CN111832126A - Low-pressure cylinder last-stage blade static stress analysis method - Google Patents
Low-pressure cylinder last-stage blade static stress analysis method Download PDFInfo
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Abstract
The invention relates to a static stress analysis method for a last-stage blade of a low-pressure cylinder, which comprises the following steps: step 1, obtaining calculation parameters of a last-stage blade; the calculation parameters comprise the height, the shape, the number, the working speed, the working temperature, the blade material, the lacing material, the pin material and the rotor material of the last-stage blade; step 2, establishing a calculation model according to calculation parameters, simulating whole-circle assembly by adopting a circular symmetry algorithm, and taking a blade shroud, a lacing wire, a pin and a rotor as a circular symmetry body; step 3, setting boundary conditions and loads of the calculation model; and 4, carrying out finite element static stress analysis on the blade based on the calculation model to obtain a blade stress result. The invention analyzes the static stress of the last-stage blade, so that the blade meets the design requirement and the safe and stable operation of the unit is ensured.
Description
Technical Field
The invention belongs to the technical field of thermal power generation, and particularly relates to a static stress analysis method for a last-stage blade of a low-pressure cylinder.
Background
In order to respond to national industrial policies, deep peak regulation of thermal power units is imperative, the conventional thermal power plant usually operates in a mode of fixing the power by heat in winter, the peak regulation capability is limited by heat load, and the problem is solved by applying a thermoelectric decoupling technology which is characterized in that the blades of a low-pressure cylinder safely operate under small volume flow by cutting off the steam inlet of the low-pressure cylinder of a steam turbine in a heat supply state, so that the aim of generating electricity and heating for residents and civilians is achieved. The last tertiary blade of unit after the low pressure jar excision is reformed transform is long-time operation under the low-load operating mode, cuts jar back to low pressure and does not have a lot of risks to last tertiary blade safe operation.
At first, when a low-pressure cylinder of a power plant is cut and transformed, in order to prevent the dynamic stress of a low-pressure last-stage blade from rising under the working condition of small volume flow, the blade is damaged, so that the volume flow of exhausted steam of the low-pressure cylinder needs to be limited, and the dynamic stress in a volume flow interval needs to meet the design requirements on strength and vibration when the blade runs for a long time.
When the last blade of the steam turbine is in small volume flow, the flow field of the blade changes, the thermal parameters of the blade along the blade height are redistributed, the steam flow is separated from the root of the moving blade and the top area of the outlet of the stationary blade cascade to form a backflow vortex area, only a small part of effective area of the whole steam passage passes through the steam flow, the volume flow is smaller, the vortex area is larger, and the relative height of separation is larger.
Secondly, the temperature of the blade after the low-pressure cutting cylinder is increased to more than 200 ℃, the elastic modulus of the material of the last-stage blade and the yield limit of the material are changed, the temperature of the power plant after the low-pressure cutting cylinder is increased, and the last-stage blade has the following risks. If the temperature is not controlled, the dynamic and static rubbing of the machine set is also one of the problems.
Thirdly, after the temperature of the blade rises, the rigidity of the blade changes, so that the whole-circle frequency of the last three-stage blade changes, and when the field temperature is higher than 200 ℃, the whole-circle frequency of the last three-stage blade has certain safety risk. Thirdly, after the temperature of the blade rises, the blade expands, which easily causes the problems of bearing elevation change, dynamic and static rubbing and the like.
Finally, after cylinder cutting at low pressure, the last three stages of blades operate for a long time under a low-load working condition, at the moment, water drops carried in the shedding flow at the root of the blades and the vortex steam flow at the tops of the blades scour the blades along with the steam backflow, so that the root and the top of the last stage of blades enter and exit steam edges to cause water erosion, for the last stage of blades, after cylinder cutting, air blast generates a large amount of heat, the temperature of the last stage of blades is obviously improved, and the water erosion of the blade tops under normal working conditions can be; however, the low-pressure last-stage blade root flows back obviously under the action of the vortex due to flow separation, and even part of the water is carried to erode the steam outlet edge of the last-stage blade root; in recent years, due to frequent peak regulation of a unit, the phenomenon of water erosion of the steam edge at the root of the last-stage blade is relatively common; the long-term operation can bring serious potential safety hazard.
