An electric propulsion ducted fan internal and external flow integration design method

Abstract

The application discloses an electric propulsion ducted fan internal and external flow integration design method, and belongs to the technical field of electric aircrafts, which comprises the following steps: (1) fan blade model simplification; (2) establishing a ducted fan geometry based on a momentum source term; (3) internal and external flow reasoning distribution law exploration; (4) fan blade design; and (5) ducted fan internal and external flow coupling calculation verification. In the initial design stage of the ducted fan, the aerodynamic coupling effect between the fan and the duct is fully considered, so that the effective coupling of the duct additional thrust and the fan thrust is realized, the problems that the existing method is difficult to quantize the duct additional thrust and cannot clearly determine the influence law of various design parameters on the duct additional thrust are solved, the overall propulsion efficiency of the ducted fan is effectively improved, the design process complexity is reduced, the design iteration number is reduced, and a ducted fan design scheme with excellent aerodynamic performance can be quickly obtained.

Description

Technical Field

[0001] This invention belongs to the field of electric aircraft technology, specifically relating to an integrated design method for the internal and external flow of an electric propulsion ducted fan. Background Technology

[0002] With the development of green aviation and the low-altitude economy, electric aircraft have broad development prospects. As an important power device for green aviation, electric propulsion ducted fans have been widely used due to their compact structure, high propulsion efficiency, high safety, and low noise. Numerous studies have been conducted both domestically and internationally on the aerodynamic characteristics of ducted fans. Research results show that under the coupling condition between the duct and the fan, the complex aerodynamic effects between the duct and the fan result in the duct providing a certain amount of additional thrust. Wind tunnel tests have shown that the additional thrust from the duct in a hovering state can account for up to 60% of the total thrust of a certain ducted fan. As an aviation power plant, the thrust requirement of an aircraft is one of the most direct and important performance indicators faced by ducted fans. The additional thrust effect of the duct under the coupling effect of the duct and the fan accounts for a certain proportion of the total thrust of the ducted fan, and it has a very important impact on the overall aerodynamic performance of the ducted fan.

[0003] Existing ducted fan design methods primarily employ a design approach based on the fan's total thrust. In the initial design phase, the fan bears the total thrust requirement, neglecting the influence of the duct's aerodynamic shape under fan-duct coupling conditions. An internal flow fan design is then developed, and after the fan blades are designed, internal and external flow coupling calculations and duct aerodynamic optimization are performed. This approach fails to fully consider the complex aerodynamic coupling between the duct and the fan, particularly failing to effectively quantify and utilize the additional thrust effect generated by their interaction. Research shows that when the fan operates inside the duct, the interaction between the fan-generated airflow and the duct's inner wall significantly affects the flow field distribution inside and outside the duct, forming a complex flow structure that, under certain conditions, generates significant additional thrust. Existing technologies often ignore this additional thrust effect, treating the duct merely as a passive aerodynamic channel. This results in ducted fan systems that cannot maximize the duct's thrust potential, thus reducing overall propulsion efficiency and limiting further performance improvements in electric aircraft.

[0004] Since there are no actual blades in the initial design stage of a ducted fan, it is impossible to directly analyze the aerodynamic coupling effect between the fan and the duct. Furthermore, iteratively designing the fan blades in a rough preliminary stage is cumbersome and consumes a significant amount of time and computational resources. Therefore, it is necessary to explore a design scheme that, without actual fan blades, investigates the internal and external thrust distribution of a ducted fan, obtains the design parameters of the fan blades, and then designs the geometric model of the ducted fan. Summary of the Invention

[0005] To address the shortcomings of existing ducted fan design methods, which design the fan and duct independently while neglecting the duct's additional thrust effect, thus failing to fully realize the overall performance of the ducted fan, this invention aims to propose an integrated internal and external flow design method for electric propulsion ducted fans. This method fully considers the aerodynamic coupling effect between the fan and duct during the initial design stage of the ducted fan, achieving effective coupling between the duct's additional thrust and the fan's thrust. This solves the problems of existing methods, such as the difficulty in quantifying the duct's additional thrust and the inability to clearly define the influence of various design parameters on the duct's additional thrust. Therefore, it effectively improves the overall propulsion efficiency of the ducted fan, reduces the complexity of the design process, decreases the number of design iterations, and quickly obtains a ducted fan design scheme with excellent aerodynamic performance.

