# Study on Noise Model of an Automotive Axial Fan Based on Aerodynamic Load Force
## 4 Calculation Simulation and Verification of Automotive Axial Fan
### Noise Verification of Automotive Axial Fan
#### 4.2.1 Automotive Axial Fan Noise Simulation Settings and Analysis Results  
Combined with the above parameters, FLUENT software is used for the simulation in this paper. The LES method is used to calculate the transient flow field and the FW-H method is used to solve the far-field noise distribution [20]. (1) Establishment of simulation model  
According to the structural parameters of the mathematical model (41) and Table 2, the corresponding simulation geometric model is built, as shown in Figure 7.  
The simulation model is divided into four parts: the inlet domain, outlet domain, dynamic domain, and static domain. The partial plan of the \(YZ\) grid profile map along the \(X\) direction (axial direction) is shown in Figure 8 and it can be seen that the fan is placed in the static domain of the pipeline as a dynamic domain; the fan diameter is 409 mm and the hub ratio is 0.4. The overall calculation domain is the cylindrical pipe; the diameter of the pipe is 2200 mm, the \(X\) direction is the flow direction, the \(X\) direction length of the inlet  
Figure 6: Calculation results of fan noise in the frequency domain. Figure 7: Fan 3D model. domain is 1650 mm, the \(X\) direction length of the outlet domain is 6050 mm, the \(X\) direction length of the static domain is 1160 mm, and the total length of the pipeline \(X\) direction is 8860 mm. Grid division  
Using ICEM as the pre-processing software, the simulation object is meshed. Unstructured grids are used in the inlet and outlet domains, rotating domains, and static domains. Pentahedral prismatic grids with regular stretching are used in the inlet and outlet domains, and the mesh size is 28 mm. The mesh sizes of the blade tip and the front and back edges in the rotating domain range from 0.3 mm to 0.8 mm. Five layers of boundary layer mesh are added to the solid surface, which is mainly pentahedral prism mesh. The size of the first layer is controlled at 0.01 mm, and the size of the rest of the rotating domain is tetrahedral mesh with a size of about 6 mm. The static domain is a tetrahedral mesh with a size of about 24 mm. The total mesh number of the model is about 9.35 million. Calculation method and setting of initial conditions  
The fluid in the fan movement area belongs to turbulent movement and the internal fluid can be considered incompressible gas. The energy conservation equation is not considered, and the influence of gravity on the flow field is ignored. The RNG \(\kappa-\)epsilon turbulence model is used for the steady calculation, SIMPLE (semi-implicit method for pressure-linked equations) is used for the pressure-velocity coupling and the multiple reference frame (MRF) is adopted for the rotating domain [21]. The unsteady flow in the rotating domain is regarded as the steady flow. The flow-field data obtained from the steady calculation convergence is taken as the initial field of calculation. Based on the large eddy simulation (LES), the sublattice Smaqorinsky-Lilly model is used to recalculate the transient flow field using the pressure-implicit second-order algorithm [22]. The Ffowcs-Williams-Hawkings (FW-H) acoustic model in the FLUENT software is used to simulate the noise prediction and the FFT method is used to process the noise time-domain data to obtain the noise spectrum characteristics. Simulation analysis results  
Based on the above simulation analysis model and boundary conditions, LES is used to calculate the transient flow field. On this basis, the FW-H acoustic model is used to simulate and obtain the variations in sound pressure with time at the fan receiving point, as shown in Figure 9, which shows that the fan noise receiving point is in a relatively stable state since the third cycle of pressure fluctuations, so the time-domain data is extracted from the third cycle; each point-sampling interval is 0.0001 s, each cycle is 0.025 s, and the stable data from eight cycles are taken for the FFT transformation to carry out the corresponding spectrum analysis. Figure 8: The mesh sketch of computing region distribution.