Structural strength numerical calculation method suitable for micro heat exchange tube bundle

Abstract

The invention discloses a structural strength numerical calculation method suitable for a fine heat exchange tube bundle, and belongs to the technical field of structural finite element analysis of the fine heat exchange tube bundle in heat exchange equipment. The method comprises the following steps: firstly, determining a specific geometric structure of the fine heat exchange tube bundle, and simplifying the structure; selecting a repetitive precooling sheet heat exchange tube bundle as a model object, establishing a corresponding structural model, and performing structured grid division; then, numerical simulation calculation is conducted on the flowing heat exchange condition of cold and hot fluid inside and outside the micro heat exchange tube bundle through the tube bundle, pressure and temperature data on the boundary of the micro tube bundle are obtained from the numerical simulation calculation, and the data are used as basic input of subsequent strength calculation; then, carrying out strength calculation; the complex micro heat exchange tube bundle is simplified into the repetitive precooling sheet heat exchange tube bundle, so that the calculation difficulty is reduced, the calculation time is effectively shortened, and the calculation efficiency is improved.

Description

Technical Field

[0001] The invention relates to a numerical calculation method for the structural strength of a micro heat exchange tube bundle, and belongs to the technical field of finite element analysis of micro heat exchange tube bundle structures in heat exchange equipment. Background Art

[0002] With the rapid development of aerospace technology, the importance of hypersonic propulsion technology at high Mach numbers in the field of modern aircraft is increasing day by day, and it has become one of the key technologies in current research. In practical applications, when the flight speed of aerospace vehicles gradually increases, the stagnation temperature of the engine flow will rise significantly, which will lead to poor air compressibility, causing the performance of the power system to drop sharply, seriously affecting the overall performance of the aircraft. At the same time, the thermal protection problem faced by aircraft under high-speed flight conditions has become more difficult, and the high temperature environment poses a huge threat to the stability and reliability of aircraft structures and components. The reasonable arrangement of precooling heat exchangers at the engine inlet position can effectively cool the incoming air, significantly improve the air compression performance, and thus improve the working efficiency of the power system. It can also effectively alleviate the pressure on thermal protection, provide reliable guarantee for the stable operation of aerospace vehicles under high Mach number flight conditions, and lay a solid foundation for the further development and application of hypersonic propulsion technology. It has important practical application value and broad development prospects.

[0003] However, existing strength calculation methods for the micro heat exchange tube bundles of pre-cooling heat exchangers are usually complicated, and due to the large number of heat exchange tube bundles inside the pre-cooling heat exchanger, the calculation process is time-consuming. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the purpose of the present invention is to numerically calculate the structural strength of the micro heat exchange tube bundle based on the fluid flow and heat exchange inside and outside the micro heat exchange tube bundle, and to reasonably simplify the complex micro heat exchange tube bundle into a repetitive pre-cooling plate heat exchange tube bundle to reduce the calculation difficulty. Then, the APDL command flow programming software is used to perform strength calculation, thereby solving the problem of complex strength calculation and slow calculation speed of the micro heat exchange tube bundle.

[0005] The present invention provides a numerical calculation method for the structural strength of a micro heat exchange tube bundle, which is performed according to the following steps:

[0006] Step 1: Determine the geometric structure of the micro heat exchange tube bundle, including defining the number of tubes, number of rows, inner diameter, outer diameter, tube spacing, number of support plates, and number and position of inlet and outlet fixed constraints of the micro heat exchange tube bundle, simplify the structural model, and select a repetitive precooler heat exchange tube bundle as the calculation model;

[0007] Step 2: Use modeling software to establish the simplified repetitive precooler heat exchange tube bundle calculation model in step 1, add a boundary layer to the interface between the heat exchange tube bundle and the fluid, and perform structured meshing on the model. Complete the meshing while ensuring the quality of the mesh.