[0006] A method for integrating internal and external flow design of an electric propulsion ducted fan includes the following steps: (1) Simplification of the fan blade model: For low-altitude, low-speed general aviation design conditions, when the initial design of the ducted fan does not have actual fan blades, the momentum theory assumption is used to simplify the fan model. The assumptions of momentum theory include: The airflow is an incompressible, non-viscous, ideal fluid; The fan can be viewed as a forward-moving impeller with an infinite number of blades; The axial velocity of the airflow is equal before and after the bladed disk, and there is a pressure difference before and after the fan; The momentum is uniform and axisymmetric, and there is no rotational component when the airflow passes through the bladed disk; Based on the above momentum theory assumptions, the fan geometry is simplified to a pressure rise surface, and the ducted fan model is simplified to a duct plus a momentum source term. A simplified ducted fan CFD calculation model without real blade geometry is constructed, forming a rapid simulation of fan-duct internal and external flow integration based on the fan momentum source term. (2) Establish the ducted fan geometry based on the momentum source term: The ducted fan design selects the maximum speed flight stage as the design condition, determines the corresponding flight altitude and flight speed, and completes the design thrust target setting for a single ducted fan. Based on the motor's size, power, and speed, select the appropriate motor and determine the ducted fan hub diameter. Based on the overall layout of the aircraft, motor matching and aerodynamic efficiency, the geometric parameters of the ducted fan are constrained, and the intake cone profile is controlled by a quadratic function to obtain the ducted fan geometry based on the momentum source term. (3) Exploring the distribution rules of inward and outward inference: Using a CFD model of a ducted fan, thrust distribution optimization was performed while satisfying the geometric constraints of the ducted fan. A duct chord length of 100 mm was selected. To focus on the impact of key variables such as fan diameter and total pressure rise on thrust, and to avoid interference from variations in chord length, a typical 100 mm chord length was chosen. This chord length represents the typical chord length of small to medium-sized ducted fans, facilitating calculation and comparison, and allowing all geometric parameters to be dimensionless using the chord length. Ducted fan geometries with different fan diameters were selected, and variable total pressure rise calculations were performed for each diameter. The total pressure rise ranged from 1000 Pa to 3000 Pa, with calculations performed every 200 Pa increase. The influence of variable total pressure rise on the additional thrust and total thrust of the ducted fan under different fan diameters was calculated. The results show that when the total pressure rise is constant, increasing the fan diameter increases both the additional thrust and the total thrust of the ducted fan; conversely, when the fan diameter is constant, increasing the total pressure rise also tends to increase both the additional thrust and the total thrust of the ducted fan. For each different fan diameter, the duct diameter-to-chord ratio is 1.5 to obtain the actual duct length for different fan diameter values. To ensure that the total thrust meets the design thrust, the total pressure rise is calculated for each fan diameter, with the total pressure rise changing by 100Pa each time. Finally, the duct and fan thrust distribution scheme for each fan diameter is obtained. Based on fan size, power consumption, and efficiency, the optimal thrust allocation scheme is determined, the fan diameter under the optimal thrust allocation scheme is obtained, and the ducted fan design parameters are obtained. (4) Fan blade design: Based on the determined design parameters of the ducted fan, flow calculations are performed on the S2 flow surface of the ducted fan. The blade twist law is selected, and the velocity triangles for different blade heights are solved radially. Then, using the method of superimposing thickness along the mid-arc line, primitive airfoils are generated on the rotating flow surfaces for different blade heights. The primitive airfoils for different blade heights are radially superimposed to perform three-dimensional modeling design of the blades. Then, the internal flow characteristics of the fan are calculated to analyze whether the fan characteristics meet the design requirements. If the internal flow characteristics of the fan meet the requirements, the fan is matched with the duct for internal and external flow coupling calculations to complete the overall design of the ducted fan with real fan blades. If the internal flow characteristics of the fan do not meet the requirements, the flow calculations for the S2 flow surface of the ducted fan are re-performed. (5) Verification of internal and external flow coupling calculations for ducted fans: The fan blades designed based on the optimal thrust distribution scheme are integrated with the determined duct, hub and intake cone to construct a complete 3D model of the ducted fan. The model is then subjected to high-fidelity internal and external flow coupling CFD calculation using the multi-reference frame method to obtain the real comprehensive performance.

