Ducted fan design method and device based on similarity criterion

Abstract

The invention discloses a ducted fan design method and device based on a similarity criterion, and the method comprises the steps: taking a small ducted fan as a prototype, obtaining basic aerodynamic performance information of the small ducted fan through aerodynamic performance simulation, and obtaining a similarity relation of the aerodynamic performance of the ducted fan through a dimension analysis method in combination with a similarity theory; basic information such as the geometric dimension, the rotating speed and the incoming flow speed of the target large ducted fan is rapidly predicted; then, numerical simulation is conducted on the predicted large ducted fan, the aerodynamic performance of the large ducted fan is further verified, and therefore rapid design and performance prediction of the large ducted fan are achieved. According to the method, the large ducted fan is designed by utilizing the existing mature small ducted fan based on the similarity criterion, so that the scientificity and accuracy of the design are improved, the test and calculation cost is remarkably reduced, and the research and development period is shortened. And meanwhile, the aerodynamic performance and efficiency of the ducted fan can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ducted fans of electric propulsion aircraft, and in particular to a ducted fan design method and a device based on a similarity criterion. Background Art

[0002] Against the background of the rapid development of electric vertical take-off and landing aircraft and new energy aircraft, ducted fan propulsion systems have attracted much attention in recent years due to their huge potential. If ducted fans are to be widely used in aircraft, improving their aerodynamic performance is the key. Although significant progress has been made in the research on similarity criteria for compressors and wind turbines, research on similarity criteria for ducted fans is still lacking. In the research and development of large-size ducted fans, related research faces many challenges due to limitations in site, equipment and computing resources. Therefore, conducting aerodynamic performance evaluation research on prototype ducted fans and scaled ducted fans based on different similarity theory frameworks is of great significance for reducing test costs, shortening R&D cycles and accurately obtaining aerodynamic performance parameters.

[0003] The inventors found that the prior art has the following shortcomings: (1) There are many studies on the aerodynamic performance of small ducted fans, which are mostly applied in the field of electric vertical take-off and landing (eVTOL) aircraft; however, due to their small thrust and high speed, small ducted fans are difficult to be directly applied in the field of large electric propulsion aircraft. In the research field of large ducted fans, there are few relevant literatures and patents, and there is a lack of a complete aerodynamic performance prediction system for large ducted fans. This makes it difficult to accurately predict the aerodynamic performance parameters of large ducted fans during the design process, increasing the design difficulty and R&D cost. (2) Although similarity criteria are widely used in engineering design, in the field of ducted fan design, especially in the design of large ducted fans, the systematic application and research of similarity criteria are relatively insufficient, which makes it difficult for designers to predict the performance of prototypes through model tests, and it is difficult to quickly design large ducted fans with the help of mature small ducted fans, so that it is impossible to quickly locate design problems and optimize them in the early stages of design. (3) Existing ducted fans still have problems with aerodynamic performance and aerodynamic efficiency that need to be further improved. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a ducted fan design method and device based on similarity criteria. The method takes a set small ducted fan as a prototype object, obtains aerodynamic performance information of the small ducted fan as basic aerodynamic information through aerodynamic performance simulation, determines the size range and performance range of the required large ducted fan according to the actual situation, and further predicts the aerodynamic performance of the large ducted fan based on similarity theory to determine its geometric size, rotation speed and incoming flow velocity; then, through numerical simulation of the large ducted fan, further determines the aerodynamic performance of the large ducted fan, so as to achieve the purpose of saving calculation cost and shortening calculation cycle, and can be extended to the research and development of rapid design and performance prediction of large ducted fans. At the same time, it can also improve the aerodynamic performance and efficiency of the ducted fan.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A ducted fan design method based on similarity criteria comprises the following steps:

[0007] Step S1: obtaining basic information of a known small ducted fan, the basic information at least including geometric model information, speed information and working state information;

[0008] Step S2: constructing a geometric model of a known small ducted fan according to basic information;

[0009] Step S3: constructing a numerical calculation model for the existing small ducted fan, realizing numerical simulation calculation of the steady-state flow field, and obtaining basic aerodynamic performance information of the small ducted fan;