[0008] Step 3: Determine the flow conditions such as temperature, pressure, velocity and flow rate of the simplified repetitive precooler heat exchange tube bundle, the cold fluid helium, and the hot fluid air outside the tube bundle, and then simulate and analyze the flow of helium in the micro heat exchange tube bundle and the air outside the tube bundle, as well as the heat exchange of the cold and hot fluids through the tube bundle;

[0009] Step 4: Based on the flow and heat transfer analysis and calculation in step 3, the temperature and pressure data of the hot and cold fluids and the interface of the micro heat exchange tube bundle are extracted respectively, and then provided to the strength calculation end of the finite element analysis platform for interpolation calculation;

[0010] Step 5: Import the simplified repetitive precooler heat exchange tube bundle mesh model into the command flow programming software, then set the calculation type and specify the unit type of the heat exchange tube bundle as the shell unit; then define the material properties of the heat exchange tube bundle, including but not limited to elastic modulus, Poisson's ratio and thermal expansion coefficient, to ensure that the parameters reflect the actual properties of the material; the command flow programming software is ANSYS Mechanical APDL.

[0011] Step 6: Add boundary conditions to the inner and outer walls of the micro heat exchange tube bundle, set the interface type between the inner and outer fluids of the tube bundle and the inner and outer walls of the tube bundle to "coupled wall", and add boundary conditions to the inner and outer walls of the tube bundle by interpolating the temperature and pressure data of the interface between the inner and outer fluids and the heat exchange tube bundle extracted in step 4 to the grid nodes; then, load temperature and pressure loads to the model to ensure that the load distribution accurately reflects the actual working conditions to support subsequent strength analysis and calculation;

[0012] Step 6-1: Use the KNN (K-Nearest Neighbors) method to interpolate the temperature and pressure loads, extract the flow field information in the CFD simulation, including the coordinates of the grid nodes, and the corresponding temperature and pressure data as a reference data set. Calculate the distance between the surface grid nodes of the heat exchange structure and all the boundary grid nodes of the flow field, and select the k nearest known node data.

[0013] Assume that the interpolation target point is , the nearby point is , then its geometric distance is:

[0014] Therefore, the neighboring k points are,

[0015]

[0016] Among them, d k is the distance range of the adjacent points.

[0017] Step 6-2: Take a weighted average of the k known node data on the flow field boundary and use it as the estimated value of the grid node on the surface of the heat exchange structure. Calculate the estimated values ​​of all the grid nodes on the surface of the heat exchange structure to obtain the temperature and pressure data corresponding to the grid nodes on the surface of the heat exchange structure, that is, the temperature and pressure load on the surface of the structure.

[0018] Taking the average value of the data of the neighboring k points as the estimated value of the target interpolation point, we can calculate:

[0019]

[0020] Among them, F 0 is the estimated value of the heat exchange structure grid node, F i is the known data of the boundary grid nodes of the flow field, λ i is the weight of the neighboring point relative to the target interpolation node. The weight of k points is calculated as follows:

[0021]

[0022] Step 6-3: Load the temperature and pressure data of the grid nodes on the heat exchange structure to the heat exchange structure to complete the loading of temperature and pressure loads. At the same time, due to the different temperature distributions at different locations on the heat exchange structure, and the physical properties of the materials at different temperatures, the material properties of the entire heat exchange structure are different at different locations; then, by retrieving the material properties at different temperatures from the material library, the various physical properties of the heat exchange structure finite element are defined.

[0023] Step 7: Add constraints on the inlet and outlet of the precooler heat exchange tube bundle and the support plate constraints distributed with the tube bundle. Set the constraints on the inlet and outlet of the precooler heat exchange tube bundle as fixed constraints. Set the constraints on the 13 support plates distributed with the tube bundle as beam units. Connect the beam unit with the shell unit to realize the constraint of the support plate on the heat exchange tube bundle. Use the RBE3 method to constrain the connection between the support plate and the heat exchange tube bundle. At the same time, the two ends of the heat exchange tube bundle are constrained by the degree of freedom of the node unit.

[0024] The RBE3 unit is an interpolation unit with no stiffness matrix. It only involves the distribution of force. It has one master node and can have six degrees of freedom, multiple slave nodes and only translational degrees of freedom are involved. The rotational degrees of freedom are not involved. The distribution of node force is similar to the internal force distribution of the cross section of the beam unit.

[0025]

[0026] Among them, F M is the main nodal force, F SiFThe force of the main node is distributed to the node force on the slave node, and the shear force distribution of the beam section; W K is the weight coefficient of the interpolation point, W i is the weight coefficient.

