Hollow fan blade damping structure

Abstract

The application relates to a hollow fan blade damping structure, which comprises a skin, a reinforcing rib and a damping zone. The blade is a hollow structure, the outside of the blade is covered by the skin, the inside of the blade is provided with the reinforcing rib along the spanwise direction of the blade, the damping zone is arranged at different heights along the spanwise direction of the blade, the damping zone is arranged along the chordwise direction of the blade, the damping zone comprises a connecting section and a friction section, the friction section is close to the skin and parallel to the inner surface of the skin, and a gap exists between the friction section and the skin when the blade is in a static state; the two sides of the friction section are rigidly connected with the inside of the blade through the connecting section. The damping zone is based on the friction damping and resonance avoidance mechanisms, and the damping size adaptively changes with the increase of the blade vibration amplitude. The damping zone has two damping mechanisms, the two mechanisms gradually play a role with the increase of the vibration stress, can adaptively adjust the damping effect according to the size of the blade vibration stress, and meets the reliability requirement of the hollow fan / air compressor blade.

Description

Technical Field

[0001] This invention relates to the field of aero-engine technology, and in particular to a vibration reduction structure for hollow fan blades. Background Technology

[0002] Fan / compressor blades are core functional components of aero engines. During operation, the blades rotate at high speeds, performing work on the air to generate thrust, which accounts for more than 70% of the total thrust of the engine. However, due to the operating characteristics of the blades, their structure is subjected to alternating loads, such as centrifugal loads, impact loads, and rotor unbalanced force excitation loads. They may also encounter alternating loads that are not designed for them, which can lead to resonance, causing fatigue damage to the metal blades and potentially resulting in abnormal failure.

[0003] Fan / compressor blades are the largest and heaviest rotor blades in an engine. Their high-speed rotation gives them enormous kinetic energy. Fatigue failure of these blades can cause damage to adjacent blades, potentially puncturing the casing, damaging the aircraft structure, and causing secondary losses of varying degrees. Damage to hydraulic lines could lead to serious accidents. Blade vibration is caused by at least the following factors: alternating airflow excitation, rotor imbalance periodic force excitation, and periodic alternating flow field excitation. When these types of alternating loads act on the blade, and the excitation frequency of the alternating load matches the blade's natural frequency, resonance will occur, significantly increasing the degree of blade deformation and generating enormous alternating stress on the blade structure. Therefore, reducing vibration stress in non-design operating conditions of the blade is crucial.

[0004] In engineering practice, there are two main types of damping methods applied to fan / compressor blades: The first is aerodynamic damping, which increases the blade width, i.e., increases the chord length, and uses the relative motion between the blade and the air to provide damping. However, this method requires careful aerodynamic design. If the design is flawed, self-excited vibration due to aerodynamic loading, i.e., flutter, will occur, which is more harmful to the integrity of the blade structure. The second method is to add damping material to the outside of the blade, usually an elastic-plastic material such as rubber. The damping material is usually located near the blade root. Energy is dissipated by the mutual motion between the structure and the damping material or by the friction loss inside the damping material when the blade vibrates. However, due to the fixed blade tenon and free blade tip installation method, the amplitude at the blade root is small, and therefore the damping generated is limited.

[0005] Advanced turbofan engines extensively utilize hollow titanium alloy fan blades, a hollow sandwich structure consisting of skin and reinforcing ribs. Commonly, this structure comprises two thin-walled skin layers connected by reinforcing ribs. This topology reduces blade weight while offering significant design flexibility for the internal structure. However, due to a lack of in-depth understanding of the new structural characteristics, the utilization of its performance remains largely focused on weight reduction. In recent years, hollow blades employing the aforementioned two vibration reduction measures have still experienced fatigue failure, resulting in substantial losses. Therefore, further measures are urgently needed to reduce the vibration stress on hollow fan / compressor blades. Summary of the Invention

[0006] (1) Technical problems to be solved

[0007] This invention provides a vibration reduction structure for hollow fan blades, solving the technical problem that vibration causes fatigue damage to hollow fan / compressor blades, which may lead to abnormal failure.

[0008] (2) Technical solution

[0009] An embodiment of the present invention provides a hollow fan blade vibration reduction structure, including a skin, reinforcing ribs, and vibration reduction zones. The blade is a hollow structure, and the outside of the blade is covered by the skin. The reinforcing ribs are arranged inside the blade along the spanwise direction. Vibration reduction zones are arranged at different heights along the spanwise direction of the blade. The vibration reduction zones are arranged along the chord direction of the blade. The vibration reduction zone includes a connecting section and a friction section. The friction section is close to the skin and parallel to the inner surface of the skin. When the blade is stationary, there is a gap between the friction section and the skin. The two sides of the friction section are rigidly connected to the inside of the blade through the connecting section.

