Variable-camber stator blade with biased rotating shaft and inclined gaps and design method of variable-camber stator blade

Abstract

The invention provides a variable-camber stator blade with a biased rotating shaft and inclined gaps and a design method thereof, and belongs to the technical field of gas turbine engines, the variable-camber stator blade comprises a front-section blade, a rear-section blade and a blade handle, the rear-section blade and the blade handle are integrally formed, and the circle center of the blade handle is located on the edge of the front-end pressure surface side of the rear-section blade; the tail edge of the front-section blade is arranged to be a concave arc curve, the front edge of the rear-section blade is arranged to be a convex arc curve, the concave arc curve and the convex arc curve are arc lines on a concentric circle respectively, and the blade handle and the circle center of the concentric circle are located at the same position; the axial length of the suction surface of the front-section blade is greater than that of the pressure surface of the front-section blade, so that a concentric circle gap formed between the tail edge of the front-section blade and the front edge of the rear-section blade is obliquely arranged relative to the suction surface; and the suction surface of the tail part of the front-section blade is preloaded. According to the scheme, the airflow flowing loss under the large adjusting angle is reduced, and the total pressure recovery coefficient of the variable camber stator is improved.

Description

Technical Field

[0001] The present application relates to the technical field of gas turbine engines, and in particular to a variable-curvature stator blade with a rotating shaft offset and a slot tilt and a design method thereof. Background Art

[0002] The next generation of variable cycle engines requires fans to have an ultra-wide flow / pressure ratio adjustment range, that is, the fan is required to achieve different pressure ratio adjustments under the same flow condition, or to achieve different flow adjustments under the same pressure ratio condition. For traditional fans, their characteristic lines are fixed at a fixed speed, and the high efficiency areas formed at different speeds are also very narrow, which is far from meeting the requirements of variable cycle engines for wide flow and pressure ratio adjustment ranges.

[0003] The adjustable blades can change the direction of the rotor flow, optimize the air intake angle, and expand the fan's operating range. The variable curvature stator is a type of adjustable blade. The conventional variable curvature stator is divided into two sections. The front section remains fixed, and the rear section changes the airflow direction by rotating around the axis. Figure 1 .

[0004] Considering the factors such as the cumulative error of the processing and assembly dimension chain, there must be a certain gap between the front and rear blades of the variable camber stator. Due to the geometric discontinuity and airflow leakage at the gap position, the total pressure recovery coefficient of the variable camber stator is reduced. Especially at a large adjustment angle, the geometric discontinuity and leakage of the front and rear blades increase sharply, resulting in a decrease in the fuel consumption rate, thrust and other performance of the engine. Summary of the invention

[0005] In view of this, an embodiment of the present application provides a variable-curvature stator blade with an offset shaft and an inclined gap and a design method thereof, which at least partially solves the problem in the prior art that when the variable-curvature stator is at a large adjustment angle, the engine's fuel consumption, thrust and other performance are reduced due to the geometric discontinuity of the front and rear sections of the blades and a sharp increase in leakage.

[0006] In the first aspect, an embodiment of the present application provides a variable-curvature stator blade with an offset shaft and an inclined gap, comprising a front blade, a rear blade and a petiole, the rear blade and the petiole are integrally formed, the upper surfaces of the front blade and the rear blade are suction surfaces, the lower surfaces of the front blade and the rear blade are pressure surfaces, the center of the petiole is located at the edge of the pressure surface side of the front end of the rear blade, the trailing edge of the front blade is set as a concave arc curve, and the leading edge of the rear blade is set as a convex arc curve, the concave arc curve and the convex arc curve are arc lines on concentric circles, respectively, and the center of the petiole is at the same position as the center of the concentric circle; the axial length of the suction surface of the front blade is greater than the axial length of the pressure surface of the front blade, so that the concentric circle gap formed between the trailing edge of the front blade and the leading edge of the rear blade is inclined relative to the suction surface; the suction surface at the rear of the front blade is preloaded so that the geometric profile of the suction surface at the rear of the front blade is deflected in advance.

[0007] According to a specific implementation of the embodiment of the present application, the deviation between the center of the petiole and the edge of the pressure surface side of the front end of the rear blade is set to ±0.5 mm.

[0008] According to a specific implementation of the embodiment of the present application, the radius of the petiole is set to 3-6 mm.

