# Structural Design and Parameter Optimization of Bionic Exhaust Tailpipe of Tractors
## 1 Introduction  
The exhaust noise generated by tractors is a problem that puzzles people. Experts and scholars have been paying attention to the goal of reducing exhaust noise. Mufflers are widely used to reduce intake and exhaust noise. In recent years, researchers proposed various methods to improve the noise reduction performance of mufflers. [PERSON] et al. used a simulated method and experimental test to obtain the transmission loss and analyzed the influence of several main parameters of mufflers on transmission loss [1, 2]. [PERSON] et al. studied curved quarter-wave resonators to solve the problem of large spaces occupied by straight cavity resonators [3]. [PERSON] et al. applied U-shaped bellows to a resistant muffler, and the noise reduction performance was significantly improved in the cutoff frequency range [4]. [PERSON] et al. used the finite element analysis method to optimize the acoustic performance of a multi-chamber reactive silencer with baffles [5]. [PERSON] et al. designed an H-type connecting fork muffler based on an H-Q tube. This muffler fundamentally changed the acoustic impedance at the sound source [6]. [PERSON] et al. studied a new type of semiactive muffler based on an H-Q pipe to control thelow-frequency noise of the exhaust pipe [7]. [PERSON] et al. analyzed the transmission loss performance of the rectangular expansion chamber with a single inlet and single outlet and single inlet and double outlet by using the three-dimensional semi-analytic formula based on the modal expansion method and [PERSON]'s function method [8]. [PERSON] et al. designed a resonator system with a helical side branch duct to control broadband noise [9]. [PERSON] et al. studied a small-scale series-parallel coupling mode broadband microperforated muffler [10]. [PERSON] et al. proposed a method for making holes in the tailpipe to improve the muffler performance. The muffler can then simultaneously suppress low-frequency and intermediate-frequency noise [11]. [PERSON] et al. designed a multicavity microperforated muffler with adjustable transmission loss to reduce the noise of the blower [12]. [PERSON] et al. used the principle of split-stream rushing to reduce the air velocity of the muffler and analyzed the acoustic performance and flow field in the pipeline. These studies improved the muffler performance in a specific frequency range by improving the overall structure, shape, and size parameters of the prototype muffler [13]. [PERSON] et al. proposed a numerical simulation method that comprehensively considered dipole and quadrupole sources to predict aerodynamic noise [14]. [PERSON] et al. based on VOF multiphase flow and Schnerr-Sauer cavitation model, established LES/FW-H coupling model to study the noise characteristics of underwater high-speed vehicle [15]. [PERSON] et al. established a one-dimensional computational fluid dynamics model integrating the intake/exhaust system and the engine based on a vehicle with an in-line four-cylinder engine, and predicted the intake noise [16]. With regard to bionic drag reduction and noise reduction, [PERSON] et al. conducted an experimental study on the aeroacoustic performance of gliding owls using sensors in a reverberation room [17]. [PERSON] et al. designed a nonsmooth surface with microscale microprotrusions and used it on an aircraft for experiments [18]. In recent years, [PERSON] et al. found that the serrated structure of barn owl wings plays an important role in airflow control and noise reduction [19]. [PERSON] et al. carried out a bionic optimization design of a NACA 0012 airfoil through numerical simulation [20]. [PERSON] et al. designed a structure on tractor bionic exhaust tailpipes [21]. [PERSON] et al. designed the inner wall of the tractor exhaust tailpipe by using the bionics method and studied the noise reduction effect of the tractor exhaust tailpipe with different texture shapes [22]. The results showed that the bionic texture has the effect of reducing exhaust liner noise.