Hybrid thermodynamic cycle light turbofan engine with thrust increasing function

Abstract

The invention relates to the technical field of engines, in particular to a hybrid thermodynamic cycle light turbofan engine with thrust increasing, which comprises a main shaft, the main shaft extends along the axial direction, the front end of the main shaft is provided with an axial fan rotor, the rear end of the axial fan rotor is provided with an intermediate case, and the intermediate case divides the whole duct into an inner duct and an outer duct. A heat exchanger is arranged in the outer duct and comprises an inner duct high-temperature tail gas channel communicated with the inner duct, and the heat exchanger further comprises an outer duct pressurized airflow channel communicated with the outer duct. The heat exchanger is additionally arranged in the engine, the fuel consumption rate is reduced, the output of usable work is improved, airflow in the inner culvert high-temperature tail gas channel and airflow in the outer culvert pressurization airflow channel are subjected to efficient heat exchange in the heat exchanger, and the temperature and pressure of the airflow in the outer culvert pressurization airflow channel are obviously improved; therefore, the expansion power capability in the outer culvert low-temperature airflow spray pipe is enhanced, the thrust of the engine is increased, and the oil consumption rate is reduced.

Description

Technical Field

[0001] This invention relates to the field of engine technology, specifically to a hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement. Background Technology

[0002] Aero engines, hailed as the crown jewel of industry, are highly complex power devices integrating materials science, energy technology, chemical engineering, and mechanical design. Their research and application have always been highly valued by technologically advanced nations, holding strategic significance not only in the military field but also playing a crucial role in commercial sectors such as civil aviation and general aviation. In recent years, with the rapid expansion of markets for unmanned aerial vehicle (UAV) exploration, logistics delivery, small flying cars, target drones, and high-end educational tools and toys, micro-aero engines, as the core power source for such aircraft, have demonstrated significant performance advantages over electric motors or small rockets. Their efficiency, cost, and reliability have a decisive impact on the development and application of the overall system.

[0003] Despite the significant progress made in aero-engine technology since World War II driven by the demand for large-scale military and civilian propulsion, the development of micro-engines still faces numerous bottlenecks. Military applications prioritize performance and stability, with lower sensitivity to cost; while the civilian sector has historically focused on large engines, resulting in relatively limited investment in research on micro-engine multi-purpose power systems. Under strong cost constraints, existing micro-engines generally suffer from insufficient thrust, low efficiency, poor operational stability, high fuel consumption, and severe pollutant emissions.

[0004] As an important type of micro-sized aero-engine, lightweight turbofan engines have attracted much attention in propulsion and energy systems due to their compact structure, light weight, low cost, high energy density and thrust-to-weight ratio, and ease of maintenance and storage. However, their miniaturization has also brought significant technical challenges: increased relative machining errors, exacerbated inter-blade leakage losses, reduced Reynolds numbers, and difficulties in combustion organization have resulted in persistently high fuel consumption rates in existing lightweight turbofan engines, severely restricting their further application. Common improvement methods, such as improving thermodynamic cycle parameters and component efficiency, have limited effectiveness due to the physical limitations imposed by miniaturization. Furthermore, although some studies have attempted to reduce fuel consumption by adjusting the duct structure or redesigning the impeller—for example, existing patent CN117552886A controls the duct outlet area by adjusting the inner plug cone to reduce airflow mixing losses, or CN210509424U uses a double-sided composite impeller structure to improve engine performance—these methods all require complex reconstruction of the engine's core components, increasing manufacturing costs and making the structure more complex and maintenance more difficult.

