Design method for dynamic stability of two-stage turbine structure containing interstage disc

Abstract

The invention provides a method for designing the dynamic stability of a two-stage turbine structure comprising an interstage disc, which comprises the following steps of: S1, preparing data, including the radial fit clearance of the interstage disc, the pressing force of the interstage disc and structural design parameters; s2, calculating a critical swing angle theta cr (omega) and a critical swing angle line according to the structural design parameters and the interstage disc pressing force; calculating a limit swing angle theta lim (omega) and a limit swing angle line according to the fit clearance and the structural design parameters; and S3, drawing a stability region, and judging the stability according to a stability criterion. The method can be used for designing a two-stage turbine structure with dynamic stability and an interstage disc, and economic losses caused by a hot end vibration fault are avoided. The design method can also be used for analyzing the dynamic stability of the two-stage turbine structure containing the interstage disc structure, and reference is provided for design improvement.

Description

Technical Field

[0001] The invention relates to the field of two-stage turbines, and in particular to a design method for dynamic stability of a two-stage turbine structure containing an interstage disk. Background Art

[0002] In the prior art, the high-pressure turbine, as a hot-end rotating component, is subjected to thermal / mechanical / aerodynamic loads of high temperature, high pressure and high stress, which places extremely high demands on the stability of its structure.

[0003] In order to improve turbine efficiency and thus improve fuel economy, the high-pressure turbine of civil large bypass ratio turbofan engines tends to adopt a two-stage turbine, which has a more complex structure than a single-stage turbine.

[0004] Figure 1 Figure 1 is a schematic diagram of the interstage disc structure and installation status. Figure 1 As shown, the interstage disk structure includes a turbine primary disk 10 , a turbine secondary disk 20 and an interstage disk 30 . The interstage disk 30 is installed on the turbine primary disk 10 and the turbine secondary disk 20 .

[0005] Considering the turbine working environment, structural limitations and assembly, a box-type clamping structure is often used for the added turbine interstage disc. The main technical difficulty of this structure is that the interstage disc is fixed by the clamping force provided by the turbine first and second discs, which poses a greater challenge to the stability of the interstage disc structure.

[0006] In view of this, the inventor of the present application has designed a dynamic stability design method for a two-stage turbine structure including an interstage disk, in order to overcome the above-mentioned technical problems. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the defect in the prior art that the compression force between high-pressure turbines has a great influence on the stability of the turbine interstage disk structure, and to provide a dynamic stability design method for a two-stage turbine structure including an interstage disk.

[0008] The present invention solves the above technical problems through the following technical solutions:

[0009] A method for designing the dynamic stability of a two-stage turbine structure including an interstage disk is characterized in that the design method comprises the following steps:

[0010] S1. Prepare data, including radial clearance of the interstage disc, clamping force of the interstage disc, and structural design parameters;

[0011] S2. Calculate the critical swing angle θ based on the structural design parameters and the interstage disk pressing force cr (ω) and critical swing angle line; according to the matching clearance and the structural design parameters, calculate the limit swing angle θlim (ω) and the limiting pendulum angle line;

[0012] S3. Draw the stability region and determine the stability based on the stability criterion.

[0013] According to one embodiment of the present invention, the radial fit clearance of the interstage disc in step S1 is obtained by finite element analysis, the interstage disc clamping force is obtained by the designed clamping amount and finite element analysis, and the structural design parameters include the fitting surface radius r, half of the axial length L of the interstage disc, and the diameter moment of inertia I T , polar moment of inertia I p .

[0014] According to one embodiment of the present invention, step S2 includes:

[0015] S 21 , the critical swing angle θ that satisfies the stability criterion of the interstage disk cr (ω) is:

[0016]

[0017] Among them, F(ω) is the axial clamping force, μ is the friction factor, r is the axial distance from the end face to the center of mass, I p is the polar moment of inertia of the interstage disk, I T is the diameter moment of inertia of the interstage disk, and ω is the vortex angular velocity of the interstage disk.

