# Structural Design and Parameter Optimization of Bionic Exhaust Tailpipe of Tractors
## 4 Conclusions  
By imitating the surface of a shark with triangular grooves, a bionic triangular convex texture was added to the inner surface of an exhaust tailpipe to address noise reduction. The bionic tailpipes produced different degrees of noise reduction on aeroacoustics and transmission loss compared with a prototype exhaust tailpipe.  
From the perspective of aeroacoustics, the total sound pressure level changes the most at 50 m/s, reaching 2.560 dB compared with other speed conditions. At this speed, the bionic texture shows the best noise reduction, corresponding to a Reynolds number of \(1.51\times 10^{5}\). The influence of texture circumferential column number n was the most significant. Texture height h influenced noise reduction, and top angle \(\theta\) had no obvious effect on the noise reduction within the research range.  
To study vibration noise reduction, bionic triangular convex textures with different size parameters were simulated and analyzed. The research showed that the transmission loss was relatively large, the reduction performance was relatively good, the number of circumferential columns was 24, the top angles were 45\({}^{\circ}\) and 60\({}^{\circ}\), and the texture heights were 0.75 mm and 1 mm. The BP neural network algorithm based on GA optimization was used to optimize the structure parameters. The corresponding transmission loss reached the maximum when the top angle \(\theta\) was 61\({}^{\circ}\) and the texture height h was 0.95 mm.  
By analyzing the noise reduction mechanism of aeroacoustics, the bionic texture can reduce the air pressure and velocity amplitude near the wall of the bionic tailpipe. The secondary vortex appears near the bionic texture, reducing aerodynamic drag and aeroacoustics. By analyzing the noise reduction mechanism of vibration noise, the bionic triangular convex texture reduced the velocity amplitude of the exhaust tailpipe and reduced the sound pressure inside the exhaust tailpipe of the tractor.  
The experimental results demonstrated that the bionic exhaust tailpipes reduced the noise. On the whole, the noise reduction effect is better when the top angle is 60\({}^{\circ}\) and the texture height is 1 mm, which is consistent with the simulation results.  
It is feasible to apply the bionic triangle texture to the tractor tailpipe. The total sound pressure level can be reduced and the transmission loss can be increased, so a certain noise reduction effect can be achieved by adding a bionic triangular convex texture inside the tailpipe without changing the overall size parameters of the prototype tailpipe.  
[PERSON], [PERSON] and [PERSON] conceived the conceptualization; [PERSON] and [PERSON] designed the experiments; [PERSON], [PERSON] and [PERSON] performed the experiments; [PERSON] and [PERSON] analyzed the data; [PERSON] and [PERSON] wrote the paper. All authors have read and agreed to the published version of the manuscript.  
This work was funded by the National Key Research and Development Program of China in the 13 th Five-year Plan Period (2016 YFD0701102) and the science and technology projects in Jilin Province Education Department (No. JJKH20211064 KJ).  
Not applicable.  
The authors declare no conflict of interest.