Ducted fan design method with flow as key variable

Abstract

The invention discloses a ducted fan design method with flow as a key variable, and belongs to the field of ducted fan design. The method comprises the specific steps that the flow needed by a duct is determined; the rotor inlet area and the throat area are calculated according to the flow; determining radial positions of rotor / stator inlet and outlet equidistant control points; constructing a speed triangle based on the set rotating speed and the calculated torque speed and axial speed; geometric feature determination of the rotor and the stator is completed; and exporting geometric data to turbine simulation software to complete three-dimensional modeling of the rotor and the stator. According to the method, the problems that traditional design depends on experience and is low in efficiency are solved, the design period is remarkably shortened while the precision is guaranteed, and the reliability and aerodynamic performance of the ducted fan are improved.

Description

Technical Field

[0001] The present invention belongs to the field of ducted fan design, and in particular relates to a ducted fan design method with flow rate as a key variable. Background Art

[0002] For ducted fan design, it is of great significance to accurately solve the blade inlet and outlet speeds and velocity distribution patterns. As the working conditions of the blades change, the geometric characteristics of the blade control points and the flow characteristics will change dramatically. In particular, as the flight Mach number increases, the impact of airflow compressibility becomes more and more significant. Flow characteristics such as shock waves will also appear in the blade channel, making the calculation of the inlet and outlet speeds of ducted fan blades more and more difficult. At the same time, the design process of ducted fans often requires several iterations, but too many calculations will prolong the entire design cycle. Therefore, its calculation method cannot be too complicated and the calculation results must have a certain degree of accuracy. Therefore, a ducted fan design method that can be designed quickly and has a certain degree of calculation accuracy is needed.

[0003] Traditional ducted fan design methods calculate blade exit velocity using methods such as momentum theory, blade element theory, and vortex theory. After the design is complete, multiple iterations and corrections are often required, making the calculation process extremely complex. Therefore, it is necessary to develop a ducted fan design method that can achieve rapid design while maintaining a certain level of calculation accuracy. This method would help designers quickly determine the rationality of design parameters and achieve a preview effect. Summary of the Invention

[0004] Technical issues to be solved:

[0005] In order to avoid the shortcomings of the existing technology, the present invention provides a ducted fan design method with flow rate as the key variable. With flow rate as the control core, combined with parametric models and commercial software tools, it solves the problems of traditional design relying on experience and low efficiency. While ensuring accuracy, it significantly shortens the design cycle and improves the reliability and aerodynamic performance of the ducted fan.

[0006] The technical solution of the present invention is: a ducted fan design method with flow rate as the key variable, the specific steps are as follows:

[0007] Based on the required pressure ratio, thrust and inlet velocity, the outlet velocity is calculated to determine the required flow rate of the duct;

[0008] Calculate the rotor inlet area and throat area based on the flow rate using the continuity equation;

[0009] Based on the rotor inlet area, throat area, and inlet section-to-hub ratio, the casing radius, rotor inlet hub radius, and throat hub radius are calculated. The hub shape is then derived using the Lee curve parameterization formula to determine the radial positions of the rotor / stator inlet and outlet equidistant control points.

[0010] Based on the flow rate and the rotor inlet and outlet areas, the rotor inlet and outlet axial speeds are calculated using aerodynamic functions. The rotor outlet total temperature is calculated based on the rotor inlet total temperature, efficiency, and pressure ratio, and then the rotor power is calculated to obtain the torque of each radial control point of the rotor. The speed is set and the speed triangle of torque, axial speed, and speed is constructed.

[0011] Based on the velocity triangle, the Carter formula is used to calculate the blade geometric inlet and outlet angles, blade bend angle, and installation angle. A constant chord length design is adopted, with the blade chord length being the difference between the inlet and outlet axial directions. A double arc is used as the mid-arc line, and the NACA0016 blade profile is superimposed with the thickness distribution to complete the determination of the geometric characteristics of the rotor stator.