[0027]

[0028] Among them, F SiM The node force of the master node is distributed to the slave nodes by the least square method, which is similar to the bending normal stress distribution of the beam section; r M r is the radius vector from the main node to the weighted geometric center; i is the radius vector from the node to the geometric center; W i is the weight coefficient.

[0029] Step 8: Solve and perform strength calculations on the model under the conditions of temperature, pressure loads and constraints to ensure that the loads and constraints accurately reflect the actual structural characteristics, thereby achieving mechanical analysis of the heat exchange tube bundle under working conditions.

[0030] The coupled solution calculation is carried out according to the structural motion equation to obtain the displacement, stress, strain, etc.

[0031]

[0032] The left side of the equation is the structural term, including the inertia force term , elastic force term ; The right side is the force term.

[0033] Where [M] is the mass matrix; [C] is the damping matrix; is the stiffness matrix; is the acceleration vector, is the velocity vector, x is the displacement vector, It is the resultant force acting on the heat exchange tube.

[0034] The external forces on the tube bundle under the action of transverse flow include the effects of fluid added mass, additional damping and additional stiffness. Generally speaking, they can be regarded as functions of the acceleration component, velocity component and displacement component of the tube bundle, so they can be expressed in the following form:

[0035]

[0036] In the formula, For additional mass; is the additional damping; For additional stiffness; The total damping value is A positive value indicates that the system has vibration energy loss, and the total stiffness value A positive value indicates that the system has the ability to maintain stability.

[0037] The present invention has the following beneficial effects:

[0038] 1) By reasonably simplifying the structure of the precooler micro heat exchange tube bundle, the complex micro heat exchange tube bundle is simplified into a repetitive precooler heat exchange tube bundle, which reduces the calculation difficulty, effectively reduces the calculation time, and improves the calculation efficiency.

[0039] 2) Combined with command flow programming technology, it can realize the effective extraction and rapid calculation of the surface temperature and pressure data of the heat exchange tube bundle. The KNN method is used to interpolate the temperature and pressure loads, accurately obtain the temperature and pressure data of the grid nodes, and reasonably add boundary conditions and loads to ensure the accuracy of the calculation results.

[0040] This method achieves effective extraction and rapid calculation of the surface temperature and pressure data of the heat exchanger bundle by reasonably simplifying the structure of the precooling heat exchanger micro heat exchanger bundle and combining it with command flow programming technology. This method not only improves the calculation efficiency, but also ensures the accuracy of the results, providing strong support for the design and optimization of the precooling heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a complete flow chart of the present invention.

[0042] Figure 2 Schematic diagram of the overall structural calculation model of the heat exchanger.

[0043] Figure 3 This is a schematic diagram of the structure of 4 rows of 98 micro heat exchange tube bundles.

[0044] Figure 4 This is the strain distribution curve of 4 rows of heat exchange micro-tube bundles.

[0045] Figure 5 This is the strain distribution waterfall diagram of 4 rows of heat exchange micro-tube bundles.

[0046] Figure 6 It is a comparison curve between the maximum strain value of the micro heat exchange tube bundle under the design conditions and the actual strain value of the micro heat exchange tube bundle in the experiment.

[0047] In the figure: 1. the first part of the heat exchanger model cavity, 2. the second part of the heat exchanger model cavity, 3. the heat exchange core, 4. the micro heat exchange tube bundle, 5. the helium outlet main pipe, 6. the helium inlet main pipe, 7. the heat exchange tube row, 8. the support plate. DETAILED DESCRIPTION

[0048] Combine the following Figure 1 The present invention is further described in detail with reference to the flowchart in FIG.

[0049] The present invention provides a numerical calculation method for the structural strength of a micro heat exchange tube bundle, which is performed according to the following steps:

[0050] Step 1: Determine the geometric structure of the micro heat exchange tube bundle, including defining the number of tubes, number of rows, inner diameter, outer diameter, tube spacing, number of support plates, and number and position of inlet and outlet fixed constraints of the micro heat exchange tube bundle, simplify the structural model, and select a repetitive precooler heat exchange tube bundle as the calculation model;

[0051] Step 2: Use the modeling software UG to establish the simplified calculation model of the repetitive precooler heat exchange tube bundle in step 1, add a boundary layer to the interface between the heat exchange tube bundle and the fluid, and perform structured meshing on the model. Complete the meshing while ensuring the mesh quality.

