A CFD-based method for calculating aerodynamic characteristics of a rotating diaphragm flow stage

Abstract

The present invention discloses a method for calculating the aerodynamic characteristics of a rotating baffle flow stage based on CFD. The calculation model of the present invention can accurately capture the three-dimensional complex mixing phenomenon between the steam flows from different rotating windows and between the steam flows and the main flow of the blade grid after the steam flows out when the circumferential opening areas of the rotating baffle windows are inconsistent. The functional relationship between different rotation angles and flow rates can be obtained, providing more accurate basic data for engineering design. The present invention adopts different numerical simulation calculation models and has strong versatility.

Description

Technical Field

[0001] The invention belongs to the technical field of flow heat exchange, and in particular relates to a method for calculating aerodynamic characteristics of a rotating baffle flow stage based on CFD. Background Art

[0002] The rotating baffle is mainly composed of a rotating ring, a plate body, assembled guide vanes, an upper cover ring, a lower cover ring, a connecting rod mechanism, an oil motor and other components. It controls and adjusts the steam extraction flow rate by rotating the rotating ring steam inlet window placed in front of the stator blades to change the flow area of ​​the stator blades.

[0003] When designing the flow stage of the rotating baffle, it is crucial to determine the mapping relationship between the rotation angle and the extraction and flow rate. Considering the premise that it is difficult to conduct actual high-temperature tests on the whole machine, it is efficient and convenient to use computational fluid dynamics methods to conduct research. Existing calculation methods usually only use periodic boundaries to focus on the characteristics of the single model. Although they can provide certain guidance, the calculation of the single model lacks global key phenomena. For example, when the circumferential opening area is inconsistent, the three-dimensional complex mixing phenomenon between the steam flows from different rotating windows and between them and the main flow of the blade grid after outflow. The simplified calculation method makes the boundary conditions of the calculation model inconsistent with the real model to a certain extent, and the simulation results will produce uncertain interpolation errors. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide a CFD-based method for calculating the aerodynamic characteristics of a rotating baffle flow stage. The method establishes a full three-dimensional calculation model, including a calculation domain model of the rotating baffle steam inlet window, a nozzle group diversion transition section, a stationary blade nozzle and a moving blade. Therefore, it is possible to accurately capture the three-dimensional complex mixing phenomenon between the steam outflows of different rotating windows and between the steam outflows and the main flow of the blade grid, making the calculation results of the rotation angle, the extraction steam and the flow rate more realistic and reliable.

[0005] In order to achieve the above object, the present invention comprises the following steps:

[0006] S1, establish a 1:1 physical size three-dimensional rotating baffle flow stage calculation domain model, the three-dimensional rotating baffle flow stage calculation domain model includes the rotating baffle steam inlet window, nozzle group drainage transition section, stationary blade nozzle and moving blade calculation domain model;

[0007] S2, meshing the three-dimensional rotating baffle flow stage calculation domain model to generate multiple structured grids;

[0008] S3, for the calculation domain model of the rotating baffle flow stage, the boundary conditions are set according to the actual physical conditions to establish a numerical simulation calculation model and perform numerical solution of the flow;

[0009] S4, using the established numerical simulation calculation model, by changing the rotation opening of the steam inlet window of the rotating partition, the functional relationship between different rotation angles and the flow rate is obtained;

[0010] By changing the rotation opening of the steam inlet window of the rotating baffle to fully closed, the aerodynamic characteristics of the flow stage behind the rotating baffle under the minimum cooling angle boundary are obtained to evaluate whether there is a safety hazard of blast heating.

[0011] In S1, the specific method of establishing the three-dimensional rotating baffle flow stage calculation domain model is as follows:

[0012] S11, establish a computational domain model of the rotating baffle steam inlet window. The circumferential opening area of ​​the rotating baffle steam inlet window is inconsistent, and it is a non-axisymmetric arrangement. The computational domain model is a full-circumference model.

[0013] S12, establishing a calculation domain model of the nozzle group drainage transition section, where the calculation domain model is a full-circle calculation model;

[0014] S13, establishing the calculation domain models of the stationary blade nozzle and the moving blade, the stationary blade nozzle is a grouped circumferential model, and the moving blade model is a rotating circumferential model.

[0015] The geometric model building software is used to build the calculation domain model of the rotating baffle steam inlet window, the calculation domain model of the nozzle group diversion transition section, and the calculation domain model of the stationary blade nozzle and the moving blade.