[0010] Step S4: using dimensional analysis method to obtain a similarity relationship of aerodynamic performance of ducted fan;

[0011] Step S5: acquiring basic information of the target large ducted fan, the basic information at least including geometric size range information, speed range information and working state range information;

[0012] Step S6: predicting basic information of the target thrust large ducted fan according to the aerodynamic performance result of the small ducted fan, the performance of the target small ducted fan and the similarity relationship, the basic information including geometric size information, rotation speed information and incoming wind speed information;

[0013] Step S7: constructing a large ducted fan geometric model according to the estimated geometric dimension information of the large ducted fan;

[0014] Step S8: construct a numerical calculation model for the estimated large ducted fan, implement numerical simulation calculation of the steady-state flow field, and obtain basic aerodynamic performance information of the large ducted fan.

[0015] Furthermore, in the step S2, based on the actual structural information of the small ducted fan with known aerodynamic performance, the main structure is extracted, the components that are not important for fluid simulation are ignored and simplified, and the external flow field area is established; in the step S3, when the known small ducted fan fluid domain is meshed and the mesh independence is verified, a suitable turbulence model and suitable boundary conditions are selected, and steady-state numerical simulation calculations under different working conditions are carried out to obtain the aerodynamic performance information of the small ducted fan under different working conditions; and the step S6 also includes: after predicting the basic information of the target thrust large ducted fan, based on the prediction results and the required goals, a design optimization plan for the target large ducted fan is customized;.

[0016] Furthermore, in the step S7, the proportional relationship between the inferred large ducted fan and the small ducted fan is quickly scaled down or enlarged using three-dimensional modeling software to complete the construction of the large ducted fan geometric model; in step S8, when meshing the inferred large ducted fan fluid domain and verifying the mesh independence, a suitable turbulence model and suitable boundary conditions are selected to carry out steady-state numerical simulation calculations under different working conditions, thereby obtaining the aerodynamic performance information of the large ducted fan under different working conditions; and also includes: based on the basic aerodynamic performance information of the large ducted fan obtained by numerical calculation, confirming that a large ducted fan model that meets the target requirements is obtained.

[0017] A ducted fan design system based on similarity criteria, comprising: an information acquisition module, a geometric model building module, an aerodynamic performance simulation module, a similarity relationship calculation module and a scheme optimization module;

[0018] The information acquisition module is used to obtain the basic information of the known small ducted fan and the basic information of the target large ducted fan, the basic information at least includes the geometric model information of the small ducted fan, the aerodynamic performance information of the small ducted fan, the geometric size range information of the large ducted fan, the speed range information of the large ducted fan and the working state range information of the large ducted fan; the geometric model construction module is used to establish the geometric model of the known ducted fan and the calculated large ducted fan; the aerodynamic performance simulation module is used to realize steady-state numerical calculation of the known ducted fan and the calculated large ducted fan to obtain the aerodynamic performance of the known small ducted fan and the calculated large ducted fan; the similarity relationship inference module is used to select and infer the aerodynamic similarity relationship between the appropriate small ducted fan and the large ducted fan in combination with the actual situation of the ducted fan flow field; the scheme optimization module is used to predict the aerodynamic performance of the target large ducted fan at different sizes, and then customize the specific design scheme of the size and speed of the target ducted fan based on the predicted results of the aerodynamic performance.

[0019] A ducted fan designed based on a similarity criterion comprises a casing (1), a motor part (2), a guide cone part (3), an impeller (4), a front guide vane (5), and a rear guide vane (6); the impeller is arranged between the guide cone part and the motor part, the impeller comprises a hub and blades, a plurality of blades are distributed along the outer circumference of the hub, the outer circumference of the guide cone part is connected to the inner circumference of the casing through a plurality of front guide vanes distributed along the circumference, and the outer circumference of the motor part is connected to the inner circumference of the casing through a plurality of rear guide vanes distributed along the circumference; the front guide vane (5) comprises a first front guide vane and a second front guide vane, a plurality of first front guide vanes and a plurality of second front guide vanes are connected to the inner circumference of the casing through a plurality of rear guide vanes distributed along the circumference; the front guide vane (5) comprises a first front guide vane and a second front guide vane, a plurality of first front guide vanes and a plurality of second front guide vanes are connected to the inner circumference of the casing through a plurality of rear guide vanes distributed along the circumference. The blades are arranged alternately at intervals along the circumferential direction, the front guide vane is composed of a first guide vane portion (51) and a second guide vane portion (52), the first guide vane portion is arranged radially outside the second guide vane portion, and the radial lengths of the first guide vane portion and the second guide vane portion are 40%-60% of the overall radial length of the front guide vane; the first front guide vane is provided with a first three-dimensional twisted blade portion (53) only on its first guide vane portion (51), the second guide vane portion (52) of the first front guide vane is provided as a two-dimensional blade portion, the second front guide vane is provided with a second three-dimensional twisted blade portion (54) only on its second guide vane portion, and the first guide vane portion of the second front guide vane is provided as a two-dimensional blade portion.