[0005] To address the aforementioned issues, a hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement is proposed. Without significantly altering the existing engine's main structure, it effectively reduces fuel consumption and improves propulsion efficiency, thus resolving the aforementioned problems. Summary of the Invention

[0006] The purpose of this invention is to provide a lightweight turbofan engine with a hybrid thermodynamic cycle and thrust enhancement. By adding a heat exchanger inside the engine, this invention achieves a significant reduction in fuel consumption and an effective increase in usable power output. It utilizes the airflow in the high-temperature exhaust gas passage and the airflow in the bypass pressurized airflow passage to carry out efficient heat exchange in the heat exchanger, which significantly increases the temperature and pressure of the airflow in the bypass pressurized airflow passage, thereby enhancing its expansion and work capacity in the low-temperature airflow nozzle of the bypass, ultimately significantly improving the overall thrust of the engine and reducing fuel consumption.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A hybrid thermodynamic cycle lightweight turbofan engine with thrust boosting includes a main shaft extending axially. An axial fan rotor is disposed at the front end of the main shaft, and an intermediate casing is disposed at the rear end of the axial fan rotor. The intermediate casing divides the entire bypass duct into an inner bypass duct and an outer bypass duct. A heat exchanger is disposed in the outer bypass duct. The heat exchanger includes an inner high-temperature exhaust gas passage communicating with the inner bypass duct, and the heat exchanger also includes an outer bypass pressurized airflow passage communicating with the outer bypass duct.

[0008] Furthermore, the inner duct includes a fan inner stator, which is located below the right side of the axial fan rotor. A diagonal flow compressor is arranged on one side of the fan inner stator relative to the axial fan rotor. A combustion chamber is arranged on one side of the diagonal flow compressor relative to the fan inner stator. A turbine rotor is arranged on one side of the combustion chamber relative to the diagonal flow compressor.

[0009] Furthermore, the outer bypass duct includes a fan outer bypass stator, which is located above and to the right of the axial fan rotor. An outer bypass rectifier blade is provided on one side of the fan outer bypass stator relative to the axial fan rotor, and a heat exchanger is provided on the other side of the outer bypass rectifier blade relative to the fan outer bypass stator.

[0010] Furthermore, the high-temperature exhaust gas channel includes a first inlet section, a first heat exchange section, and a first outlet section. One end of the first inlet section is connected to the inner channel, and the other end of the first inlet section is connected to the first heat exchange section. The side of the first heat exchange section opposite to the first inlet section is connected to one end of the first outlet section, and the other end of the first outlet section is connected to the high-temperature gas flow nozzle.

[0011] Furthermore, the first inlet section of the high-temperature exhaust gas passage is composed of a converging curved passage with a gradually decreasing cross-sectional area and a straight passage with a constant cross-sectional area connected sequentially.

[0012] Furthermore, the first heat exchange section of the high-temperature exhaust gas channel is composed of an expanding channel with a gradually increasing cross-sectional area and a straight channel with a constant cross-sectional area connected sequentially.

[0013] Furthermore, the bypass pressurized airflow channel includes a second inlet section, a second heat exchange section, and a second outlet section. One end of the second inlet section is connected to the bypass duct, and the other end of the second inlet section is connected to the second heat exchange section. The side of the second heat exchange section relative to the second inlet section is connected to one end of the second outlet section, and the other end of the second outlet section is connected to the bypass cryogenic airflow nozzle.

[0014] Furthermore, both the first outlet section and the second inlet section are equipped with inclined plates to guide the heat-exchanged airflow toward the inner high-temperature airflow nozzle and to assist in guiding the airflow of the second inlet section of the outer bypass pressurized airflow channel into the heat exchange section.

[0015] Furthermore, the second heat exchange section is composed of a straight channel with a constant cross-sectional area and a converging channel with a gradually decreasing cross-sectional area connected in sequence, and the second outlet section is an expanding channel with a gradually increasing cross-sectional area.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention achieves a significant reduction in fuel consumption and an increase in usable power output by adding a heat exchanger inside the engine. The high-temperature exhaust gas inside the engine and the low-temperature airflow outside the engine undergo efficient heat exchange in the heat exchanger, which significantly increases the temperature and pressure of the low-temperature airflow outside the engine, thereby enhancing its expansion and work capacity in the low-temperature airflow nozzle outside the engine, ultimately increasing the overall thrust of the engine and reducing the fuel consumption rate.

