Combined structure for suppressing rotor amplitude in sudden load unbalance state

Abstract

The invention discloses a combined structure for suppressing rotor amplitude in a sudden load unbalance state, which comprises a squirrel cage, the squirrel cage is cylindrical and comprises a front fixed end, a rear fixed end and a plurality of barrier-shaped combined ribs for connecting the front fixed end and the rear fixed end, and the combined ribs comprise first ribs and second ribs, the first ribs and the second ribs are alternately and uniformly distributed, each first rib comprises a wide rib part and a narrow rib part, the cross sectional area of each narrow rib part is smaller than that of each wide rib part, and the cross sectional area of each wide rib part of each first rib is the same as that of each second rib. Comprising an amplitude limiting ring sleeved on a rotating shaft of an engine rotor, and a gap exists between the amplitude limiting ring and the rotating shaft. When rotor blades of an aircraft engine are broken to cause sudden unbalanced load, the maximum dynamic load and the radial amplitude of the rotor are reduced under the combined action of the elastic support of the combined rib squirrel cage and the amplitude limiting ring.

Description

Technical Field

[0001] The invention relates to elastic support and shaft amplitude limiting in an aeroengine, and in particular to a combined structure for suppressing rotor amplitude in a sudden unbalanced state. Background Art

[0002] In recent years, with the rapid development of aviation technology, the number of commercial and military aircraft has continued to increase, and the requirements for aircraft performance and safety have also increased. When an engine blade breaks, the lack of mass will cause a sharp increase in the imbalance of the engine rotor. When the engine is near the critical speed, the radial amplitude of the blade increases sharply, and the blades and the casing collide with each other, which will trigger 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 cause a flight accident. Summary of the invention

[0003] Purpose of the invention: In view of the above disadvantages, the present invention provides a combined structure that reduces the maximum dynamic load and the radial amplitude of the rotor and suppresses the amplitude of the rotor under a sudden unbalanced state.

[0004] Technical solution: To solve the above problems, the present invention adopts a combined structure for suppressing the rotor amplitude under the sudden unbalanced state, including a squirrel cage, which is cylindrical, and includes a front fixed end, a rear fixed end, and a plurality of combined ribs in the shape of a fence connecting the front fixed end and the rear fixed end, and the combined ribs include a first rib and a second rib, and the first rib and the second rib are alternately and evenly distributed, and the first rib includes a wide rib part and a narrow rib part, and the cross-sectional area of ​​the narrow rib part is smaller than the cross-sectional area of ​​the wide rib part, and the cross-sectional area of ​​the wide rib part of the first rib is the same as the cross-sectional area of ​​the second rib. The limiting ring is sleeved on the rotating shaft of the engine rotor, and there is a gap between the limiting ring and the rotating shaft.

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

[0006] Furthermore, the outer wall of the front fixed end has a fixed installation 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 is the same 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 total stiffness K0 of the squirrel cage is calculated as follows:

[0009]

[0010] Among them, n1 is the number of first ribs, E is the elastic modulus of the combined rib material, b1 is the cross-sectional width of the narrow rib portion of the first rib, h is the cross-sectional height of the combined rib, L is the length of the combined rib, n2 is the number of second ribs, and b2 is the cross-sectional width of the second rib.

[0011] Furthermore, when the narrow rib portion of the first rib is broken, the total stiffness K1 of the squirrel cage is calculated as follows:

[0012]

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

[0014] Furthermore, it comprises two bearings sleeved on the engine rotor, the two bearings are sleeved with squirrel cages, and the limiting ring is arranged between the two squirrel cages.

[0015] Furthermore, the limiting ring is a circular ring column, and the inner diameter of the limiting ring is d+2Δr, wherein 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, wherein A1 is the amplitude of the shaft section inside the limiting ring under the critical speed state when the mass of the engine blade is not lost, and A2 is the amplitude of the shaft section 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 significant advantages: when the rotor blades of an aircraft engine are damaged by foreign objects and break, causing mass loss, the maximum dynamic load and radial amplitude of the blades are reduced under the joint action of the combined rib cage elastic support and the limiting ring. When the engine rotor is suddenly unbalanced due to factors such as blade loss when passing the first-order critical speed, the squirrel cage elastic support is affected by the sudden imbalance, and the support ribs of the squirrel cage elastic support are subjected to increased force due to the influence of the sudden imbalance. The ribs with smaller cross-sectional areas of the squirrel cage elastic support break due to reaching the strength limit, while the ribs with larger cross-sectional areas are still within the elastic range. The overall stiffness of the squirrel cage decreases, and the critical speed of the rotor is reduced. Finally, when the speed decreases to the critical speed during the engine shutdown process, the dynamic load is reduced. When the amplitude exceeds the reserved gap, the shaft contacts the limiting ring, the maximum amplitude of the rotor is limited, and the vibration amount is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the longitudinal section and cross section of a squirrel cage in the prior art.

