Design method of inclined-plane thrust tilting pad for reversing gas turbine

Abstract

The invention provides a design method of an inclined-plane thrust tilting pad for a reversing gas turbine. The design method comprises the following steps that S1, bearing design input is given; s2, determining the number z of tiles; s3, determining an inclined plane angle alpha and a plane angle beta of the tile; s4, the slope height size h of the tile slope is determined; s5, verifying the average specific pressure of the inclined-plane thrust tilting pad of the reversing gas turbine; s6, for the oblique-plane thrust tilting pad bearing of the reversing gas turbine, calculating the key parameters of the bearing bush, the oil film gap, the oil film temperature, the lubricating oil amount, the specific pressure and other parameters by adopting ANSYS, a self-programming fluid calculation program or commercial bearing software, and adjusting the number of the pads, the wrap angle and the lubricating oil amount when the design requirements are not met; and the key parameters meet the design requirements. The method is high in applicability, clear in design process and high in guidance, and the efficiency of the oil supply device for the sliding bearing tile of the gas turbine capable of reversing is greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of gas turbines and aero engines, and in particular relates to a design method of an oblique-plane thrust tilting pad for a reversible gas turbine. Background Art

[0002] Compared with rolling bearings, sliding bearings are more suitable for working environments with large thrust loads and high speeds; and sliding bearings are less sensitive to damage from water, dust and impurities; sliding bearings tend to wear gradually and have a long service life. Even if the sliding bearing fails, the machine can continue to work for a period of time to avoid accidents caused by sudden shutdowns. The manufacturing accuracy, difficulty and cost of sliding bearings are all superior to rolling bearings. In theory, sliding bearings are more suitable for the high-speed and high-thrust working environment of gas turbines. However, there are few sliding bearings in gas turbines at home and abroad. This is mainly based on the following reasons: on the one hand, the structure of gas turbines is very compact and the working temperature is extremely high. The working temperature environment in the bearing area is very harsh, and sliding bearings are easily damaged at high temperatures; on the other hand, gas turbines are used on ships, and the working load environment is harsh. They are often affected by ocean waves, resulting in complex operating environments such as pitch, roll, bow swing, sway, sway, heave, etc., which make the bearings bear complex alternating loads and cause them to fail.

[0003] With the continuous expansion of gas turbine demand and the development of gas turbines, the initial temperature of gas turbine power is constantly increasing, and the power is constantly increasing. Therefore, the working temperature of the sliding bearing is constantly increasing, and the load is constantly increasing. The design of the sliding bearing has become one of the bottlenecks in the design of reversible gas turbines. The following problems and difficulties have arisen in the design and application of sliding bearings for reversible gas turbines:

[0004] Question 1: The load of conventional sliding bearings used in steam turbines and various common machines is small, usually not exceeding 10 tons. However, the axial thrust of the turbine rotor of a gas turbine power plant cannot usually be balanced and eliminated inside the machine, so the thrust of the sliding bearing is very large. The thrust of a medium-sized gas turbine is basically in the order of more than 20 tons, or even up to 40 tons. On the other hand, gas turbines have high power and compact structure, and work at high temperatures and high speeds. The working environment of sliding bearings is very harsh, above 100°C, up to 120°C, or even higher. Therefore, the design of sliding bearings in reversible gas turbines is difficult.

[0005] Improvement of existing technology: In the design of gas turbine bearings, mature tilting pad sliding bearings are usually selected in China, and babbitt alloy pads are used. The working temperature of babbitt alloy is usually lower than 80℃, and it will melt and fail when working at 100℃. Improvements have also been made to the pad materials, using materials such as lead bronze to increase the working temperature of the pads.

[0006] One of the deficiencies of the existing technology is that by selecting the common tilting pad sliding bearing forms and structures at home and abroad, the common sliding bearings often wear out in the edge area of ​​the pad under the high temperature, high speed and high thrust of the gas turbine, and gradually extend to the entire pad, resulting in the failure of the bearing. The main reason is that the conventional bearing uses a nozzle or pad to supply oil, and the oil supply area can only cover the middle position of the pad, such as Figure 1 As shown, the edge area often lacks oil, causing wear at the edge.

