Ma5斜激波串动态特性实验研究

Experimental Investigation of Dynamic Characteristics of

关键词:  激波串  激波振荡  风洞实验  动态特性

Key words:  Shock Train  Shock oscillation  Wind tunnel experiment  Dynamic Characteristics

摘要:

为加深对激波串动态特性的认识,进行了简单管道模型在Ma5风洞中的实验研究,探讨了两种不同背压变化条件下斜激波串的流动结构和动态特性。背压的生成和控制通过模型尾部两块斜板的闭合运动实现。为了更好观察实验现象,实验过程中动态压力传感器和高速纹影实行同步采集。研究发现:随着背压升高,激波串逐渐前移,由对称形态发展为非对称形态,并持续整个移动过程。背压增加的速度对激波串前缘的前移速度没有影响。激波串在管道内的前移过程并不是一个恒定运动过程,而是存在有稳定前移和急剧前移两种状态,其特性与管道内流场结构、壁面压强分布、背压大小以及距离管道出口的距离等因素相关。在不同的背压条件下,管道内的斜激波串表现出不同的频谱特征,但在同一工况中,激波串区域内不同位置处壁面压强的频谱特性相似。在Case 1状态中,压强振荡主频为f1=512Hz；在Case 2状态中,振荡主频为f1=578Hz,次级频率约为f2=260Hz。两次实验的主频均大于Piponniau模型理论计算值,而Case 2中频率f2和声学振荡频率相近。

Abstract:

The structure and dynamics characteristics of oblique shock train in a simple duct model are investigated experimentally in a Mach 5 hypersonic wind tunnel. Back pressure of model is produced and varied by the close of two ramps at the end of model. Measurements made include high-speed schlieren imaging and simultaneous fast-response wall pressure along the length of model. Results show that the leading edge of shock train propagates upstream,and translates to be asymmetry with the increase of back pressure. The asymmetry state maintained throughout the last whole propagation process. Varying the rise speed of back pressure did not show any discernible effects with regard to propagated speed of the leading edge of oblique shock train. There are two kinds of motion in the shock train propagation process: steadily forward and rapidly forward. The characters of shock train propagation are decided by the fluid structure,the pressure distribution of wall,the magnitude of back pressure,and the distance to the isolator exit,etc. Different wall pressure spectral characteristics of oblique shock train in duct are explored with different back pressure. But in the same case,all the pressure spectral characteristics of transducers in the shock train region are similar. In Case 1,the dominant frequency is f1=512Hz；in Case 2,the dominant frequency is f1=578Hz,the secondary frequency is f2=260Hz that is close to the acoustic resonance frequency. Both the dominant frequencies obtained in the experiments are higher than those of the theoretical prediction of Piponniau model.