Movable blade margin plate, movable blade and movable blade margin plate design method

Abstract

The invention aims to provide a moving blade margin plate, a moving blade and a moving blade margin plate design method, the moving blade margin plate is used for the moving blade, the moving blade comprises the moving blade margin plate and a blade body arranged on a runner surface of the moving blade margin plate, the blade body is provided with a suction surface side and a pressure surface side in the incoming flow direction, and the blade body further comprises a front edge and a tail edge; wherein the movable blade margin plate is provided with a convex part protruding from a runner surface and a concave part concave from the runner surface, the convex part is arranged on the pressure surface side of the front edge, and the concave part is arranged on the suction surface side of the front edge. By means of the movable blade margin plate, the aerodynamic efficiency of the movable blade and the downstream blade can be improved.

Description

Technical Field

[0001] The invention relates to the field of gas turbine engines, and in particular to a moving blade edge plate, a moving blade and a moving blade edge plate design method. Background Art

[0002] Faced with rising fuel prices and increasingly stringent carbon emission requirements, high efficiency and low fuel consumption have become the main design goals of civil turbofan engines. The bypass ratio is one of the important design parameters of turbofan engines. It is defined as the ratio of the mass flow rate flowing through the outer bypass to the mass flow rate of the core engine. Increasing the bypass ratio under a certain thrust level means allowing a larger proportion of air to be discharged through the fan at a lower speed, which can reduce the average exhaust velocity of the turbofan engine and improve the engine propulsion efficiency.

[0003] The most direct way to improve the bypass ratio is to increase the flow through the outer duct. The increase in the flow area of ​​the outer duct leads to an increase in the diameter of the fan and nacelle. At present, the diameter of the nacelle of advanced engines has exceeded 2m. The increase in the nacelle diameter will increase the weight and wind resistance of the whole machine. The oversized nacelle size will also bring great difficulties to the manufacture and installation of the engine. These problems force the industry to consider reducing the size of the core engine and reducing the flow of the core engine to further improve the bypass ratio of the civil turbofan engine while keeping the fan diameter unchanged. Therefore, the miniaturization of the core engine has become a key technology for the development of high-performance civil turbofan engines in the future.

[0004] The direct impact of the miniaturization of the core engine on the turbine is that its flow area is reduced and the blade length is shortened, which puts higher requirements on processing and assembly deviations. The end zone loss becomes a key factor restricting engine performance. For the rotor blades, the lower end zone is constrained by aerodynamics, centrifugal force, thermal load and wheel life, which increases the difficulty of controlling the secondary flow in the end zone.

[0005] There is an urgent need to provide a moving blade with a new configuration to improve aerodynamic efficiency and improve turbine efficiency at the same time. Summary of the invention

[0006] The object of the present invention is to provide a moving blade edge plate which can improve the aerodynamic efficiency of the moving blade.

[0007] A moving blade edge plate for achieving the above-mentioned purpose is used for a moving blade, the moving blade comprising a moving blade edge plate and a blade body arranged on a flow path surface of the moving blade edge plate, the blade body having a suction surface side and a pressure surface side along the incoming flow direction, the blade body also comprising a leading edge and a trailing edge;

[0008] The moving blade edge plate has a convex portion protruding from the flow path surface and a concave portion recessed from the flow path surface, the convex portion is arranged on the pressure surface side of the leading edge, and the concave portion is arranged on the suction surface side of the leading edge.

[0009] In one or more embodiments, the convex portion has a convex portion height, and the convex portion height is the distance from the flow channel surface to the apex of the convex portion;

[0010] Wherein, the height of the convex portion is not greater than 10% of the height of the blade body.

[0011] In one or more embodiments, the recess has a recess depth, and the recess depth is the distance from the bottom of the recess to the flow channel surface;

[0012] Wherein, the depth of the recess is not greater than 10% of the height of the blade body.

[0013] In one or more embodiments, the boundary of the flow channel surface is defined in one direction by a top edge of the moving blade edge plate close to the trailing edge and a bottom edge close to the leading edge, and in another direction by a first side edge of the edge plate close to the suction surface side and a second side edge close to the pressure surface side;

[0014] A guide portion is provided on the first side edge, and the airflow can be guided by the guide portion. The guide portion extends from the top edge toward the bottom edge to a termination point, and the termination point is the intersection of the streamline of the upper end wall of the flow channel surface and the first side edge.

[0015] In one or more embodiments, the termination point is obtained by offsetting the intersection of the upper wall streamline of the flow channel surface and the first side edge toward the bottom edge by a first distance;

[0016] Among them, 0<the first distance≤0.5 mm.

