Fan blade

Abstract

The application provides a fan blade. The fan blade comprises a blade body, a tenon and a root extension; the root extension connects the blade body and the tenon; the blade body, the tenon and the root extension are limited from three aspects of axial offset limitation, thickness change rate limitation and circumferential offset limitation. The fan blade can avoid local stress concentration and improve processability.

Description

Technical Field

[0001] This invention relates to engine fan blade structures, and more particularly to a fan blade. Background Technology

[0002] To achieve economic efficiency and reduce fuel consumption, the bypass ratio of fan blades is increased, the boost ratio is decreased, and the hub ratio is reduced. On the other hand, the decrease in boost ratio and the requirement for low noise also lead to a decrease in the tangential velocity at the fan blade tip. Consequently, the decrease in hub ratio and the decrease in blade tip tangential velocity both result in a decrease in the tangential velocity at the fan blade root.

[0003] In the blade tip region, i.e., the area near the hub flow channel, the blade root tangential velocity decreases, and to ensure the boost ratio at the fan root, the blade profile at the root has a large twist angle. However, for fan tenons, especially for composite fan blades, straight tenons are preferred to improve forming and processing capabilities. Compared to rounded tenons, straight tenons have a flatter contact surface, resulting in higher surface smoothness during composite material molding; and the blades are less prone to excessive local stress caused by insufficient flatness.

[0004] However, the transition from a large bend at the blade root to a straight tenon within a very small radial space can easily lead to localized twisting, especially in the leading edge region. In terms of manufacturing, composite blades are molded using RTM (Resin Transfer Molding). Due to the localized twisting of the blade profile, resin filling can easily be incomplete, creating internal porosity defects, which is detrimental to prototyping and final molding. In terms of strength, blade twisting can cause localized stress concentration, forming high-stress zones that result in insufficient local static or fatigue strength, reducing blade life. Summary of the Invention

[0005] The purpose of this invention is to provide a fan blade that can avoid local stress concentration and improve manufacturability.

[0006] The present invention provides a fan blade, comprising a blade body, a tenon, and an extension segment; wherein the extension segment connects the blade body and the tenon; and the ratio of the absolute value of the thickness difference between any two equal-height front faces of the extension segment to their relative height is less than 1.0.

[0007] In one embodiment, the leaf body is a composite material body; the root extension segment connects the composite material body and the tenon.

[0008] In one embodiment, the blade includes a composite body and a metal reinforcing edge; the metal reinforcing edge is disposed at the front end of the composite body; the root extension connects the composite body and the tenon, and is connected to the metal reinforcing edge.

[0009] In one embodiment, the angle between the line connecting the front end point of the composite body at the blade flow channel section and the intersection of the midline of the front face of the tenon and the top section of the tenon and the blade radial line is less than 20°.

[0010] In one embodiment, the ratio of the distance between the leading edge of the metal reinforcing edge and the leading end point of the composite body at the blade flow channel section to the chord length at the blade flow channel section is less than 0.05.

[0011] In one embodiment, the ratio of the distance between the front end point of the composite body at the blade flow channel section and the intersection of the midline of the front face of the tenon and the top section of the tenon to the length of the tenon is less than 0.04.

[0012] In one embodiment, the tenon is a straight tenon, and the cross-section of the straight tenon at its height is rectangular.

[0013] The fan blade of the present invention restricts the absolute value of the thickness difference between the front end faces of any two equal blade height cross sections of the root extension section and the ratio of their relative heights. This allows the fan blade to smoothly transition from the blade shape at the flow channel end area to the tenon, avoiding twisting of the blade root extension section at the leading edge. This solves the problems of local stress concentration and difficult manufacturing process, meets strength design requirements, and improves blade life. Attached Figure Description

[0014] The above and other features, properties and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, wherein:

[0015] Figure 1 This is a schematic diagram of an aircraft engine fan;

[0016] Figure 2 yes Figure 1 A partial sectional view of the fan shown;

[0017] Figure 3 This is a schematic diagram of an embodiment of a fan blade according to the present invention;

[0018] Figure 4 yes Figure 3 A top view of the root element blade profile of the fan blade shown;

[0019] Figure 5 yes Figure 3 A magnified view of a portion of the fan blades shown;