[0009] According to a specific implementation of the embodiment of the present application, the angle range of the geometric profile deflection of the suction surface at the tail of the front blade is set to 5°-10°.

[0010] In a second aspect, an embodiment of the present application further provides a method for designing a variable-camber stator blade with a rotating shaft offset and a slot tilt as described in any embodiment of the first aspect, the method comprising: According to the proportion of the axial length of the pressure surface of the front blade to the axial length of the entire blade, the front blade and the rear blade are divided, and the division point s is determined; The center point c of the concentric circle is determined according to the segmentation point s, the angle alfi at the segmentation point s, and the radius Rf of the concave arc curve of the trailing edge of the front blade. The angle alfi is the angle between the air inlet side of the concentric circle gap and the x-axis. According to the radius Rf of the concave arc curve of the trailing edge of the front blade and the width of the concentric circle gap, the radius Rb of the convex arc curve and the radius Rc of the middle arc line of the concentric circle gap are determined. According to the radius Rf, the radius Rb, the radius Rc and the center point c, the construction of the front leaf shape concentric circles, the rear leaf shape concentric circles and the petiole is completed; According to the air outlet angle alfo of the concentric circle gap and the center point c, the concentric circles of the front blade and the rear blade are cut off, and a tangent line is used to intersect the suction surface of the blade at the cutoff point to obtain a complete front blade, rear blade and inclined concentric circle gap; The rear blade is rotated to obtain the suction surface fitting line; According to the suction surface fitting line, a distribution curve of the angle between the suction surface fitting line and the x-axis is obtained; The non-smooth area of ​​the angle distribution curve is smoothed to obtain the angle distribution smooth curve; According to the angle distribution smoothing curve, the suction surface profile with preload on the tail suction surface of the front blade is obtained.

[0011] According to a specific implementation of the embodiment of the present application, obtaining a suction surface profile with a preload on the suction surface of the tail of the front blade according to the angle distribution smoothing curve includes: The angle distribution smoothing curve is used to calculate the suction surface profile of the front blade using an integral formula to obtain the suction surface profile of the front blade; The suction surface profile of the front blade is cut using the concentric circles of the front blade profile to obtain a suction surface profile with a preload on the tail suction surface of the front blade.

[0012] According to a specific implementation of the embodiment of the present application, the integral formula is: , In the formula, x a ≤x g ≤x e , x b =x e ;x a is the horizontal coordinate of the starting point a of the front blade suction surface profile fitting, y a is the ordinate of the starting point a of the front blade suction surface profile fitting, x g is the horizontal coordinate of any point on the suction surface of the front blade, y g is the ordinate of any point on the suction surface of the front blade, beta is the angle between the suction surface fitting line on the angle distribution smoothing curve and the x-axis, x e is the abscissa of the end point e of the suction surface profile of the front blade before preloading, x b It is the abscissa of the end point b of the suction surface profile of the front blade after preloading.

[0013] According to a specific implementation of the embodiment of the present application, the value of the concentric circle gap air outlet side angle alfo is less than 15°.

[0014] According to a specific implementation of the embodiment of the present application, the axial length of the pressure surface of the front blade accounts for 0.3-0.5 of the axial length of the entire blade.

[0015] According to a specific implementation of the embodiment of the present application, the angle alfi at the segmentation point s is in the range of 80°-90°.