[0017] 2. This invention does not require redesigning or making complex modifications to the core components of the engine. Performance improvement can be achieved simply by integrating a heat exchanger, which greatly saves research and development and manufacturing costs, while maintaining the advantages of simple engine structure, high reliability and easy maintenance.

[0018] 3. By optimizing the airflow parameters in the internal high-temperature exhaust gas channel and the external bypass pressurized airflow channel, and through heat exchanger structural design, the thermodynamic cycle is optimized, further improving thermal efficiency and thrust output, achieving a comprehensive effect of increased thrust and energy saving. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2This is a PV comparison diagram of the hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement of the present invention and a conventional lightweight engine. Figure 3 This is a schematic diagram of the internal high-temperature exhaust gas passage on the front of the heat exchanger of the present invention. Figure 4 This is a schematic diagram of the external bypass pressurized airflow channel on the reverse side of the heat exchanger of the present invention; Figure 5 This is a schematic diagram of the axial fan rotor of the present invention.

[0020] In the diagram: 1. Main spindle; 2. Axial fan rotor; 3. Intermediate housing; 4. Internal Dao; 41. Fan Internal Stator; 42. Diagonal Flow Compressor; 5. Outer bypass duct; 51. Fan outer bypass stator; 52. Outer bypass rectifier blades; 6. Combustion chamber; 61. Turbine rotor; 7. Heat exchanger; 71. Inner high-temperature exhaust gas passage; 711. First inlet section; 712. First heat exchange section; 713. First outlet section; 72. Outer bypass pressurized airflow passage; 721. Second inlet section; 722. Second heat exchange section; 723. Second outlet section; 8. Inclined plate; 9. Inner high-temperature airflow nozzle; 10. Outer low-temperature airflow nozzle. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be described below with reference to the accompanying drawings. The embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0023] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0024] Please refer to the reference. Figure 1-5 This invention provides a lightweight turbofan engine with a hybrid thermodynamic cycle and thrust enhancement, the technical solution of which is as follows: A hybrid thermodynamic cycle lightweight turbofan engine with thrust boosting includes a main shaft 1 extending axially. An axial fan rotor 2 is disposed at the front end of the main shaft 1, and an intermediate casing 3 is disposed at the rear end of the axial fan rotor 2. The intermediate casing 3 divides the entire bypass duct into an inner bypass duct 4 and an outer bypass duct 5. A heat exchanger 7 is disposed in the outer bypass duct 5. The heat exchanger 7 includes an inner high-temperature exhaust gas passage 71 communicating with the inner bypass duct 4, and an outer bypass pressurized airflow passage 72 communicating with the outer bypass duct 5. The intermediate casing 3 structurally separates the inner duct 4 and the outer bypass duct 5, forming a dual-bypass airflow path and optimizing airflow distribution. The heat exchanger 7, through the interaction between the inner high-temperature exhaust gas passage 71 and the outer bypass pressurized airflow passage 72, utilizes the airflow in the inner high-temperature exhaust gas passage 71 to heat the airflow in the outer bypass pressurized airflow passage 72, achieving heat energy recovery and increasing the temperature and pressure of the airflow in the outer bypass pressurized airflow passage 72, thereby significantly increasing engine thrust, improving thermal efficiency, and reducing energy consumption. Through heat exchange between the airflow in the outer bypass pressurized airflow passage and the airflow in the inner high-temperature exhaust gas passage through optimized cycle parameters, the combined thrust of the outer bypass pressurized airflow passage and the inner high-temperature exhaust gas passage is optimized, achieving engine thrust enhancement.