[0020] Further, the coverage range of the first three-dimensional twisted blade portion (53) is substantially the entire radial length of the first guide vane portion (51), and the coverage range of the second three-dimensional twisted blade portion (54) is substantially the entire radial length of the second guide vane portion (52).

[0021] Furthermore, relative to the two-dimensional blade portion, the first three-dimensional twisted blade portion (53) is extended toward the circumferential right side of the adjacent two-dimensional blade portion; relative to the two-dimensional blade portion, the second three-dimensional twisted blade portion (54) is extended toward the circumferential right side of the adjacent two-dimensional blade portion, that is, the inclined extension directions of the first three-dimensional twisted blade portion and the second three-dimensional twisted blade portion are consistent or the same.

[0022] Furthermore, the blade inlet angle of the first three-dimensional twisted blade portion (53) is smaller than its blade outlet angle, and the blade inlet angle of the second three-dimensional twisted blade portion (54) is smaller than its blade outlet angle; and the blade inlet angle of the first three-dimensional twisted blade portion (53) is equal to or greater than the blade inlet angle of the second three-dimensional twisted blade portion (54), and the blade outlet angle of the first three-dimensional twisted blade portion (53) is greater than the blade outlet angle of the second three-dimensional twisted blade portion (54).

[0023] Furthermore, the radial length of the first guide vane portion (51) and the second guide vane portion (52) is 50% of the overall radial length of the front guide vane (5).

[0024] A ducted fan design method and device based on similarity criterion of the present invention takes a set small ducted fan as a prototype object, obtains aerodynamic performance information of the small ducted fan as basic aerodynamic information through aerodynamic performance simulation, determines the size range and performance range of the required large ducted fan according to actual conditions, and further predicts the aerodynamic performance of the large ducted fan based on similarity theory to determine its geometric size, rotation speed and incoming flow velocity; then, through numerical simulation of the large ducted fan, further determines the aerodynamic performance of the large ducted fan, thereby achieving the purpose of saving calculation cost and shortening calculation cycle, and can be extended to the research and development of rapid design and performance prediction of large ducted fans.

[0025] The present invention can reduce the vortex between the flow channels of the leading guide vanes, reduce the collision flow and vortex at the top and root of the leading guide vanes, improve the guiding effect of the leading guide vanes, and reduce the flow loss caused by the vortex, thereby improving the aerodynamic performance and efficiency of the ducted fan. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flow chart of a ducted fan design method based on similarity criteria of the present invention;

[0027] Figure 2 is a system principle diagram of a ducted fan design method based on similarity criteria of the present invention;

[0028] Figure 3 It is a schematic diagram of the structure of the ducted fan of the present invention;

[0029] Figure 4 It is a schematic diagram of the front guide vane structure of the ducted fan of the present invention.

[0030] In the figure: a cover 1, a motor part 2, a guide cone part 3, an impeller 4, a front guide vane 5, a first guide vane part 51, a second guide vane part 52, a first three-dimensional twisted blade part 53, a second three-dimensional twisted blade part 54, and a rear guide vane 6. DETAILED DESCRIPTION

[0031] In order to make the technical solution and advantages of the present invention clearer, the technical solution of the present invention will be further described in detail in detail with reference to the accompanying drawings. It can be understood that the specific embodiments described here are only partial embodiments of the present invention, which are only used to explain the present invention, not to limit the present invention. It should be noted that, for the convenience of description, only the parts / structures related to the present invention are shown in the accompanying drawings, and other related parts can refer to the general design. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other to obtain new embodiments.

