Hydraulic and thermal coupling simulation method for steam pipeline secondary windward delay correction

Abstract

The application discloses a kind of hydraulic thermal coupling simulation methods of steam pipeline secondary windward delay correction, belong to steam pipe network simulation technical field.The method includes: establishing the water power-thermal coupling control equation group including condensation phase change source term;Space is dispersed using staggered grid, and space is dispersed using secondary windward format to momentum equation, balance precision and stability are handled in combination with delay correction;Pressure-enthalpy is used as main required solution variable, temperature and density are accurately updated after each iteration by calling IAPWS-IF97 property library, form strong coupling closed loop;With condensate water total amount stability and system mass conservation as convergence criterion.The application significantly improves the prediction accuracy of key parameters such as transient pressure peak, enhances the adaptability of complex working conditions, and provides a reliable simulation tool for safe and economic operation of pipe network.

Description

Technical Field

[0001] This invention belongs to the field of energy and power system simulation and control technology, specifically relating to the field of steam pipeline network simulation technology, and particularly to a hydraulic-thermal coupling simulation method for secondary windward delay correction of steam pipelines. Background Technology

[0002] As centralized heating systems become larger and more complex, and the "dual carbon" goals place higher demands on the refined control of energy systems, the safe and economical operation of long-distance steam transmission pipelines under non-steady-state conditions has become a focus of industry attention. Under conditions of drastic load fluctuations (such as instantaneous flow rate changes exceeding 30%), equipment start-up and shutdown (such as heat source tripping or emergency valve shut-off), or accidental events, the pipeline network exhibits strongly nonlinear and strongly coupled transient hydraulic-thermal response characteristics, manifested as pressure shock wave propagation, transient changes in steam state, and drastic temperature field shifts. Accurate prediction of such transient processes is crucial for pipeline design optimization, safety valve setting verification, control strategy formulation, and emergency plan development. Traditional simulation methods based on steady-state assumptions can no longer meet the dynamic analysis needs of modern intelligent heating systems.

[0003] Current unsteady-state simulations of steam pipeline networks are mainly based on the following two types of methods: (1) Simplified model based on the method of characteristics (MOC): This type of method is widely used in one-dimensional hydraulic transient analysis by transforming transient partial differential equations into ordinary differential equations and solving them along characteristic lines. However, it essentially assumes that the fluid is incompressible or slightly compressible, which introduces significant errors when dealing with the strong compressibility of high-temperature and high-pressure steam. At the same time, the method of characteristics usually adopts a decoupling sequence solution strategy when dealing with thermo-mechanical coupling, ignoring the interaction between pressure waves and temperature fields, which leads to distortion of calculation results at phase transition critical points and large temperature gradient scenarios. In addition, the fixed-grid method of characteristics suffers from interpolation dissipation, especially with a significant decrease in accuracy at topologically complex locations such as pipe diameter changes and branch confluences.

[0004] (2) CFD Coupled Model Based on Finite Volume Method (FVM): In recent years, some studies have attempted to use commercial CFD software (such as Fluent and OpenFOAM) for three-dimensional full-scale transient simulation, which can theoretically accurately capture compressible turbulence and conjugate heat transfer processes. However, actual engineering pipelines are often tens of kilometers in scale, and the amount of three-dimensional computation increases exponentially. A single simulation takes several days to several weeks, which cannot meet the needs of online real-time scheduling. In order to reduce the computational cost, some scholars have proposed a simplified one-dimensional finite volume model, but it generally uses a first-order upwind discrete convection term, which has serious numerical dissipation and excessive smoothing in high gradient regions such as shock waves and contact discontinuities. The prediction deviation of transient pressure peak can reach 15%-25%. Although higher-order schemes (such as MUSCL (MonotonicUpstream-Centered Scheme for Conservation Laws) and WENO (Weighted EssentiallyNon-Oscillatory)) can be used to improve accuracy, the time step is strictly limited by the CFL (Courant–Friedrichs–Lewy condition), resulting in limited improvement in computational efficiency. Furthermore, higher-order schemes are prone to numerical oscillations in strongly compressible two-phase flows, leading to insufficient robustness.

[0005] The above methods have the following common problems in the transient simulation of multiphysics coupled steam pipeline networks: ① The fundamental contradiction between numerical dissipation and computational efficiency: First-order schemes offer good stability but low accuracy, while higher-order schemes offer high accuracy but poor stability and high computational cost, making it difficult to achieve a balance between real-time performance and accuracy in engineering applications. ② Lack of handling for hydraulic-thermal coupling hysteresis effects: Existing algorithms mostly employ explicit or semi-implicit coupling, failing to consider the order-of-magnitude difference between the propagation velocity of pressure waves (sound speed level) and the thermal diffusion velocity (several m / s) in compressible steam flow, leading to distortion in the simulation of non-equilibrium thermodynamic states during transient processes. ③ Poor dynamic adaptability to unsteady-state conditions: In scenarios with drastic changes in boundary conditions, such as sudden load changes or accidental shutdowns, traditional fixed schemes cannot adaptively adjust the discretization strategy, easily causing numerical oscillations or convergence failures. ④ Lack of engineering-grade acceleration methods: Existing research focuses primarily on the theoretical accuracy of algorithms, without designing dedicated acceleration convergence mechanisms for the characteristics of pipeline network topology, resulting in a heavy computational burden for large-scale pipeline network simulations and making it difficult to deploy on online monitoring platforms.

[0006] In summary, existing technologies cannot simultaneously meet the comprehensive requirements of high accuracy, strong robustness, low numerical dissipation, and fast computation speed for unsteady-state simulation of steam pipe networks. This is especially true when dealing with transient hydraulic-thermal coupling problems of compressible steam, where core technical bottlenecks exist, such as the difficulty in balancing scheme accuracy and stability, mismatch in time scales across multiple physics fields, and insufficient real-time performance in engineering applications. Therefore, there is an urgent need to develop a novel transient coupling simulation method that possesses high-order scheme accuracy characteristics, suppresses oscillations through delay correction mechanisms, and achieves high computational efficiency through secondary upwind reconstructed equilibrium calculations. This method would support the digital operation and maintenance and safety early warning of intelligent heating systems. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines. Through the synergistic innovation of spatial discretization format and coupling algorithm, it can achieve high-precision, robust and fast numerical simulation of the transient hydraulic-thermal coupling process of compressible steam under complex working conditions such as load change and accident shutdown. It overcomes the defects of serious numerical dissipation, multi-physics coupling distortion, poor non-steady-state adaptability and limited computational efficiency in the existing technology.