[0017] In one or more embodiments, the first distance is 0.5 mm.

[0018] In one or more embodiments, the guide portion is chamfered.

[0019] In one or more embodiments, the angle between the chamfered surface of the chamfer and the plane where the flow channel surface is located is 30° to 45°, and the distance between the lowest point of the chamfered surface and the plane where the flow channel surface is located is 0.5 to 0.7 mm.

[0020] On the other hand, according to some embodiments of the present application, a moving blade is provided, which includes the moving blade edge plate as described above.

[0021] On the other hand, according to some embodiments of the present application, a method for designing a moving blade edge plate is provided, which includes the following steps:

[0022] Obtain the center camber line of the blade body located on the flow path surface of the moving blade edge plate;

[0023] A plurality of control points are arranged along the extending direction of the median camber line, wherein the control points include a first control point, and the first control point is located at the leading edge;

[0024] Get the offset distance;

[0025] Acquire a convex point position, wherein the convex point position is obtained by offsetting the first control point toward a side edge of the flow path surface close to a pressure surface side of the blade body by the offset distance;

[0026] Acquire a concave point position, wherein the concave point position is obtained by offsetting the first control point toward a side edge of the flow channel surface close to a suction surface of the blade body by the offset distance;

[0027] A convex portion protruding from the flow channel surface is provided at the convex portion point of the flow channel surface, and a concave portion concave from the flow channel surface is provided at the concave portion point of the flow channel surface.

[0028] In one or more embodiments, it is characterized in that

[0029] The height of the protrusion is configured to be no greater than 10% of the height of the blade body; and

[0030] The depth of the recess is configured to be no greater than 10% of the height of the blade airfoil.

[0031] The beneficial effects of the present invention are:

[0032] The present moving blade edge plate design method and the moving blade edge plate reduce the risk of combustion backflow caused by stagnation of the moving blade leading edge by arranging a concave portion on the leading edge of the blade and on the suction side of the leading edge, thereby obtaining a more uniform circumferential pressure distribution and improving the sealed outflow; a convex portion is arranged on the leading edge of the pressure surface side, and the lateral pressure gradient of the end wall is reduced through the concave-convex shape design of the end wall, thereby delaying the development of the channel vortex and its climbing along the blade surface, and weakening the secondary flow intensity and the loss of interaction with the blade surface.

[0033] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0035] Figure 1 A three-dimensional schematic diagram of a moving blade edge plate according to some embodiments of the present application is shown;

[0036] Figure 2 A schematic top view of a moving blade edge plate according to some embodiments of the present application is shown;

[0037] Figure 3 A schematic diagram of a three-dimensional configuration of a moving blade edge plate according to some embodiments of the present application is shown;

[0038] Figure 4 A schematic diagram showing the total pressure loss distribution of the conventional design and the present moving blade edge plate is shown;

[0039] Figure 5 A schematic diagram of the non-axisymmetric end wall calculation model for the high-pressure turbine rotor-static seal cavity effect is shown;

[0040] Figure 6 A schematic diagram of the control point distribution is shown;

[0041] Figure 7 Schematic top views of some embodiments of the moving blade edge plate are shown;

[0042] Figure 8 A three-dimensional schematic diagram of another viewing angle of some embodiments of the moving blade edge plate is shown;

[0043] Fig. 9 for Figure 8 A partial enlarged schematic diagram of part A;

[0044] Fig. 10A The end wall limiting streamline diagram of the moving blade edge plate with conventional design is shown;

[0045] Fig. 10B The end wall limit streamline diagram using the present moving blade edge plate is shown;

[0046] Fig.11A The limiting streamlines on the blade surface and the wall shear stress cloud diagram of the conventionally designed blade edge plate are shown;

[0047] Fig. 11B The limiting streamlines on the blade surface and the wall shear stress cloud diagram using the present moving blade edge plate are shown. DETAILED DESCRIPTION

[0048] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0050] In order to effectively control the channel vortex loss, on the one hand, according to some embodiments of the present application, a moving blade edge plate is provided. Figure 1 shows a three-dimensional schematic diagram of a moving blade edge plate according to some embodiments of the present application, Figure 1 The overall shape of the moving blade where the moving blade edge plate is located is also shown. Figure 2 shows a schematic top view of a moving blade edge plate according to some embodiments of the present application, Figure 3 A schematic diagram of a three-dimensional configuration of a moving blade edge plate according to some embodiments of the present application is shown.

