence along the flow direction. The second-stage low-pressure turbine includes at least a second-stage low-pressure turbine guide vane 20 and a second-stage low-pressure turbine rotor 21 arranged in sequence along the flow direction. The first-stage low-pressure turbine rotor 19 and the second-stage low-pressure turbine rotor 21 are both connected to the low-pressure shaft 2 in transmission connection and are connected to the rotor part of the low-pressure fan assembly through the low-pressure shaft 2 and provide driving power.

[0038] In the medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention, the inner casing includes at least one inlet section located upstream and a main section located downstream of the inlet section along the flow direction, the high-pressure fan assembly is arranged in the inlet section of the inner casing, the core engine assembly is arranged in the main section of the inner casing, and a second duct 12 connecting the inner flow channel 24 and the outer duct 8 is formed between the inlet section and the main section of the inner casing. The second duct 12 is located between the high-pressure fan assembly and the high-pressure compressor 13 in the core engine assembly in the flow direction. A variable diverter cone 6 is provided at the upstream leading edge of the inlet section of the inner casing, and the variable diverter cone 6 is connected to the upstream leading edge of the inlet section of the inner casing through a diverter cone rotating shaft 7 in a radially adjustable angle manner. When the variable diverter cone 6 is adjusted to flip outward, the air flow rate entering the outer duct 8 is reduced and the air flow rate entering the inner duct 24 is increased. Conversely, when the variable diverter cone 6 is adjusted to flip inward, the air flow rate entering the inner duct 24 is reduced and the air flow rate entering the outer duct 8 is increased.

[0039] The medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention has the following working principle: during the operation of the engine, air is inhaled through the low-pressure fan 4, and after being pressurized by the low-pressure fan 4, it is divided into two streams by the variable splitter cone 6, one stream enters the outer duct 8, and the other stream enters the inner flow channel 24. The flow direction of the airflow is adjusted by the high-pressure fan inlet guide vane 9, and then enters the high-pressure fan rotor 10 and the stator 11 for supercharging, and then further split, one stream enters the high-pressure compressor 13, and the other stream enters the outer duct 8 through the second duct 12. The airflow after being pressurized by the high-pressure compressor 13 enters the combustion chamber 14, and after combustion to increase the temperature, enters the high-pressure turbine 16 to do work, and then enters the low-pressure turbines 19 and 20 to do work. The exhaust gas is mixed with the airflow 8 in the outer flow channel in the lobe mixer 22, and the evenly mixed airflow is ejected through the adjustable nozzle 23 to generate thrust.

[0040] Figure 2 This is the rotor structure of this engine. The low-pressure fan 4 and low-pressure turbine 19 are connected by the low-pressure shaft 2, and the power required by the low-pressure fan 4 is provided by the low-pressure turbine 19. The high-pressure fan 10, high-pressure compressor 13, and high-pressure turbine 16 are connected by the high-pressure shaft 3, and the power of the high-pressure fan 10 and high-pressure compressor 13 is provided by the high-pressure turbine 16. They rotate at the same speed.

[0041] Figure 3 This is the flow path of the compression system of a medium variable bypass ratio turbofan engine. A variable splitter cone 6 is set after the low-pressure fan. It has a rotating shaft 7 and can be adjusted according to different internal intake air flow rates to achieve a better splitter cone attack angle and reduce flow losses in the splitter cone and transition section accessories. An adjustable inlet guide vane 9 is set before the high-pressure fan 10. By adjusting its outlet angle, the Figure 4, achieving airflow direction adjustment at the low-pressure fan inlet. A second duct 12 is provided between the high-pressure fan 10 and the high-pressure compressor 13. It automatically adjusts the angle of the inlet guide vanes to achieve optimal matching with the high-pressure compressor. When the bypass ratio changes, the adjustable nozzle 23 adjusts the tail nozzle size according to the exhaust conditions, achieving optimal engine aerodynamic performance.