[0007] Furthermore, in step (3), different fan diameters are selected as follows: D =240mmD =250 mm D =260 mm D =270 mm D =280 mm D =290 mm D =300 mm.

[0008] Furthermore, in step (2), the constraints imposed on the geometric parameters of the ducted fan include the design thrust of a single ducted fan, the ducted fan hub diameter, the ducted fan diameter, the duct reference profile, the duct cone angle β, the fan axial position X, the duct diameter-to-chord ratio, and the intake cone profile.

[0009] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. In this invention, an integrated design method for the internal and external flow of an electric propulsion ducted fan is proposed. In the initial design stage of the ducted fan, the aerodynamic coupling effect between the fan and the duct is fully considered to achieve effective coupling between the additional thrust of the duct and the thrust of the fan, thereby effectively improving the overall propulsion efficiency of the ducted fan, reducing the complexity of the design process, reducing the number of design iterations, and quickly obtaining a ducted fan design scheme with excellent aerodynamic performance.

[0010] 2. In this invention, based on momentum theory assumptions, the fan geometry is simplified into a momentum source term. During calculation, a pressure rise surface is used to simulate the fan's pressurization effect, thus forming a rapid simulation scheme for integrated internal and external flow of the fan / duct based on the fan momentum source term. This allows for CFD calculations of coupled internal and external flow during the initial design of the ducted fan, fully considering the aerodynamic coupling effect between the fan and the duct, quantifying the duct's additional thrust, and allocating thrust between the duct and the fan based on the total thrust index. This fundamentally solves the problems of performance loss and lengthy design cycles caused by traditional design methods that optimize the duct and fan independently and ignore their strong coupling aerodynamic effects, providing an innovative solution for the rapid development of high-performance electric propulsion ducted fans. Attached Figure Description

[0011] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a design flowchart of the present invention; Figure 2 This is a schematic diagram showing the geometric structure of the ducted fan of the present invention; Figure 3This is a schematic diagram of the geometry of the ducted fan based on the momentum source term of the present invention; Figure 4 This is a schematic diagram illustrating the effect of the total pressure rise of the variable fan on the additional thrust of the duct under different fan diameters according to the present invention. Figure 5 This is a schematic diagram illustrating the effect of the total pressure rise of the variable fan on the total thrust under different fan diameters according to the present invention. Figure 6 This is a flowchart illustrating the design process of the fan blades for this invention. Figure 7 This is a schematic diagram of the integrated internal and external flow design model of the electric propulsion ducted fan of the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0013] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0014] It should be noted that the labels and letters in the following figures represent similar items, therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0015] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only used for the purpose of simplifying the description of this invention 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 limitations on this invention. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0016] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0017] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0018] Refer to the instruction manual. Figure 1-7 , A method for integrating internal and external flow design of an electric propulsion ducted fan includes the following steps: Step 1. Simplify the fan blade model This invention addresses the design conditions of low-altitude, low-speed general aviation. Since the initial design of the ducted fan does not include actual fan blades, a momentum theory assumption is used to simplify the fan model in order to quantify the additional thrust of the duct and incorporate it into the design scheme. 1. The airflow is an incompressible, inviscid, ideal fluid: This assumption simplifies the behavior of the airflow, ignores the viscosity and compressibility effects of the airflow, and helps to simplify the calculation process, especially in the preliminary design stage.