[0051] The moving blade includes a moving blade edge plate 1 and a blade body 2 arranged on the flow path surface 10 of the moving blade edge plate 1. The edge plate is a wall structure formed by a blade channel rotating circumferentially along the flow path profile line where the blade is located. The airflow flows above the flow path surface. The blade body 2 has a suction surface side 21 (blade back side) and a pressure surface side 22 (blade basin side) along the incoming direction of the airflow. The blade body also includes a leading edge 23 and a trailing edge 24.

[0052] The impeller edge plate has a convex portion 11 protruding from the flow path surface 10 and a concave portion 12 recessed from the flow path surface 10 . The convex portion 11 is arranged on the pressure surface side 22 of the leading edge 23 , and the concave portion 12 is arranged on the suction surface 21 side of the leading edge 23 .

[0053] On the other hand, according to some embodiments of the present application, a design method for a moving blade edge plate is also provided, wherein the positions of the convex portion 11 and the concave portion 12 are further explained in the design method.

[0054] First, Figure 5 The schematic diagram of the non-axisymmetric end wall calculation model showing the effect of the high-pressure turbine rotor and static seal cavity is shown. Figure 5 The calculation model shown in Figure 6 ,

[0055] Figure 5 In order to optimize the full three-dimensional CFD calculation model of the edge plate, it is proposed to use the real trailing edge split structure 1040 to carry out the non-axisymmetric end wall optimization design, structured grid, and the blade cooling air is simulated by the split method. In order to be closer to the real end zone flow structure inside the turbine, a non-axisymmetric end wall calculation model considering the influence of the rim sealing air flow 1050 is proposed.

[0056] The blade edge plate design method includes the following steps:

[0057] The center camber line of the blade on the flow path surface of the moving blade edge plate is obtained. Specifically, the pressure surface and suction surface data of the blade are identified from the intersection line of the modeling blade row and the end wall, and the center camber line of the blade on the flow path surface of the moving blade edge plate and the front and rear extension lines of the center camber line are obtained according to the blade geometry interpolation, such as Figure 6 As shown, the camber line a extends from the leading edge 23 of the blade to the trailing edge 24. The camber line is defined as the line connecting the centers of the inscribed circles of the blade, and extending from the centers of the leading and trailing edges in the tangent direction to the line intersecting the leading and trailing edges.

[0058] A plurality of control points x are arranged along the extending direction of the median arc line a, and the control points include a first control point x1 , and the first control point x1 is located at the leading edge 23 .

[0059] Obtain the offset distance h. It can be understood that the offset distance h is obtained by dividing the local grid pitch by 4. In a specific embodiment, the offset distance h is 5.78 mm.

[0060] Then, the convex point x2 is obtained, and the convex point x2 is obtained by offsetting the first control point x1 toward the side of the flow path surface close to the pressure surface side of the blade body by an offset distance h.

[0061] Then, the concave point x3 is obtained, and the concave point x3 is obtained by the side offset distance h of the first control point x1 toward the flow channel surface close to the blade suction surface side;

[0062] Finally, a convex portion 11 protruding from the flow channel surface 10 is provided at the convex portion point x2 of the flow channel surface 10, and a concave portion 12 concave from the flow channel surface is provided at the concave portion point x3 of the flow channel surface.

[0063] In a specific embodiment, Figure 6 The multiple control points x shown are NURBS surface control points. By setting the numerical values ​​of the multiple control points x, its profile can be controlled. For example, a control point with a value greater than 0 is a convex surface, and a control point with a value less than 0 is a concave surface. In a specific embodiment, the coordinates of the five control points from the leading edge x1 and x2 of the blade to the leading edge x1 of the adjacent blade (from the pressure surface to the suction surface) are respectively: 0, 4.04, -2.92, -2.59, 0, forming a smooth NURBS surface.

[0064] According to the Bernoulli equation, concave streamlines reduce flow velocity and increase local pressure; convex streamlines increase flow velocity and reduce local pressure. The present moving blade edge plate design method and moving blade edge plate reduce the risk of backflow caused by stagnation of the moving blade leading edge by setting a recess 12 on the suction surface side 21 of the leading edge of the blade, obtain a more uniform circumferential pressure distribution, and improve the sealing outflow. In a specific embodiment, the concave amplitude of the recess 12 is located at the leading edge of the suction side of the moving blade. A convex portion 11 is set at the leading edge of the pressure surface side 22. Through the concave and convex shape design of the end wall, the lateral pressure gradient of the end wall is reduced, the development of the channel vortex and its climbing along the blade surface are delayed, and the secondary flow intensity and the interaction loss with the blade surface are weakened.

