S-shaped nonlinear skew distribution stator for pump-jet propeller and design method of S-shaped nonlinear skew distribution stator

Abstract

The invention belongs to the field of underwater vehicle propellers, and particularly discloses an S-shaped nonlinear skew distribution stator for a pump jet propeller and a design method. Comprising the steps of preliminarily determining side oblique angles of a stator at different radiuses according to side oblique angles theta of a rotor at different radiuses, then determining the maximum side oblique angle according to the influence on the propulsion efficiency and unsteady force of a pump-jet propeller, and obtaining the optimal molded line of the S-shaped nonlinear side oblique distribution stator according to the maximum side oblique angle. According to the characteristic that the rotating direction of the rotor and the side inclination of the rotor are distributed along with the radius, the profile line type and the side inclination angle of each section of the stator are properly changed, so that fluid passes through the stator to be pre-rotated, and meanwhile, the phase difference of wake peak circumferential phase angles at different radiuses in the wake of the stator is increased; therefore, the orthogonality of the distribution characteristic of the wake peak circumferential phase angle along with the radius of the rotor disc surface and the distribution characteristic of the phase angle along with the radius of the section of the rotor blade is increased, the exciting force and noise of the pump-jet propeller are effectively reduced, and the propelling efficiency of the propeller is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater vehicle propulsion, and more specifically, relates to an S-shaped nonlinear side-slant distribution stator for a pump-jet propulsion and a design method thereof. Background Art

[0002] The pump-jet propulsor is an underwater propulsor composed of a duct, a rotor, and a stator. It has the advantages of delaying the occurrence of cavitation, reducing the radiation noise of underwater vehicles, and improving propulsion efficiency. It has been widely used in various underwater vehicles, ranging from nuclear submarines to unmanned UUVs. The pump-jet propulsor is generally installed at the tail of the vehicle, and a stern rudder and other appendages are usually arranged in front of it. When the underwater vehicle is sailing, the fluid flows through the stern rudder and other appendages, forming a complex non-uniform wake field at the stern of the hull. The uneven distribution of the stern flow field on the rotor disk of the pump-jet propulsor will cause periodic changes in the rotor surface pressure, thereby generating low-frequency line spectrum noise, while the turbulent pulsation of the flow field at the stern of the hull will cause irregular pulsation of the rotor surface pressure, thereby generating low-frequency broadband noise. In addition to the radiation noise, when the rotor works in the non-uniform flow field at the stern of the hull, the unsteady bearing force it generates will act on the hull through the bearing, causing the vibration of the hull structure to generate vibration noise. Whether it is low-frequency line spectrum noise, low-frequency broadband noise or hull structure vibration noise caused by rotor bearing force, they are all closely related to the unevenness of the flow field at the rotor disk surface. Therefore, improving the flow field at the rotor disk surface by optimizing the stator structure is a direct and effective way to reduce submarine noise.

[0003] As one of the important components of the pump-jet propulsion, the stator blades in the front-stator pump-jet propulsion generally have an asymmetric profile and form a certain geometric angle of attack with the axis, which can make the incoming flow uniform and improve the flow field. However, it is generally a structural form without side tilt, and the effect of improving the incoming flow by only adjusting the blade profile shape and the geometric angle of attack is very limited. On the rotor inlet surface, the phase angles corresponding to the peak values ​​of the accompanying flow at each radius are basically consistent, resulting in a large bearing force when the rotor blades rotate. Although the bearing force of the rotor can be reduced by increasing the side tilt of the rotor blades, due to strength limitations, the side tilt angle of the rotor cannot be too large, resulting in a large bearing force when the rotor rotates.

[0004] Considering that the basic reason for the vibration and noise reduction of the large skew propeller is that there is a large phase difference in the space of the profiles at each radius of the large skew propeller, and the phase angle corresponding to the wake peak of the submarine wake at each radius is basically consistent, when the propeller is working, there is a large difference between the spatial phase distribution of the profiles at each radius and the spatial phase distribution of the wake peak at each radius. We call this difference in phase distribution the orthogonality (or mismatch) between the two. This orthogonality will cause a certain time difference in the corresponding moment when each radius profile enters the wake peak area, that is, there is asynchrony in the time when each blade profile enters the wake peak area. Since there is asynchrony in the time when each radius profile of the large skew propeller enters the wake peak area, the load of each radius profile cannot reach the maximum value or the minimum value at the same time, so that the maximum value of the overall load of the blade during the rotation process can be reduced, and the minimum value of the overall load of the blade can be increased, so that the amplitude of the load fluctuation of the propeller blade during the rotation process is small. The larger the propeller skew value, the greater the positive intersection of each radius profile with the wake peak at each radius in phase, the asynchronism of each radius profile entering the wake peak area in time will also increase, and the fluctuation amplitude of the entire blade load over time will be smaller. However, excessive rotor skew will cause the stiffness of the rotor blades to decrease. When the rotor is running, the rotor tip will vibrate, which will increase the noise of the pump-jet propulsion. Therefore, without increasing the rotor skew, we can only start by changing the rotor inflow and directly adjust the phase distribution of the wake peak at each radius of the rotor disk, so as to increase the positive intersection with the propeller profile phase distribution, thereby reducing the exciting force of the pump-jet propulsion and reducing the propeller noise.

[0005] The most effective and simplest way to change the inflow of the rotor in a pump-jet propulsor is to change the geometric shape of the front stator of the pump-jet propulsor, set a larger geometric angle of attack and camber at the root of the stator blade, and set a smaller geometric angle of attack and camber at the tip of the blade, so as to expand the difference in the phase of the peak value of the wake flow at each radius of the rotor disk, thereby increasing the orthogonality with the phase distribution of the propeller profile. In order to increase the orthogonality of the spatial phase distribution of the peak value of the wake flow at each radius of the rotor disk and the spatial phase distribution of each radial section of the rotor, it is usually achieved by increasing the geometric angle of attack and camber of the small radius section of the stator, but a larger angle of attack and camber will lead to a larger resistance and torque of the stator itself, which will then lead to a lower overall efficiency of the pump-jet propulsor and a larger torque imbalance of the propeller. The "S"-shaped nonlinear skew distribution stator adjusts the skew angle of the blade section at each radius. Under the premise of a smaller stator attack angle and camber distribution, it achieves the purpose of increasing the orthogonality of the spatial phase distribution of the wake peak at each radius of the rotor disk surface and the spatial phase distribution of each radius section of the rotor. This can not only significantly reduce the exciting force and low-frequency line spectrum noise of the pump-jet propulsor rotor.