Disclosure of Invention
The invention aims to provide a static stress analysis method for a last-stage blade of a low-pressure cylinder, which is used for carrying out static stress analysis on the last-stage blade, so that the blade meets the design requirement and the safe and stable operation of a unit is ensured.
The invention provides a static stress analysis method for a last-stage blade of a low-pressure cylinder, which comprises the following steps:
step 1, obtaining calculation parameters of a last-stage blade; the calculation parameters comprise the height, the shape, the number, the working speed, the working temperature, the blade material, the lacing material, the pin material and the rotor material of the last-stage blade;
step 2, establishing a calculation model according to calculation parameters, simulating whole-circle assembly by adopting a circular symmetry algorithm, and taking a blade shroud, a lacing wire, a pin and a rotor as a circular symmetry body;
step 3, setting boundary conditions and loads of the calculation model;
and 4, carrying out finite element static stress analysis on the blade based on the calculation model to obtain a blade stress result.
Further, the step 3 comprises:
setting contact constraints between the blade shroud band and the shroud band, between the lacing wire and the lacing wire hole, between the blade root and the blade root, between the blade root and the wheel groove, between the pin and the blade root, between the pin and the wheel groove, and taking the friction coefficient as 0.2;
under the column coordinate, the radial constraint U1 is applied to the bottom of the center of the rotor to be 0, and the axial constraint U2 and the circumferential constraint U3 are applied to the two end faces of the rotor to be 0;
the blade is subjected to centrifugal force, a region to which a load is applied is selected, the entire calculation model is given a rotation axis, and a rotation angular velocity of 3000 revolutions is given.
By means of the scheme, the static stress analysis is carried out on the last-stage blade through the static stress analysis method of the last-stage blade of the low-pressure cylinder, so that the blade meets the design requirement, and the safe and stable operation of a unit is guaranteed.
The foregoing is a summary of the present invention, and in order to provide a clear understanding of the technical means of the present invention and to be implemented in accordance with the present specification, the following is a detailed description of the preferred embodiments of the present invention.
Detailed Description
The following examples are given to further illustrate the embodiments of the present invention. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
The embodiment provides a static stress analysis method for a last-stage blade of a low-pressure cylinder, which comprises the following steps:
step 1, calculating and analyzing dynamic and static stress and mode of a final-stage blade under different loads and elongation at different temperatures by CFD simulation;
and 2, judging whether the blades meet the design requirements or not according to the calculation and analysis results, and ensuring the safe and stable operation of the final stage minimum flow of the low-pressure cylinder of the unit by enabling the blades to meet the design requirements.
By the method for analyzing the static stress of the last-stage blade of the low-pressure cylinder, CFD fluid numerical calculation is performed on the last-stage blade, and the dynamic and static stress and the blade mode of the last-stage blade are analyzed, so that the blade meets the design requirements, and the safe and stable operation of a unit can be guaranteed.
In this embodiment, step 1 includes:
analyzing the flow change condition of the last stage blade under the conditions of a rated working condition, an exhaust pressure of 4.9KPa, a flow rate of 30t/h, an exhaust pressure of 2.2KPa and a flow rate of 40 t/h;
carrying out finite element analysis on the last-stage blade, establishing a full-circle blade model, carrying out static analysis, modal analysis and dynamic stress analysis on the last-stage blade, and checking the safety of the last-stage blade by taking the dynamic stress as a main checking index;
and analyzing the change of the elongation of the blade at the working temperature of 100 ℃, 150 ℃ and 200 ℃ according to the calculation result of the elongation of the final stage blade.
The present invention is described in further detail below.
The embodiment carries out CFD fluid numerical value to final stage blade and calculates, carries out the analysis to final stage blade dynamic and static stress and blade mode, makes the blade satisfy the design requirement, guarantees the unit safety and stability operation. The method specifically comprises the following steps:
fluid calculation at different loads of last stage blade
1. Mesh partitioning
The grid of the static blades and the movable blades adopts an ATM Optimized topological structure, the orthogonality of the ATM Optimized topological structure grid is good, the maximum included angle and the minimum included angle are between 130 degrees and 50 degrees, the ATM Optimized topological structure grid is easy to adjust, the information such as vortex state, position and the like under the simulated working condition can be accurately captured, the specific height of each stage of low-pressure movable and static blades is comprehensively considered, and the number of grid nodes in a calculation domain where each blade is located is about 45 thousands.