[0008] To achieve the above objectives, the present invention provides a hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines, comprising the following steps: S1: Input steam pipeline parameters, boundary conditions, and initial state parameters; S2: Establish a set of one-dimensional hydraulic-thermal coupling control equations for compressible fluids that consider water vapor condensation, including the mass conservation equation, momentum conservation equation, energy conservation equation, steam state equation, and enthalpy equation for saturated condensate. S3: Construct a discrete staggered grid and use the staggered grid to spatially discretize the hydraulic-thermal coupling control equations. Pressure, temperature, density, and enthalpy are defined at the center of the main grid, and velocity is defined at the center of the velocity grid. S4: The momentum conservation equation is spatially discretized using a quadratic upwind scheme, and the momentum equation after discretization of the partial differential momentum conservation equation is constructed for each velocity grid. S5: Construct a pressure correction equation based on the continuity equation and the momentum conservation equation, and discretize it on an interlaced grid; construct the pressure equation after discretization of the pressure correction equation for each main grid; S6: Spatial discretize the energy conservation equation on an interlaced grid, and construct the energy equation after discretization of the energy conservation equation for each main grid; S7: Solve the discrete momentum equation, pressure correction equation, and energy equation simultaneously in sequence; update the steam velocity at the velocity grid and update the steam velocity, steam pressure, and steam enthalpy at the main grid; S8: Determine the steam state based on the updated pressure and enthalpy. If it is saturated, calculate the condensate loss rate. S9: Based on the updated pressure and enthalpy, use the IAPWS-IF97 property library to calculate the steam temperature and density for the next iteration; S10: Determine if the convergence condition is met. If not, return to S7 to continue iterating. If yes, output the steam parameter distribution at the current moment.

[0009] More preferably, in S2, the specific form of the hydraulic-thermal coupling control equations is as follows: mass conservation equation: Momentum conservation equation: Energy conservation equation The steam state equation includes the steam density equation: ; Steam enthalpy equation: ; Equation for the enthalpy of saturated condensate: ; in, For vapor density, u For steam velocity, t For time ，x For position coordinates, P For steam pressure, f The friction resistance factor, D The inner diameter of the pipe. g It is the acceleration due to gravity. For pipe slope, T For steam temperature, Outdoor air temperature h This refers to the enthalpy of vapor. The heat loss rate per unit area A The cross-sectional area of ​​the pipe. The rate of condensate loss per unit volume. Enthalpy of saturated condensate The formula for calculating steam density using IAPWS-IF97 international steam property parameters based on steam pressure and steam temperature; The formula for calculating steam enthalpy based on steam pressure and steam temperature using the IAPWS-IF97 international steam property parameters is provided. The formula for calculating the enthalpy of saturated condensate is based on steam pressure and steam temperature, using the IAPWS-IF97 international steam property parameters.

[0010] Further preferably, in S4, the momentum conservation equation is spatially discretized using a quadratic upwind scheme, including for the numbered... i , The internal velocity grid, the first algebraic equation obtained after adopting the quadratic upwind discrete momentum conservation equation is in the form of: in, u i For the current time layer, velocity grid i Steam velocity at the location; u i-1 For the current time layer, velocity grid i- Steam velocity at point 1; a i,i For velocity grid i Velocity in the spatially discrete algebraic equations of the momentum conservation equation u i Term coefficient; a i-1,i For velocity grid i Velocity in the spatially discrete algebraic equations of the momentum conservation equation u i-1 Term coefficient; b u,i For velocity grid i The constant term in the spatially discrete algebraic equation of the momentum conservation equation; P i-1 For the current moment, the main grid i- 1 steam pressure P i For the current moment, the main grid i Steam pressure at the point, To control the cross-sectional area of ​​the volume.

[0011] Further preferably, in S5, the following formula is used for the main grid 1 to the main grid 2. For each principal grid, construct the discretized algebraic equations of the pressure correction equation: in, For the current time layer, velocity grid i Iterative value of steam velocity at the location; For the current time layer, velocity grid i+1 Iterative value of steam velocity at the location; For the current moment, the main grid vapor density at that location; For the current moment, the main grid i vapor density at that location; For the current moment, the main grid vapor density at that location; For the previous moment, the main grid i vapor density at that location; a i,i For velocity grid i Velocity in the spatially discrete algebraic equations of the momentum conservation equation u i Term coefficient; a i+1,i+1 For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation u i+1 Term coefficient; For the current moment, the main grid Steam pressure correction value; For the current moment, the main grid Steam pressure correction value; For the current moment, the main grid Steam pressure correction value; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Pressure correction equation in spatially discretized algebraic equations at the master grid Term coefficient; b c,i Main grid The constant term in the spatially discrete algebraic equation of the pressure correction equation; For the current moment, the main grid The iterative value of the condensate loss rate per unit volume per unit time; A is the cross-sectional area of ​​the control volume; To control the length of the body; For time intervals.

[0012] Furthermore, in S6, the following formula is used to construct the algebraic equations after discretization of the energy conservation equations for each master grid: in: For the current time layer velocity grid i Steam velocity at the location; For the current time layer velocity grid i+ Steam velocity at point 1; The current time-layer main grid i- Enthalpy of vapor at point 1; The current time-layer main grid i Enthalpy of vapor; For the current time layer, the main grid i+ The iterative value of the vapor enthalpy at point 1; For the previous time layer, the main grid i Enthalpy of vapor; The main grid at the current moment i vapor density at that location; For the current moment, the main grid i Iterative value of steam temperature at the location; T a D represents the outdoor air temperature; D represents the inner diameter of the steam pipe. Main grid i The vapor enthalpy in the spatially discrete algebraic equations of the energy conservation equation h i Term coefficient; Main grid i The vapor enthalpy in the spatially discrete algebraic equations of the energy conservation equation h i Term coefficient; Main grid i The vapor enthalpy in the spatially discrete algebraic equations of the energy conservation equation Term coefficient; Main grid i The constant term in the discrete algebraic equation of the energy conservation equation; k 2,i For the current moment, the main grid i The rate of heat loss per unit area per unit time; To control the length of the body; denoted as the time interval; A represents the cross-sectional area of ​​the control volume.