[0006] In addition, when the effect of the rotor is not considered, after the fluid passes through the stator blades in the duct of the pump-jet propulsor, a certain degree of pre-swirl will be generated in the opposite direction of the rotor, so that there is a certain circumferential velocity component in the flow field at each radius in the stator wake. Since the blades are in a rotating state when the rotor is working, the rotor will cause the wake to produce axial induced velocity and circumferential induced velocity. The kinetic energy formed by the axial induced velocity and circumferential induced velocity in the wake is loss energy. The reverse pre-swirl flow in the rotor inlet flow offsets the circumferential velocity component of the induced velocity to a certain extent, reducing the circumferential velocity component in the rotor wake, which is beneficial to reducing the kinetic energy loss caused by the circumferential velocity in the rotor wake and improving the propulsion efficiency of the pump-jet propulsor. The "S"-shaped nonlinear side-slant distribution stator can make this reverse pre-swirl effect more prominent. Under the premise that the stator torque remains unchanged, the geometric attack angle and camber of the stator are smaller than those of the conventional stator, and the resistance of the stator is reduced, which can further improve the propulsion efficiency of the pump-jet propulsor. . Summary of the invention

[0007] In view of the above defects or improvement needs of the prior art, the present invention provides an S-shaped nonlinear skew distribution stator and design method for a pump-jet propulsor, wherein, in combination with the characteristics of the propeller stator and rotor themselves and the flow field characteristics, an "S"-shaped nonlinear skew distribution stator is designed accordingly for reducing the exciting force and noise of the pump-jet propulsor, reducing the kinetic energy loss caused by the circumferential induced velocity in the wake of the pump-jet propulsor, and improving the propulsion efficiency of the propeller. The stator is based on a conventional straight stator of a pump-jet propulsor and according to the characteristics of the rotor rotation direction and the rotor skew distribution with the radius, and the stator profile line shape and skew angle are appropriately changed to make the fluid pre-rotate when passing through the stator, and at the same time, the phase difference of the circumferential phase angle of the peak wake at different radii in the stator wake is increased, thereby increasing the positive intersection (or mismatch) of the distribution characteristics of the circumferential phase angle of the peak wake at the rotor disk surface with the radius and the distribution characteristics of the rotor blade profile phase angle with the radius.

[0008] To achieve the above object, according to one aspect of the present invention, a design method for an S-shaped nonlinear side-skew distributed stator for a pump-jet propulsor is proposed, comprising the following steps:

[0009] Step 1: construct a hull-rudder-pump-jet propulsion integrated computational model to simulate the actual working environment;

[0010] Step 2: By performing self-propulsion numerical calculations on the hull-rudder-pump-jet propulsion integrated model, the stator's side skew angle θ at different radii is preliminarily determined based on the detailed data of the flow field in the duct and the rotor's side skew angle θ at different radii. Based on the original straight stator, a preliminary scheme for an "S"-shaped nonlinear side skew distribution stator is obtained.

[0011] Step three, according to the above preliminary plan, on the basis of not changing the stator skew distribution law, by changing the maximum skew angle θ0 of the stator with "S"-shaped nonlinear skew distribution, analyze the influence of different maximum skew angles θ0 on the propulsion efficiency and unsteady force of the pump-jet propulsor, and obtain the optimal maximum skew angle θ0 of the stator with "S"-shaped nonlinear skew distribution according to the influence law, and re-optimize the stator skew angle θ at different radii according to the influence of the maximum skew angle θ0, the propulsion efficiency of the pump-jet propulsor and the unsteady force;

[0012] Step 4: Based on the "S"-shaped nonlinear skew distribution stator optimized in step 3, the geometric attack angle α of the stator blade section at different radii and the chord-wise distribution of the stator blade section are optimized in turn, thereby completing the design of the "S"-shaped nonlinear skew distribution stator of the pump-jet propulsion system.

[0013] As a further preferred embodiment, in step 2, the side skew angle θ satisfies: the side skew angle θ shows a nonlinear change along the radial direction of the stator blades, the stator side skew angle θ has a circumferential bending form opposite to the rotor side skew direction, and from the stator blade root to the blade tip, as the radius increases, the stator phase angle gradually increases in absolute value in the clockwise direction, with counterclockwise being positive, and the side skew angle reaches a negative peak at the stator blade tip section. In this way, through the design of the side skew angle, the stator can cause the fluid to produce a pre-swirl in the opposite direction of the rotor rotation direction when flowing through, while increasing the phase difference of the peak circumferential phase angle of the wake at different radii in the stator wake, thereby increasing the positive intersection or mismatch between the distribution characteristics of the peak circumferential phase angle of the wake at the rotor disk surface with the radius and the distribution characteristics of the phase angle of the rotor blade section with the radius.

[0014] As further preferred, step three specifically includes the following steps:

[0015] (31) Based on the CFD method, the self-propulsion numerical simulation of the pump-jet propulsor with straight stator and S-shaped nonlinear side-slant distributed stator was carried out on the underwater vehicle. The thrust and torque of each component of the propulsion system were monitored at the self-propulsion point. The propulsion efficiency η0 and the unsteady force amplitude of the two propulsion systems were obtained by data processing. Thus, the influence of the "S"-shaped nonlinear side-slant distribution stator on the propulsion efficiency and unsteady force of the pump-jet propulsor is analyzed;

[0016] (32) Based on the "S"-shaped nonlinear skew distribution stator of step (31), the distribution characteristics of the flow field between the stator trailing edge and the rotor disk in the duct are analyzed. On the basis of not changing the stator skew distribution law, by changing the maximum skew angle θ0 of the "S"-shaped nonlinear skew distribution stator, the positive intersection of the peak circumferential phase distribution characteristics of the flow field between the stator and the rotor at each radius and the profile phase distribution characteristics at each radius of the rotor blade is increased. The underwater vehicle with the new "S"-shaped nonlinear skew distribution stator pump-jet propulsion is re-installed with a self-propulsion test simulation, and the influence of different maximum skew angles θ0 on the propulsion efficiency and unsteady force of the pump-jet propulsion ...