[0019] Figure 2 It is a schematic diagram of the structure of the combined reinforced squirrel cage in the present invention.

[0020] Figure 3 It is a schematic cross-sectional view of the combined reinforced squirrel cage of the present invention.

[0021] Figure 4 It is a schematic diagram of the structure in which the elastic support is installed on the engine rotor in the present invention.

[0022] Figure 5 It is a schematic diagram of the structure in which the limiting ring is sleeved on the rotating shaft in the present invention.

[0023] Figure 6 It is a schematic diagram of the relationship between the amplitude of the limiting shaft section and the maximum amplitude allowed by the blade in the present invention.

[0024] Figure 7 The figure is the rotation speed and amplitude distribution curve of squirrel cages with different stiffness in the present invention.

[0025] Figure 8 It is a schematic diagram of the state of the rotating shaft when the engine rotor mass balance working state in the present invention.

[0026] Fig. 9 It is a schematic diagram for comparing the effects of the infinite amplitude ring when the blade loses mass and the rotor enters an unbalanced state in the present invention. DETAILED DESCRIPTION

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

[0028]

[0029] like Figure 2 and Figure 3As shown, in this embodiment, a combined structure for suppressing the rotor amplitude under a sudden unbalanced state is used, and the cage 3 uses combined ribs of different widths. The cage 3 is cylindrical, including a front fixed end 31, a rear fixed end 33, and a plurality of combined ribs in the shape of a fence connecting the front fixed end 31 and the rear fixed end 33. The combined ribs include a first rib 321 and a second rib 322. The first rib 321 and the second rib 322 are alternately and evenly distributed. The first rib 321 includes a wide rib part and a narrow rib part. The cross-sectional area of ​​the narrow rib part is smaller than the cross-sectional area of ​​the wide rib part. The cross-sectional area of ​​the wide rib part of the first rib 321 is the same as the cross-sectional area of ​​the second rib 322. Both ends of the narrow rib part of the first rib 321 are connected to the wide rib part. The first rib 321 is connected to the front fixed end 31 and the rear fixed end 33 through the wide rib part, and the central axis of the wide rib part and the narrow rib part coincide. The outer wall of the front fixed end 31 has a fixed installation surface, and the narrow rib part of the first rib 321 is close to the front fixed end. The cross section of the first rib wide rib portion is the same as the cross section of the second rib 322, the height of the cross section of the first rib narrow rib portion is the same as the height of the cross section of the first rib wide rib portion, and the width of the cross section of the first rib narrow rib portion is smaller than the width of the cross section of the first rib wide rib portion.

[0030] Due to the different cross-sectional areas of the elastic support bars, the bars with smaller cross-sectional areas have lower strength under the same load and will break first. The ANSYS simulation software can be used to calculate b1 and b2 that will make the narrow bar group break while the wide bar group is still within the linear elastic range under the sudden unbalanced state. When the narrow bar does not break, the total stiffness of the squirrel cage is K0, and when the narrow bar breaks, the total stiffness of the squirrel cage is K1.

[0031]

[0032] Among them, n1 is the number of first ribs, E is the elastic modulus of the combined rib material, b1 is the cross-sectional width of the narrow rib portion of the first rib, h is the cross-sectional height of the combined rib, L is the length of the combined rib, n2 is the number of second ribs, and b2 is the cross-sectional width of the second rib.

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

[0034] like Figure 5As shown, the limiting ring 4 is a circular ring column, and the inner diameter of the limiting ring is 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 is 15 mm thick, and the structure is analyzed as a whole by the finite element analysis method, and the size of Δr is controlled so that the amplitude of the rotor system remains unchanged under normal working conditions, and the radial amplitude of the blade is limited under unbalanced conditions so 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 section inside the limit ring under the critical speed state when the mass of the engine blade is not lost, which is calculated by ANSYS software to simulate the rotor model. A2 is the amplitude of the shaft section of the limit ring when the engine blade is working under the maximum allowable amplitude, which can be calculated by finite element analysis software. The relationship between the amplitude of the limit shaft section and the maximum allowable amplitude of the blade is as follows: Figure 6 As shown, the maximum allowable amplitude of aircraft engine compressor blades does not have a fixed value. It is determined based on factors such as the blade design, material, engine type and operating environment.