[0020] Figure 6 yes Figure 3 A schematic diagram showing the thickness variation rate of the fan blades;

[0021] Figure 7 yes Figure 3 The diagram shows the circumferential offset of the fan blades. Detailed Implementation

[0022] To achieve economic efficiency and reduce fuel consumption, the bypass ratio of fan blades is increased, the boost ratio is decreased, and the hub ratio is reduced. On the other hand, the decrease in boost ratio and the requirement for low noise also lead to a decrease in the tangential velocity at the fan blade tip. Consequently, the decrease in hub ratio and the decrease in blade tip tangential velocity both result in a decrease in the tangential velocity at the fan blade root.

[0023] In the blade tip region, i.e., the area near the hub flow channel, the blade root tangential velocity decreases, and to ensure the boost ratio at the fan root, the blade profile at the root has a large twist angle. However, for fan tenons, especially for composite fan blades, straight tenons are preferred to improve forming and processing capabilities. Compared to rounded tenons, straight tenons have a flatter contact surface, resulting in higher surface smoothness during composite material molding; and the blades are less prone to excessive local stress caused by insufficient flatness.

[0024] Figure 1 and Figure 2 The structure of an aircraft engine fan and fan blades are shown respectively. Figure 1 This defines the typical characteristics of the end region of the blade. The fan blades rotate circumferentially around the engine axis 8, driving the airflow 1 into the flow channel formed by the casing 2 and the hub 4. Figure 2 The hub 4 in the design can be understood as the flow channel. The blade 3 is attached to the blade disk 7 via a dovetail 6. When the dovetail 6 is a straight dovetail, the cross-sectional shape of the dovetail area is rectangular. The transition area between the dovetail 6 and the blade profile within the flow channel is the blade shank 5, whose cross-sectional shape is non-rectangular, achieving the transition from the rectangular cross-section at the dovetail 6 to the blade profile within the flow channel. Generally, because the fan hub 4 has an upward slope along the flow direction, the radial length of the trailing edge of the shank 5 is longer than the leading edge. Compared to the trailing edge, the radial space for the transition from the blade profile within the flow channel to the dovetail 6 at the leading edge is more compact.

[0025] In summary, the transition of the leading edge of the root extension segment 5 is more difficult than that of the trailing edge, and it is prone to local twisting. In terms of manufacturing, composite blades are molded using RTM (Resin Transfer Molding). Local twisting of the blade shape can easily lead to incomplete resin filling, creating internal porosity defects, which is detrimental to trial production and final molding. In terms of strength, blade twisting easily causes localized stress concentration, forming high-stress zones, resulting in insufficient local static or fatigue strength to meet requirements, thus reducing blade life.

[0026] Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided to explain the invention and not to limit it. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the invention without departing from the scope or spirit thereof. For example, a feature shown or described as part of one embodiment may be used with another embodiment to produce yet another embodiment. Therefore, the invention is intended to cover these modifications and variations that fall within the scope of the appended claims and their equivalents.

[0027] As used herein, the term "aero-engine" refers to a highly complex and sophisticated thermodynamic machine used to power aircraft, including various types such as turbojet / turbofan engines and turboshaft / turboprop engines. The term "composite fan blade" refers to a fan blade designed and manufactured using composite materials according to aerodynamic airfoil profiles. The term "cold blade profile" refers to the external shape of the blade.

[0028] refer to Figure 2 The fan blade of the present invention includes a blade body 3, a tenon 6, and an extension segment 5. The extension segment 5 connects the blade body 3 and the tenon 6 to achieve a transitional connection between the extension segment 5 and the blade body 3. The tenon 6 is a straight tenon 6, and the cross-section of the straight tenon 6 at its height is rectangular.

[0029] It should be noted that, in this invention, the tenon 6 refers to the region with a rectangular cross-section at the blade root, and the root extension 5 refers to the region above the tenon 6 up to the blade flow channel line cross-section (also referred to as the "root element level"). The main difference between the tenon 6 and the root extension 5 is that the tenon 6 has a rectangular cross-section, while the root extension 5 does not have a rectangular cross-section but rather a shape formed by the transition from the rectangle of the tenon 6 to the blade shape at the flow channel line. The root element level is the cross-section formed by cutting the blade along the flow channel line.