[0052] Step 3: Determine the flow conditions such as temperature, pressure, velocity and flow rate of the simplified repetitive precooler heat exchange tube bundle and the cold fluid helium tube bundle and the hot fluid air outside the tube bundle, and then simulate and analyze the flow of helium in the repetitive precooler heat exchange tube bundle and the air outside the tube bundle, as well as the heat exchange of the cold and hot fluids through the tube bundle;

[0053] Step 4: Based on the flow and heat transfer analysis and calculation in step 3, the temperature and pressure data of the hot and cold fluids and the interface of the micro heat exchange tube bundle are extracted respectively, and then provided to the strength calculation end of the finite element analysis platform for interpolation calculation;

[0054] Step 5: Import the simplified repetitive precooler heat exchange tube bundle mesh model into the command flow programming software ANSYS Mechanical APDL, then set the calculation type and specify the unit type of the heat exchange tube bundle as shell unit; then use the parametric language command flow programming to define the material properties of the heat exchange tube bundle, including but not limited to elastic modulus, Poisson's ratio and thermal expansion coefficient, to ensure that the parameters reflect the actual characteristics of the material;

[0055] Step 6: Add boundary conditions to the inner and outer walls of the micro heat exchange tube bundle, set the interface type between the inner and outer fluids of the tube bundle and the inner and outer walls of the tube bundle to "coupled wall", and use parameterized language command flow programming to interpolate the temperature and pressure data of the interface between the inner and outer fluids and the heat exchange tube bundle extracted in step 4 to the grid nodes to add boundary conditions to the inner and outer walls of the tube bundle; then, load temperature and pressure loads to the model to ensure that the load distribution accurately reflects the actual working conditions to support subsequent strength analysis and calculation;

[0056] Step 6-1: Use the KNN (K-Nearest Neighbors) method to interpolate the temperature and pressure loads, extract the flow field information in the CFD simulation, including the coordinates of the grid nodes, and the corresponding temperature and pressure data as a reference data set. Calculate the distance between the surface grid nodes of the heat exchange structure and all the boundary grid nodes of the flow field, and select the k nearest known node data.

[0057] Assume that the interpolation target point is , the nearby point is , then its geometric distance is:

[0058] Therefore, the neighboring k points are,

[0059]

[0060] Among them, d k is the distance range of the adjacent points.

[0061] Step 6-2: Take a weighted average of the k known node data on the flow field boundary and use it as the estimated value of the grid node on the surface of the heat exchange structure. Calculate the estimated values ​​of all the grid nodes on the surface of the heat exchange structure to obtain the temperature and pressure data corresponding to the grid nodes on the surface of the heat exchange structure, that is, the temperature and pressure load on the surface of the structure.

[0062] Taking the average value of the data of the neighboring k points as the estimated value of the target interpolation point, we can calculate:

[0063]

[0064] Among them, F 0 is the estimated value of the heat exchange structure grid node, F i is the known data of the boundary grid nodes of the flow field,

[0065] λ i is the weight of the neighboring point relative to the target interpolation node. The weight of k points is calculated as follows:

[0066]

[0067] Step 6-3: Load the temperature and pressure data of the grid nodes on the heat exchange structure to the heat exchange structure to complete the loading of temperature and pressure loads. At the same time, due to the different temperature distributions at different locations on the heat exchange structure, and the physical properties of the materials at different temperatures, the material properties of the entire heat exchange structure are different at different locations; then, by retrieving the material properties at different temperatures from the material library, the various physical properties of the heat exchange structure finite element are defined.

[0068] Step 7: Use command flow programming to add constraints on the inlet and outlet of the micro heat exchange tube bundle and the support plate constraints distributed with the tube bundle. Set the constraints on the inlet and outlet of the precooler heat exchange tube bundle as fixed constraints. Set the constraints on the 13 support plates distributed with the tube bundle as beam units. Connect the beam unit with the shell unit to realize the constraint of the support plate on the heat exchange tube bundle. Use the RBE3 method to constrain the connection between the support plate and the heat exchange tube bundle. At the same time, the two ends of the heat exchange tube bundle are constrained by the degree of freedom of the node unit.