[0017] (33) Based on the "S"-shaped nonlinear skew distribution stator of step (32), on the basis of determining the maximum inclination angle θ0, by changing the skew angle θ of the "S"-shaped nonlinear skew distribution stator at each radius, the skew distribution law of the stator is adjusted, thereby changing the distribution characteristics of the peak circumferential phase angle of the wake flow at each radius of the rotor disk surface, increasing the positive intersection of the peak circumferential phase distribution characteristics of the flow field between the stator and the rotor at each radius and the profile phase distribution characteristics at each radius of the rotor blade, and re-installing the new "S"-shaped nonlinear skew distribution stator pump-jet propulsion The underwater vehicle is simulated by a self-propulsion test, and the influence of different skew distribution laws on the propulsion efficiency and unsteady force of the pump-jet propulsion The influence of different skew distribution laws of the "S"-shaped nonlinear skew distribution stator on the propulsion efficiency and unsteady force of the pump-jet propulsion is obtained. Considering the increase in the propulsion efficiency of the pump-jet propulsion and the reduction in the amplitude of the unsteady force, the most suitable "S"-shaped nonlinear skew distribution stator skew distribution law is selected as the optimization result.

[0018] As a further preferred embodiment, in step four, the optimization of the geometric angle of attack α of the cross-section of the stator blade at different radii includes: based on the optimization result of step three, adjusting the geometric angle of attack α (the angle between the chord of the blade cross-section and the axis) of the cross-section of the stator blade at different radii, obtaining the influence of the distribution of the radial geometric angle of attack α on the propulsion efficiency and unsteady force of the pump-jet propulsor, comprehensively considering the increase in the propulsion efficiency of the pump-jet propulsor and the reduction in the amplitude of the unsteady force, and selecting the most suitable distribution of the geometric angle of attack α as the optimization result.

[0019] As a further preference, in step four, the optimization of the chord-wise distribution form of the stator blade profile includes: based on the optimization result of step three, changing the chord-wise distribution form of the stator blade profile, obtaining the influence of the chord-wise distribution form of the blade profile on the propulsion efficiency and unsteady force of the pump-jet propulsor, comprehensively considering the increase in the propulsion efficiency of the pump-jet propulsor and the reduction in the amplitude of the unsteady force, and selecting the most suitable chord-wise distribution form of the blade profile as the optimization result.

[0020] As a further preferred embodiment, the calculation formula of the propulsion efficiency η includes:

[0021]

[0022] Where n is the propeller speed, Q is the rotor torque, V S is the sailing speed, R0 is the towing resistance, and F is the combined force of pump jet and hull.

[0023] According to another aspect of the present invention, there is also provided an S-shaped nonlinear side-skew distributed stator for a pump-jet propulsor, which is implemented using the design method of any of the above embodiments or a combination of multiple embodiments.

[0024] As a further preference, the stator as a whole is in an "S"-shaped circumferential bending form, the side skew angle θ of the stator has a nonlinear side skew distribution characteristic, and the stator side skew angle θ has a circumferential bending form opposite to the rotor side skew direction.

[0025] As a further preference, the side inclination angle θ of the stator satisfies: at the root of the stator blade, the side inclination angle is approximately 0°, and as the radius increases, the side inclination angle increases with the increase of the radius, but the side inclination angle first increases with the change in radius, and the rate of change reaches a maximum value at a certain radius in the middle of the stator blade, and then the rate of change gradually decreases with the increase of the radius, and the rate of change of the side inclination angle with the radius is almost close to 0 at the blade tip, so that the stator as a whole is in the form of an "S" shaped circumferential bend, and the stator blade tip part is almost perpendicular to the inner wall of the duct.

[0026] According to another aspect of the present invention, there is also provided a propeller, comprising a rotor and an S-shaped nonlinear side-skew distribution stator designed using the design method of any of the above embodiments or a combination of multiple embodiments, wherein the stator can cause the fluid to generate a pre-swirl in the opposite direction of the rotor rotation direction when flowing through, while increasing the phase difference of the peak circumferential phase angle of the wake at different radii in the stator wake, thereby increasing the positive intersection or mismatch between the distribution characteristics of the peak circumferential phase angle of the wake at the rotor disk surface with the radius and the distribution characteristics of the phase angle of the rotor blade section with the radius.

[0027] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0028] 1. The present invention changes the side skew angle of the stator at different radial positions so that the phases of the high wake areas at different radii in the flow field behind the stator trailing edge are inconsistent, and the change trend of the phase angle of the high wake area from the inner radius to the outer radius is opposite to the change trend of the rotor side skew angle, which is equivalent to greatly increasing the rotor side skew angle, and can significantly reduce the propeller exciting force and noise. The "S"-shaped nonlinear side skew distribution stator can also cause the rotor inlet flow to produce pre-swirl, and the direction of the pre-swirl flow is opposite to the direction of rotor rotation, thereby reducing the kinetic energy loss caused by the circumferential induced velocity in the rotor wake and improving the propeller propulsion efficiency.

[0029] 2. The present invention changes the spatial distribution of the flow field at the rotor disk surface, which is equivalent to increasing the side tilt angle of the propeller, so that the phase angle of the high wake area at each radius in the rotor disk surface inlet flow behind the stator trailing edge is favorably changed, thereby reducing the vibration noise and flow noise of the rotor structure; at the same time, the angle of attack formed by the incoming flow and the rotor blades is increased, the relative rotation speed is increased, the load of the rotor blades becomes larger, and the work done to overcome the unbalanced torque formed by the rotation is greater. Therefore, the pre-swirling flow originally flowing through the rotor working area can be better absorbed and utilized by the rotor because the proportion of circumferential energy increases. After the incoming flow is absorbed by the rotor, the circumferential induced velocity is correspondingly reduced, so that the pressure on the suction surface of the rotor blade becomes smaller, the pressure on the pressure surface becomes larger, the pressure difference on both sides increases, the thrust and torque of the propeller are correspondingly increased, and the circumferential energy originally lost in the incoming flow is reused, thereby reducing the speed required for the pump-jet propulsion rotor when the aircraft is self-propelled, reducing the power consumption of the main engine, improving the propulsion efficiency of the pump-jet propulsion, and realizing efficient aircraft propulsion. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 (a) is a side geometric diagram of a pump-jet propulsor with an S-shaped nonlinear side-slant distribution stator according to an embodiment of the present invention. Figure 1 (b) is a frontal geometric diagram of a pump-jet propulsor with an S-shaped nonlinear side-slant distribution stator according to an embodiment of the present invention;

