A simulation method for defrosting the rear windshield of a car based on STAR-CCM+

Abstract

The present invention relates to a vehicle rear windshield defrosting simulation method based on STAR‑CCM+, the method comprising the following steps: S01, establishing a rear windshield defrosting heat exchange model based on STAR‑CCM+, completing boundary condition setting according to pre-collected attribute parameters of the rear windshield and the resistance wire, and performing transient simulation analysis of rear windshield defrosting of the whole vehicle, and calibrating the heat transfer coefficient of the rear windshield inside and outside the whole vehicle by comparing with the rear windshield defrosting test results of the whole vehicle; S02, according to the relationship between the resistivity and temperature of the resistance wire, writing the functional relationship between the heating power of the resistance wire and the temperature change through a custom function user code, and performing rear windshield defrosting coupling simulation. The present invention can complete the electric-thermal coupling calculation of rear windshield defrosting only by using STAR‑CCM+ without increasing the software procurement cost, and has the advantages of efficient and convenient calculation while the simulation accuracy can meet the engineering application, and can be used for the rear windshield defrosting performance evaluation of the whole vehicle, and provides effective guidance for the design of the rear windshield electric heating defrosting system.

Description

Technical Field

[0001] The present invention belongs to the technical field of automobile windshield defrosting and defogging, and in particular is an automobile rear windshield defrosting simulation technology based on STAR-CCM+. Background Art

[0002] The defrosting performance of automobile windshields is related to driving safety. It is an important new energy indicator in the development process of the whole vehicle and is subject to relevant regulations. Unlike the hot air blowing method used for the front windshield, the rear windshield usually uses the thin film metal wire electric heating method. The rear windshield is defrosted by electric heating. The heating power of the resistance wire is large and the defrosting effect is also good. The heating resistance wire is printed on the inner surface of the glass by screen printing. The printed glass is tempered by high temperature and high pressure to sinter the conductive silver paste to the glass surface. Because the resistance wire has inherent resistance, it heats up after power is applied to both ends. The heat is transferred to the outer surface through the glass, and finally the frost on the outer surface of the glass is eliminated. It is very important to reasonably design the rear windshield point heating defrosting system to ensure that its defrosting performance meets the regulatory requirements while taking into account cost reduction and efficiency improvement.

[0003] The traditional design method of electric heating defrost system is usually to modify the existing product structure, conduct multiple tests, and verify repeatedly until it is qualified. This method is mainly based on experience, with a long design cycle and high cost. In addition, with the rapid development of numerical computing technology and high-performance computing equipment, mainstream rear windshield suppliers have also begun to use numerical calculations to design electric heating defrost systems, but this method usually requires the use of dedicated simulation software, which will increase software procurement costs and learning costs. Summary of the invention

[0004] The purpose of the present invention is to provide a car rear windshield defrosting simulation method based on STAR-CCM+ to solve the following technical problems: the traditional electric heating defrosting system design method is mainly based on experience, with a long design cycle and high cost. In addition, with the rapid development of numerical computing technology and high-performance computing equipment, mainstream rear windshield suppliers have begun to use numerical calculations to design electric heating defrosting systems. However, dedicated simulation software is usually used, which increases software procurement costs and learning costs.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a vehicle rear windshield defrosting simulation method based on STAR-CCM+, comprising the following steps:

[0006] S01, based on STAR-CCM+, a rear windshield defrosting heat transfer model is established. The boundary conditions are set according to the pre-collected property parameters of the rear windshield and the resistance wire, and a transient simulation analysis of the rear windshield defrosting of the whole vehicle is performed. By comparing with the rear windshield defrosting test results of the whole vehicle, the heat transfer coefficient of the rear windshield inside and outside the whole vehicle is calibrated;

[0007] S02, based on the relationship between the resistivity and temperature of the resistance wire, the function relationship between the heating power of the resistance wire and the temperature is written through the custom function user code to perform rear windshield defrosting coupling simulation.

[0008] Preferably,

[0009] In the S01, the property parameters of the rear windshield include density, specific heat, and thermal conductivity of the glass according to the structural dimensions of the glass;

[0010] The property parameters of the resistance wire include heating power curve, resistivity and geometric dimensions.

[0011] Preferably,

[0012] In the step S01, the rear windshield defrosting heat transfer model includes a glass solid internal heat conduction model, a double-layer melting empirical model, and a resistance wire, glass and surrounding air convection heat transfer model;

[0013] Preferably, in said S01, the step of establishing a rear windshield defrosting heat exchange model is:

[0014] S0101, cutting out a resistance wire area on the inner wall surface of the rear windshield according to geometric parameters of the resistance wire, and dividing the resistance wire area and each surface of the rear windshield into surface grids;

[0015] S0102, import the boundary surface meshes of the resistance wire and the rear windshield into STAR-CCM+ and divide the volume mesh;

[0016] S0103, select the physical model, select the three-dimensional, solid, implicit non-steady-state calculation model, select the DeIcing model for defrosting and turn on the Thin Film model;

[0017] S0104, setting boundary conditions, including heating power curve of resistance wire, heat transfer coefficient of inner and outer walls of rear windshield, and ambient temperature;

[0018] S0105, set the solution time step, and select the second order time discrete format;

[0019] S0106, run calculations, detect the cloud map of the thickness of the rear windshield frost layer, record the time taken to completely remove the frost layer in the rear windshield field of view, and compare it with the test results;

[0020] S0107, if the difference between the test value and the simulation value of the time taken for rear windshield defrosting exceeds expectations, it is necessary to correct the heat transfer coefficient of the inner and outer walls of the rear windshield, and repeat steps S0104, S0105, and S0106 until the error of the simulation result meets expectations.