[0030] In one embodiment, the blade body 3 of the fan blade is a composite material body, that is, the entire blade body 3 of the fan blade is a composite material, without any edging. The leading edge point of the blade body 3 is the leading edge point of the composite material body, and the trailing edge point of the blade body 3 is the trailing edge point of the composite material body.

[0031] Figure 3 The structure of a fan blade according to the present invention is shown. In another embodiment, Figure 3 The fan blade shown has a blade body 3 comprising a composite material body and a metal reinforcing edge 200 (or metal edging). The metal reinforcing edge 200 is disposed at the front end of the composite material body. In this embodiment, the leading edge point of the blade body 3 is the leading edge point of the metal reinforcing edge 200, and the trailing edge point of the blade body 3 is the trailing edge point of the composite material body.

[0032] To address the localized twisting problem caused by the transition between the root extension segment 5 and the tenon 6, the fan blades of this invention are constrained in three aspects: axial offset constraint, thickness variation rate constraint, and circumferential offset constraint, in order to design the blade shape.

[0033] The following embodiments that impose limitations on the above three aspects are as follows: Figure 3 The structure of the fan blades shown is illustrated using an example, and does not imply that the fan blades in the following embodiments must be equipped with [specific features]. Figure 3 The metal reinforcing edge 200 shown in the figure can also be a fan blade without the metal reinforcing edge 200.

[0034] Figure 4 A top view of the root element blade profile of a fan blade is shown. Figure 4 In the diagram, the blue and yellow areas represent the blade profile section. The blade profile section is the cross-section formed by cutting the blade along the flow channel line; it can also be called the root element level of the blade. Figure 4 The medium gray rectangular surface represents the cross-section of tenon 6.

[0035] refer to Figure 4 In one embodiment, regarding the axial offset limitation, the ratio of the distance between the leading edge point of the composite body and the leading end point of the composite body at the blade flow channel section to the chord length at the blade flow channel section is less than 0.05. This offset must meet the thickness requirement of the composite body, that is, the fan blade of the present invention satisfies the relationship (1):

[0036]

[0037] In relation (1), L1 is the distance between the leading edge of the composite body and the leading end point of the composite body at the blade flow channel section, and L2 is the chord length at the blade flow channel section.

[0038] exist Figure 4 In the diagram, L1 represents the distance between point 201 and point 202. Point 201 is the leading edge of the composite body, which can also be understood as the front end of the elementary level, hence the name leading edge point. Point 202 is the leading end point of the composite body at the blade flow channel section, which can also be understood as the starting position of the root elementary level composite body, that is, the centerline of the foremost part of the composite body in the root elementary level.

[0039] It should be noted that, in cases such as Figure 3 and Figure 4 In the fan blade shown with a metal reinforcing edge 200, point 201 is the leading edge of the metal reinforcing edge 200; in the fan blade without a metal reinforcing edge 200, that is, only a composite material body, point 201 and point 202 coincide, that is, L1 = 0.

[0040] exist Figure 4 In this diagram, L2 represents the distance between point 201 and point 204. Point 204 can be understood as the end of the primitive level, called the tail edge point. The line connecting points 201 and 204 can also be understood as the flow channel line.

[0041] Figure 5 A partial enlarged view of the fan blades is shown, namely... Figure 3 The area circled in the middle. Figure 5 In the middle, points 201, 202, and 203 and Figure 4 The positions of all points are the same; the horizontal gray parts represent wear-resistant strips to reduce fretting wear when mating with other parts.

[0042] refer to Figure 5 In one embodiment, regarding axial offset limitation, the ratio of the distance between the front end point of the composite body at the blade flow channel section and the intersection of the midline of the front face of the tenon 6 and the top section of the tenon 6 to the length of the tenon 6 is less than 0.04, that is, the fan blade of the present invention satisfies relation (2):

[0043]

[0044] In equation (2), L3 is the distance between the front end of the composite body at the blade flow channel section and the intersection of the center line of the front end face of the tenon 6 and the top section of the tenon 6, and L4 is the length of the tenon 6. The ratio of L3 to L4 can preferably be 0.03.