[0012] Export the geometric data to the turbine anti-vibration software to complete the three-dimensional modeling of the rotor stator.

[0013] A further technical solution of the present invention is: the calculation formula for the required flow rate of the duct is as follows:

[0014] q m =T req / (V5-V0)

[0015] Where, T req is the required thrust, V5 and V0 are the outlet and inlet velocities respectively.

[0016] A further technical solution of the present invention is: the calculation formula of the rotor inlet area is as follows:

[0017]

[0018] Where, are the stagnation pressure and temperature on the rotor inlet section respectively; q(λ) is the gas dynamics function on the section; K is a comprehensive constant that depends on the gas specific heat ratio k and the gas constant R;

[0019] The throat area calculation formula is consistent with the rotor inlet area calculation formula, and only the corresponding variables need to be changed.

[0020] A further technical solution of the present invention is: the casing radius R Shroud The calculation formula is as follows:

[0021]

[0022] Where H is the inlet section to hub ratio.

[0023] A further technical solution of the present invention is: the hub radius R at the rotor inlet 1hub The calculation formula is as follows:

[0024] R 1hub =H*R Shroud .

[0025] A further technical solution of the present invention is: the hub radius R at the throat hub The calculation formulas are as follows:

[0026]

[0027] Where x th is the axial position of the throat, ΔY is the difference in radial direction between the rotor inlet and the throat hub, R 1hub is the hub radius at the rotor inlet; Lee A Lee B and Lee C is the coefficient that controls the shape of the curve.

[0028] A further technical solution of the present invention is: the Lee curve expression of the wheel hub is as follows:

[0029] Lee A =(18x1 2 -12x1) / (6x1 2 -6x1+1)

[0030] Lee C =(6x1-3) / (6x1 2 -6x1+1)

[0031] Lee B =(-12x1 2 +4) / (6x1 2 -6x1+1)

[0032] Where x1 is the axial position of the rotor inlet.

[0033] A further technical solution of the present invention is: the double arc expression is:

[0034]

[0035] Where R1 and R2 are the radii of the two ends of the double arc, a is the maximum deflection position of the mid-arc, b is the chord length, θ1 and θ2 represent the leading edge angle and the trailing edge angle;

[0036] A ducted fan is designed by a ducted fan design method using flow rate as a key variable. The hub of the ducted fan adopts a Lee curve shape, the blade mid-arc is a double arc, the blade thickness distribution is NACA0016, and the rotor and stator outlet speed directions are axial.

[0037] A ducted fan design system with flow rate as the key variable includes the following functional modules:

[0038] Input parameter configuration module, used to receive target pressure ratio, thrust, inlet velocity and gas physical properties;

[0039] The flow calculation module calculates the outlet velocity based on the required pressure ratio, thrust, and inlet velocity, and thus determines the required flow rate of the duct;

[0040] A geometric parameter generation module determines the rotor inlet and throat areas based on the flow rate using a continuity equation, and generates the casing radius, hub shape, and radial positions of the rotor / stator inlet and outlet control points by combining the hub ratio and a parameterized Lee curve formula;

[0041] An aerodynamic characteristic calculation module calculates the rotor inlet and outlet axial velocities based on the flow rate and geometric parameters using an aerodynamic function, derives the power and torque in combination with the total temperature, pressure ratio, and efficiency, and constructs a velocity triangle;

[0042] The blade profile generation module uses Carter's formula to calculate the blade's geometric inlet and outlet angles, bend angles, and installation angles, and generates blade profiles based on double arcs and standard thickness distribution;

[0043] The 3D modeling module exports geometric data to 3D modeling software to generate a 3D model of the ducted fan.

[0044] Beneficial effects

[0045] The present invention provides a beneficial effect: It uses flow rate as a key parameter for ducted fan design. By inputting certain key variables, it can rapidly create three-dimensional models of the casing, hub, and blades while maintaining a certain level of computational accuracy. After generating the geometric model of the ducted fan, subsequent numerical simulation and other processing can be directly performed on it, enabling rapid design of the ducted fan and helping designers quickly determine the rationality of design parameters, providing a preview effect.

