CN115510713A - Three-dimensional computing system and method for dynamic stress of ultra-low load blade of steam turbine - Google Patents
Three-dimensional computing system and method for dynamic stress of ultra-low load blade of steam turbine Download PDFInfo
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Abstract
The invention relates to a three-dimensional computing system and a three-dimensional computing method for dynamic stress of an ultra-low load blade of a steam turbine, and belongs to the technical field of dynamic stress prediction of blades. The method solves the problem of blade dynamic stress calculation under the ultra-low load working condition. The device comprises a thermal boundary calculation module, a blade three-dimensional flow field calculation module, a blade finite element calculation module and a blade dynamic stress calculation module; a thermodynamic boundary calculation module: the system is used for obtaining thermal data of flow, total enthalpy and pressure of the inlet and the outlet of the blade and providing a thermal boundary for the calculation of a three-dimensional flow field of the blade; the blade three-dimensional flow field calculation module: the method is used for obtaining the calculation results of the steady-state and transient flow fields of the blade and providing input data for the calculation of the static stress and the dynamic stress of the structural field of the blade; blade finite element calculation module: the method is used for obtaining the calculation results of the static stress and the resonance frequency of the blade and providing input data for the calculation of the dynamic stress of the blade; the blade dynamic stress calculation module: the method is used for obtaining the calculation result of the dynamic stress of the blade and providing data for the dynamic stress assessment module of the blade.
Description
Technical Field
The invention relates to a system and a method for calculating the dynamic stress of an ultra-low load blade of a steam turbine, belonging to the technical field of blade dynamic stress prediction.
Background
The global energy pattern is developing from relying on traditional fossil energy to increasing and popularizing clean and efficient energy. The new energy represented by wind power, photoelectricity and the like is beneficial to carbon reduction, but is easily influenced by factors such as natural environment and the like, and has the properties of obvious fluctuation, intermittence, instability and the like. The practice at home and abroad proves that the new energy is greatly increased, and meanwhile, a flexible, stable and schedulable power supply which is cooperated with the new energy and matched with the new energy needs to be enhanced to be used as a support. The natural energy resources of China determine that safe and reliable coal-fired power stations can play a key role in a long time. According to the principle of 'bottom-in-pocket protection', the key technical problem of overcoming the full-working-condition flexible operation of the main equipment of the power station is imperative.
A large number of technical developments and engineering practices of related enterprises at home and abroad show that the key technology of the full-working-condition flexible operation of the modern large-scale steam turbine is focused on a low-pressure through-flow part, particularly a last-stage long blade, and the development and development level of the key technology is an important mark of comprehensive technical capability. When the unit runs under low load and variable working conditions for a long time, the long blade in the low-pressure module inevitably responds with vortex excitation, so that the dynamic stress of the blade fluctuates, and a high-value area is difficult to determine. The blade dynamic stress test has high test cost and harsh test conditions, is difficult to realize, and is not beneficial to the examination and evaluation of the ultralow load operation safety of the long blade of the steam turbine. Therefore, a blade dynamic stress calculation method suitable for the turbine under the ultralow-load operation condition needs to be provided, and a technical means is provided for blade dynamic stress evaluation.
At present, a three-dimensional simulation calculation and assessment method for dynamic stress of blades in the industry mainly aims at harmonic vibration of the blades, and excitation factors are related to harmonic numbers. For the blade vibration characteristics under an ultra-low load and turbulent flow field, the blade vibration characteristics generally belong to random vibration caused by vortex effect, are irrelevant to harmonic vibration, and are used for calculating the dynamic stress of the blade by starting from the flow field characteristics and extracting and analyzing the excitation force. However, an effective blade dynamic stress calculation method aiming at the ultra-low load working condition is still lacked at present.
Based on the above problems, it is necessary to provide a three-dimensional calculation system and a calculation method thereof for dynamic stress of ultra-low load blades of a steam turbine to solve the above technical problems.
Disclosure of Invention
The invention provides a three-dimensional calculation method for dynamic stress of an ultra-low load blade of a steam turbine, which is researched and developed to solve the problem of calculation of the dynamic stress of the blade under an ultra-low load working condition. The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. It should be understood that this summary is not an exhaustive overview of the invention. It is not intended to determine the key or critical elements of the present invention, nor is it intended to limit the scope of the present invention.
