Structure for improving the aerodynamic efficiency of a low-pressure turbine cascade

Abstract

The present invention provides a structure for improving the aerodynamic efficiency of a low-pressure turbine cascade, comprising: an end wall and a blade body; the end wall is the cascade passage surface perpendicular to the blade body; several first concave structures are arranged on the end wall, and the several first concave structures are located between two adjacent blade bodies. The first concave structures are used to enhance the momentum exchange between the boundary layer flow and the external mainstream, enhance the flow kinetic energy near the wall surface, and change the flow direction near the wall surface; the blade body is provided with a blade suction surface and a blade pressure surface, the blade suction surface is the convex surface of the blade body, and the blade pressure surface is the concave surface of the blade body; several second concave structures are arranged on the blade suction surface, and the second concave structures are used to suppress the flow separation on the blade suction surface and avoid the generation of separation vortices. By using the concave structures on the blade suction surface and the end wall, the present invention can significantly improve the flow in the cascade passage, reduce the aerodynamic loss of the low-pressure turbine cascade, and improve the aerodynamic efficiency of the turbine.

Description

Technical Field

[0001] The present invention relates to the technical field of aeroengine power equipment, and particularly to a structure for improving the aerodynamic efficiency of a low-pressure turbine cascade. Background Art

[0002] In an aero turbofan engine, the output work of the low-pressure turbine is used to drive the fan of the turbofan engine. The fan drives a large flow of air through the engine and generates the main engine thrust. Therefore, the working efficiency and aerodynamic performance of the low-pressure turbine have an important impact on the engine performance.

[0003] The development of modern aeroengines has put forward requirements for lightweight and high efficiency of the low-pressure turbine. Therefore, the number of blades of the low-pressure turbine needs to be reduced, and the load on the low-pressure turbine blades is continuously increasing. The consequence is that the spacing between the low-pressure turbine blades increases, the flow between the blades becomes more complex, the secondary flow loss on the cascade end wall increases, which increases the aerodynamic loss of the low-pressure turbine cascade and reduces the aerodynamic efficiency of the low-pressure turbine. This will reduce the flow capacity of the low-pressure turbine, reduce the turbine energy conversion efficiency, and increase the engine fuel consumption.

[0004] The patent document with the publication number CN105507955A discloses a design method for a high-pressure turbine transonic guide vane cascade. The design method for the high-pressure turbine transonic guide vane cascade includes the following steps: enhancing the load in the region from the inlet of the cascade passage to the geometric throat of the cascade passage; dividing the cascade into a front region, a throat region, and a diffusion region; improving the acceleration of the airflow in the front region and increasing the length of the diffusion region; weakening the expansion acceleration of the supersonic airflow in the throat region; reducing the acceleration of the airflow in the diffusion region; constructing a compression wave near the outlet position of the passage in the diffusion region for deceleration; and completing the cascade design according to the cascade 11 parameter modeling method. However, this patent document is not applicable to the low-pressure turbine, and the technical solution is different from the present application. Summary of the Invention

[0005] Aiming at the defects in the prior art, the purpose of the present invention is to provide a structure for improving the aerodynamic efficiency of a low-pressure turbine cascade.

[0006] A structure for improving the aerodynamic efficiency of a low-pressure turbine cascade according to the present invention includes: an end wall and a blade body; the end wall is the cascade passage surface perpendicular to the blade body;

[0007] A plurality of first concave structures are provided on the end wall. The plurality of first concave structures are located between two adjacent blade bodies, and the first concave structures are used to enhance the momentum exchange between the boundary layer flow and the external mainstream;

[0008] The blade body is provided with a blade suction surface and a blade pressure surface. The blade suction surface is the convex surface of the blade body, and the blade pressure surface is the concave surface of the blade body;

[0009] The blade suction surface is provided with a plurality of second recessed structures, which are used to suppress flow separation on the blade suction surface and avoid the generation of separation vortices.

[0010] Preferably, a plurality of the first recessed structures are arranged along an alignment line, and the alignment line is parallel to the mean camber line of the blade body.

[0011] Preferably, the second recessed structures are provided in multiple numbers, and the depth of the second recess is 0 - 6.0 mm;

[0012] Every two of the second recessed structures form a pair to form a V-shaped structure, and a plurality of the V-shaped structures are formed on the blade suction surface.

[0013] Preferably, the second recessed structures are arranged near the most convex position of the blade body and are located on the surface at a distance of 0.1 - 10 times the recess diameter d downstream of the most convex position.