[0021] Preferably,

[0022] In the S02, the steps of programming the functional relationship between the heating power of the resistance wire and the temperature change through the user code of the custom function are as follows:

[0023] S0201, based on the attribute parameters collected in S01, and based on the relationship between resistivity and temperature: ρ=ρ0 (1+aT), and the resistor heating power calculation company: P=U2 / R, use void name to write the relationship between the heating power of the resistor wire and its temperature, and control the heating power of the resistor wire to update over time, where the temperature and time step data can be called using ucfunc;

[0024] S0202, load the written user code into STAR-CCM+, specify the corresponding heating power custom function for each resistor wire, run the calculation, and complete the rear gear defrost transient simulation.

[0025] By adopting the above technical scheme, the beneficial technical effects that can be achieved by the present invention are as follows: the present invention corrects the heat transfer coefficient of the rear windshield defrosting heat transfer model through test results. The user-defined function user code is used to compile the relationship between the heating power and temperature of the resistance wire in the electric heating defrosting system, thereby realizing the electric-thermal coupling calculation of the rear windshield defrosting in the general CFD calculation software, reducing the purchase and learning costs of special calculation software, while having the advantages of high calculation efficiency and high precision, and providing an effective rear windshield defrosting performance optimization method for automobile research and development and manufacturers. Without increasing the software procurement cost, the present invention can complete the electric-thermal coupling calculation of the rear windshield defrosting using only STAR-CCM+. While the simulation accuracy can meet the engineering application, it has the advantages of high efficiency and convenience in calculation, and can be used for the evaluation of the rear windshield defrosting performance of the whole vehicle, providing effective guidance for the design of the rear windshield electric heating defrosting system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the process of the present invention;

[0027] Figure 2 This is the transient simulation result of rear window defrosting. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings.

[0029] STAR-CCM+ is a new generation CFD solver developed by CD-adapco using the most advanced computational continuum mechanics algorithms. It is equipped with CD-adapco's original latest network generation technology, which can complete a series of operations required for grid generation, such as complex shape data input, surface preparation - such as wrapping (maintaining shape, simplifying geometry, automatically filling holes, preventing component contact, checking leakage, etc.), surface mesh reconstruction, automatic volume mesh generation (including polyhedral mesh, hexahedral core mesh, dodecahedral core mesh, tetrahedral mesh), etc.

[0030] STAR-CCM+ uses the polyhedral network advocated by CD-adapco, which can achieve a 3 to 10 times improvement in computing performance compared to the original tetrahedral mesh while maintaining the same computing accuracy.

[0031] STAR-CCM+ software is a new generation of general computational fluid dynamics (CFD) analysis software developed by CD-adapco Group.

[0032] like Figure 1 The present invention provides a simulation method for defrosting the rear windshield of an automobile based on STAR-CCM+. Overall, the steps include: the first step is to obtain the attribute parameters of the windshield and the resistance wire from the rear windshield supplier; the second step is to establish a rear windshield defrosting heat exchange model; the third step is to compare the defrosting time t of the simulation and the test; the fourth step is to determine the defrosting time t of the test. 试验 The simulated defrost time t 仿真 Is the difference less than or equal to the expected standard? Step 5: In step 4, if yes, go to step 6; Step 6: load usercode user-defined function; Step 7: electrothermal coupling simulation; Step 8: analyze the rear defrost result; Step 9: If no, correct the heat transfer coefficient of the inner and outer walls in step 4, and then return to step 3.

[0033] Specifically, the present invention provides a vehicle rear windshield defrosting simulation method based on STAR-CCM+, which includes the following steps:

[0034] The first step is to collect the property parameters of the rear windshields and resistance wires of various models. The property parameters of the rear windshield include the density, specific heat, thermal conductivity and structural dimensions of the glass; the property parameters of the resistance wire include the heating power curve, resistivity and geometric dimensions of the resistance wire.

[0035] In the second step, based on the collected data, a rear windshield defrost heat transfer model was established in STAR-CCM+, the boundary parameter settings and solver settings were completed, and the rear windshield defrost transient solution calculation was run. By comparing with the test results, the heat transfer coefficients of the inner and outer walls of the rear windshield were continuously corrected.

[0036] Specifically, the steps of establishing the rear windshield defrosting heat transfer model and continuously correcting the heat transfer coefficients of the inner and outer walls of the rear windshield are as follows:

[0037] a1. According to the geometric parameters of the resistance wire, a resistance wire area is cut out on the inner wall surface of the rear windshield, and surface grids are divided for the resistance wire area and each surface of the rear windshield.