[0018] According to one embodiment of the present invention, when θ<θ cr When θ>θ, the gyroscopic torque of the interstage disk is smaller than the friction torque, and the connection interface will not slip. cr When the gyroscopic torque of the interstage disk is greater than the friction torque, the gyroscopic torque will overcome the friction torque, and the interstage disk will slip at the connection interface.

[0019] According to one embodiment of the present invention, the step S 21 The critical swing angle line is also obtained: when the static friction factor μ and the axial distance r from the end face to the center of mass are constants, and the change of the axial clamping force F(ω) with the speed is not considered, the critical swing angle θ cr is a single variable function of ω, the critical swing angle θ cr A critical swing angle curve is formed on the speed-swing angle plane, dividing the speed-swing angle plane into a non-slip zone and a slip zone.

[0020] According to one embodiment of the present invention, step S2 further includes:

[0021] S 22 , calculate the limit swing angle θ lim (ω), when the swing angle θ is equal to the limit swing angle θ lim(ω), the following relationship holds:

[0022] dR(θ lim )=e(ω)

[0023] dR=R(1-cosθ)

[0024]

[0025] Wherein, dR is the radial dimension change caused by the swing of the interstage disk, e is the radial clearance of the mating surface, θ is the swing angle of the interstage disk, r is the radius of the mating surface, and L is half of the axial length of the interstage disk;

[0026] When θ<2°, sin(θ)≈θ, the calculation formula for the limit swing angle is:

[0027]

[0028] According to one embodiment of the present invention, when θ<θ lim When θ>θ lim When the stage disc is rotated, it will not be able to swing in the designed axial compression box structure due to structural limitations.

[0029] According to one embodiment of the present invention, the step S 22 The limit swing angle line is also included: when the speed ω changes, the radial structural clearance of the interstage disk will change due to deformation; the limit swing angle θ at each speed lim On the speed-swing angle plane, a limit swing angle line is formed, which divides the speed-swing angle plane into a possible swing angle area and an impossible swing angle area.

[0030] According to one embodiment of the present invention, step S3 includes:

[0031] S 31 , Draw the stability area: divide the speed-swing angle plane into stable area, unstable area, redundant stability area and impossible swing area through the critical swing angle line and the limit swing angle line;

[0032] The stable region satisfies: θ(ω)<min[θ cr (ω),θ lim (ω)];

[0033] The unstable region satisfies: θ cr *ω)<θ*ω)<θ lim (ω);

[0034] The redundant stable region satisfies: θ lim (ω)<θ(ω)<θ cr (ω);

[0035] The impossible swing region satisfies: θ(ω)>max[θ cr (ω),θ lim (ω)].

[0036] According to one embodiment of the present invention, step S3 further includes:

[0037] S 32 , Determine the stability according to the stability criterion. The criterion for the stability of the interstage disk connection is:

[0038] θ cr (ω)>θ lim (ω)

[0039] When the criterion is met, the interstage disk is unconditionally stable; when the criterion is not met, but during the actual rotation of the rotor, when the swing angle of the interstage disk is in the stable zone, the interstage disk is also stable.

[0040] The positive and progressive effects of the present invention are:

[0041] The dynamic stability design method of the two-stage turbine structure with interstage disk of the present invention has the following advantages:

[0042] 1. It can be used to design a two-stage turbine structure with an interstage disk that has dynamic stability, thus avoiding hot end vibration failures that may cause economic losses.

[0043] 2. It can be used to analyze the dynamic stability of a two-stage turbine structure with an interstage disk structure, providing a reference for design improvements. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The above and other features, properties and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings and embodiments, in which the same reference numerals always represent the same features, wherein:

[0045] Figure 1 This is a schematic diagram of the interstage disc structure and installation status.

[0046] Figure 2 The present invention is a flow chart of a method for designing dynamic stability of a two-stage turbine structure including an interstage disk.

[0047] Figure 3 This is a schematic diagram of the interstage disk force.

[0048] Figure 4 It is a schematic diagram of the critical swing angle line in the dynamic stability design method of the two-stage turbine structure containing the interstage disk of the present invention.

[0049] Figure 5 Schematic diagram of the interstage disc swing structure.

