A design method for spiral bag-type damping seal

Abstract

A design method for a spiral bag-type damping seal. Select a straight-through labyrinth seal located on the stator surface and obtain its geometric parameters. In the seal structure, change all the seal teeth except the first and the last one to spiral teeth with a direction opposite to the rotation direction of the rotor, and add axial baffles to the seal. Select the number of spiral teeth, the spiral pitch, and the number of axial baffles as experimental factors, specify the value ranges to be analyzed, and evenly select 5 values within the value ranges of each parameter to generate a three-factor five-level coding table. Obtain the performance evaluation index of each seal structure under the rated working conditions, normalize the value ranges of the three experimental factors, and at the same time select the performance evaluation index. Use a quadratic fitting polynomial for fitting, and obtain the contribution rate of each experimental factor to the performance index from the fitting coefficients. Select the spiral bag-type damping seal structures in different combinations where the seal leakage amount does not increase compared with the original structure, and select the scheme with better stability from them.

Description

Technical Field

[0001] The present invention belongs to the technical field of rotary machinery, and particularly relates to a design method for a spiral pocket damping seal. Background Art

[0002] The rotor in an impeller machine needs to be supported on bearings and pass through the cylinder, leaving a gap between the rotor and the cylinder. An annular seal structure is installed between the rotor and the stator components in a turbomachine to control the leakage flow under a high pressure difference. In impeller machines such as steam turbines, gas turbines, pumps, and compressors, a rotary seal is installed between the rotating component and the stationary component to control the leakage flow from the high-pressure area to the low-pressure area through the dynamic and static clearance, which has a significant impact on the operating efficiency of the impeller machine.

[0003] In addition to controlling the leakage of the working medium, the force exerted by the working medium in the seal section on the rotor will also affect the stability of the shafting. Compared with damping seal structures such as orifice seals and pocket seals, non-damping seals are more likely to cause insufficient rotor stability due to the unsteady airflow excitation force generated by rotor whirling. As a damping seal developed from a labyrinth seal by adding circumferential baffles, the pocket seal is currently widely used in impeller machines. Adding baffles in the labyrinth seal will effectively weaken the circumferential flow of the airflow in the seal chamber and increase the damping coefficient, ultimately achieving the purpose of enhancing rotor stability. Using a rotary damping seal instead of a traditional labyrinth seal is a very effective method to suppress rotor vibration. The damping seal technology with low leakage and high damping performance is of great significance for further improving the energy conversion efficiency and operating stability of impeller machines.

[0004] However, there are two obvious deficiencies in the current pocket damping seal: 1. As the number of seal teeth increases, the damping coefficient will decrease. However, reducing the number of seal teeth will also bring greater leakage losses. Therefore, the selection of the number of seal teeth will be weighed between leakage characteristics and rotor stability. 2. After adding circumferential baffles in the labyrinth seal, not only the direct damping but also the cross stiffness is increased. This will result in an obvious negative value of the effective damping at low frequencies, which is not conducive to rotor stability. Summary of the Invention

[0005] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a design method for a spiral pocket damping seal, which realizes stability enhancement and vibration suppression by effectively reducing the cross stiffness in the pocket seal with a large number of seal teeth, and increases the operating stability of the impeller machine.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A design method for a spiral pocket damping seal, comprising the following steps:

[0008] S1. Select a straight-through labyrinth seal on the stator surface and obtain its geometric parameters. The geometric parameters include the number of teeth, seal clearance, seal tooth width, chamber length, and depth.

[0009] S2. In the seal structure, change all the seal teeth except the first and the last one to helical teeth with a direction opposite to the rotor rotation direction, and add axial baffles to the seal.

[0010] S3. Select three key geometric parameters, namely the number of helical teeth, helical pitch, and number of axial baffles, as test factors. Given the value range to be analyzed for each parameter, and evenly select 5 values within the value range of each parameter.

[0011] S4. Generate a three-factor five-level coding table based on the parameter test of the central composite design method. Each item in the coding table gives a set of geometric parameter combinations of the number of helical teeth, helical pitch, and number of axial baffles.

[0012] S5. Under the rated working conditions, use the numerical simulation method of solving the steady RANS equation to obtain the performance evaluation indexes of each seal structure. The performance evaluation indexes include the stability evaluation index and the leakage evaluation index. The stability evaluation index is the gas flow excitation force, and the leakage evaluation index is the seal leakage. The gas flow excitation force includes the rotor radial gas flow excitation force and the rotor tangential gas flow excitation force.

