A pressure resistance simulation method for magnetic liquid rotary seals considering the influence of thermal expansion

Abstract

The present invention discloses a pressure-resistant simulation method for a magnetic liquid rotary seal considering the influence of thermal expansion, which is carried out according to the following steps: Step S1: Determine the theoretical parameters of the seal geometric model and establish a simplified two-dimensional axisymmetric magnetic liquid rotary seal model; Step S2: Establish a steady-state thermal expansion model, solve the thermal expansion deformation by coupling the flow field, temperature field and solid mechanics field, and derive the grid results; Step S3: Call the grid results and establish a transient magnetic-fluid coupling model; Calculate the pressure-resistant capacity at different rotational speeds by using the transient magnetic-fluid coupling model; The present invention can comprehensively consider the influence of the temperature field on the magnetic field and the flow field, can quickly and accurately simulate the thermal expansion phenomenon of the magnetic liquid rotary seal, can also improve the simulation of the magnetic liquid seal, and provides a theoretical basis for the design and optimization of the magnetic liquid seal.

Description

Technical Field

[0001] The present invention relates to the field of magnetic fluid seal simulation, and particularly to a method for simulating the pressure resistance of a magnetic fluid rotary seal considering the influence of thermal expansion. Background Art

[0002] Magnetic fluid is an intelligent material, which is widely used in the fields of machinery, flotation, acoustics, thermodynamics, medical treatment, etc. The most mature application at present is magnetic fluid seal. As a new type of seal, it has irreplaceable advantages over traditional seals such as zero leakage, high reliability, long life, and no friction, and is suitable for high-speed seal conditions in these specific fields.

[0003] Under the action of a magnetic field, magnetic fluid is adsorbed in the gap between the rotating shaft and the pole shoe. Under high-speed seal conditions, the rotating shaft drives the magnetic fluid to move. Due to the viscous dissipation heat generation of the magnetic fluid, the temperature of the seal gap rises. Due to the thermal expansion effect of the rotating shaft and the pole shoe materials, the seal gap expands and deforms due to heat, and the change of the seal gap will lead to the change of the magnetic field distribution in the gap, thereby affecting the magnetic fluid seal ability.

[0004] Therefore, the research on the influence of thermal expansion on magnetic fluid rotary seals is of great significance. With the rapid development of computer hardware and finite element software, numerical calculation has become the main method for studying magnetic fluid seal problems. The simulation method has the advantages of less research cost and short cycle compared with the experimental method, and can easily reveal the complex internal structure mechanism of magnetic fluid seals. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for simulating the pressure resistance of a magnetic fluid rotary seal considering the influence of thermal expansion. The present invention can comprehensively consider the influence of the temperature field on the magnetic field and the flow field, can quickly and accurately simulate the thermal expansion phenomenon of the magnetic fluid rotary seal, and can also improve the simulation of the magnetic fluid seal, providing a theoretical basis for the design and optimization of the magnetic fluid seal.

[0006] The technical solution of the present invention: A method for simulating the pressure resistance of a magnetic fluid rotary seal considering the influence of thermal expansion, the specific steps are as follows:

[0007] Step S1: Determine the theoretical parameters of the seal geometric model, and establish a simplified two-dimensional axisymmetric magnetic fluid rotary seal model;

[0008] Step S2: Establish a steady-state thermal expansion model, and use the coupling of the flow field, temperature field and solid mechanics field to solve the thermal expansion deformation and export the mesh results;

[0009] Step S3: Call the mesh results to establish a transient magnetic-fluid coupling model; use the transient magnetic-fluid coupling model to calculate the pressure resistance at different rotational speeds.

[0010] The two-dimensional axisymmetric magnetic fluid rotary seal model in step S1 includes a housing, a rotating shaft is provided on the housing, two pole shoes arranged up and down are sleeved on the rotating shaft, a permanent magnet that fits with both of them is arranged between the pole shoes, and there are multiple magnetic circuits among the permanent magnet, the pole shoes and the rotating shaft, and magnetic fluid is arranged in the magnetic circuits.