[0019] 2. The fan can be viewed as a forward-moving impeller with an infinite number of blades: In this model, the fan is not considered in terms of the specific structure of the blades, but rather as an impeller with no thickness. When airflow passes through this impeller, it is affected by a uniform thrust distribution, thereby changing the momentum of the airflow.

[0020] 3. The ducted fan design method of the present invention is aimed at low-speed general aviation aircraft, where the incoming airflow is subsonic and operates in the incompressible Ma range. It assumes that the axial velocity of the airflow is equal before and after the bladed disk, and that there is a pressure difference before and after the fan. This assumption ignores the influence of the bladed disk thickness on the airflow, and also assumes that the airflow velocity is the same before and after the fan. The pressurization effect of the fan is simulated only by the pressure difference.

[0021] 4. The momentum is uniform and axisymmetric, and there is no rotational component when the airflow passes through the impeller: This assumption further simplifies the problem. It is assumed that the airflow remains axisymmetric and has no rotational component when passing through the fan, which facilitates the solution of the overall flow field.

[0022] Based on the above assumptions, the fan geometry can be simplified to a pressure rise surface, and the ducted fan model can be simplified to a duct plus a momentum source term, forming a rapid simulation of the fan-duct internal and external flow integration based on the fan momentum source term.

[0023] Step 2. Establish the ducted fan geometry based on the momentum source term. Before constructing the ducted fan model for integrated design, it is necessary to first clarify its design specifications and geometric constraints, which stem from its specific application scenario as a power unit for a distributed electric propulsion aircraft. Under this implementation method, the ducted fan design selects the maximum speed flight stage as the design condition, with a flight altitude of 3km and a flight speed of 75m / s. The design thrust target for a single ducted fan is set at 103.33N.

[0024] Ducted fans are used in fixed-wing aircraft. The size of the motor determines the size of the hub. An excessively large motor results in a large hub, a large frontal area, and high drag. Therefore, it is necessary to select a motor that is as small as possible in size but still meets the power and speed requirements. Through research, the TP Power TP 100L motor was selected. The motor's performance parameters are shown in Table 1, meeting the power and speed requirements.

[0025] In summary, to achieve the aforementioned thrust targets and meet the comprehensive requirements of overall aircraft layout, motor matching, and aerodynamic efficiency, the key constraints shown in Table 2 were imposed on the geometric parameters of the ducted fan. By controlling the inlet cone profile using a quadratic function, the ducted fan geometry based on the momentum source term was ultimately obtained, as shown below. Figure 3 As shown.

[0026] Table 1 Performance parameters of TP 100L motor Table 2 Geometric Design Specifications and Constraints for Electric Propulsion Ducted Fans Step 3. Exploring the distribution patterns of internal and external flow reasoning By utilizing rapid simulation of the integrated internal and external flow of a ducted fan based on momentum source term (MSM), the thrust distribution law between the duct and the fan is systematically, efficiently, and quickly explored under the premise of satisfying geometric constraints. This allows for the scientific determination of the optimal ratio of duct additional thrust to fan thrust under the total thrust requirement. Consequently, in the aerodynamic design of the fan, the goal is no longer to provide the full 103.33N thrust, but only about 76.4N. This quantitative reduction in design load is a prerequisite for achieving a low-load, high-flow-through-flow design of the fan, thereby optimizing system power consumption and improving propulsion efficiency.