[0016] Beneficial effects: The variable-curvature stator blades with shaft offset and gap tilt and the design method thereof in the embodiments of the present application maintain the size of the gap between the front and rear blades unchanged when the blades are adjusted by means of variable-curvature stator shaft offset, tail preloading of the suction surface of the front blade and concentric inclined gaps, leaving a margin for errors such as accumulation of machining and assembly dimension chains, ensuring structural feasibility while greatly reducing airflow losses at large adjustment angles and improving the total pressure recovery coefficient of the variable-curvature stator. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is a schematic diagram of the structure of a variable-camber stator blade in the prior art; Figure 2 is a schematic structural diagram of a variable-camber stator blade according to an embodiment of the present invention; Figure 3 is a schematic diagram of a variable camber stator blade after rotation according to an embodiment of the present invention; Figure 4 A schematic diagram of segmentation point confirmation according to an embodiment of the present invention; Figure 5 A schematic diagram of constructing concentric circles of front and rear blades according to an embodiment of the present invention; Figure 6 A schematic diagram of constructing concentric circular gaps according to an embodiment of the present invention; Figure 7 It is a schematic diagram of fitting of the suction surface profile of a variable camber stator blade after rotation according to an embodiment of the present invention; Figure 8 Schematic diagram of the distribution of angles between the suction surface of a variable-camber stator blade and the horizontal direction according to an embodiment of the present invention; Fig. 9 is a schematic diagram of the suction surface profile distribution formed after integration according to an embodiment of the present invention; Fig.10 is a schematic diagram of a suction surface profile after cutting according to an embodiment of the present invention; Fig.11 It is a schematic diagram of the distribution of the angles between the suction surface of another variable-camber stator blade and the horizontal direction according to an embodiment of the present invention; Fig.121 is a comparison diagram of flow field calculation results when the rear blades according to an embodiment of the present invention are not adjusted, (a) is the flow field calculation result of the blades of the prior art, and (b) is the flow field calculation result of the blades of the present application; Fig.13 1. A comparison diagram of flow field calculation results when the rear blade of an embodiment of the present invention is adjusted to a 38° state, (a) is the flow field calculation result of the blade of the prior art, and (b) is the flow field calculation result of the blade of the present application; Fig.14 1 is a diagram of the gap between the front and rear blades of a variable-camber stator blade according to an embodiment of the present invention, wherein (a) is the rear blade with an adjustment angle of 0°, and (b) is the rear blade with an adjustment angle of 38°.

[0019] Fig.15 This is a comparison diagram of the intersection angle between the gap center line and the suction surface line when the rear section blade is adjusted by 38° according to an embodiment of the present invention, (a) is a blade using the prior art, and (b) is a blade using the present application.

[0020] In the figure: 101, front blade, 102, rear blade, 103, petiole, A, trailing edge of front blade, B, suction surface at the tail of front blade, C, leading edge of rear blade. DETAILED DESCRIPTION

[0021] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0022] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0023] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0024] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The illustrations only show the components related to the present application rather than being drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed at will, and the component layout may also be more complicated.

[0025] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects described may be practiced without these specific details.

[0026] First, refer to Figure 2 and Figure 3 The embodiment of the present application provides a variable-curvature stator blade with a rotating shaft offset and a gap tilt, including a front blade 101, a rear blade 102 and a petiole 103, the rear blade 102 and the petiole 103 are integrally formed, the upper surfaces of the front blade 101 and the rear blade 102 are suction surfaces, the lower surfaces of the front blade 101 and the rear blade 102 are pressure surfaces, the center of the petiole 103 is located at the edge of the pressure surface side of the front end of the rear blade, the trailing edge A of the front blade is set to an inwardly concave arc curve, and the leading edge of the rear blade is set to an inwardly concave arc curve. (C) is set as an outward convex arc curve, the inward concave arc curve and the outward convex arc curve are arc lines on concentric circles respectively, and the center of the petiole 103 and the center of the concentric circle are located at the same position; the axial length of the suction surface of the front blade is greater than the axial length of the pressure surface of the front blade, so that the concentric circle gap formed between the trailing edge A of the front blade and the leading edge (C) of the rear blade is inclined relative to the suction surface; the suction surface B at the rear of the front blade is preloaded so that the geometric profile of the suction surface B at the rear of the front blade is deflected in advance.

[0027] In this embodiment, the airflow loss at large adjustment angles is greatly reduced and the total pressure recovery coefficient of the variable curvature stator is improved by means of variable curvature stator rotation axis offset, front blade suction surface tail preloading and concentric circle inclined gaps. Specifically, by adjusting the position of the petiole 103, the rotation axis of the variable curvature stator is offset from the inside of the blade to the outside of the blade, thereby increasing the smoothness of the first-order derivatives of the geometric profile lines of the suction surfaces of the front and rear blades after the rear blade 102 rotates (representing the angle between the suction surface and the axial direction); by preloading the tail of the front blade (the geometric profile at position B is deflected in advance), the smoothness of the first-order derivatives of the geometric profile lines of the suction surfaces of the front and rear blades after the rear blade 102 rotates is further increased; the gap between the front and rear blades is a concentric circle, and the angle at which the midline of the gap (the central arc of the gap) intersects with the suction surface profile line is greatly reduced, that is, the concentric circle gap is inclined relative to the suction surface, which also increases the smoothness of the first-order derivatives of the geometric profile lines of the suction surfaces of the front and rear blades after the rear blade 102 rotates, thereby reducing the airflow loss at a large adjustment angle and improving the total pressure recovery coefficient of the variable curvature stator.