[0011] The specific steps of step S2 are as follows:

[0012] Step S2.1: Set the material properties of the flow field, temperature field and solid mechanics, set the flow field and heat transfer boundary conditions, and set the mesh division;

[0013] Step S2.2: Couple and calculate the deformation caused by thermal expansion, use the dynamic mesh method to describe the gap change, set the solver, complete the drawing group result setting, and export the mesh result after expansion deformation.

[0014] In the flow field of the thermal expansion model, the rotating wall velocity is set, and the contact pair is set in the solid mechanics field of the thermal expansion model; in the temperature field, the absolute heat source and heat flux are set, and the heat flux is the convective heat flux; the mesh division of the thermal expansion model uses free triangular meshes.

[0015] The specific steps of step S3 are as follows:

[0016] Step S3.1: Set the material properties of the magnetic field and flow field, set the magnetic field and flow field boundary conditions, write the magnetic field force into the fluid N-S equation, and set the mesh division;

[0017] Step S3.2: Use the dynamic mesh method to couple and solve the liquid dynamic boundary, set the solver, and complete the drawing group result setting of the liquid film state, and calculate the pressure resistance of the magnetic fluid seal structure affected by thermal expansion at different rotational speeds.

[0018] The boundary condition of the magnetic field is defined as determining the magnetization ability of the permanent magnet and the magnetization curve of the magnetic material on the magnetic field; the boundary condition of the flow field is defined as determining the rotational speed, pressure inlet, pressure outlet and fluid interface in the flow field, and writing the volume force of the magnetic field on the magnetic fluid into the flow field as a bridge for coupling the magnetic field and the flow field.

[0019] The transient magnetic-fluid coupling model setting of step S3 includes defining the time step, total time, solution type and stop condition; the stop condition means stopping the calculation when the pressure resistance of the magnetic fluid is broken through.

[0020] Compared with the prior art, a mathematical model is established based on the thermal expansion effect, taking into account the thermal expansion change of the magnetic liquid sealing structure, and analyzing the pressure resistance of the magnetic liquid seal; the addition of the influence of thermal expansion in the present invention can more accurately obtain the pressure resistance performance of the magnetic liquid rotary seal; researchers can reasonably combine magnetic materials according to the thermal expansion effect of different magnetic materials, thereby improving the sealing performance, and helping to deepen the understanding of the working state of the magnetic liquid seal, which has guiding significance for the design and application of the magnetic liquid seal, and has the characteristics of simple method implementation and less calculation amount. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the first process schematic diagram of the present invention;

[0022] Figure 2 is the second process schematic diagram of the present invention;

[0023] Figure 3 is the geometric model in the embodiment of the present invention;

[0024] Figure 4 is the viscosity coefficient of the magnetic liquid in the embodiment of the present invention;

[0025] Figure 5 is the transient laminar boundary condition in the embodiment of the present invention;

[0026] Figure 6 is the transient laminar mesh division in the embodiment of the present invention;

[0027] Figure 7 is the simulation result of the thermal expansion displacement of the seal gap in the embodiment of the present invention;

[0028] Figure 8 is the simulation result of the magnetic liquid boundary state under the critical pressure in the embodiment of the present invention;

[0029] Figure 9 is the comparison result of the pressure resistance considering the influence of thermal expansion in the embodiment of the present invention.

[0030] The reference signs in the drawings are: 1, rotating shaft; 2, magnetic liquid; 3, pole shoe; 4, permanent magnet; 5, housing; 6, inlet; 7, air domain; 8, outlet. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The present invention will be further described below with reference to the drawings and embodiments, but it shall not be used as a basis for limiting the present invention.