[0032] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In addition, unless otherwise defined, the technical terms or scientific terms used in the description of the present invention should be the common meanings understood by ordinary technicians in the field to which the present invention belongs.

[0033] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0034] like Figure 1-2 As shown, a ducted fan design method based on similarity criteria includes the following steps:

[0035] Step S1: obtaining basic information of a known small ducted fan, the basic information at least including geometric model information (structural information), speed information and working status information;

[0036] Step S2: constructing a geometric model of a known small ducted fan according to basic information;

[0037] Specifically, based on the actual structural information of a small ducted fan with known aerodynamic performance, the main structure is extracted, components that are not important for fluid simulation are ignored and simplified, and the outer flow field region is established.

[0038] Step S3: constructing a numerical calculation model for the existing small ducted fan, realizing numerical simulation calculation of the steady-state flow field, and obtaining basic aerodynamic performance information of the small ducted fan;

[0039] Specifically, when meshing and verifying the mesh independence of a known small ducted fan fluid domain, a suitable turbulence model and appropriate boundary conditions are selected to carry out steady-state numerical simulation calculations under different working conditions, thereby obtaining the aerodynamic performance information of the small ducted fan under different working conditions.

[0040] Step S4: using dimensional analysis method to obtain a similarity relationship of aerodynamic performance of ducted fan;

[0041] Specifically, the similarity relationship between the small ducted fan and the large ducted fan is solved as follows:

[0042] S4-1: Analyze the basic flow conditions during the operation of the ducted fan. When the ducted fan is in the air, the blades are affected by the flow of the incoming wind speed to produce lift resistance, thereby generating torque M and axial thrust T.

[0043] S4-2: Take the three independent dimensions of mass M, length L, and time T to form the MLT correlation relationship / function;

[0044] S4-3: Obtain the physical quantities and dimensions related to the aerodynamic performance of the ducted fan:

[0045] Including: blade number Z, blade twist angle θ, blade radius R, blade chord length c, fluid density ρ, fluid viscosity μ, incoming wind speed V ∞ , speed n;

[0046]

[0047]

[0048] S4-4: Take the blade radius R, fluid density ρ and incoming wind speed V ∞ As basic quantities, the geometric characteristics, fluid properties and motion characteristics are characterized as basic quantities, and other physical quantities are dimensionless;

[0049] S4-5: According to the π theorem, we can get 7 dimensionless numbers;

[0050] S4-6:

[0051] [Z]=1=[R a1 ρ b1 V ∞ c1 ]=L a1 (ML -3 ) b1 (LT -1 ) c1

[0052]

[0053] The solution is,

[0054] but,

[0055] S4-7: Similarly, other dimensionless numbers can be obtained, which are:

[0056]

[0057]

[0058] During design calculations, each parameter can take the dimensionless numerical part for design calculations.

[0059] S4-8: Analyze the feasibility of various similarity criteria for ducted fans according to the design objectives, where π6 and π7 are the torque coefficient and thrust coefficient respectively;

[0060] The π1 criterion requires that the number of blades of small ducted fans and large ducted fans remain the same;

[0061] The π2 criterion requires that the blade twist angles of small ducted fans and large ducted fans remain consistent;

[0062] The π3 criterion requires that the geometric dimensions of small ducted fans and large ducted fans be equally enlarged or reduced;

[0063] The π4 criterion is the Reynolds number. The flow field of the ducted fan is located in the "self-modeling area". If π3 is satisfied, π4 is satisfied.

[0064] The π5 criterion is the tip speed ratio, which needs to satisfy Among them, n0, R0, V ∞0 All are physical quantities of small ducted fans; n1, R1, V ∞1 All are physical quantities of large ducted fans;

[0065] On the basis of satisfying the π3 criterion, there are two solutions to satisfy the π5 criterion:

[0066] Option 1: V ∞0 =V ∞1 ,but

[0067] Furthermore, the torque thrust

[0068] Solution 2: n0 = n1, then

[0069] Furthermore, the torque thrust

[0070] During design calculations, each parameter can take the dimensionless numerical part for design calculations.