[0014] Preferably, the ratio of the recess diameter d of the first recessed structure to the blade pitch P of the blade body is 0.01 - 0.2;

[0015] The ratio of the recess depth h of the first recessed structure to the recess diameter d of the first recessed structure is 0.05 - 0.3.

[0016] Preferably, the axial arrangement pitch s of the first recessed structure x has a ratio to the recess diameter d of the first recessed structure of 1.1 - 1.5;

[0017] Starting from the upstream, the distance between the center point of the first recessed structure on the alignment line and the inlet section of the cascade is 1.0 - 1.5d;

[0018] The axial distance between the center points of the two first recessed structures at the head and tail on the alignment line is L = 5 - 10d, and the axial distance between the last first recessed structure and the outlet section of the cascade is 0.25 - 0.5 times the chord length Cx.

[0019] Preferably, the first recessed structures are arranged at a position of 0.5P - 0.8P in the circumferential direction within the cascade passage, P is the blade pitch of the blade body, and the first recessed structures are arranged closer to the adjacent blade pressure surface.

[0020] Preferably, starting from the upstream, the first one of the first recessed structures is located at a position 1.0d to 1.5d upstream of the inlet section of the cascade, and the most downstream one of the first recessed structures is located at a position 0.2 to 0.5 times the chord length c upstream of the outlet section of the cascade x ;

[0021] d is the recessed diameter of the first recessed structure, and d ranges from 1.0 to 50 mm; c x is the length of the blade body in the axial direction of the cascade, and c x The length is 5 to 20 times the recessed diameter d.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. By arranging the second recessed structure on the suction surface of the low-pressure turbine blade and arranging the first recessed structure on the end wall of the turbine cascade, the present invention changes the movement direction of the near-wall fluid, realizes the improvement of the aerodynamic efficiency of the low-pressure turbine cascade. By arranging the second recessed structure on the suction surface of the low-pressure turbine blade, the inner arc surface of the second recessed structure interacts with the relatively low-speed near-wall fluid, and a near-wall flow vorticity system is induced and formed downstream of the second recessed structure, increasing the momentum exchange between the near-wall flow and the mainstream. At the same time, the flow shear induced by the near-wall flow vorticity system promotes the transition of the near-wall flow, enhances the ability of the near-wall fluid to overcome the adverse pressure gradient, and finally weakens or eliminates the laminar separation phenomenon occurring on the suction surface of the blade, thereby reducing the shear between the laminar separation recirculation zone and the mainstream, narrowing the flow wake of the cascade, and thus reducing the profile loss brought by both;

[0024] 2. Through the interaction between the first recessed structure on the end wall surface of the low-pressure turbine cascade and the secondary eddy current on the end wall surface, the present invention generates eddy currents, enhances the movement energy of the near-wall fluid, and changes the movement direction of the eddy currents, suppressing the accumulation of the eddy currents towards the suction side of the adjacent blade; weakening the strength of the horseshoe vortex at the root of the blade leading edge, and also weakening the strength of the secondary flow vortex systems such as the passage vortex, corner vortex, and trailing edge shedding vortex induced and formed thereafter, thereby reducing the secondary flow loss brought by it;

[0025] 3. Through the design that the first recessed arrangement line on the end wall surface of the low-pressure turbine cascade is parallel to the blade mean camber line, the present invention suppresses or weakens the end wall cross-flow, suppresses the effect of the horseshoe vortex on the development of the secondary flow on the end wall in the cascade passage, and also weakens the strength of the secondary flow vortex systems in the end region of the cascade, thereby reducing the secondary flow loss brought by it;

[0026] 4. The present invention solves the problem of reduced aerodynamic efficiency caused by the secondary flow of the end wall of the low-pressure turbine cascade. At the same time, the recessed arrangement processing technology used in the present invention is simple and effective under a wide range of incoming flow Reynolds number conditions, especially significantly improving the aerodynamic efficiency of the ultra-high load low-pressure turbine cascade. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other features, objects, and advantages of the present invention will become more apparent by reading the following detailed description of non - restrictive embodiments with reference to the accompanying drawings:

[0028] Figure 1 Schematic diagram of the dimensional structure of the structure for improving the aerodynamic efficiency of a low - pressure turbine cascade according to the present invention;

[0029] Figure 2 Flow schematic of the structure for improving the aerodynamic efficiency of a low - pressure turbine cascade according to the present invention Figure 1 ;

[0030] Figure 3 Flow schematic of the structure for improving the aerodynamic efficiency of a low - pressure turbine cascade according to the present invention Figure 2 ;

[0031] Figure 4 Schematic diagram highlighting the second recess structure of the structure for improving the aerodynamic efficiency of a low - pressure turbine cascade according to the present invention;

[0032] Figure 5 Schematic diagram highlighting the first recess structure of the structure for improving the aerodynamic efficiency of a low - pressure turbine cascade according to the present invention.

