Method for calculating strength of engine cooling fan assembly based on one-way fluid-solid coupling

Abstract

The application discloses a kind of engine cooling fan assembly strength calculation method based on one-way fluid-solid coupling, comprising: the geometric model of cooling fan assembly is established;Utilize the finite element model of cooling fan assembly and external flow field generated by mesh division software;In structural analysis software, respectively, to cooling fan and fan support plate is endowed with material mechanics characteristics, and boundary condition is set;In computational fluid dynamics software, set the turbulence model and boundary condition of external flow field;Blade surface is set as fluid-solid coupling surface, first solve flow field using computational fluid dynamics software, pass blade surface pressure in calculation result to finite element software by interpolation, and finite element software is used as boundary condition to simulate and analyze the structural strength of cooling fan assembly, and obtain cooling fan assembly strength.The application improves the accuracy of the model and ensures the calculation efficiency by taking the aerodynamic pressure load on the blade as the boundary condition when predicting the structural strength of the cooling fan.

Description

Technical Field

[0001] This invention relates to the field of automotive engine cooling fan development, and in particular to a method for calculating the strength of an engine cooling fan assembly based on unidirectional fluid-structure interaction. Background Technology

[0002] The engine cooling fan is a key component of the cooling system. Its function is to drive and guide airflow through the radiator to forcibly cool the engine and control its operating temperature within the optimal range. Cooling fans typically operate at high speeds, and under significant centrifugal and aerodynamic pressure loads, both the fan blades and fan support plates may break. If a separate structural analysis is used to predict the strength of the cooling fan, the influence of aerodynamic pressure will be neglected.

[0003] Currently, the industry's development of cooling fans mainly focuses on improving their aerodynamic performance. Researchers both domestically and internationally have achieved significant results in areas such as cooling fan blade design and computational fluid dynamics models. However, for the strength analysis of cooling fan assemblies, separate finite element simulations are typically used. These models often do not consider aerodynamic pressure loads, or they apply uniformly distributed pressure loads to the blades to simulate wind pressure. Clearly, this modeling method does not reflect reality, and the model accuracy needs improvement.

[0004] Fluid-structure interaction (FSI) methods are generally classified into unidirectional and bidirectional FSI methods. In bidirectional FSI systems, the interaction between the fluid system and the structural system needs to be considered; that is, the deformation of the structure is affected by aerodynamic pressure, and the deformation also changes the flow field distribution. Although bidirectional FSI can obtain a more accurate flow field distribution, it requires multiple data exchanges, resulting in high computational costs. Furthermore, the mesh quality of the external flow field after blade deformation is difficult to control, which can easily lead to non-convergence of the calculation results. For unidirectional FSI, it is only necessary to solve the flow field first, and then use the solution of the flow field as boundary conditions to solve the structural stress field. Therefore, existing flow field calculation results can be utilized, resulting in a significant improvement in computational efficiency. However, existing fan structure analyses often do not consider aerodynamic loads or apply an average load to the fan surface to simulate wind pressure, both of which introduce errors in the results. Summary of the Invention

[0005] This invention provides a method for calculating the strength of an engine cooling fan assembly based on unidirectional fluid-structure interaction, which to some extent overcomes the problem of inaccurate strength calculation models for cooling fan assemblies. Simultaneously, this method can utilize existing flow field calculation results, ensuring computational efficiency and reducing computational costs, and can be used for strength prediction of cooling fan assemblies. The pressure distribution on the blade surface obtained from computational fluid dynamics is applied to the structural analysis of the cooling fan.

[0006] To achieve the objective of this invention, the present invention provides a method for calculating the strength of an engine cooling fan assembly based on unidirectional fluid-structure interaction, comprising the following steps:

[0007] Step 1: Establish a geometric model of the cooling fan and fan support plate based on the actual structure of the cooling fan, and mesh the geometric model of the cooling fan to obtain the finite element model of the cooling fan assembly.

[0008] Step 2: Import the finite element model of the cooling fan assembly into the finite element software, assign material properties to the cooling fan and fan support plate respectively, and set boundary conditions.

[0009] Step 3: Establish a finite element model of the external flow field. Import the finite element model of the external flow field into the computational fluid dynamics software and set the turbulence model and boundary conditions of the external flow field.

[0010] Step 4: Set the blade surface as the fluid-structure interaction surface, establish a connection between the two closest nodes on the interaction surface, and transfer data between the associated nodes. The physical quantity transferred is set as the aerodynamic pressure on the blade surface. First, use computational fluid dynamics software to solve the steady-state flow field to obtain the aerodynamic pressure on the blade surface. Then, use this aerodynamic pressure as the boundary condition and use finite element software to calculate the structural strength of the cooling fan assembly to obtain the strength of the cooling fan assembly.