[0071] Step S5: acquiring basic information of the target large ducted fan, the basic information at least including geometric size range information, speed range information and working state range information;

[0072] Step S6: predicting basic information of the target thrust large ducted fan according to the aerodynamic performance result of the small ducted fan, the performance of the target small ducted fan and the similarity relationship, the basic information including geometric size information, rotation speed information and incoming wind speed information;

[0073] Furthermore, it also includes: after predicting the basic information of the target thrust large ducted fan, based on the prediction results and the required goals, customizing the design optimization scheme of the target large ducted fan;

[0074] Step S7: constructing a large ducted fan geometric model according to the estimated geometric dimension information of the large ducted fan;

[0075] Specifically, the calculated proportional relationship between the large ducted fan and the small ducted fan is quickly scaled (reduced or enlarged) using 3D modeling software to complete the construction of the large ducted fan geometric model;

[0076] Step S8: constructing a numerical calculation model for the estimated large ducted fan, realizing numerical simulation calculation of the steady-state flow field, and obtaining basic aerodynamic performance information of the large ducted fan;

[0077] Specifically, when meshing the fluid domain of the extrapolated large ducted fan and verifying the mesh independence, a suitable turbulence model and appropriate boundary conditions are selected, and steady-state numerical simulation calculations are carried out under different working conditions to obtain the aerodynamic performance information of the large ducted fan under different working conditions.

[0078] Furthermore, it also includes: confirming that a large ducted fan model that meets the target requirements is obtained based on basic aerodynamic performance information of the large ducted fan obtained through numerical calculations.

[0079] like Figure 2 As shown, a ducted fan design system based on similarity criteria includes: an information acquisition module, a geometric model building module, an aerodynamic performance simulation module, a similarity relationship calculation module and a scheme optimization module;

[0080] The information acquisition module is used to obtain the basic information of the known small ducted fan and the basic information of the target large ducted fan, the basic information at least includes the geometric model information of the small ducted fan, the aerodynamic performance information of the small ducted fan, the geometric size range information of the large ducted fan, the speed range information of the large ducted fan and the working state range information of the large ducted fan; the geometric model construction module is used to establish the geometric model of the known ducted fan and the calculated large ducted fan; the aerodynamic performance simulation module is used to realize steady-state numerical calculation of the known ducted fan and the calculated large ducted fan to obtain the aerodynamic performance of the known small ducted fan and the calculated large ducted fan; the similarity relationship inference module is used to select and infer the aerodynamic similarity relationship between the appropriate small ducted fan and the large ducted fan in combination with the actual situation of the ducted fan flow field; the scheme optimization module is used to predict the aerodynamic performance of the target large ducted fan at different sizes, and then customize the specific design scheme of the size, speed, etc. of the target ducted fan based on the predicted results of the aerodynamic performance.

[0081] A ducted fan design method based on similarity criteria of the present invention takes a set small ducted fan as a prototype object, obtains aerodynamic performance information of the small ducted fan as basic aerodynamic information through aerodynamic performance simulation, determines the size range and performance range of the required large ducted fan according to the actual situation, and further predicts the aerodynamic performance of the large ducted fan based on similarity theory to determine its geometric size, rotation speed and incoming flow velocity; then, through numerical simulation of the large ducted fan, further determines the aerodynamic performance of the large ducted fan, so as to achieve the purpose of saving calculation cost and shortening calculation cycle, and can be extended to the research and development of rapid design and performance prediction of large ducted fans; through the guidance of similarity criteria, designers can more accurately predict the performance of ducted fans under different working conditions, thereby greatly reducing the number of tests and iteration cycles. The application of similarity criteria will promote the development of ducted fan design towards a more intelligent and efficient direction, and provide more advanced and reliable propulsion system solutions for multiple fields such as drones, aerospace, etc.