[0033] [[ID=SO]]As shown in the figure:

[0034] Blade body 1, First recess structure 201

[0035] Blade suction surface 101, Arrangement line 3

[0036] Second recess structure 1011, Mean camber line 4

[0037] Blade pressure surface 102, Cascade inlet section 5

[0038] End wall 2, Cascade outlet section 6 DETAILED DESCRIPTION OF THE EMBODIMENTS[[ID=SO]]

[0039] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all fall within the protection scope of the present invention.

[0040] Example 1:

[0041] Such as Figures 1 to 4As shown in the figure, this embodiment provides a structure for improving the aerodynamic efficiency of a low-pressure turbine cascade, including: an end wall 2 and a blade body 1. The end wall 2 is the cascade passage surface perpendicular to the blade body 1. There are several first recessed structures 201 on the end wall 2. The several first recessed structures 201 are located between two adjacent blade bodies 1. The first recessed structure 201 is used to enhance the momentum exchange between the boundary layer flow and the external mainstream and change the near-wall flow direction. There are a blade suction surface 101 and a blade pressure surface 102 on the blade body 1. The blade suction surface 101 is the convex surface of the blade body 1, and the blade pressure surface 102 is the concave surface of the blade body 1. There are several second recessed structures 1011 on the blade suction surface 101. The second recessed structure 1011 is used to suppress the flow separation on the blade suction surface 101 and avoid the generation of separation vortices.

[0042] The leading edge of the blade body 1 is tangent to the cascade inlet section 5, and the trailing edge of the blade body 1 is tangent to the cascade outlet section 6.

[0043] The second recessed structure 1011 is set to be multiple. The depth of the second recess is 0 - 6.0 mm. Every two second recessed structures 1011 form a V-shaped structure as a pair, and several V-shaped structures are formed on the blade suction surface 101. The second recessed structure 1011 is arranged near the most convex position of the blade body 1 and is located on the surface at a distance of 0.1 - 10 times the recess diameter d downstream of the most convex position.

[0044] The several first recessed structures 201 are arranged along the arrangement line 3, and the arrangement line 3 is parallel to the mean camber line 4 of the blade body 1.

[0045] The axial arrangement pitch s of the first recessed structure 201 x The ratio to the recess diameter d of the first recessed structure 201 is 1.1 - 1.5. Starting from the upstream, the center point of the first first recessed structure 201 on the arrangement line 3 is at a distance of 1.0 - 1.5d from the cascade inlet section. The axial distance between the center points of the two first recessed structures 201 at the head and tail on the arrangement line 3 is L = 5 - 10d, and the axial distance between the last first recessed structure 201 and the cascade outlet section 6 is 0.25 - 0.5 times the chord length Cx.

[0046] The ratio of the recess diameter d of the first recessed structure 201 to the blade pitch P of the blade body 1 is 0.01 - 0.1, and the ratio of the recess depth h of the first recessed structure 201 to the recess diameter d of the first recessed structure 201 is 0.05 - 0.3.

[0047] Starting from the upstream, the first first recessed structure 201 is located at a position 1.0d - 1.5d upstream of the cascade inlet section 5, and the most downstream first recessed structure 201 is located upstream of the cascade outlet section 6 at 0.2 - 0.5 times the chord length c xThe position of the first concave structure 201 is shown in FIG. 2 , d is the concave diameter of the first concave structure 201, and the value of d is 1.0 to 50 mm. x is the length of the blade body 1 in the axial direction of the blade cascade, c x The length is 5 to 20 times the diameter d of the depression.

[0048] The first recessed structures 201 are arranged at positions 0.5P to 0.8P in the circumferential direction in the cascade channel, where P is the blade pitch of the blade body 1 . The first recessed structures 201 are arranged closer to the adjacent blade pressure surfaces.