[0032] Embodiment: A pressure resistance simulation method for a magnetic liquid rotary seal considering the influence of thermal expansion, as shown in the attached Figure 1 and attached Figure 2 figures, is carried out according to the following steps:

[0033] Step S1: Establishing the theoretical parameters of the sealing geometric model, and establishing a simplified two-dimensional axisymmetric magnetic liquid rotating sealing model; the two-dimensional axisymmetric magnetic liquid rotating sealing model in step S1 includes a housing 5, a rotating shaft 1 is provided on the housing, two pole shoes 3 are sleeved on the rotating shaft, a permanent magnet 4 is provided between the pole shoes and the two pole shoes, a plurality of magnetic circuits are provided between the permanent magnets, the pole shoes and the rotating shaft, a magnetic liquid 2 is provided in the magnetic circuit, and the magnetic liquid forms a plurality of sealing liquid films. The key geometric parameters are shown in Table 1, and the air domain model is not shown as shown in the attached figure. Figure 3 shown.

[0034]

[0035] Table 1 Key geometric parameters

[0036] Step S2: Establish a steady-state thermal expansion model, solve the thermal expansion deformation by coupling the flow field, temperature field and solid mechanics field, and derive the grid results;

[0037] The specific steps of step S2 are as follows:

[0038] Step S2.1: Set the material properties of flow field, temperature field and solid mechanics, set the flow field and heat transfer boundary conditions, and set the meshing;

[0039] 1) Establish a two-dimensional axisymmetric model and give the initial interface of the magnetic liquid.

[0040] 2) The material parameters of the shaft, pole piece, permanent magnet, magnetic fluid and shell are shown in Table 2.

[0041]

[0042]

[0043] Table 2 Material definition

[0044] 3) The material properties of the air domain adopt the software's own properties; the initial temperature is 20°C; the dynamic viscosity of the magnetic fluid is as shown in the attached Figure 4 As shown, the "interpolation" function form is used to link with the simulation; set "Contact Pair 1", "Source Boundary" to the lower boundary of the permanent magnet, and "Target Boundary" to the contact boundary between the lower pole shoe and the permanent magnet; set "Contact Pair 2", "Source Boundary" to the upper boundary of the permanent magnet, and "Target Boundary" to the contact boundary between the upper pole shoe and the permanent magnet.

[0045] 4) Select the magnetic fluid in the "Laminar Flow" domain, set it to "Incompressible Flow", and select "Eddy Current"; set the "Wall", select the interface between the magnetic fluid and the rotating shaft as the boundary, set the "Moving Wall Velocity" phi direction to V, and set the "Wall Condition" to "No Slip"; set the "Pressure Point Constraint" to ensure the simulation convergence.

[0046] 5) The "Solid Mechanics" domain includes a rotating shaft, pole shoes, permanent magnets, and a housing. Set the permanent magnets and pole shoes to be in "contact", and the "pair selection" to be "Contact Pair 1" and "Contact Pair 2"; set the outer edge of the pole shoes to be "roller supported".

[0047] 6) The "Solid and Fluid Heat Transfer" domain includes all components and the air domain surrounded by the components; set the outer side of the housing as the "heat flux" boundary, and its type is "convective heat flux"; the remaining outer boundaries are all adiabatic.

[0048] 7) Add "Multiphysics" - "Non-isothermal Flow", and its coupling interfaces are "Laminar Flow" and "Solid and Fluid Heat Transfer"; the "Flow Heating" is "Viscous Dissipation", and add the "Thermal Expansion" multiphysics.

[0049] 8) For all meshes, the "Sequence Type" adopts "Physics Field Controlled Mesh".

[0050] Step S2.2: Couple and calculate the deformation caused by thermal expansion, use the dynamic mesh method to describe the gap change, set the solver, complete the result setting of the drawing group, and export the mesh result after expansion deformation;

[0051] 1) Set "Dynamic Mesh", and the "Deformation Domain" includes all domains of air and magnetic liquid; the "Mesh Smoothing Type" is "Yeoh", and the "Hardening Factor" is 10.

[0052] 2) Set "Parametric Sweep", add "V (rotational speed)" for sweeping, the parameter value range is 0 - 10 m / s, and the step size is 1.

