本文指出非零的周期平均热声效应在本质上是非线性的,应保留到二阶精度。在小振幅条件下,利用摄动方法,以无限大平板流道为例,建立了二阶精度的弱非线性热声理论模型,并在不同条件下对模型做了进一步简化。这一理论为理解热声系统的工作机制以及设计优化热声系统提供了强有力的理论工具。 This paper points out that the non-zero periodic average thermoacoustic effect is nonlinear in nature and should be preserved to the second-order accuracy. Under the condition of small amplitude, using the perturbation method, an infinitely large plate flow channel is taken as an example to establish a second-order weak weak nonlinear thermoacoustic theory model, and the model is further simplified under different conditions. This theory provides a powerful theoretical tool for understanding the working mechanism of thermoacoustic systems and for designing and optimizing thermoacoustic systems.