[0046] The specific effect analysis is as follows:

[0047] 1. This invention employs an inverse design method with flow rate as the core variable, inferring geometric parameters from target performance (pressure ratio, thrust), replacing the traditional empirically driven, multiple-iteration process. Combined with parametric models (such as Lee curves and double arcs), this method enables rapid geometry generation, shortening the design cycle by approximately 40% to 60%.

[0048] 2. The present invention uses aerodynamic functions, continuity equations and Carter's formula to accurately match flow and geometric parameters, and combines discretized control points (20 radial segments) with cubic spline interpolation to optimize the distribution of aerodynamic parameters and avoid local flow mutations. NUMECA simulation verification shows that the relative error between the static pressure distribution on the blade mid-diameter surface and the design value is ≤4.3%, and the error between the actual pressure ratio and the design pressure ratio is ≤7.7%. Figure 5 shown.

[0049] 3. The present invention optimizes the distribution of blade power through active flow control, ensures reasonable blade tip twist speed, avoids flow separation and stall risks caused by too low flow, and improves aerodynamic stability and operational safety.

[0050] 4. The parametric hub shape (Lee curve formula) and double arc design of the present invention support rapid adjustment of geometric shape to adapt to different flight Mach numbers, pressure ratios and thrust requirements, expanding the design application range.

[0051] 5. The present invention generates geometric data through Matlab and directly imports it into NUMECA for three-dimensional modeling and simulation, realizing full process automation from theoretical calculation to engineering verification, reducing manual intervention, lowering design error rate, and improving production efficiency.

[0052] 6. The systematic design process (flow → area → geometry → shape) of the present invention forms a standardized operating framework, reduces reliance on experience, ensures the consistency and repeatability of design results, and is suitable for mass production and multi-model development. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The figure is a flow chart of a ducted fan design method with flow rate as a key variable, which is optional according to an embodiment of the present invention.

[0054] Figure 2 The present invention provides a method for recalculating the distribution of added power along the blade height according to an embodiment of the present invention.

[0055] Figure 3 The present invention provides a method for calculating a median arc according to an embodiment of the present invention.

[0056] Figure 4 This is an effect diagram achieved after the program-generated cloud points in an embodiment of the present invention are imported into NUMECA three-dimensional modeling.

[0057] Figure 5 This is a distribution diagram of the static pressure along the axial direction at the blade mid-diameter position obtained by simulation using the commercial software NUMECA according to an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0059] Based on the problem that the calculation process of traditional ducted fan design methods is extremely complex, this paper proposes a ducted fan design method with flow rate as the key variable. The specific steps are as follows:

[0060] Step 1: Based on the required pressure ratio, thrust, and inlet velocity, calculate the outlet velocity and determine the required flow rate of the duct.

[0061] Step 2: Calculate the rotor inlet area and throat area based on the flow rate using the continuity equation;

[0062] Step 3: Based on the rotor inlet area, throat area, and inlet section-to-hub ratio, calculate the casing radius, rotor inlet hub radius, and throat hub radius. Combined with the Lee curve parameterization formula, the hub shape is obtained, and the radial positions of the rotor / stator inlet and outlet equidistant control points are determined.

[0063] Step 4: Based on the flow rate and the rotor inlet and outlet areas, the rotor inlet and outlet axial velocities are calculated using the aerodynamic function. The rotor outlet total temperature is calculated based on the rotor inlet total temperature, efficiency, and pressure ratio, and then the rotor work is calculated to obtain the torque of each radial control point of the rotor. The speed is set and the speed triangle of torque, axial speed, and speed is constructed.

[0064] Step 5: Based on the velocity triangle, use Carter's formula to calculate the blade geometric inlet and outlet angles, blade bend angle, and installation angle. Adopt a constant chord design, where the blade chord length is the difference between the inlet and outlet axes. Use a double arc as the mid-arc line, and superimpose the NACA0016 blade profile thickness distribution to complete the determination of the rotor stator's geometric characteristics.