[0011] Furthermore, when establishing the finite element model of the cooling fan, a single blade is extracted, meshed, and a complete fan model is generated by rotation and replication.

[0012] Furthermore, the cooling fan and fan support plate are all meshed using triangular elements. Ten-node high-order tetrahedral elements are generated through closed triangular meshes to ensure the accuracy of the model and control the size of the mesh.

[0013] Furthermore, the computational fluid dynamics model of the external flow field ignores the specific structure of the cooling fan support plate and uses a hub structure instead to reduce the mesh size. The blade mesh of the external flow field is directly copied to ensure that the mesh node distribution on the coupling surface remains consistent.

[0014] Furthermore, the established external flow field model includes a test bench model and a sufficiently large external flow domain model, which can be divided into an inlet region, a front transition region, a rotating region, a rear transition region, and an outlet region along the airflow direction. The rotating region and the transition region are divided into tetrahedral elements, while the inlet region and the outlet region are divided into hexahedral elements.

[0015] Furthermore, computational fluid dynamics software was used to solve the Reynolds-averaged Navier-Stokes equations. A pressure-based solver was used, the fluid was considered to be incompressible, the turbulence model was the RNG k-epsilon model, the multiple reference frame method was used to handle the rotating region, and a semi-implicit method for the pressure-velocity coupled equations was used to solve the pressure-velocity coupled equations.

[0016] Furthermore, the finite element software employs an adaptive time increment step.

[0017] Furthermore, the boundary conditions applied to the cooling fan include: applying full constraints to the fan bracket mounting holes; applying a rotational speed to the entire cooling fan; and applying accelerations in three directions to the cooling fan to simulate vibration.

[0018] Furthermore, a neighborhood search algorithm is used to associate the two closest nodes on the coupling surface, and the physical quantity is transferred through an interpolation method. The transferred physical quantity is relative pressure, which should satisfy the conservation relationship.

[0019] Furthermore, for isolated nodes on the coupling surface, a diffusion algorithm is used for value assignment.

[0020] Furthermore, it also includes:

[0021] Step 5: Post-process the calculation results to obtain the stress distribution and deformation distribution of the fan blades and fan support plate.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] 1) The present invention provides a method for calculating the strength of an engine cooling fan assembly based on unidirectional fluid-structure interaction. When calculating the strength of the cooling fan assembly, the influence of aerodynamic pressure is considered, which reduces the error of the simulation model to a certain extent and improves the calculation accuracy.

[0024] 2) The present invention provides a method for calculating the strength of an engine cooling fan assembly based on unidirectional fluid-structure interaction. For the same blade structure, existing flow field calculation results can be used, thereby improving calculation efficiency.

[0025] 3) The present invention provides a method for calculating the strength of an engine cooling fan assembly based on unidirectional fluid-structure interaction. By controlling the inlet flow rate and three-term acceleration, the working conditions of the cooling fan can be changed, and the structural strength of the fan assembly under different working conditions can be calculated.

[0026] 4) The flow field analysis results in this invention can be saved and reused, which improves the efficiency of subsequent fan improvements. Attached Figure Description

[0027] Figure 1This is a schematic diagram of the steps in an embodiment of the present invention.

[0028] Figure 2(a) is a schematic diagram of the cooling fan assembly according to an embodiment of the present invention.

[0029] Figure 2(b) is a schematic diagram of the fan support structure according to an embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram of the finite element model of the cooling fan according to an embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram of the external flow field finite element model according to an embodiment of the present invention.

[0032] Figure 5 This is a schematic diagram of the rotating area model and the simplified fan model according to an embodiment of the present invention.

[0033] Figure 6 This is a schematic diagram showing the experimental and calculated values ​​of the static pressure of the cooling fan in an embodiment of the present invention.

[0034] Figure 7 is a schematic diagram of the calculation results of the maximum deformation of the leading and trailing edges of the cooling fan blade tip in an embodiment of the present invention.

[0035] Figure 8 is a schematic diagram of the maximum stress calculation results of the cooling fan and support plate according to an embodiment of the present invention. Detailed Implementation

[0036] The invention will now be described in more detail through a specific embodiment. It should be noted that the embodiment includes many specific details to enable a fuller understanding of the implementation, but the implementation of the invention is not limited to the following embodiment, and any modifications and / or alterations made to the invention will fall within the scope of protection of the invention.