[0082] like Figure 3-4 As shown, a ducted fan designed based on similarity criteria is designed based on the above design method, and includes a casing 1, a motor part 2, a guide cone part 3, an impeller 4 (moving blades), a front guide vane 5 (stationary blades), and a rear guide vane 6 (stationary blades). The impeller 4 is arranged between the guide cone part 3 and the motor part 2. The impeller 4 includes a hub and blades. A plurality of blades are evenly distributed along the outer circumference of the hub. The outer circumference of the guide cone part 3 is connected to the inner circumference of the casing 1 through a plurality of front guide vanes 5 evenly distributed along the circumference. The outer circumference of the motor part 2 is connected to the inner circumference of the casing 1 through a plurality of rear guide vanes 6 evenly distributed along the circumference. It is characterized in that the front guide vane 5 includes a first front guide vane and a second front guide vane, and the plurality of first front guide vanes and the plurality of second front guide vanes are alternately arranged along the circumference, that is, The arrangement sequence is: first leading guide vane, second leading guide vane, first leading guide vane, second leading guide..., the leading guide vane 5 is composed of a first guide vane portion 51 and a second guide vane portion 52, the first guide vane portion 51 is arranged radially outside the second guide vane portion 52, and the radial lengths of the first guide vane portion 51 and the second guide vane portion 52 are both approximately 50% (specifically 45%-55%, φD is a dividing circle) of the overall radial length of the leading guide vane 5; the first leading guide vane is provided with a first three-dimensional twisted blade portion 53 only in its first guide vane portion 51, and the second guide vane portion 52 of the first leading guide vane is provided as a two-dimensional blade portion, the second leading guide vane is provided with a second three-dimensional twisted blade portion 54 only in its second guide vane portion 52, and the first guide vane portion 51 of the second leading guide vane is provided as a two-dimensional blade portion.

[0083] The first three-dimensional twisted blade portion 53 covers substantially the entire radial length of the first guide vane portion 51 , and the second three-dimensional twisted blade portion 54 covers substantially the entire radial length of the second guide vane portion 52 .

[0084] A ducted fan designed based on a similarity criterion of the present invention, through the design of the leading guide vane 5, specifically, the first leading guide vane is only provided with a first three-dimensional twisted blade portion 53 on its first guide vane portion 51, the second guide vane portion 52 of the first leading guide vane is set as a two-dimensional blade portion, the second leading guide vane is only provided with a second three-dimensional twisted blade portion 54 on its second guide vane portion 52, and the first guide vane portion 51 of the second leading guide vane is set as a two-dimensional blade portion. This can reduce the vortex between the flow channels of the leading guide vane 5, reduce the collision flow and vortex at the top and root of the leading guide vane 5, improve the guiding effect of the leading guide vane 5, and reduce the flow loss caused by the vortex, thereby improving the aerodynamic performance and efficiency of the ducted fan.

[0085] Further, relative to the two-dimensional blade portion, the first three-dimensional twisted blade portion 53 is extended toward the circumferential right side of the adjacent two-dimensional blade portion; relative to the two-dimensional blade portion, the second three-dimensional twisted blade portion 54 is extended toward the circumferential right side of the adjacent two-dimensional blade portion (such as Figure 4 As shown), that is, the inclined extension directions of the first three-dimensional twisted blade portion 53 and the second three-dimensional twisted blade portion 54 are consistent / same.

[0086] The blade inlet angle / inlet installation angle of the first three-dimensional twisted blade portion 53 is smaller than its blade outlet angle / outlet installation angle, and the blade inlet angle of the second three-dimensional twisted blade portion 54 is smaller than its blade outlet angle; and the blade inlet angle of the first three-dimensional twisted blade portion 53 is equal to or greater than the blade inlet angle of the second three-dimensional twisted blade portion 54, and the blade outlet angle of the first three-dimensional twisted blade portion 53 is greater than the blade outlet angle of the second three-dimensional twisted blade portion 54.

[0087] The present invention further optimizes the design of the leading guide vane 5, specifically, the inclined extension directions of the first three-dimensional twisted blade portion 53 and the second three-dimensional twisted blade portion 54 are consistent / same, the blade inlet angle of the first three-dimensional twisted blade portion 53 is equal to or greater than the blade inlet angle of the second three-dimensional twisted blade portion 54, and the blade outlet angle of the first three-dimensional twisted blade portion 53 is greater than the blade outlet angle of the second three-dimensional twisted blade portion 54. This can further reduce the vortex between the flow channels of the leading guide vane 5, reduce the collision flow and vortex at the top and root of the leading guide vane 5, improve the guiding effect of the leading guide vane 5, and reduce the flow loss caused by the vortex, thereby improving the aerodynamic performance and efficiency of the ducted fan.