2. Boundary condition
In the embodiment, a total energy equation is adopted in numerical calculation, an SST model equation is adopted in a turbulence model, and a high-order precision windward difference format is adopted. In the selection of the differential format, the first-order precision windward differential format has faster convergence, but has poorer precision when the convection is severe; the second-order precision windward difference format has high precision when convection is severe, but has slower convergence. And a high-precision difference grid mode is adopted, a first-order precision windward format is adopted in a region with weak convection strength, and a second-order precision windward format is adopted in a region with strong convection, so that the calculation precision is ensured, and the calculation time is reduced. According to the heat providing relevant data and the practical solving requirement, under different flow conditions, the total temperature and the total pressure are given to the inlet boundary condition, and the static pressure is given to the outlet boundary. In order to accurately predict the separation amount of the fluid under the negative pressure gradient, the turbulence model is selected as an SST model.
3. Grid independence verification
In order to accurately simulate the pneumatic characteristics under different working conditions, the grid number should be increased as much as possible theoretically, the difference equation is changed into a differential mode, and the numerical solution is more accurate. In fact, due to the limitation of computer conditions, an infinite number of grids cannot be divided, and only a proper number of grids can be adopted for different problems. In the numerical simulation of the engineering problem, when the grid number is increased to a certain value, the grid number is increased, the change of the calculation result is smaller and smaller, and even unchanged, and at this time, the grid number slightly larger than the certain value is selected to perform the numerical simulation on the actual working condition, so that the calculation time and the calculation resources are saved. In this embodiment, the static and dynamic leaf calculation domain is divided into 10 ten thousand, 20 ten thousand, 25 ten thousand, 30 ten thousand, 40 ten thousand, 60 ten thousand and 95 ten thousand grids respectively, numerical simulation calculation is performed, and the grid independence is verified by using the total pressure difference value of the inlet and the outlet as a reference value. Under the condition of ensuring the accuracy of the calculation result, in order to save calculation resources and improve calculation efficiency, the static and dynamic leaf flow calculation domain takes about 45 ten thousand grids.
4. Pneumatic computing
For each given flow, a fluid calculation is performed. And performing fluid calculation on a rated working condition, a back pressure working condition of 2.2KPa \40t/h flow, a back pressure working condition of 2.2KPa \30t/h flow and a back pressure working condition of 4.9KPa \30t/h flow to obtain a calculation result.
The following conclusion is obtained through carrying out numerical simulation on the rated working condition of the blade and analyzing the calculation result:
1. the numerical simulation result proves that under the rated working condition, a slight positive attack angle exists at the small steam inlet circle, the streamline is smoothly and stably transited from the inlet to the outlet, and no obvious flow separation phenomenon occurs on the inner suction surface.
2. The gas flows in the movable blade channel stably, the speed reaches the maximum at the throat position of the channel, and then the gas starts to flow in a counter-pressure mode. No significant flow separation occurred due to the short backpressure section.
3. Under the rated working condition, the limit streamlines of most areas of the surfaces of the moving blades are nearly parallel, and two-dimensional flow is presented. The three-dimensional flow behavior is only manifested at local locations.
When the back pressure is 4.9KPa and the flow rate is 30t/h, the final-stage moving blade is in a low-flow high-back pressure, flow separation is easy to form at this time, and a backflow phenomenon is easy to cause. Swirl occurs in most of the vane passage and is greatest in the middle of the vane; high-speed vortex exists in the blade grid channel, particularly near the middle section, so that the efficiency of the blade is greatly reduced on one hand, and the energy of gas is dissipated on the other hand; the rotor blade pressure surface limiting streamlines are no longer nearly parallel in most areas, and most areas are intermingled.