[0007] The second insufficiency of existing technology improvement: conventional sliding bearings use bus alloy coatings to basically meet the use requirements of conventional mechanical bearings, and lead bronze sliding bearings are rarely used. Lead bronze can theoretically meet the use requirements, but due to the relatively weak development of domestic gas turbines, the application technology of lead bronze is not mature under high temperature, high speed and high thrust load working conditions. The lead bronze tiles used in China will crack on the surface and fall off when the temperature exceeds 120℃.

[0008] Problem 2: The reversible gas turbine rotor not only needs to work at high temperature and high speed, but also requires the rotor to be able to achieve forward and reverse rotation. It is very difficult for the sliding bearing to achieve stable operation under forward and reverse conditions under high load, high speed and high temperature environment. When the sliding bearing is working, due to friction and the viscosity of the lubricating oil, the journal drives the lubricating oil to form a wedge-shaped oil film between the journal and the pad, such as Figure 2 As shown in Figure 1, the rotor axial thrust is transmitted to the pads through the oil film. The oil film pressure distribution along the arc length of the pad surface is shown in Figure 1. Figure 3 As shown, the maximum oil film pressure point is approximately located at 60% of the arc length on the oil inlet side, and the point of action of the resultant force of the oil film is also located near 60% of the arc length on the oil inlet side. For tilting pad sliding bearings, the most ideal state of the pad support point is to coincide with the axial position of the oil film resultant force point on the pad. In this state, the sliding bearing runs most stably; on the contrary, the greater the deviation between the pad support point and the oil film resultant force point in the axial position, the greater the pad deflection during operation, and the more unstable it is. Therefore, under normal circumstances, the fulcrum of the sliding bearing pad is generally located at about 60% of the arc length on the oil inlet side of the pad.

[0009] However, for a rotor that can rotate forward and reverse, if a conventional sliding bearing is used (the fulcrum is located at 60% of the arc length), the rotor can run stably when rotating forward, but when reversing, the effect of the pad is as follows: Figure 4 As shown, the oil film thrust on the pad is far away from the pad fulcrum, and the pad will rotate, which may easily cause the pad to become unstable and cause damage.

[0010] A first improvement method of the prior art: For machines that can rotate forward and reverse, rolling bearings are usually used because the working state of rolling bearings is the same when they work forward and reverse.

[0011] The first disadvantage of the existing technical improvement method is that the bearing capacity of the rolling bearing is too low to meet the large load requirement of the reversible gas turbine.

[0012] Existing technology improvement method 2: For gas turbines that can rotate forward and reverse, the most common method is to set the support point of the sliding bearing pad in the middle of the pad, such as Figure 5 shown.

[0013] The second improvement method of the prior art is insufficient: for a gas turbine that can rotate forward and reverse, the fulcrum of the sliding bearing pad is set in the middle position of the pad, such as Figure 5 As shown, the working state of the pad is roughly the same for forward and reverse rotation. However, the oil film thrust on the pad and the pad fulcrum cannot always be in the same position. When the axial force is small, this bearing can operate normally. However, under large thrust load, the sliding bearing is also very easy to become unstable and cause failure. Summary of the invention

[0014] The object of the present invention is to provide a design method for an inclined-plane thrust tilting pad for a reversible gas turbine.

[0015] A design method for an oblique-plane thrust tilting pad for a reversible gas turbine comprises the following steps:

[0016] S1, given bearing design input;

[0017] S2, determine the number of tiles z;

[0018] S3, determining the slope angle α and plane angle β of the tile;

[0019] S4, determine the slope height h of the tile slope;

[0020] S5, verification of the average specific pressure of the tilting pad of the oblique-plane thrust of the reversible gas turbine;

[0021] S6, for the tilting-plane thrust tilting pad bearing of the reversible gas turbine, ANSYS, self-programmed fluid calculation program or commercial bearing software are used to calculate the key parameters of the bearing, oil film clearance, oil film temperature, lubricating oil quantity, specific pressure and other parameters. If the design requirements are not met, the number of pads, wrap angle and lubricating oil quantity are adjusted to make its key parameters meet the design requirements.