[0010] Furthermore, the vibration damping zone comprises one or more groups, and is respectively disposed at one or more locations in the spanwise direction of the blade.

[0011] Furthermore, the vibration damping zone is located on the upper part of the blade.

[0012] Furthermore, the thickness of the damping zone is 0.4–2.0 mm.

[0013] Furthermore, the damping zone is distributed along the chord direction of the blade, and the geometric center line of the spanwise boundary of the damping zone has an arc in the spanwise direction of the blade.

[0014] Furthermore, the gap is less than or equal to 0.1 mm.

[0015] Furthermore, the vibration damping zone is made of titanium alloy.

[0016] Furthermore, the formula for calculating the size of the vibration damping zone is as follows: Where σ cr F is the critical stress in the vibration reduction zone. cr Where A is the spanwise cross-sectional area of ​​the damping zone, H is the height of the damping zone, t is the thickness of the damping zone, and E is the elastic modulus of the damping zone.

[0017] (3) Beneficial effects

[0018] In summary, this invention leverages the high design flexibility of the internal structure of blades to propose a vibration reduction structure based on frictional damping and resonance avoidance mechanisms, with damping magnitude adaptively varying with increasing blade vibration amplitude. This structure possesses two vibration reduction mechanisms, each functioning progressively as vibration stress increases, and its damping effect can be adaptively adjusted according to the magnitude of blade vibration stress. When blade vibration stress is low, energy is dissipated through frictional energy dissipation, reducing vibration. When the amplitude is large and the vibration duration is long, frictional heat generation raises the structure's temperature, altering the blade's inherent characteristics and changing its natural frequency. Once the blade's natural frequency deviates significantly from the excitation frequency, resonance is eliminated. This, combined with the frictional mechanism, prevents vibration, meeting the reliability requirements of hollow fan / compressor blades. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the overall structure of a hollow fan blade vibration reduction structure;

[0021] Figure 2 yes Figure 1 Schematic diagram of AA section;

[0022] Figure 3 yes Figure 1 Schematic diagram of the BB cross section;

[0023] In the diagram: 1. Skin; 2. Reinforcing rib; 3. Vibration damping zone; 4. Connecting section; 5. Friction section; 6. Gap. Detailed Implementation

[0024] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention. That is, the present invention is not limited to the described embodiments, and any modifications, substitutions and improvements to the parts, components and connection methods are covered without departing from the spirit of the present invention.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] Please refer to Figures 1-3 As shown, an embodiment of the present invention proposes a hollow fan blade vibration reduction structure, including a skin 1, reinforcing ribs 2, and vibration reduction zones 3. The blade is a hollow structure, and the outside of the blade is covered by the skin 1. The reinforcing ribs 2 are arranged inside the blade along the spanwise direction of the blade. Vibration reduction zones 3 are arranged at different heights along the spanwise direction of the blade. The vibration reduction zones 3 are arranged along the chord direction of the blade. The vibration reduction zone 3 includes a connecting section 4 and a friction section 5. The friction section 5 is close to the skin 1 and parallel to the inner surface of the skin 1. When the blade is stationary, there is a gap 6 between the friction section 5 and the skin 1. The two sides of the friction section 5 are rigidly connected to the inside of the blade through the connecting section 4.

[0027] Taking advantage of the high designability of the internal structure of the blade, a damping zone 3 is proposed, which is based on friction damping and resonance avoidance as the damping magnitude changes adaptively with the increase of blade vibration amplitude. The damping zone 3 has two damping mechanisms, which play a role step by step as the vibration stress increases, and can adaptively adjust the damping effect according to the magnitude of blade vibration stress.

[0028] When the blade vibrates during operation, and the amplitude exceeds a certain threshold but the vibration time is short, the first type of vibration reduction mechanism will be triggered: the blade bends and deforms, the distance between the two ends of the vibration reduction zone 3 is shortened, and the vibration reduction zone 3 is subjected to compressive force. Since the thickness of the vibration reduction zone 3 is less than the thickness of the skin 1, the deformation of the vibration reduction zone 3 is greater than that of the skin 1, and the vibration reduction zone 3 is "C" shaped, which causes the friction section 5 to come into contact with the skin 1. Subsequently, the two undergo fretting friction, thereby consuming the blade vibration energy and reducing the blade amplitude.

