# Study on Noise Model of an Automotive Axial Fan Based on Aerodynamic Load Force
## 4 Calculation Simulation and Verification of Automotive Axial Fan
### Theoretical Calculation of Automotive Axial Fan Noise
#### 4.1.2 Analysis of Theoretical Calculation Results of Noise  
Based on the above numerical analysis model, MATLAB software is used for the simulation, and the blade loading force and time-domain data are obtained. Since the first  
\begin{table}
\begin{tabular}{c c c c} \hline
**Sections** & **Radius/m** & **Installation Angle\({}^{\circ}\)** & **Chord Length/m** \\ \hline Section 1 & 0.088000 & 35.0 & 0.0544 \\ Section 2 & 0.097708 & 32.8 & 0.0568 \\ Section 3 & 0.107417 & 30.7 & 0.0589 \\ Section 4 & 0.117125 & 28.7 & 0.061 \\ Section 5 & 0.126833 & 26.9 & 0.0631 \\ Section 6 & 0.136542 & 25.1 & 0.0652 \\ Section 7 & 0.146250 & 23.6 & 0.0674 \\ Section 8 & 0.155958 & 22.2 & 0.0699 \\ Section 9 & 0.165667 & 21.1 & 0.0721 \\ Section 10 & 0.175375 & 20.0 & 0.0746 \\ Section 11 & 0.185083 & 19.2 & 0.0775 \\ Section 12 & 0.194792 & 18.6 & 0.0806 \\ Section 13 & 0.204500 & 18.0 & 0.0728 \\ \hline \end{tabular}
\end{table}
Table 1: Blade structural parameters.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Radii/m** & **0.0818** & **0.112475** & **0.14315** & **0.2045** \\ \hline Bending angles/ & 0 & \(-4\) & 0 & 12 \\ \hline \end{tabular}
\end{table}
Table 2: Circumferential bending angles of different radii.  
six order blade pulsating loads are taken as unsteady loading forces, the first six order blade pulsating noise spectrums are extracted after FFT.  
(1) Calculation results of load distribution  
As described above, a single blade is divided into 12 equal parts along the radius and 4 equal parts along the chord length, with a total of 48 sound source surfaces. According to Equation (30), the loading force on each sound source surface is calculated and the loading force at the center of every four microelements with the same radius from the blade root to the blade tip (four equal parts along the chord length) is phase-superimposed. The calculation results of the loading force on a blade are shown in Figure 4. It is shown in Figure 4 that the loading force increases gradually along the radius. In the vicinity of the blade tip, considering the influence of the tip vortexes, the blade tip loss is corrected. The chord length decreases, which reduces the area of the sound source near the blade tip, so the loading force decreases accordingly.  
(2) Noise calculation results  
The rotation speed of the fan is 2400 r/m so the fan runs for 0.025 s. Figure 5 shows the time-domain data of fan noise calculated according to Equations (35) and (36). It can be seen in Figure 5 that seven obvious noise peaks occur within a period, corresponding to the fan operating noise of the seven blades.  
(3) Calculation results of noise spectrum  
The spectrum characteristics of the fan noise are obtained based on an FFT transformation of the time-domain data and then the calculation results of the fan noise in the frequency domain are obtained by being converted into a weighted sound pressure level, as shown in Figure 6. It can be seen in Figure 6 that the first six orders of pulsating noise  
Figure 4: Blade surface loading force distribution along the blade radius.  
Figure 5: Calculation results of fan noise in the time domain.  
from the fan make a major contribution in the whole-frequency band, and the amplitude from the first to the sixth orders decreases gradually.