[0027] Traditional ducted fan coupling design relies on MRF (Multi-Reference Frame) CFD simulations that incorporate real 3D blade geometry. Such high-precision simulations typically require at least 1.25 million mesh cells for a single design case to obtain reliable flow field and thrust data, and steady-state solutions on conventional computing workstations take approximately 12 to 24 hours. This time and computational cost severely restricts the feasibility of rapid exploration of the design space and parameter optimization in the early stages of design. The rapid integrated simulation method employed in this invention, while ensuring the capture of the coupled aerodynamic effects of the duct and fan core, greatly simplifies the model. CFD calculations for a single design case require only about 200,000 mesh cells, and the convergence time can be reduced to about one hour, improving efficiency by an order of magnitude. This method makes it possible to systematically analyze multiple design combinations in batches within a limited timeframe, thereby achieving rapid and scientific thrust allocation optimization, rather than relying on experience or costly trial and error.

[0028] The specific implementation plan based on this rapid method is as follows: Thrust allocation optimization is performed within a defined constraint framework, with a duct chord length of 100 mm selected. To focus on the impact of key variables such as fan diameter and total pressure rise on thrust, and to avoid interference from variations in chord length, a typical 100 mm duct chord length is chosen. This represents the typical chord length of small to medium-sized ducted fans, facilitating calculation and comparison, and allowing all geometric parameters to be dimensionless using the chord length. Ducted fan geometries with different fan diameters are selected respectively. D =240mm D =250 mm D =260 mm D =270 mm D =280 mm D =290 mm D =300 mm, for each ducted fan with a different diameter, the total pressure rise was calculated. The total pressure rise of the fan ranged from 1000 Pa to 3000 Pa, and a calculation was performed every 200 Pa increase. The influence of the variable total pressure rise on the additional thrust and total thrust of the ducted fan was calculated for different fan diameters. The calculation results are as follows. Figure 4 , Figure 5 As shown in the figure. The calculation results show that when the total fan pressure rise is constant, increasing the fan diameter leads to an increase in both the duct's additional thrust and the total thrust. When the fan diameter is constant, an increase in the total fan pressure rise also leads to an increase in both the duct's additional thrust and the total thrust.

[0029] For each different fan diameter, the duct diameter-to-chord ratio is 1.5 to obtain the actual duct length for different fan diameters. To ensure that the total thrust meets the design thrust, the total pressure rise is calculated for each fan diameter, with the total pressure rise changing by 100Pa each time. Finally, the duct and fan thrust distribution schemes for each fan diameter are obtained, as shown in Table 3.

[0030] Table 3. Duct and fan thrust distribution schemes for different fan diameters The ducted fan designed in this invention is a high-flow-through-rate, low-pressure-ratio compressor. Its design parameters mainly include three aspects: design flow rate, design pressure rise, and design speed. Since a TP100L motor with a rated speed of 10,000 rpm is selected, the fan's design speed is n = 10,000 rpm to ensure good matching between the motor and the fan. Next, the design schemes for different fan diameters are determined, thereby determining the design flow rate and design pressure rise of the ducted fan. The parameters of ducted fans with different diameters that meet the total thrust conditions are shown in Table 7. For a single ducted fan, the fan diameter should not be too large, as an excessively large fan will directly affect the distributed layout space. Simultaneously, the power of the ducted fan should be as small as possible to ensure normal operation with high propulsion efficiency at rated power. Finally, by comprehensively balancing size, power consumption, and efficiency, the optimal thrust distribution point is determined from the scientific schemes listed in Table 4: fan diameter D = 270 mm, with a ducted additional thrust ratio of approximately 27.6%. This decision-making process fully demonstrates the key advantages of the rapid integrated simulation method developed in this invention in achieving high-efficiency and precise thrust distribution design.