[0050] Figure 6 It is a schematic diagram of the limit swing angle line in the dynamic stability design method of the two-stage turbine structure containing the interstage disk of the present invention.

[0051] Figure 7 It is a schematic diagram of the rotation speed-swing angle plane partitioning in the dynamic stability design method of the two-stage turbine structure containing the interstage disk of the present invention. DETAILED DESCRIPTION

[0052] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0053] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Reference will now be made in detail to preferred embodiments of the present invention, examples of which are shown in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings to represent the same or similar parts.

[0054] Furthermore, although the terms used in the present invention are selected from well-known and commonly used terms, some terms mentioned in the present invention specification may be selected by the applicant at his or her discretion, and their detailed meanings are explained in the relevant parts of the description of this document.

[0055] Furthermore, it is required that the present invention be understood not only by the actual terms used but also by the meanings connoted by each term.

[0056] like Figure 2 As shown, the present invention discloses a method for designing dynamic stability of a two-stage turbine structure including an interstage disk, which comprises the following steps:

[0057] Step S1, preparing data, including radial fit clearance of the interstage disk, interstage disk clamping force, and structural design parameters.

[0058] Preferably, in step S1, attention should be paid to the radial clearance e(ω) of the interstage disc at each speed, which can be obtained through finite element analysis. The interstage disc clamping force F is obtained through the designed clamping amount and finite element analysis, and the clamping value under the design state of 0rpm can be used. The structural design parameters include the radius of the mating surface r, half of the axial length of the interstage disc L, and the diameter moment of inertia I T , polar moment of inertia I p wait.

[0059] Step S2: Calculate the critical swing angle θ according to the structural design parameters and the interstage disc clamping force cr (ω) and critical swing angle line; according to the matching clearance and the structural design parameters, calculate the limit swing angle θ lim (ω) and the limiting pendulum angle line.

[0060] Preferably, the step S2 includes: critical swing angle θ cr Definition, calculation method and critical sway angle line of (ω).

[0061] Due to the effect of rotational inertia, a gyroscopic torque will be generated. Figure 3 The force diagram of the interstage disc shown in the figure shows that when there is a gap between the two ends of the interstage disc in the radial fit, if the friction force generated by the axial clamping force is not enough to offset the gyroscopic torque, the interstage disc will slip at the two-point contact point and swing between the turbine first disc and the turbine second disc. As a result, the interstage disc connection is unstable.

[0062] From the cause of unstable connection, it can be seen that the key to improving the stability of the interstage disk is to reduce or weaken the swing of the interstage disk, that is, the axial compression structure has the ability to constrain the gyroscopic torque.

[0063] For the convenience of analysis, it is assumed that the interstage disk swings as a rigid body (Assumption 1), then Figure 1 The stress state of the interstage disc shown must meet the following requirements:

[0064] F axis1 -F axis2 =0

[0065] f axis2 -f axis1 =0

[0066] f=μ*F

[0067] f axis1 *r1+f axis2 *r2-M gyroscopic =0

[0068] Where f is the friction force, μ is the friction factor, r1 is the axial distance from the left end face to the center of mass, r2 is the axial distance from the right end face to the center of mass, M gyroscopic is the gyroscopic torque of the interstage disk.

[0069] The calculation formula of the gyroscopic torque of the interstage disk is:

[0070]

[0071] Among them, I T is the diameter moment of inertia of the interstage disk, I p is the polar moment of inertia of the interstage disk, ω is the vortex angular velocity of the interstage disk, Ω is the rotation angular velocity of the interstage disk, and θ is the angle between the normal direction of the interstage disk and the rotation axis.

[0072] When the gyroscopic torque cannot cause the interstage disk to swing, the interstage disk is considered stable, that is, the stability condition is:

[0073] M gyroscopic <f axis1*r1+f axis2 *r2

[0074] When r1=r2 and the rotor whirls synchronously (assumption 2), according to the above analysis, the critical swing angle θ that satisfies the interstage disk stability criterion is cr Degenerates to:

[0075]

[0076] Among them, F(ω) is the axial clamping force, μ is the friction factor, r is the axial distance from the end face to the center of mass, I p is the polar moment of inertia of the interstage disk, I T is the diameter moment of inertia of the interstage disk, and ω is the vortex angular velocity of the interstage disk.

