A combined structure for restraining rotor amplitude in a sudden unbalance state

Abstract

The application discloses a combined structure for inhibiting rotor amplitude under sudden unbalance state, which comprises a squirrel cage, the squirrel cage is in a cylindrical shape, and comprises a front fixed end, a rear fixed end and a plurality of combined ribs in a fence shape connecting the front fixed end and the rear fixed end; the combined ribs comprise first ribs and second ribs, the first ribs and the second ribs are alternately and uniformly distributed; the first rib comprises a wide rib part and a narrow rib part, the cross-sectional area of the narrow rib part is smaller than that of the wide rib part, and the cross-sectional area of the wide rib part of the first rib is the same as that of the second rib; the combined structure further comprises a limiting ring sleeved on a rotating shaft of an engine rotor, and a gap exists between the limiting ring and the rotating shaft; when sudden unbalance load is caused by the rupture of a rotor blade of an airplane engine, the maximum dynamic load and the radial amplitude of the rotor are reduced under the joint action of the combined rib squirrel cage elastic support and the limiting ring.

Description

Technical Field

[0001] This invention relates to elastic supports and shaft limiting in aero engines, specifically to a combined structure for suppressing rotor amplitude under sudden unbalanced conditions. Background Technology

[0002] In recent years, with the rapid development of aviation technology, the number of commercial and military aircraft has been increasing, and the requirements for aircraft performance and safety have also been rising. When an engine blade breaks, the loss of mass leads to a sharp increase in the imbalance of the engine rotor. When the engine is near its critical speed, the radial amplitude of the blade increases sharply, and the collision between the blade and the casing triggers a series of chain reactions, which have a very serious impact on the engine and may lead to a series of adverse consequences, or even a flight accident. Summary of the Invention

[0003] Purpose of the invention: To address the above-mentioned shortcomings, the present invention provides a combined structure for reducing the maximum dynamic load and the rotor radial amplitude and suppressing the rotor amplitude under sudden unbalanced conditions.

[0004] Technical Solution: To solve the above problems, this invention employs a combined structure to suppress rotor amplitude under sudden unbalanced conditions, including a squirrel cage, which is cylindrical. The squirrel cage includes a front fixed end, a rear fixed end, and a series of combined ribs in a grid-like structure connecting the front and rear fixed ends. Each combined rib includes a first rib and a second rib, which are evenly distributed alternately. The first rib includes a wide rib portion and a narrow rib portion, with the cross-sectional area of ​​the narrow rib portion being smaller than that of the wide rib portion. The cross-sectional area of ​​the wide rib portion of the first rib is the same as that of the second rib. A limiting ring is fitted onto the rotor shaft of the engine, with a gap between the limiting ring and the shaft.

[0005] Furthermore, both ends of the narrow rib of the first rib are connected to the wide rib, and the first rib is connected to the front fixed end and the rear fixed end through the wide rib, and the central axes of the wide rib and the narrow rib coincide.

[0006] Furthermore, the outer wall of the front fixed end has a fixed mounting surface, and the narrow rib portion of the first rib is close to the front fixed end.

[0007] Furthermore, the cross-section of the wide rib portion of the first rib has the same shape and size as the cross-section of the second rib, the height of the cross-section of the narrow rib portion of the first rib is the same as the height of the cross-section of the wide rib portion of the first rib, and the width of the cross-section of the narrow rib portion of the first rib is smaller than the width of the cross-section of the wide rib portion of the first rib.

[0008] Furthermore, the formula for calculating the total stiffness K0 of the mouse cage is as follows:

[0009]

[0010] Where n1 is the number of first reinforcing bars, E is the elastic modulus of the composite reinforcing bar material, b1 is the cross-sectional width of the narrow section of the first reinforcing bar, h is the cross-sectional height of the composite reinforcing bar, L is the length of the composite reinforcing bar, n2 is the number of second reinforcing bars, and b2 is the cross-sectional width of the second reinforcing bar.

[0011] Furthermore, when the narrow section of the first rib breaks, the formula for calculating the total stiffness K1 of the cage is:

[0012]

[0013] Furthermore, it also includes a bearing and a limiting ring fitted on the engine rotor, with the rear fixed end of the squirrel cage fixedly fitted outside the bearing.