[0037] This invention provides a method for calculating the strength of an engine cooling fan assembly based on unidirectional fluid-structure interaction. First, a unidirectional fluid-structure interaction simulation model of the fan assembly needs to be established (the unidirectional fluid-structure interaction model of the fan assembly includes a finite element model of the fan assembly and a finite element model of the external flow field). The flowchart is shown below. Figure 1 As shown, it includes the following steps:

[0038] Step 1: Establish the geometric model and finite element model of the cooling fan assembly.

[0039] Based on the actual structural dimensions of the cooling fan, a geometric model of the fan and fan support plate is created using 3D modeling software. In some embodiments of the present invention, a 7-blade cooling fan with a diameter of 700mm is used, the hub thickness is 35mm, the inner diameter of the hub is 215mm, and the outer diameter of the hub is 250mm.

[0040] In some embodiments of the present invention, the fan support plate is a circular thin plate with a diameter of 220 mm and a thickness of 4.5 mm. Twenty-four circular holes with a diameter of 13 mm are distributed on the outer side of the support plate, arranged on a circumference with a diameter of 190 mm, for connecting a cooling fan; six mounting holes with a diameter of 11.6 mm are distributed on the inner side of the support plate, arranged on a circumference with a diameter of 99 mm, for connecting a silicone oil clutch.

[0041] In some embodiments of the present invention, when establishing a three-dimensional model of the cooling fan assembly, the Z-axis is taken as the rotation axis of the cooling fan, the positive direction of the Z-axis is the airflow direction, and according to the right-hand rule, the negative direction of the Z-axis is determined as the fan rotation direction. The geometric model of the cooling fan assembly is shown in Figure 2(a), and the geometric model of the fan support plate is shown in Figure 2(b).

[0042] Based on the established three-dimensional geometric model of the cooling fan assembly, mesh generation is performed in finite element preprocessing software to generate the finite element model of the cooling fan assembly. In some embodiments of this invention, to control the size and quality of the mesh, triangular mesh elements are used for both the cooling fan and the fan support plate. The fan support plate, which experiences greater stress, uses mesh elements with a size of approximately 2.5 mm; the blade tips and edges have a greater impact on the flow field calculation results, so mesh elements with a size of approximately 2.5 mm are used, while the blade center and hub use mesh elements with a size of 3–5 mm. The finite element model of the cooling fan assembly is shown below. Figure 3 As shown.

[0043] In some embodiments of the present invention, to improve preprocessing efficiency, individual blades of the cooling fan can be divided into mesh cells, and a complete cooling fan model can be generated by rotation copying and sharing nodes between the meshes. Simultaneously, the entire fan support plate can be directly divided into mesh cells, and a mesh model of the cooling fan assembly can be generated by sharing nodes with the fan mesh. It is necessary to ensure that the periodic boundaries of the blades and the mesh node distribution at the hub-support plate connection are consistent in order to generate a closed surface mesh.

[0044] Using the established cooling fan assembly surface mesh elements, tetrahedral elements for the cooling fan and fan support plate are generated separately, and all tetrahedral elements are converted into second-order ten-node tetrahedral elements. Finally, the quality of the tetrahedral element mesh is optimized to ensure that the element twist is below 0.8 and the element collapse is above 0.2.

[0045] Step 2: Import the finite element model of the cooling fan assembly into the finite element software, assign material properties to the cooling fan and fan bracket respectively, and set boundary conditions.

[0046] In some embodiments of the present invention, the finite element model of the cooling fan assembly includes a cooling fan model and a fan support plate model, with shared nodes at their connection points, eliminating the need for constraint relationships. Material properties are assigned to both the fan model and the fan support plate model, wherein the fan material is engineering plastic PA6 with a density of 1.36 × 10⁻⁶. 3 kg / m 3 The elastic modulus is 7.71 GPa, and the Poisson's ratio is 0.41; the fan support plate material is Q235, with a density of 7.83 × 10⁻⁶. 3 kg / m 3 Its elastic modulus is 210 GPa and its Poisson's ratio is 0.274.

[0047] In some embodiments of the present invention, the boundary conditions applied to the cooling fan assembly include: applying full constraints to the inner surfaces of the six mounting holes of the fan plate, applying a rotational speed of 2100 rpm to the entire cooling fan assembly, and applying accelerations in the x-axis, y-axis, and z-axis directions to the entire cooling fan assembly, with acceleration magnitudes of 2g, 3g, and 4g, respectively.

[0048] In some embodiments of the present invention, a static universal analysis step is employed, along with an adaptive time increment step. The initial increment step size is 0.1, the maximum increment step size is 0.5, and the maximum number of increment steps is 100, to ensure convergence of the calculation results. Furthermore, the mesh elements on the fan blade surface must be set as fluid-structure interaction surfaces.