[0025] like Figure 1 As shown, the inner duct 4 includes a fan inner stator 41, located below and to the right of the axial fan rotor 2. A diagonal-flow compressor 42 is positioned on the side of the fan inner stator 41 opposite to the axial fan rotor 2. A combustion chamber 6 is positioned on the side of the diagonal-flow compressor 42 opposite to the fan inner stator 41. A turbine rotor 61 is positioned on the side of the combustion chamber 6 opposite to the diagonal-flow compressor 42. The fan inner stator 41 guides and stabilizes the airflow in the inner duct 4. The diagonal-flow compressor 42 improves compression efficiency and increases airflow pressure in the inner duct 4 through its diagonal-flow design. The combustion chamber 6 mixes and burns the compressed air with fuel to generate high-temperature, high-pressure gas. The turbine rotor 61 captures the thermal and pressure energy of the high-temperature, high-pressure gas generated in the combustion chamber 6 and converts it into mechanical energy, thereby maintaining the continuous thermodynamic cycle of compression, combustion, and expansion of the entire engine.

[0026] like Figure 1As shown, the outer bypass duct 5 includes a fan outer bypass stator 51, which is located above and to the right of the axial fan rotor 2. An outer bypass rectifier blade 52 is positioned on the side of the fan outer bypass stator 51 opposite to the axial fan rotor 2, and a heat exchanger 7 is positioned on the side of the outer bypass rectifier blade 52 opposite to the fan outer bypass stator 51. The fan outer bypass stator 51 and the outer bypass rectifier blade 52 work together to guide the flow of low-temperature airflow within the outer bypass duct 5, improving the stability of the low-temperature airflow within the outer bypass duct 5. The heat exchanger 7 is arranged behind the outer bypass rectifier blade 52, fully utilizing the low-temperature characteristics of the airflow within the outer bypass duct 5. By exchanging with the high-temperature airflow within the inner bypass duct 4, it achieves pressurization and heating of the low-temperature airflow within the outer bypass duct 5, thereby enhancing thrust output.

[0027] like Figure 3 As shown, the high-temperature exhaust gas passage 71 includes a first inlet section 711, a first heat exchange section 712, and a first outlet section 713. One end of the first inlet section 711 is connected to the inner passage 4, and the other end of the first inlet section 711 is connected to the first heat exchange section 712. The side of the first heat exchange section 712 relative to the first inlet section 711 is connected to one end of the first outlet section 713, and the other end of the first outlet section 713 is connected to the inner high-temperature gas flow nozzle 9. Figure 3 For Figure 1 When viewed from the front, the high-temperature exhaust gas passage 71 is the front view of the heat exchanger 7. The first inlet section 711 guides the high-temperature gas flow into the first heat exchange section 712. The first heat exchange section 712 guides the heat-exchanged gas flow to the high-temperature gas flow nozzle 9 through the first outlet section 713 for discharge. This structure achieves efficient heat transfer while maintaining the smoothness of the airflow path.

[0028] like Figure 3 As shown, the first inlet section 711 of the high-temperature exhaust gas passage 71 is composed of a converging curved passage with a gradually decreasing cross-sectional area and a straight passage with a constant cross-sectional area connected sequentially. The converging curved passage accelerates the high-temperature gas flow velocity and increases kinetic energy, while the straight passage stabilizes the airflow and reduces pressure loss, ensuring that the airflow enters the heat exchange section uniformly and improving heat exchange efficiency.

[0029] like Figure 3 As shown, the first heat exchange section 712 of the high-temperature exhaust gas passage 71 is composed of an expanding channel with a gradually increasing cross-sectional area and a straight channel with a constant cross-sectional area connected sequentially. The expanding channel reduces the high-temperature gas velocity and increases the heat exchange time, while the straight channel maintains stable flow, ensuring sufficient heat conduction and maximizing thermal energy utilization.