[0069] The RBE3 unit is an interpolation unit with no stiffness matrix. It only involves the distribution of force. It has one master node and can have six degrees of freedom, multiple slave nodes and only translational degrees of freedom are involved. The rotational degrees of freedom are not involved. The distribution of node force is similar to the internal force distribution of the cross section of the beam unit.

[0070]

[0071] Among them, F SiF The force of the main node is distributed to the node force on the slave node, and the shear force distribution of the beam section; W i is the weight coefficient.

[0072]

[0073] Among them, F SiM The node force of the master node is distributed to the slave nodes by the least square method, which is similar to the bending normal stress distribution of the beam section; r M r is the radius vector from the main node to the weighted geometric center; i is the radius vector from the node to the geometric center; W i is the weight coefficient.

[0074] Step 8: Solve in the command flow programming environment and perform strength calculations on the model under the conditions of temperature, pressure loads and constraints to ensure that the loads and constraints accurately reflect the actual structural characteristics, thereby achieving mechanical analysis of the heat exchange tube bundle under working conditions.

[0075] The coupled solution calculation is carried out according to the structural motion equation to obtain the displacement, stress, strain, etc.

[0076]

[0077] The left side of the equation is the structural term, including the inertia force term , elastic force term ; The right side is the force term.

[0078] Where [M] is the mass matrix; [C] is the damping matrix; is the stiffness matrix; is the acceleration vector, is the velocity vector, x is the displacement vector, It is the resultant force acting on the heat exchange tube.

[0079] The external forces on the tube bundle under the action of transverse flow include the effects of fluid added mass, additional damping and additional stiffness. Generally speaking, they can be regarded as functions of the acceleration component, velocity component and displacement component of the tube bundle, so they can be expressed in the following form:

[0080]

[0081] In the formula, For additional mass; is the additional damping; For additional stiffness; The total damping value is A positive value indicates that the system has vibration energy loss, and the total stiffness value A positive value indicates that the system has the ability to maintain stability.

[0082] Example

[0083] The following is a clear and complete description of the technical solutions in the implementation cases of the present invention. The examples described below are merely design condition cases in the calculation process.

[0084] The present invention provides a numerical calculation method for the structural strength of a micro heat exchange tube bundle based on a parameterized language command flow programming environment. Figure 1 The present invention is further explained. The heat exchanger model cavity includes two parts, namely, the first part 1 of the heat exchanger model cavity and the second part 2 of the heat exchanger model cavity. A heat exchange core 3 and a fine heat exchange tube bundle 4 are arranged in the second part 2 of the heat exchanger model cavity. A helium outlet manifold 5 and a helium inlet manifold 6 are arranged at both ends of the heat exchange tube bundle 4. Thirteen support plates 8 are arranged between the heat exchange tube rows 7, and the angle between two adjacent support plates 8 is 30°. There are 4 rows of heat exchange tube rows 7, with a total of 98 tubes;

[0085] The method specifically includes the following specific steps: Step 1: Determine the geometric structure of the micro heat exchange tube bundle, specifically including defining a single row of 24 heat exchange tubes, 4 rows of 98 tubes, a heat exchange tube outer diameter of 1 mm, an inner diameter of 0.8 mm, a tube spacing of 1.25 mm, 13 support plates, and the number and position of two fixed constraints at the inlet and outlet of the micro heat exchange tube bundle, simplify the structural model, and select a repetitive precooler heat exchange tube bundle as the calculation model;

[0086] Step 2: Establish the simplified repetitive precooler heat exchange tube bundle calculation model in step 1 in the 3D modeling software UG, add a boundary layer to the interface between the heat exchange tube bundle and the fluid, and perform structured meshing on the model. Complete the meshing while ensuring the quality of the mesh, with a mesh quantity of more than 20 million.

