Abstract:

The tobacco industry is one of the important pillar industries of national economy in China, and, with the expansion of tobacco factories as well as a larger number of high-speed unit equipment into the tobacco industry, noise pollution in the industry is becoming more and more prominent, in which the noise pollution in wrapping workshops is particularly serious. The noise source in such a workshop is mainly from the dust removal system, the noise characteristics of which are usually low to medium frequency noise, with strong penetration and energy difficult to attenuate. The air inlet end of the dust removal system is the closest to the workers, and the long time exposure of the workers to the noise environment will lead to damage of hearing organs as well as tinnitus, palpitation, sleep disorders, etc. Therefore, it is necessary to analyze the noise of the air inlet of the dust removal system as well as to optimize the structure of the air inlet to reduce the noise.

Most of tobacco factories for the optimization of the noise reduction of the dust removal system is mainly done through the experimental method, but with the development of computer technology and numerical computation methods, the digital simulation method has become one of the most effective ways to solve complex engineering problems. Compared with the analytical method which is only applicable to the noise analysis of simple structures, it can be used to solve the aerodynamic noise of large and complex structures of air inlet ducts. At present, the research on the noise of the dust removal system of a tobacco plant mainly focuses on covering the pipe wall with acoustic materials and installing mufflers at the inlet and outlet of the pipe, etc. There are few researches on the noise reduction by optimizing the internal structure of the air inlet, and the establishment of a mathematical model to optimize the internal structure of the air inlet is a brand-new attempt.

In this paper, the air inlet of the dust removal system in a tobacco factory in Hubei province is taken as the research object. The CFD software Fluent and the acoustic software LMS Virtual.lab are used to jointly simulate and establish an air inlet model of the dust removal system with a valve. Through the established digital model, the causes of the pneumatic noise of the valve are analyzed, and the characteristics of the pneumatic noise generated by gas flowing through the valve in the pipe are discussed. The influence rule of valve opening on noise is studied and the valve opening structure is optimized. The results show that the aerodynamic noise of the inlet is mainly concentrated in the low frequency range. Valve opening affects the sound pressure level of the pneumatic noise but does not change the spectral characteristics. Under different valve opening degrees from 30° to 75°, the difference of the maximum noise pressure level drop is about 6.62 dB, 5.42 dB and 1.43 dB respectively, when the valve increases by 15°. The mean values of the sound pressure levels and the maximum sound pressure levels decrease with the number of valve opening. The mean sound pressure level with 9 holes reduces by about 25.69% compared with that without holes. The relevant results provide research ideas and practical cases for the noise reduction design of the air inlet of the dust removal system in a tobacco factory based on multi-software co-simulation.