When the back pressure is 2.2Kpa and the flow rate is 40t/h, the flow rate is smaller relative to the rated working condition, and the positive attack angle is reduced to a certain extent. But near the top section, the pressure surfaces of the blades are slightly separated; the flow rate is smaller relative to the rated working condition, and the positive attack angle is reduced to a certain extent. But near the top section, the pressure surfaces of the blades are slightly separated; compared with the rated working condition, the maximum speed position of the gas moves forwards in the movable blade channel under the working condition of 40t/h, so that the gas flows in a longer counter-pressure section, and the gas separation of the blades is promoted under the condition; the extreme streamlines are positioned close to parallel to each other except at local locations, which indicates that the flow of boundary layers on the pressure surface is two-dimensional. In most of the blade span, the limiting flow directions are basically parallel and two-dimensional flow is presented, but in an end region surrounded by the intersection line of the channel vortex three-dimensional separation line and the suction surface and the end wall, the behavior of the limiting flow line shows that the end region flow has three-dimensionality.
When the back pressure is 2.2Kpa and the flow rate is 30t/h, the flow rate is smaller relative to the rated working condition, and the positive attack angle is reduced to a certain extent. But above the middle section, the pressure surface of the blade has greater separation than the working conditions of 2.2Kpa and 40 t/h; the maximum Mach number is 2.2Kpa, the working condition of 40t/h is advanced, so that the counter pressure section under the working condition is longer, and the promotion effect on the gas separation on the surface of the blade is realized; the limit streamline of the pressure surface of the moving blade is no longer nearly parallel in most areas and is worse than the flow of the working condition of 2.2Kpa and 40 t/h.
The working conditions of THA, back pressure 2.2KPa, 40t/h, back pressure 2.2KPa, 30t/h, back pressure 4.9KPa, 30t/h are sequentially obtained by pneumatic calculation of the blades under 4 working conditions. As the flow rate decreases, the degree of the blade surface gas detachment from the surface increases and the flow in the blade channel deteriorates.
As the back pressure of the working points of 40t/h and 30t/h is reduced to 2.2KPa, the flow is only small, the high back pressure is not reached to cause the gas backflow of the channel, the vortex phenomenon does not occur on the blades, and the streamline is smoothly and stably transited from the inlet to the outlet. At 4.9KPa and 30t/h, a low flow and high back pressure are achieved, the gas in the channel is separated by flow separation obviously, the vortex is mixed at the part of almost the whole blade height, the gas flow is seriously deteriorated, and the blast effect is caused.
Last stage blade static stress analysis
1. Calculating parameters
The height of the last-stage blade is 668mm, the last-stage blade is provided with a shroud ring, a perforated lacing wire and a forked blade root, the number of the blades is 106, the working speed is 3000r/min, the working temperature is 44.63 ℃, the blade material is 2Cr13, the lacing wire material is 1Cr12, the pin material is 25Cr2MoVA, and the rotor material is 30Cr2Ni4 MoV.
2. Calculation model
The calculation model selects blades, lacing wires, pins and rotor wheel grooves, adopts a circular symmetry algorithm to simulate whole-circle assembly, and takes blade shroud rings, lacing wires, pins and rotors as circular symmetry bodies. The computational model grid application software ANSA is divided by adopting a volume grid with a hexahedron as a main part, a small number of tetrahedral grids are adopted in a local transition region, the number of grid units is 136943, and the number of grid nodes is 156365.
3. Boundary conditions and loads
The calculation model takes the shroud band, the lacing wire, the pin and the wheel groove to be circularly symmetrical, the whole circle assembly of the blade is simulated, the contact constraint is set between the shroud band and the shroud band, between the lacing wire and the lacing wire hole, between the blade root and the blade root, between the blade root and the wheel groove, between the pin and the blade root, and between the pin and the wheel groove, and the friction coefficient is 0.2. Under the column coordinate, the radial constraint U1 is applied to the bottom of the center of the rotor to be 0, and the axial constraint U2 and the circumferential constraint U3 are applied to the two end faces of the rotor to be 0. The application of centrifugal force to the blade can directly utilize the related functions of a loading module in ABAQUS, the area of applied load is selected, the whole model is provided with a rotating shaft, and the rotating angular speed of 3000 turns is given.
