The fluid motion characteristics have an important influence on the evolution of the backflow vortex near the pipe wall. The instantaneous velocity and instantaneous temperature of the outlet flow channel section, the shear stress of the outlet flow channel wall, the boundary layer thickness, and the Nusselt number under different ratios of the upstream and downstream pipe diameter are studied at the inlet pressure of 12,000 Pa, using the large eddy simulation numerical method. The research results show that a pulsating flow is presented in the outlet channel of the self-excited oscillation chamber, and a backflow vortex can be formed near the wall of the outlet channel. The heat exchange between the fluid near the wall and the wall is accelerated due to the backflow vortex. The thickness of the boundary layer near the wall first decreases and then increases when the ratio of the upstream and downstream pipe diameters of the self-excited oscillation chamber is 1 to 1.8, whereas the heat transfer efficiency first increases and then decreases. The minimum boundary layer thickness is 0.385 mm. The maximum comprehensive evaluation factor $PI$ is 1.23 when the $d_2/d_1$ is 1.5. The total heat exchange efficiency increases by 23%.

流体运动特性对管壁附近回流涡流的演变有重要影响。研究了在入口压力为12,000时，上，下游管径比不同时出口流道截面的瞬时速度和瞬时温度，出口流道壁的剪应力，边界层厚度和Nusselt数。 Pa，采用大涡模拟数值方法。研究结果表明，在自激振荡腔的出口通道中出现脉动流，并在出口通道壁附近形成回流涡流。壁附近的流体与壁之间的热交换由于回流涡流而加速。当自激振荡室的上，下游管径之比为1到1.8时，壁附近的边界层厚度先减小然后增大，而传热效率先增大然后减小。最小边界层厚度为0.385毫米。最高综合评价系数$P\mathrm{一世}$ 当1.23 $d_2/d_{\mathrm{1个}}$是1.5。总换热效率提高了23％。