[0065] Step 6: Export the geometric data to the turbine anti-vibration software to complete the three-dimensional modeling of the rotor stator.

[0066] The present invention adopts an inverse problem design method centered on flow rate, combined with parametric modeling and high-precision computational models, to shorten the design cycle while improving aerodynamic performance and reliability. It also achieves rapid three-dimensional verification through an engineering tool chain, providing a systematic solution for the efficient design and optimization of ducted fans.

[0067] The above technical solution is further analyzed below with reference to the accompanying drawings:

[0068] In one embodiment, referring to Figure 1As shown in the figure, first determine the required flow rate of the ducted fan. The blades need to be discretized into multiple segments along the radial direction. The midpoint of each segment is defined as a control point. The continuous parameter values on the blades are thus discretized into values at multiple control points. Parameters include: thrust and flow values on the blades. From this, the radial distribution law of parameters such as thrust and flow values can be obtained. Then determine the blade inlet velocity distribution, which also needs to be discretized into values at the control points. Then determine the geometric characteristics of the blades, including the number of blades, blade diameter, blade hub ratio, etc. Based on the obtained discretized thrust, flow value, inlet velocity and blade geometric characteristics, the blade outlet circumferential velocity and axial velocity at each control point are calculated. Finally, the velocity triangle at each control point can be obtained, and the key geometric parameters such as the geometric inlet and outlet angles, blade bend angle, and installation angle of each control point can be determined. Then, the fan components and casing can be three-dimensionally modeled.

[0069] Furthermore, when the blade is discretized into multiple segments along the radial direction, the number of segments is selected as 20, that is, each blade is discretized into 20 segments, and the continuous parameter values on the blade are thus discretized into values at 20 control points.

[0070] Furthermore, according to the required flow rate, the continuity equation is used to calculate the inlet area of the rotor blade, and then the radial distribution position of the control points on the blade is further calculated, thereby calculating the circumferential velocity of each control point.

[0071] Furthermore, according to the flow rate and area corresponding to each control point, the aerodynamic function q(λ) of each control point can be obtained using the continuity equation, and the axial velocity of each control point can be obtained according to the aerodynamic function q(λ) of each control point.

[0072] Furthermore, the torque velocity corresponding to each control point is calculated based on the amount of work applied to the blade. Given the torque velocity, axial velocity, and circumferential velocity at each control point, it is easy to determine its velocity triangle. Based on the velocity triangle at each control point, the corresponding blade geometry can be obtained.

[0073] In one embodiment, a ducted fan design method using flow rate as a key variable includes the following steps:

[0074] Step 1: Determine the required flow rate of the ducted fan. The static pressure at the ducted outlet needs to be calculated by the known pressure ratio, and the outlet Mach number is calculated based on the outlet static pressure. Then, based on the known inlet speed, the required thrust and the calculated outlet speed, the required flow rate q of the ducted fan is obtained. m for:

[0075] q m =T req / (V5-V0)

[0076] Where Treq is the required thrust, V5 and V0 are the outlet and inlet velocities respectively.

[0077] Step 2: Determine the rotor inlet and throat area of the ducted fan. Using the required duct flow rate obtained in step 1, the areas of the rotor inlet and throat can be calculated using the continuity equation. The rotor inlet area can be expressed as:

[0078]

[0079] Where, are the stagnation pressure and temperature at the rotor inlet section, respectively; q(λ) is the gas dynamics function at the section; and K is a composite constant that depends on the gas specific heat ratio k and the gas constant R. The throat area calculation process is similar.

[0080] Step 3: Determine the casing radius, the hub Lee curve shape, and the radial positions of the finite number of blade control points. Using the rotor inlet and throat areas calculated in Step 2 and the known hub-to-hub ratio, the casing radius and the hub radius at the rotor inlet and throat can be determined.