[0065] like Figure 4 A schematic diagram of the total pressure loss distribution of the conventional design and the moving blade edge plate of the present application is shown. In the figure, the solid line 101 shows the total pressure loss distribution of the moving blade edge plate of the conventional design, and the dotted line 102 shows the total pressure loss distribution of the moving blade edge plate of the present application. It can be seen from the figure that by adopting the non-axial design moving blade edge plate of the present application, the peak value of the channel vortex loss is reduced and the affected range is reduced.

[0066] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0067] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0068] In an embodiment of the present moving blade edge plate, the convex portion 11 has a convex portion height, which is defined as the distance between the flow path surface 10 and the vertex, ie, the peak value, of the convex portion 11 . The convex portion height is not greater than 10% of the blade body height.

[0069] In an embodiment of the present moving blade edge plate, the recess 12 has a recess depth, which is defined as the distance between the flow path surface 10 and the bottom of the recess 12, ie, the valley value. The recess depth is not greater than 10% of the blade height.

[0070] Furthermore, in some embodiments, the height of the convex part and the depth of the concave part are both less than 10% of the blade body height. Such a configuration can meet the strength design requirements of the blade edge plate, avoid excessive concave or convex amplitudes leading to thin edge plate thickness, and avoid crack damage under centrifugal force and thermal load.

[0071] Figure 7 Schematic top views of some embodiments of the moving blade edge plate are shown. Figure 8 A three-dimensional schematic diagram showing another perspective of some embodiments of the moving blade edge plate of the present invention is shown. Fig. 9 for Figure 8 In one embodiment of the moving blade edge plate, a guide portion 3 is further provided on the moving blade edge plate. For further description of the location of the guide portion 3, please refer to Figure 7 , the boundary of the flow passage surface 10 of the moving blade edge plate is defined as follows. The boundary of the flow passage surface 10 is defined in one direction by the top edge 103 near the trailing edge 24 and the bottom edge 104 near the leading edge 23 of the moving blade edge plate, and in another direction by the first side edge 105 near the suction side 21 and the second side edge 106 near the pressure side 22 of the edge plate. The guide portion 3 is arranged on the first side edge 105, and the airflow can be guided by the guide portion 3. The guide portion 3 extends from the top edge 103 toward the bottom edge 104 to the end point 30, and the end point 30 is the intersection of the end wall streamline on the flow passage surface 10 and the first side edge 105. Among them, the end wall streamline is the motion trajectory of the fluid near the wall.

[0072] In a specific embodiment, the guide portion 3 is chamfered.

[0073] Due to the convex part 11 and concave part 12 structure set on the moving blade edge plate, the secondary flow is concentrated in the smaller blade height range in the proximal area. While the total root loss of the moving blade and the downstream blade end area is reduced, the local mixing loss in the proximal area of ​​the moving blade will also increase, weakening the non-axial effect and benefit. Based on this, in order to further improve the non-axial benefit, the rear part of the channel adopts the guide part 3 to form a step-like design of the edge plate, reduce the mixing loss in the end area and the additional loss caused by the assembly error, improve the turbine efficiency by 0.3%, and suppress the direct impact of high-temperature combustion gas on the edge plate. According to the relationship that the loss is proportional to the square of the speed, the guide part 3 with a chamfered structure is set in the high-speed area behind the throat to construct the step-like flow, reduce the flow mixing loss, and reduce the impact of the combustion gas on the end wall. Fig. 10A The figure shows the limit streamline diagram of the end wall of the moving blade edge plate with conventional design. Fig. 10B The diagram of the limiting streamlines of the end wall using the present moving blade edge plate is shown. As shown in the figure, by using the present moving blade edge plate configuration, the lateral flow 91 of the end wall of the moving blade lower edge plate is significantly controlled. Fig.11A The limiting streamlines and wall shear stress cloud diagram of the blade surface of the conventionally designed moving blade edge plate are shown. Fig. 11BThe limiting streamlines and wall shear stress cloud diagram of the blade surface using the present moving blade edge plate are shown. As shown in the figure, the wall shear stress cloud diagram of the moving blade edge plate using the present configuration shows that the mutual interference 92 between the end wall boundary layer and the blade surface boundary layer is significantly weakened, and the limiting streamlines on the suction surface show that the secondary flow influence range 93 is reduced.

[0074] Further, in some embodiments of the present moving blade edge plate, as Fig. 9 As shown, the angle 94 between the chamfered surface and the plane where the flow channel surface is located is 30° to 45°, and the distance 95 between the lowest point of the chamfered surface and the plane where the flow channel surface is located is 0.5 to 0.7 mm.