[0028] In one embodiment, the deviation between the center of the petiole 103 and the edge of the pressure surface side of the front end of the rear blade is set to ±0.5 mm.

[0029] In one embodiment, the radius of the petiole 103 is set to 3-6 mm.

[0030] In one embodiment, the angle range of the geometric profile deflection of the suction surface B at the tail of the front blade is set to 5°-10°.

[0031] In a second aspect, an embodiment of the present application further provides a method for designing a variable-camber stator blade with a rotating shaft offset and a slot tilt as described in any embodiment of the first aspect, the method comprising: Step 1: According to the proportion of the axial length of the pressure surface of the front blade to the axial length of the entire blade, the front blade 101 and the rear blade 102 are divided, and the division point s is determined. The coordinates of the division point s are (x s ,y s ), the front and rear blades 102 are divided; wherein the axial length of the pressure surface of the front blade is L1, and the axial length of the entire blade is L2, then the proportion a1=L1 / L2, refer to Figure 4 ; Step 2: Determine the center point c of the concentric circle according to the segmentation point s, the angle alfi at the segmentation point s, and the radius Rf of the concave arc curve of the trailing edge A of the front blade. The angle alfi is the angle between the air inlet side of the concentric circle gap and the x-axis. Figure 5 , the coordinates of point c are (x c ,y c ),in: x c =x s +Rf*sin(alfi), y c =y s -Rf*cos(alfi); Step 3, according to the radius Rf of the concave arc curve of the trailing edge A of the front blade and the width of the concentric circle gap, determine the radius Rb of the convex arc curve and the radius Rc of the middle arc line of the concentric circle gap, and complete the construction of the front blade concentric circles, the rear blade concentric circles and the petiole 103 according to the radius Rf, the radius Rb, the radius Rc and the center point c; wherein, Rf=Rb+0.8, Rc=(Rf+Rb)*0.5, and the width of the concentric circle gap in this embodiment is set to 0.8mm; Step 4: According to the concentric circle gap outlet angle alfo and the center point c, the front blade concentric circle and the rear blade concentric circle are cut off, and the tangent line is used to intersect the suction surface of the blade at the cutoff point to obtain the complete front blade 101, the rear blade 102 and the inclined concentric circle gap. Figure 6 ; Step 5: Rotate the rear blade 102 to obtain the suction surface fitting line L1; for details, refer to Figure 7 , taking the center point c of the concentric circle as the rotation axis, rotating the rear blade 102 according to the use angle alf (the value of alf is generally 15°-45°, and the variable curvature stator is used in the rear fan of the variable cycle engine, then the alf angle value is 40°), and fitting the suction surface, analyzing the distribution of the angle beta between the suction surface fitting line L1 and the x-axis, beta is defined as follows: beta=atan(dy / dx), x, y are the coordinate values ​​of the points on the suction surface fitting line respectively; Step 6, obtaining an angle distribution curve between the suction surface fitting line L1 and the x-axis according to the suction surface fitting line L1; Step 7: Smooth the non-smooth area of ​​the angle distribution curve to obtain the angle distribution smooth curve. Figure 8 , the angle distribution curve before preloading in the figure is the angle distribution curve between the suction surface fitting line L1 and the x-axis, and the angle distribution curve of the suction surface given after preloading is the angle distribution smoothing curve; Step 8: According to the angle distribution smoothing curve, obtain the suction surface profile of the tail suction surface B of the front blade with preload.

[0032] Furthermore, the method of obtaining the suction surface profile of the tail suction surface B of the front blade with a preload according to the angle distribution smoothing curve includes: The angle distribution smoothing curve is used to calculate the suction surface profile of the front blade using the integral formula to obtain the suction surface profile of the front blade. Fig. 9 The ab curve in the figure is the integral profile after preloading, and the ae curve is the profile before preloading (i.e. the profile before smoothing). Use the front blade concentric circle to cut the front blade suction surface line to obtain the front blade tail suction surface B with preloaded suction surface line, refer to Fig.10 .