[0031] Table 4. Parameters of ducted fans of different diameters that meet the total thrust condition. Step 4. Fan blade design The fan design is based on the design methodology for aero-engine compressors, and the design process is as follows: Figure 6As shown, the design parameters are first determined. For this ducted fan, the design parameters are the design flow rate, design total pressure rise, and design speed. As discussed in the previous section, the design parameters of the ducted fan using the integrated internal and external flow design method have been determined. Next, flow calculations are performed on the S2 flow surface of the ducted fan. The blade twist law is selected, and the velocity triangles for different blade heights are solved radially. Then, using a mid-arc superposition thickness method, primitive airfoils are generated on the rotating flow surfaces at different blade heights. These primitive airfoils are then radially superimposed to perform a three-dimensional blade design. Finally, the internal flow characteristics of the fan are calculated to analyze whether the fan characteristics meet the design requirements. If the internal flow characteristics meet the requirements, the fan is matched with the duct for internal and external flow coupling calculations. At this point, the overall design of the ducted fan with actual fan blades is complete.

[0032] Step 5. Integrated design calculation and verification of electric propulsion ducted fan for internal and external flow. To verify the effectiveness of the integrated design method described in this invention, the fan blades designed based on the optimal thrust distribution scheme are integrated with the determined duct, hub, and intake cone to construct a complete 3D model of the ducted fan, as shown below. Figure 7 As shown. The multiple reference frame (MRF) method was used to perform high-fidelity CFD calculations on the model, coupling internal and external flows, to obtain its true comprehensive performance. The final calculation results are: under design conditions, the design flow rate... The total design pressure rises to 1679.21 Pa, isentropic efficiency is 0.852, total thrust is F =105.7N, the additional thrust of the duct is =14.95N, the ducted thrust accounts for 14.14% of the total thrust, the power is 11.42kW, and the propulsion efficiency is 0.6896.

[0033] Traditional methods neglect the duct coupling effect and design the fan solely based on total thrust requirements, matching a simple straight-walled duct. Under the same total thrust requirement of 105N and design conditions, the traditional design scheme yields the following results: a total pressure rise of 2295.43 Pa and an isentropic efficiency of... 0.8879, total thrust is F =105.4N, the additional thrust of the duct is =0.512N, the ducted thrust accounts for 0.5% of the total thrust, the power is 12.17kW, and the propulsion efficiency is 0.6471. Among them, the ducted thrust accounts for only 0.5% of the total thrust, and the total thrust meets the design requirements.

[0034] This invention successfully increases the proportion of ducted thrust to 14.14%, significantly reducing fan load and power consumption. The input power is reduced by approximately 6.2%, demonstrating significant energy savings. While maintaining the same thrust, the system's propulsion efficiency is improved by approximately 6.6% compared to traditional solutions. This clearly demonstrates that simply maximizing fan component efficiency is not the optimal solution; rather, by optimizing the duct and fan as a whole for thrust synergy, this invention achieves the best system-level performance.

[0035] The above description constitutes an embodiment of the present invention. The foregoing descriptions are preferred embodiments of the present invention. Unless there is a clear contradiction or a prerequisite for a particular preferred embodiment, the preferred embodiments can be arbitrarily combined and used. The embodiments and specific parameters described are merely for clearly illustrating the verification process of the invention and are not intended to limit the scope of patent protection of the present invention. The scope of patent protection of the present invention is still determined by its claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention should also be included within the scope of protection of the present invention.