[0053] 3) Set the solver and use the default solver.

[0054] 4) Complete the result setting of the drawing group and export the mesh result.

[0055] Step S3: Call the mesh result to establish a transient magneto-fluid coupling model; use the transient magneto-fluid coupling model to calculate the pressure resistance at different rotational speeds;

[0056] The specific steps of step S3 are as follows:

[0057] Step S3.1: Set the material properties of the magnetic field and the flow field, set the boundary conditions of the magnetic field and the flow field, write the magnetic field force into the fluid N - S equation, and set the mesh division. The boundary condition of the magnetic field is defined to determine the magnetization ability of the permanent magnet and the magnetization curve of the magnetic material on the magnetic field; the boundary condition of the flow field is defined to determine the rotational speed, pressure inlet, pressure outlet, and fluid interface in the flow field, and write the volume force of the magnetic field on the magnetic liquid into the flow field as a bridge to couple the magnetic field and the flow field;

[0058] 1) Define the pressure parameter P0 = 1e6 Pa; define the step function step1 and the ramp function rm1 for applying the rotational speed and loading pressure, with the aim of controlling the pressure loading after the speed reaches stability; define the point directly below the midpoint of the pole tooth on the shaft side as the critical point, and set a "domain point probe" at this point, with the "point probe expression" being "root.material.domain"; write the magnetization curves of the magnetic fluid and 2Cr13 (shaft, pole shoe) into COMSOL; for the magnetic fluid and air domains, set the "deformed domain"; the "mesh smoothing type" is "Yeoh", and the "hardening factor" is 10.

[0059] 2) The "magnetic field" domain includes all domains. For the shaft, pole shoe, and magnetic fluid, in the "magnetic flux conservation" setting, set the "B-H curve" as the "magnetization model", the "magnetic flux density modulus" source as "from material", and the "magnetic co-energy density" source as "from material"; for the permanent magnet, in the "magnetic flux conservation" setting, set "magnetization" as the "magnetization model", and set the z-direction of "magnetization" to "960000"; set the zero scalar magnetic potential.

[0060] 3) To simplify the calculation, simulate the sealing ability of one pole tooth here. So the "laminar flow" domain includes the magnetic fluid 2 and air domain 7 in the colored area in the attachment. Check the "eddy current" in the "physical model"; set the "inlet" 6, with the "static pressure" being "P0*rm1(t[1 / s])"; set the "outlet" 8, with the "static pressure" being "0"; set the "fluid-fluid interface", and the "boundary selection" includes the boundary between air and magnetic fluid; set the "wall", with the "boundary selection" being the shaft side, and set the "moving wall velocity component" to "V*step1(t[1 / s])"; set the "body force", with the "domain selection" including air and magnetic fluid, and set the r-direction of the "body force" to "(mfnc.Mr*d(mfnc.Br,r)+mfnc.Mz*d(mfnc.Br,z))*step1(t[1 / s])", and the z-direction of the "body force" to "(mfnc.Mr*d(mfnc.Bz,r)+mfnc.Mz*d(mfnc.Bz,z))*step1(t[1 / s])". Figure 5

[0061] 4) The "mesh sequence type" adopts the "user-controlled mesh"; for the magnetic fluid, select free triangular mesh generation and customize the "element size" to 2e-2 mm; for the air domain, select free triangular mesh generation and customize the "element size" to 0.1 mm; for other domains, select free triangular mesh generation, predefined as "more refined"; the mesh generation of the fluid is as shown in the attachment. Figure 6

[0062] Step S3.2: Use the dynamic mesh method to couple and solve the liquid dynamic boundary, set the solver, and complete the result setting of the liquid film state drawing group, and calculate the pressure resistance of the magnetic liquid seal structure affected by thermal expansion at different rotational speeds;

[0063] 1) In the "Transient" step of the study, the "Output Time" is defined as "Logarithmic", "Start" is 1e-6, "End" is 1, and "Steps per decade" is 10, that is, the "Output Time" is "0, 10^{range(log10(1.0e-6), 1 / 10, log10(0.5))}".