[0013] Furthermore, prior to S7, the process includes initializing the steam pressure and enthalpy at the main grid and calculating the condensate loss rate, providing a reasonable initial guess for the coupled solution and accelerating computational convergence. The initialization of steam pressure at the main grid includes: based on the known steam pressure at the upstream boundary of the steam pipe, using the initialization calculation formula at each main grid to estimate an initial pressure distribution for all internal main grids and downstream boundaries; Steam enthalpy initialization includes: calculating the boundary enthalpy based on the known steam pressure and temperature at the upstream boundary of the steam pipeline using IAPWS-IF97, and estimating the initial enthalpy distribution for all internal master grids using the steam enthalpy initialization calculation formula; The condensate loss rate includes determining the steam state at each main grid based on the initial steam pressure and steam enthalpy. If the steam state is determined to be saturated, the condensate loss rate of that main grid is calculated based on the initial steam pressure and steam enthalpy.

[0014] Further preferably, in S8, the steam state is determined based on the updated steam pressure and steam enthalpy, including: comparing the current steam enthalpy at the main grid. h With the current steam pressure at that location p Corresponding saturated vapor enthalpy value h sat （p） ;like h＜ h sat （p） If the steam is saturated and condensation occurs, then the steam at that location is determined to be in a saturated state; otherwise, it is in a superheated state; if it is saturated, then the condensate loss rate is calculated.

[0015] More preferably, in S10, the convergence condition includes: The change in saturated condensate loss in the entire pipe section is less than the first threshold. At the same time, the difference between the steam loss and the saturated condensate loss at the upstream and downstream boundaries of the steam pipe section, calculated based on steam velocity and steam density, meets the preset error.

[0016] The hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines disclosed in this application has at least the following advantages compared with the prior art: 1. Improve simulation accuracy: The convection term is reconstructed using a second-order upwind scheme, achieving a discretization accuracy of second order or higher. The prediction deviation of transient pressure peak is controlled within 5%, accurately capturing parameter changes in high gradient regions. The compressibility of steam is fully considered, avoiding errors caused by improper assumptions in traditional methods.

[0017] 2. Enhance the realism of coupling: The delay correction algorithm solves the lag effect of hydraulic-thermal coupling, and considers the interaction between pressure wave and temperature field to realistically simulate the dynamic coupling process of multi-physics field under unsteady conditions. The results are more reliable, especially in phase transition critical point and large temperature gradient scenarios.

[0018] 3. Adaptable to complex working conditions: It can adaptively adjust the discretization strategy according to changes in unsteady working conditions, avoid numerical oscillations and convergence failures, and stably simulate complex scenarios such as sudden load changes and accidental shutdowns; it can effectively handle complex topology problems such as pipe diameter changes and branch pipe confluences, and improve the accuracy of complex pipe network simulation.

[0019] 4. Improve computational efficiency: Balance accuracy and computational cost, avoid the low efficiency and oscillation problems of high-order formats; for large-scale pipeline network optimization algorithms, shorten the calculation time, meet the needs of online real-time scheduling, and support the digital operation and maintenance and safety early warning of smart heating systems.

[0020] 5. Support full-cycle analysis: It can be embedded into the entire process of pipeline design, operation optimization, and emergency plan evaluation to help optimize design, dynamically verify safety valve settings, optimize water hammer protection strategies, and improve the safety margin and economic operation level of pipeline network. Attached Figure Description

[0021] Figure 1 This is a flowchart of the unsteady-state hydraulic-thermal coupling simulation method for secondary upwind pattern correction of steam pipelines according to the present invention.

[0022] Figure 2 This is a schematic diagram of the staggered grid used in this invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1 As shown, the unsteady-state hydraulic-thermal coupling simulation method for steam pipelines with secondary upwind pattern delay correction provided by one embodiment of the present invention includes the following steps: S1: Input steam pipeline parameters, boundary conditions, and initial state parameters; the specific parameters to be input include: Upstream boundary steam pressure P of long-distance steam pipeline ub Steam temperature Steam density enthalpy of vapor parameter; downstream steam velocity of long-distance steam pipeline parameter; Physical parameters of long-distance steam pipelines: inner diameter of steam pipelines Steam pipe cross-sectional area Steam pipe slope Steam pipe length ; Friction resistance factor at each main grid point of the long-distance steam pipeline Heat loss rate ; (Optional) The steam velocity at the velocity grid in the previous time layer. Steam pressure at the main grid Steam temperature Steam density enthalpy of vapor .

[0025] (Optional) Steam pressure at the upstream boundary of the steam pipe section in the previous time layer. Steam temperature Steam density enthalpy of vapor parameter.

[0026] S2. Establish a set of one-dimensional hydraulic-thermal coupled governing equations for compressible fluids considering water vapor condensation, including the mass conservation equation, momentum conservation equation, energy conservation equation, steam state equation, and enthalpy equation for saturated condensate; as detailed below: mass conservation equation: in, For vapor density, u For steam velocity, t For time ，x For position coordinates, The rate of condensate loss per unit volume; Momentum conservation equation: In the formula, For vapor density, u For steam velocity, P For steam pressure, f The friction resistance factor, D The inner diameter of the pipe. g It is the acceleration due to gravity. For pipe slope, t For time ，x These are the position coordinates.

[0027] Energy conservation equation In the formula, For vapor density, u For steam velocity, T For steam temperature, Outdoor air temperature h This refers to the enthalpy of vapor. Enthalpy of saturated condensate The heat loss rate per unit area The rate of condensate loss per unit volume. t For time ，x These are the position coordinates.

[0028] The steam state equation includes the steam density equation: ; In the formula, For vapor density, P For steam pressure, T For steam temperature, This is a formula for calculating steam density using the IAPWS-IF97 international steam property parameters based on steam pressure and steam temperature.

[0029] Steam enthalpy equation: ; In the formula, P For steam pressure, T For steam temperature, h This refers to the enthalpy of vapor. The formula for calculating steam enthalpy based on steam pressure and steam temperature using the IAPWS-IF97 international steam property parameters is provided. Equation for the enthalpy of saturated condensate: ; In the formula, P For steam pressure, T For steam temperature, The enthalpy of saturated condensate. The formula for calculating the enthalpy of saturated condensate is based on steam pressure and steam temperature, using the IAPWS-IF97 international steam property parameters.

[0030] The unsteady-state equations are summarized as follows: like Figure 2 As shown, to accurately capture the strong coupling characteristics and nonlinear parameter changes in the steam phase change process, this invention employs a staggered grid strategy to spatially discretize the governing equations. Scalar parameters such as pressure, temperature, density, and enthalpy are defined at the center of the main grid control volume element (the center of the blue grid in the staggered grid diagram), while the velocity vector component is placed at the center of the velocity grid control volume element (the center of the red grid in the staggered grid diagram, which is also the interface of the main grid control volume element). The importance of this layout lies in its fundamental solution to the non-physical oscillation problem caused by pressure and velocity coupling in co-located grids, effectively avoiding a checkerboard distribution of the pressure field. It also significantly improves the stability of the numerical solution and the accuracy of mass conservation, especially when dealing with drastic density changes caused by steam condensation and compressible flows, enabling a more accurate characterization of the dynamic balance between pressure gradient and mass flux.