[0077] When θ<θ cr When θ>θ, the gyroscopic torque of the interstage disk is smaller than the friction torque, and the connection interface will not slip. cr When the gyroscopic torque of the interstage disk is greater than the friction torque, the gyroscopic torque will overcome the friction torque, and the interstage disk will slip at the connection interface.

[0078] like Figure 4 As shown, the step S 21 The critical swing angle line is obtained from: When the static friction factor μ and the axial distance r from the end face to the center of mass are constants, and the change of the axial clamping force F(ω) with the speed is not considered, the critical swing angle θ ccr is a single variable function of ω, the critical swing angle θ cr A critical swing angle curve is formed on the speed-swing angle plane, dividing the speed-swing angle plane into a non-slip zone and a slip zone.

[0079] Further preferably, the step S2 further includes: a limit swing angle θ lim Definition, calculation method and limiting swing angle line.

[0080] When the interstage disc swings between the first and second stage discs of the turbine, it is limited by the structural parameters (radial clearance). When the swing angle θ increases to a certain extent, the radial clearance is 0. The swing angle at this time is the limit swing angle θ of the interstage disc under the limitation of the structural parameters. lim .

[0081] When the interstage disc swings, several structural parameters that affect the radial clearance are as follows: Figure 5 shown.

[0082] Depend on Figure 5 It can be seen that when the swing angle θ is equal to the limit swing angle θ lim , there is the following relationship:

[0083] dR(θ lim )=e(ω)

[0084] dR=R(1-cosθ)

[0085]

[0086] Among them, dR is the radial size change caused by the swing of the interstage disk, e is the radial clearance of the mating surface, θ is the swing angle of the interstage disk, r is the radius of the mating surface, and L is half of the axial length of the interstage disk.

[0087] When θ is small, the calculation formula of the limit swing angle can be obtained as:

[0088]

[0089] When θ<θ lim When θ<2°, sin(θ)≈θ, the interstage disc can swing in the designed axial compression box structure; when θ>θ lim When the stage disc is rotated, it will not be able to swing in the designed axial compression box structure due to structural limitations.

[0090] like Figure 6 As shown, the step S 22 The limit swing angle line is also included: when the speed ω changes, the radial structural clearance of the interstage disk will change due to deformation; the limit swing angle θ at each speed lim On the speed-swing angle plane, a limit swing angle line is formed, which divides the speed-swing angle plane into a possible swing angle area and an impossible swing angle area.

[0091] Step S3: draw a stability region and determine the stability according to a stability criterion.

[0092] Preferably, step S3 comprises:

[0093] Step S 31 , draw the stability region: such as Figure 7 As shown, the speed-swing angle plane is divided into a stable area, an unstable area, a redundant stable area and an impossible swing area by the critical swing angle line and the limit swing angle line.

[0094] The stable region satisfies: θ(ω)<min[θ cr (ω),θ lim (ω)];

[0095] The unstable region satisfies: θ cr (ω)<θ(ω)<θ lim (ω);

[0096] The redundant stable region satisfies: θ lim (ω)<θ(ω)<θ cr (ω);

[0097] The impossible swing region satisfies: θ(ω)>max[θ cr (ω),θ lim (ω)].

[0098] When the interstage disk swing angle is less than the critical swing angle and the limit swing angle, it indicates that the generated gyroscopic torque can be offset by the friction torque. This is the stable zone.

[0099] When the interstage disk swing angle is greater than the critical swing angle and less than the limit swing angle, it indicates that the generated gyroscopic torque cannot be offset by the friction force. However, since it is less than the limit swing angle, the structure allows swing of this amplitude, which is the unstable zone.

[0100] When the interstage disk swing angle is greater than the limit swing angle and less than the critical swing angle, it indicates that the generated gyroscopic torque can be offset by the friction torque. However, because it is greater than the limit swing angle, the area is outside the allowable swing range of the structure, which is the redundant stability zone.