[0088] Compared with the prior art, the ducted fan design method and device based on similarity criteria of the present invention have the following advantages / beneficial technical effects.

[0089] (1) It takes a set small ducted fan as the prototype object, obtains the aerodynamic performance information of the small ducted fan as the basic aerodynamic information through aerodynamic performance simulation, determines the size range and performance range of the required large ducted fan according to the actual situation, and further predicts the aerodynamic performance of the large ducted fan based on the similarity theory to determine its geometric size, rotation speed and incoming flow velocity; then, through the numerical simulation of the large ducted fan, the aerodynamic performance of the large ducted fan is further determined, so as to achieve the purpose of saving calculation cost and shortening calculation cycle, and can be extended to the research and development of rapid design and performance prediction of large ducted fans.

[0090] (2) The present invention can reduce the vortex between the flow channels of the leading guide vanes, reduce the collision flow and vortex at the top and root of the leading guide vanes, improve the flow guidance effect of the leading guide vanes, and reduce the flow loss caused by the vortex, thereby improving the aerodynamic performance and efficiency of the ducted fan.

[0091] The above-mentioned implementation modes are for explanation of the present invention rather than limitation of the present invention. It can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A ducted fan design method based on similarity criteria, comprising the following steps: Step S1: obtaining basic information of a known small ducted fan, the basic information at least including geometric model information, speed information and working state information; Step S2: constructing a geometric model of a known small ducted fan according to basic information; Step S3: constructing a numerical calculation model for the existing small ducted fan, realizing numerical simulation calculation of the steady-state flow field, and obtaining basic aerodynamic performance information of the small ducted fan; Step S4: using dimensional analysis method to obtain a similarity relationship of aerodynamic performance of ducted fan; Step S5: acquiring basic information of the target large ducted fan, the basic information at least including geometric size range information, speed range information and working state range information; Step S6: predicting basic information of the target thrust large ducted fan according to the aerodynamic performance result of the small ducted fan, the performance of the target small ducted fan and the similarity relationship, the basic information including geometric size information, rotation speed information and incoming wind speed information; Step S7: constructing a large ducted fan geometric model according to the estimated geometric dimension information of the large ducted fan; Step S8: construct a numerical calculation model for the estimated large ducted fan, implement numerical simulation calculation of the steady-state flow field, and obtain basic aerodynamic performance information of the large ducted fan.

2. A ducted fan design method based on similarity criteria as claimed in claim 1, characterized in that: In the step S2, according to the actual structural information of the small ducted fan with known aerodynamic performance, the main structure is extracted, the components that are not important for fluid simulation are ignored and simplified, and the external flow field area is established; in the step S3, when the meshing and mesh independence verification are performed on the fluid domain of the known small ducted fan, a suitable turbulence model and suitable boundary conditions are selected, and steady-state numerical simulation calculations under different working conditions are carried out, so as to obtain the aerodynamic performance information of the small ducted fan under different working conditions; Step S6 also includes: after predicting the basic information of the target thrust large ducted fan, based on the prediction result and the required target, customizing the design optimization scheme of the target large ducted fan; 。 3. A ducted fan design method based on similarity criteria as claimed in claim 2, characterized in that: In the step S7, the proportional relationship between the inferred large ducted fan and the small ducted fan is quickly scaled down or enlarged using three-dimensional modeling software to complete the construction of the large ducted fan geometric model; in step S8, when meshing the inferred large ducted fan fluid domain and verifying the mesh independence, a suitable turbulence model and suitable boundary conditions are selected to carry out steady-state numerical simulation calculations under different working conditions, thereby obtaining the aerodynamic performance information of the large ducted fan under different working conditions; it also includes: based on the basic aerodynamic performance information of the large ducted fan obtained by numerical calculation, confirming that a large ducted fan model that meets the target requirements is obtained.