[0031] The main grid is numbered from 0 to n, where ub represents the upper boundary of the steam pipe and db represents the lower boundary of the steam pipe; the velocity grid is numbered from 0 to n+1, where velocity grid 0 and velocity grid n+1 are both half grids, located at the upper and lower boundaries of the steam pipe, respectively.

[0032] S3: Construct a discrete staggered grid. Use the staggered grid to spatially discretize the hydraulic-thermal coupling control equations. Pressure, temperature, density, and enthalpy are defined at the center of the main grid, and velocity is defined at the center of the velocity grid. After the discrete grid is constructed, discretize it according to the steps from S4 to asa6de below.

[0033] S4. The momentum conservation equation is spatially discretized using a quadratic upwind scheme, and a set of momentum conservation algebraic equations after discretization of the partial differential momentum conservation equation is constructed for each velocity grid.

[0034] In time interval Internally, based on Control volume is achieved by spatially discretizing the momentum conservation equation. For a single pipe segment, control volumes are uniformly divided, and the length of each control volume is... Cross-sectional area All are consistent.

[0035] For velocity grid 0, the discretized algebraic equation of the partial differential momentum conservation equation is shown below: in: For the current time layer, at velocity grid 0, the steam velocity is expressed in units of: ; For the previous time layer, at velocity grid 0, the steam velocity is expressed in units of: ; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 0, ... Term coefficient; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 0, ... Term coefficient; For the constant term in the algebraic equation of the momentum conservation equation at velocity grid 0, which is spatially discretized; The steam pressure at the upstream boundary of the steam pipe section at the current moment, in Pa. The current steam density at the upstream boundary of the steam pipe section, in units of: ; The current steam pressure at point 0 on the main grid, in Pa. To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The length of the control volume is expressed in meters (m). The time interval is expressed in seconds (s). This refers to the inner diameter of the steam pipe, in meters (m). This represents the frictional resistance factor of the steam pipe at velocity grid 0 in the current time layer. Acceleration due to gravity, unit: ; For the slope of the steam pipe; For velocity grid 1, the discretized algebraic equation of the partial differential momentum conservation equation is shown below: in: The current time layer shows the steam velocity at position 0 of the velocity grid, in units of: ; The current steam velocity at velocity grid 1, in units of: ; The steam velocity at position 0 of the velocity grid in the previous time layer, in units of: ; The steam velocity at velocity grid 1 in the previous time layer, unit: ; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 1 Term coefficient; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 1 Term coefficient; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 1 Term coefficient; For the constant term in the algebraic equation of the momentum conservation equation at velocity grid 1, which is spatially discretized; The current steam pressure at point 0 on the main grid, in Pa. The current steam pressure at point 1 of the main grid, in Pa. The current vapor density at point 0 on the main grid, in units of: ; The current vapor density at point 1 of the main grid, in units of: ; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The length of the control volume is expressed in meters (m). The time interval is expressed in seconds (s). This refers to the inner diameter of the steam pipe, in meters (m). The current time layer shows the steam pipe friction resistance factor at velocity grid 1, in units of 1. Acceleration due to gravity, unit: ; Slope of steam pipe, unit: 1; For velocity grid 2 ~ velocity grid The algebraic equation after discretization of the partial differential momentum conservation equation is shown below: in: For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Iterative values ​​of steam velocity at the specified location, in units: ; For the current time layer, velocity grid Iterative values ​​of steam velocity at the specified location, in units: ; For the previous time layer, velocity grid Steam velocity, unit: ; For the previous time layer, velocity grid Steam velocity, unit: ; For the previous time layer, velocity grid Steam velocity, unit: ; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient, delay correction term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid The constant term in the spatially discrete algebraic equation of the momentum conservation equation; For the current moment, the main grid Steam pressure at the point of application, unit: Pa; For the current moment, the main grid Steam pressure at the point of application, unit: Pa; For the current moment, the main grid Steam density at [location], unit: ; For the current moment, the main grid Steam density at [location], unit: ; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The length of the control volume is expressed in meters (m). The time interval is expressed in seconds (s). This refers to the inner diameter of the steam pipe, in meters (m). For the current time layer, velocity grid Friction resistance factor of steam pipeline, unit: 1; Acceleration due to gravity, unit: ; Slope of steam pipe, unit: 1; For a velocity grid n+1, the discretized algebraic equation of the partial differential momentum conservation equation is shown below: in: For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Iterative values ​​of steam velocity at the specified location, in units: ; For the current time layer, velocity grid Iterative values ​​of steam velocity at the specified location, in units: ; For the previous time layer, velocity grid Steam velocity, unit: ; For the previous time layer, velocity grid Steam velocity, unit: ; For the previous time layer, velocity grid Steam velocity, unit: ; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient, delay correction term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid The constant term in the spatially discrete algebraic equation of the momentum conservation equation; At the current moment, the lower boundary of the steam pipe section (velocity grid) Steam pressure at ( ), unit: Pa; For the current moment, the main grid Steam pressure at the point of application, unit: Pa; For the current moment, the main grid Steam pressure at the point of application, unit: Pa; At the current moment, the lower boundary of the steam pipe section (velocity grid) Steam density at ( ), unit: ; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The length of the control volume is expressed in meters (m). The time interval is expressed in seconds (s). This refers to the inner diameter of the steam pipe, in meters (m). For the current time layer, velocity grid Friction resistance factor of steam pipeline, unit: 1; Acceleration due to gravity, unit: ; Slope of steam pipe, unit: 1; S5: Construct a pressure correction equation based on the continuity equation and the momentum conservation equation, and discretize it on an interlaced grid; construct the pressure equation after discretization of the pressure correction equation for each main grid; In time interval Internally, based on the main control volume, the pressure correction equation constructed based on the continuity equation and the momentum conservation equation is spatially discretized. For a single pipe segment, the control volume is uniformly divided, and the length of each control volume is... Cross-sectional area All are consistent.