[0022] Furthermore, in S1, the speed n, the maximum axial load t, the lubricating oil grade, the lubricating oil supply temperature, the lubricating oil supply pressure and the maximum flow rate are determined according to the gas turbine design parameters, and the maximum outer diameter D of the bearing is determined according to the space of the gas turbine bearing cavity and the diameter D of the gas turbine shaft. o and minimum inner diameter D i The maximum linear velocity of the tile surface is located at the outer diameter of the tile, and its circumferential velocity must satisfy the following relationship:

[0023] v=πD o n / 60<120m / s (1)

[0024] If the maximum linear velocity of the tile does not meet the above conditions, the outer diameter of the tile should be reduced to satisfy formula (1).

[0025] Furthermore, the S2 defines Determine the number of tiles and select z=8 for the gas turbine sliding bearing.

[0026] Furthermore, the angle θ of a single pad in S3 is 360K / z, K is the wrap angle coefficient, usually 0.75, which is adjusted according to the actual load, and then the pad surface bevel angle α and the pad surface plane angle β are determined according to the working principle of the bearing.

[0027] Furthermore, the total area of ​​a single pad in the pad S5 is S. Regardless of whether the bearing rotates forward or reverse, the effective angle of the area involved in the pad surface is α+β=5θ / 6, the effective area of ​​the pad is S'=5S / 6, and the average pressure ratio of the pad should satisfy P≯7MPa, where

[0028]

[0029] The beneficial effects of the present invention are:

[0030] (1) The present invention is the first in China and abroad to adopt a structural form that combines an inclined-plane thrust bearing and a tilting pad bearing, which improves the stability of the bearing under large loads and high speeds and has unique innovation in structural form.

[0031] (2) The present invention is the first in China and abroad to adopt a double-sided inclined surface structure to ensure that the bearing has high stability in both forward and reverse working conditions.

[0032] (3) The present invention has strong applicability, clear design process, and strong guidance, which greatly improves the efficiency of the reversible gas turbine sliding bearing pad oil supply device. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a map of the area where the prior art tile slots are used for oil supply and the nozzles are not able to supply oil sufficiently;

[0034] Figure 2 It is a schematic diagram of the working principle of the sliding bearing in the prior art;

[0035] Figure 3 It is a distribution diagram of the pressure on the pad surface of the prior art sliding bearing along the length of the pad surface arc;

[0036] Figure 4 This is the working principle diagram of conventional bearing when it is reversed;

[0037] Figure 5 It is a diagram showing the working forward and reverse states of the intermediate support tile in the prior art;

[0038] FIG6( a ) is a schematic diagram A of a tile of the present invention;

[0039] FIG6( b ) is a schematic diagram B of a tile of the present invention;

[0040] FIG6( c ) is a schematic diagram C of a tile of the present invention;

[0041] Figure 7 This is a working principle diagram of the oblique-plane thrust tilting pad of the present invention when it rotates forward;

[0042] Figure 8 This is a working principle diagram of the oblique-plane thrust tilting pad of the present invention when it is reversed;

[0043] Fig. 9 The number of tiles selected according to the present invention is shown in the figure;

[0044] Fig.10 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with the accompanying drawings.

[0046] The present invention adopts a fixed-pad oblique-plane thrust pad structure in the structural design of the pad surface, and an oblique surface is opened on the pad surface as shown in Figure 6 (a, b, c), which has the advantage of high bearing capacity; at the same time, the pad support adopts the structural characteristics of the tilting pad thrust pad, the bearing pad can be rotated and adjusted around the fulcrum, and can be swung and adjusted by adaptive axial force, so that the bearing pad can work stably. Therefore, the bearing has the advantages of stable bearing of the oblique-plane thrust bearing and automatic adjustment of the bearing capacity of the tilting pad sliding bearing, and the rotor is more stable and reliable.