[0029] When the blade vibration amplitude continues to increase and the vibration time is long, the second type of vibration reduction mechanism will be activated: the mutual friction between friction section 5 and skin 1 will be further intensified as the blade amplitude increases. The friction generates heat, causing the temperature of the local area of ​​skin 1, friction section 5 and its surrounding area to rise. The temperature rise leads to a decrease in the elastic modulus of the material, which in turn changes the inherent characteristics of the blade. The difference between the external excitation frequency and the natural frequency of the structure increases, that is, the excitation frequency deviates from the natural frequency. The synergistic friction mechanism prevents vibration from occurring and meets the reliability requirements of hollow fan / compressor blades.

[0030] In some embodiments, the vibration damping zone 3 includes one or more groups, and is respectively disposed at one or more locations in the spanwise direction of the blade, which can be the upper, middle and lower parts of the blade. Further, the vibration damping zone 3 is disposed on the upper part of the blade, since the vibration stress in the upper part of the blade is greater than that in other areas, and its vibration damping effect is better when disposed on the upper part of the blade, but it is not limited to the vibration damping zone 3 being disposed on the upper part of the blade.

[0031] In some embodiments, the thickness of the damping zone 3 is 0.4 to 2.0 mm, and its thickness should be less than that of the skin 1 to ensure that the deformation of the damping zone 3 is greater than that of the skin 1. When the blade vibrates, the friction section 5 contacts the skin 1, and then the two undergo fretting friction, thereby consuming the blade vibration energy and reducing the blade amplitude.

[0032] In some embodiments, the damping zone 3 is distributed along the chord direction of the blade, and the geometric center line of the spanwise boundary of the damping zone 3 has an arc in the spanwise direction of the blade, so that the reinforcing ribs 2 are evenly distributed in the spanwise direction of the blade, which can reduce the weakening of the structural strength of the blade in the spanwise direction by the damping zone 3.

[0033] In some embodiments, the gap 6 is less than or equal to 0.1 mm to ensure that the friction section 5 contacts the skin 1 when the blade vibrates.

[0034] In some embodiments, the vibration damping zone 3 is made of titanium alloy material, which has good elasticity and vibration absorption effect.

[0035] In some embodiments, the formula for calculating the size of the damping zone 3 is as follows: Where σ cr For the critical stress of vibration reduction zone 3, F cr Let A be the spanwise cross-sectional area of ​​damping zone 3, H be the height of damping zone 3, t be the thickness of damping zone 3, and E be the elastic modulus of damping zone 3. Based on blade design criteria, the allowable critical stress of the blade is obtained. The blade amplitude corresponding to this stress is then obtained using the finite element method. The load borne by damping zone 3 is then determined based on the blade amplitude. The initial thickness and height of damping zone 3 are calculated using formulas. The structural design is completed through iterative optimization using the finite element method.

[0036] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and techniques are omitted here.

[0037] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art without departing from the scope of the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A hollow fan blade vibration damping structure characterized by: The blade is a hollow structure, the outside of the blade is covered by the skin, the inside of the blade is provided with the reinforcing rib along the spanwise direction of the blade, and the damping zone is provided at different heights in the spanwise direction of the blade, the damping zone is arranged along the chordwise direction of the blade, the damping zone comprises a connecting section and a friction section, the friction section is close to the skin and parallel to the inner surface of the skin, and a gap exists between the friction section and the skin when the blade is in a static state; the two sides of the friction section are rigidly connected with the inside of the blade through the connecting section.

2. The hollow fan blade vibration reduction structure of claim 1, wherein: The damping zone comprises one or more groups and is arranged at one or more positions in the spanwise direction of the blade.

3. The hollow fan blade vibration reduction structure of claim 2, wherein: The damping zone is arranged at the upper part of the blade.

4. The hollow fan blade vibration reduction structure of claim 1, wherein: The thickness of the damping zone is 0.4-2.0 mm.

5. The hollow fan blade vibration reduction structure of claim 1, wherein: The damping zone is distributed along the chordwise direction of the blade, and the geometric center line of the spanwise boundary of the damping zone has an arc in the spanwise direction of the blade.

6. The hollow fan blade vibration reduction structure of claim 1, wherein: The gap is less than or equal to 0.1 mm.

7. The hollow fan blade vibration reduction structure of claim 1, wherein: The damping zone is made of titanium alloy material.

8. The hollow fan blade vibration reduction structure of claim 1, wherein: The size calculation formula of the damping zone is: wherein ​ cr is a critical stress of the damping region, F cr is a critical load, A is a spanwise cross-sectional area of the damping region, H is a height of the damping region, t is a thickness of the damping region, E is an elastic modulus of the damping region.

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