[0016] In S2, the specific method of grid division is as follows:

[0017] S21, meshing the three-dimensional computational domain model of the steam inlet window of the rotating baffle and the nozzle group diversion transition section, and generating a structural grid of multiple topological blocks in a top-down manner; mesh encryption is performed on the wall surface during mesh generation, and an O-type mesh is used to generate a boundary layer. When generating the mesh, the maximum aspect ratio of the mesh is less than 100, and the orthogonal angle is greater than 45 degrees;

[0018] S22, mesh the three-dimensional computational domain model of the stationary blade nozzle and the moving blade. The topological structure of the stationary blade inlet flow channel and the blade inlet and outlet extension adopts the HOH structured grid, and the stationary blade surface adopts the O-type topological body-fitting grid. The circumferential, axial and radial nodes are encrypted respectively to ensure the subsequent numerical solution.

[0019] The three-dimensional computational domain model of the steam inlet window of the rotating baffle and the nozzle group diversion transition section is imported into the mesh generation software ICEM for meshing;

[0020] The three-dimensional computational domain model of the stationary blade nozzle and the moving blade is imported into the mesh generation software NUMECA AUTO GRID for meshing.

[0021] The specific methods in S3 are as follows:

[0022] S31, the total pressure, total temperature and turbulence boundary conditions are set at the mainstream inlet of the rotating baffle steam inlet window, and the flow direction is perpendicular to the inlet surface;

[0023] The outlet average static pressure boundary condition is set at the moving blade outlet;

[0024] The computational domain is set as a stationary domain and a rotating domain. The rotating domain and rotating wall are set to rotate at a speed according to the actual rotation speed. The data transmission mode of the dynamic and static interface area is a mixed plane. The remaining solid walls are set to be uniform adiabatic and non-slip walls.

[0025] S32, solve the three-dimensional viscous compressible unsteady flow heat transfer control equations, and introduce the Boussinesq turbulence model assumption to make the turbulence calculation Reynolds-averaged Navier-Stokes equations closed, and obtain the aerodynamic parameters of the fluid calculation domain pressure, temperature and flow velocity through calculation.

[0026] The stationary domain includes the rotating baffle steam inlet window, the nozzle group diversion transition section and the stationary blades; the rotating domain includes the moving blades.

[0027] The general form of the governing equations for three-dimensional viscous compressible unsteady flow heat transfer is as follows:

[0028]

[0029] Where ρ is the fluid density; is a universal variable, Can represent u, v, w, T, and the solution variables of k and ε, is the generalized diffusion coefficient, is the generalized source term, where and The expression is the definition given based on specific variables in the numerical calculation model;

[0030] The turbulent viscosity based on the Boussinesq hypothesis is introduced, and the Reynolds stress is expressed as a function of the turbulent viscosity, that is:

[0031]

[0032]

[0033]

[0034] In the formula, μ t is the turbulent viscosity, k is the turbulent kinetic energy, δ ij is the Kronecker symbol.

[0035] Compared with the prior art, the calculation model of the present invention can accurately capture the three-dimensional complex mixing phenomenon between the steam flows from different rotating windows and between the steam flows and the main flow of the blade cascade when the circumferential opening areas of the rotating baffle windows are inconsistent. The functional relationship between different rotation angles and flow rates can be obtained, providing more accurate basic data for engineering design. The present invention adopts different numerical simulation calculation models and has strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A calculation model diagram of a rotary baffle flow-through stage structure according to an embodiment of the present invention;

[0037] Figure 2 The computational grid of the flow-through stage of the rotating baffle of the embodiment of the present invention; wherein (a) is the computational grid of the nozzle of the stationary blade, (b) is the computational domain grid of the moving blade, and (c) is the computational domain grid of the nozzle group diversion transition section;

[0038] Figure 3 The rotating window distribution of the rotating baffle flow level calculation model of the embodiment of the present invention;

[0039] Figure 4 This is a pressure distribution diagram of a stationary blade inlet cross section according to an embodiment of the present invention;

[0040] Figure 5 This is a pressure distribution diagram of a stationary blade outlet cross section according to an embodiment of the present invention;

[0041] Figure 6 It is a velocity vector distribution diagram at different windows of an embodiment of the present invention;

[0042] Figure 7 is a relationship diagram corresponding to different rotation angles and flow rates according to an embodiment of the present invention;

[0043] Figure 8 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings.