[0047] The tile surface is divided into three areas (I, II, III), such as Figure 7 As shown, the structure form of the double-sided inclined surface (I and III zones), the middle II zone is a plane, and its working principle is as follows:

[0048] First, when the gas turbine rotates forward, the tile surface is slightly tilted, such as Figure 7 As shown (the oil film angle is magnified for illustration), a continuous wedge-shaped oil film is formed in areas Ⅰ and Ⅱ. Due to the existence of the inclined surface in area Ⅲ, the clearance of the lubricating oil through this area increases, and the lubricating oil pressure suddenly decreases, making it impossible to form an effective oil film. Therefore, the pad surface in area Ⅲ does not participate in the work during forward rotation. Therefore, the effective working length of the oil film on the pad surface is L. Although the fulcrum position is located in the middle of the pad (50% L'), the fulcrum is located at 60% L of the effective length of the pad surface, that is, the fulcrum position basically coincides with the position of the resultant force point of the oil film, which can ensure that the pad can work stably under large loads.

[0049] Secondly, when the gas turbine is reversed, the tile surface is slightly tilted, forming a continuous wedge-shaped oil film in the III and II regions, such as Figure 3 As shown (the oil film angle is magnified for illustration), due to the existence of the inclined surface in zone I, the clearance of the lubricating oil through this area increases, the lubricating oil pressure suddenly decreases, and an effective oil film cannot be formed. Therefore, during reversal, the pad surface in zone I does not participate in the work, so the effective working length of the pad surface is L. Although the fulcrum position is located in the middle of the pad (50% L'), the fulcrum is located at 60% L of the effective length of the pad surface, that is, the fulcrum position is basically the same as the position of the resultant force point of the oil film, which can also ensure that the pad can work stably under large loads.

[0050] A design method for an oblique-plane thrust tilting pad for a reversible gas turbine is implemented by the following steps:

[0051] S1: Given bearing design input. Determine the speed n, maximum axial load t, lubricant grade, lubricant supply temperature, lubricant supply pressure and maximum flow rate based on the gas turbine design parameters. Determine the maximum outer diameter D of the bearing based on the space of the gas turbine bearing cavity and the diameter D of the gas turbine shaft. O and minimum inner diameter D i The maximum linear velocity of the tile surface is located at the outer diameter of the tile, and its circumferential velocity must satisfy the following relationship:

[0052] v=πD o n / 60<120m / s. (l)

[0053] If the maximum linear velocity of the tile does not meet the above conditions, the outer diameter of the tile should be reduced to satisfy formula (1).

[0054] S2: Determine the number of pads z. According to the number of pads in the Mechanical Design Manual Sliding Bearings, define according to Fig. 9 Determine the number of tiles. Generally, z=8 is recommended for gas turbine sliding bearings.

[0055] S3: Determine the bevel angle α and plane angle β of the pad. First, determine the angle θ of a single pad in Figure 6 = 360K / z, where K is the wrap coefficient, which is usually recommended to be 0.75 and can be adjusted according to the actual load. Then, determine the bevel angle α and plane angle β of the pad surface based on the working principle of the bearing pad.

[0056] According to the working principle of a reversible gas turbine oblique-plane thrust tilting pad, Figure 7 , Figure 8 As shown, the relationship between the angles of the inclined plane and the flat plane in the tile is as follows:

[0057] 0.5L'=0.6L (2)

[0058] The arc length of the tile is:

[0059] L′=(2α+β)R (3)

[0060] The actual working effective arc length of the tile is:

[0061] L=(α+β)R (4)

[0062] Where R is the tile radius;

[0063] Substituting formula (3) and (4) into formula (2), we can obtain

[0064]

[0065] Simplifying gives:

[0066] 4α=β (6)

[0067] The wrap angle of a single tile is θ, then the following relationship exists:

[0068] 2α+β=θ (7)

[0069] From formula (6) and (7), we can get:

[0070] α=θ / 6 (8)

[0071] β=2θ / 3 (9)

[0072] The angles of the inclined surface and the flat surface on the bearing determined by formulas (8) and (9) can ensure that the point of action of the resultant oil film pressure on the bearing surface coincides with the bearing support point when the bearing rotates forward or reversely, thus ensuring the stability of the bearing under large loads.