[0045] exist Figure 5 In the diagram, L3 represents the distance between point 202 and point 203. Figure 5 Point 202 and shown Figure 4 The position of point 202 is the same as above, so it will not be described again. Point 203 is the intersection of the center line of the front face of tenon 6 and the top section of tenon 6. Among them, the frontmost plane of tenon 6 is called the front face of tenon 6, and the rearmost plane is called the rear face of tenon 6. The top section of tenon 6 is the section where tenon 6 and the extension segment 5 are connected.

[0046] exist Figure 5 In the diagram, L4 represents the distance between points 203 and 205. Point 203 is as shown previously. Point 205 is the intersection of the centerline of the rear end face of tenon 6 and the top section of tenon 6.

[0047] Axial offset restriction mainly affects the tilt of the front end of the blade root extension segment 5. If the axial offset restriction is not reasonable, the axial misalignment between the front end of the root element level and the front end of the tenon 6 will be too great, and the root extension segment 5 will need to be shortened very quickly, which is not conducive to the strength and manufacturability of the blade.

[0048] Figure 6 and Figure 7The front view of the fan blade of the present invention is shown, which is a view of the blade root from front to back.

[0049] refer to Figure 6 As indicated in the annotation, in one embodiment, regarding the limitation of the thickness variation rate, the ratio of the absolute value of the thickness difference between the front end faces of any two equal-height cross sections of the root extension segment 5 and the relative height of the two is within a preset variation rate range.

[0050] In related technologies, only the difference between the thickness of the neck of the tenon 6 and the thickness of the upper end face of the root section 5 is limited to the ratio of their relative heights. The thickness of the neck of the tenon 6 and the upper end face of the root section 5 are two fixed cross sections with equal leaf heights.

[0051] The fan blade of the present invention restricts the ratio of the thickness difference to the height difference between any two equal blade height cross sections of the root extension section 5. Compared with related technologies, the restriction requirements on the blade are higher, which can make the fan blade smoothly transition from the blade shape in the flow channel end area to the tenon 6 without twisting. It avoids the twisting of the blade root extension section 5 at the leading edge, and can better avoid the stress concentration problem in the middle part of the tenon 6. In this way, it solves the problems of local stress concentration and difficult process forming, meets the strength design requirements, and improves the blade life.

[0052] refer to Figure 6 Furthermore, regarding the limitation of the rate of change of thickness, the fan blades of the present invention satisfy the relationship (3):

[0053]

[0054] In equation (3), L7 and L6 represent the thickness of the front face of any two equal-leaf-height cross sections within the root extension segment 5, |L7-L6| represents the absolute value of the thickness difference of the front face of any two equal-leaf-height cross sections within the root extension segment 5, and L8 represents the height difference between the front faces of the two equal-leaf-height cross sections. Then ω can represent the thickness change rate of the front face of any two equal-leaf-height cross sections within the root extension segment 5 per unit length.

[0055] It should be noted that the positional relationship between the two equal-height cross sections represented by L7 and L6 is not limited to... Figure 6 As shown, the equal-blade height cross section represented by L6 can be below the equal-blade height cross section represented by L7.

[0056] A larger thickness variation rate ω will result in poorer manufacturability of the fan blades. The thickness variation rate ω is preferably 0.5-0.7.

[0057] The thickness change rate limit is to control the expansion speed of the root extension section 5 from top to bottom. If the thickness change rate is not reasonable, the thickness of the root extension section 5 will change too rapidly from top to bottom, and the ratio and positional relationship of resin and carbon fiber will change drastically, resulting in a significant decrease in processability.

[0058] refer to Figure 7 In one embodiment, regarding the circumferential offset, the angle between the line connecting the front end point of the composite body at the blade flow channel section and the intersection of the midline of the front face of the tenon 6 and the top section of the tenon 6 and the radial line of the blade is less than 20°, which needs to meet the requirements of the tenon strength design, that is, the fan blade of the present invention satisfies the relation (4):

[0059]

[0060] In relation (4), It is the angle between the line connecting the front end point of the composite body at the blade flow channel section and the intersection of the center line of the front face of the tenon 6 and the top section of the tenon 6, and the radial line of the blade. The preferred range is 10°-15°, and more preferably 12°. Too small a size may affect the center of gravity of the fan blades.