[0045] See also Figures 1 to 8 , the present invention comprises the following steps:

[0046] Step 1: Based on the actual size of the geometric drawings and referring to the flow structure, a 1:1 solid-size three-dimensional rotating baffle flow stage calculation domain model is established through three-dimensional modeling software, including the calculation domain models of the rotating baffle steam inlet window, nozzle group diversion transition section, stationary blade nozzle and moving blade. The specific steps are as follows:

[0047] Step 1-1: Use the geometric model building software to establish the calculation domain model of the rotating baffle steam inlet window. The number of windows is selected according to the actual drawings. The circumferential opening area of ​​the rotating baffle steam inlet window is inconsistent, which is a non-axisymmetric arrangement. The calculation domain model is a full-circumference model;

[0048] Step 1-2: Use the geometric model building software to establish the calculation domain model of the nozzle group diversion transition section. The flow area of ​​the stationary blade nozzle corresponding to the diversion transition section is determined according to the actual drawings. The calculation domain model is a full-circle calculation model;

[0049] Step 1-3: Use geometric model building software to build the calculation domain model of the stationary blade nozzle and the moving blade. The stationary blade nozzle is a grouped circumferential model, and the moving blade model is a rotating circumferential model;

[0050] Step 2: The three-dimensional rotating baffle flow-through calculation domain model obtained in step 1 is meshed to generate multiple structured grids. The specific steps are as follows:

[0051] Step 2-1: Import the three-dimensional computational domain model of the rotating baffle steam inlet window and the nozzle group diversion transition section into the grid generation software ICEM for grid division, and generate a structural grid of multiple topological blocks through a top-down "sculpting" method. When generating the grid, the grid is encrypted on the wall surface, and the boundary layer is generated using an O-type grid. When generating the grid, ensure that the maximum aspect ratio of the grid is less than 100 and the orthogonal angle is above 45 degrees.

[0052] Step 2-2: Import the three-dimensional computational domain model of the stationary blade nozzle and the moving blade into the mesh generation software NUMECA AUTOGRID for meshing. The topological structure of the stationary blade inlet flow channel and the blade inlet and outlet extensions adopts the HOH structured grid, and the stationary blade surface adopts the O-type topological body-fitting grid. The circumferential, axial and radial node encryption are performed separately to ensure the subsequent numerical solution.

[0053] Step 3: For the calculation domain model of the rotating baffle flow stage, boundary conditions are set according to actual physical conditions and flow numerical solutions are performed. The specific steps are as follows:

[0054] Step 3-1: Set the total pressure, total temperature and turbulence boundary conditions at the mainstream inlet of the rotating baffle steam inlet window, and the flow direction is perpendicular to the inlet surface; set the outlet average static pressure boundary condition at the moving blade outlet; set the static domain and rotating domain in the calculation domain respectively, the static domain includes the rotating baffle steam inlet window, the nozzle group drainage transition section and the stationary blade, and the rotating domain mainly includes the moving blade; set the rotation speed of the rotating domain and the rotating wall according to the actual speed, the data transmission mode of the dynamic and static interface area is the mixed plane (stage), and the remaining solid walls are set to be uniform adiabatic non-slip walls;

[0055] Step 3-2: Solve the three-dimensional viscous compressible unsteady flow heat transfer control equations, and introduce the Boussinesq turbulence model hypothesis to make the turbulence calculation Reynolds-averaged Navier-Stokes equations closed, and obtain important aerodynamic parameters such as pressure, temperature and flow velocity in the fluid calculation domain through calculation;

[0056] The general form of the three-dimensional viscous compressible unsteady flow heat transfer control equations is as follows:

[0057]

[0058] Where ρ is the fluid density; It is a universal variable that can represent u, v, w, T, as well as solution variables such as k and ε; is the generalized diffusion coefficient; is the generalized source term. and The expression is a definition given based on specific variables in the numerical calculation model.

[0059] The turbulent viscosity based on the Boussinesq hypothesis is introduced, and the Reynolds stress is expressed as a function of the turbulent viscosity, that is:

[0060]

[0061]

[0062]

[0063] In the formula, μ t is the turbulent viscosity, k is the turbulent kinetic energy, δ ij is the Kronecker symbol.

[0064] Step 4: Using the established numerical simulation model, by changing the rotation opening of the rotating baffle steam inlet window, obtain the functional relationship between different rotation angles and flow rate. By changing the rotation opening of the rotating baffle steam inlet window to fully closed, obtain the aerodynamic characteristics of the flow stage behind the rotating baffle under the minimum cooling angle boundary, and evaluate whether there is a safety hazard of blast heating.