[0030] like Figure 4As shown, the bypass pressurized airflow channel 72 includes a second inlet section 721, a second heat exchange section 722, and a second outlet section 723. One end of the second inlet section 721 is connected to the bypass duct 5, and the other end of the second inlet section 721 is connected to the second heat exchange section 722. The side of the second heat exchange section 722 relative to the second inlet section 721 is connected to one end of the second outlet section 723, and the other end of the second outlet section 723 is connected to the bypass cryogenic airflow nozzle 10. Figure 4 For Figure 1 When viewed from the front, the outer bypass pressurized airflow channel 72 is the reverse view of the heat exchanger 7. The second inlet section 721 guides the low-temperature airflow into the second heat exchange section 722. The second heat exchange section 722 absorbs the heat from the high-temperature airflow, increasing the temperature and pressure of the low-temperature airflow. The second outlet section 723 guides the heated airflow to the outer bypass low-temperature airflow nozzle 10 for ejection, increasing thrust. This structure achieves energy enhancement of the low-temperature airflow. The larger heat exchange area is beneficial to improving heat exchange efficiency. To further improve heat exchange efficiency, the entire wall of the first heat exchange section 712 and the second heat exchange section 722 can be designed as a wave shape. This provides a larger heat exchange area compared to a flat plate of the same size and also contributes to controlling the overall mass of the heat exchanger 7.

[0031] like Figure 4 As shown, both the first outlet section 713 and the second inlet section 721 are equipped with inclined plates 8, which are used to guide the heat-exchanged airflow towards the inner high-temperature airflow nozzle 9, and to assist in guiding the gas flow of the second inlet section 721 of the outer bypass pressurized airflow channel 72 into the second heat exchange section 722. The inclined plates 8 optimize the direction of the low-temperature gas and the high-temperature gas, reduce flow losses, and finally discharge them into the outside atmosphere.

[0032] like Figure 4 As shown, the second heat exchange section 722 is composed of a straight channel with a constant cross-sectional area and a converging channel with a gradually decreasing cross-sectional area connected sequentially. The second outlet section 723 is an expanding channel with a gradually increasing cross-sectional area. The straight channel ensures stable heat exchange of the low-temperature airflow, the converging channel accelerates the flow of the low-temperature airflow and increases its kinetic energy, and the expanding channel reduces the flow velocity of the low-temperature airflow and increases its pressure. Finally, the airflow is efficiently ejected through the outer bypass low-temperature airflow nozzle 10, maximizing thrust enhancement and energy recovery.

[0033] Working principle: The axial fan rotor 2 rotates to draw in air. The intermediate casing 3 divides the entire bypass duct into two paths: the inner bypass duct 4 and the outer bypass duct 5. The airflow in the outer bypass duct 5 is guided and rectified by the fan outer bypass stator 51 and the outer bypass rectifier blades 52, forming a stable low-temperature airflow. The airflow in the inner bypass duct 4 is guided by the fan inner bypass stator 41 and then enters the mixed-flow compressor 42 for compression. The mixed-flow design improves compression efficiency and pressure. The compressed high-pressure air enters the combustion chamber 6, mixes with fuel, and burns to generate high-temperature, high-pressure gas. The gas drives the turbine rotor 61 to rotate, converting thermal and pressure energy into mechanical energy, which drives the fan inner bypass stator 41 and the mixed-flow compressor 42 to operate continuously, maintaining the thermodynamic cycle. The high-temperature airflow from the turbine rotor 61 exits through the first inlet section 711 of the inner high-temperature exhaust gas passage 71 and enters the first heat exchange section 712, achieving efficient heat transfer. The low-temperature airflow in the outer bypass duct 5 enters the second heat exchange section 722 through the second inlet section 721, absorbing heat from the high-temperature airflow, resulting in a significant increase in temperature and pressure. The heated and pressurized airflow is then ejected at high speed from the outer bypass low-temperature airflow nozzle 10 through the second outlet section 723, generating additional thrust. The high-temperature airflow is discharged from the inner high-temperature airflow nozzle 9 through the first outlet section 713. The two airflows work synergistically to significantly increase the total thrust, while simultaneously achieving heat recovery and energy consumption reduction. Through the optimization of airflow parameters in the inner high-temperature exhaust gas passage 71 and the outer bypass pressurized airflow passage 72, and the structural design of the heat exchanger 7, the thermodynamic cycle is optimized, further improving thermal efficiency and thrust output, achieving a comprehensive effect of increased thrust and energy saving.