[0014] Furthermore, it includes two bearings fitted onto the engine rotor, each bearing having a squirrel cage fitted around it, and the limiting ring being positioned between the two squirrel cages.

[0015] Furthermore, the limiting ring is a cylindrical ring with an inner diameter of d+2Δr, where d is the diameter of the engine rotor shaft and Δr is the gap between the limiting ring and the engine rotor shaft.

[0016] Furthermore, the value of Δr is: A1≤Δr≤A2, where A1 is the amplitude of the shaft segment inside the limiting ring under the critical speed state when the engine blade mass is not lost, and A2 is the amplitude of the shaft segment of the limiting ring under the maximum allowable amplitude working state of the engine blade.

[0017] Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages: When an aircraft engine rotor blade suffers damage from foreign objects and fractures, resulting in mass loss, the maximum dynamic load and blade radial amplitude are reduced under the combined action of the combined ribbed squirrel cage elastic support and the limiting ring. When the engine rotor experiences a sudden imbalance due to factors such as blade loss while passing the first critical speed, the support ribs of the squirrel cage elastic support experience increased stress due to the sudden imbalance. Ribs with smaller cross-sectional areas in the squirrel cage elastic support fracture due to reaching their strength limit, while ribs with larger cross-sectional areas remain within the elastic range. This reduces the overall stiffness of the squirrel cage and lowers the rotor's critical speed. Ultimately, when the engine stops and the speed decreases to the critical speed, the dynamic load decreases. When the amplitude exceeds the reserved gap, the shaft contacts the limiting ring, limiting the maximum rotor amplitude and reducing the vibration. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the longitudinal and cross-sectional sections of a rat cage in the prior art.

[0019] Figure 2 This is a schematic diagram of the combined rib cage for rats in this invention.

[0020] Figure 3 This is a schematic cross-sectional view of the combined rib cage of the present invention.

[0021] Figure 4 This is a schematic diagram of the structure in this invention where the elastic support is installed on the engine rotor.

[0022] Figure 5 This is a schematic diagram of the structure in this invention where the limiting ring is sleeved on the rotating shaft.

[0023] Figure 6 This is a schematic diagram showing the relationship between the amplitude of the limited shaft segment and the maximum allowable amplitude of the blade in this invention.

[0024] Figure 7 The curves showing the rotational speed and amplitude distribution of squirrel cages with different stiffnesses in this invention are shown.

[0025] Figure 8 This is a schematic diagram of the shaft state under the working condition of the engine rotor mass balance in this invention.

[0026] Figure 9 This is a schematic diagram comparing the effects of an infinite-amplitude loop when the rotor enters an unbalanced state due to mass loss of the blades in this invention. Detailed Implementation

[0027] like Figure 1 As shown, the main factors affecting the stiffness of the squirrel cage spring support include the number of ribs n, the elastic modulus E of the material, the rib length L, the rib cross-sectional width b, and the rib cross-sectional height h. The theoretical calculation of the squirrel cage spring support stiffness K is expressed as follows:

[0028]

[0029] like Figure 2 and Figure 3As shown in the figure, this embodiment presents a combined structure for suppressing rotor amplitude under sudden unbalanced conditions. The squirrel cage 3 employs combined ribs of different widths. The squirrel cage 3 is cylindrical, including a front fixed end 31, a rear fixed end 33, and a series of grid-like combined ribs connecting the front fixed end 31 and the rear fixed end 33. The combined ribs include first ribs 321 and second ribs 322, which are evenly distributed alternately. The first rib 321 includes a wide rib portion and a narrow rib portion. The cross-sectional area of ​​the narrow rib portion is smaller than that of the wide rib portion, and the cross-sectional area of ​​the wide rib portion of the first rib 321 is the same as that of the second rib 322. Both ends of the narrow rib portion of the first rib 321 are connected to the wide rib portion. The first rib 321 is connected to the front fixed end 31 and the rear fixed end 33 through the wide rib portion, and the central axes of the wide rib portion and the narrow rib portion coincide. The outer wall of the front fixed end 31 has a fixed mounting surface, and the narrow rib portion of the first rib 321 is close to the front fixed end. The cross-section of the wide section of the first reinforcing bar has the same shape and size as the cross-section of the second reinforcing bar 322. The height of the cross-section of the narrow section of the first reinforcing bar is the same as the height of the cross-section of the wide section of the first reinforcing bar. The width of the cross-section of the narrow section of the first reinforcing bar is smaller than the width of the cross-section of the wide section of the first reinforcing bar.