[0087] Step 3: By adding boundary conditions of 3 m / s and 750 K at a gauge pressure of 0.128 MPa to the air inlet of the intake precooling heat exchange structure model, and adding boundary conditions of 166.7 m / s and 190 K at a gauge pressure of 4 MPa to the helium inlet, the flow conditions such as temperature, pressure, flow rate and flow rate of the cold fluid helium tube bundle in the simplified repetitive precooling plate heat exchange tube bundle and the hot fluid air outside the tube bundle are determined, and then the flow of helium in the repetitive precooling plate heat exchange tube bundle and the air outside the tube bundle and the heat exchange of the cold and hot fluids through the tube bundle are simulated and analyzed;

[0088] Step 4: Based on the flow and heat transfer analysis and calculation in step 3, the temperature and pressure data of the interface between the hot and cold fluids and the tube bundle of the repetitive precooler heat exchange tube bundle are extracted respectively. The temperature load ranges from 223.384K to 934.905K and the pressure load ranges from 3.2718MPa to 3.89227MPa with the position of the tube bundle. Then, it is provided to the strength calculation end of the finite element analysis platform for interpolation calculation;

[0089] Step 5: Import the simplified repetitive precooler heat exchange tube bundle mesh model into the command flow programming software ANSYS Mechanical APDL, then set the calculation type and specify the unit type of the heat exchange tube bundle as shell unit; then use the parametric language command flow programming to define the material properties of the heat exchange tube bundle, define the elastic modulus as 20400, Poisson's ratio as 0.32, and thermal expansion coefficient as 0.000018, to ensure that the parameters reflect the actual characteristics of the material;

[0090] Step 6: Add boundary conditions to the inner and outer walls of the repetitive precooler heat exchange tube bundle, set the interface type between the inner and outer fluids of the tube bundle and the inner and outer walls of the tube bundle to "coupled wall", and add boundary conditions to the inner and outer walls of the tube bundle by interpolating the temperature and pressure data of the interface between the inner and outer fluids and the heat exchange tube bundle extracted in step 4 to the grid nodes; then, load temperature and pressure loads to the model to ensure that the load distribution accurately reflects the actual working conditions to support subsequent strength analysis and calculation;

[0091] Step 6-1: Use the KNN (K-Nearest Neighbors) method to interpolate the temperature and pressure loads, extract the flow field information in the CFD simulation, including the coordinates of the grid nodes, and the corresponding temperature and pressure data as a reference data set. Calculate the distance between the surface grid nodes of the heat exchange structure and all the boundary grid nodes of the flow field, and select the k nearest known node data.

[0092] Assume that the interpolation target point is , the nearby point is , then its geometric distance is:

[0093] Therefore, the neighboring k points are,

[0094]

[0095] Among them, d k is the distance range of the adjacent points.

[0096] Step 6-2: Take a weighted average of the k known node data on the flow field boundary and use it as the estimated value of the grid node on the surface of the heat exchange structure. Calculate the estimated values ​​of all the grid nodes on the surface of the heat exchange structure to obtain the temperature and pressure data corresponding to the grid nodes on the surface of the heat exchange structure, that is, the temperature and pressure load on the surface of the structure.

[0097] Taking the average value of the data of the neighboring k points as the estimated value of the target interpolation point, we can calculate:

[0098]

[0099] Among them, F 0 is the estimated value of the heat exchange structure grid node, F i is the known data of the boundary grid nodes of the flow field,

[0100] λ i is the weight of the neighboring point relative to the target interpolation node. The weight of k points is calculated as follows:

[0101]

[0102] Step 6-3: Load the temperature and pressure data of the grid nodes on the heat exchange structure to the heat exchange structure to complete the loading of temperature and pressure loads. At the same time, due to the different temperature distributions at different locations on the heat exchange structure, and the physical properties of the materials at different temperatures, the material properties of the entire heat exchange structure are different at different locations; then, by retrieving the material properties at different temperatures from the material library, the various physical properties of the heat exchange structure finite element are defined.

[0103] Step 7: Add constraints on the inlet and outlet of the precooler heat exchange tube bundle and the support plate constraints distributed with the tube bundle. Set the constraints on the inlet and outlet of the micro heat exchange tube bundle as fixed constraints. Set the constraints on the 13 support plates distributed with the tube bundle as beam units. Connect the beam unit with the shell unit to realize the constraint of the support plate on the heat exchange tube bundle. Use the RBE3 method to constrain the connection between the support plate and the heat exchange tube bundle. At the same time, the two ends of the heat exchange tube bundle are constrained by the degree of freedom of the node unit.