[0049] This embodiment can reduce the secondary flow loss in the end area of the low-pressure turbine blade cascade, improve the aerodynamic efficiency of the low-pressure turbine blade cascade, suppress the secondary flow vortex system in the end area of the low-pressure turbine blade cascade, or weaken the intensity of the secondary flow vortex system, reduce the secondary flow loss in the end area of the blade cascade, and improve the aerodynamic efficiency of the low-pressure turbine blade cascade.

[0050] In the structure of this embodiment, the first recessed structures 201 are arranged on the end wall 2, and the arrangement curve of the first recessed structures 201 is parallel to the blade mid-arc line 4, as shown in FIG. Figure 2 and Figure 3 As shown in the figure, when the airflow A flows through the end wall 2 and hits the root of the leading edge of the blade body 1, due to the low flow velocity in the boundary layer, the boundary layer flow will form a multi-layer horseshoe vortex structure at the root of the leading edge of the blade. The horseshoe vortex will develop into a channel vortex B of oblique flow and induce an angular vortex at the root of the suction surface 101 of the adjacent blade and a shedding vortex D at the trailing edge of the blade. These vortex structures are called secondary flow vortex systems at the end of the cascade.

[0051] In the structure of this embodiment, the first recessed structure 201 on the wall surface of the end wall 2 can enhance the momentum exchange between the boundary layer flow and the external mainstream, thereby enhancing the kinetic energy of the boundary layer flow near the wall surface. When the secondary flow from the blade pressure surface 102 passes over the first recessed structure 201 on the end wall 2, it will rush into the interior of the first recessed structure 201 and interact with the curved wall surface of the first recessed structure 201. The first recessed structure 201 changes the flow direction of the near-wall vortex, causing the near-wall vortex to flow into the mainstream and obtain energy for downstream flow. This reduces the accumulation and intrusion of the secondary flow with the low-energy flow near the suction surface 101 of the adjacent blade, thereby weakening the lateral flow of the end wall 2, suppressing or reducing the horseshoe vortex structure and vortex intensity, and thus reducing the secondary flow vortex system in the blade end area and the secondary flow losses it brings.

[0052] In the structure of this embodiment, a second recessed structure 1011 is arranged on the turbine blade suction surface 101. The second recessed structures 1011 are arranged in pairs in a V-shape on the blade suction surface 101. The second recessed structures 1011 form an inclination angle β with the airflow. Typically, the second recessed structures 1011 are arranged downstream of the most convex position of the blade suction surface 101. The second recessed structure 1011 has an oblong or spherical shape.

[0053] In the structure of this embodiment, the second recessed structure 1011 on the blade suction surface 101 functions to suppress flow separation on the blade suction surface 101 and avoid the generation of separation vortices, reduce the aerodynamic losses caused by such separation vortices, and also suppress the entrainment effect of the separation vortices on the blade suction surface 101 on the passage vortex B, reduce the aerodynamic losses, significantly improve the flow in the cascade passage, and improve the aerodynamic efficiency of the turbine.

[0054] Specific geometric parameters of the preferred recessed structure when applied to a very high load low-pressure turbine cascade:

[0055] a. The relative diameter d / P (diameter of the recessed structure / blade pitch) of the recessed structure = 0.077, ranging from 0.01 to 0.1;

[0056] b. The depth-diameter ratio h / d (depth of the recessed structure / diameter of the recessed structure) of the recessed structure = 0.15, ranging from 0.1 to 0.2;

[0057] c. The relative axial arrangement pitch s x / d (axial arrangement pitch of the recessed structure / diameter of the recessed structure) = 1.2;

[0058] d. The relative circumferential arrangement pitch s θ / P (circumferential arrangement pitch of the recessed structure / blade pitch) = 0.1;

[0059] e. For the first recessed structure 201, calculated from the center point of the first recessed structure upstream, the first first recessed structure 201 extends 1.2d forward from the cascade inlet section;

[0060] f. For the first recessed structure 201, calculated from the distance between the center points of the head and tail recessed structures, the axial length of the arrangement of the first recessed structure 201 is 7.2d;

[0061] g. The first recessed structure 201 is arranged at a position of 0.6P circumferentially in the cascade passage, closer to the pressure side;

[0062] h. The arrangement curve of the first recessed structure 201 is parallel to the blade median line 4.

[0063] Example 2:

[0064] Those skilled in the art can understand this embodiment as a specific illustration of Embodiment 1.