[0030] Because the cross-sectional areas of the elastic support ribs are different, the ribs with smaller cross-sectional areas have lower strength under the same load and will therefore fracture first. ANSYS simulation software can be used to calculate b1 and b2, which, under a sudden unbalanced condition, cause the narrow rib group to fracture while the wide rib group remains within the linear elastic range. When the narrow ribs have not fractured, the total stiffness of the squirrel cage is K0; when the narrow ribs fracture, the total stiffness of the squirrel cage is K1.

[0031]

[0032] Where n1 is the number of first reinforcing bars, E is the elastic modulus of the composite reinforcing bar material, b1 is the cross-sectional width of the narrow section of the first reinforcing bar, h is the cross-sectional height of the composite reinforcing bar, L is the length of the composite reinforcing bar, n2 is the number of second reinforcing bars, and b2 is the cross-sectional width of the second reinforcing bar.

[0033] like Figure 4 As shown, two bearings 2 and 5 are fitted on the shaft 1 of the engine rotor, and squirrel cages 3 and 6 are fitted on the outside of the two bearings. A limiting ring 4 is fitted on the shaft 1 of the engine rotor and is positioned between the two squirrel cages 3 and 6. The rear fixed end of the squirrel cage is fixedly fitted on the outside of the bearing.

[0034] like Figure 5As shown, the limiting ring 4 is a cylindrical ring with an inner diameter of d + 2Δr, where d is the diameter of the engine rotor shaft and Δr is the gap between the limiting ring and the engine rotor shaft. The limiting ring thickness is 15mm. The structure is analyzed as a whole using the finite element method. The magnitude of Δr is controlled to keep the rotor system amplitude constant under normal operating conditions and to limit the radial amplitude of the blades under unbalanced conditions, thus ensuring that the blade amplitude does not exceed the maximum allowable range.

[0035] The value of Δr is: A1≤Δr≤A2, where A1 is the amplitude of the shaft segment inside the limiting ring at the critical speed when the engine blade mass is not lost, calculated by ANSYS software from the rotor model simulation; A2 is the amplitude of the shaft segment of the limiting ring under the maximum allowable amplitude operating state of the engine blade, which can be calculated by finite element analysis software. The relationship between the amplitude of the limiting shaft segment and the maximum allowable amplitude of the blade is as follows: Figure 6 As shown, there is no fixed value for the maximum allowable amplitude of an aircraft engine compressor blade. It is determined based on factors such as blade design, materials, engine type, and operating environment.

[0036] In an unbalanced rotor system, the dynamic load F = mω 2 r (m is the mass of the lost blade, ω is the rotational speed, and r is the radius of rotation of the lost blade). Figure 7 The amplitude fluctuation curves of the rotor using squirrel cage elastic supports with different stiffnesses (corresponding to variable cross-section squirrel cages with stiffness of K0 = 7500 N / mm and K1 = 4500 N / mm) when 16g of blades are lost at the rotation radius r = 100mm (sudden unbalance of 1600g·mm) in the range of 0 to 18000 r / min are shown in Table 1. The speed corresponding to the peak point is the critical speed.

[0037] Table 1 Peak Point Data

[0038]

[0039] The initial stiffness of the squirrel cage is 7500 N / mm. When the rotor system operates past the second critical speed and mass loss occurs, the sudden increase in imbalance increases the stress on the elastic support of the squirrel cage. The narrower rib roots fracture first due to reaching their strength limit, causing the overall stiffness of the squirrel cage to drop to 4500 N / mm. This decrease in stiffness alters the amplitude-frequency response curve, shifting the critical speed forward. When the rotor slows down and the engine is shut down, the reduction in dynamic load at the vibration peak point compared to a conventional squirrel cage with a stiffness of 7500 N / mm is ΔF = m(ω). 高 2 -ω 低 2 )r, where ω 高 ω represents the second-order critical rotational speed corresponding to the high stiffness state of the squirrel cage.低 This represents the second-order critical speed corresponding to the low stiffness state of the squirrel cage.

[0040] Under balanced operating conditions, since the amplitude of the shaft at the limiting ring does not exceed the gap of the limiting ring, the shaft does not contact the limiting ring, and the rotor vibration is unaffected. Figure 8 As shown.