Claims

1. A method for integrated internal and external flow design of an electric propulsion ducted fan, characterized in that, Includes the following steps: (1) Simplification of the fan blade model: For low-altitude, low-speed general aviation design conditions, when the initial design of the ducted fan does not have actual fan blades, the momentum theory assumption is used to simplify the fan model. The assumptions of momentum theory include: The airflow is an incompressible, non-viscous, ideal fluid; The fan can be viewed as a forward-moving impeller with an infinite number of blades; The axial velocity of the airflow is equal before and after the bladed disk, and there is a pressure difference before and after the fan; The momentum is uniform and axisymmetric, and there is no rotational component when the airflow passes through the bladed disk; Based on the above momentum theory assumptions, the fan geometry is simplified to a pressure rise surface, and the ducted fan model is simplified to a duct plus a momentum source term. A simplified ducted fan CFD calculation model without real blade geometry is constructed, forming a rapid simulation of fan-duct internal and external flow integration based on the fan momentum source term. (2) Establish the ducted fan geometry based on the momentum source term: The ducted fan design selects the maximum speed flight stage as the design condition, determines the corresponding flight altitude and flight speed, and completes the design thrust target setting for a single ducted fan. Based on the motor's size, power, and speed, select the appropriate motor and determine the ducted fan hub diameter. Based on the overall layout of the aircraft, motor matching and aerodynamic efficiency, the geometric parameters of the ducted fan are constrained, and the intake cone profile is controlled by a quadratic function to obtain the ducted fan geometry based on the momentum source term. (3) Exploring the distribution rules of inward and outward inference: Using a CFD model of a ducted fan, thrust distribution optimization was performed while satisfying the geometric constraints of the ducted fan. A duct chord length of 100mm was selected, and ducted fan geometries with different diameters were chosen. For each diameter, a variable total pressure rise calculation was performed, ranging from 1000Pa to 3000Pa, with calculations repeated every 200Pa increase. The influence of the variable total pressure rise on the additional thrust and total thrust of the ducted fan under different fan diameters was calculated. The results show that when the total pressure rise is constant, increasing the fan diameter increases both the additional thrust and the total thrust of the ducted fan; when the fan diameter is constant, increasing the total pressure rise also tends to increase both the additional thrust and the total thrust of the ducted fan. For each different fan diameter, the duct diameter-to-chord ratio is 1.5 to obtain the actual duct length for different fan diameter values. To ensure that the total thrust meets the design thrust, the total pressure rise is calculated for each fan diameter, with the total pressure rise changing by 100Pa each time. Finally, the duct and fan thrust distribution scheme for each fan diameter is obtained. Based on fan size, power consumption, and efficiency, the optimal thrust allocation scheme is determined, the fan diameter under the optimal thrust allocation scheme is obtained, and the ducted fan design parameters are obtained. (4) Fan blade design: Based on the determined design parameters of the ducted fan, flow calculations are performed on the S2 flow surface of the ducted fan. The blade twist law is selected, and the velocity triangles for different blade heights are solved radially. Then, using the method of superimposing thickness along the mid-arc line, primitive airfoils are generated on the rotating flow surfaces for different blade heights. The primitive airfoils for different blade heights are radially superimposed to perform three-dimensional modeling design of the blades. Then, the internal flow characteristics of the fan are calculated to analyze whether the fan characteristics meet the design requirements. If the internal flow characteristics of the fan meet the requirements, the fan is matched with the duct for internal and external flow coupling calculations to complete the overall design of the ducted fan with real fan blades. If the internal flow characteristics of the fan do not meet the requirements, the flow calculations for the S2 flow surface of the ducted fan are re-performed. (5) Verification of internal and external flow coupling calculations for ducted fans: The fan blades designed based on the optimal thrust distribution scheme are integrated with the determined duct, hub and intake cone to construct a complete 3D model of the ducted fan. The model is then subjected to high-fidelity internal and external flow coupling CFD calculation using the multi-reference frame method to obtain the real comprehensive performance.

2. The integrated design method for internal and external flow of an electric propulsion ducted fan according to claim 1, characterized in that, In step (3), different fan diameters are selected as follows: D =240mm D =250 mm D =260 mm D =270 mm D =280 mm D =290 mm D =300 mm.

3. The integrated design method for internal and external flow of an electric propulsion ducted fan according to claim 1, characterized in that, In step (2), the constraints imposed on the geometric parameters of the ducted fan include the design thrust of a single ducted fan, the ducted fan hub diameter, the ducted fan diameter, the duct reference profile, the duct cone angle β, the fan axial position X, the duct diameter-to-chord ratio, and the intake cone profile.

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