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

[0037] Table 1 Peak point data

[0038]

[0039] The initial stiffness of the cage is 7500N / mm. When the rotor system loses mass when working at a state of passing the second-order critical speed, the force on the cage elastic support increases due to the sudden increase in unbalance. The root of the narrower rib breaks first due to reaching the strength limit, causing the overall stiffness of the cage to drop to 4500N / mm. As the amplitude-frequency characteristic curve changes due to the decrease in cage stiffness, the critical speed moves forward. When the rotor is stopped and the engine is turned off at a reduced speed, the dynamic load reduction of the present invention at the vibration peak point is ΔF=m(ω 高 2 -ω 低 2 )r, where ω 高 is the second-order critical speed corresponding to the high stiffness state of the squirrel cage, ω低 It is the second-order critical speed corresponding to the low stiffness state of the squirrel cage.

[0040] In the mass balance working state, since the amplitude of the shaft at the limit ring does not exceed the gap of the limit ring, the shaft does not contact the limit ring and the vibration of the rotor is not affected. Figure 8 shown.

[0041] When blade 7 loses mass and the rotor enters an unbalanced state, the vibration amplitude in the limiting shaft section exceeds the reserved gap of the limiting ring, the shaft contacts the limiting ring, and the radial movement of the shaft is restricted. Compared with the shaft without the limiting ring, the radial amplitude of the blade is greatly reduced. Fig. 9 shown.

Claims

1. A combined structure for suppressing rotor amplitude under sudden unbalanced state, characterized in that: The invention comprises a squirrel cage (3), the squirrel cage (3) is cylindrical, the squirrel cage (3) comprises a front fixed end (31), a rear fixed end (33), and a plurality of combined ribs in a fence shape connecting the front fixed end (31) and the rear fixed end (33), the combined ribs comprise a first rib (321) and a second rib (322), the first rib (321) and the second rib (322) are alternately and evenly distributed, the first rib (321) comprises a wide rib portion and a narrow rib portion, the cross-sectional area of ​​the narrow rib portion is smaller than the cross-sectional area of ​​the wide rib portion, and the cross-sectional area of ​​the wide rib portion of the first rib (321) is the same as the cross-sectional area of ​​the second rib (322).

2. The combined structure for suppressing rotor amplitude under sudden unbalanced state according to claim 1 is characterized in that: 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) via the wide rib portion, and the central axes of the wide rib portion and the narrow rib portion coincide.

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

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

5. The combined structure for suppressing rotor amplitude under sudden unbalanced state according to claim 4 is characterized in that: The total stiffness K0 of the squirrel cage (3) is calculated as follows: Among them, n1 is the number of first ribs, E is the elastic modulus of the combined rib material, b1 is the cross-sectional width of the narrow rib portion of the first rib, h is the cross-sectional height of the combined rib, L is the length of the combined rib, n2 is the number of second ribs, and b2 is the cross-sectional width of the second rib.

6. The combined structure for suppressing rotor amplitude under sudden unbalanced state according to claim 5 is characterized in that: When the narrow rib portion of the first rib (321) breaks, the total stiffness K1 of the squirrel cage (3) is calculated as follows:

7. The combined structure for suppressing rotor amplitude under sudden unbalanced state according to claim 4 is characterized in that: It also includes a bearing (2) and a limiting ring (4) sleeved on the engine rotor, and the rear fixed end (33) of the squirrel cage (3) is fixedly sleeved outside the bearing (2).

8. The combined structure for suppressing rotor amplitude under sudden unbalanced state according to claim 7 is characterized in that: It comprises two bearings (2) sleeved on the engine rotor, the two bearings (2) are sleeved with a squirrel cage (3) outside, and the limiting ring (4) is arranged between the two squirrel cages (3).

9. The combined structure for suppressing rotor amplitude under sudden unbalanced state according to claim 8, characterized in that: The limiting ring (4) is a circular ring column, and the inner diameter of the limiting ring (4) is d+2Δr, wherein d is the diameter of the engine rotor shaft (1), and Δr is the gap between the limiting ring (4) and the engine rotor shaft (1).

10. The combined structure for suppressing rotor amplitude under sudden unbalanced state according to claim 9, characterized in that: The value of Δr is: A1≤Δr≤A2, wherein A1 is the amplitude of the shaft section inside the limit ring (4) under the critical speed state when the mass of the engine blade is not lost, and A2 is the amplitude of the shaft section inside the limit ring (4) when the engine blade is under the maximum allowable amplitude working state.

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