[0049] Step 3: Establish a finite element model of the external flow field based on the test bench structure, import the finite element model of the external flow field into the computational fluid dynamics software, and set the turbulence model and boundary conditions of the external flow field.

[0050] In some embodiments of the present invention, a computational fluid dynamics model of the external flow field of the fan is established based on an aerodynamic performance test bench. The finite element model of the external flow field is as follows: Figure 4 As shown, the established finite element model of the external flow field can be divided into the inlet region, the front transition region, the fan rotation region, the rear transition region, and the outlet region according to the airflow direction. The rotation region and the transition region are discretized using tetrahedral elements, while the inlet region and the outlet region are discretized using hexahedral elements. The mesh element size gradually increases from the rotation region to the transition region, the inlet region, and the outlet region. Simultaneously, for the tetrahedral elements in the rotation region and the transition region, the element twist rate must be less than 0.8, and the element collapse rate must be greater than 0.2.

[0051] like Figure 5As shown, the rotating zone contains the boundary of the cooling fan. The cooling fan model is reasonably simplified; the fan blade model can be directly copied from the existing fan mesh model, and the support structure is replaced by a hub structure. Triangular mesh elements are used on the outer surface of the rotating zone, with a mesh size of approximately 13mm. The closed space between the outer surface mesh of the rotating zone and the outer mesh of the cooling fan is filled with tetrahedral elements. To ensure model accuracy, a sufficient number of mesh elements needs to be generated in the rotating zone, especially at the blade tip clearance, where a sufficient number of mesh layers are required. Therefore, interpolation is used to generate the tetrahedral elements for the rotating zone. The closed space between the transition zone and the rotating zone is filled with tetrahedral elements. The mesh distribution in the transition zone has a relatively small impact on the simulation results; therefore, a standard method is used to generate the tetrahedral elements for the transition zone to control the mesh size. The inlet and outlet zones are far from the fan rotating zone and have relatively regular shapes, so they can be discretized using hexahedral elements. The meshes of the inlet and outlet zones do not share nodes with the transition zone; a data interaction surface needs to be generated to ensure normal data transmission.

[0052] The finite element model of the external flow field is imported into computational fluid dynamics software to solve the Reynolds-averaged Navier-Stokes equations. In some embodiments of this invention, due to the low gas velocity, the fluid is considered incompressible, the operating pressure is set to standard atmospheric pressure, and temperature and gravity factors are ignored. A steady-state pressure-based solver is used, and the turbulence model is the RNG k-epsilon model. A multiple reference frame method is employed for the rotating region, transforming the rotation of the cooling fan into a coordinate system rotation, thus converting the unsteady-state problem into a steady-state problem. The inlet is set as a mass flow rate inlet, allowing for different airflow rates, while the outlet is set as a pressure outlet, with the outlet gauge pressure set to zero, i.e., atmospheric pressure. The fan surface is set as a rotating wall, with the rotation direction determined by the right-hand rule; other walls are set as fixed walls. A semi-implicit method using pressure-coupled equations is employed for iterative solution. If the residuals of each equation are less than 1 × 10⁻⁶, the solution is considered complete. -3 If the calculation is converged, then the computation can be considered to be converged.

[0053] Step 4: Set the blade surface as the fluid-structure interaction surface, establish a connection between the two closest nodes on the interaction surface, transfer data between the associated nodes, and transfer the calculation results of the computational fluid dynamics software to the finite element software for cooling fan structure analysis.

[0054] The finite element model of the cooling fan assembly and the finite element model of the external flow field were imported into a multiphysics coupling interface software for co-simulation. The fluid-structure interaction surface was set as the mesh of the fan blade surface. A neighborhood search algorithm based on kd-trees was used to determine the two closest nodes on the coupling surface and pair them up. The transferred physical quantity was set as the aerodynamic pressure on the blade surface. The data was transferred between the two nodes through interpolation. If isolated nodes existed, a diffusion algorithm was used for assignment. The co-simulation process was as follows: first, the steady-state flow field was solved using computational fluid dynamics software to obtain the aerodynamic pressure on the blade surface. This aerodynamic pressure was then used as the boundary condition, and the structural strength of the cooling fan assembly was calculated using the finite element software. In addition, for the same blade structure, existing flow field calculation results could be used, thereby reducing the computational cost.

[0055] Step 5: Post-process the calculation results to obtain the stress distribution and deformation distribution of the fan blades and fan support plate.

