热声回热器自激振荡特性的研究

从热动力学理论出发,定量地证明回热器的自激振荡特性为负阻尼振荡。回热器是热机系统的热声源,从外热源吸收热能补偿热机系统的能量耗散,维持系统的热声振荡。对不同的回热器填料进行比较,为回热器的填料选择提供了理论依据。

基于自激振荡脉冲特性的磨粒流抛光不锈钢细管内壁的仿真与实验研究

目的解决传统抛光方法对细管件或微孔内表面抛光困难的问题。方法提出一种基于自激振荡脉冲特性的磨粒流抛光方法。利用自激振荡腔,使磨粒流产生振荡脉冲,实现对细管件或微孔内壁高效抛光。建立自激振荡脉冲磨粒流流体区域的数学模型,并通过数值仿真计算获得自激振荡腔体的结构参数d2/d1和L/D以及过渡角β。搭建实验平台,实验验证了自激振荡脉冲特性磨粒流抛光方法的有效性。结果不锈钢细管件的抛光结果表明,加工12 h后,不锈钢细管件内壁的粗糙度Ra从480 nm降到50 nm,内壁面轮廓无明显的单向性纹理;14 h后,不锈钢细管内壁有明显镜面效果。而无振荡腔的情况下需要磨粒流抛光14 h,管件内壁表面粗糙度才达到55 nm,壁面轮廓存在明显的磨粒流抛光流动方向的纹路。结论通过仿真和实验证明了自激振荡脉冲效应抛光方法(SOAFP)的有效性。此外,在本实验条件下,自激振荡腔体的结构参数d2/d1=1.6、L/D=0.5和过渡角β=60°时,抛光效率和抛光后表面质量最佳。

Characteristic and Mechanism of Pressure Fluctuation Caused by Self-Induced Oscillation of Supersonic Impinging Jet

When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow os- cillation occurs. This oscillation depends on the pressure ratio in the flowfield, the position of an obstacle and is related with the noise problems of aeronautical and other industrial engineering. The characteristic and the mechanism of self-induced flow oscillation, have to be clarified to control various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of an oscillation have to be more cleared to control the oscillation. This paper aims to clarify the effect of the pressure ratio and the obstacle position and the mechanism of self-induced flow oscillation by numerical analysis and experiment, when the underexpanded su- personic jet impinges on the cylindrical body. From the result of this study, it is clear that occurrence of the self-induced flow osciUation depends on the pressure balance in the flowfield.