[0064] 2) Set the transient solver, select "MUMPS" for the "Direct" solver; add a "Stop Condition", and the "Stop Expression" is "root.comp1.ppb1<5", and the satisfaction condition is "True(>=1)".

[0065] 3) Generate and save the thermal expansion contour map and the magnetic liquid boundary state contour map of the seal structure, as shown in Appendix Figure 7 and Appendix Figure 8 as shown.

[0066] 4) Obtain the difference in pressure resistance considering and not considering thermal deformation. The simulation results are shown in Appendix Figure 9 as shown. The critical pressure of the simulation group considering thermal expansion is greater than that without considering thermal expansion.

Claims

1. A pressure resistance simulation method for magnetic liquid rotary seals considering the influence of thermal expansion, characterized in that: Proceed as follows: Step S1: Establish the theoretical parameters of the sealed geometric model and build a two-dimensional axisymmetric magnetic liquid rotary seal model; Step S2: Establish a steady-state thermal expansion model, use the coupling solution of the flow field, temperature field and solid mechanics field to solve the thermal expansion deformation and derive the grid results; Step S3: Call the grid results and establish a transient magneto-fluid coupling model; use the transient magneto-fluid coupling model to calculate the pressure resistance at different rotational speeds; The specific steps of Step S2 are as follows: Step S2.1: Set the material properties of the flow field, temperature field and solid mechanics, set the flow field and heat transfer boundary conditions, and set the grid division; Step S2.2: Coupling calculation of the deformation caused by thermal expansion, use the dynamic grid method to describe the gap change, set the solver, complete the drawing group result setting, and export the grid results after expansion deformation; The flow field in the thermal expansion model sets the rotating wall velocity, and the solid mechanics field in the thermal expansion model sets the contact pair; the temperature field sets the absolute heat source and heat flux, and the heat flux is the convective heat flux; The grid division in the thermal expansion model uses free triangular grids.

2. The magnetic fluid rotary seal pressure-resistant simulation method considering the influence of thermal expansion according to claim 1, characterized in that: The two-dimensional axisymmetric magnetic liquid rotary seal model in Step S1 includes a housing, a rotating shaft is provided on the housing, two upper and lower pole shoes are sleeved on the rotating shaft, a permanent magnet is provided between the pole shoes and is attached to both of them, and there are multiple magnetic circuits between the permanent magnet, the pole shoes and the rotating shaft, and magnetic liquid is provided in the magnetic circuits.

3. The magnetic fluid rotary seal pressure resistance simulation method considering thermal expansion effects according to claim 1, characterized in that: The specific steps of Step S3 are as follows: Step S3.1: Set the material properties of the magnetic field and flow field, set the magnetic field and flow field boundary conditions, write the magnetic field force into the fluid N-S equation, and set the grid division; Step S3.2: Use the dynamic grid method to couple and solve the liquid dynamic boundary, set the solver, and complete the drawing group result setting of the liquid film state, and calculate the pressure resistance of the magnetic liquid seal structure affected by thermal expansion at different rotational speeds.

4. The magnetic liquid rotary seal pressure-resistant simulation method considering the influence of thermal expansion according to claim 3, characterized in that: The boundary condition of the magnetic field is defined as determining the magnetization ability of the permanent magnet and the magnetization curve of the magnetic material on the magnetic field; the boundary condition of the flow field is defined as determining the rotational speed, pressure inlet, pressure outlet and fluid interface in the flow field, and writing the volume force of the magnetic field on the magnetic liquid into the flow field as a bridge between the coupling magnetic field and the flow field.

5. The magnetic fluid rotary seal pressure resistance simulation method considering the influence of thermal expansion according to claim 1, characterized in that: The setting of the transient magneto-fluid coupling model in Step S3 includes defining the time step, total time, solution type and stop condition; the stop condition means stopping the calculation when the pressure resistance of the magnetic liquid is broken through.

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