[0031] Figure 2 This is the rear view of a conventional straight stator;

[0032] Figure 3 It is a rear view of an "S"-shaped nonlinear side-skew distribution stator involved in an embodiment of the present invention;

[0033] Figure 4 is a geometric comparison diagram of an "S"-shaped nonlinear skew distribution stator and a conventional straight stator involved in an embodiment of the present invention;

[0034] Figure 5 is the axial velocity distribution cloud diagram of the rotor inlet surface;

[0035] Figure 6 is the circumferential velocity distribution cloud diagram of the rotor inflow surface;

[0036] Figure 7 It is the comparison of the rotor axial force of pump-jet propulsors with different stators;

[0037] Figure 8 It is the comparison of the rotor lateral force of pump-jet propulsors with different stators;

[0038] Fig. 9 It is the comparison of vertical force of rotor of pump-jet propulsors with different stators;

[0039] Fig.10 It is the amplitude diagram of the unsteady forces in different directions of the rotor of different stator pump-jet propulsors at different blade frequencies;

[0040] Fig.11 It is the amplitude diagram of the unsteady torque of the rotor in different directions of different stator pump-jet thrusters at different blade frequencies;

[0041] Fig.12 It is a design flow chart of an "S"-shaped nonlinear side-skew distributed stator for reducing noise and increasing efficiency of a pump-jet propulsion system according to an embodiment of the present invention.

[0042] In all the drawings, the same reference numerals represent the same technical features, specifically: 1 - rotor, 2 - conventional straight stator, 3 - "S"-shaped nonlinear side-skewed distributed stator. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0044] like Figure 1As shown, an embodiment of the present invention provides an "S"-shaped nonlinear skew distribution stator for reducing noise and increasing efficiency of a pump-jet propulsion system. The "S"-shaped nonlinear skew distribution stator is based on a conventional straight stator of a pump-jet propulsion system and according to the characteristics of the rotor rotation direction and the rotor skew distribution with the radius, and appropriately changes the profile line shape and skew angle of each stator to cause pre-rotation of the fluid passing through the stator, while increasing the phase difference of the peak circumferential phase angle of the wake at different radii in the stator wake, thereby increasing the positive intersection (or mismatch) of the distribution characteristics of the peak circumferential phase angle of the wake at the rotor disk surface with the radius and the distribution characteristics of the rotor blade profile phase angle with the radius. That is, the non-uniform incoming flow forms a pre-rotation state opposite to the rotation direction of the rotor through the stator, and the phases of the high wake zones at different radii are inconsistent. From the inner radius to the outer radius, the change trend of the phase angle of the high wake zone is opposite to the change trend of the phase (side tilt angle) of each radial section of the rotor. The orthogonality of the distribution characteristics of the circumferential phase angle of the wake peak of the stator wake field with the radius and the distribution characteristics of the phase angle of the rotor blade section with the radius is increased, so that the time difference of the corresponding moments when each radial section of the rotor enters the peak wake area is increased, and the time asynchronism of each blade section entering the peak wake area is increased. The phase distribution of the change curves of the load of each radial section with time (or with the rotor rotation angle) is more different, and the time difference corresponding to the peak of the load change curve of each radial section with time is larger. After the loads of each radial section are superimposed to form the overall load of a single blade, the fluctuation of the entire blade load with time will be smoother and the fluctuation amplitude will be smaller, so that the amplitude of the load fluctuation of the pump-jet propulsor rotor during rotation is smaller, that is, the bearing force of the rotor during rotation is smaller. The "S"-shaped nonlinear skew distribution stator makes the phase distribution of the load variation curves of each section of the rotor blade greater than that of the time. The radiated noise sound pressure curves caused by the load fluctuations of each section will also show a large phase difference, and the hydrodynamic line spectrum noise sound pressure level of the entire rotor will also decrease accordingly. The decrease in the bearing force of the rotor will also cause the structural vibration noise caused by the bearing force to decrease accordingly. Therefore, the "S"-shaped nonlinear skew distribution stator can achieve the purpose of reducing the bearing force, line spectrum radiation noise and structural vibration noise of the submarine propulsion system and improving the propulsion efficiency of the pump-jet propulsion system only by changing the skew distribution of the stator blades.

[0045] Taking the right-hand skew rotor as an example, looking from the stern to the bow, the angle position at 12 o'clock is 0°, and the counterclockwise direction is the positive direction of the skew angle, that is, the angle position corresponding to 3 o'clock is -90°, and the corresponding angle position at 9 o'clock is 90°. The skew angle of the rotor blade at the root section is generally small. As the radius increases, the skew angle generally increases in the clockwise direction first. At a certain radius in the middle, the skew angle reaches a negative maximum value (the minimum skew angle). Then, as the radius increases, the skew angle gradually increases in the counterclockwise direction. At the blade tip section, the skew angle reaches a positive maximum value (the maximum skew angle). Since the absolute value of the maximum skew angle is generally significantly greater than the absolute value of the minimum skew angle, the rotor blade skew angle generally presents a counterclockwise characteristic. During the rotation of the rotor, the distribution characteristics of the side inclination angle of the rotor section at each radius make the rotor sections at each radius always have different circumferential phase angles. From the section with the smallest side inclination to the blade tip, as the section radius increases, its circumferential phase angle becomes smaller. Considering that the unsteady load on the rotor blades is mainly concentrated above the middle radius, and the load below the middle radius is relatively small, it is only necessary to control the stator wake to show that the circumferential phase angle of the peak value of the wake at each radius increases with the increase of the radius.