[0081] The casing radius R Shroud The calculation formula is as follows:

[0082]

[0083] Where H is the inlet section to hub ratio.

[0084] The hub radius R at the rotor inlet 1hub The calculation formula is as follows:

[0085] R 1hub =H*R Shroud

[0086] The hub radius R at the throat hub The calculation formulas are as follows:

[0087]

[0088] Where x th is the axial position of the throat, ΔY is the difference in radial direction between the rotor inlet and the throat hub, R 1hub is the hub radius at the rotor inlet; Lee A Lee B and Lee C is the coefficient that controls the shape of the curve.

[0089] The wheel hub Lee curve formula is:

[0090] Lee A =(18x1 2-12x1) / (6x1 2 -6x1+1)

[0091] Lee c =(6x1-3) / (6x1 2 -6x1+1)

[0092] Lee B =(-12x1 2 +4) / (6x1 2 -6x1+1)

[0093] Based on the hub shape and casing radius, the radial positions of a limited number of equidistant control points at the inlet and outlet of the rotor stator can be calculated.

[0094] Step 4: Calculate the velocity triangle of a finite number of rotor control points. Based on the flow calculated in step 1 and the rotor inlet and outlet areas calculated in step 3, the aerodynamic function q(λ) at the rotor inlet and outlet can be obtained through the continuity equation, from which the axial velocity at the rotor inlet and outlet can be obtained. Given the rotor inlet total temperature, efficiency, and pressure ratio, the outlet total temperature can be calculated:

[0095]

[0096] Where, and is the total temperature of the rotor inlet and outlet, is the rotor pressure ratio, is the rotor efficiency, and k is the gas specific heat ratio. Based on the known inlet total temperature and the outlet total temperature, the rotor power can be calculated. In order to avoid the blade tip twist speed being too low, resulting in a negative blade angle, the power needs to be redistributed:

[0097]

[0098] Where, He Lu i are the flow rate and work amount corresponding to each control point, q m and Lu are the total flow and total work. The radial distribution of work can be recalculated by the above formula, as follows: Figure 2 shown.

[0099] From this, the torque of each radial control point of the rotor can be obtained

[0100]

[0101] Where u i is the rotational speed for each control point.

[0102] Knowing the torque, axial velocity, and rotational speed allows us to derive the velocity triangle at each control point. The calculation method for the stator is the same as that for the rotor, with the only difference being that the stator does not need to calculate the power added. Instead, the torque calculated by the rotor is used directly, ensuring that the direction of the stator's outlet velocity is axial.

[0103] Step 5: Determine the geometric characteristics of the rotor stator. Based on the velocity triangle calculated in step 4, the inlet and outlet angles of each control point can be calculated. To ensure that the calculated inlet and outlet angles are at the same radial position, cubic spline interpolation is performed on the inlet and outlet angles at the 20 control points, and the inlet and outlet angles at 20 equal radial positions are recalculated. Using the Carter formula as the lagging angle model, the geometric inlet and outlet angles, blade bend angle, and installation angle of the blade can be obtained.

[0104] Geometric inlet and outlet angles:

[0105]

[0106] Where β1 and β2 are the geometric inlet and outlet angles of the blade, v 1a and v 2a is the axial velocity of the blade inlet and outlet, u and Δw are the rotational speed and torsion speed respectively.

[0107] Blade angle:

[0108]

[0109] Where θ is the blade bending angle, m is the empirical coefficient, t and b are the grid pitch and chord length, i * The angle of attack is used as a known input.

[0110] Mounting angle:

[0111] β y =β1+θ1

[0112] Where, β y is the installation angle, θ1 is the blade leading edge angle.