[0065] As Figure 1 shown, a row of second recessed structures 1011 is arranged on the blade suction surface 101, and a row of first recessed structures 201 is arranged on the end wall 2. The axial distance of the cascade of the first second recessed structure 1011 from the cascade inlet section 5 is x bFor the first concave structure 201, the diameter of a single first concave structure 201 is d, and the distance between adjacent first concave structures 201 in the axial direction of the cascade is s. x The total length of a row of first recessed structures 201 in the axial direction of the blade cascade is L=7.2d, and the length from the blade cascade inlet section 5 to the upstream is l.

[0066] The first concave structure 201 is arranged along the arrangement line 3, which is parallel to the blade mid-arc line 4. The distance between the arrangement line 3 and the blade mid-arc line 4 in the cascade circumferential direction is p. The arrangement spacing of the blade body 1 in the cascade circumferential direction is P, and the length of the blade body 1 in the cascade axial direction is c. x The blade body 1 is tangent to the blade leading edge at the blade inlet section 5 , and the blade body 1 is tangent to the blade trailing edge at the blade outlet section 6 .

[0067] The first recessed structures 201 arranged on the wall surface of the end wall 2 induce the mainstream to interact with it and generate near-wall spiral vortices, thereby promoting momentum exchange between the low-speed fluid in the near-wall boundary layer and the mainstream high-speed fluid, enhancing the kinetic energy of the near-wall fluid, resisting the lateral pressure gradient in the blade channel, reducing the deflection of the near-wall fluid toward the suction side, thereby reducing the flow into the horseshoe vortex on the suction side of the blade, and weakening the strength of the horseshoe vortex on the suction side.

[0068] The arrangement line 3 of the first recessed structure 201 is parallel to the blade center arc line 4. The near-wall spiral vortex formed by it blocks the cross flow from the pressure side to the suction side, prompting this part of the near-wall fluid to flow along the blade center arc line 4, thereby improving the flow organization structure of the near-wall area.

[0069] The spanwise position of the first recessed structure 201 just intercepts the weak point of the pressure side horseshoe vortex. The swirling flow in the pressure side horseshoe vortex will rush into the first recessed structure 201 and interact with the wall of the first recessed structure 201 to generate a vortex, causing the kinetic energy of the pressure side horseshoe vortex to diffuse and weaken the strength of the pressure side horseshoe vortex.

[0070] The above-mentioned effects on the suction side horseshoe vortex, pressure side horseshoe vortex, and flow organization structure in the near-wall area will ultimately weaken the intensity of secondary flow vortex systems such as channel vortex, reduce the generation of unnecessary flow shear, and ultimately reduce secondary flow losses, improve the flow velocity, flow direction distribution and flow performance in the blade channel, and improve the efficiency of the low-pressure turbine.

[0071] The first recessed structures 201 are arranged forward from the blade inlet section 5 and begin to influence the boundary layer flow at the thinner boundary layer in front, thereby having a stronger ability to form near-wall spiral vortices, thereby being able to block the cross flow on the end wall 2 to a greater extent and suppress the tendency of the fluid in the near-wall area of the end wall 2 to collide with the suction side.

[0072] The first concave structure 201 is a downward concave structure, and the depth of the depression is close to the thickness of the near-wall boundary layer. It does not penetrate into the high-speed mainstream region, only affects the fluid within the near-wall boundary layer, does not affect the flow velocity of the mainstream, does not generate additional form drag, and has significant advantages over traditional upward convex structures.

[0073] The length of the first concave structure 201. The first concave structure 201 is located at a position 1.0d to 1.5d upstream of the inlet section 5 of the cascade, and the most downstream first concave structure 201 is located at a position 0.2 to 0.5 times the chord length c upstream of the outlet section 6 of the cascade. x of the position. The arrangement line 3 of the first concave structure 201 on the end wall 2 is parallel to the mean camber line 4 of the cascade, and the arrangement of the first concave structure 201 crosses the most convex part of the arrangement line 3. Since in the downstream of the cascade passage, due to the development and thickening of the near-wall boundary layer, the passage vortex has approached the suction side and gradually lifted off the end wall 2. The first concave structure 201 on the end wall 2 in the downstream of the cascade passage will not be able to affect the relatively thick boundary layer and the secondary flow vortex system far from the end wall 2, and will increase the flow loss due to the turbulence induced by itself.