The technical scheme of the invention is as follows:
the dynamic stress three-dimensional calculation system for the ultra-low load blade of the steam turbine comprises a thermal boundary calculation module, a blade three-dimensional flow field calculation module, a blade finite element calculation module and a blade dynamic stress calculation module;
a thermodynamic boundary calculation module: the system is used for obtaining thermal data of flow, total enthalpy and pressure of an inlet and an outlet of the blade and providing a thermal boundary for the calculation of a three-dimensional flow field of the blade;
the blade three-dimensional flow field calculation module: the method is used for obtaining the calculation results of the steady-state and transient flow fields of the blade and providing input data for the calculation of the static stress and the dynamic stress of the structural field of the blade;
the blade three-dimensional flow field calculation module comprises: the device comprises a blade flow field calculation domain modeling module, a steady-state flow field calculation module and a transient flow field calculation module;
blade finite element calculation module: the method is used for obtaining the calculation results of the static stress and the resonance frequency of the blade and providing input data for the calculation of the dynamic stress of the blade;
the blade finite element calculation module comprises: the device comprises a blade structural field calculation domain modeling module, a blade static stress calculation module and a blade resonance frequency calculation module;
the blade dynamic stress calculation module: the method is used for obtaining the calculation result of the dynamic stress of the blade and providing data for the dynamic stress assessment module of the blade.
Preferably: still include the blade dynamic stress examination module: the method is used for evaluating and examining the dynamic stress safety of the blade and guiding the optimal design of the blade.
The three-dimensional calculation method for the dynamic stress of the ultra-low load blade of the steam turbine comprises the following steps:
the method comprises the following steps: calculating a thermal boundary; adopting a thermodynamic boundary calculation module, aiming at a target blade, adopting a thermodynamic calculation program to obtain a blade thermodynamic boundary of the steam turbine under different load conditions, and extracting blade inlet flow, a total enthalpy value, outlet pressure and a temperature value as an input boundary of blade three-dimensional flow field calculation;
step two: calculating a three-dimensional flow field of the blade; adopting a blade three-dimensional flow field calculation module, firstly adopting a blade flow field calculation domain modeling module to carry out blade flow field calculation domain modeling, then adopting a steady-state flow field calculation module to carry out blade flow field steady-state calculation, and finally adopting a transient flow field calculation module to carry out blade flow field transient calculation;
step three: calculating finite elements of the blades; adopting a blade finite element calculation module, firstly adopting a blade structure field calculation domain modeling module to carry out blade structure field calculation domain modeling, then adopting a blade static stress calculation module to carry out blade static stress calculation, and finally adopting a blade resonance frequency calculation module to carry out blade resonance frequency calculation;
step four: and calculating the dynamic stress of the blade by adopting a blade dynamic stress calculation module.
Preferably: the thermal boundary of the blade comprises 5%, 10%, 15%, 20%, 25% and 30% of typical ultra-low load working points.
Preferably: in the second step, modeling of a blade flow field calculation domain: adopting CFD calculation software to establish a blade three-dimensional flow field calculation domain model, carrying out grid division on the blade, wherein the number of grid nodes meets the grid independence requirement, the calculation domain takes a stationary blade inlet as a calculation domain inlet, the inlet flow and the total enthalpy value are given, a moving blade outlet as a calculation domain outlet, and the outlet pressure and the temperature are given; the static blade calculation domain is static, the movable blade calculation domain is rotating, the rotating speed is the working rotating speed of the steam turbine, a cyclic symmetry method is adopted for simulation, and the working medium in the calculation domain adopts water vapor;
blade flow field steady state calculation, adopting a steady state CFD calculation mode to obtain a blade flow field steady state result of a blade thermal boundary, grasping the distribution characteristics of flow field separation and flow separation, taking a steady state CFD calculation result file as an input file of transient flow field calculation, and taking blade surface pressure data calculated by the steady state CFD as an input file of finite element static stress calculation of a structural field;
transient calculation of a blade flow field is carried out, a transient CFD calculation mode is adopted, statistical parameter calculation is carried out on steam pressure on the surface of a blade in the transient calculation process, a blade flow field transient result of a thermal boundary of the blade is obtained, mean square difference values of the steam pressure of all nodes on the surface of the blade are extracted, an excitation force input file of a dynamic stress calculation module is compiled, the format of the excitation force input file is in a csv format, four rows of data are counted, the first three rows are coordinates of the nodes in the x direction, the y direction and the z direction, and the fourth row is the mean square difference value of the steam pressure.