[0034] Embodiments of the present invention have been shown and described. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A lightweight turbofan engine with a hybrid thermodynamic cycle and thrust enhancement, characterized in that: Includes a main shaft (1) that extends axially, an axial fan rotor (2) is provided at the front end of the main shaft (1), an intermediate casing (3) is provided at the rear end of the axial fan rotor (2), the intermediate casing (3) divides the entire duct into an inner duct (4) and an outer duct (5), a heat exchanger (7) is provided in the outer duct (5), the heat exchanger (7) includes an inner high-temperature exhaust gas passage (71) that communicates with the inner duct (4), and the heat exchanger (7) also includes an outer duct pressurized airflow passage (72) that communicates with the outer duct (5).

2. The hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement according to claim 1, characterized in that: The inner channel (4) includes a fan inner stator (41), which is located below the right side of the axial fan rotor (2). A diagonal flow compressor (42) is provided on one side of the fan inner stator (41) relative to the axial fan rotor (2). A combustion chamber (6) is provided on one side of the diagonal flow compressor (42) relative to the fan inner stator (41). A turbine rotor (61) is provided on one side of the combustion chamber (6) relative to the diagonal flow compressor (42).

3. The hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement according to claim 1, characterized in that: The outer bypass duct (5) includes a fan outer bypass stator (51), which is located above the right side of the axial fan rotor (2). The fan outer bypass stator (51) has an outer bypass rectifier blade (52) on one side relative to the axial fan rotor (2), and a heat exchanger (7) is provided on the other side of the outer bypass rectifier blade (52) relative to the fan outer bypass stator (51).

4. The hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement according to claim 1, characterized in that: The high-temperature exhaust gas passage (71) includes a first inlet section (711), a first heat exchange section (712), and a first outlet section (713). One end of the first inlet section (711) is connected to the inner passage (4), and the other end of the first inlet section (711) is connected to the first heat exchange section (712). The side of the first heat exchange section (712) relative to the first inlet section (711) is connected to one end of the first outlet section (713), and the other end of the first outlet section (713) is connected to the high-temperature gas flow nozzle (9).

5. The lightweight turbofan engine with thrust enhancement hybrid thermodynamic cycle according to claim 4, characterized in that: The first inlet section (711) of the high-temperature exhaust gas channel (71) is composed of a converging curved channel with a gradually decreasing cross-sectional area and a straight channel with a constant cross-sectional area connected in sequence.

6. The hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement according to claim 5, characterized in that: The first heat exchange section (712) of the high-temperature exhaust gas channel (71) is composed of an expanding channel with a gradually increasing cross-sectional area and a straight channel with a constant cross-sectional area connected in sequence.

7. The hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement according to claim 3, characterized in that: The outer bypass pressurized airflow channel (72) includes a second inlet section (721), a second heat exchange section (722), and a second outlet section (723). One end of the second inlet section (721) is connected to the outer bypass (5), and the other end of the second inlet section (721) is connected to the second heat exchange section (722). The side of the second heat exchange section (722) relative to the second inlet section (721) is connected to one end of the second outlet section (723), and the other end of the second outlet section (723) is connected to the outer bypass cryogenic airflow nozzle (10).

8. The hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement according to claim 7, characterized in that: Both the first outlet section (713) and the second inlet section (721) are equipped with inclined plates (8) to guide the heat exchanged airflow to the inner high-temperature airflow nozzle (9) and to assist in guiding the airflow of the second inlet section (721) of the outer bypass pressurized airflow channel (72) into the heat exchange section.

9. The hybrid thermodynamic cycle lightweight turbofan engine with thrust enhancement according to claim 8, characterized in that: The second heat exchange section (722) is composed of a straight channel with a constant cross-sectional area and a converging channel with a gradually decreasing cross-sectional area connected in sequence, and the second outlet section (723) is an expanding channel with a gradually increasing cross-sectional area.

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