[0041] When blade 7 experiences mass loss and the rotor enters an unbalanced state, the vibration amplitude within the limiting shaft section exceeds the pre-reserved gap of the limiting ring. The shaft contacts the limiting ring, restricting the radial movement of the shaft. Compared to the shaft without the limiting ring, the radial amplitude of the blade is significantly reduced. Figure 9 As shown.

Claims

1. A combined structure for suppressing rotor amplitude under sudden unbalanced conditions, characterized in that, Includes a mouse cage (3), which is cylindrical. The mouse cage (3) includes a front fixed end (31), a rear fixed end (33), and a series of combined reinforcing bars in the form of a fence connecting the front fixed end (31) and the rear fixed end (33). The combined reinforcing bars include a first reinforcing bar (321) and a second reinforcing bar (322). The first reinforcing bar (321) and the second reinforcing bar (322) are evenly distributed alternately. The first reinforcing bar (321) includes a wide reinforcing bar portion and a narrow reinforcing bar portion. The cross-sectional area of ​​the narrow reinforcing bar portion is smaller than that of the wide reinforcing bar portion. The cross-sectional area of ​​the wide rib of the first rib (321) is the same as that of the second rib (322). Both ends of the narrow rib of the first rib (321) are connected to the wide rib. The first rib (321) is connected to the front fixed end (31) and the rear fixed end (33) through the wide rib. The central axes of the wide rib and the narrow rib coincide. Due to the sudden unbalance, the supporting rib of the elastic support of the rat cage is subjected to increased force. The rib with a smaller cross-sectional area of ​​the elastic support of the rat cage breaks due to reaching the strength limit.

2. The combined structure for suppressing rotor amplitude under sudden unbalanced conditions according to claim 1, characterized in that, The outer wall of the front fixed end (31) has a fixed mounting surface, and the narrow rib portion of the first rib (321) is close to the front fixed end (31).

3. The combined structure for suppressing rotor amplitude under sudden unbalanced conditions according to claim 2, characterized in that, The cross-section of the wide part of the first rib (321) has the same shape and size as the cross-section of the second rib (322). The height of the cross-section of the narrow part of the first rib (321) is the same as the height of the cross-section of the wide part of the first rib (321). The width of the cross-section of the narrow part of the first rib (321) is smaller than the width of the cross-section of the wide part of the first rib (321).

4. The combined structure for suppressing rotor amplitude under sudden unbalanced conditions according to claim 3, characterized in that, The overall stiffness of the rat cage (3) The calculation formula is: ； in, The number of the first rib. The elastic modulus of the composite reinforcement material. The width of the cross-section of the narrow section of the first reinforcing bar. The cross-sectional height of the composite reinforcement is... The length of the composite reinforcement. The number of the second reinforcing bars. The width of the cross section of the second reinforcing bar.

5. The combined structure for suppressing rotor amplitude under sudden unbalanced conditions according to claim 4, characterized in that, When the narrow section of the first rib (321) breaks, the overall stiffness of the rat cage (3) decreases. The calculation formula is: 。 6. The combined structure for suppressing rotor amplitude under sudden unbalanced conditions according to claim 3, characterized in that, It also includes a bearing (2) and a limiting ring (4) fitted on the engine rotor, with the rear fixed end (33) of the squirrel cage (3) fixedly fitted outside the bearing (2).

7. The combined structure for suppressing rotor amplitude under sudden unbalanced conditions according to claim 6, characterized in that, It includes two bearings (2) fitted on the engine rotor, and a squirrel cage (3) fitted on both bearings (2). The limiting ring (4) is set between the two squirrel cages (3).

8. The combined structure for suppressing rotor amplitude under sudden unbalanced conditions according to claim 7, characterized in that, The limiting ring (4) is a cylindrical ring, and the inner diameter of the limiting ring (4) is... ,in, The diameter of the engine rotor shaft (1) is... The gap between the limiting ring (4) and the engine rotor shaft (1).

9. The combined structure for suppressing rotor amplitude under sudden unbalanced conditions according to claim 8, characterized in that, The The value can be: ,in, The amplitude of the inner shaft section of the limiting ring (4) is the value at the critical speed when the engine blade mass is not lost. The amplitude of the limiting ring (4) shaft segment is the maximum amplitude of the engine blade under the allowed operating conditions.

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