[0013] S6. Normalize the value ranges of the three test factors to [-1, 1]. At the same time, select a performance evaluation index, and use the quadratic fitting polynomial for fitting. Obtain the contribution rate of each test factor to the analyzed performance index from the fitting coefficients in the polynomial.

[0014] S7. Select the helical pocket damper seal structure in which the seal leakage does not increase compared with the original structure among different combinations, and select the scheme with better stability from them.

[0015] In the embodiment of the present invention, in S2, the axial baffles are parallel to the axial direction of the seal chamber, are located in the seal chamber and penetrate through the seal inlet and outlet. The number of the axial baffles is set to an even number greater than 2 and is evenly distributed circumferentially.

[0016] In the embodiment of the present invention, in S3, the selected helical teeth are connected to the front and rear seal straight teeth and are connected by at least one axial baffle.

[0017] In the embodiment of the present invention, in S3, the value range to be analyzed for the number of helical teeth is greater than 1, the value range to be analyzed for the helical pitch is greater than 0° and less than 90°, and the value range to be analyzed for the number of axial baffles is an even number greater than 2.

[0018] In an embodiment of the present invention, in S4, a total of 15 test schemes are generated based on the central composite design method for the coding table, including 8 full factorial experiment schemes, 1 central point experiment scheme, and 6 axial point test schemes.

[0019] In an embodiment of the present invention, in S5, a numerical simulation method for steady-state solving of the rotor static eccentricity model is used to obtain the tangential gas flow excitation force and the radial gas flow excitation force of the spiral pocket damper seal under each combination of geometric parameters, that is, the rotor tangential gas flow excitation force and the rotor radial gas flow excitation force; when the steady-state solution of the rotor static eccentricity model calculation is completed, the mass flow rate is extracted at the inlet or outlet, and the seal leakage amount is obtained.

[0020] In an embodiment of the present invention, in S6, the normalized factor and any one response are input into the commercial software Isight for quadratic polynomial fitting to obtain a Pareto chart and a main effect chart, so as to obtain the contribution rate of each test factor to the performance index to be analyzed; the response is the leakage amount, tangential gas flow excitation force, and radial gas flow excitation force obtained by numerical calculation.

[0021] In an embodiment of the present invention, in S7, a geometric parameter interval with a leakage amount not greater than that of the original seal structure is obtained, and a parameter combination scheme with better stability is selected therefrom.

[0022] Compared with the prior art, the present invention can determine the number of axial baffles, the number of spiral tooth heads, and the spiral pitch of the spiral pocket damper seal through finite numerical calculations, thereby controlling the leakage amount of the spiral pocket damper seal within a lower range, and at the same time obtaining more excellent rotor centering ability and stability. Description of the Drawings

[0023] Figure 1 It is a schematic flow chart of the present invention.

[0024] Figure 2 It is a straight-through labyrinth seal located on the stator surface.

[0025] Figure 3 It is the spiral pocket damper seal of the present invention.

[0026] Figure 4 It is a schematic diagram of rotor static eccentricity.

[0027] Figure 5 It is a comparison chart of the tangential gas flow excitation force and the radial gas flow excitation force of the labyrinth seal and the spiral pocket damper seal. Detailed Embodiment

[0028] The embodiments of the present invention will be described in detail below with reference to the drawings and embodiments.

[0029] In view of the requirements of damping seals for increasing stability and suppressing vibration, which have been widely applied in industrial impeller machinery, the present invention proposes a design method for spiral pocket damping seals that can meet the requirements of rapidly and efficiently improving leakage characteristics and damping performance during the engineering design process, thereby effectively improving the seal leakage characteristics and rotor dynamic characteristics.

[0030] The present invention analyzes the fitting relationship between the gas flow excitation force, leakage rate (response), and spiral tooth geometric parameters and baffle number (factors) by means of numerical simulation and DOE test methods, and then determines the key test factors and the optimal parameter combination scheme. Refer to Figure 1 , the implementation process of the spiral pocket damping seal design method of the present invention is as follows:

[0031] 1. Generate a test plan based on the central composite design method

[0032] S11, select a straight-through labyrinth seal located on the stator surface and obtain its geometric parameters such as the number of teeth, seal clearance, seal tooth width, chamber length, and depth. In an embodiment of the present invention, the straight-through labyrinth seal located on the stator surface is from the paper (Rotordynamic Characteristics of a Novel Labyrinth Seal With Swirl Brakes at Seal Entrance and Cavity), and its trapezoidal labyrinth seal teeth located on the stator surface are changed to rectangular labyrinth seal teeth, and the structure is as Figure 2 shown.