[0075] Further, in some embodiments of the present impeller edge plate, the end point 30 is obtained by offsetting the intersection of the flow path surface upper end wall streamline and the first side edge toward the bottom edge by a first distance, wherein 0<first distance≤0.5 mm. Preferably, the first distance is 0.5 mm, so that the influence of the three-dimensional feature design and the working condition deviation on the end zone flow can be considered to avoid the reverse step phenomenon.

[0076] On the other hand, according to some embodiments of the present application, a moving blade is further provided, which includes a moving blade edge plate as described in one or more of the above embodiments.

[0077] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0078] It should be understood that the two directions mentioned in the text as "perpendicular", "consistent", "parallel", etc. do not need to meet strict angle requirements in the mathematical sense, but allow a certain tolerance range, for example, the angle is within 10° compared to the angle required in the mathematical sense, and "along" a certain direction means that there is at least a component in that direction, preferably, the angle with that direction is within 10°, and more preferably, the angle is within 5°.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A moving blade edge plate, characterized in that: For a moving blade, the moving blade comprises a moving blade edge plate and a blade body arranged on the flow path surface of the moving blade edge plate, along the incoming flow direction, the blade body has a suction surface side and a pressure surface side, and the blade body also comprises a leading edge and a trailing edge; The moving blade edge plate has a convex portion protruding from the flow path surface and a concave portion recessed from the flow path surface, the convex portion is arranged on the pressure surface side of the leading edge, and the concave portion is arranged on the suction surface side of the leading edge.

2. The moving blade edge plate according to claim 1, characterized in that: The convex portion has a convex portion height, and the convex portion height is the distance from the flow channel surface to the apex of the convex portion; Wherein, the height of the convex portion is not greater than 10% of the height of the blade body.

3. The moving blade edge plate according to claim 1, characterized in that: The concave portion has a concave portion depth, and the concave portion depth is the distance from the bottom of the concave portion to the flow channel surface; Wherein, the depth of the recess is not greater than 10% of the height of the blade body.

4. The moving blade edge plate according to claim 1, characterized in that: The boundary of the flow channel surface is defined in one direction by a top edge of the moving blade edge plate close to the trailing edge and a bottom edge close to the leading edge, and in another direction by a first side edge of the edge plate close to the suction surface side and a second side edge close to the pressure surface side; A guide portion is provided on the first side edge, and the airflow can be guided by the guide portion. The guide portion extends from the top edge toward the bottom edge to a termination point, and the termination point is the intersection of the streamline of the upper end wall of the flow channel surface and the first side edge.

5. The moving blade edge plate according to claim 4, characterized in that: The end point is obtained by shifting the intersection of the flow path surface upper end wall streamline and the first side edge toward the bottom edge by a first distance; Among them, 0<the first distance≤0.5 mm.

6. The moving blade edge plate according to claim 5, characterized in that: The first distance is 0.5 mm.

7. The moving blade edge plate according to claim 4, characterized in that: The guide portion is chamfered.

8. The moving blade edge plate according to claim 7, characterized in that: The angle between the chamfered surface of the chamfer and the plane where the flow channel surface is located is 30° to 45°, and the distance between the lowest point of the chamfered surface and the plane where the flow channel surface is located is 0.5 to 0.7 mm.

9. A moving blade, characterized in that: It comprises the moving blade edge plate according to any one of claims 1 to 8.

10. A method for designing a moving blade edge plate, characterized in that: The steps include: Obtain the center camber line of the blade body located on the flow path surface of the moving blade edge plate; A plurality of control points are arranged along the extending direction of the median camber line, wherein the control points include a first control point, and the first control point is located at the leading edge; Get the offset distance; Acquire a convex point position, wherein the convex point position is obtained by offsetting the first control point toward a side edge of the flow path surface close to a pressure surface side of the blade body by the offset distance; Acquire a concave point position, wherein the concave point position is obtained by offsetting the first control point toward a side edge of the flow channel surface close to a suction surface of the blade body by the offset distance; A convex portion protruding from the flow channel surface is provided at the convex portion point of the flow channel surface, and a concave portion concave from the flow channel surface is provided at the concave portion point of the flow channel surface.

11. The method for designing a moving blade edge plate according to claim 10, characterized in that: The height of the protrusion is configured to be no greater than 10% of the height of the blade body; and The depth of the recess is configured to be no greater than 10% of the height of the blade airfoil.

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