4. A ducted fan design system based on similarity criteria, based on a ducted fan design method based on similarity criteria as claimed in claim 3, comprising: Information acquisition module, geometric model building module, aerodynamic performance simulation module, similarity relationship calculation module and solution optimization module; The information acquisition module is used to obtain the basic information of the known small ducted fan and the basic information of the target large ducted fan, the basic information at least includes the geometric model information of the small ducted fan, the aerodynamic performance information of the small ducted fan, the geometric size range information of the large ducted fan, the speed range information of the large ducted fan and the working state range information of the large ducted fan; the geometric model construction module is used to establish the geometric model of the known ducted fan and the calculated large ducted fan; the aerodynamic performance simulation module is used to realize steady-state numerical calculation of the known ducted fan and the calculated large ducted fan to obtain the aerodynamic performance of the known small ducted fan and the calculated large ducted fan; the similarity relationship inference module is used to select and infer the aerodynamic similarity relationship between the appropriate small ducted fan and the large ducted fan in combination with the actual situation of the ducted fan flow field; the scheme optimization module is used to predict the aerodynamic performance of the target large ducted fan at different sizes, and then customize the specific design scheme of the size and speed of the target ducted fan based on the predicted results of the aerodynamic performance.

5. A ducted fan designed based on similarity criteria, comprising a casing (1), a motor part (2), a guide cone part (3), an impeller (4), a front guide vane (5), and a rear guide vane (6), wherein the impeller is arranged between the guide cone part and the motor part, the impeller comprises a hub and blades, a plurality of blades are distributed along the outer circumference of the hub, the outer circumference of the guide cone part is connected to the inner circumference of the casing through a plurality of front guide vanes distributed along the circumference, and the outer circumference of the motor part is connected to the inner circumference of the casing through a plurality of rear guide vanes distributed along the circumference; characterized in that: The front guide vane (5) comprises a first front guide vane and a second front guide vane, wherein a plurality of first front guide vanes and a plurality of second front guide vanes are alternately arranged at intervals along the circumferential direction, the front guide vane is composed of a first guide vane portion (51) and a second guide vane portion (52), the first guide vane portion is arranged radially outside the second guide vane portion, and the radial lengths of the first guide vane portion and the second guide vane portion are 40%-60% of the overall radial length of the front guide vane; the first front guide vane is provided with a first three-dimensional twisted blade portion (53) only on its first guide vane portion (51), the second guide vane portion (52) of the first front guide vane is provided as a two-dimensional blade portion, the second front guide vane is provided with a second three-dimensional twisted blade portion (54) only on its second guide vane portion, and the first guide vane portion of the second front guide vane is provided as a two-dimensional blade portion.

6. The ducted fan designed based on similarity criteria according to claim 5, characterized in that: The coverage range of the first three-dimensional twisted blade portion (53) is substantially the entire radial length of the first guide vane portion (51), and the coverage range of the second three-dimensional twisted blade portion (54) is substantially the entire radial length of the second guide vane portion (52).

7. A ducted fan designed based on similarity criteria as claimed in claim 6, characterized in that: Relative to the two-dimensional blade portion, the first three-dimensional twisted blade portion (53) is extended toward the circumferential right side of the adjacent two-dimensional blade portion; relative to the two-dimensional blade portion, the second three-dimensional twisted blade portion (54) is extended toward the circumferential right side of the adjacent two-dimensional blade portion, that is, the inclined extension directions of the first three-dimensional twisted blade portion and the second three-dimensional twisted blade portion are consistent or the same.

8. The ducted fan designed based on similarity criteria according to claim 7, characterized in that: The blade inlet angle of the first three-dimensional twisted blade portion (53) is smaller than its blade outlet angle, and the blade inlet angle of the second three-dimensional twisted blade portion (54) is smaller than its blade outlet angle; and the blade inlet angle of the first three-dimensional twisted blade portion (53) is equal to or greater than the blade inlet angle of the second three-dimensional twisted blade portion (54), and the blade outlet angle of the first three-dimensional twisted blade portion (53) is greater than the blade outlet angle of the second three-dimensional twisted blade portion (54).

9. The ducted fan designed based on similarity criteria according to claim 5, characterized in that: The radial lengths of the first guide vane portion (51) and the second guide vane portion (52) are 50% of the overall radial length of the front guide vane (5).

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