[0073] S4: Determine the height h of the inclined surface of the pad. According to the recommended principle of inclined surface dimensions for oblique-plane thrust bearings in the Mechanical Design Manual Sliding Bearings, the height h / h of the inclined surface of the pad in Figure 6 min =3, the oblique-plane thrust bearing has better working performance. Usually, the minimum oil film clearance of the gas turbine bearing under the maximum load should be greater than 10um or the filtration accuracy of the lubricating oil system. For example, if the filtration accuracy of the lubricating oil entering the bearing is 20um, the minimum oil film thickness should be greater than 20um, otherwise impurities will scratch the tiles. The minimum oil film thickness recommended under the maximum load of the gas turbine is h min ≈10~20um, so the slope height size h=30~60um can be obtained.

[0074] S5: Verification of the average specific pressure of the tilting pads of the reversible gas turbine with inclined-plane thrust. The total area of ​​a single pad is S. Regardless of whether the bearing rotates forward or reverse, the effective angle of the area involved in the work of the pad surface is α+β=5θ / 6, so the effective area of ​​the pad is S'=5S / 6, and the average specific pressure of the pad should satisfy P≯7MPa.

[0075]

[0076] S6: For the tilting pad bearing of the reversible gas turbine oblique-plane thrust, use ANSYS, self-programmed fluid calculation program or commercial bearing software to calculate the key parameters of the bearing, such as oil film clearance, oil film temperature, lubricating oil quantity, specific pressure and other parameters. If the design requirements are not met, the number of pads, wrap angle and lubricating oil quantity are adjusted to make the key parameters meet the design requirements.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A design method for an oblique-plane thrust tilting pad for a reversible gas turbine, characterized in that: The following steps are involved: S1, given bearing design input; S2, determine the number of tiles z; S3, determining the slope angle α and plane angle β of the tile; S4, determine the slope height h of the tile slope; S5, verification of the average specific pressure of the tilting pad of the oblique-plane thrust of the reversible gas turbine; S6, for the tilting-plane thrust tilting pad bearing of the reversible gas turbine, ANSYS, self-programmed fluid calculation program or commercial bearing software are used to calculate the key parameters of the bearing, oil film clearance, oil film temperature, lubricating oil quantity, specific pressure and other parameters. If the design requirements are not met, the number of pads, wrap angle and lubricating oil quantity are adjusted to make its key parameters meet the design requirements.

2. The design method of the oblique-plane thrust tilting pad for a reversible gas turbine according to claim 1, characterized in that: In S1, the speed n, the maximum axial load t, the lubricating oil grade, the lubricating oil supply temperature, the lubricating oil supply pressure and the maximum flow rate are determined according to the design parameters of the gas turbine, and the maximum outer diameter D of the bearing is determined according to the space of the gas turbine bearing cavity and the diameter D of the gas turbine shaft. o and minimum inner diameter D i The maximum linear velocity of the tile surface is located at the outer diameter of the tile, and its circumferential velocity must satisfy the following relationship: v=πD o n / 60<120m / s (1) If the maximum linear velocity of the tile does not meet the above conditions, the outer diameter of the tile should be reduced to satisfy formula (1).

3. The design method of the oblique-plane thrust tilting pad for a reversible gas turbine according to claim 1, characterized in that: The S2 is defined Determine the number of tiles and select z=8 for the gas turbine sliding bearing.

4. The design method of the oblique-plane thrust tilting pad for a reversible gas turbine according to claim 1, characterized in that: The angle θ of a single bearing block in S3 is 360K / z, where K is the wrap angle coefficient, usually 0.75, which is adjusted according to the actual load, and then the bearing surface bevel angle α and the bearing surface plane angle β are determined according to the working principle of the bearing.

5. The design method of the oblique-plane thrust tilting pad for a reversible gas turbine according to claim 1, characterized in that: The total area of ​​a single tile in the S5 is S. Regardless of whether the bearing rotates forward or reverse, the effective angle of the area involved in the work of the tile surface is α+β=5θ / 6, the effective area of ​​the tile is S'=5S / 6, and the average specific pressure of the tile should satisfy in

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