[0113] The blade profile is generated by superimposing the NACA_0016 thickness distribution on the mid-arc line, and the mid-arc line adopts a double arc, such as Figure 3 In the double-arc blade profile shown, one end of circle O1 and circle O2 lies on the x-axis, and the other end is tangent to each other, with the point of tangency at the point of maximum deflection of the mid-arc line. The radii of the two arcs are R1 and R2, respectively, and the leading and trailing edge angles of the mid-arc line are θ1 and θ2, respectively. The blade bending angle is θ. The following geometric relationship can be obtained through calculation:

[0114]

[0115] From this formula, we can see that if the maximum deflection position a, chord length b and blade bending angle θ are known, the leading edge angle θ1 and trailing edge angle θ2 can be calculated by solving nonlinear equations. The formula for the arc radius at both ends is as follows:

[0116]

[0117] Get the double arc expression:

[0118]

[0119] Next, by superimposing the NACA_0016 thickness distribution, the point coordinates of the blade profile at each radial position of the blade can be obtained.

[0120] Step 6: 3D modeling of the rotor stator. Given the geometric features of the rotor stator, the point coordinates of the rotor stator are exported into a geomturbo file using Matlab, and then the file is imported into the commercial software NUMECA for 3D modeling.

[0121] Step 7: Ducted fan modeling. Same as step 6, import the coordinates of the casing and hub points determined in step 3 into NUMECA for 3D modeling, as shown in the following example: Figure 4 shown.

[0122] In one embodiment, a ducted fan is designed by a ducted fan design method using flow rate as a key variable, characterized in that: the hub of the ducted fan is shaped like a Lee curve, the center arc line of the blade is a double arc, the blade thickness distribution is NACA0016, and the rotor and stator outlet velocity directions are axial.

[0123] In one embodiment, a ducted fan design system with flow rate as a key variable includes the following functional modules:

[0124] Input parameter configuration module, used to receive target pressure ratio, thrust, inlet velocity and gas physical properties;

[0125] The flow calculation module calculates the outlet velocity based on the required pressure ratio, thrust, and inlet velocity, and thus determines the required flow rate of the duct;

[0126] A geometric parameter generation module determines the rotor inlet and throat areas based on the flow rate using a continuity equation, and generates the casing radius, hub shape, and radial positions of the rotor / stator inlet and outlet control points by combining the hub ratio and a parameterized Lee curve formula;

[0127] An aerodynamic characteristic calculation module calculates the rotor inlet and outlet axial velocities based on the flow rate and geometric parameters using an aerodynamic function, derives the power and torque in combination with the total temperature, pressure ratio, and efficiency, and constructs a velocity triangle;

[0128] The blade profile generation module uses Carter's formula to calculate the blade's geometric inlet and outlet angles, bend angles, and installation angles, and generates blade profiles based on double arcs and standard thickness distribution;

[0129] The 3D modeling module exports the geometric data to the 3D modeling software to generate a 3D model of the ducted fan.

[0130] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A ducted fan design method with flow rate as the key variable, characterized by The specific steps are as follows: Based on the required pressure ratio, thrust and inlet velocity, the outlet velocity is calculated to determine the required flow rate of the duct; Calculate the rotor inlet area and throat area based on the flow rate using the continuity equation; Based on the rotor inlet area, throat area, and inlet section-to-hub ratio, the casing radius, rotor inlet hub radius, and throat hub radius are calculated. The hub shape is then derived using the Lee curve parameterization formula to determine the radial positions of the rotor / stator inlet and outlet equidistant control points. Based on the flow rate and the rotor inlet and outlet areas, the rotor inlet and outlet axial speeds are calculated using aerodynamic functions. Based on the rotor inlet total temperature, efficiency, and pressure ratio, the rotor outlet total temperature is calculated, and then the rotor work is calculated to obtain the torque of each radial control point of the rotor. Set the speed and construct the speed triangle of torque, axial speed and speed; Based on the velocity triangle, the Carter formula is used to calculate the blade geometric inlet and outlet angles, blade bend angle, and installation angle. A constant chord length design is adopted, with the blade chord length being the difference between the inlet and outlet axial directions. A double arc is used as the mid-arc line, and the NACA0016 blade profile is superimposed with the thickness distribution to complete the determination of the geometric characteristics of the rotor stator. The geometric feature data is exported to the impeller simulation software to complete the three-dimensional modeling of the rotor stator, thus obtaining the ducted fan.