Claims

1. A CFD-based method for calculating the aerodynamic characteristics of a rotating baffle flow stage, characterized in that: The following steps are involved: S1, establish a 1:1 physical size three-dimensional rotating baffle flow stage calculation domain model, the three-dimensional rotating baffle flow stage calculation domain model includes the rotating baffle steam inlet window, nozzle group drainage transition section, stationary blade nozzle and moving blade calculation domain model; S2, meshing the three-dimensional rotating baffle flow stage calculation domain model to generate multiple structured grids; S3, for the calculation domain model of the rotating baffle flow stage, the boundary conditions are set according to the actual physical conditions to establish a numerical simulation calculation model and perform numerical flow solution; the specific method is as follows: S31, the total pressure, total temperature and turbulence boundary conditions are set at the mainstream inlet of the rotating baffle steam inlet window, and the flow direction is perpendicular to the inlet surface; The outlet average static pressure boundary condition is set at the moving blade outlet; The computational domain is set as a stationary domain and a rotating domain. The rotating domain and rotating wall are set to rotate at a speed according to the actual rotation speed. The data transmission mode in the dynamic and static interface area is a mixed plane, and the remaining solid walls are set to be uniform adiabatic non-slip walls. The stationary domain includes the rotating baffle steam inlet window, the nozzle group diversion transition section and the stationary blades; the rotating domain includes the moving blades. S32, solve the three-dimensional viscous compressible unsteady flow heat transfer control equations, and introduce the Boussinesq turbulence model to make the turbulence calculation Reynolds time-averaged Navier-Stokes equations closed, and obtain the aerodynamic parameters of the fluid calculation domain pressure, temperature and flow velocity through calculation; the general form of the three-dimensional viscous compressible unsteady flow heat transfer control equations is as follows: Where ρ is the fluid density; is a universal variable, Can represent u, v, w, T, and the solution variables of k and ε, is the generalized diffusion coefficient, is the generalized source term, where and The expression is the definition given based on specific variables in the numerical calculation model; The turbulent viscosity based on the Boussinesq hypothesis is introduced, and the Reynolds stress is expressed as a function of the turbulent viscosity, that is: In the formula, μ t is the turbulent viscosity, k is the turbulent kinetic energy, δ ij is the Kronecker symbol; S4, using the established numerical simulation calculation model, by changing the rotation opening of the steam inlet window of the rotating partition, the functional relationship between different rotation angles and the flow rate is obtained; By changing the rotation opening of the steam inlet window of the rotating baffle to fully closed, the aerodynamic characteristics of the flow stage behind the rotating baffle under the minimum cooling angle boundary are obtained to evaluate whether there is a safety hazard of blast heating.

2. The CFD-based aerodynamic characteristics calculation method for a rotating baffle flow stage according to claim 1, characterized in that: In S1, the specific method of establishing the three-dimensional rotating baffle flow stage calculation domain model is as follows: S11, establish a computational domain model of the rotating baffle steam inlet window. The circumferential opening area of ​​the rotating baffle steam inlet window is inconsistent, and it is a non-axisymmetric arrangement. The computational domain model is a full-circumference model. S12, establishing a calculation domain model of the nozzle group drainage transition section, where the calculation domain model is a full-circle calculation model; S13, establishing the calculation domain models of the stationary blade nozzle and the moving blade, the stationary blade nozzle is a grouped circumferential model, and the moving blade model is a rotating circumferential model.

3. The CFD-based aerodynamic characteristic calculation method of a rotating baffle flow stage according to claim 2, characterized in that: The geometric model building software is used to build the calculation domain model of the rotating baffle steam inlet window, the calculation domain model of the nozzle group diversion transition section, and the calculation domain model of the stationary blade nozzle and the moving blade.

4. The CFD-based aerodynamic characteristics calculation method for a rotating baffle flow stage according to claim 1, characterized in that: In S2, the specific method of grid division is as follows: S21, meshing the three-dimensional computational domain model of the steam inlet window of the rotating baffle and the nozzle group diversion transition section, and generating a structural grid of multiple topological blocks in a top-down manner; mesh encryption is performed on the wall surface during mesh generation, and an O-type mesh is used to generate a boundary layer. When generating the mesh, the maximum aspect ratio of the mesh is less than 100, and the orthogonal angle is greater than 45 degrees; S22, mesh the three-dimensional computational domain model of the stationary blade nozzle and the moving blade. The topological structure of the stationary blade inlet flow channel and the blade inlet and outlet extension adopts the HOH structured grid, and the stationary blade surface adopts the O-type topological body-fitting grid. The circumferential, axial and radial nodes are encrypted respectively to ensure the subsequent numerical solution.

5. The CFD-based aerodynamic characteristic calculation method of a rotating baffle flow stage according to claim 4, characterized in that: The three-dimensional computational domain model of the steam inlet window of the rotating baffle and the nozzle group diversion transition section is imported into the mesh generation software ICEM for meshing; The three-dimensional computational domain model of the stationary blade nozzle and the moving blade is imported into the mesh generation software NUMECA AUTO GRID for meshing.

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