4. Analysis result of static stress of blade
And analyzing the static stress of the blade to obtain a blade stress result, wherein the peak stress/allowable value of the blade is 0.68 at the position of a pin hole of the blade root, the peak stress/allowable value of the wheel groove is 0.68 at the position of the pin hole of the wheel groove, and the peak stress/allowable value of the wheel groove is 0.68.
And analyzing the finite element static stress of the blade to obtain a blade stress result, wherein the blade static stress meets the design requirement according to the allowable stress of the material and the blade static stress assessment criterion, and can be obtained according to the peak stress/allowable value of the blade, and the blade static stress meets the working condition of cutting the cylinder in the low-pressure cylinder.
Last stage blade modal analysis
On the basis of static stress analysis, modal analysis steps are added, the whole-circle dynamic frequency of the blade is analyzed and calculated by using a Lanczos iteration method, and dynamic frequency changes of the blade at different temperatures are analyzed by combining with dynamic frequency test values.
The method comprises the steps that the dynamic frequency of a final-stage blade is measured in a whole circle mode, the blade is a frequency-modulated blade, the dynamic frequency of the blade is measured in the design process, test data exist below the rotating speed of 3000rpm, no test data exist above the rotating speed of 3000rpm due to the fact that a resonance point is far away from the working rotating speed, the dynamic frequency change of the blade at different temperatures is analyzed, the resonance point above 3000rpm is calculated through finite element supplement to be in the order of 1M 3, and the whole circle dynamic frequency of the blade at different temperatures is analyzed.
The blade resonance rotating speed can be obtained according to the final-stage blade full-circle dynamic frequency test value, the blade has no resonance point between the rotating speeds of 2820-3090, and the blade resonance rotating speed does not enter the range of 2820-3090 from the rated temperature of 44.6 ℃ to 250 ℃, so that the full-circle blade resonance rotating speed meets the design requirement within the temperature of 250 ℃.
Dynamic stress analysis of final stage blade under different loads
And on the basis of modal calculation, the aerodynamic force of the surface of the blade obtained by full three-dimensional pneumatic calculation is used as an exciting force and is loaded on a blade structure, and the dynamic stress of the blade under different loads is calculated. And (3) the blade surface pressure result after fluid calculation is subjected to fluid-solid coupling, the blade fluid surface pressure is accurately mapped to the blade structure surface, and the mapped structure surface pressure data are well matched.
According to the dynamic stress calculation result and the vibration-resistant intensity curve of the blade, the dynamic stress of the blade under the rated working condition, the 2.2KPa working condition and the 40t/h working condition is obtained to meet the design requirement, the dynamic stress of the blade under the 4.9KPa working condition, the 30t/h working condition, the 2.2KPa working condition and the 30t/h working condition exceeds the vibration-resistant intensity of the blade, the maximum value of the dynamic stress of the blade under the four working conditions is on the steam outlet side of the blade profile root of the blade, and the allowable value of the vibration-resistant intensity of the blade is lower because the peak stress of the static stress of the blade is also on the steam outlet side of the blade.
According to the dynamic stress relation line of the blade load back pressure, the dynamic stress curve of the blade of the unit under small volume flow and high back pressure is larger when the back pressure of the blade is higher, so that the dynamic stress of the blade can be reduced by reducing the back pressure of the blade at proper volume flow for the unit.
Elongation analysis of last stage blade at different temperatures
The elongation of the blade at different temperatures is calculated to prevent the blade from dynamic and static rubbing after the temperature of the unit is increased, and the detailed calculation results are shown in the following table 1.
TABLE 1 calculation of blade elongation at different temperatures
According to the blade elongation calculation result, the elongation of the blade at different temperatures can be obtained, and the blade steam seal can be adjusted according to the actual situation of the unit site to prevent the blade from being rubbed and rubbed.