[0036] For the master grid 0, the pressure correction equation, after discretization in the staggered grid space, is shown below: in: This is the iterative value of the steam velocity at velocity grid 0 in the current time layer, in units of: ; This is the iterative value of the steam velocity at velocity grid 1 in the current time layer, in units of: ; The current steam density at the upstream boundary of the steam pipe section, in units of: ; The current vapor density at point 0 on the main grid, in units of: ; The current vapor density at point 1 of the main grid, in units of: ; The vapor density at point 0 of the main grid at the previous time step, in units of: ; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 0, ... Term coefficient; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 1 Term coefficient; This is the corrected steam pressure value at the upstream boundary of the steam pipeline at the current moment, in Pa. This is the current steam pressure correction value at point 0 of the main grid, in Pa. This is the current steam pressure correction value at main grid 1, in Pa. Pressure correction in the spatially discretized algebraic equations of the pressure correction equation at the master grid 0 Term coefficient; Pressure correction in the spatially discretized algebraic equations of the pressure correction equation at the master grid 0 Term coefficient; Pressure correction in the spatially discretized algebraic equations of the pressure correction equation at the master grid 0 Term coefficient; The constant term in the spatially discretized algebraic equation of the pressure correction equation at the main grid 0; This represents the iterative value of the condensate loss rate per unit volume per unit time at location 0 of the main grid at the current moment, in units of: ; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The length of the control volume is expressed in meters (m). The time interval is expressed in seconds (s). For main grid 1 to main grid The algebraic equations of the pressure correction equation after discretization in the staggered grid space are shown below: in: For the current time layer, velocity grid Iterative value of steam velocity at the location; For the current time layer, velocity grid Iterative value of steam velocity at the location; For the current moment, the main grid vapor density at that location; For the current moment, the main grid Steam density at [location], unit: ; For the current moment, the main grid Steam density at [location], unit: ; For the previous moment, the main grid Steam density at [location], unit: ; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For the current moment, the main grid Steam pressure correction value, unit: Pa; For the current moment, the main grid Steam pressure correction value, unit: Pa; For the current moment, the main grid Steam pressure correction value, unit: Pa; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Main grid The constant term in the spatially discrete algebraic equation of the pressure correction equation; For the current moment, the main grid Iterative value of condensate loss rate per unit volume per unit time, unit: ; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The length of the control volume is expressed in meters (m). The time interval is expressed in seconds (s). For the main grid The algebraic equations of the pressure correction equation after discretization in the staggered grid space are shown below: in: For the current time layer, velocity grid Steam velocity iteration value, unit: ; For the current time layer, velocity grid Steam velocity iteration value, unit: ; For the current moment, the main grid Steam density at [location], unit: ; For the current moment, the main grid Steam density at [location], unit: ; The current steam density at the downstream boundary of the steam pipe section, in units of: ; For the previous moment, the main grid Steam density at [location], unit: ; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For the current moment, the main grid Steam pressure correction value, unit: Pa; For the current moment, the main grid Steam pressure correction value, unit: Pa; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Main grid The constant term in the spatially discrete algebraic equation of the pressure correction equation; For the current moment, the main grid Iterative value of condensate loss rate per unit volume per unit time, unit: ; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The length of the control volume is expressed in meters (m). The time interval is expressed in seconds (s). S6: Spatial discretize the energy conservation equation on an interlaced grid, and construct the energy equation after discretization of the energy conservation equation for each main grid; In time interval Internally, based on the main control volume, the energy conservation equation is spatially discretized. For a single pipe segment, the control volume is uniformly divided, and the length of each control volume is... Cross-sectional area All are consistent. If the main control body If the internal steam state is superheated (superheated steam), then the main grid... The condensate loss rate of the control volume is 0, that is... ; If the vapor state within the body is controlled to be superheated, condensation will not occur. Therefore, there is no condensate term. During the time interval... Internally, based on the main control volume, the energy conservation equation is spatially discretized. For a single pipe segment, the control volume is uniformly divided, and the length of each control volume is... Cross-sectional area All are consistent.

[0037] For the principal grid 0, the algebraic equations of the energy conservation equation after discretization in the staggered grid space are as follows: in: For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current time layer, the main grid (Extrapolated) Iterative value of vapor enthalpy, unit: ; For the previous time layer, the main grid Enthalpy of vapor, unit: ; For the current moment, the main grid Steam density at [location], unit: ; For the current moment, the main grid Iterative values ​​of steam temperature, in K; Outdoor air temperature, unit: K; This refers to the inner diameter of the steam pipe, in meters (m). Main grid The vapor enthalpy in the spatially discrete algebraic equations of the energy conservation equation Term coefficient; Main grid The vapor enthalpy in the spatially discrete algebraic equations of the energy conservation equation Term coefficient; Main grid The vapor enthalpy in the spatially discrete algebraic equations of the energy conservation equation Term coefficient; Main grid The constant term in the discrete algebraic equation of the energy conservation equation; For the current moment, the main grid Heat loss rate per unit area per unit time, unit: ; The length of the control volume is expressed in meters (m). The time interval is expressed in seconds (s). To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The steam pressure and enthalpy at the main grid are initialized, and the condensate loss rate is calculated to provide a reasonable initial guess for the coupled solution and accelerate computational convergence. The initialization of steam pressure at the main grid includes: based on the known steam pressure at the upstream boundary of the steam pipe, using the initialization calculation formula at each main grid to estimate an initial pressure distribution for all internal main grids and downstream boundaries; Based on the steam pressure at the upstream boundary of the steam pipeline, the steam pressure of each main grid in the steam pipeline segment is initialized. The formula for initializing the steam pressure at main grid 0 is shown below: in: The current steam pressure at point 0 on the main grid, in Pa. The steam pressure at the upstream boundary of the steam pipe section at the current moment, in Pa. For the current time layer, at velocity grid 0, the steam velocity is expressed in units of: ; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 0, ... Term coefficient; For the constant term in the algebraic equation of the momentum conservation equation at velocity grid 0, which is spatially discretized; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ;

[0038] in: The current time layer shows the steam velocity at position 0 of the velocity grid, in units of: ; The current steam velocity at velocity grid 1, in units of: ; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 1 Term coefficient; For the velocity in the spatially discretized algebraic equation of the momentum conservation equation at velocity grid 1 Term coefficient; For the constant term in the algebraic equation of the momentum conservation equation at velocity grid 1, which is spatially discretized; The current steam pressure at point 0 on the main grid, in Pa. The current steam pressure at point 1 of the main grid, in Pa. To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; Main Mesh 2 ~ Main Mesh The formula for initializing the steam pressure is shown below: in: For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Steam velocity, unit: ; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid The constant term in the spatially discrete algebraic equation of the momentum conservation equation; For the current moment, the main grid Steam pressure at the point of application, unit: Pa; For the current moment, the main grid Steam pressure at the point of application, unit: Pa; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ;

[0039] in: For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Steam velocity, unit: ; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid Velocity in the spatially discrete algebraic equations of the momentum conservation equation Term coefficient; For velocity grid The constant term in the spatially discrete algebraic equation of the momentum conservation equation; At the current moment, the lower boundary of the steam pipe section (velocity grid) Steam pressure at ( ), unit: Pa; For the current moment, the main grid Steam pressure at the point of application, unit: Pa; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; Steam enthalpy initialization includes: calculating the boundary enthalpy based on the known steam pressure and temperature at the upstream boundary of the steam pipeline using IAPWS-IF97, and estimating the initial enthalpy distribution for all internal master grids using the steam enthalpy initialization calculation formula; Based on the steam pressure and steam temperature at the upstream boundary of the steam pipeline, the steam enthalpy value of each main grid of the steam pipeline segment is initialized.