[0046] In view of the skew distribution characteristics of the right-handed skew rotor, the stator described in the present application has a circumferential bending form opposite to the rotor skew direction. From the stator blade root to the blade tip, as the radius increases, the stator phase angle gradually increases in absolute value in the clockwise direction, with counterclockwise being positive. At the stator blade tip section, the skew angle reaches a negative peak. Since the phase angle of the stator wake peak at each radius is directly related to the phase angle of the stator section, the distribution form of the phase angle of each radius section of the stator determines the distribution form of the phase angle of the stator wake peak at each radius. Since the phase angle of each radius section of the stator decreases with the increase of radius and drops to a negative peak at the blade tip, the phase angle of the stator wake peak also decreases with the increase of radius. Contrary to the trend of the phase angle of each rotor section with the radius, the phase distribution of each radius section of the rotor always shows a large orthogonality with the phase distribution of the stator wake peak. When the blade root section enters the wake peak area of ​​the stator wake field, other sections still have a large phase difference with the wake peak area at the corresponding radius, that is, the radius of other sections is in the area with relatively low wake values. During the rotation of the rotor blades, the load fluctuation amplitude of each radius section of the rotor becomes smaller over time, thereby reducing the rotor exciting force, hydrodynamic noise and structural vibration noise.

[0047] If the side inclination angle of the stator increases linearly with the radius, the above improvement effect can also be achieved. However, due to the linear side inclination angle distribution of the stator, a relatively sharp angle is formed at the connection between the stator tip and the inner wall of the duct. When the fluid flows through the connection between the stator tip and the inner wall of the duct, a relatively strong unsteady vortex structure will be formed. This unsteady vortex structure has a certain negative impact on the inflow quality of the rotor. There is a certain gap between the rotor and the inner wall of the duct. The rotor usually performs a certain tip unloading at the tip. Moreover, after the stator tip and the inner wall of the duct form a relatively sharp angle, a relatively strong pre-swirl flow will be formed at the stator tip, resulting in the formation of an excessively strong pre-swirl flow and unsteady vortex flow at the stator tip, which has an adverse effect on the propulsion efficiency of the pump-jet propulsion, the rotor bearing force, the stator unsteady force, and the duct unsteady force. Therefore, the present invention adjusts the side bevel angle near the tip of the linear side bevel angle distribution stator, reduces the gradient of the side bevel angle of the stator blade tip section with the increase of the radius, makes the intersection of the stator tip and the inner wall of the duct present a greater orthogonality, and forms the "S"-shaped nonlinear side bevel distribution stator of the present invention. In addition, since the angle between the stator tip of the linear side bevel angle distribution and the inner wall of the duct is small, it is not convenient to install and position the stator and the duct during the processing, while the "S"-shaped stator blade tip has better orthogonality with the inner wall of the duct, which facilitates the precise installation and positioning of the stator blade and the duct.

[0048] The "S"-shaped nonlinear side-skew distribution stator of the present invention is in the form of an "S"-shaped circumferential bend as a whole, and the side-skew angle has the characteristics of nonlinear side-skew distribution, that is, at the root of the stator blade, the side-skew angle is about 0°, and as the radius increases, the side-skew angle increases with the increase of the radius, but the side-skew angle first increases with the change of the radius, and the rate of change reaches a maximum value at a certain radius in the middle of the stator blade, and then the rate of change gradually decreases with the increase of the radius, and the rate of change of the side-skew angle with the radius is almost close to 0 at the blade tip, so that the stator is in the form of an "S"-shaped circumferential bend as a whole, and the stator blade tip part is almost perpendicular to the inner wall of the duct.

[0049] like Fig.12 As shown, the present application also provides a design method for a pump-jet propulsor "S"-shaped nonlinear skew distribution stator opposite to the skew direction of the rotor, comprising the following steps:

[0050] (1) A hull-rudder-pump-jet propulsion calculation model was established. The rotation speed of the pump-jet propulsion rotor was determined based on the CFD method when the vehicle reached the self-propulsion point and the flow field data in the pump-jet propulsion duct was obtained. According to the side skew angle θ of the rotor at different radii, the side skew angle θ of the stator at different radii was preliminarily determined. Based on the original straight stator, a preliminary scheme of an "S"-shaped nonlinear side skew distribution stator was obtained.

[0051] (2) Based on the CFD method, a self-propulsion test simulation was carried out on an underwater vehicle with a straight stator and an S-shaped nonlinear side-slant distributed stator pump-jet propulsor. The thrust and torque of each component of the two propulsors were monitored at the self-propulsion point. The propulsion efficiency η0 and the unsteady force amplitude of the two propulsors were obtained by data processing. Thus, the influence of the "S"-shaped nonlinear side-slant distribution stator on the propulsion efficiency and unsteady force of the pump-jet propulsor is analyzed;

[0052] (3) Based on the "S"-shaped nonlinear skew distribution stator of step (2), the distribution characteristics of the flow field between the stator trailing edge and the rotor disk in the duct are analyzed. On the basis of not changing the stator skew distribution law, by changing the maximum skew angle θ0 of the "S"-shaped nonlinear skew distribution stator, the positive intersection of the peak circumferential phase distribution characteristics of the flow field between the stator and the rotor at each radius and the profile phase distribution characteristics at each radius of the rotor blade is increased. The underwater vehicle with the new "S"-shaped nonlinear skew distribution stator pump-jet propulsion is re-installed with a self-propulsion test simulation, and the influence of different maximum skew angles θ0 on the propulsion efficiency and unsteady force of the pump-jet propulsion ...

[0053] (4) Based on the "S"-shaped nonlinear skew distribution stator of step (3), on the basis of determining the maximum inclination angle θ0, by changing the skew angle θ of the "S"-shaped nonlinear skew distribution stator at each radius, the skew distribution law of the stator is adjusted, thereby changing the distribution characteristics of the peak circumferential phase angle of the wake flow at each radius of the rotor disk surface, increasing the positive intersection of the peak circumferential phase distribution characteristics of the flow field between the stator and the rotor at each radius and the profile phase distribution characteristics at each radius of the rotor blade, re-installing the new "S"-shaped nonlinear skew distribution stator pump-jet propulsion The underwater vehicle is simulated by a self-propulsion test, and the influence of different skew distribution laws on the propulsion efficiency and unsteady force of the pump-jet propulsion The influence of different skew distribution laws of the "S"-shaped nonlinear skew distribution stator on the propulsion efficiency and unsteady force of the pump-jet propulsion is obtained. Considering the increase in the propulsion efficiency of the pump-jet propulsion and the reduction in the amplitude of the unsteady force, the most suitable "S"-shaped nonlinear skew distribution stator skew distribution law is selected as the optimization result;

[0054] (5) Based on the optimization result of step (4), the geometric angle of attack α (the angle between the chord line of the blade section and the axis) of the cross section at different radii of the stator blade is adjusted to obtain the influence of the distribution form of the radial geometric angle of attack α on the propulsion efficiency and unsteady force of the pump-jet propulsor. The increase in the propulsion efficiency of the pump-jet propulsor and the reduction in the amplitude of the unsteady force are comprehensively considered, and the most suitable distribution form of the geometric angle of attack α is selected as the optimization result;

[0055] (6) Based on the optimization result of step (5), the chord-wise distribution of the stator blade profile is changed to obtain the influence of the chord-wise distribution of the blade profile on the propulsion efficiency and unsteady force of the pump-jet propulsor. The increase in the propulsion efficiency of the pump-jet propulsor and the reduction in the amplitude of the unsteady force are comprehensively considered, and the most suitable chord-wise distribution of the blade profile is selected as the optimization result.