Preferably: in the third step, the leaf structure field calculation domain modeling: establishing a blade structure field model by adopting finite element calculation software, wherein the blade structure field model comprises blades and wheel grooves, the blade roots are connected with the wheel grooves, the blade structure field model is divided into grids, a calculation domain comprises all structural characteristics of the blades, the structural characteristics comprise shroud bands at the end parts of the blades, lacing wires in the middle parts of the blades, blade bodies of the blades and blade roots at the end parts of the blades, and friction contact is arranged between the adjacent shroud bands and between the lacing wires; a friction foundation is arranged between the blade root and the wheel groove, a cyclic symmetry method is adopted for simulation, the wheel groove is fixedly restrained, the rotating speed of the moving blades and the wheel groove is the working rotating speed of the steam turbine, and the action of centrifugal force is simulated;
calculating the static stress of the blade: based on a blade structure field model, taking a blade surface pressure result of blade flow field steady state calculation of a steady state flow field calculation module as a static stress calculation input file, simulating the action of steam force, calculating the static stress of the blade, obtaining the static stress distribution characteristics of the blade, and taking the static stress calculation result as input data of a blade dynamic stress assessment module;
blade resonance frequency calculation: and calculating the resonant frequency of the blade based on the blade structure field model, obtaining the resonant frequency of the blade of the first 2 orders at the working rotating speed of the steam turbine, and taking the resonant frequency result as the input of a blade dynamic stress calculation module.
Preferably: blade structural field computational domain modeling: when the grid division is carried out on the blade structure field model, grids are added at the positions of the movable blade radius, the movable blade steam inlet and outlet radius and the wheel groove radius.
Preferably, the following components: and in the fourth step, based on the blade structure field model, taking the blade surface pressure mean square error calculated by the transient flow field of the transient flow field calculation module as an excitation force input file, taking the resonance frequency corresponding to the resonance mode closest to the working rotating speed calculated by the blade resonance frequency calculation of the blade resonance frequency calculation module as an input file, calculating the dynamic stress of the blade, obtaining the dynamic stress distribution characteristics of the blade, and taking the dynamic stress calculation result as the input data of the dynamic stress assessment module of the blade.
Preferably, the following components: further comprises the following steps: and (4) assessing the dynamic stress of the blade by adopting a blade dynamic stress assessment module.
Preferably: step five, compiling a blade dynamic stress checking table;
the second column of the examination table, namely the leaf height of the leaf, and the unit is mm; the third column of the reference table, "condition", refers to the calculated ultra low load condition point; the assessment positions of the assessment positions given in the examination table are divided into two categories of blade body assessment and blade root assessment, the blade body assessment is divided into an assessment position A and an assessment position B, and the blade root assessment is divided into an assessment position C and an assessment position D;
the allowable value of the dynamic stress given in the examination table refers to the maximum value of the dynamic stress of the blade, which meets the design safety requirement;
the dynamic stress allowable value obtaining process comprises the following steps: based on a GOODMAN test curve of a blade material, static stress data is used as input, the vibration resistance strength of the material is inquired, and a safety coefficient specified by a manufacturer is used as a criterion, and a dynamic stress allowable value is calculated;
the allowable dynamic stress value is calculated by adopting the following formula: the allowable dynamic stress value = vibration resistance intensity/safety factor;
the safety criterion of blade dynamic stress evaluation is as follows: the dynamic stress of the blade body and the blade root at the checking position is less than or equal to a dynamic stress allowable value, and when the checking is unqualified, the blade is optimally designed in a mode of increasing the blade damping and the blade rigidity or improving the blade material grade, so that the dynamic stress checking of the blade is qualified.
The invention has the following beneficial effects:
the method is suitable for the blade vibration characteristics under the ultra-low load and turbulent flow field, generally belongs to random vibration caused by vortex effect, and starts with the flow field characteristics to extract and analyze the exciting force, thereby realizing the calculation of the dynamic stress of the blade.
The method extracts the flow field pulsating pressure as the exciting force and is used for calculating the dynamic stress of the blade.
The invention has verified the effectiveness of the algorithm through a blade dynamic stress test, the deviation between the calculated value and the test value of the invention is about 13.6%, and the engineering application requirements are met.
Drawings
FIG. 1 is a frame diagram of a three-dimensional calculation method for dynamic stress of an ultra-low load blade of a steam turbine;
FIG. 2 is a schematic view of a modeling of a computational domain of a blade flow field;
FIG. 3 shows the calculation results of the steady-state flow field of the blade under low-load conditions (15% for example);
fig. 4 is a schematic view of a blade structure.
In the figure: 1-stationary blade, 2-moving blade, 3-stationary blade inlet, 4-moving blade outlet, 5-wheel groove, 6-blade root, 7-lacing wire and 8-shroud.
Detailed Description
In order that the objects, aspects and advantages of the invention will become more apparent, the invention will be described by way of example only, and with reference to the accompanying drawings. It is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
The connection mentioned in the invention is divided into fixed connection and detachable connection, the fixed connection is non-detachable connection and includes but is not limited to folding edge connection, rivet connection, bonding connection, welding connection and other conventional fixed connection modes, the detachable connection includes but is not limited to threaded connection, snap connection, pin connection, hinge connection and other conventional detachment modes, when the specific connection mode is not clearly limited, at least one connection mode can be found in the existing connection modes by default to realize the function, and the skilled person can select according to the needs. For example: the fixed connection selects welded connection, and the detachable connection selects hinged connection.