[0040] The formula for initializing the vapor enthalpy at point 0 of the main grid is shown below: in: The current time layer shows the steam velocity at position 0 of the velocity grid, in units of: ; The current steam velocity at velocity grid 1, in units of: ; This is the steam enthalpy value at the upstream boundary of the steam pipe section at the current time level, in units of: ; This is the vapor enthalpy value at position 0 of the main grid in the current time layer, in units of: ; The current vapor density at point 0 on the main grid, in units of: ; This is the current iterative value of the steam temperature at position 0 of the main grid, in K. Outdoor air temperature, unit: K; This refers to the inner diameter of the steam pipe, in meters (m). The heat loss rate per unit area per unit time at point 0 of the main grid at the current moment, in units of: ; The length of the control volume is expressed in meters (m). To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; Main Mesh 1 ~ Main Mesh The formula for initializing the vapor enthalpy is shown below: in: For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current moment, the main grid Steam density at [location], unit: ; For the current moment, the main grid Iterative values ​​of steam temperature, in K; Outdoor air temperature, unit: K; This refers to the inner diameter of the steam pipe, in meters (m). For the current moment, the main grid Heat loss rate per unit area per unit time, unit: ; The length of the control volume is expressed in meters (m). To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The initial calculation formula for the steam enthalpy value at the downstream boundary of the steam pipe section is as follows: in: For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; This is the enthalpy of steam at the downstream boundary of the steam pipe section at the current time level, in units of: ; Based on iapws-if97, calculate the vapor pressure at each master grid. and Saturated steam temperature below and and saturated vapor enthalpy and enthalpy of saturated condensate and ; in: Steam pressure at the main grid The saturated steam temperature below, in units ; Steam pressure at the downstream boundary of the steam pipe section The saturated steam temperature below, in units ; Steam pressure at the main grid The saturated vapor enthalpy value at the specified temperature, in units of... ; Steam pressure at the downstream boundary of the steam pipe section The saturated vapor enthalpy value at the specified temperature, in units of... ; Steam pressure at the main grid The enthalpy of saturated condensate at the specified value, in units of ; Steam pressure at the downstream boundary of the steam pipe section The enthalpy of saturated condensate at the specified value, in units of ; If the main grid enthalpy of vapor at the location Less than steam pressure saturated vapor enthalpy value Then the main grid The steam is saturated steam, let , , Simultaneously, the saturated condensate loss rate is calculated based on the formula for calculating the saturated condensate loss rate. .

[0041] in: For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current time layer, the main grid Enthalpy of saturated condensate, unit: ; Steam pressure at the main grid The saturated vapor enthalpy value at the specified temperature, in units of... ; Steam pressure at the main grid The enthalpy of saturated condensate at the specified value, in units of ; To represent the main grid The steam at that location is saturated steam; To represent the main grid The steam at that location is superheated steam; If the steam enthalpy at the downstream boundary of the steam pipe section Less than steam pressure saturated vapor enthalpy value Then the steam at the downstream boundary of the steam pipe section is saturated steam, let ; The condensate loss rate includes determining the steam state at each main grid based on the initial steam pressure and steam enthalpy. If the steam state is determined to be saturated, the condensate loss rate of that main grid is calculated based on the initial steam pressure and steam enthalpy.

[0042] If the main control body The internal vapor state is saturated, and the pressure distribution can be derived based on the momentum conservation equation and the continuity equation. Determine the vapor enthalpy value of each control unit. enthalpy of saturated condensate This allows us to determine the condensate of each control body. .

[0043] For the 0th master grid, if the steam state is saturated, the formula for calculating the condensate loss rate is as follows: in: The current time layer shows the steam velocity at position 0 of the velocity grid, in units of: ; The current steam velocity at velocity grid 1, in units of: ; This is the steam enthalpy value at the upstream boundary of the steam pipe section at the current time level, in units of: ; This is the vapor enthalpy value at position 0 of the main grid in the current time layer, in units of: ; This is the saturated condensate enthalpy at position 0 of the main grid in the current time layer, in units of: ; This is the vapor enthalpy value at main grid 1 in the current time layer, in units of: ; This represents the vapor enthalpy at position 0 of the main grid in the previous time layer, in units of: ; The current vapor density at point 0 on the main grid, in units of: ; This is the current iterative value of the steam temperature at position 0 of the main grid, in K. Outdoor air temperature, unit: K; This refers to the inner diameter of the steam pipe, in meters (m). The heat loss rate per unit area per unit time at point 0 of the main grid at the current moment, in units of: ; The condensate loss rate per unit volume per unit time at location 0 of the main grid at the current moment, in units of: ; The length of the control volume is expressed in meters (m). The time interval is expressed in seconds (s). For the 1st to n-1th master grid nodes, if the steam state is saturated, the condensate loss rate is calculated as follows: in: For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current time layer, the main grid Enthalpy of saturated condensate, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; For the previous time layer, the main grid Enthalpy of vapor, unit: ; For the current moment, the main grid Steam density at [location], unit: ; For the current moment, the main grid Iterative values ​​of steam temperature, in K; Outdoor air temperature, unit: K; This refers to the inner diameter of the steam pipe, in meters (m). For the current moment, the main grid Heat loss rate per unit area per unit time, unit: ; For the current moment, the main grid Condensation loss rate per unit volume per unit time, unit: ; For the nth master grid, if the steam state is saturated, the formula for calculating the condensate loss rate is as follows: in: For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, velocity grid Steam velocity, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current time layer, the main grid Enthalpy of vapor, unit: ; For the current time layer, the main grid Enthalpy of saturated condensate, unit: ; For the previous time layer, the main grid Enthalpy of vapor, unit: ; For the current moment, the main grid Steam density at [location], unit: ; For the current moment, the main grid Iterative values ​​of steam temperature, in K; Outdoor air temperature, unit: K; This refers to the inner diameter of the steam pipe, in meters (m). For the current moment, the main grid Heat loss rate per unit area per unit time, unit: ; For the current moment, the main grid Condensation loss rate per unit volume per unit time, unit: .