[0033] S12, in this spiral pocket damping seal structure, change all the seal teeth except the first and the last seal teeth to spiral teeth with the opposite rotation direction to the rotor, that is, change it to a spiral seal structure, and add an axial baffle in the seal.

[0034] The setting of the axial baffle can refer to Figure 3 , its direction is parallel to the axis of the seal chamber, located in the seal chamber, and runs through the seal inlet and outlet. The number of axial baffles is set to an even number greater than 2 and is evenly distributed circumferentially.

[0035] S13, keep the seal tooth profile unchanged, select three key geometric parameters of the spiral pocket damping seal, namely the number of spiral tooth heads, spiral pitch, and number of axial baffles, as test factors, give the value range to be analyzed for each parameter, and evenly select 5 levels (different values of the factors) within the value range of each parameter.

[0036] In this embodiment, the selected spiral teeth are connected to the front and rear sealing straight teeth and are separated by at least one axial baffle. The range of the number of spiral teeth to be analyzed is greater than 1. The spiral pitch is the angle between the tangent of the spiral on the middle diameter cylinder and the plane perpendicular to the thread axis, and the range to be analyzed is greater than 0° and less than 90°. The range of the number of axial baffles to be analyzed is an even number greater than 2.

[0037] S14. Generate a three-factor five-level coding table based on the parameter experiment of the central composite design method, as shown in Table 1. Each item in the coding table gives a set of geometric parameter combinations of the number of spiral teeth, spiral pitch, and number of axial baffles. For example, the range of the number of spiral heads is 3 - 15, and the five levels are respectively selected as 3, 6, 9, 12, and 15.

[0038] In this embodiment, using commercial software Isight and other methods, a total of 15 test schemes (geometric parameter combination schemes) are generated for the coding table based on the central composite design method. Referring to Table 2, it includes 8 full-factor experimental schemes (test schemes 2 - 9), the permutations and combinations of the 2nd and 4th levels; 1 center point experimental scheme (test scheme 1), where each parameter selects the 3rd level; and 6 axial point test schemes (test schemes 10 - 15), one parameter selects level 1 or 5, and the other two parameters select level 3.

[0039] According to Table 2, a total of 15 spiral pocket damper seal structures can be generated, and then a numerical simulation method is used to model, mesh, and perform steady numerical solutions for these 15 seal structures.

[0040] Table 1 Three-factor five-level coding table

[0041] Horizontal number Number of spiral heads Spiral pitch / mm Number of baffles 1 3 32.5 4 2 6 65 6 3 9 97.5 8 4 12 130 10 5 15 195 12

[0042] Table 2 Test schemes

[0043]

[0044]

[0045] 2. Steady solution parameters

[0046] S21. According to the established test scheme, under the rated working conditions, use the numerical simulation method of steady solution of the RANS equation to perform steady rotor eccentricity numerical simulation, and obtain the performance evaluation indexes of each seal structure. The performance evaluation indexes include stability evaluation indexes and leakage evaluation indexes. The stability evaluation index is the airflow excitation force, including two types: rotor radial airflow excitation force and rotor tangential airflow excitation force. The leakage evaluation index is the seal leakage amount.

[0047] The present invention uses a method of solving the Reynolds-averaged equations in a steady state to obtain the aerodynamic excitation force under static eccentricity of the rotor. Among them, the numerical calculations for different seal structures have the same inlet and outlet boundary conditions. Figure 4 The schematic diagram of the static eccentricity of the rotor is given. The static eccentricity of the rotor means that the center C point of the rotor does not coincide with the center O point of the stator, and the rotor whirls around the O point. The seal eccentricity calculation grid is obtained by using the dynamic grid technology to solve the displacement diffusion equation on the basis of the static and dynamic concentric grid. Table 3 gives the parameter settings for the steady-state solution of the RANS equation, where the amplitude of the static and dynamic eccentricity is given as 10% of the seal clearance. By using the static eccentricity model of the rotor, the magnitude of the aerodynamic force acting on the rotor surface by the working medium can be obtained. By projecting the aerodynamic force onto the circumferential and radial directions, the tangential aerodynamic excitation force and the radial aerodynamic excitation force can be obtained. Based on this numerical simulation method, the tangential aerodynamic excitation force and the radial aerodynamic excitation force of the spiral pocket damper seal under various geometric parameter combinations can be finally obtained, that is, the rotor tangential aerodynamic excitation force and the rotor radial aerodynamic excitation force; when the steady-state solution of the static eccentricity model of the rotor is completed, the mass flow rate is extracted at the inlet or outlet, and the seal leakage amount can be obtained.