[0056] The "S"-shaped nonlinear side-skew distribution stator for pump-jet propulsion vibration reduction, noise reduction and efficiency enhancement of the present application changes the side-skew angle of the stator at different radial positions, so that the phases of the high wake areas at different radii in the flow field behind the stator trailing edge are inconsistent, and the change trend of the phase angle of the high wake area from the inner radius to the outer radius is opposite to the change trend of the rotor side-skew angle, which is equivalent to a significant increase in the rotor side-skew angle, which can significantly reduce the propeller exciting force and noise. The "S"-shaped nonlinear side-skew distribution stator can also cause the rotor inlet flow to produce pre-swirl, and the direction of the pre-swirl flow is opposite to the direction of rotor rotation, thereby reducing the kinetic energy loss caused by the circumferential induced velocity in the rotor wake and improving the propulsion efficiency of the propeller.

[0057] In combination with the design optimization method of the present application, changing the spatial distribution of the flow field at the rotor disk surface is equivalent to increasing the side tilt angle of the propeller, so that the phase angle of the high wake area at each radius in the rotor disk surface inlet flow behind the stator trailing edge changes favorably, reducing the rotor structure vibration noise and flow noise; at the same time, the angle of attack formed by the incoming flow and the rotor blades increases, the relative rotation speed increases, the rotor blade load increases, and the work done to overcome the unbalanced torque formed by the rotation is greater. Therefore, the pre-swirling flow originally flowing through the rotor working area can be better absorbed and utilized by the rotor because the proportion of circumferential energy increases. After the incoming flow is absorbed by the rotor, the circumferential induced velocity decreases accordingly, so that the pressure on the suction surface of the rotor blade becomes smaller, the pressure on the pressure surface becomes larger, the pressure difference on both sides increases, and the thrust and torque of the propeller increase accordingly, so that the circumferential energy originally lost in the incoming flow is reused, thereby reducing the speed required for the pump-jet propulsion rotor when the aircraft is self-propelled, reducing the power consumption of the main engine, and improving the propulsion efficiency of the pump-jet propulsion, so as to achieve efficient aircraft propulsion.

[0058] In addition, in this embodiment, a pump-jet propulsion model on a certain underwater vehicle is used as a fact verification. The pump-jet propulsion used in the embodiment is as follows: Figure 1As shown, the stator has 17 blades and the rotor has 7 blades. The calculation coordinate system adopts the Cartesian coordinate system, follows the right-hand rule, takes the center of the pump-jet propulsor rotor disk as the coordinate origin, the positive direction of the x-axis points from the bow to the stern, the positive direction of the y-axis points to the starboard side of the hull, and the z-axis is vertically upward.

[0059] After the incoming flow passes through the stern rudder, an uneven incoming flow is formed. The incoming flow flows into the duct and reaches the rotor through the stator blades. Although the uneven incoming flow is improved to a certain extent under the action of the stator, it will still cause the rotor to produce large structural vibration noise and flow noise. In addition, since the angle of attack formed by the incoming flow and the rotor disk is too small, the circumferential velocity component of the flow field at the rotor disk accounts for a small proportion, resulting in a large circumferential induced velocity in the propeller wake and a loss of some circumferential energy.

[0060] In order to solve the above problems, the present invention proposes an "S" shaped nonlinear side-slant distribution stator installed on a pump-jet propulsor. Figure 2 As shown in the figure, based on the characteristics of the rotor rotation direction and the rotor skew distribution with the radius, the stator profile and skew angle are appropriately changed to obtain an "S"-shaped nonlinear skew distribution stator (as shown in the figure). Figure 3 As shown in the figure), the geometric comparison of the two stators is as follows Figure 4 As shown in the figure, this design makes the uneven incoming flow form a pre-swirl state opposite to the rotor rotation direction after passing through the stator. The spatial distribution of the pre-swirl flow makes the phase angle of the high wake area at each radius in the stator wake field change favorably relative to the phase angle of each radius section of the rotor blade, which is beneficial to reduce the bearing force formed by the operation of the rotor, thereby reducing the structural vibration noise of the rotor. At the same time, due to the change in the phase angle, the flow noise caused by the blade pressure pulsation will also be reduced, thereby improving the submarine's stealth performance.

[0061] In addition, when the pre-swirling flow reaches the rotor disk, the proportion of the circumferential velocity component of the fluid increases and can be better absorbed and utilized by the rotor. The circumferential energy loss in the incoming flow is reduced, the rotor can provide greater thrust, the speed required for the vehicle to propel itself is reduced, and the propulsion efficiency of the thruster is improved, achieving the purpose of increasing efficiency.

[0062] In order to analyze the propulsion performance of pump-jet propulsion with different stators, it is necessary to conduct a self-propulsion test of the vehicle model. This application numerically calculates the underwater unmanned vehicle based on the unsteady method. A hull-rudder-pump-jet propulsion coupling model is established. S The self-propulsion test of the underwater unmanned vehicle is simulated under the working conditions of 1000 rpm and 1000 rpm, and the resultant force F of the hull-pump-jet propulsion and the rotor torque Q are obtained. In addition, before calculating the propulsion efficiency, the towing resistance of the underwater unmanned vehicle without the pump-jet propulsion needs to be obtained. Finally, the obtained data are summarized as shown in Table 1.

[0063] Table 1 Comparison of underwater hydrodynamic parameters in self-propelled state

[0064]

[0065] The towing resistance without pump-jet propulsion is denoted as R0, and the pump-jet-hull force after the pump-jet propulsion is installed is denoted as F. The propulsion efficiency η can be calculated using formula (1).