[0074] The wall shape of the first concave structure 201 is spherical or conical. The shape of the first concave structure 201 can also be oblong. For example, if the first concave structure 201 is oblong, and the direction of the oblong depression is along the direction of the arrangement line 3.

[0075] The first concave structure 201 is arranged on the end wall 2 of the cascade passage. The distance between the arrangement line 3 of the first concave structure 201 and the mean camber line 4 is 0.5P to 0.8P. The arrangement line 3 of the first concave structure 201 is closer to the pressure side of the adjacent blade. As Figure 1 shown, the arrangement line 3 of the first concave structure 201 is closer to the blade pressure surface 102 of the upper blade body 1.

[0076] The present invention uses the concave structures on the blade suction surface and the end wall, which can significantly improve the flow in the cascade passage and increase the aerodynamic efficiency of the turbine.

[0077] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0078] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be arbitrarily combined with each other.

Claims

1. A structure for improving the aerodynamic efficiency of a low-pressure turbine cascade, characterized in that: include: An end wall (2) and a blade body (1); the end wall (2) is a cascade channel surface perpendicular to the blade body (1); A plurality of first recessed structures (201) are provided on the end wall (2), and the plurality of first recessed structures (201) are located between two adjacent blade bodies (1). The first recessed structures (201) are used to enhance momentum exchange between boundary layer flow and external mainstream flow, enhance kinetic energy of flow near the wall, and change the direction of flow near the wall; The blade body (1) is provided with a blade suction surface (101) and a blade pressure surface (102), the blade suction surface (101) being the outer convex surface of the blade body (1), and the blade pressure surface (102) being the inner concave surface of the blade body (1); The blade suction surface (101) is provided with a plurality of second recessed structures (1011), and the second recessed structures (1011) are used to suppress flow separation on the blade suction surface (101) and avoid the generation of separation vortices; A plurality of the first recessed structures (201) are arranged along an arrangement line (3), and the arrangement line (3) is parallel to a mid-arc line (4) of the blade body (1); The depth of the second recessed structure (1011) is 0 to 6.0 mm; Every two of the second recessed structures (1011) form a pair to form a V-shaped structure, and a plurality of the V-shaped structures are formed on the blade suction surface (101).

2. The structure for improving the aerodynamic efficiency of a low-pressure turbine blade cascade according to claim 1, characterized in that: The second recessed structure (1011) is arranged close to the most convex position of the blade body (1) and is located on a surface at a distance 0.1 to 10 times the recessed diameter d downstream of the most convex position.

3. The structure for improving the aerodynamic efficiency of a low-pressure turbine blade cascade according to claim 1, characterized in that: The ratio of the concave diameter d of the first concave structure (201) to the blade pitch P of the blade body (1) is 0.01 to 0.1; The ratio of the depression depth h of the first depression structure (201) to the depression diameter d of the first depression structure (201) is 0.05 to 0.

3.

4. The structure for improving the aerodynamic efficiency of a low-pressure turbine blade cascade according to claim 3, characterized in that: The axial arrangement spacing s of the first recessed structures (201) x The ratio of the diameter of the first concave structure (201) to the concave diameter d is 1.1 to 1.5; Starting from upstream, the distance between the center point of the first first recessed structure (201) on the arrangement line (3) and the blade inlet cross section is 1.0 to 1.5d; The axial distance between the center points of the first and last two recessed structures (201) on the arrangement line (3) is L=5-10d, and the axial distance between the first recessed structure (201) at the tail and the blade cascade outlet section (6) is 0.25-0.5 times the chord length Cx.

5. The structure for improving the aerodynamic efficiency of a low-pressure turbine blade cascade according to claim 4, characterized in that: The first recessed structure (201) is arranged at a position of 0.5P to 0.8P in the circumferential direction in the blade channel, where P is the blade pitch of the blade body (1), and the first recessed structure (201) is arranged closer to the adjacent blade pressure surface.

6. The structure for improving the aerodynamic efficiency of a low-pressure turbine blade cascade according to claim 1, characterized in that: Starting from the upstream, the first first concave structure (201) is located 0.05 to 0.3 times the chord length c upstream of the blade inlet section (5). x The first recessed structure (201) at the most downstream side is located 0.2 to 0.5 times the chord length c upstream of the cascade outlet section (6). x location; d is the concave diameter of the first concave structure (201), and the value of d is 1.0 to 50 mm; c x is the length of the blade body (1) in the axial direction of the blade cascade, c x The length is 5 to 20 times the diameter d of the depression.

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