[0038] a2. Import the boundary surface meshes of the resistance wire and the rear windshield into STAR-CCM+ and divide the volume mesh.

[0039] a3, select the physical model, select the three-dimensional, solid, implicit non-steady-state calculation model, select the DeIcing model for defrosting and turn on the Thin Film model.

[0040] a4, set boundary conditions, including the heating power curve of the resistance wire, the heat transfer coefficient of the inner and outer walls of the rear windshield, and the ambient temperature.

[0041] a5, set the solution time step, and select second order as the time discretization format.

[0042] a6. Run the calculation, check the cloud diagram of the frost layer on the rear windshield, record the time taken to completely remove the frost from the rear windshield viewing area, and compare it with the test results.

[0043] a7. If the difference between the experimental value and the simulation value of the time taken for rear windshield defrosting exceeds expectations, it is necessary to correct the heat transfer coefficient of the inner and outer walls of the rear windshield, and repeat a4 to a6 until the error of the simulation result meets expectations.

[0044] The third step is to use the user-defined function user code to write the functional relationship between the heating power of the resistor wire and the temperature change, and perform the electric-thermal coupling simulation of rear windshield defrosting.

[0045] Specifically, STAR-CCM+ user-defined function user code is used to write the relationship between the heating power of the resistance wire and the temperature. The steps for performing the electrothermal coupling calculation are as follows:

[0046] b1, based on the relevant parameters collected in the first step, and according to the relationship between resistivity and temperature: ρ=ρ0 (1+aT), and the calculation formula of resistance heating power: P=U2 / R, use void name(result, int size, args ...) to write the relationship between the heating power of the resistance wire and its temperature, and control the heating power of the resistance wire to update with the time step. Among them, the temperature and time step data can be called using ucfunc(void *func, char *type, char *name);

[0047] like Figure 2 As shown in b2, load the written user code into STAR-CCM+, specify the corresponding heating power user-defined function for each resistor wire, run the calculation, and complete the rear gear defrost transient simulation.

[0048] The fourth step is to post-process the rear windshield defrost results, check the frost thickness cloud map, analyze the results and guide the optimization design of the rear windshield defrost performance.

Claims

1. A simulation method for defrosting the rear windshield of an automobile based on STAR-CCM+, characterized in that: The steps involved are: S01, based on STAR-CCM+, a rear windshield defrosting heat transfer model is established. The boundary conditions are set according to the pre-collected property parameters of the rear windshield and the resistance wire, and a transient simulation analysis of the rear windshield defrosting of the whole vehicle is performed. By comparing with the rear windshield defrosting test results of the whole vehicle, the heat transfer coefficient of the rear windshield inside and outside the whole vehicle is calibrated; S02, based on the relationship between the resistivity and temperature of the resistance wire, the function relationship between the heating power of the resistance wire and the temperature is written through the custom function user code to perform rear windshield defrosting coupled simulation, including: S0201, based on the property parameters collected in S01, and based on the relationship between resistivity and temperature: ρ=ρ0(1+aT), and the resistance heating power calculation formula: P=U 2 / R, use void name to write the relationship between the heating power of the resistance wire and its temperature, and control the heating power of the resistance wire to update over time. Among them, the temperature and time step data are called using ucfunc; S0202, load the written user code into STAR-CCM+, specify the corresponding heating power custom function for each resistor wire, run the calculation, and complete the rear gear defrost transient simulation.

2. The method according to claim 1, characterized in that In the S01, the property parameters of the rear windshield include density, specific heat, and thermal conductivity of the glass according to the structural dimensions of the glass; The property parameters of the resistance wire include heating power curve, resistivity and geometric dimensions.

3. The method according to claim 1, characterized in that In the step S01, the rear windshield defrosting heat transfer model includes a glass solid internal heat conduction model, a double-layer melting empirical model, and a resistance wire, glass and surrounding air convection heat transfer model; In the step S01, the steps of establishing the rear windshield defrosting heat exchange model are: S0101, cutting out a resistance wire area on the inner wall surface of the rear windshield according to geometric parameters of the resistance wire, and dividing the resistance wire area and each surface of the rear windshield into surface grids; S0102, import the boundary surface meshes of the resistance wire and the rear windshield into STAR-CCM+ and divide the volume mesh; S0103, select the physical model, select the three-dimensional, solid, implicit non-steady-state calculation model, select the DeIcing model for defrosting and turn on the Thin Film model; S0104, setting boundary conditions, including heating power curve of resistance wire, heat transfer coefficient of inner and outer walls of rear windshield, and ambient temperature; S0105, set the solution time step, and select the second order time discrete format; S0106, run calculations, detect the cloud map of the thickness of the rear windshield frost layer, record the time taken to completely remove the frost layer in the rear windshield field of view, and compare it with the test results; S0107, if the difference between the test value and the simulation value of the time taken for rear windshield defrosting exceeds expectations, it is necessary to correct the heat transfer coefficient of the inner and outer walls of the rear windshield, and repeat steps S0104, S0105, and S0106 until the error of the simulation result meets expectations.

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