[0104] The RBE3 unit is an interpolation unit with no stiffness matrix. It only involves the distribution of force. It has one master node and can have six degrees of freedom. It has multiple slave nodes and only translational degrees of freedom. The rotational degrees of freedom are not involved. The distribution of node force is similar to the internal force distribution of the cross section of the beam unit. The node force is expressed as follows:

[0105]

[0106] Among them, F SiF The force of the main node is distributed to the node force on the slave node, and the shear force distribution of the beam section; W i is the weight coefficient.

[0107]

[0108] Among them, F SiM The node force of the master node is distributed to the slave nodes by the least square method, which is similar to the bending normal stress distribution of the beam section; r M r is the radius vector from the main node to the weighted geometric center; i is the radius vector from the node to the geometric center; W i is the weight coefficient.

[0109] Step 8: Solve and perform strength calculations on the model under the conditions of temperature, pressure loads and constraints to ensure that the loads and constraints accurately reflect the actual structural characteristics, thereby achieving mechanical analysis of the heat exchange tube bundle under working conditions.

[0110] The coupled solution calculation is carried out according to the structural motion equation to obtain the displacement, stress, strain, etc.

[0111]

[0112] The left side of the equation is the structural term, including the inertia force term , elastic force term ; The right side is the force term.

[0113] Where [M] is the mass matrix; [C] is the damping matrix; is the stiffness matrix; is the acceleration vector, is the velocity vector, x is the displacement vector, It is the resultant force acting on the heat exchange tube.

[0114] The external forces on the tube bundle under the action of transverse flow include the effects of fluid added mass, additional damping and additional stiffness. Generally speaking, they can be regarded as functions of the acceleration component, velocity component and displacement component of the tube bundle, so they can be expressed in the following form:

[0115]

[0116] In the formula, For additional mass; is the additional damping; For additional stiffness; The total damping value is A positive value indicates that the system has vibration energy loss, and the total stiffness value A positive value indicates that the system has the ability to maintain stability.

[0117] Through the above calculation, the maximum stress and maximum deformation displacement under the design condition can be obtained, as shown in Table 1.

[0118] Table 1

[0119]

[0120] At the same time, the numerical simulation results and the test results under normal temperature conditions were compared through calculation, and it was found that the deviation between the vibration deformation displacement obtained by numerical simulation and the test value was within 8%, indicating that the numerical calculation method for the structural strength of the micro heat exchange tube bundle is feasible, verifying the reliability of the results of the present invention.