[0033] Furthermore, the integral formula is: , In the formula, x a ≤x g ≤x e , x b =x e ;x a is the horizontal coordinate of the starting point a of the front blade suction surface profile fitting, y a is the ordinate of the starting point a of the front blade suction surface profile fitting, x g is the horizontal coordinate of any point on the suction surface of the front blade, y g is the ordinate of any point on the suction surface of the front blade, beta is the angle between the suction surface fitting line on the angle distribution smoothing curve and the x-axis, x e is the abscissa of the end point e of the suction surface profile of the front blade before preloading, x b It is the abscissa of the end point b of the suction surface profile of the front blade after preloading.

[0034] Furthermore, the value of the concentric circle gap outlet angle alfo is less than 15°. In this embodiment, the concentric circle gap outlet angle is limited to reduce the loss of the outlet gap airflow after mixing with the mainstream.

[0035] Furthermore, the axial length of the pressure surface of the front blade accounts for 0.3-0.5 of the axial length of the entire blade.

[0036] Furthermore, the angle alfi at the segmentation point s ranges from 80° to 90°.

[0037] The following is a fitting of the suction surface of the variable camber stator blade of the prior art and the novel variable camber stator blade in the embodiment of the present application after rotation, and an analysis of the angle distribution between the suction surface and the axial direction after fitting. The results are as follows: Fig.11As shown, when the axial relative position changes from 0.288 to 0.379, the angle change of the suction surface of the variable camber stator blade in the prior art is 42.7°, and the angle change of the new variable camber stator blade in the present application is 22.0°. When the axial relative position of the variable camber stator blade in the present application changes from 0.288 to 0.379, the angle change decreases by 48.5%. Therefore, the data shows that after the rear blade 102 is rotated and adjusted, the smoothness of the first-order derivative of the suction surface geometry of the front and rear blades is greatly improved.

[0038] Further analysis of the startup performance shows that in the 0° unadjusted state, the total pressure recovery coefficients of the new variable curvature stator blades of the present application and the variable curvature stator blades of the prior art are both 0.9967. When the adjustment angle is 38°, the total pressure recovery coefficient of the new variable curvature stator blades of the present application is 3.9% higher than that of the variable curvature stator blades of the prior art. The detailed results are shown in Table 1. This is because the angle change of the axial relative position of the variable curvature stator blades in the present application from 0.288 to 0.379 is reduced by 48.5%, eliminating the separation of the airflow in this area. The calculation results are shown in Fig.12 and Fig.13 .

[0039] Table 1 Comparison of aerodynamic calculation results

[0040] In addition, the inclined concentric circle gap of the present application ensures that the gap size between the front and rear blades remains unchanged during adjustment, leaving a margin for errors such as processing and assembly dimension chain accumulation, thus ensuring the feasibility of the structure (such as Fig.14 After the concentric gap is tilted, the angle between the gap centerline and the suction surface line is reduced by 26°, which reduces the angle between the leakage flow and the mainstream (as shown in Fig.15 as shown), reducing the loss of leakage flow.

[0041] The embodiments provided by the present invention (1) adjust the position of the petiole 103 so that the variable curvature stator rotation axis is offset from the inside of the blade to the outside of the blade, thereby increasing the smoothness of the first-order derivative of the geometric profile of the suction surface of the front and rear blades (representing the angle between the suction surface and the axial direction) after the rear blade 102 rotates; (2) by preloading the tail of the front blade, the smoothness of the first-order derivative of the geometric profile of the suction surface of the front and rear blades after the rear blade 102 rotates is further increased; (3) The gap between the front and rear blades is a concentric circle, and the angle between the gap centerline outlet and the suction surface profile is greatly inclined; Through the above three forms of structural settings, the size of the gap between the front and rear blades is maintained unchanged when the blades are adjusted, leaving a margin for errors such as accumulation of processing and assembly dimension chains. While ensuring the feasibility of the structure, it greatly reduces the airflow loss at large adjustment angles and improves the total pressure recovery coefficient of the variable curvature stator.