[0044] S7: Solve the discrete momentum equation, pressure correction equation, and energy equation simultaneously; update the steam velocity at the velocity grid and update the steam velocity, steam pressure, and steam enthalpy at the main grid. The momentum conservation equation is combined with the algebraic equations discretized in the velocity grid space to solve for the steam velocity at each velocity grid. The TDMA algorithm is then used to solve the problem, and the resulting matrix calculation format is shown below: The system of algebraic equations after discretizing the main grid space of the pressure correction equation is combined to solve for the steam pressure correction value at the main grid. The TDMA algorithm is then used to solve the problem, and the combined matrix calculation format is shown below: The corrected pressure calculation formula is as follows: The formula for calculating the velocity correction value for velocity grid 0 is as follows: The formula for calculating the velocity correction value for velocity grid 1 is as follows: For velocity grid 2 to velocity grid The formula for calculating the speed correction value is as follows: For velocity grid The formula for calculating the speed correction value is as follows: The system of algebraic equations after discretizing the main grid space of the energy conservation equation is combined to solve for the vapor enthalpy at the main grid. The TDMA algorithm is then used to solve the problem, and the combined matrix calculation format is shown below: Based on iapws-if97, calculate the vapor pressure at each master grid. and Saturated steam temperature below and and saturated vapor enthalpy and enthalpy of saturated condensate and ; If the main grid enthalpy of vapor at the location Less than steam pressure saturated vapor enthalpy value Then the main grid The steam is saturated steam, let Simultaneously calculate the saturated condensate loss rate. .

[0045] If the steam enthalpy at the downstream boundary of the steam pipe section Less than steam pressure saturated vapor enthalpy value Then the steam at the downstream boundary of the steam pipe section is saturated steam, let ; The principal grids are determined based on either "simultaneous solution of the momentum conservation equation, pressure correction equation, and energy conservation equation discretized algebraic equation system" or "steam pressure initialization and steam enthalpy initialization". Steam pressure at the location and vapor enthalpy The steam temperature and steam density calculation functions of iapws-if97 were used to calculate the values ​​of each main grid. Steam temperature at and steam density .

[0046] Based on the steam pressure at the downstream boundary of the steam pipe section and vapor enthalpy The steam temperature at the downstream boundary of the steam pipe section is calculated using the steam temperature and steam density calculation functions of iapws-if97. and steam density .

[0047] Update the iterative value of the vapor pressure at the main grid in the current time layer. Steam temperature iteration value Iterative values ​​of steam density Iterative value of steam enthalpy Iterative value of condensate loss rate ; Update the steam velocity iteration value at the velocity grid in the current time layer. ; S8: Determine the steam state based on the updated steam pressure and steam enthalpy. If it is saturated, calculate the condensate loss rate. Compare the current vapor enthalpy at the main grid. h With the current steam pressure at that location p Corresponding saturated vapor enthalpy value h sat （p） ;like h < h sat （p） If the steam is saturated and condensation occurs, then the steam at that location is determined to be in a saturated state; otherwise, it is in a superheated state; if it is saturated, then the condensate loss rate is calculated.

[0048] S9: Based on the updated pressure and enthalpy, use the IAPWS-IF97 property library to calculate the steam temperature and density for the next iteration; S10: Determine if the convergence condition is met. If not, return to S7 to continue iterating. If yes, output the steam parameter distribution at the current moment.

[0049] Convergence Criteria: The saturated condensate loss remains essentially constant throughout the entire pipe section, and the difference between the steam loss at the upstream and downstream boundaries of the steam pipe section calculated based on steam velocity and steam density and the saturated condensate loss meets the error tolerance. The requirements and relevant calculation formulas are as follows: in: This represents the saturated condensate loss of the entire steam pipe section, per unit. ; For the current moment, the main grid Condensation loss rate per unit volume per unit time, unit: ; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; The length of the control volume is expressed in meters (m). in: This refers to the steam loss at the upstream and downstream boundaries of the steam pipe section, expressed in units of... ; The current time layer shows the steam velocity at position 0 of the velocity grid, in units of: ; For the current time layer, velocity grid Steam velocity, unit: ; To control the cross-sectional area (steam pipe section cross-sectional area), unit: ; Final output: Vapor pressure at the main grid in the current time layer. Steam temperature Steam density enthalpy of vapor Update the current time layer and the steam velocity at the velocity grid. .

[0050] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines, characterized in that, Includes the following steps: S1: Input steam pipeline parameters, boundary conditions, and initial state parameters; S2: Establish a set of hydraulic-thermal coupling control equations for compressible fluids that consider water vapor condensation. The set of hydraulic-thermal coupling control equations includes the mass conservation equation, momentum conservation equation, energy conservation equation, steam state equation, and enthalpy equation for saturated condensate. S3: Construct a discrete staggered grid and use the staggered grid to spatially discretize the hydraulic-thermal coupling control equations. The steam pressure, steam temperature, steam density, and steam enthalpy are defined at the center of the main grid, and the steam velocity is defined at the center of the velocity grid. S4: The momentum conservation equation is spatially discretized using a quadratic upwind scheme, and the momentum conservation algebraic equation after discretization of the partial differential momentum conservation equation is constructed for each velocity grid. S5: Construct pressure correction equations based on the mass conservation equation and the momentum conservation equation, and discretize them on staggered grids; construct pressure correction algebraic equations after discretization of pressure correction equations for each master grid; S6: Spatial discretize the energy conservation equation on an interlaced grid, and construct the energy conservation algebraic equation after discretization of the partial differential energy conservation equation for each principal grid. S7: Solve the discrete momentum conservation algebraic equations, pressure correction algebraic equations, and energy conservation algebraic equations in sequence; update the steam velocity at the velocity grid and update the steam velocity, steam pressure, and steam enthalpy at the main grid; S8: Determine the steam state based on the steam pressure and steam enthalpy at the updated main grid. If it is saturated, calculate the condensate loss rate. S9: Based on the updated steam pressure and steam enthalpy, call the IAPWS-IF97 property library to calculate the steam temperature and steam density for the next iteration; S10: Determine if the convergence condition is met. If not, return to S7 to continue iterating. If yes, output the steam parameter distribution at the current moment.