The first specific implementation way is as follows: the embodiment is described with reference to fig. 1 to fig. 4, and the turbine ultra-low load blade dynamic stress three-dimensional calculation system of the embodiment includes a thermal boundary calculation module, a blade three-dimensional flow field calculation module, a blade finite element calculation module and a blade dynamic stress calculation module;
a thermodynamic boundary calculation module: the system is used for obtaining thermal data of flow, total enthalpy and pressure of the inlet and the outlet of the blade and providing a thermal boundary for the calculation of a three-dimensional flow field of the blade;
the blade three-dimensional flow field calculation module: the method is used for obtaining the calculation results of the steady-state and transient flow fields of the blade and providing input data for the calculation of the static stress and the dynamic stress of the structural field of the blade;
the blade three-dimensional flow field calculation module comprises: the blade flow field calculation domain modeling module 2.1, the steady-state flow field calculation module 2.2 and the transient flow field calculation module 2.3;
blade finite element calculation module: the method is used for obtaining the calculation results of the static stress and the resonance frequency of the blade and providing input data for the calculation of the dynamic stress of the blade;
the blade finite element calculation module comprises: a blade structure field calculation domain modeling module 3.1, a blade static stress calculation module 3.2 and a blade resonance frequency calculation module 3.3;
the blade dynamic stress calculation module: the dynamic stress assessment module is used for obtaining the dynamic stress calculation result of the blade and providing data for the dynamic stress assessment module of the blade;
the dynamic stress assessment module of the blade is also included: the method is used for evaluating and examining the dynamic stress safety of the blade and guiding the optimal design of the blade.
The second embodiment is as follows: the embodiment is described with reference to fig. 1 to fig. 4, and the method for calculating the dynamic stress of the ultra-low load blade of the steam turbine in the embodiment comprises a thermal boundary calculation module, a blade three-dimensional flow field calculation module, a blade finite element calculation module and a blade dynamic stress calculation module;
a thermodynamic boundary calculation module: the system is used for obtaining thermal data of flow, total enthalpy and pressure of the inlet and the outlet of the blade and providing a thermal boundary for the calculation of a three-dimensional flow field of the blade;
the blade three-dimensional flow field calculation module: the method is used for obtaining the calculation results of the steady-state and transient flow fields of the blade and providing input data for the calculation of the static stress and the dynamic stress of the structural field of the blade;
the blade three-dimensional flow field calculation module comprises: a blade flow field calculation domain modeling module 2.1, a steady-state flow field calculation module 2.2 and a transient flow field calculation module 2.3;
blade finite element calculation module: the method is used for obtaining the calculation results of the static stress and the resonance frequency of the blade and providing input data for the calculation of the dynamic stress of the blade;
the blade finite element calculation module comprises: a blade structure field calculation domain modeling module 3.1, a blade static stress calculation module 3.2 and a blade resonance frequency calculation module 3.3;
the blade dynamic stress calculation module: the dynamic stress assessment module is used for obtaining the dynamic stress calculation result of the blade and providing data for the dynamic stress assessment module of the blade;
the dynamic stress assessment module of the blade is also included: the method is used for evaluating and examining the safety of the dynamic stress of the blade and guiding the optimal design of the blade;
the method comprises the following steps:
the method comprises the following steps: with reference to fig. 1, thermodynamic boundary calculations; adopting a thermodynamic boundary calculation module, aiming at a target blade, adopting a thermodynamic calculation program to obtain a blade thermodynamic boundary of the steam turbine under different load conditions, and extracting blade inlet flow, a total enthalpy value, outlet pressure and a temperature value as an input boundary of blade three-dimensional flow field calculation;
the thermal boundary of the blade comprises typical ultralow-load working points such as 5%, 10%, 15%, 20%, 25%, 30% and the like;
step two: calculating a three-dimensional flow field of the blade; adopting a blade three-dimensional flow field calculation module, firstly adopting a blade flow field calculation domain modeling module 2.1 to carry out blade flow field calculation domain modeling, then adopting a steady-state flow field calculation module 2.2 to carry out blade flow field steady-state calculation, and finally adopting a transient flow field calculation module 2.3 to carry out blade flow field transient calculation;
with reference to fig. 2, in step two, modeling of a blade flow field calculation domain: adopting CFD calculation software to establish a blade three-dimensional flow field calculation domain model, wherein each blade consists of a static blade 1 and a moving blade 2, the static blade 1 is communicated with the moving blade 2, the static blade side is provided with a static blade inlet 3, the moving blade side is provided with a moving blade outlet 4, the blades are divided into grids, the number of grid nodes meets the grid independence requirement, the calculation domain takes the static blade inlet as a calculation domain inlet, the inlet flow and the total enthalpy value are given, the moving blade outlet as a calculation domain outlet, and the outlet pressure and the temperature are given; the static blade calculation domain is static, the movable blade calculation domain is rotating, the rotating speed is the working rotating speed (3000 r/mim) of the steam turbine, a cyclic symmetry method is adopted for simulation, a cyclic symmetry boundary can be automatically generated by CFD calculation software, a working medium in the calculation domain adopts steam, and physical property data of the steam is sourced from an NIST library and can be called by the CFD calculation software;