[0101] When the interstage disk swing angle is greater than the critical swing angle and the limit swing angle, it indicates that the generated gyroscopic torque cannot be offset by the friction force. However, since it is greater than the limit swing angle, the structure does not allow swing of this amplitude. This is the impossible swing zone.

[0102] Furthermore, the step S3 further includes:

[0103] Step S 32 , judge the stability according to the stability criteria.

[0104] Since the actual swing angle θ of the interstage disk is unknown when the rotor is running, the stability of the interstage disk at a certain speed can be judged by the size of the critical swing angle and the limit swing angle at that speed.

[0105] Among the four zones of the speed-swing angle plane, the redundant stability zone should be paid special attention to in terms of design. Based on this, the criterion for the stability of the interstage disk connection is given as follows:

[0106] θ cr (ω)>θ lim (ω)

[0107] According to the definition of interstage disc stability in this article, this criterion is actually a sufficient condition for stability. When the criterion is met, the interstage disc is unconditionally stable. When the criterion is not met, and the swing angle of the interstage disc is in the stable zone during the actual rotation of the rotor, the interstage disc is also stable.

[0108] In addition, the dynamic stability design method of the two-stage turbine structure with interstage disks is designed according to the critical swing angle θ cr , limit swing angle θ limDefinition: The means to increase the critical swing angle and reduce the limit swing angle include: increasing the interstage disc clamping force F; increasing the matching surface radius r; reducing the difference between the interstage disc polar moment of inertia and the diameter moment of inertia (I p -I T ); reduce the radial mating surface clearance e of the interstage disk; set an overlap structure between the interstage disk center and the first-stage disk, change the two-point contact of the interstage disk to a three-point contact, and limit the ultimate swing angle.

[0109] In the clamping force design stage, according to the stability criteria of the interstage disc:

[0110] θ cr >θ lim

[0111] The requirement for axial clamping force can be calculated as:

[0112]

[0113] Due to the amplification effect of the critical speed, the clamping force at the first-order critical speed should meet the above requirements.

[0114] When the axial clamping force changes little at 0 speed and the first critical speed, the requirements for the axial clamping force in the design state are:

[0115]

[0116] Among them, ω cr is the first critical speed of the rotor.

[0117] The present invention discloses a method for designing the dynamic stability of a two-stage turbine structure including an interstage disk. According to the structure and assembly parameters of the turbine interstage disk and the preliminary finite element deformation analysis results, a method for judging the stability of the interstage disk based on the "critical swing angle line" and the "limit swing angle line" is designed, and the design key points and quantitative judgment criteria of the interstage disk connection structure are summarized.

[0118] In summary, the dynamic stability design method of the two-stage turbine structure with interstage disk of the present invention has the following advantages:

[0119] 1. It can be used to design a two-stage turbine structure with an interstage disk that has dynamic stability, thus avoiding hot end vibration failures that may cause economic losses.

[0120] 2. It can be used to analyze the dynamic stability of a two-stage turbine structure with an interstage disk structure, providing a reference for design improvements.

[0121] For those skilled in the art, the above invention disclosure is only used as an example and does not constitute a limitation of the present application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and amendments to the present application. Such modifications, improvements and amendments are suggested in the present application, so such modifications, improvements and amendments still belong to the spirit and scope of the exemplary implementation of the present application.

[0122] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0123] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that these are only examples, and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A method for designing dynamic stability of a two-stage turbine structure with an interstage disk, characterized in that: The design method comprises the following steps: S1. Prepare data, including radial clearance of the interstage disc, clamping force of the interstage disc, and structural design parameters; S2. Calculate the critical swing angle θ based on the structural design parameters and the interstage disk pressing force cr (ω) and critical swing angle line; according to the matching clearance and the structural design parameters, calculate the limit swing angle θ lim (ω) and the limiting pendulum angle line; S3. Draw the stability region and determine the stability based on the stability criterion.

2. The method for designing dynamic stability of a two-stage turbine structure with an interstage disk according to claim 1, characterized in that: In step S1, the radial clearance of the interstage disc is obtained by finite element analysis, the clamping force of the interstage disc is obtained by the designed clamping amount and finite element analysis, and the structural design parameters include the radius of the mating surface r, half of the axial length of the interstage disc L, and the diameter moment of inertia I T , polar moment of inertia I p .