[0066]

[0067] Where n is the propeller speed and Q is the rotor torque.

[0068] Table 2 Comparison of propulsion efficiency components

[0069] Stator type η Conventional straight stator 0.8010 "S" shaped nonlinear side skew distribution stator 0.8181

[0070] It can be concluded from Table 1 and Table 2 that the pump-jet propeller with an S-shaped nonlinear skew distribution stator has a greater pump-jet-hull force and rotor torque than the pump-jet propeller with a conventional straight stator under the same speed and rotation speed conditions. At this time, the efficiency η increases by 2.13%. When the thrust and resistance are balanced, when the underwater unmanned vehicle reaches the self-propulsion point at the same speed, the speed n required by the S-shaped nonlinear skew distribution stator scheme is less than the speed n required by the conventional straight stator scheme. Compared with the conventional straight stator scheme, the propulsion efficiency of the S-shaped nonlinear skew distribution stator scheme will be further increased.

[0071] Figure 5-6 The pump-jet propeller with different stators has a flow velocity of V. S The circumferential velocity and axial velocity distribution cloud diagram of the flow field on the cross section at the middle position of the stator and the rotor shows that under the action of the "S"-shaped nonlinear side-skew distribution stator, the circumferential phase distribution of the wake peak at different radii in the stator wake field is orthogonal to the circumferential phase distribution of each radial section of the rotor. When the rotor blade root section enters the wake peak area of ​​the stator wake field, other sections still have a large phase difference with the wake peak area at the corresponding radius, that is, the radius of other sections is in the area with relatively low wake values. During the rotation of the rotor blades, the fluctuation amplitude of the load of each radial section of the rotor becomes smaller over time, thereby reducing the rotor excitation force, hydrodynamic noise and structural vibration noise.

[0072] In order to further analyze the effect of the "S"-shaped nonlinear skew distribution stator on the suppression of the rotor excitation force, the unsteady forces in various directions of the pump-jet propulsor rotor under the self-propulsion state were monitored respectively. In the simulation, the rotor rotates 1.5° per unit time step. After the calculation is stable, the data within two rotation periods of the rotor are taken and the average value is subtracted for comparison, such as Figure 7 to Figure 9 shown.

[0073] After Fourier transforming the above calculation results, the unsteady force frequency domain curves within two rotation periods are obtained. The amplitude results of the first three solutions are as follows: Figure 10-11 As shown, it can be seen that the amplitude of the unsteady force of the propeller in one cycle reaches the maximum value at the first-order blade frequency. The specific amplitude comparison of the first-order blade frequency is shown in Tables 3 and 4 below.

[0074] Table 3 Comparison of the unsteady bearing force amplitude of pump-jet propulsor rotor with different stators

[0075]

[0076] Table 4 Comparison of unsteady torque amplitude of pump-jet propulsor rotor with different stators

[0077]

[0078] By comparing the unsteady force and unsteady torque amplitudes of the pump-jet propulsor rotors with two stator schemes, it is found that compared with the conventional straight stator scheme, the maximum unsteady bearing force amplitude of the pump-jet propulsor rotor with the "S"-shaped nonlinear skew distribution stator is reduced by 36.86%, and the maximum unsteady torque amplitude is reduced by 32.56%. This shows that the "S"-shaped nonlinear skew distribution stator can greatly reduce the bearing force formed by the operation of the pump-jet propulsor rotor, can effectively alleviate the structural vibration noise emitted by the rotor during operation, and improve the acoustic stealth of the submarine.

[0079] In summary, the “S”-shaped nonlinear skew distribution stator changes the spatial distribution of the rotor inflow, causing a favorable change in the phase angle of the high wake zone at each radial section of the rotor disk, thereby improving the rotor inflow quality, significantly reducing the exciting force of the pump-jet propulsion rotor, and reducing the structural vibration noise and hydrodynamic noise of the pump-jet propulsion, which is of great significance to improving the acoustic stealth combat capability of modern submarines. In addition, the “S”-shaped nonlinear skew distribution stator further improves the pre-swirl effect of the inflow, offsets the circumferential velocity component of the induced velocity to a certain extent, and reduces the circumferential velocity component in the rotor wake, which is beneficial to reducing the kinetic energy loss caused by the circumferential velocity in the rotor wake, improving the propulsion efficiency of the pump-jet propulsion, and providing a new way to improve the propulsion performance of submarines.

[0080] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A design method for an S-shaped nonlinear side-slant distributed stator for a pump-jet propulsor, characterized in that: The following steps are involved: Step 1: construct a hull-rudder-pump-jet propulsion integrated calculation model; Step 2: Under the self-propulsion state, the integrated model of the hull-rudder-pump-jet propulsion system is numerically simulated. Based on the detailed data of the flow field in the duct and the side skew angle θ of the rotor at different radii, the side skew angle θ of the stator at different radii is preliminarily determined. Based on the original straight stator, a preliminary scheme of an "S"-shaped nonlinear side skew distribution stator is obtained. Step three, according to the above preliminary plan, on the basis of not changing the stator skew distribution law, by changing the maximum skew angle θ0 of the "S"-shaped nonlinear skew distribution stator, analyze the influence of different maximum skew angles θ0 on the propulsion efficiency and unsteady force of the pump-jet propulsor, and obtain the optimal maximum skew angle θ0 of the "S"-shaped nonlinear skew distribution stator according to the influence law, and re-optimize the stator skew angle θ at different radii according to the influence of the maximum skew angle θ0, the propulsion efficiency of the pump-jet propulsor and the unsteady force; Step 4: Based on the "S"-shaped nonlinear skew distribution stator optimized in step 3, the geometric attack angle α of the stator blade section at different radii and the chord-wise distribution of the stator blade section are optimized in turn, thereby completing the design of the S-shaped nonlinear skew distribution stator of the pump-jet propulsion system.

2. The design method of an S-shaped nonlinear side-skew distribution stator for a pump-jet propulsor according to claim 1, characterized in that: In step 2, the side skew angle θ satisfies: the side skew angle θ presents a nonlinear change along the radial direction of the stator blades, the stator side skew angle θ has a circumferential bending form opposite to the rotor side skew direction, from the stator blade root to the blade tip, as the radius increases, the stator phase angle gradually increases in absolute value in the clockwise direction, with counterclockwise being positive, and the side skew angle reaches a negative peak value at the stator blade tip section. In this way, through the design of the side skew angle, the stator can cause the fluid to produce a pre-swirl in the opposite direction of the rotor rotation direction when flowing through, while increasing the phase difference of the peak circumferential phase angle of the wake at different radii in the stator wake, thereby increasing the positive intersection or mismatch between the distribution characteristics of the peak circumferential phase angle of the wake at the rotor disk surface with the radius and the distribution characteristics of the phase angle of the rotor blade section with the radius.

