Discussion on airflow noise solution and management

Unit noise control: During the operation of the unit, the mechanical noise radiates strongly through the casing. It is characterized by frequency bandwidth and intermediate frequency, which has a great influence on indoor operators. For this purpose, an acoustic enclosure can be installed on the unit. In addition to considering the ventilation and heat dissipation of the unit during design, it is also necessary to consider the observation and maintenance of the operator. Since the air compressor has large vibration during operation, it is necessary to consider the vibration isolation design, paying special attention to the non-rigid contact between the sound insulation cover and the body, so as to avoid the sound bridge and the sound insulation failure. Driver noise control: The air compressor is driven by a motor, and its noise is secondary to the noise of the entire unit, and can be used only for general protection. If the diesel engine is used as the power, the noise is often more than ten decibels higher than the motor, and the diesel engine needs to be noise-reduced.

Noise control of internal combustion engine: noise characteristics of internal combustion engine The internal combustion engine (diesel engine, gasoline engine) noise consists of three parts: internal combustion engine intake and exhaust noise; fuel combustion noise: mechanical motion noise of internal combustion engine. The noise characteristic of the internal combustion engine is the frequency bandwidth, which is mainly composed of medium and low frequencies. Noise reduction technology of internal combustion engine, exhaust noise control the noise of the internal combustion engine during operation, with the highest exhaust noise, the frequency is: f=2nk60T (Hz) where: f noise frequency, Hz; k engine cylinder number; n Engine revolutions, revolutions per minute; T engine strokes. The frequency is in the range of 63Hz-250Hz, mainly low frequency. The muffler design should be based on low frequency resistance. At the same time, the high temperature of the internal combustion engine (400e-500e) should be considered. The flow rate is large (V50m/s80m/s) and high (3kg/). Special environment such as cm24kg/cm2) makes the muffler have high temperature resistance, impact resistance and oil resistance. Body noise control For the body with high noise, the sound insulation cover can be considered. Since the temperature of the internal combustion engine is higher than that of the general machine during operation, the ventilation and cooling of the internal combustion engine should be considered simultaneously when designing the sound insulation cover.

Basic vibration reduction or vibration isolation In order to prevent the internal combustion engine from running, the vibration of the body will propagate outward through the foundation in the form of elastic waves. The foundation needs to be vibration-damping or vibration-isolating. Exhaust jet noise control, exhaust jet noise characteristics Exhaust jet noise is a typical aerodynamic noise, the source of which comes from the turbulent motion of high-pressure airflow, which can be divided into subsonic injection noise, blocking injection noise and Supersonic injection noise. The characteristics of exhaust injection noise are: continuous wide-band noise, and most of the exhaust injection in the city comes from high-pressure gas evacuation and aerodynamic equipment exhaust. Although the distribution is less than the first three types of noise, most of the exhaust injection noise The power is high, the impact is large, and the surrounding residents react strongly. Urban airflow noise has many types, wide distribution, complex sound sources and wide influence surface, which has always been considered as a kind of pollution that is difficult to control. However, according to the frequency characteristics of various types of airflow noise, the specific parts of the sound source sound, the design, the device-compatible muffler and the sound insulation cover, combined with key noise reduction and comprehensive remediation, urban airflow noise pollution is completely controllable.

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