三通管路的管壁声传递损失测试方法

Duct wall transmission loss test method of three-channel tube wall

针对汽车进气系统三通管路的特点,提出了多通管路的管壁传递损失测试方法。并以某车型的双涡轮增压发动机进气三通管道为例,采用该方法评价其用塑料代替铝后的声学性能,主要以声传递损失来评价涡轮增压器噪声通过三通连接管路管壁的辐射和透射特性。测试过程中,三通管道的两个连接涡轮增压器端口分别用声源两次发声,靠近进气歧管端口采用两种不同反射末端,然后在每段管路布置两个压力场扬声器进行测试,并基于平面波分离入射波和反射波,同时在三通管道外用声功率半球面十点分布法自由场扬声器测试,经过3次测量来计算管道管壁的声传递损失。由于声传递损失是管道本身特性决定,所以该测试方法能够准确找出塑料件和金属件在不同频率的声学特性差异。而后,在声传递损失测试结果的基础上,结合近场声全息方法和波束形成原理进行声源识别,可知该三通管路材质改为塑料后主要噪声来自焊缝薄弱处的中高频透射声和管壁结构的低频辐射声。

A physical test method of transmission loss is proposed corresponding to the structural attribute of multi-channel duct.It is performed based on three-channel duct of a twin-turbo engine to evaluate the acoustic performance of aluminum and plastic replacement ducts.Transmission loss value is adopted to extract inherent properties of the duct wall including the sound radiation and transmission.In the test setup,the sources at the two ends of turbo outlets generate sound separately and two different kinds of reflection terminals are placed in series at the air intake manifold end.Two pressure microphones are positioned at each segment of multi-channel duct to separate incident and reflection wave based on a plane wave theory.Ten free-field microphones are placed at a hemisphere with radius of 1m around the duct to capture sound emissions.Three test iterations are performed to calculate the transmission loss.Since transmission loss is decided by the inherent property of the duct,transmission loss results can compare acoustic performance differences between plastic and metal ducts in the frequency domain.Then based on the results,the sound source regions of the multi-channel duct are identified with near-field acoustical holography and beamforming theories.For the plastic ducts,the noise emission mainly include noise transmitted from the regions of welding areas of ducts in higher frequency range and radiated from the duct wall at low frequencies.