[0042] In the medium variable bypass ratio turbofan engine configuration based on the dual-fan structure of the present invention, the outlet angle of the high-pressure fan inlet guide vanes 9 is adjustable. When it is necessary to increase the engine bypass ratio and increase the external flow rate and reduce the internal flow rate, the high-pressure fan inlet guide vanes 9 are adjusted to increase their outlet angle, thereby reducing the gas flow rate entering the downstream high-pressure fan assembly. Accordingly, the angle of the variable diverter cone 6 is adjusted to flip it inward to reduce the gas flow rate diverted to the internal flow channel 24. Conversely, when it is necessary to reduce the engine bypass ratio and increase the internal flow rate and reduce the external flow rate, the high-pressure fan inlet guide vanes 9 are adjusted to decrease their outlet angle, thereby increasing the gas flow rate entering the downstream high-pressure fan assembly. Accordingly, the angle of the variable diverter cone 6 is adjusted to flip it outward to reduce the gas flow rate diverted to the external flow channel 8. Figure 4 A schematic diagram of the high-pressure fan inlet guide vane adjustment is provided. As can be seen from the figure, when the outlet angle of the inlet guide vane 9 changes, the high-pressure fan inlet velocity triangle changes. For example, when the high-pressure fan rotor inlet angle is 0 degrees above and 30 degrees below, the high-pressure fan rotor blade inlet geometric angle ∠1 remains unchanged, the bending angle ∠2 remains unchanged, and the tangential velocity U remains unchanged. However, the inlet airflow angle ∠3 of the airflow C1 changes from 0 degrees to 30 degrees, resulting in a change in the high-pressure fan flow rate. The flow rate is primarily determined by Cm. Based on the triangle relationship, it can be found that Cm>Cm', so the flow rate will decrease. In addition, the high-pressure fan's pressure ratio will be reduced, which is primarily determined by U*△Wu. Based on the geometric relationship, it can be found that when U remains unchanged, △Wu>△Wu', so the pressure ratio decreases. In this example, the engine bypass ratio can be adjusted from 6 to 4.5.

[0043] In summary, the medium variable bypass ratio turbofan engine configuration based on a dual-fan structure of the present invention has higher bypass ratio adjustment potential and a wider operating range by adopting a dual-fan structure, which is conducive to achieving medium variable bypass ratio. By setting an adjustable splitter cone and adjustable blades at the high-pressure fan inlet, it is a simple and effective means to achieve different bypass ratios, which can significantly reduce the difficulty of achieving medium variable bypass ratio. By setting a second bypass, the bypass ratio adjustment range can be further increased, which provides the possibility of achieving medium variable bypass ratio in the range of 3 to 6. The engine structure of the present invention can achieve continuous adjustment of the bypass ratio, meeting the fine control requirements of the bypass ratio for high-altitude and long-endurance unmanned aerial vehicles, and can achieve relatively independent control of the low-pressure fan and the high-pressure fan, which is conducive to achieving the required bypass ratio change while ensuring the engine operating performance. It can effectively reduce the difficulty of achieving medium variable bypass ratio and achieve fine adjustment of the bypass ratio in the range of 3 to 6. This has important application value for the power requirements of high-altitude and long-endurance unmanned aerial vehicles.