[0042] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A variable-camber stator blade with an offset shaft and an inclined gap, characterized in that: The invention comprises a front blade (101), a rear blade (102) and a petiole (103), wherein the rear blade (102) and the petiole (103) are integrally formed, the upper surfaces of the front blade (101) and the rear blade (102) are suction surfaces, the lower surfaces of the front blade (101) and the rear blade (102) are pressure surfaces, the center of the petiole (103) is located at the edge of the pressure surface side of the front end of the rear blade, the trailing edge (A) of the front blade is set to be an inwardly concave arc curve, and the leading edge (C) of the rear blade is set to be an outwardly convex arc curve. The concave arc curve and the convex arc curve are arcs on concentric circles, respectively, and the center of the petiole (103) and the center of the concentric circle are located at the same position; the axial length of the suction surface of the front blade is greater than the axial length of the pressure surface of the front blade, so that the concentric circle gap formed between the trailing edge (A) of the front blade and the leading edge (C) of the rear blade is inclined relative to the suction surface; and the suction surface (B) at the rear of the front blade is preloaded so that the geometric profile of the suction surface (B) at the rear of the front blade is deflected in advance.

2. The variable camber stator blade with shaft offset and slot inclination according to claim 1, characterized in that: The deviation between the center of the petiole (103) and the edge on the pressure surface side of the front end of the rear blade is set to ±0.5 mm.

3. The variable camber stator blade with shaft offset and slot inclination according to claim 1, characterized in that: The radius of the petiole (103) is set to 3-6 mm.

4. The variable camber stator blade with shaft offset and slot inclination according to claim 1, characterized in that: The angle range of the geometric profile deflection of the suction surface (B) at the tail of the front blade is set to 5°-10°.

5. A design method for a variable-camber stator blade with a shaft offset and a slot tilt as claimed in any one of claims 1 to 4, characterized in that: The method comprises: The front blade (101) and the rear blade (102) are segmented according to the proportion of the axial length of the pressure surface of the front blade to the axial length of the entire blade, and a segmentation point s is determined; The center point c of the concentric circle is determined according to the segmentation point s, the angle alfi at the segmentation point s, and the radius Rf of the concave arc curve of the trailing edge (A) of the front blade. The angle alfi is the angle between the air inlet side of the concentric circle gap and the x-axis. According to the radius Rf of the concave arc curve of the trailing edge (A) of the front blade and the width of the concentric circle gap, the radius Rb of the convex arc curve and the radius Rc of the middle arc line of the concentric circle gap are determined, and according to the radius Rf, the radius Rb, the radius Rc and the center point c, the front blade concentric circle, the rear blade concentric circle and the petiole (103) are constructed; According to the air outlet angle alfo of the concentric circle gap and the center point c, the front blade concentric circle and the rear blade concentric circle are cut off, and a tangent straight line is used to intersect the suction surface of the blade at the cutoff point to obtain a complete front blade (101), a rear blade (102) and an inclined concentric circle gap; Rotating the rear blade (102) to obtain a suction surface fitting line; According to the suction surface fitting line, a distribution curve of the angle between the suction surface fitting line and the x-axis is obtained; The non-smooth area of ​​the angle distribution curve is smoothed to obtain the angle distribution smooth curve; According to the angle distribution smoothing curve, the suction surface profile (B) of the tail of the front blade with preload is obtained.

6. The design method according to claim 5, characterized in that: The method of obtaining the suction surface profile of the tail of the front blade (B) with a preload according to the angle distribution smoothing curve includes: The angle distribution smoothing curve is used to calculate the suction surface profile of the front blade using an integral formula to obtain the suction surface profile of the front blade; The suction surface profile of the front blade is cut using the concentric circle of the front blade profile to obtain the suction surface profile of the tail of the front blade (B) with preload.

7. The design method according to claim 6, characterized in that: The integral formula is: ， In the formula, x a ≤x g ≤x e , x b =x e ;x a is the horizontal coordinate of the starting point a of the front blade suction surface profile fitting, y a is the ordinate of the starting point a of the front blade suction surface profile fitting, x g is the horizontal coordinate of any point on the suction surface of the front blade, y g is the ordinate of any point on the suction surface of the front blade, beta is the angle between the suction surface fitting line on the angle distribution smoothing curve and the x-axis, x e is the abscissa of the end point e of the suction surface profile of the front blade before preloading, x b It is the abscissa of the end point b of the suction surface profile of the front blade after preloading.

8. The design method according to claim 5, characterized in that: The value of the concentric circle gap air outlet side angle alfo is less than 15°.

9. The design method according to claim 5, characterized in that: The axial length of the pressure surface of the front blade accounts for 0.3-0.5 of the axial length of the entire blade.

10. The design method according to claim 5, characterized in that: The angle alfi at the dividing point s ranges from 80° to 90°.

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