combining with the figure 3, calculating the steady state of the blade flow field, obtaining the steady state result of the blade flow field of the thermal boundary of the blade by adopting a steady state CFD calculation mode, grasping the distribution characteristics of flow field separation and flow separation, taking a result file of the steady state CFD calculation as an input file of transient flow field calculation, and taking the surface pressure data of the blade calculated by the steady state CFD as an input file of finite element static stress calculation of a structural field;
transient calculation of a blade flow field is carried out, a transient CFD calculation mode is adopted, statistical parameter calculation is carried out on the steam pressure on the surface of a blade in the transient calculation process, the statistical parameters comprise a pressure average value, a mean square difference value, a maximum value and a minimum value in a calculation period, the transient result of the blade flow field of the thermal boundary of the blade is obtained, the mean square difference value of the steam pressure of each node on the surface of the blade is extracted, an excitation force input file of a dynamic stress calculation module is compiled, the format of the excitation force input file is in a csv format, four rows of data are counted, the first three rows are coordinates of the node in the directions of x, y and z, and the fourth row is the mean square difference value of the steam pressure;
with reference to fig. 4, step three: calculating finite elements of the blades; adopting a blade finite element calculation module, firstly adopting a blade structure field calculation domain modeling module 3.1 to carry out blade structure field calculation domain modeling, then adopting a blade static stress calculation module 3.2 to carry out blade static stress calculation, and finally adopting a blade resonance frequency calculation module 3.3 to carry out blade resonance frequency calculation;
in the third step, the leaf structure field calculation domain modeling: establishing a blade structure field model by adopting finite element calculation software, wherein the blade structure field model comprises blades and wheel grooves 5, blade roots 6 are connected with the wheel grooves 5, the blade structure field model is divided into grids, a calculation domain comprises all structural characteristics of the blades, the structural characteristics comprise shroud bands 8 at the end parts of the blades, lacing wires 7 in the middle parts of the blades, blade bodies of the blades and blade roots 6 at the end parts of the blades, frictional contact is arranged between the adjacent shroud bands 8 and between the lacing wires 7, and the friction coefficient is 0.2; a friction foundation is arranged between the blade root 6 and the wheel groove 5, the friction coefficient is 0.25, a cyclic symmetry method is adopted for simulation, the cyclic symmetry boundary is usually a periodic surface of a shroud and the wheel groove, the wheel groove is fixedly restrained, the rotating speed of the moving blade and the wheel groove is the working rotating speed (3000 r/mim) of the steam turbine, the centrifugal force action is simulated, and the materials of the moving blade and the wheel groove are derived from material test data and mainly comprise the elastic modulus, the Poisson ratio and the density;
blade structural field computational domain modeling: when the grid division is carried out on the blade structure field model, grids are added at the positions of the movable blade radius, the movable blade steam inlet and outlet radius and the wheel groove radius, so that the calculation precision is ensured;
calculating the static stress of the blade: based on the blade structure field model, taking a blade surface pressure result of the blade flow field steady-state calculation of the steady-state flow field calculation module 2.2 as a static stress calculation input file, simulating the action of steam force, calculating the static stress of the blade, obtaining the static stress distribution characteristics of the blade, and taking the static stress calculation result as input data of a blade dynamic stress assessment module;
blade resonance frequency calculation: based on a blade structure field model, calculating blade resonance frequency to obtain the blade resonance frequency of the first 2 orders at the working speed (3000 r/mim) of the steam turbine, and taking the resonance frequency result as the input of a blade dynamic stress calculation module;
step four: calculating the dynamic stress of the blade by adopting a blade dynamic stress calculation module;
in the fourth step, based on the blade structure field model, the blade surface pressure mean square error calculated by the transient flow field of the transient flow field calculation module 2.3 is used as an excitation force input file, the resonance frequency corresponding to the resonance mode closest to the working rotating speed (3000 r/min) calculated by the blade resonance frequency of the blade resonance frequency calculation module 3.3 is used as an input file, the dynamic stress of the blade is calculated, the dynamic stress distribution characteristics of the blade are obtained, and the dynamic stress calculation result is used as the input data of the dynamic stress assessment module of the blade;