Claims

1. A numerical calculation method for the structural strength of a micro heat exchange tube bundle, characterized in that: The following steps are involved: Step 1: Determine the geometric structure of the micro heat exchange tube bundle and simplify the structural model into a repetitive precooler heat exchange tube bundle calculation model; Step 2: Use modeling software to establish the calculation model of the repetitive precooler heat exchange tube bundle in step 1, and perform structured meshing on the model, add a boundary layer to the interface between the heat exchange tube bundle and the fluid, and complete the meshing while ensuring the mesh quality; Step 3: Determine the flow conditions of temperature, pressure, velocity and flow rate of the cold fluid helium in the repetitive precooler heat exchange tube bundle and the hot fluid air outside the tube bundle, and then simulate and analyze the flow of helium in the micro heat exchange tube bundle and the air outside the tube bundle, as well as the heat exchange of the cold and hot fluids through the tube bundle; Step 4: Based on the flow and heat transfer analysis and calculation in step 3, the temperature and pressure data of the cold and hot fluids in the micro heat exchange tube bundle and the interface of the tube bundle are extracted respectively; Step 5: Import the simplified repetitive precooler heat exchange tube bundle grid model into the command flow programming software, set the calculation type, specify the unit type of the heat exchange tube bundle as shell unit; and define the material properties of the heat exchange tube bundle; Step 6: Add boundary conditions to the inner and outer walls of the micro heat exchange tube bundle by interpolating the temperature and pressure data of the interface between the hot and cold fluids of the micro heat exchange tube bundle and the tube bundle to the grid nodes, set the interface type between the inner and outer fluids of the tube bundle and the inner and outer walls of the tube bundle to "coupled wall"; then load the temperature and pressure loads to the model; Step 6-1: Use the KNN method to interpolate the temperature and pressure loads and extract the flow field information in the CFD simulation; calculate the distance between the surface grid nodes of the heat exchange structure and all the boundary grid nodes of the flow field, and select the k nearest known node data; Assume that the interpolation target point is , the nearby point is , then its geometric distance is: ; Therefore, the k adjacent points are: ； Among them, d k is the distance range of the adjacent points; Step 6-2: Perform weighted average of k known node data on the flow field boundary and use it as the estimated value of the grid node on the surface of the heat exchange structure. Calculate the estimated value of all the grid nodes on the surface of the heat exchange structure to obtain the temperature and pressure data corresponding to the grid nodes on the surface of the heat exchange structure, that is, the temperature and pressure load on the surface of the structure; The average value of the data of the neighboring k points is used as the estimated value of the target interpolation point, and thus it is calculated that: ； Where F0 is the estimated value of the heat exchange structure grid node, F i is the known data of the boundary grid nodes of the flow field, λ i is the weight of the neighboring point relative to the target interpolation node. The weight of k points is calculated as follows: ； Step 6-3: Load the temperature and pressure data of the grid nodes on the heat exchange structure to the heat exchange structure to complete the loading of temperature and pressure loads; define the various physical properties of the heat exchange structure finite element by retrieving material properties at different temperatures from the material library; Step 7: Add constraints on the inlet and outlet of the micro heat exchange tube bundle and the support plate constraints distributed with the tube bundle. Set the constraints on the inlet and outlet of the precooler heat exchange tube bundle as fixed constraints, and set the support plate constraints distributed with the tube bundle as beam units. Connect the beam unit with the shell unit to realize the constraint of the support plate on the heat exchange tube bundle. Use the RBE3 method to constrain the connection between the support plate and the heat exchange tube bundle. At the same time, the two ends of the heat exchange tube bundle are constrained by the degree of freedom of the node unit. Step 8: Perform strength calculation on the model under the conditions of temperature, pressure load and imposed constraints to realize mechanical analysis of the heat exchange tube bundle under working condition; According to the following structural motion equations, coupled solution calculations are performed to obtain displacement and stress strain; ； Where [M] is the mass matrix; [C] is the damping matrix; is the stiffness matrix; is the acceleration vector, is the velocity vector, x is the displacement vector, is the resultant force acting on the heat exchange tube; The external forces on the tube bundle under the action of the transverse flow include the effects of the fluid added mass, additional damping and additional stiffness, which are considered as functions of the acceleration component, velocity component and displacement component of the tube bundle: ； In the formula, For additional mass; is the additional damping; For additional stiffness; The total damping value is the fluid force on the tube bundle. A positive value indicates that the system has vibration energy loss, and the total stiffness value A positive value indicates that the system has the ability to maintain stability.

2. A numerical calculation method for structural strength of a micro heat exchange tube bundle according to claim 1, characterized in that: In step 1, the geometric structure of the fine heat exchange tube bundle includes the number of tubes, number of rows, inner diameter, outer diameter, tube spacing, number of support plates, and number and position of inlet and outlet fixed constraints of the fine heat exchange tube bundle.

3. A numerical calculation method for structural strength of a micro heat exchange tube bundle according to claim 1, characterized in that: In step 5, the material properties include elastic modulus, Poisson's ratio and thermal expansion coefficient.

4. A numerical calculation method for structural strength of a micro heat exchange tube bundle according to claim 1, characterized in that: In step 6-1, the flow field information in the CFD simulation includes the coordinates of the grid nodes and the corresponding temperature and pressure data.

5. A numerical calculation method for structural strength of a micro heat exchange tube bundle according to claim 1, characterized in that: The step 7 is specifically as follows: The RBE3 element is an interpolation element without a stiffness matrix. The node force is expressed as follows: ； Among them, F M is the main nodal force, F SiF The force of the main node is distributed to the node force on the slave node, and the shear force distribution of the beam section; W K is the weight coefficient of the interpolation point, W i is the weight coefficient; ； Among them, F SiM is the node force of the master node distributed to the slave nodes by the least square method; r M r is the radius vector from the main node to the weighted geometric center; i is the radius vector from the node to the geometric center.

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