According to the invention, CFD numerical simulation is carried out on the last-stage blade, three-dimensional flow lines of the last stage under different working conditions are obtained through pneumatic calculation of the blades under 4 working conditions, the THA working conditions, the back pressure 2.2KPa, the back pressure 40t/h working conditions, the back pressure 2.2KPa, the back pressure 30t/h, the back pressure 4.9KPa and the back pressure 30t/h working conditions are sequentially carried out, along with the continuous reduction of flow, the degree of separation of gas on the surface of the movable blade from the surface is gradually increased, and the flow in the movable blade channel is continuously deteriorated. As the back pressure of the working points of 40t/h and 30t/h is reduced to 2.2KPa, the flow is only small, the high back pressure is not reached to cause the gas backflow of the channel, the vortex phenomenon does not occur on the blades, and the streamline is smoothly and stably transited from the inlet to the outlet. At 4.9KPa and 30t/h, a low flow and high back pressure are achieved, the gas in the channel is separated by defluidization, and the vortex is mixed in almost the whole blade height part and causes the blast effect.
And obtaining a blade stress result by analyzing finite element static stress of the blade, wherein the blade static stress meets the design requirement according to the allowable stress of the material and the blade static stress assessment criterion, and can be obtained according to the blade peak stress/allowable value allowance, and the blade static stress meets the working condition of cutting the cylinder of the low-pressure cylinder.
The blade resonance rotating speed can be obtained according to the final-stage blade full-circle dynamic frequency test value, the blade has no resonance point between the rotating speeds of 2820-3090, and the blade resonance rotating speed does not enter the range of 2820-3090 from the rated temperature of 44.6 ℃ to 250 ℃, so that the full-circle blade resonance rotating speed meets the design requirement within the temperature of 250 ℃.
According to the dynamic stress calculation result and the vibration-resistant intensity curve of the blade, the dynamic stress of the blade under the rated working condition, the 2.2KPa working condition and the 40t/h working condition is obtained to meet the design requirement, the dynamic stress of the blade under the 4.9KPa working condition, the 30t/h working condition, the 2.2KPa working condition and the 30t/h working condition exceeds the vibration-resistant intensity of the blade, the maximum value of the dynamic stress of the blade under the four working conditions is on the steam outlet side of the blade profile root of the blade, and the allowable value of the vibration-resistant intensity of the blade is lower because the peak stress of the static stress of the blade is also on the steam outlet side of the blade.
According to the blade elongation calculation result, the elongation of the blade at different temperatures is obtained, and the blade steam seal can be adjusted according to the actual situation on site to prevent the blade from dynamic and static rubbing.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (2)
1. A static stress analysis method for a last-stage blade of a low-pressure cylinder is characterized by comprising the following steps:
step 1, obtaining calculation parameters of a last-stage blade; the calculation parameters comprise the height, the shape, the number, the working speed, the working temperature, the blade material, the lacing material, the pin material and the rotor material of the last-stage blade;
step 2, establishing a calculation model according to calculation parameters, simulating whole-circle assembly by adopting a circular symmetry algorithm, and taking a blade shroud, a lacing wire, a pin and a rotor as a circular symmetry body;
step 3, setting boundary conditions and loads of the calculation model;
and 4, carrying out finite element static stress analysis on the blade based on the calculation model to obtain a blade stress result.
2. The method for analyzing the static stress of the last stage blade of the low-pressure cylinder according to claim 1, wherein the step 3 comprises:
setting contact constraints between the blade shroud band and the shroud band, between the lacing wire and the lacing wire hole, between the blade root and the blade root, between the blade root and the wheel groove, between the pin and the blade root, between the pin and the wheel groove, and taking the friction coefficient as 0.2;
under the column coordinate, the radial constraint U1 is applied to the bottom of the center of the rotor to be 0, and the axial constraint U2 and the circumferential constraint U3 are applied to the two end faces of the rotor to be 0;
the blade is subjected to centrifugal force, a region to which a load is applied is selected, the entire calculation model is given a rotation axis, and a rotation angular velocity of 3000 revolutions is given.
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Cited By (2)
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| CN112699505A (en) * | 2020-12-28 | 2021-04-23 | 哈尔滨汽轮机厂有限责任公司 | Dynamic stress finite element calculation method for long blade of low-pressure cylinder of nuclear power unit |
| WO2024066170A1 (en) * | 2022-09-29 | 2024-04-04 | 哈电发电设备国家工程研究中心有限公司 | Three-dimensional calculation system and calculation method for blade dynamic stress of steam turbine under ultra-low load |
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