further comprises the following steps: the dynamic stress of the blade is checked (monitored), and a dynamic stress checking module of the blade is adopted;
in the fifth step, a blade dynamic stress checking table is compiled, and the table is shown in table 1:
TABLE 1 vane dynamic stress examination and examination table
The second column of the examination table, namely the leaf height of the leaf, and the unit is mm; the third column "condition" of the reference table refers to the calculated ultra-low load condition point; the assessment positions of the assessment positions given in the examination table are divided into two categories of blade body assessment and blade root assessment, the blade body assessment is divided into an assessment position A and an assessment position B, and the blade root assessment is divided into an assessment position C and an assessment position D;
the assessment position A refers to the position of the static stress peak of the blade body; the static stress peak value is calculated and extracted from the static stress of the blade static stress calculating module 3.2; the dynamic stress value comprises a 1-order resonance examination point and a 2-order resonance examination point; the resonance examination point refers to a resonance mode which is calculated by the blade resonance frequency calculation module 3.3 and is closest to the working rotating speed (3000 r/min); the dynamic stress values of the 1 st order resonance examination point and the 2 nd order resonance examination point are extracted from the blade dynamic stress calculation;
the assessment position B refers to the position of the dynamic stress peak of the blade body; the dynamic stress peak value position comprises a 1-order resonance checking point and a 2-order resonance checking point; the resonance examination point refers to a resonance mode which is calculated by the blade resonance frequency calculation module 3.3 and is closest to the working rotating speed (3000 r/min); extracting dynamic stress peak values of the 1-order resonance examination point and the 2-order resonance examination point from blade dynamic stress calculation; static stress values of 1 st order and 2 nd order are extracted from the blade static stress calculation of the blade static stress calculation module 3.2.
The assessment position C refers to the position of a blade root static stress peak; the static stress peak value is calculated and extracted from the static stress of the middle blade of the blade static stress calculation module 3.2; the dynamic stress value comprises a 1-order resonance examination point and a 2-order resonance examination point; the resonance examination point refers to a resonance mode which is calculated by a blade resonance frequency calculation module of the blade resonance frequency calculation module 3.3 and is closest to the working rotating speed (3000 r/min); the dynamic stress values of the 1 st order resonance examination point and the 2 nd order resonance examination point are extracted from the blade dynamic stress calculation module;
the examination position D refers to the position of the dynamic stress peak value of the blade root; the dynamic stress peak value position comprises a 1-order resonance checking point and a 2-order resonance checking point; the resonance examination point refers to a resonance mode which is calculated by the blade resonance frequency calculation module 3.3 and is closest to the working rotating speed (3000 r/min); the dynamic stress peak values of the 1 st order resonance examination point and the 2 nd order resonance examination point are extracted from the blade dynamic stress calculation module; static stress values of 1 order and 2 orders are extracted from a blade static stress calculation module of a blade static stress calculation module 3.2;
the allowable dynamic stress value given in the examination table refers to the maximum value of the dynamic stress of the blade meeting the design safety requirement;
the dynamic stress allowable value obtaining process comprises the following steps: based on a GOODMAN test curve of a blade material, static stress data is used as input, the vibration resistance strength of the material is inquired, and a safety coefficient specified by a manufacturer is used as a criterion, and a dynamic stress allowable value is calculated;
the allowable dynamic stress value is calculated by adopting the following formula: allowable dynamic stress value = vibration resistance intensity/safety factor;
the safety criterion of blade dynamic stress evaluation is as follows: the dynamic stress of the examined positions of the blade body and the blade root is less than or equal to a dynamic stress allowable value, and when the examination is unqualified, the blade needs to be optimally designed in the modes of increasing the blade damping, the blade rigidity or improving the blade material grade and the like, so that the dynamic stress examination of the blade is qualified;
the method is suitable for calculating the dynamic stress of the blade under the ultralow-load operation condition of the steam turbine, and provides a technical means for predicting and checking the dynamic stress of the blade.
It should be noted that, in the above embodiments, as long as the technical solutions can be aligned and combined without contradiction, a person skilled in the art can exhaust all possibilities according to the mathematical knowledge of the alignment and combination, and therefore the invention does not describe the technical solutions after alignment and combination one by one, but it should be understood that the technical solutions after alignment and combination have been disclosed by the invention.
This embodiment is only illustrative of the patent and does not limit the scope of protection thereof, and those skilled in the art can make modifications to its part without departing from the spirit of the patent.