[0056] The structural strength calculation results of the cooling fan assembly were post-processed in the finite element method software. The correctness of the computational fluid dynamics model of the external flow field could be verified by aerodynamic performance tests, such as... Figure 6 As shown.

[0057] In some embodiments of the present invention, stress distribution cloud maps and deformation distribution cloud maps of the cooling fan and fan support plate were extracted respectively. Figure 7 shows the maximum deformation of the leading and trailing edges of the blade tip at various speeds. The results show that, considering the aerodynamic load, the maximum deformation of the blade tip increases, which is closer to the experimental data. Figure 8 shows the maximum stress values ​​of the fan blade and support plate. It can be observed that, considering the aerodynamic load, the maximum stress of the fan blade and support plate increases to a certain extent.

[0058] The strength calculation method for engine cooling fan assemblies based on unidirectional fluid-structure interaction proposed in this invention considers the aerodynamic pressure loads on the blade surfaces when performing strength analysis on the cooling fan assembly. This overcomes, to some extent, the inaccuracy of individual finite element models caused by deficiencies in modeling methods, while also utilizing existing flow field calculation results to ensure computational efficiency. Therefore, this method can be applied to the development of cooling fans.

[0059] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for calculating the strength of an engine cooling fan assembly based on one-way fluid-structure coupling, characterized in that, Includes the following steps: Step 1: Establish a geometric model of the cooling fan and fan support plate based on the actual structure of the cooling fan, and mesh the geometric model of the cooling fan to obtain the finite element model of the cooling fan assembly. Step 2: Import the finite element model of the cooling fan assembly into the finite element software, assign material properties to the cooling fan and the fan bracket respectively, and set boundary conditions. The boundary conditions applied to the cooling fan include: applying full constraints to the mounting holes of the fan bracket; applying a rotational speed to the entire cooling fan; and applying accelerations in three directions to the cooling fan to simulate vibration. Step 3: Establish a finite element model of the external flow field. Import the finite element model of the external flow field into the computational fluid dynamics software and set the turbulence model and boundary conditions of the external flow field. Step 4: Define the blade surface as the fluid-structure interaction surface. Establish a connection between the two closest nodes on the interaction surface and transfer data between the connected nodes. The physical quantity transferred is set as the aerodynamic pressure on the blade surface. First, use computational fluid dynamics software to solve the steady-state flow field to obtain the aerodynamic pressure on the blade surface. Use this aerodynamic pressure as the boundary condition and use finite element software to calculate the structural strength of the cooling fan assembly to obtain the strength of the cooling fan assembly. In this process, a neighborhood search algorithm is used to connect the two closest nodes on the interaction surface, and the physical quantity is transferred through interpolation. The transferred physical quantity is relative pressure and should satisfy the conservation relationship. For isolated nodes on the interaction surface, a diffusion algorithm is used for assignment.

2. The method of claim 1, wherein, In step one, when establishing the finite element model of the cooling fan, a single blade is extracted, meshed, and then a complete fan model is generated by rotation and copying.

3. The method of claim 1, wherein, The cooling fan and fan mount are all meshed using triangular elements, and ten-node high-order tetrahedral elements are generated through closed triangular meshes.

4. The method of claim 1, wherein, The computational fluid dynamics model of the external flow field ignores the specific structure of the cooling fan support plate and uses a hub structure instead; the blade mesh of the external flow field is directly copied and generated to ensure that the mesh node distribution on the coupling surface remains consistent.

5. The method of calculating the strength of a unidirectional fluid-structure coupling-based engine cooling fan assembly according to claim 1, wherein, The established external flow field model includes a test bench model and a sufficiently large external flow domain model. Along the airflow direction, it can be divided into an inlet region, a front transition region, a rotating region, a rear transition region, and an outlet region. The rotating region, the front transition region, and the rear transition region are divided into tetrahedral elements, while the inlet region and the outlet region are divided into hexahedral elements.

6. The method of calculating the strength of an engine cooling fan assembly based on one-way fluid-structure coupling according to claim 1, wherein The Reynolds-averaged Navier-Stokes equations were solved using computational fluid dynamics software. A pressure-based solver was used, the fluid was considered incompressible, the RNG k-epsilon model was used for the turbulence model, the multiple reference frame method was used to handle the rotating region, and a semi-implicit method for the pressure-velocity coupled equations was used to solve the pressure-velocity coupled equations.

7. The method of calculating the strength of a cooling fan assembly for an engine based on one-way fluid-structure coupling according to any one of claims 1 to 6, characterized in that, Also includes: Step 5: Post-process the calculation results to obtain the stress distribution and deformation distribution of the fan blades and fan support plate.

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