3. The design method of an S-shaped nonlinear side-skew distribution stator for a pump-jet propulsor according to claim 1, characterized in that: Step three specifically includes the following steps: (31) Based on the CFD method, a straight stator and an S-shaped nonlinear side-slant distributed stator pump-jet propulsor were placed on an underwater vehicle, and a self-propulsion numerical simulation was performed. The thrust and torque of each component of the two propulsion units were monitored at the self-propulsion point. By processing the data, the propulsion efficiency η0 and the unsteady force amplitude of the two propulsion units were obtained. Thus, the influence of "S"-shaped nonlinear side-slant distribution stator on the propulsion efficiency and unsteady force of pump-jet propulsor is analyzed; (32) Based on the "S"-shaped nonlinear skew distribution stator of step (31), the distribution characteristics of the flow field between the stator trailing edge and the rotor disk in the duct are analyzed. On the basis of not changing the stator skew distribution law, by changing the maximum skew angle θ0 of the "S"-shaped nonlinear skew distribution stator, the positive intersection of the circumferential phase distribution characteristics of the flow field between the stator and the rotor at each radius and the cross-sectional phase distribution characteristics at each radius of the rotor blade is increased. The underwater vehicle with the new "S"-shaped nonlinear skew distribution stator pump-jet propulsion is re-performed with a self-propulsion numerical simulation, and the influence of different maximum skew angles θ0 on the propulsion efficiency and unsteady force of the pump-jet propulsion is analyzed. The influence law of the maximum skew angle θ0 of the "S"-shaped nonlinear skew distribution stator on the propulsion efficiency and unsteady force of the pump-jet propulsion is obtained. According to the increase in the propulsion efficiency of the pump-jet propulsion and the reduction in the amplitude of the unsteady force, the most suitable "S"-shaped nonlinear skew distribution stator maximum skew angle θ0 is selected as the optimization result; (33) Based on the "S"-shaped nonlinear skew distribution stator of step (32), on the basis of determining the maximum inclination angle θ0, by changing the skew angle θ of the "S"-shaped nonlinear skew distribution stator at each radius, the skew distribution law of the stator is adjusted, thereby changing the distribution characteristics of the peak circumferential phase angle of the wake flow at each radius of the rotor disk surface, increasing the positive intersection of the peak circumferential phase distribution characteristics of the flow field between the stator and the rotor at each radius and the profile phase distribution characteristics at each radius of the rotor blade, and re-installing the new "S"-shaped nonlinear skew distribution stator pump-jet propulsion The underwater vehicle is simulated by a self-propulsion test, and the influence of different skew distribution laws on the propulsion efficiency and unsteady force of the pump-jet propulsion The influence of different skew distribution laws of the "S"-shaped nonlinear skew distribution stator on the propulsion efficiency and unsteady force of the pump-jet propulsion is obtained. Considering the increase in the propulsion efficiency of the pump-jet propulsion and the reduction in the amplitude of the unsteady force, the most suitable "S"-shaped nonlinear skew distribution stator skew distribution law is selected as the optimization result.

4. The design method of an S-shaped nonlinear side-skew distribution stator for a pump-jet propulsor according to claim 1, characterized in that: In step four, the optimization of the geometric angle of attack α of the cross-section of the stator blade at different radii includes: based on the optimization result of step three, adjusting the geometric angle of attack α (the angle between the chord of the blade cross-section and the axis) of the cross-section of the stator blade at different radii, obtaining the influence of the distribution of the radial geometric angle of attack α on the propulsion efficiency and unsteady force of the pump-jet propulsor, comprehensively considering the increase in the propulsion efficiency of the pump-jet propulsor and the reduction in the amplitude of the unsteady force, and selecting the most suitable distribution of the geometric angle of attack α as the optimization result.

5. The design method of an S-shaped nonlinear side-skew distribution stator for a pump-jet propulsor according to claim 1, characterized in that: In step four, the optimization of the chord-wise distribution of the stator blade profile includes: based on the optimization result of step three, changing the chord-wise distribution of the stator blade profile, obtaining the influence of the chord-wise distribution of the blade profile on the propulsion efficiency and unsteady force of the pump-jet propulsor, comprehensively considering the increase in the propulsion efficiency of the pump-jet propulsor and the reduction in the amplitude of the unsteady force, and selecting the most suitable chord-wise distribution of the blade profile as the optimization result.

6. The design method of an S-shaped nonlinear side-skew distribution stator for a pump-jet propulsor according to claim 1, characterized in that: The calculation formula of the propulsion efficiency η includes: Where n is the propeller speed, Q is the rotor torque, V S is the sailing speed, R0 is the towing resistance, and F is the combined force of pump jet and hull.

7. An S-shaped nonlinear side-slant distribution stator for a pump-jet propulsor, characterized in that: The method is implemented by using the design method described in any one of claims 1 to 7.

8. The S-shaped nonlinear side-slant distributed stator for a pump-jet propulsor according to claim 8, characterized in that: The stator as a whole is in an "S"-shaped circumferential bending form, and the side skew angle θ of the stator has a nonlinear side skew distribution characteristic, and the stator side skew angle θ has a circumferential bending form opposite to the rotor side skew direction.

9. The S-shaped nonlinear side-slant distributed stator for a pump-jet propulsor according to claim 8, characterized in that: The side inclination angle θ of the stator satisfies: at the root of the stator blade, the side inclination angle is about 0°, and as the radius increases, the side inclination angle increases with the increase of the radius, but the side inclination angle increases with the change of the radius first, and the change rate reaches the maximum value at a certain radius in the middle of the stator blade, and then the change rate gradually decreases with the increase of the radius, and the change rate of the side inclination angle with the radius is almost close to 0 at the blade tip, so that the stator as a whole is in the form of an "S" shaped circumferential bend, and the stator blade tip part is almost perpendicular to the inner wall of the duct.

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