[0048] Table 3 Calculation method and parameters of the whirl model

[0049] Item Value, attribute Solver ANSYS CFX 18.2 Discrete format High-precision format Solution method Steady numerical method, dynamic mesh technology Turbulence model Standard k-ε turbulence model, improved wall function method Working medium Ideal air Vortex frequency / Hz 0 Eccentric amplitude / mm <![CDATA[δ = 10%C r >

[0050] 3. Parameter optimization with leakage amount and tangential aerodynamic excitation force as the objectives

[0051] For the leakage amount, the positive effects include the number of spiral heads and the number of baffles; the negative effect is the spiral pitch. The leakage amount decreases with the increase of the number of spiral heads and the number of baffles, and increases with the increase of the spiral pitch. Therefore, while increasing the spiral pitch, it is necessary to increase the number of spiral heads and the number of baffles to maintain the stability of the leakage amount. A geometric parameter interval with a leakage amount not greater than that of the original seal structure can be found through the Isight post-processing. If there is no such interval, the selection range of the three geometric parameters should be expanded, and the analysis should be repeated until such an interval is found.

[0052] The tangential aerodynamic excitation force is used as an index to judge the stability of the seal rotor, and the greater the negative tangential aerodynamic excitation force (opposite to the rotation direction of the rotor), the better the stability of the seal rotor. The radial aerodynamic excitation force is used as an index to judge the centering ability of the seal rotor, and the greater the negative tangential aerodynamic excitation force (direction towards the axis), the better the stability of the seal rotor. By bringing the measured tangential aerodynamic excitation force and radial aerodynamic excitation force of 15 spiral pocket damper seal structures into the Isight post-processing. The Pareto chart and the main effect chart based on the tangential aerodynamic excitation force and the radial aerodynamic excitation force can be obtained. Select appropriate numbers of spiral heads, spiral pitches, and baffles within the parameter interval screened by the leakage amount before.

[0053] The specific means of this step can be as follows:

[0054] S31. Normalize the value ranges of the three factors to [-1, 1]. Meanwhile, select a performance evaluation index (airflow excitation force or leakage rate), and perform fitting using a quadratic fitting polynomial. Obtain the contribution rate of each test factor to the analyzed performance index from the fitting coefficients in the polynomial. And the change of the response with the factors can be predicted.

[0055] In this embodiment, the normalized factors and any one response can be input into the commercial software Isight for quadratic polynomial fitting. Through the post-processing of the DOE test method, Pareto charts or main effect charts of the axial baffle number, spiral pitch, and spiral head number on the leakage rate, tangential airflow excitation force, or radial airflow excitation force can be obtained, thereby obtaining the contribution rate of each test factor to the analyzed performance index; here, the response is the leakage rate, tangential airflow excitation force, and radial airflow excitation force obtained by numerical calculation.

[0056] S32. Select the spiral pocket damper seal structures with leakage rates not increased relative to the original structure among different combinations, and select the scheme with better stability from them. Specifically, obtain the geometric parameter intervals with leakage rates not greater than that of the original seal structure, and select the parameter combination scheme with better stability from them.

[0057] In one embodiment, a comparison of the tangential airflow excitation force and radial airflow excitation force between the labyrinth seal and the spiral pocket damper seal was carried out. Refer to Figure 5 . The boundary conditions are: inlet total pressure 3.0 bar, total temperature 20 °C; outlet static pressure 1.0 bar, rotational speed 9000 rpm; inlet pre-whirl ratio 0.13. The spiral pocket damper seal is designed by the method of the present invention, with the selected number of baffles being 8, the spiral pitch being 65.0 mm, and the number of spiral heads being 12. The two seals have the same leakage rate, that is, 0.0396 kg / s. Among them, the tangential airflow excitation force is positive in the rotor rotation direction, and the radial airflow excitation force is positive in the radius increasing direction. In terms of the radial force, the new spiral pocket damper seal is reduced from 0.72 N of the labyrinth seal to -21.02 N, and the rotor centering ability is significantly improved. In terms of the tangential force, the new spiral pocket damper seal is reduced from -3.54 N of the labyrinth seal to -17.94 N, and the rotor stability is significantly enhanced.