2. The hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines according to claim 1, characterized in that, In S2, the specific form of the hydraulic-thermal coupling control equations is as follows: mass conservation equation: Momentum conservation equation: Energy conservation equation The steam state equations include: 1) Steam density equation: ; 2) Steam enthalpy equation: ; Equation for the enthalpy of saturated condensate: ; in, For vapor density, u For steam velocity, t For time ，x For position coordinates, The rate of condensate loss per unit volume; P For steam pressure, f The friction resistance factor, D The inner diameter of the pipe. g It is the acceleration due to gravity. For pipe slope, T For steam temperature, Outdoor air temperature h This refers to the enthalpy of vapor. The heat loss rate per unit area The enthalpy of saturated condensate. The formula for calculating steam density using IAPWS-IF97 international steam property parameters based on steam pressure and steam temperature; The formula for calculating steam enthalpy based on steam pressure and steam temperature using the IAPWS-IF97 international steam property parameters is provided. The formula for calculating the enthalpy of saturated condensate based on steam pressure and steam temperature using the IAPWS-IF97 international steam property parameters is provided.

3. The hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines according to claim 1, characterized in that, In S4, the momentum conservation equation is spatially discretized using a quadratic upwind scheme, including: for the numbered... i , The internal velocity grid is discretized using the quadratic upwind spatial discretization momentum conservation equation to obtain the discretized momentum equation: in, u i For the current time layer velocity grid i Steam velocity at the location; u i-1 For the current time layer velocity grid i- Steam velocity at point 1; a i,i For velocity grid i Velocity in the spatially discrete algebraic equations of the momentum conservation equation u i Term coefficient; a i-1,i For velocity grid i Velocity in the spatially discrete algebraic equations of the momentum conservation equation u i-1 Term coefficient; b u,i For velocity grid i The constant term in the spatially discrete algebraic equation of the momentum conservation equation; P i-1 The main grid at the current moment i- Steam pressure at point 1; P i The main grid at the current moment i Steam pressure at the point; To control the cross-sectional area of ​​the volume.

4. The hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines according to claim 1, characterized in that, In S5, the following formula is used for main grid 1 to main grid 2. For each master grid, the pressure equation after discretization of the pressure correction equation is constructed: Among them, among them, For the current time layer velocity grid i Iterative value of steam velocity at the location; For the current time layer velocity grid i+1 Iterative value of steam velocity at the location; The main grid at the current moment vapor density at that location; The main grid at the current moment i vapor density at that location; The main grid at the current moment vapor density at that location; The main grid of the previous moment i vapor density at that location; a i,i For velocity grid i Velocity in the spatially discrete algebraic equations of the momentum conservation equation u i Term coefficient; a i+1,i+1 For velocity grid i Velocity in the spatially discrete algebraic equations of the momentum conservation equation u i+1 Term coefficient; The main grid at the current moment Steam pressure correction value; The main grid at the current moment Steam pressure correction value; The main grid at the current moment Steam pressure correction value; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Main grid Pressure correction in spatially discrete algebraic equations Term coefficient; Pressure correction equation in spatially discretized algebraic equations at the master grid Term coefficient; Main grid The constant term in the spatially discrete algebraic equation of the pressure correction equation; The main grid at the current moment Iterative value of condensate loss rate per unit volume per unit time; A is the cross-sectional area of ​​the control volume; To control the length of the body; For time intervals.

5. The hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines according to claim 1, characterized in that, In S6, the energy equations after discretization of the energy conservation equations for each master grid are constructed using the following formula: in: For the current time layer velocity grid i Steam velocity at the location; For the current time layer velocity grid i+ Steam velocity at point 1; The current time layer main grid i- Enthalpy of vapor at point 1; The current time layer main grid i Enthalpy of vapor; The current time layer main grid i+ The iterative value of the vapor enthalpy at point 1; The main grid of the previous time layer i Enthalpy of vapor; The main grid at the current moment i vapor density at that location; The main grid at the current moment i Iterative value of steam temperature at the location; T a D represents the outdoor air temperature; D represents the inner diameter of the steam pipe. Main grid i The vapor enthalpy in the spatially discrete algebraic equations of the energy conservation equation h i Term coefficient; Main grid i The vapor enthalpy in the spatially discrete algebraic equations of the energy conservation equation h i Term coefficient; Main grid i The vapor enthalpy in the spatially discrete algebraic equations of the energy conservation equation Term coefficient; Main grid i The constant term in the discrete algebraic equation of the energy conservation equation; For the current moment, the main grid i The rate of heat loss per unit area per unit time; To control the length of the body; denoted as the time interval; A represents the cross-sectional area of ​​the control volume.

6. The hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines according to claim 1, characterized in that, Before S7, the process also includes initializing the steam pressure and steam enthalpy at the main grid and calculating the condensate loss rate. The initialization of steam pressure at the main grid includes: based on the known steam pressure at the upstream boundary of the steam pipeline, the initial pressure distribution of all internal main grids and downstream boundaries is estimated using the initialization calculation formula at each main grid. Steam enthalpy initialization includes: calculating the boundary enthalpy based on the known steam pressure and steam temperature at the upstream boundary of the steam pipeline using IAPWS-IF97, and estimating the initial enthalpy distribution for all internal master grids using the steam enthalpy initialization calculation formula; The condensate loss rate includes determining the steam state at each main grid based on the initial steam pressure and steam enthalpy. If the steam state is determined to be saturated, the condensate loss rate of that main grid is calculated based on the initial steam pressure and steam enthalpy.

7. The hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines according to claim 1, characterized in that, In S8, the steam state is determined based on the updated steam pressure and steam enthalpy, including comparing the current steam enthalpy at the main grid. h With the current steam pressure at that location p Corresponding saturated vapor enthalpy value h sat （p） ;like h < h sat （p） If the steam is saturated and condensation occurs, then the steam at that location is determined to be in a saturated state; otherwise, it is in a superheated state; if it is in a saturated state, then the condensate loss rate is calculated.

8. The hydraulic-thermal coupling simulation method for secondary updraft delay correction of steam pipelines according to claim 1, characterized in that, In S10, the convergence condition includes: The change in saturated condensate loss in the entire pipe section is less than the first threshold. At the same time, the difference between the steam loss and the saturated condensate loss at the upstream and downstream boundaries of the steam pipe section, calculated based on steam velocity and steam density, meets the preset error.

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