上游激波干扰时斜激波串受迫振荡特性实验研究

Experimental Study of Forced Oblique Shock Train Oscillation

关键词:  斜激波串  斜楔  压力扰动  受迫振荡  顺压梯度

Key words:  Oblique shock train  Ramp  Pressure perturbation  Forced oscillation  Favorable pressure gradient

摘要:

为了研究斜激波串在与上游激波相互干扰时对下游周期性扰动的响应特征，在来流为马赫数2.7的直管道上游设计了一种等宽度斜楔，在下游中心截面位置安装了旋转的椭圆凸轮，以产生类正弦形式的周期性反压扰动，采用了动态压力测量、高速纹影和粒子图像测速技术等手段进行了试验。结果表明:内置斜楔在管道内产生入射激波、分离激波、膨胀波、再附激波和激波诱导分离等复杂背景流场，在分离区附近形成有顺压梯度和逆压梯度的区域。下游产生的正弦形式的周期性扰动会沿着边界层亚声速混合区域逆流前传，引起壁面压力脉动和斜激波串的周期性振荡运动，振荡频率与反压扰动频率相同。在管道内均匀流场中，斜激波串受迫振荡运动的幅值随着反压扰动频率的增加而逐渐减小。在内置斜楔的管道中，斜激波串受迫振荡运动的幅值大大减小，而且随着反压扰动频率的增加基本保持不变。以文中[fs]=21Hz为例，斜激波串在上游激波干扰中的受迫振荡幅值仅为在均匀来流中振荡幅值的22%。

Abstract:

To study the response of an oblique shock train and upstream shocks interaction to downstream periodic pressure perturbations， a ramp with equal width was installed inside a Ma=2.7 straight duct， and the experiments were conducted with high frequency pressure measurements， high-speed Schlieren visualizations and particle image velocimetry (PIV) testing. The shock train was forced to oscillate by a rotating elliptical shaft which produced nearly sinusoidal periodic pressure perturbation and located in the middle of the downstream channel section. The results show that the ramp generates a complex background flow field inside the duct， which includes an incident shock， separation shock， expansion wave， reattached shock， shock induced separation， and flow region with favorable and adverse pressure gradients. The downstream sinusoidal pressure perturbations propagate upstream to the oblique shock train through the subsonic mixed region and cause the oblique shock train to oscillate at the same frequency with downstream pressure perturbations. The amplitude of shock oscillation was negative correlated with frequency in the uniform ducted flow. During the uniform ducted flow， the amplitude of forced oblique shock train oscillation was decreased with the increasing frequency. While in the ducted flow with a ramp， the amplitude of forced shock train oscillation was decreased rapidly and was almost the same with the increasing frequency. As shown in case of [fs]=21Hz， the amplitude of forced shock train oscillation was only 22% of that in the uniform ducted flow.