Claims

1. A design method for a spiral bag-type damping seal, characterized in that It includes the following steps: S1. Select a straight-through labyrinth seal located on the stator surface and obtain its geometric parameters. The geometric parameters include the number of teeth, seal clearance, seal tooth width, chamber length, and depth. S2. In the seal structure, change all the seal teeth except the first and the last seal teeth into helical teeth with a direction opposite to the rotation direction of the rotor, and add axial baffles to the seal. S3. Select three key geometric parameters, namely the number of helical tooth heads, helical pitch, and the number of axial baffles, as test factors. Given the value ranges to be analyzed for each parameter, and evenly select 5 values within the value ranges of each parameter. S4. Generate a three-factor five-level coding table based on the parameter test of the central composite design method. Each item in the coding table gives a set of geometric parameter combinations of the number of helical tooth heads, helical pitch, and the number of axial baffles. S5. Under the rated working conditions, use the numerical simulation method of solving the steady-state RANS equation to obtain the performance evaluation indexes of each seal structure. The performance evaluation indexes include the stability evaluation index and the leakage evaluation index. The stability evaluation index is the air flow excitation force, and the leakage evaluation index is the seal leakage amount. The air flow excitation force includes the rotor radial air flow excitation force and the rotor tangential air flow excitation force. S6. Normalize the value ranges of the three test factors to [-1, 1]. At the same time, select a performance evaluation index and use a quadratic fitting polynomial for fitting. Obtain the contribution rate of each test factor to the analyzed performance index from the fitting coefficients in the polynomial. S7. Select the helical pocket damper seal structures in different combinations where the seal leakage amount does not increase compared with the original structure, and select the scheme with better stability from them.

2. The spiral bag-type damping seal design method according to claim 1, characterized in that, In S2, the axial baffles are parallel to the axis of the seal chamber, are located in the seal chamber and penetrate through the seal inlet and outlet. The number of the axial baffles is set to an even number greater than 2 and is evenly distributed circumferentially.

3. The spiral bag-shaped damping seal design method according to claim 1, characterized in that, In S3, the selected helical teeth are connected to the front and rear straight seal teeth and pass through at least one axial baffle.

4. The spiral bag-shaped damping seal design method according to claim 1, characterized in that In S3, the value range to be analyzed for the number of helical tooth heads is greater than 1, the value range to be analyzed for the helical pitch is greater than 0° and less than 90°, and the value range to be analyzed for the number of axial baffles is an even number greater than 2.

5. The spiral bag-type damping seal design method according to claim 1, characterized in that In S4, based on the central composite design method, the coding table generates 15 test schemes in total, including 8 full-factor experimental schemes, 1 central point experimental scheme, and 6 axial point experimental schemes.

6. The spiral bag-type damping seal design method according to claim 1, characterized in that, In S5, use the numerical simulation method of solving the steady-state rotor static eccentricity model to obtain the tangential air flow excitation force and the radial air flow excitation force of the helical pocket damper seal under each geometric parameter combination, that is, the rotor tangential air flow excitation force and the rotor radial air flow excitation force. When the calculation of solving the steady-state rotor static eccentricity model is completed, extract the mass flow rate at the inlet or outlet, and then obtain the seal leakage amount.

7. The spiral bag-type damping seal design method according to claim 1, characterized in that In S6, input the normalized factors and any one response into the commercial software Isight for quadratic polynomial fitting, obtain the Pareto chart and the main effect chart, so as to obtain the contribution rate of each test factor to the analyzed performance index. The response is the leakage amount, tangential air flow excitation force, and radial air flow excitation force obtained by numerical calculation.

8. The spiral bag-type damping seal design method according to claim 1, characterized in that, The S7 obtains the geometric parameter interval with the leakage not greater than that of the original sealing structure, and selects the parameter combination scheme with better stability from it.

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