2. The method for designing a ducted fan with flow rate as a key variable according to claim 1, characterized in that: The calculation formula for the required flow rate of the duct is as follows: q m =T req / (V5-V0) Where, T req is the required thrust, V5 and V0 are the outlet and inlet velocities respectively.

3. The method for designing a ducted fan with flow rate as a key variable according to claim 2, characterized in that: The calculation formula of the rotor inlet area is as follows: Where, are the stagnation pressure and temperature on the rotor inlet section respectively; q(λ) is the gas dynamics function on the section; K is a comprehensive constant that depends on the gas specific heat ratio k and the gas constant R; The throat area calculation formula is consistent with the rotor inlet area calculation formula, and only the corresponding variables need to be changed.

4. The method for designing a ducted fan with flow rate as a key variable according to claim 3, wherein: The casing radius R Shroud The calculation formula is as follows: Where H is the inlet section to hub ratio.

5. The method for designing a ducted fan with flow rate as a key variable according to claim 4, characterized in that: The hub radius R at the rotor inlet 1hub The calculation formula is as follows: R 1hub =H*R Shroud 。 6. The method for designing a ducted fan with flow rate as a key variable according to claim 5, characterized in that: The hub radius R at the throat hub The calculation formulas are as follows: Where x th is the axial position of the throat, ΔY is the difference in radial direction between the rotor inlet and the throat hub, R 1hub is the hub radius at the rotor inlet; Lee a Lee B and Lee C is the coefficient that controls the shape of the curve.

7. The method for designing a ducted fan with flow rate as a key variable according to claim 6, characterized in that: The Lee curve expression of the wheel hub is as follows: Lee A =(18x1 2 -12x1) / (6x1 2 -6x1+1) Lee C =(6x1-3) / (6x1 2 -6x1+1) Lee B =(-12x1 2 +4) / (6x1 2 -6x1+1) Where x1 is the axial position of the rotor inlet.

8. The method for designing a ducted fan with flow rate as a key variable according to claim 7, characterized in that: The double arc expression is: Where R1 and R2 are the radii of the two ends of the double arc, a is the maximum deflection position of the mid-arc, b is the chord length, θ1 and θ2 represent the leading edge angle and the trailing edge angle; 9. A ducted fan designed by the ducted fan design method with flow rate as a key variable according to any one of claims 1 to 8, characterized in that: The hub of the ducted fan adopts a Lee curve shape, the middle arc line of the blade is a double arc, the blade thickness distribution is NACA0016, and the rotor and stator outlet speed directions are axial.

10. A ducted fan design system with flow rate as a key variable, used to implement the ducted fan design method with flow rate as a key variable as claimed in any one of claims 1 to 8, characterized in that Includes the following functional modules: Input parameter configuration module, used to receive target pressure ratio, thrust, inlet velocity and gas physical properties; The flow calculation module calculates the outlet velocity based on the required pressure ratio, thrust, and inlet velocity, and thus determines the required flow rate of the duct; A geometric parameter generation module determines the rotor inlet and throat areas based on the flow rate using a continuity equation, and generates the casing radius, hub shape, and radial positions of the rotor / stator inlet and outlet control points by combining the hub ratio and a parameterized Lee curve formula; An aerodynamic characteristic calculation module calculates the rotor inlet and outlet axial velocities based on the flow rate and geometric parameters using an aerodynamic function, derives the power and torque in combination with the total temperature, pressure ratio, and efficiency, and constructs a velocity triangle; The blade profile generation module uses Carter's formula to calculate the blade's geometric inlet and outlet angles, bend angles, and installation angles, and generates blade profiles based on double arcs and standard thickness distribution; The 3D modeling module exports the geometric data to the 3D modeling software to generate a 3D model of the ducted fan.

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