[0044] The above embodiments fully and effectively achieve the objectives of the present invention. Those skilled in the art will appreciate that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the above specific embodiments. Although the present invention has been described with reference to the embodiments currently considered to be the most practical and preferred, it should be understood that the present invention is not limited to the disclosed embodiments, and any modifications that do not deviate from the functional and structural principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A medium variable bypass ratio turbofan engine configuration based on a dual-fan structure, comprising at least one air inlet located at its head, an inner casing extending axially along the center of rotation of the engine is provided downstream of the air inlet, the inner casing divides the flow channel into an outer duct located radially outside and extending axially and an inner duct located radially inside and extending axially, the outer side of the outer duct is the outer casing, at least one low-pressure fan assembly is provided in the air inlet, at least one high-pressure fan assembly and a core engine assembly are provided in sequence along the flow direction in the inner duct, at least one adjustable tail nozzle is provided at the downstream tail of the outer casing, and at least one lobe mixer is provided at the downstream tail of the inner casing, characterized in that, The inner casing includes at least an inlet section located upstream and a main body section located downstream of the inlet section along the flow direction. The high-pressure fan assembly is arranged in the inlet section of the inner casing, and the core engine assembly is arranged in the main body section of the inner casing. Moreover, a second duct is formed between the inlet section and the main section of the inner casing to connect the inner flow channel and the outer flow channel. The second duct is located between the high-pressure fan assembly and the high-pressure compressor in the core engine assembly in the flow direction. Furthermore, a variable diverter cone is provided at the upstream leading edge of the inlet section of the inner casing. The variable diverter cone is connected to the upstream leading edge of the inlet section of the inner casing via a diverter cone rotating shaft in a radially adjustable manner. When the variable diverter cone is adjusted to flip outward, the air flow rate entering the outer duct is reduced while the air flow rate entering the inner duct is increased. Conversely, when the variable diverter cone is adjusted to flip inward, the air flow rate entering the inner duct is reduced while the air flow rate entering the outer duct is increased. And among them, The high-pressure fan assembly is arranged in the inlet section of the inner flow channel and comprises at least a high-pressure fan inlet guide vane, a high-pressure fan rotor and a high-pressure fan stator arranged in sequence along the flow direction, wherein: The outlet angle of the high-pressure fan inlet guide vane is adjustable. When it is necessary to improve the engine bypass ratio and increase the external flow rate and reduce the internal flow rate, the high-pressure fan inlet guide vane is adjusted to increase its outlet angle, thereby reducing the gas flow entering the downstream high-pressure fan assembly. Correspondingly, the angle of the variable diverter cone is adjusted to flip it inward to reduce the gas flow diverted to the internal flow channel; when it is necessary to reduce the engine bypass ratio and increase the internal flow rate and reduce the external flow rate, the high-pressure fan inlet guide vane is adjusted to reduce its outlet angle, thereby increasing the gas flow entering the downstream high-pressure fan assembly. Correspondingly, the angle of the variable diverter cone is adjusted to flip it outward to reduce the gas flow diverted to the external flow channel.

2. The medium variable bypass ratio turbofan engine configuration based on a dual-fan structure according to claim 1 is characterized in that: The low-pressure fan assembly at least includes a low-pressure fan rotor and a low-pressure fan stator located downstream of the low-pressure fan rotor, and the low-pressure fan stator is arranged near the outlet position of the air inlet duct.

3. The medium variable bypass ratio turbofan engine configuration based on a dual-fan structure according to claim 1 is characterized in that: A control valve with adjustable opening is provided in the second duct, and the opening of the control valve is adjusted according to the working condition of the engine.

4. The medium variable bypass ratio turbofan engine configuration based on a dual-fan structure according to claim 1, characterized in that: The core engine assembly is arranged in the main section of the internal flow channel, and includes at least a high-pressure compressor, a combustion chamber, a high-pressure turbine assembly, and a low-pressure turbine assembly arranged in sequence along the flow direction. The axial space between the high-pressure turbine assembly and the low-pressure turbine assembly is a high-low-pressure turbine transition section. The high-pressure turbine assembly is connected to the high-pressure fan assembly and the high-pressure compressor through a high-pressure shaft and provides driving power. The low-pressure turbine assembly is connected to the low-pressure fan assembly through a low-pressure shaft and provides driving power.

5. The medium variable bypass ratio turbofan engine configuration based on a dual-fan structure according to claim 4 is characterized in that: The high-pressure turbine assembly at least includes a high-pressure turbine guide vane and a high-pressure turbine rotor arranged in sequence along the flow direction. The high-pressure turbine rotor is transmission-connected to the high-pressure fan assembly and the rotor part of the high-pressure compressor through a high-pressure shaft and provides driving power. The low-pressure turbine assembly at least includes a first-stage low-pressure turbine and a second-stage low-pressure turbine arranged in sequence along the flow direction. The first-stage low-pressure turbine at least includes a first-stage low-pressure turbine guide vane and a first-stage low-pressure turbine rotor arranged in sequence along the flow direction. The second-stage low-pressure turbine at least includes a second-stage low-pressure turbine guide vane and a second-stage low-pressure turbine rotor arranged in sequence along the flow direction. The first-stage low-pressure turbine rotor and the second-stage low-pressure turbine rotor are both transmission-connected to the low-pressure shaft and transmission-connected to the rotor part of the low-pressure fan assembly through the low-pressure shaft and provide driving power.

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