# Structural Design and Parameter Optimization of Bionic Exhaust Tailpipe of Tractors
## 3 Results and Discussion
### Aeroacoustics and Transmission Loss Analysis
Figure 10(a\({}_{5}\)) shows that \(\rm TL_{1 mm}>TL_{1.25 mm}>TL_{0.75 mm}>TL_{0.5 mm}>TL_{1.5 mm}\) when the top angle \(\theta\) is 90\({}^{\circ}\), the maximum transmission loss is increased by 4.917 dB, and the minimum transmission loss is increased by 0.155 dB for a texture height of 1 mm. As shown from the transmission loss curves in Figure 10(a\({}_{1}\)-a\({}_{5}\)), the transmission loss generally increases first and then decreases as the texture height increases under the same top angle \(\theta\) and the number of circumferential columns n. The increase in transmission loss is larger near heights of 0.75 mm and 1 mm. The trend of the transmission loss curve is not obvious as the top angle increases, and the transmission loss is larger when the top angle is near 45\({}^{\circ}\), 60\({}^{\circ}\), and 90\({}^{\circ}\). As shown in Figure 10(b\({}_{1}\)-b\({}_{5}\)), the transmission loss is improved compared to the prototype in the target frequency range of 10-490 Hz. Figure 10(b\({}_{1}\)) shows that the transmission loss is maximum when the top angle \(\theta\) is 30\({}^{\circ}\) and the texture height h is 1 mm. The transmission loss maximum is increased by 4.651 dB and the minimum is increased by 0.356 dB compared with the prototype. Figure 10(b\({}_{2}\)) shows that the transmission loss is maximum when the top angle \(\theta\) is 45\({}^{\circ}\) and the texture height h is 1 mm. The transmission loss maximum is increased by 5.159 dB and the minimum is increased by 0.446 dB at a height of 1 mm compared with the prototype. Figure 10(b\({}_{3}\)) shows that the transmission loss reaches a maximum when the top angle \(\theta\) is 60\({}^{\circ}\) and the texture height h is 1 mm. The transmission loss maximum is increased by 6.7 dB and the minimum is increased by 0.832 dB compared with the prototype. Figure 10(b\({}_{4}\)) shows that the transmission loss is at maximum when the top angle \(\theta\) is 75\({}^{\circ}\), texture height h is 1.5 mm, transmission loss maximum is increased by 2.927 dB, and minimum is decreased by 0.19 dB compared with the prototype. Figure 10(b\({}_{5}\)) shows that the transmission loss is at maximum when the top angle \(\theta\) is 90\({}^{\circ}\) and the texture height h is 1.5 mm. The transmission loss is maximum when it is increased by 5.720 dB and the minimum when it is increased by 0.539 dB compared with the prototype. It can be seen from Figure 10(b\({}_{1}\)-b\({}_{5}\)) that the transmission loss of the circumferential columns is 24 is improved compared to columns is 18. The transmission loss tends to increase first and then decrease as the height increases. The increase in transmission loss is larger near a height of 1 mm. As the top angle increases, the trend of the transmission loss curve is not obvious, and the transmission loss is larger near 45\({}^{\circ}\), 60\({}^{\circ}\), and 90\({}^{\circ}\). From the transmission loss curves in Figure 10(c\({}_{1}\)-c\({}_{5}\),d\({}_{1}\)-d\({}_{5}\)), it can be seen that compared with the cases of 18 and 24 circumferential columns, as shown in Figure 10(a\({}_{1}\)-a\({}_{5}\)b\({}_{1}\)-b\({}_{5}\)), the transmission loss decreases as the number of circumferential columns increases. The transmission loss is reduced at some frequencies, but the whole transmission loss is improved compared with the prototype. It can be seen from Figure 10 that within the scope of the study, the number of circumferential columns has a large effect on the transmission loss. As the number of circumferential columns was 24, the transmission loss improved more obviously. As the height increases, the transmission loss tends to increase first and then decrease. The bionic texture has a larger transmission loss near heights of 0.75 mm and 1 mm. As the top angle increases, the trend of the transmission loss curve is not obvious. When the top angles are approximately 45\({}^{\circ}\) and 60\({}^{\circ}\), the transmission loss is relatively large.