Claims (10)
1. The three-dimensional computing system of the dynamic stress of the ultra-low load blade of the steam turbine is characterized in that: the device comprises a thermal boundary calculation module, a blade three-dimensional flow field calculation module, a blade finite element calculation module and a blade dynamic stress calculation module;
a thermodynamic boundary calculation module: the system is used for obtaining thermal data of flow, total enthalpy and pressure of an inlet and an outlet of the blade and providing a thermal boundary for the calculation of a three-dimensional flow field of the blade;
the blade three-dimensional flow field calculation module: the method is used for obtaining the calculation results of the steady-state and transient flow fields of the blade and providing input data for the calculation of the static stress and the dynamic stress of the structural field of the blade;
the blade three-dimensional flow field calculation module comprises: the device comprises a blade flow field calculation domain modeling module (2.1), a steady-state flow field calculation module (2.2) and a transient flow field calculation module (2.3);
blade finite element calculation module: the method is used for obtaining the calculation results of the static stress and the resonance frequency of the blade and providing input data for the calculation of the dynamic stress of the blade;
the blade finite element calculation module comprises: the device comprises a blade structure field calculation domain modeling module (3.1), a blade static stress calculation module (3.2) and a blade resonance frequency calculation module (3.3);
the blade dynamic stress calculation module: the method is used for obtaining the calculation result of the dynamic stress of the blade and providing data for the dynamic stress assessment module of the blade.
2. The three-dimensional calculation system for dynamic stress of the ultra-low load blade of the steam turbine according to claim 1, wherein: still include the blade dynamic stress examination module: the method is used for evaluating and examining the dynamic stress safety of the blade and guiding the optimal design of the blade.
3. The three-dimensional calculation method for the dynamic stress of the ultra-low load blade of the steam turbine is characterized by comprising the following steps of: the three-dimensional calculation system for the dynamic stress of the ultra-low load blade of the steam turbine, which adopts the method as claimed in claim 2, comprises the following steps:
the method comprises the following steps: calculating a thermal boundary; adopting a thermal boundary calculation module, aiming at a target blade, adopting a thermal calculation program to obtain a blade thermal boundary of the steam turbine under different load conditions, and extracting blade inlet flow, a total enthalpy value, outlet pressure and a temperature value as an input boundary of blade three-dimensional flow field calculation;
step two: calculating a three-dimensional flow field of the blade; adopting a blade three-dimensional flow field calculation module, firstly adopting a blade flow field calculation domain modeling module (2.1) to carry out blade flow field calculation domain modeling, adopting a steady-state flow field calculation module (2.2) to carry out blade flow field steady-state calculation, and finally adopting a transient flow field calculation module (2.3) to carry out blade flow field transient calculation;
step three: calculating finite elements of the blades; adopting a blade finite element calculation module, firstly adopting a blade structure field calculation domain modeling module (3.1) to carry out blade structure field calculation domain modeling, then adopting a blade static stress calculation module (3.2) to carry out blade static stress calculation, and finally adopting a blade resonance frequency calculation module (3.3) to carry out blade resonance frequency calculation;
step four: and calculating the dynamic stress of the blade by adopting a blade dynamic stress calculation module.
4. The three-dimensional calculation method for the dynamic stress of the ultralow-load blade of the steam turbine according to claim 2, wherein the three-dimensional calculation method comprises the following steps: the thermal boundary of the blade comprises 5%, 10%, 15%, 20%, 25% and 30% of typical ultra-low load working points.
5. The three-dimensional calculation method for the dynamic stress of the ultra-low load blade of the steam turbine according to claim 4, characterized by comprising the following steps of: in the second step, modeling of a blade flow field calculation domain: adopting CFD calculation software to establish a blade three-dimensional flow field calculation domain model, carrying out grid division on the blades, wherein the number of grid nodes meets the grid independence requirement, the calculation domain takes a stationary blade inlet as a calculation domain inlet, gives inlet flow and a total enthalpy value, takes a moving blade outlet as a calculation domain outlet, and gives outlet pressure and temperature; the static blade calculation domain is static, the movable blade calculation domain is rotating, the rotating speed is the working rotating speed of the steam turbine, a cyclic symmetry method is adopted for simulation, and the working medium in the calculation domain adopts water vapor;
blade flow field steady state calculation, adopting a steady state CFD calculation mode to obtain a blade flow field steady state result of a blade thermal boundary, grasping the distribution characteristics of flow field separation and flow separation, taking a steady state CFD calculation result file as an input file of transient flow field calculation, and taking blade surface pressure data calculated by the steady state CFD as an input file of finite element static stress calculation of a structural field;
transient calculation of a blade flow field is carried out, a transient CFD calculation mode is adopted, statistical parameter calculation is carried out on steam pressure on the surface of a blade in the transient calculation process, a blade flow field transient result of a thermal boundary of the blade is obtained, mean square difference values of the steam pressure of all nodes on the surface of the blade are extracted, an excitation force input file of a dynamic stress calculation module is compiled, the format of the excitation force input file is in a csv format, four rows of data are counted, the first three rows are coordinates of the nodes in the x direction, the y direction and the z direction, and the fourth row is the mean square difference value of the steam pressure.