3. The method for designing dynamic stability of a two-stage turbine structure with an interstage disk according to claim 1, characterized in that: The step S2 includes: S 21 , the critical swing angle θ that satisfies the stability criterion of the interstage disk cr (ω) is: Among them, F(ω) is the axial clamping force, μ is the friction factor, r is the axial distance from the end face to the center of mass, I p is the polar moment of inertia of the interstage disk, I T is the diameter moment of inertia of the interstage disk, and ω is the vortex angular velocity of the interstage disk.

4. The method for designing dynamic stability of a two-stage turbine structure with an interstage disk according to claim 3, characterized in that: When θ<θ cr When θ>θ, the gyroscopic torque of the interstage disk is smaller than the friction torque, and the connection interface will not slip. cr When the gyroscopic torque of the interstage disk is greater than the friction torque, the gyroscopic torque will overcome the friction torque, and the interstage disk will slip at the connection interface.

5. The method for designing dynamic stability of a two-stage turbine structure with an interstage disk according to claim 4, characterized in that: The step S 21 The critical swing angle line is also obtained: when the static friction factor μ and the axial distance r from the end face to the center of mass are constants, and the change of the axial clamping force F(ω) with the speed is not considered, the critical swing angle θ cr is a single variable function of ω, the critical swing angle θ cr A critical swing angle curve is formed on the speed-swing angle plane, dividing the speed-swing angle plane into a non-slip zone and a slip zone.

6. The method for designing dynamic stability of a two-stage turbine structure with an interstage disk according to claim 3, characterized in that: The step S2 also includes: S 22 , calculate the limit swing angle θ lim (ω), when the swing angle θ is equal to the limit swing angle θ lim (ω), the following relationship holds: dR(θ lim )=e(ω) dR=R(1-cosθ) Wherein, dR is the radial dimension change caused by the swing of the interstage disk, e is the radial clearance of the mating surface, θ is the swing angle of the interstage disk, r is the radius of the mating surface, and L is half of the axial length of the interstage disk; When θ<2°, sin(θ)≈θ, the calculation formula for the limit swing angle is:

7. The method for designing dynamic stability of a two-stage turbine structure with an interstage disk according to claim 6, characterized in that: When θ<θ lim When θ>θ lim When the stage disc is rotated, it will not be able to swing in the designed axial compression box structure due to structural limitations.

8. The method for designing dynamic stability of a two-stage turbine structure with an interstage disk according to claim 7, characterized in that: The step S 22 The limit swing angle line is also included: when the speed ω changes, the radial structural clearance of the interstage disk will change due to deformation; the limit swing angle θ at each speed lim On the speed-swing angle plane, a limit swing angle line is formed, which divides the speed-swing angle plane into a possible swing angle area and an impossible swing angle area.

9. The method for designing dynamic stability of a two-stage turbine structure with an interstage disk according to claim 1, characterized in that: The step S3 comprises: S 31 , Draw the stability area: divide the speed-swing angle plane into stable area, unstable area, redundant stability area and impossible swing area through the critical swing angle line and the limit swing angle line; The stable region satisfies: θ(ω)<min[θ cr (ω),θ lim (ω)]; The unstable region satisfies: θ cr (ω)<θ(ω)<θ lim (ω); The redundant stable region satisfies: θ lim (ω)<θ(ω)<θ cr (ω); The impossible swing region satisfies: θ(ω)>max[θ cr (ω),θ lim (ω)].

10. The method for designing dynamic stability of a two-stage turbine structure with an interstage disk according to claim 1, characterized in that: The step S3 further comprises: S 32 , Determine the stability according to the stability criterion. The criterion for the stability of the interstage disk connection is: i cr (ω)>θ lim (oh) When the criterion is met, the interstage disk is unconditionally stable; when the criterion is not met, but during the actual rotation of the rotor, when the swing angle of the interstage disk is in the stable zone, the interstage disk is also stable.

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