[0061] exist Figure 7 middle, Let be the angle between the line connecting points 202 and 203 and the radial line. Points 202 and 203 are... Figure 4 and Figure 5 Points 202 and 203 are in the same position, so I will not repeat the details.

[0062] exist Figure 7 In the diagram, the radial line is represented by the line connecting points 203 and 210. Point 210 represents the midpoint of the bottom surface of tenon 6.

[0063] The circumferential offset restriction is mainly to avoid excessive tilting of the root extension segment in the 5th circumference upward.

[0064] In conjunction with the above-described fan blade embodiments, the fan blade of the present invention restricts and designs the three-dimensional shape of the fan blade in three aspects: axial offset restriction, thickness change rate restriction, and circumferential offset restriction. The main purpose is to avoid geometric distortion of the root extension segment 5 of the fan blade, thereby avoiding the occurrence of local stress increase, internal porosity defects, and reduced blade life.

[0065] The range of values ​​for the above relationships (1) to (4) is obtained based on the test results of multiple engines and design experience. If the value is too small, the design freedom of the fan blade will be too low, affecting the design function of the blade (aerodynamic performance and structural requirements for cooperation with other components and space occupation) or significantly increasing the design iteration cycle; if the value is too large, it will cause a reduction in the blade's manufacturability and strength performance.

[0066] Fan blades that are constrained in the above three aspects have improvements in parameters such as internal quality (porosity deviation), static stress level, and maximum strain at the root of the blade when impacted by a foreign object.

[0067] In the actual research and development process, compared with the original fan blade (blade thickness change rate of about 1.8, circumferential offset angle of about 28°), the internal quality deviation rate of the improved fan blade, which was restricted in the above three aspects, was reduced from 100% to 23%, the maximum stress level at the root was reduced by about 15%, and the maximum strain at the root due to foreign object impact was reduced by about 20%.

[0068] In summary, by limiting the three aspects of axial offset, circumferential offset, and thickness variation, the three-dimensional shape of the fan blade of the present invention is designed to achieve a smooth transition from the leading edge of the composite fan blade to the tenon 6, avoiding the twisted transition of the leading edge region.

[0069] The three-dimensional shape of the fan blade of the present invention involves the shape features of the near-root end area within the blade flow channel, the blade root extension section 5, and the blade straight tenon 6. This allows for a smooth and adaptive transition of the blade from the root end area within the flow channel to the straight tenon 6, solving the transition difficulties caused by localized twisting, improving manufacturability, and increasing the strength and lifespan of the blade.

[0070] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A fan blade, characterized in that, This includes the leaf blade, tenon, and root extension; among which, The root extension segment connects the leaf body and the tenon; The ratio of the absolute value of the thickness difference between any two leaf-height front faces of the root extension segment to their relative height is less than 1.

0.

2. The fan blade as described in claim 1, characterized in that, The blade is made of composite material. The extension segment connects the composite material body and the tenon.

3. The fan blade as described in claim 1, characterized in that, The blade includes a composite material body and metal reinforcing edges; The metal reinforcing edge is disposed at the front end of the composite material body; The extension segment connects the composite body and the tenon, and is also connected to the metal reinforcing edge.

4. The fan blade as described in claim 2 or 3, characterized in that, The angle between the line connecting the front end point of the composite body at the blade flow channel section and the intersection of the center line of the front face of the tenon and the top section of the tenon and the radial line of the blade is less than 20°.

5. The fan blade as described in claim 3, characterized in that, The ratio of the distance between the leading edge of the metal reinforcing edge and the leading end point of the composite body at the blade flow channel section to the chord length at the blade flow channel section is less than 0.

05.

6. The fan blade as described in claim 2 or 3, characterized in that, The ratio of the distance between the front end point of the composite body at the blade flow channel section and the intersection of the midline of the front face of the tenon and the top section of the tenon to the length of the tenon is less than 0.

04.

7. The fan blade as described in claim 3 or 4, characterized in that, The tenon is a straight tenon, and the cross-section of the straight tenon at the same height is rectangular.

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