6. The three-dimensional calculation method for dynamic stress of the ultra-low load blade of the steam turbine according to claim 5, characterized in that: in the third step, the leaf structure field calculation domain modeling: adopting finite element calculation software to establish a blade structure field model, wherein the blade structure field model comprises blades and wheel grooves (5), blade roots (6) are connected with the wheel grooves (5), the blade structure field model is divided into grids, a calculation domain comprises all structural characteristics of the blades, the structural characteristics comprise shroud bands (8) at the end parts of the blades, lacing wires (7) in the middle parts of the blades, blade bodies of the blades and the blade roots (6) at the end parts of the blades, and friction contact is arranged between the adjacent shroud bands (8) and between the lacing wires (7); a friction foundation is arranged between the blade root (6) and the wheel groove (5), a cyclic symmetry method is adopted for simulation, the wheel groove is in fixed constraint, the rotating speed of the moving blades and the wheel groove is the working rotating speed of the steam turbine, and the centrifugal force action is simulated;
blade static stress calculation: based on the blade structure field model, taking a blade surface pressure result of blade flow field steady state calculation of a steady state flow field calculation module (2.2) as a static stress calculation input file, simulating the action of steam force, calculating blade static stress, obtaining blade static stress distribution characteristics, and taking a static stress calculation result as input data of a blade dynamic stress assessment module;
blade resonance frequency calculation: and calculating the resonant frequency of the blade based on the blade structure field model, obtaining the resonant frequency of the blade of the first 2 orders at the working rotating speed of the steam turbine, and taking the resonant frequency result as the input of a blade dynamic stress calculation module.
7. The three-dimensional calculation method for dynamic stress of the ultra-low load blade of the steam turbine according to claim 6, characterized in that: blade structural field computational domain modeling: when the grid division is carried out on the blade structure field model, grids are added at the positions of the rotor blade rounding, the rotor blade steam inlet and outlet rounding and the wheel groove rounding.
8. The three-dimensional calculation method for dynamic stress of the ultra-low load blade of the steam turbine according to claim 6, characterized in that: in the fourth step, based on the blade structure field model, the blade surface pressure mean square error calculated by the transient flow field of the transient flow field calculation module (2.3) is used as an excitation force input file, the resonance frequency corresponding to the resonance mode closest to the working rotating speed calculated by the blade resonance frequency calculation of the blade resonance frequency calculation module (3.3) is used as an input file, the dynamic stress of the blade is calculated, the dynamic stress distribution characteristics of the blade are obtained, and the dynamic stress calculation result is used as input data of the dynamic stress assessment module of the blade.
9. The three-dimensional calculation method for dynamic stress of the ultra-low load blade of the steam turbine according to claim 8, characterized in that: the method also comprises the following five steps: and (4) assessing the dynamic stress of the blade by adopting a blade dynamic stress assessment module.
10. The three-dimensional calculation method for dynamic stress of the ultra-low load blade of the steam turbine according to claim 9, characterized in that: step five, compiling a blade dynamic stress checking table;
the second column of the examination table, namely the leaf height of the leaf, and the unit is mm; the third column "condition" of the reference table refers to the calculated ultra-low load condition point; the assessment positions of the assessment positions given in the assessment core table are divided into two categories, namely, blade body assessment and blade root assessment, the blade body assessment is divided into an assessment position A and an assessment position B, and the blade root assessment is divided into an assessment position C and an assessment position D;
the allowable dynamic stress value given in the examination table refers to the maximum value of the dynamic stress of the blade meeting the design safety requirement;
the dynamic stress allowable value obtaining process comprises the following steps: based on a GOODMAN test curve of a blade material, static stress data is used as input, the vibration resistance strength of the material is inquired, and a safety coefficient specified by a manufacturer is used as a criterion, and a dynamic stress allowable value is calculated;
the allowable dynamic stress value is calculated by adopting the following formula: the allowable dynamic stress value = vibration resistance intensity/safety factor;
the safety criterion of blade dynamic stress evaluation is as follows: and when the dynamic stress at the checking positions of the blade body and the blade root is not more than a dynamic stress allowable value, the blade is optimally designed in a mode of increasing the damping and the rigidity of the blade or improving the grade of the material of the blade when the checking is unqualified, so that the dynamic stress checking of the blade is qualified.
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